Circulatory System – The Circle of Blood Page 2 The circulatory orcardiovascular system is theblood circulation with heart,arteries and veins. It is madeup of the vessels and themuscles that help and controlthe flow of the blood aroundthe body. This process iscalled circulation. The mainparts of the system are theheart, arteries, capillaries andveins. As blood begins tocirculate, it leaves the heartfrom the left ventricle andgoes into the aorta. The aortais the largest artery in thebody. The blood leaving theaorta is full of oxygen. Thisis important for the cells inthe brain and the body to dotheir work. The oxygen richblood travels throughout thebody in its system of arteriesinto the smallest arterioles. On its way back to bloodstream by passing through thethe heart, the blood travels through a walls of the small intestine into thesystem of veins. As it reaches the lungs, capillaries. The blood then carries mostthe carbon dioxide (a waste product) is of the nutrients to the liver, where someremoved from the blood and replace of these are extracted and stored forwith fresh oxygen that we have inhaled release back into the blood as and whenthrough the lungs. the body needs them. Other nutrients are converted byFUNCTIONS OF THE SYSTEM the liver into substances which are The circulatory system plays an required in the production of energy,important role in many of the bodys enzymes, and new building materials forprocesses including respiration, the body. Hormones, which affect ornutrition, and the removal of wastes and control the activities of various organspoisons. In respiration it delivers oxygen and tissues, are produced by theto the bodys cells and removes carbon endocrine glands – including the thyroid,dioxide from them. In nutrition, it carries pituitary, adrenal, and sex glands – anddigested food substances to the cells. they too are transported by the bloodNutrients from food enter the through the body.
Circulatory System – The Circle of Blood Page 3TYPES OF THE CIRCULATORY Arteries therefore require strong walls toSYSTEM withstand the pressure of the bloodOpen Circulatory System. The Open flowing through them. They have elasticCirculatory System is a system in which tissue in their walls that can stretch andfluid (called hemolymph) in a cavity recoil with the force of the blood. Arterycalled the hemocoel bathes the organs walls also contain muscle and thisdirectly with oxygen and nutrients and determines the amount of blood that canthere is no distinction between blood and flow through them, and the bloodinterstitial fluid; this combined fluid is pressure.called hemolymph or haemolymph. Heart. The heart is actually two separateMuscular movements by the animal pumps. The left side pumps blood to theduring locomotion can facilitate body (systemic circulation) and the righthemolymph movement, but diverting side pumps blood to the lungsflow from one area to another is limited. (pulmonary circulation). Each side hasWhen the heart relaxes, blood is drawn an atrium and a ventricle. They do notback toward the heart through open- work on their own, but together as aended pores (ostia). team. The bodys blood is circulatedClose Circulatory System. The through the heart more than 1,000 timescardiovascular systems of humans are per day. Between five and six thousandclosed, meaning that the blood never quarts of blood are pumped each day.leaves the network of blood vessels. In Your heart is about the same size as yourcontrast, oxygen and nutrients diffuseacross the blood vessel layers and entersinterstitial fluid, which carries oxygenand nutrients to the target cells, andcarbon dioxide and wastes in theopposite direction. The other componentof the circulatory system, the lymphaticsystem, is not closed. The heart islocated more towards the left side of thebody because it is accompanying thelungs. fist.MAIN COMPONENTS The job of the heart is to pumpBlood Vessels. There are three major blood around your body. Its musclestypes of blood vessels: arteries that carry contract and squeeze out blood. The left-blood from the heart; veins that return hand side pumps blood from the lungs toblood to the heart; and capillaries – the rest of your body. The right-handextremely tiny vessels connecting the side pumps stale blood from your bodyarteries and the veins. When blood is back to your lungs for a fresh supply ofpumped out of the heart into the arteries oxygen.it is forced out at high pressure bycontractions of the muscular ventricles.
Blood. Blood is thicker than water andhas a little bit salty taste. In an adultsbody there is 10.6 pints of bloodCirculatory System – The Circle of Blood Page 4circulating around. In their blood there isbillions of living blood cells floating in a WASTE DISPOSALliquid called plasma. If you took a small In addition to feeding andsample of this blood and poured it into a nourishing the body, the circulatorytest tube and then put it in a machine system also helps to dispose of wastecalled a centrifuge, you would be able to products and poisons which would provesee the layers of this blood. This harmful if allowed to accumulate.machine spins the blood around so fast Carbon dioxide, produced by the bodysthat it separates the red blood cells, from cells as they respire, diffuses through thethe white blood cells, from the platelets. walls of the capillaries into the blood.The red blood cells sink to the bottom The blood containing carbon dioxide isbecause they are the heavier, more solid returned via the heart to the lungs andparts, but the plasma remains at the top passed out of the body on expiration. Inbecause it is lighter. The plasma is 95% processing food, the liver removeswater and the other 5% is made up of ammonia and other wastes, together withdissolved substances including salts. various poisons that enter the body through the digestive system. These are converted into water-soluble substances, which are carried by the blood to the kidneys. The kidneys then filter out these wastes and expel them from the body in urine. TEMPERATURE CONTROL As well as the heat produced generally by cells during respiration, some parts of the body, such as the liver Human blood has two parts, and muscles, produce heat in the courseliquid (plasma) and cells. Plasma of their activities. This heat iscontains dissolved gasses, nutrients, transported by the blood to warm otherwastes, salts, and proteins. Cells are red parts of the body. As the temperature ofblood cells which are biconcave disks the body rises, the flow of blood intofilled with hemoglobin and continuously vessels in the skin increases as a result ofproduced in the red marrow of the skull, small arteries expanding, and excess heatribs, vertebrae, and ends of the long is conveyed to the surface where it isbones; and white blood cells or lost. When the temperature of the bodyleukocytes are cells of the immune drops the flow of blood to the skin issystem defending the body against both restricted. Thus, the circulatory systeminfectious disease and foreign materials.
acts as a natural thermostat allowing thebody to maintain an optimum and stabletemperature.Digestive System – The Food Processor Page 5 The human digestive system isa complex series of organs and glandsthat processes food. In order to use thefood we eat, our body has to break thefood down into smaller molecules thatit can process; it also has to excretewaste. Most of the digestive organs(like the stomach and intestines) aretube-like and contain the food as itmakes its way through the body. Thedigestive system is essentially a long,twisting tube that runs from the mouthto the anus, plus a few other organs(like the liver and pancreas) thatproduce or store digestive chemicals.system defending the body against bothinfectious disease and foreignmaterials.THE DIGESTIVE PROCESSThe start of the process: the mouth.The digestive process begins in themouth. Food is partly broken down bythe process of chewing and by thechemical action of salivary enzymes(these enzymes are produced by the This muscle movement gives us thesalivary glands and break down starches ability to eat or drink even when wereinto smaller molecules). upside-down.On the way to the stomach: the In the stomach. The stomach is a large,esophagus. After being chewed and sack-like organ that churns the food andswallowed, the food enters the bathes it in a very strong acid (gastricesophagus. The esophagus is a long tube acid). Food in the stomach that is partlythat runs from the mouth to the stomach. digested and mixed with stomach acidsIt uses rhythmic, wave-like muscle is called chyme.movements (called peristalsis) to force In the small intestine. After being in thefood from the throat into the stomach. stomach, food enters the duodenum, the
first part of the small intestine. It then the small intestine help in the breakdownenters the jejunum and then the ileum of food.(the final part of the small intestine). In In the large intestine. After passingthe small intestine, bile (produced in the through the small intestine, food passesliver and stored in the gall bladder), into the large intestine. In the largepancreatic enzymes, and other digestive intestine, some of the water andenzymes produced by the inner wall of electrolytes (chemicals like sodium) areDigestive System – The Food Processor Page 6removed from the food. Many microbes acids. Chyme goes on to the small(bacteria like Bacteroides, Lactobacillus intestine for further digestion.acidophilus, Escherichia coli, and Descending colon. The part of the largeKlebsiella) in the large intestine help in intestine that run downwards after thethe digestion process. The first part of transverse colon and before the sigmoidthe large intestine is called the cecum colon.(the appendix is connected to the Duodenum. The first part of the smallcecum). Food then travels upward in the intestine; it is C-shaped and runs fromascending colon. The food travels across the stomach to the jejunum.the abdomen in the transverse colon, Epiglottis. The flap at the back of thegoes back down the other side of the tongue that keeps chewed food frombody in the descending colon, and then going down the windpipe to the lungs.through the sigmoid colon. When you swallow, the epiglottisThe end of the process. Solid waste is automatically closes. When you breathe,then stored in the rectum until it is the epiglottis opens so that air can go inexcreted via the anus. and out of the windpipe. Esophagus. The long tube between theDIGESTIVE SYSTEM GLOSSARY mouth and the stomach. It uses rhythmicAnus. The opening at the end of the muscle movements (called peristalsis) todigestive system from which feces force food from the throat into the(waste) exits the body. stomach.Appendix. A small sac located on the Gall bladder. A small, sac-like organcecum. located by the duodenum. It stores andAscending colon. The part of the large releases bile (a digestive chemical whichintestine that run upwards; it is located is produced in the liver) into the smallafter the cecum. intestine.Bile. A digestive chemical that is Ileum. The last part of the smallproduced in the liver, stored in the gall intestine before the large intestinebladder, and secreted into the small begins.intestine. Jejunum. The long, coiled mid-sectionCecum. The first part of the large of the small intestine; it is between theintestine; the appendix is connected to duodenum and the ileum.the cecum. Liver. A large organ located above andChyme. Food in the stomach that is in front of the stomach. It filters toxinspartly digested and mixed with stomach from the blood, and makes bile (which
breaks down fats) and some blood intestines. Enzymes from the pancreasproteins. help in the digestion of carbohydrates,Mouth. The first part of the digestive fats and proteins in the small intestine.system, where food enters the body. Peristalsis. Rhythmic muscleChewing and salivary enzymes in the movements that force food in themouth are the beginning of the digestive esophagus from the throat into theprocess (breaking down the food). stomach. Peristalsis is involuntary - youPancreas. An enzyme-producing gland cannot control it. It is also what allowslocated below the stomach and above the you to eat and drink while upside-down.Digestive System – The Food Processor Page 7Rectum. The lower part of the large Stomach. A sack-like, muscular organintestine, where feces are stored before that is attached to the esophagus. Boththey are excreted. chemical and mechanical digestion takesSalivary glands. Glands located in the place in the stomach. When food entersmouth that produce saliva. Saliva the stomach, it is churned in a bath ofcontains enzymes that break down acids and enzymes.carbohydrates (starch) into smaller Transverse colon. The part of the largemolecules. intestine that runs horizontally across theSigmoid colon. The part of the large abdomen.intestine between the descending colonand the rectum.
Endocrine System – The Communicator Page 8 Although we rarely thinkabout the endocrine system, itinfluences almost every cell,organ, and function of ourbodies. The endocrine system isinstrumental in regulating mood,growth and development, tissuefunction, metabolism, and sexualfunction and reproductiveprocesses. In general, the endocrinesystem is in charge of bodyprocesses that happen slowly,such as cell growth. Fasterprocesses like breathing and A gland is a group of cells thatbody movement are controlled by the produces and secretes, or gives off,nervous system. But even though the chemicals. A gland selects and removesnervous system and endocrine system materials from the blood, processesare separate systems, they often work them, and secretes the finished chemicaltogether to help the body function product for use somewhere in the body.properly. The major glands that make up the The foundations of the endocrine human endocrine system include the:system are the hormones and glands. As hypothalamus, pituitary gland, thyroid,the bodys chemical messengers, parathyroids, adrenal glands, pinealhormones transfer information and body, and reproductive glands (whichinstructions from one set of cells to include the ovaries and testes).another. Many different hormones move Hypothalamus. The hypothalamus, athrough the bloodstream, but each type collection of specialized cells that isof hormone is designed to affect only located in the lower central part of thecertain cells. brain, is the main link between the endocrine and nervous systems. NerveMAJOR GLANDS cells in the hypothalamus control the
pituitary gland by producing chemicals The production and secretion ofthat either stimulate or suppress pituitary hormones can be influenced byhormone secretions from the pituitary. factors such as emotions and changes inPituitary. Although it is no bigger than the seasons. To accomplish this, thea pea, the pituitary (pronounced: puh- hypothalamus provides informationtoo-uh-ter-ee) gland, located at the base sensed by the brain (such asof the brain just beneath the environmental temperature, lighthypothalamus, is considered the most exposure patterns, and feelings) to theimportant part of the endocrine system. pituitary.Its often called the "master gland" The tiny pituitary is divided intobecause it makes hormones that control two parts: the anterior lobe and theseveral other endocrine glands.Endocrine System – The Communicator Page 9posterior lobe. The ANTERIOR LOBE contractions of the uterus in a womanregulates the activity of the thyroid, having a baby.adrenals, and reproductive glands. The Thyroid. The thyroid, located in theanterior lobe produces hormones such front part of the lower neck, is shapedas: like a bow tie or butterfly and producesGrowth hormone, which stimulates the the thyroid hormones thyroxine andgrowth of bone and other body tissues triiodothyronine. These hormonesand plays a role in the bodys handling of control the rate at which cells burn fuelsnutrients and minerals; from food to produce energy.Prolactin, which activates milk The production and release ofproduction in women who are thyroid hormones is controlled bybreastfeeding; thyrotropin, which is secreted by theThyrotropin, which stimulates the pituitary gland. The more thyroidthyroid gland to produce thyroid hormone there is in a personshormones; bloodstream, the faster chemicalCorticotropin, which stimulates the reactions occur in the body.adrenal gland to produce certain Parathyroids. Attached to the thyroidhormones. are four tiny glands that function The pituitary also secretes together called the parathyroids. Theyendorphins, chemicals that act on the release parathyroid hormone, whichnervous system and reduce feelings of regulates the level of calcium in thepain. In addition, the pituitary secretes blood with the help of calcitonin, whichhormones that signal the reproductive is produced in the thyroid.organs to make sex hormones. The Adrenal Glands. The adrenal glandspituitary gland also controls ovulation have two parts, each of which produces aand the menstrual cycle in women. set of hormones and has a different The POSTERIOR LOBE of the function: The OUTER PART, thepituitary releases antidiuretic hormone, adrenal cortex, produces hormoneswhich helps control the balance of water called corticosteroids that influence orin the body. The posterior lobe also regulate salt and water balance in theproduces oxytocin, which triggers the body, the bodys response to stress,
metabolism, the immune system, andsexual development and function. TheEndocrine System – The Communicator Page 10INNER PART, the adrenal medulla, These hormones tell a guys body whenproduces catecholamines, such as its time to make the changes associatedepinephrine. Also called adrenaline, with puberty, like penis and heightepinephrine increases blood pressure and growth, deepening voice, and growth inheart rate when the body experiences facial and pubic hair. Working withstress. hormones from the pituitary gland,Pineal. The pineal body, also called the testosterone also tells a guys body whenpineal gland, is located in the middle of its time to produce sperm in the testes.the brain. It secretes melatonin, a A girls gonads, the ovaries, arehormone that may help regulate when located in her pelvis. They produce eggsyou sleep at night and when you wake in and secrete the female hormonesthe morning. estrogen and progesterone. Estrogen is involved when a girl begins to go through puberty. During puberty, a girl will experience breast growth, will begin to accumulate body fat around the hips and thighs, and will have a growth spurt. Estrogen and progesterone are also involved in the regulation of a girls menstrual cycle. These hormones also play a role in pregnancy. The pancreas is also part of the bodys hormone-secreting system, even though it is also associated with the digestive system because it produces andReproductive Glands. The GONADS secretes digestive enzymes. Theare the main source of sex hormones. pancreas produces two importantMost people dont realize it, but both hormones, insulin and glucagon. Theyguys and girls have gonads. work together to maintain a steady level In guys the male gonads, or of glucose, or sugar, in the blood and totestes, are located in the scrotum. They keep the body supplied with fuel tosecrete hormones called androgens, the produce and maintain stores of energy.most important of which is testosterone.
Excretory System – The Waste-Eliminator Page 11 The urinary system ismade-up of the kidneys, ureters,bladder, and urethra. Thenephron, an evolutionarymodification of the nephridium, isthe kidneys functional unit.Waste is filtered from the bloodand collected as urine in eachkidney. Urine leaves the kidneysby ureters, and collects in thebladder. The bladder can distendto store urine that eventuallyleaves through the urethra. Excretion is the removalof the metabolic wastes of anorganism. Wastes that areremoved include carbon dioxide,water, salt, urea and uric acid. Allexcreted wastes travel at sometime in the blood.Nephron. The nephron consistsof a cup-shaped capsulecontaining capillaries and theglomerulus, and a long renal tube.Blood flows into the kidney Proximal Convoluted Tubule, Reabsorbsthrough the renal artery, which branches 75% of the water, salts, glucose, andinto capillaries associated with the amino acids;glomerulus. Arterial pressure causes Loop of Henle, Countercurrentwater and solutes from the blood to filter exchange, which maintains theinto the capsule. Fluid flows through the concentration gradient;proximal tubule, which include the loop Distal Convoluted Tubule, Tubularof Henle, and then into the distal tubule. secretion of H ions, potassium, andThe distal tubule empties into a certain drugs.collecting duct. Fluids and solutes are Functions of Nephron. (a) Glomerularreturned to the capillaries that surround filtration of water and solutes from thethe nephron tubule. blood; (b) tubular reabsorption of water There are several components of and conserved molecules back into theNephron, these are: blood; and (c) tubular secretion of ionsGlomerulus, mechanically filters blood; and other waste products fromBowmans Capsule, mechanically filters surrounding capillaries into the distalblood; tubule.
Excretory System – The Waste-Eliminator Page 12Nephrons filter 125 ml of body fluid per Urinary System. Kidneys filter theminute; filtering the entire body fluid blood to form urine, which is excesscomponent 16 times each day. In a 24 water, salt, urea and uric acid.hour period nephrons produce 180 litersof filtrate, of which 178.5 liters are THE URINARY SYSTEMreabsorbed. The remaining 1.5 liters Urine. The first nitrogenous waste to beforms urine. formed from the breakdown of protein isUrine Production. (a) Filtration in the ammonia, a highly toxic chemical that isglomerulus and nephron capsule; (b) quickly converted by the liver to ureareabsorption in the proximal tubule; and and uric acid. These are less toxic than(c) tubular secretion in the Loop of ammonia and are transported in theHenle. blood to the kidneys for excretion inKidney Stones. In some cases, excess urine. Urine consists of excess water,wastes crystallize as kidney stones. They excess salt, urea and uric acid.grow and can become a painful irritantthat may require surgery or ultrasound PARTS OF THE URINARYtreatments. Some stones are small SYSTEMenough to be forced into the urethra, Renal Arteries. 2 renal arteriesothers are the size of huge, massive constantly transport blood to theboulders. kidneys. Infection, environmental toxins Kidneys. 2 kidneys composed ofsuch as mercury, and genetic disease can millions of nephrons constantly filterhave devastating results by causing about 170 to 200 litres of blood todisruption of kidney function. Many produce about 1.5 to 2 litres of urinekidney problems can be treated by daily.dialysis, where a machine acts as a Renal Veins. 2 renal veins return usefulkidney. Kidney transplants are an nutrients back into the bloodstream.alternative to dialysis. Ureters. 2 ureters carry urine from the kidneys to the urinary bladder.ORGANS OF EXCRETORY Urinary Bladder. The urinary bladderSYSTEM temporarily stores urine until it isLungs. Removal of excess carbon released from the body.dioxide. Urethra. The urethra is the tube thatLiver. Produces urea and uric acid as a carries urine from the urinary bladder toby-product of the breakdown of proteins. the outside of the body. The outer end ofSkin. Removal of excess water, salt, the urethra is controlled by a circularurea and uric acid. muscle called a sphincter.
Immune System – The Defender Page 13 The humanimmune system is madeup of a number ofinterdependent celltypes whichcollectively protect thepersons body fromvarious parasitic,fungal, bacterial andviral infections, as wellas from the growth oftumor cells. The humanimmune system is madeup of a number ofinterdependent celltypes whichcollectively protect thepersons body from Bone Marrow. Every cell involved in avarious parasitic, fungal, bacterial and persons immune system is initiallyviral infections, as well as from the derived from bone marrow. These cellsgrowth of tumor cells. A number of form through a process referred to as,these cell types have specialized Hematopoiesis. During hematopoiesisfunctions, are able to kill parasites, bone marrow derived stem cellsengulf bacteria, or kill tumor cells or differentiate into one of two things;viral-infected cells. Frequently, these either mature cells of the immunecells are dependent upon the, T, helper system, or precursors of cells which thensubset for activation signals in the form migrate out of the persons bone marrow,of secretions which are more formally continuing their maturation elsewhere inreferred to as, Lymphokines, the body. Bone marrow produces, B,Cytokines, or specifically as, cells, killer cells, immature thymocytes,Interleukins. An understanding of the T and granulocytes, as well as platelets andhelper subset may assist in red blood cells.comprehension of the root of immune Thymus. The Thymus function is todeficiencies, as well as perception of the produce mature, T, cells. Immaturepotential avenues that the human Tymocytes, also referred to as,immune system can be modulated in the Prothymocytes, emerge from thecase of particular diseases. persons bone marrow and move into their thymus. Through a process called,IMMUNE SYSTEM ORGANS
Thymic Education, these T cells which response are removed. Mature T cellsare beneficial to the persons immune are released into the persons bloodsystem are spared while T cells that may stream.cause a detrimental autoimmuneImmune System – The Defender Page 14Spleen. A persons spleen is an subsets is the, T Helper Subset, alsoimmunological filter, filtering their referred to as the, CD4+ T Cell, whichblood. The spleen is comprised of T is a coordinator of a persons immunecells, B cells dendritic cells, regulation. The primary function of themacrophages, red blood cells and natural T helper cell is augmentation of thekiller cells. Macrophages and dendritic persons immune responses throughcells not only capture foreign materials secretion of specialized factors whichcalled, Antigens, from a persons blood activate additional white blood cells inwhich passes through the spleen, they order to fight off an infection.bring these antigens to the spleen itself CD8+ T Cells. CD8+ T Cells are alsofrom the persons blood stream. A called T killer/suppressor cells and arepersons body experiences an immune important because they are involved inresponse when the macrophage or directly killing viral infected cells,dendritic cells present the antigen to specific tumor cells, and sometimesappropriate T or B cells. In a persons parasites. CD8+ T cells are importantspleen, B cells are activated and produce because they also down-regulategreat amounts of antibody. The spleen immune responses. While both types ofalso destroys old red blood cells. T cells are found throughout a personsLymph Nodes. A persons lymph nodes body, they are many times dependent onwork as an immunological filter for their the lymph nodes and spleen as placesbodily fluid referred to as, Lymph. where activation happens, yet are alsoPeople have lymph nodes throughout found in other tissues in a persons body,their body. Lymph nodes are made notably the persons lungs, liver, bloodmostly of B cells, T cells, macrophages, and intestinal and reproductive tracts.and dendritic cells. A persons lymph Natural Killer Cells. Natural killer cellsnodes drain fluid from the majority of are also called, NK Cells, and aretheir tissues. Lymph nodes filter out similar to cells from the killer T cellantigens from lymph prior to returning subset. Natural killer cells work aslymph to the persons body for effector cells, killing specific tumors likecirculation. In a manner much like the lymphomas, melanomas, and viralspleen, dendritic cells and macrophages infected cells such as herpes andthat capture antigens present foreign cytomegalovirus infected cells. Naturalmaterials to both B and T cells, initiating killer cells kill their targets in thean immune response. persons lymphoid organs; however, these cells which have been activatedIMMUNE SYSTEM CELLS through secretions from CD4+ T cellsT Cells. T Lymphocytes are commonly will kill viral-infected targets or tumorsplaced into two major subsets which are more efficiently.identifiably different. One of these
B Cells. The primary function of B cells bind to one other particular proteinis to produce antibodies in response to which also specifically recognize andforeign proteins such as viruses, bacteria bind to one particular protein. Theand tumor cells. Antibodies are proteins production of antibodies and binding tothat specifically first recognize and thenImmune System – The Defender Page 15foreign substances or antigens is often Dendritic Cells. Dendritic cells alsocritical as a means of signaling originate in a persons bone marrow,additional cells to engulf and kill, or working as antigen presenting cellsremove a substance from the persons (APCs). Interestingly, dendritic cells arebody. more efficient APCs than macrophages.Polymorphonuclear (PMN) Dendritic cells are commonly found inLeukocytes or Granulocytes. There is a the structural compartment of a personsgroup of white blood cells which is lymphoid organs, such as their spleen,collectively referred to by medical lymph nodes and thymus. These cellspersonnel as, Polymorphonuclear can also be found in the persons bloodLeukocytes (PMNs), or, Granulocytes. stream, as well as in other tissues in theirGranulocytes are made of three cell body. Science believes that these cellstypes which are referred to as, capture antigen, or bring it to theEosinophils, Neutrophils, and, persons lymphoid organs, where anBasophils. The names for them are immune response is initiated. One of thebased on their staining characteristics reasons that scientists know very littlewith specific dyes. The cells are about dendritic cells is because they areimportant because they are involved in difficult to isolate; something that isthe removal of parasites and bacteria often a prerequisite for studying thefrom a persons body. These cells first functional qualities of exact cell types.engulf foreign bodies and then degrade Of particular note is a recent finding thatthem by using their powerful enzymes. dendritic cells bind high amount of HIVMacrophages. Macrophages are and could be a reservoir of virus whichimportant due to their function in the is transmitted to CD4+ T cells duringregulation of immune responses. and activation event.Macrophages are many times referred toas, scavengers, or, Antigen-Presenting IMMUNE RESPONSECells (APCs), because they both pick The presence of an APC,up and ingest foreign materials, and then combined with a T cell or B cell, ispresent these antigens to other cells in a required in order for there to be anpersons immune system like B cells and immune response to a foreign antigen.T cells. The process is one of the steps Should an APC present an antigen on itsinvolved in initiating an immune cell surface to a B cell, for example, theresponse. Microphages that have been B cell is signaled to proliferate andstimulated show increased levels of, produce antibodies. The antibodies thenPhagocytosis, and are also secretory. specifically bind to that antigen. If the antibodies bind to antigens on parasites
or bacteria, it acts as a signal for referred to as, Complement, first bind tomacrophages or PMNs to engulf and kill immobilized antibodies, and thenthem. One addition and important destroy the bacteria through creatingfunction of antibodies is to start holes in the bacteria. Antibodies maysomething referred to as a, Complement also signal macrophages and naturalDestruction Cascade. When antibodies killer cells to kill bacterial infected cellsbind to bacteria or cells, serum proteins or viral cells.Integumentary System – Skin, Hair & Nails Page 16 The integumentary system, eyelashes to the thick skin of the soles—formed by the skin, hair, nails, and the integumentary system protects theassociated glands, enwraps the body. It body from the outside world and itsis the most visible organ system and one many harmful substances. It utilizes theof the most complex. Diverse in both Suns rays while at the same timeform and function—from delicate shielding the body from their damaging
effects. In addition, the system helps to tissues that performs a specializedregulate body temperature, serves as a function. As an organ, the skin is theminor excretory organ, and makes the largest and heaviest in the body. In aninner body aware of its outer average adult, the skin covers about 21.5environment through sensory receptors. square feet (2 square meters) andSkin. Although the skin is not often accounts for approximately 7 percent ofthought of as an organ, such as the heart body weight, or about 11 pounds (5or liver, medically it is. An organ is any kilograms) in a 160-pound (73-kilogram)part of the body formed of two or more person. It ranges in thickness from 0.04Integumentary System – Skin, Hair & Nails Page 16to 0.08 inches (1 to 2 millimeters), but Integument, in animals and plants, anycan measure up to 0.2 inches (6 natural outer covering, such as skin,millimeters) thick on the palms of the shell, membrane, or husk.hands and the soles of the feet. The skin Keratin, tough, fibrous, water-resistantin these areas is referred to as thick skin protein that forms the outer layers of(skin elsewhere on the body is called hair, calluses, and nails and coats thethin skin). surface of the skin. Lunula, white, crescent-shaped area ofPARTS OF THE the nail bed near the nail root.INTEGUMENTARY SYSTEM Melanocyte, cell found in the lowerApocrine sweat glands, sweat glands epidermis that produces the proteinlocated primarily in the armpit and pigment melanin.genital areas. Organ, any part of the body formed ofArrector pili muscle, smooth muscle two or more tissues that performs aattached to a hair follicle that, when specialized function.stimulated, pulls on the follicle, causing Sebaceous gland, exocrine gland in thethe hair shaft to stand upright. dermis that produces sebum.Dermal papillae, finger-like projections Sebum, mixture of oily substances andextending upward from the dermis fragmented cells secreted by sebaceouscontaining blood capillaries, which glands.provide nutrients for the lower layer of Squamous cells, cells that are flat andthe epidermis; also form the scalelike.characteristic ridges on the skin surface Subcutaneous, tissues between theof the hands (fingerprints) and feet. dermis and the muscles.Dermi , thick, inner layer of the skin.Eccrine sweat glands, bodys most FUNCTIONS OF THEnumerous sweat glands, which produce INTEGUMENTARY SYSTEMwatery sweat to maintain normal body The integumentary system hastemperature. multiple roles in homeostasis. All bodyEpidermis, thin, outer layer of the skin. systems work in an interconnectedEpithelial tissue, tissue that covers the manner to maintain the internalinternal and external surfaces of the conditions essential to the function of thebody and also forms glandular organs. body. The skin has an important job of protecting the body and acts as the
body’s first line of defense against d. Protect the body against abruptinfection, temperature change, and other changes in temperaturechallenges to homeostasis. Functions e. Help excrete waste materials throughinclude: perspirationa. Protect the body’s internal living f. Act as a receptor for touch, pressure,tissues and organs pain, heat, and coldb. Protect against invasion by infectious g. Protect the body against sunburnsorganisms h. Generate vitamin D through exposurec. Protect the body from dehydration to ultraviolet light i. Participate in temperature regulationIntegumentary System – Skin, Hair & Nails Page 17TWO PRINCIPAL LAYERS OFTHE SKIN The skin has two principal only layer of the epidermis that receiveslayers: the epidermis and the dermis. nutrients (from the underlying dermis).The epidermis is the thin, outer layer, The cells of this layer, called basal cells,and the dermis is the thicker, inner layer. are constantly dividing and creating newBeneath the dermis lies the subcutaneous cells daily, which push the older cellslayer or hypodermis, which is composed toward the surface. Basal cells produceof adipose or fatty tissue. Although not keratin, an extremely durable and water-technically part of the skin, it does resistant fibrous protein.anchor the skin to the underlying Another type of cell found in the lowermuscles. It also contains the major blood epidermis is the melanocyte.vessels that supply the dermis and Melanocytes produce melanin, a proteinhouses many white blood cells, which pigment that ranges in color from yellowdestroy foreign invaders that have to brown to black. The amount ofentered the body through breaks in the melanin produced determines skin color,skin. which is a hereditary characteristic. TheEpidermis. The epidermis is made of melanocytes of dark-skinned individualsstratified squamous epithelial tissue. continuously produce large amounts ofEpithelial tissue covers the internal and melanin. Those of light-skinnedexternal surfaces of the body and also individuals produce less. Freckles are theforms glandular organs. Squamous cells result of melanin clumping in one spot.are thin and flat like fish scales. The outermost layer of theStratified simply means having two or epidermis consists of about twenty tomore layers. In short, the epidermis is thirty rows of tightly joined flat deadcomposed of many layers of thin, cells. All that is left in these cells is theirflattened cells that fit closely together keratin, which makes this outer layerand are able to withstand a good deal of waterproof. It takes roughly fourteenabuse or friction. days for cells to move from the inner The epidermis can be divided layer of the epidermis to the outer layer.into four or five layers. Most important Once part of the outer layer, the deadof these are the inner and outer layers. cells remain for another fourteen days orThe inner or deepest cell layer is the so before flaking off slowly and steadily.
Dermis. The dermis, the second layer of Connective tissue forms theskin, lies between the epidermis and the dermis. Bundles of elastic and collagensubcutaneous layer. Much thicker than (tough fibrous protein) fibers blend intothe epidermis, the dermis contains the the connective tissue. These fibersaccessory skin structures. Hair, sweat provide the dermis strength andglands, and sebaceous (oil) glands are all flexibility.rooted in the dermis. This layer also The upper layer of the dermis hascontains blood vessels and nerve fibers. fingerlike projections that extend intoNourished by the blood and oxygen the epidermis. Called dermal papillae,provided by these blood vessels, the they contain blood capillaries thatcells of the dermis are alive. provide nutrients for the basal cells inIntegumentary System – Skin, Hair & Nails Page 18the epidermis. On the skin surface of the system. In 1901, he establishedhands and feet, especially on the tips of Englands first fingerprint bureau, calledthe fingers, thumbs, and toes, the dermal the Fingerprint Branch, within thepapillae form looped and whorled ridges. Scotland Yard police force. HenrysThese print patterns, known as system is still used today in Greatfingerprints or toeprints, increase the Britain and the United States.gripping ability of the hands and feet. Within the dermis are sensoryGenetically determined, the patterns are receptors for the senses of touch,unique to every individual. pressure, heat, cold, and pain. A specific Fingerprints (the pattern of ridges type of receptor exists for eachon an individuals fingertips and thumbs sensation. For pain, the receptors are freeformed by dermal papillae) are unique to nerve endings. For the other sensations,each individual and the patterns never the receptors are encapsulated nervechange. People have long known about endings, meaning they have a cellularthe distinctiveness of fingerprints, but structure around their endings. Thetheir use in identifying people did not number and type of sensory receptorsarise until the nineteenth century. present in a particular area of skin It is generally acknowledged that determines how sensitive that area is to aEnglish scientist Francis Galton (1822– particular sensation. For example,1911) was the first person to devise a fingertips have many touch receptorssystem of fingerprint identification. In and are quite sensitive. The skin of thethe 1880s, Galton obtained the first upper arm is less sensitive because it hasextensive collection of fingerprints for very few touch receptors.his studies on heredity. He alsoestablished a bureau for the registration ACCESSORY STRUCTURESof civilians by means of fingerprints and The accessory structures of themeasurements. integumentary system include hair, nails, and sweat and sebaceous glands. Galtons ideas were further Hair. Roughly 5 million hairs cover thedeveloped by fellow Englishman body of an average individual. AboutEdward R. Henry (1850–1931). In the 100,000 of those hairs appear on the1890s, Henry developed a more scalp. Almost every part of the body issimplified fingerprint classification covered by hair, except the palms of the
hands, the soles of the feet, the sides of follicle, epithelial cells grow and divide,the fingers and toes, the lips, and certain forming the hair bulb or enlarged hairparts of the outer genital organs. base. Keratin, the primary component in Each hair originates from a tiny these epithelial cells, coats and stiffenstubelike structure called a hair follicle the hair as it grows upward through thethat extends deep into the dermis layer. follicle. The part of the hair enclosed inOften, the follicle will project into the the follicle is called the hair root. Oncesubcutaneous layer. Capillaries and the hair projects from the scalp or skin, itnerves attach to the base of the follicle, is called a hair shaft.providing nutrients and sensory The older epithelial cells forminginformation. Inside the base of the the hair root and hair shaft die as theyIntegumentary System – Skin, Hair & Nails Page 19are pushed upward from the nutrient-rich Nails. Nails in humans correspond to thefollicle base by newly formed cells. Like hooves of horses and cattle and thethe upper layers of the epidermis, the claws of birds and reptiles. Found on thehair shaft is made of dead material, ends of fingers and toes, nails arealmost entirely protein. The hair shaft is produced by nail follicles just as hair isdivided into two layers: the cuticle or produced by hair follicles. The nail rootouter layer consists of a single layer of is that portion of the nail embedded inflat, overlapping cells; the cortex or the skin, lying very near the bone of theinner layer is made mostly of keratin. fingertip. Here, cells produce a stronger Hair shafts differ in size, shape, form of keratin than is found in hair. Asand color. In the eyebrows, they are new cells are formed, older cells areshort and stiff, but on the scalp they are pushed forward, forming the nail bodylonger and more flexible. Elsewhere on or the visible attached portion of the nail.the body they are nearly invisible. Oval- The free edge is that portion of the nailshaped hair shafts produce wavy hair. that extends over the tip of the finger orFlat or ribbonlike hair shafts produce toe. Healthy fingernails grow about 0.04kinky or curly hair. Perfectly round hair inches (1 millimeter) per week, slightlyshafts produce straight hair. The faster than toenails.different types of melanin—yellow, rust, The nail body is made of deadbrown, and black—produced by cells, but the nail bed (the tissuemelanocytes at the follicle base combine underneath the nail body) is alive. Theto create the many varieties of hair color, blood vessels running through the nailfrom the palest blonde to the richest bed give the otherwise transparent nailblack. With age, the production of body a pink color. Near the nail root,melanin decreases, and hair color turns however, these blood vessels aregray. obscured. The resulting white crescent is Attached to each hair follicle is a called the lunula (from the Latin wordribbon of smooth muscle called an luna , meaning "moon").arrector pili muscle. When stimulated, Sweat Glands. More than 2.5the muscle contracts and pulls on the million sweat glands are distributed overfollicle, causing the hair shaft to stand most surfaces of the human body. Theyupright.
are divided into two types: eccrine sweat waste materials such as urea, andglands and apocrine sweat glands. vitamin C form the remainder (the salts Eccrine glands, the more give sweat its characteristic salty taste).numerous of the two types, are found all Sebaceous Gland. Sebaceous glands,over the body. They are especially also known as oil glands, are found innumerous on the forehead, upper lip, the dermis all over the body, except forpalms, and soles. The glands are simply the palms and soles. They secrete sebum,coiled tubes that originate in the dermis. a mixture of lipids (fats), proteins, andA duct extends from the gland to the fragments of dead fatproducing cells.skins surface, where it opens into a pore. The function of sebum is to prevent theEccrine glands produce sweat or drying of skin and hair. It also containsperspiration, a clear secretion that is 99 chemicals that kill bacteria present onpercent water. Some salts, traces ofIntegumentary System – Skin, Hair & Nails Page 20the skin surface. While most sebaceous Arrector pili muscles, which contract toglands secrete sebum through ducts into elevate hairs, also squeeze sebaceoushair follicles, some secrete sebum glands, forcing out sebum.directly onto the surface of the skin.
Muscular System – Movement using Muscles Page 21 The muscular system is thebodys network of tissues that controlsmovement both of the body and withinit. Walking, running, jumping: all theseactions propelling the body throughspace are possible only because of thecontraction (shortening) and relaxationof muscles. These major movements,however, are not the only ones directedby muscular activity. Muscles make itpossible to stand, sit, speak, and blink.Even more, were it not for muscles,blood would not rush through bloodvessels, air would not fill lungs, andfood would not move through thedigestive system. In short, muscles arethe machines of the body, allowing it towork.PARTS OF THE MUSCULARSYSTEM The muscles of the body aredivided into three main types: skeletal,smooth, and cardiac. As their nameimplies, skeletal muscles are attached tothe skeleton and move various parts ofthe body. They are composed of tissue from the pattern of the filamentsfibers that are striated or striped. The (threadlike proteins) within each musclealternating bands of light and dark result cell. Skeletal muscles are called
voluntary muscles because a person and vein walls, and in various hollowcontrols their use, such as in the flexing organs. They are called involuntaryof an arm or the raising of a foot. muscles because a person generally There are just over 650 skeletal cannot consciously control them. Theymuscles in the whole human body. Some are regulated by the autonomic nervousauthorities state there are as many as 850 system (a division of the nervous systemmuscles in the body. No exact figure is that affects internal organs such as theavailable because scientists disagree heart, lungs, stomach, and liver). Unlikeabout which ones are separate muscles skeletal muscles, smooth muscles haveand which ones are part of larger no striations or stripes.muscles. There is also some variability In a vessel or organ, smooth muscles arein muscular structure between arranged in sheets or layers. Often, thereindividuals. are two layers, one running circularly Smooth muscles are found in the (around) and the otherstomach and intestinal walls, in arteryMuscular System – Movement using Muscles Page 22longitudinally (up and down). As the Muscle tone, sustained partialtwo layers alternately contract and relax, contraction of certain muscle fibers in allthe shape of the vessel or organ changes muscles.and fluid or food is propelled along. Myofibrils, cylindrical structures lyingSmooth muscles contract slowly and can within skeletal muscle fibers that areremain contracted for a long period of composed of repeating structural unitstime without tiring. called sarcomeres.Acetylcholine, neurotransmitter chemical Myofilament, protein filamentreleased at the neuromuscular junction composing the myofibrils; can be eitherby motor neurons that translates thick (composed of myosin) or thinmessages from the brain to muscle (composed of actin).fibers. Neuromuscular junction, region where aAdenosine triphosphate, high-energy motor neuron comes into close contactmolecule found in every cell in the body. with a muscle fiber.Aerobic metabolism, Chemical reactions Prime mover (or agonist), muscle whosethat require oxygen in order to create contractions are chiefly responsible foradenosine triphosphate. producing a particular movement.Antagonist, muscle that acts in Rigor mortis, rigid state of the body afteropposition to a prime mover. death due to irreversible muscleCramp, prolonged muscle spasm. contractions.Fascicle, Bundle of myofibrils wrapped Sarcomere, unit of contraction in atogether by connective tissue. skeletal muscle fiber containing aLactic acid, chemical waste product precise arrangement of thick and thincreated when muscle fibers break down myofilaments.glucose without the proper amount of Spasm, sudden, involuntary muscleoxygen contraction. Strain, slight tear in a muscle; also called a pulled muscle.
Synergist, muscle that cooperates with many as 100 or more nuclei. The nucleianother to produce a particular are located on the surface of the fiber,movement. just under its thin membrane. AnotherTendon, tough, white, cordlike tissue difference between muscle fibers andthat attaches muscle to bone. other body cells is their size. They can extend the entire length of a muscle. ForSTRUCTURE OF MUSCLE CELLS example, a muscle fiber in a thigh Each muscle is made of hundreds muscle could measure 0.0004 inchto thousands of individual muscle cells. (0.001 centimeter) in diameter and 12 toUnlike most other cells in the body, 16 inches (30 to 40 centimeters) inthese cells are unusually shaped: they are length.elongated like a cylinder or a long rod. When a person dies, blood stopsBecause of their shape, muscle cells are circulating through the body. Thenormally referred to as muscle fibers. skeletal muscles (along with all otherWhereas most cells have a single parts of the body) are deprived ofnucleus (the part of the cell that controlsits activities), muscle fibers have asMuscular System – Movement using Muscles Page 23oxygen and nutrients, including ATP. contains bundles of threadlike proteinsCalcium ions leak out of their storage or filaments called myofilaments, whicharea in the membranes of muscle fibers, can be either thick or thin. The largercausing thick myofilaments to attach to thick myofilaments are made mostly ofand pull thin myofilaments. While the bundled molecules of the proteinmuscle fibers still have a stored supply myosin. The thin myofilaments areof ATP, the heads of thick myofilaments composed of the protein actin. In eachare able to detach from the thin myofibril, the thick and thinmyofilaments. When the supply of ATP myofilaments are combined intoruns out, however, the heads cannot thousands of units or segments thatdetach and the muscle fibers stay in a repeat over and over. These units arecontracted position. The rigid state of called sarcomeres. Thick myofilamentsmuscle contraction that results is called lie in the center of a sarcomere. Thinrigor mortis. Depending on the persons myofilaments are attached at either endphysical condition at death, the onset of of a sarcomere and extend toward therigor mortis may vary from ten minutes center, passing among the thickto several hours after death. Facial myofilaments. This regular arrangementmuscles are usually affected first, of the varying myofilaments within eachfollowed by other parts of the body. sarcomere produces the striated orRigor mortis lasts until the muscle fibers striped appearance of each myofibrilbegin to decompose fifteen to twenty- and, by extension, of muscle fibers.five hours after death. As are most living cells, muscle Each muscle fiber is composed fibers are soft and fragile. Even so, theyof hundreds of smaller filaments or can exert tremendous power withoutthreads called myofibrils (the prefix being ripped apart. The reason is thatmyocomes from the Latin word myos , muscles are composed of different typesmeaning "muscle"). Each myofibril of tissue (like all other organs in the
body). In addition, those tissues are muscle usually converge or comebundled together, providing strength and together at the end of the muscle to formsupport. Each myofibril is enclosed in a a tough, white, cord-like tissue called adelicate sheath or covering made of tendon. Tendons attach muscles to bone.connective tissue (tissue found Because they contain fibers of the tougheverywhere in the body that connects protein collagen, tendons are muchbody parts, providing support, storage, stronger than muscle tissue. Theand protection). Numerous sheathed collagen fibers are arranged in a tendonmyofibrils are then bundled together and in a wavy way so that it can stretch andwrapped with thicker connective tissue provide additional length at the muscle-to form what is called a fascicle (from bone junction. As muscles are used, thethe Latin word fasciculus , meaning "a tendons are able to withstand thebundle"). Many fascicles are then constant pulling and tugging.bundled together by an even tougher Muscles are always attached at both ofcoat of connective tissue to form the their ends. The end that is attached to amuscle. bone that moves when theTendons. The layers of connectivetissue that bundle the various parts of aMuscular System – Movement using Muscles Page 24muscle contracts is called the insertion. bone of the skull. Other muscles areThe other end, attached to a bone that named for their relative size. Terms suchdoes not move when the muscle as maximus (largest), minimuscontracts, is called the origin. It is (smallest), and longus (long) are oftenimportant to note that not all muscles are used as part of a muscles name. Stillattached to bones at both ends. The ends other muscles are named for their shape.of some muscles are attached to other The deltoid muscle is so named becausemuscles; some are attached to the skin. it has the shape of the Greek letter delta , which is triangular-shaped. And someMAJOR MUSCLES OF THE BODY muscles are named for their actions. Skeletal muscles that support the Terms such as flexor (to flex or bend in),skull, backbone, and rib cage are called extensor (to extend or straighten out),axial skeletal muscles. These include the adductor (to draw toward a line that runsmuscles of the head and neck and those down the middle of the body), andof the trunk. Roughly 60 percent of all abductor (to draw away from a line thatskeletal muscles in the body are axial runs down the middle of the body) aremuscles. The skeletal muscles of the often added as part of a muscles name.limbs (arms and legs) are called distal or Muscles of the Head and Neck. Theappendicular skeletal muscles. These muscles of the face are unique: they areinclude the muscles of the shoulders and attached to the skull on one end and toarms and those of the hip and legs. the skin or other muscles on the other Muscle names are descriptive. end. Muscles that are attached to the skinSome muscles are named according to of the face allow people to expresstheir location in the body. For example, emotions through actions such asthe frontalis muscle overlies the frontal smiling, frowning, pouting, and kissing.
As mentioned, the frontalis side of the head, allows the head tocovers the frontal bone or forehead. The rotate and the neck to flex.temporalis is a fan-shaped muscle Muscles of the Trunk. On the frontoverlying the temporal bone on each side part of the trunk or torso, the pectoralisof the head above the ear. The major are the large, fan-shaped musclesorbicularis oculi encircles each eye and that cover the upper part of the chest.helps close the eyelid. The orbicularis They flex the shoulders and pull theoris is the circular muscle around the arms into the body. The rectuslips. It closes and extends the lips. abdominis are the strap-like muscles of The masseter, located over the the abdomen, extending from the ribs torear of the lower jaw on each side of the the pelvis. Better known as the stomachface, opens and closes the jaw, allowing muscles, they flex the vertebral columnchewing. The buccinator, running or backbone and provide support for thehorizontally across each cheek, flattens abdomen and its many organs. Thethe cheek and pulls back the corners of muscles making up the side walls of thethe mouth. The sternocleidomastoid, abdomen are the external oblique. Inlocated on either side of the neck and addition to helping compress theextending from the clavicle or abdomen, they rotate the trunk and allowcollarbone to the temporal bone on the it to bend sideways.Muscular System – Movement using Muscles Page 25 On the rear part of the trunk, the thin and long. Of these many muscles,trapezius are the kite-shaped muscles the flexor carpi bend the wrist and thethat run from the back of the neck and flexor digitorum bend the fingers. Theupper back down to the middle of the muscles that have the opposite effect,back. They raise, lower, and adduct the extending the wrist and fingers, are theshoulders. The large, flat muscles that extensor carpi and the extensorcover the lower back are the latissimus digitorum.dorsi. They adduct and rotate the arms Muscles of the Hips and Legs. Musclesand help extend the shoulders. of the lower limbs cause movement atMuscles of the Shoulders and Arms. the hip, knee, and foot joints. TheseThe fleshy, triangular-shaped muscles muscles are among the largest andthat form the rounded shape of the strongest muscles in the body. Musclesshoulders are the deltoid. They help on the thigh (upper portion of the leg)abduct the arm, or move it away from are especially massive and powerfulthe middle of the body. The most since they hold the body upright againstfamiliar muscle of the upper arm is the the force of gravity.biceps brachii Located on the front of The gluteus maximus are thethe upper arm, the bicep makes a large muscles that form most of the fleshprominent bulge as it flexes the elbow. of the buttocks. These powerful musclesOn the rear portion of the upper arms is help extend the hip in activities such asthe triceps brachii. Its action is just the climbing stairs and jumping. Theopposite of the biceps: it extends or adductor muscles are a group of musclesstraightens the forearm. that form a mass on the inside of the The muscles of the forearm, thighs. As their name indicates, theywhich move the bones of the hands, are adduct or press the thighs together.
On the front of the thigh is a legged position with the knees widegroup of four muscles known apart.collectively as the quadriceps. Together, On the back part of the lower legthe quadriceps help powerfully extend or is the calf muscle, properly known as thestraighten the knee, such as when an gastrocnemius. This diamond-shapedindividual kicks a soccer ball. On the muscle, formed in two sections, helpsback of the thigh, a group of three extend or lower the foot, such as whenmuscles performs the opposite effect. an individual walks on his or her toes.Known as hamstrings, these muscles flex The strong tendon that attaches theor bend the knee. The sartorius is long, gastrocnemius to the heel of the foot isstraplike muscle that crosses the front of the well-known Achilles tendon inthe thigh diagonally from the outside of Greek mythology, a hero of the Trojanthe hip to the inside of the knee. War who is killed by an arrow shot intoAlthough it is not that powerful, it does his heel. The main muscle on the frontlie on upper surface of the thigh and is part of the lower leg, the tibialis anterior,easily seen. The sartorius helps rotate the opposes the action of the gastrocnemius.leg so an individual can sit in a cross- It flexes and inverts or elevates the foot.Nervous System – Brain and Nerves Page 26 The nervous system is the master body. It interprets incoming sensorycontroller of the body. Each thought, information, then sends out instructionseach emotion, each action—all result on how the body should react. The CNSfrom the activity of this system. Through consists of two major parts: the brainits many parts, the nervous system and the spinal cord.monitors conditions both within and The peripheral nervous systemoutside the body. It then processes that (PNS) is the part of the nervous systeminformation and decides how the body outside of the CNS. It consists mainly ofshould respond, if at all. Finally, if a nerves that extend from the brain andresponse is needed, the system sends out spinal cord to areas in the rest of theelectrical signals that spur the body into body. Cranial nerves carry impulses toimmediate action. Although one of the and from the brain while spinal nervessmallest of the bodys systems in terms carry impulses to and from the spinalof weight, the nervous system is the cord. The PNS can be divided into twomost complex and versatile. systems: the somatic nervous system and the autonomic nervous system. ThePARTS OF THE NERVOUS somatic nervous system controls theSYSTEM voluntary movements of the skeletal The nervous system is a muscles. The autonomic nervous systemcollection of cells, tissues, and organs. It control activities in the body that arecan be split into two separate divisions: involuntary or automatic. These includethe central nervous system and the the actions of the heart, glands, andperipheral nervous system. digestive organs and associated parts. The central nervous system The autonomic nervous system(CNS) acts as the command center of the can be divided further into two
subdivisions: the parasympathetic and Axon, taillike projection extending out asympathetic nervous systems. These two neuron that carries impulses away fromsubdivisions work against each other. the cell body.The parasympathetic nervous system Basal ganglia, paired masses of grayregulates involuntary activities that keep matter within the white matter of thethe body running smoothly under cerebrum that help coordinatenormal, everyday conditions. The subconscious skeletal muscularsympathetic nervous system controls movement.involuntary activities that help the body Brain, central controlling andrespond to stressful situations. coordinating organ of the nervousArachnoid, weblike middle layer of the system.three meninges covering the brain and Cauda equine, spinal nerves that hangspinal cord. below the end of the spinal cord.Autonomic nervous system, part of the Central nervous system, part of theperipheral nervous system that controls nervous system consisting of the braininvoluntary actions, such as the and spinal cord.heartbeat, gland secretions, and Cerebral cortex, outermost layer of thedigestion. cerebrum made entirely of gray matter. Cerebrum, largest part of the brain, involved with conscious perception,Nervous System – Brain and Nerves Page 27voluntary actions, memory, thought, and Gyri, outward folds on the surface of thepersonality. cerebral cortex.Corpus callosum, large band of neurons Hippocampus, structure in the limbicconnecting the two cerebral system necessary for the formation ofhemispheres. long-term memory.Dendrites, branchlike extensions of Hypothalamus, region of the brainneurons that carry impulses toward the containing many control centers forcell body. body functions and emotions; alsoDiencephalon, rear part of the forebrain regulates the pituitary glands secretions.that connects the midbrain to the Limbic system, group of structures in thecerebrum and that contains the thalamus cerebrum and diencephalon that areand hypothalamus. involved with emotional states andDura mate, outermost and toughest of memory.the three meninges covering the brain Medulla oblongata, part of the brainand spinal cord. located at the top end of the spinal cordGanglion, any collection of nerve cell that controls breathing and otherbodies forming a nerve center in the involuntary functions.peripheral nervous system. Meninges, membranes that cover theGray matter, grayish nerve tissue of the brain and spinal cord.central nervous system containing Midbrain, part of the brain between theneuron cell bodies, neuroglia, and hypothalamus and the pons thatunmyelinated axons. regulates visual, auditory, and rightening reflexes.
Myelin, soft, white, fatty material that system that controls involuntaryforms a sheath around the axons of most activities that keep the body runningneurons. smoothly under normal, everydayNerve, bundle of axons in the peripheral conditions.nervous system. Peripheral nervous system, part of theNeuroglia, also known as glial cells, nervous system consisting of the cranialcells that support and protect neurons in and spinal nerves.the central nervous system. Pia mater, delicate innermost layer ofNeuron, nerve cell. the three meninges covering the brainNeurotransmitter, chemical released by and spinal cord.the axon of a neuron that travels across a Pons, part of the brain connecting thesynapse and binds to receptors on the medulla oblongata with the midbrain.dendrites of other neurons or body cells. Reflex, involuntary and rapid response toNode of Ranvier, small area between a stimulus.Schwann cells on an axon that is Schwann cell, cell that forms the myelinunmyelinated or uncovered. sheath around axons of neurons in theOligodendrocyte, cell that produces the peripheral nervous system.myelin sheath around the axons of Somatic nervous system, part of theneurons in the central nervous system. peripheral nervous system that controlsParasympathetic nervous system, the voluntary movements of the skeletaldivision of the autonomic nervous musclesNervous System – Brain and Nerves Page 28Spinal cord, long cord of nerve tissue Neurons. The cells making up the brain,running through the spine or backbone spinal cord, and nerves are calledthat transmits impulses to and from the neurons. They are special cells capablebrain and controls some reflex actions. of receiving a stimulus (nerve orSulci, shallow grooves on the surface of electrical impulse), transmitting thatthe cerebral cortex. stimulus throughout their length, andSympathetic nervous system, division of then delivering that stimulus to otherthe autonomic nervous system that cells next to them. The human bodycontrols involuntary activities that help contains about 200 billion neurons.the body respond to stressful situations. Almost half of them are located in theSynapse, small space or gap where a brain.nerve impulse passes between the axon A neuron consists of three mainof one neuron and a dendrite of the next parts: the cell body, dendrites, and anneuron. axon (dendrites and axons are bothThalamus, part of the brain behind the referred to as nerve fibers). The cellhypothalamus that acts as the brains body has most of the same structuresmain relay station, sending information found in typical body cells, such as ato the cerebral cortex and other parts of nucleus (the part of the cell that controlsthe brain. its activities). It is ball shaped, aboutWhite matter, whitish nerve tissue of the 0.001 inch (0.002 centimeter) incentral nervous system containing diameter.bundles of myelinated axons.
Dendrite comes from the Greek Some (such as those in the centralword dendron , meaning "tree." nervous system) are very short, noDendrites are hairlike threads branching longer than 0.01 inch (0.02 centimeter).off of the cell body like branches of a Others (such as those in the peripheraltree. Extensions of the cell body, they nervous system) can be 3 feet (1 meter)contain the same cytoplasm or cellular long.fluid found in the cell body. Dendrites Most long axons are surroundedare the points through which signals by a white, fatty material called myelin.from adjacent neurons enter a particular The tubelike covering formed is knownneuron (the signal is then transmitted to as a myelin sheath. It serves the samethe cell body). Since each neuron kind of function as the wrapping on acontains many dendrites, a neuron can telephone line or an electrical cable. Itreceive signals from many other protects the axon and prevents electricalsurrounding neurons. impulses traveling through it from An axon is a taillike projection becoming lost.extending out of one end of the cell Special cells form the myelinbody. It ends in a cluster of branches sheath by wrapping themselves aroundcalled terminal branches or axon the axons of neurons. In the CNS, theterminals. Axons have the opposite cells forming the myelin sheath arefunction of dendrites: they carry nerve called oligodendrocytes. In the PNS,impulses away from the cell body. special cells known as Schwann cellsAxons vary in length and diameter. form the myelin sheath. The gap orNervous System – Brain and Nerves Page 29 Types of Neurons. Neurons in the bodyindentation on an axon where one may be divided into three groups:Schwann cell ends and another begins is sensory neurons, motor neurons, andknown as a node of Ranvier. The nodes interneurons. As their name implies,are unmyelinated (lack a myelin sheath), sensory neurons carry impulses orand the nerve or electrical impulse jumps sensations from receptors to the brain orfrom node to node as it passes along an spinal cord (central nervous system).axon (in unmyelinated axons, the Receptors, which are located in the skin,impulse travels continuously along the skeletal muscles, joints, and internalaxon). Scientists believe Schwann cells organs, detect changes both inside andproduce a chemical that helps regenerate outside the body. Motor neurons work inor restore damaged neurons in the the opposite direction. They carryperipheral nervous system. For example, impulses from the brain or spinal cord toif surgeons are able to reattach a persons muscles and glands, causing muscles tosevered hand, that person may regain contract and glands to secrete. Bothsome sensation and movement in that sensory and motor neurons make up thehand as neurons grow and make peripheral nervous system. Interneuronsconnections. Conversely, work entirely within the central nervousoligodendrocytes lack this ability. This is system. They conduct impulses fromwhy an injury to the brain or spinal cord sensory to motor neurons.often results in some permanent loss offunction.
Supporting Cells. Neuroglia, or glial Nerves are categorized likecells, are cells that surround neurons in neurons according to the direction inthe central nervous system. They do not which they conduct impulses. Sensoryconduct impulses, but help to support nerves, made of the axons of sensoryand protect neurons, combining with neurons, carry impulses to the brain andthem to form what is known as nerve spinal cord. Motor nerves, made of thetissue. They also supply neurons with axons of motor neurons, carry impulsesnutrients and remove their wastes. to the muscles and glands. Mixed nervesNeuroglia are abundant, accounting for contain axons of both sensory and motorsome ten times the number of neurons. neurons. The most abundant nerves,An example of neuroglia in the CNS are mixed nerves can conduct impulses botholigodendrocytes. to and from the central nervous system.Nerves. A nerve is a bundle of axons in The Brain. The human brain is a soft,the PNS. Each axon or nerve fiber is shiny, grayish white, mushroom-shapedwrapped in delicate connective tissue. structure encased within the skull. AtGroups of axons are then bound in birth, a typical human brain weighscoarser connective tissue to form between 12 and 14 ounces (350 and 400bundles. Finally, many bundles are grams). By the time an average personbound together (along with blood vessels reaches adulthood, the brain weighsto nourish the axons and Schwann cells) about 3 pounds (1.36 kilograms).by even tougher connective tissue to Because of greater average body size,form a nerve. the brains of male are generally about 10 percent larger than those of females.Nervous System – Brain and Nerves Page 30Although brain size varies considerably cerebrospinal fluid, a liquid thatamong humans, there is no correlation or circulates between the arachnoid.link between brain size and intelligence. The Brain Stem. The brain stem is the The human brain is composed of stalk of the brain and is a continuation ofup to one trillion nerve cells. One the spinal cord. It consists of the medullahundred billion of these are neurons, and oblongata, pons, and midbrain. Thethe remainder are the supporting medulla oblongata is actually a portionneuroglia. The brain consists of gray and of the spinal cord that extends into thewhite matter. Gray matter is nerve tissue brain. All messages that are transmittedin the CNS composed of neuron cell between the brain and spinal cord passbodies, neuroglia, and unmyelinated through the medulla. Nerves on the rightaxons; white matter is nerve tissue in the side of the medulla cross to the left sideCNS composed chiefly of bundles of of the brain, and those on the left crossmyelinated axons. to the right. The result of this The brain is protected by the arrangement is that each side of the brainskull and by three membranes called the controls the opposite side of the body.meninges. The outermost membrane is Three vital centers in the medullaknown as the dura mater, the middle as control heartbeat, rate of breathing, andthe arachnoid, and the innermost as the diameter of the blood vessels. Centerspia mater. Also protecting the brain is that help coordinate swallowing,
vomiting, hiccuping, coughing, information from the eyes. The onlysneezing, and other basic functions of exception is the vagus nerve (vaguslife are also located in the medulla. A comes from the Latin word meaningregion within the medulla helps to "wandering"). It is the lone cranial nervemaintain the conscious state. The pons that serves other areas of the body. The(from the Latin word meaning "bridge") vagus nerve branches extensively to theconducts messages between the spinal larynx, heart, lungs, stomach, andcord and the rest of the brain, and intestines. Among other functions, itbetween the different parts of the brain. helps promote digestive activity andThe midbrain conveys impulses from the regulate heart activity.hypothalamus to the pons and spinal The Diecephalon. The diencephaloncord. It also contains visual and audio lies above the brain stem, and includesreflex centers involving the movement the thalamus and hypothalamus. Theof the eyeballs and head. thalamus is an important relay station for Twelve pair of cranial nerves sensory information coming to theoriginate in the underside of the brain, cerebral cortex from other parts of themostly from the brain stem. They leave brain. The thalamus also interpretsthe skull through openings and extend as sensations of pain, pressure,peripheral nerves to their destinations. temperature, and touch, and is concernedCranial nerves bring information to the with some of our emotions and memory.brain from regions in the face, head, and It receives information from the outsideneck. For example, the olfactory nerve environment in the form of sound, smell,transmits messages about smell from the and taste.nose and the optic nerve transmits visualNervous System – Brain and Nerves Page 31The Cerebrum. The cerebrum makes up The Cerebellum. The cerebellum isabout 80 percent of the brains weight. It located below the cerebrum and behindlies above the diencephalon. The the brain stem, and is shaped like acerebrums outer layer, the cerebral butterfly. The "wings" are the cerebellarcortex, is made entirely of gray matter hemispheres, and each consists of lobes(white matter makes up the inner portion that have distinct grooves or fissures.of the cerebrum). The tissue of the The cerebellum controls the actions ofcerebral cortex is about 0.08 to 0.16 inch the muscular system needed for(2 to 4 millimeters) thick. The cerebral movement, balance, and posture. Allcortex is folded extensively. The folds motor activity in the body depends onare called convolutions or gyri, and the the cerebellum.shallow grooves between the folds are The Limbic System. The limbic systemsulci. Deeper grooves, which are less is a horseshoe-shaped area of the brainnumerous, are called fissures. The folds located along the border between thegreatly increase the surface area of the cerebrum and diencephalon. Keycerebral cortex—it would have a surface structures of the limbic system includearea of about 5 square feet (1.5 square the almond-shaped amygdala and the seameters) if spread out—and thus the total horse-shaped hippocampus. The limbicnumber of nerve cell bodies it contains. system is concerned with emotional
states (such as rage, fear, and sexual to and from the brain and controls somearousal) and memory. The hippocampus, reflex actions. On average, the spinalin particular, plays a vital role in cord measures about 18 inches (45learning and long-term memory. centimeters) in length and about 0.5 inchThe Spinal Cord. The spinal cord, a (14 centimeters) in width. It weighsglistening white rope, is a continuation about 1.25 ounces (35 grams).of the brain stem. It transmits impulsesRespiratory System – Breathing Page 32 Breathing, controlled by the respiratory system, is a continuous process of which a person is normally unaware. If breathing stops, however, a person becomes acutely aware of the fact. An individual can go days without food and water and hours without sleep, but only five or six minutes without air. Anything beyond that would be fatal. The trillions of cells in the body
need a constant and generous amount of cell parts and chemicals, and theoxygen to carry out their vital functions. movement of compounds through cellsAs they use that oxygen, they give off and the body as a whole.carbon dioxide as a waste product. It isthe role of the respiration system, PARTS OF THE RESPIRATORYworking in conjunction with the SYSTEMcardiovascular system, to supply the Breathing describes the processoxygen and dispose of the carbon of inhaling and exhaling air. Thedioxide. exchange of gases (oxygen and carbonMain Function. The main function of dioxide) between living cells and thethe respiratory system is to provide environment is a process known asoxygen for the bodys cells and remove respiration. The respiratory system,the carbon dioxide they produce. which controls breathing and respiration,Oxygen is the most important energy consists of the respiratory tract and thesource for the cells. They need it for lungs.cellular respiration: the process by which The respiratory tract cleans,the simple sugar glucose is oxidized warms, and moistens air on its way to(combined with oxygen) to form the the lungs. The tract can be divided intoenergy-rich compound adenosine an upper and a lower part. The uppertriphosphate (ATP). Glucose is produced part consists of the nose, nasal cavity,in cells by the breakdown of more pharynx (throat), larynx, and upper partcomplex carbohydrates, including starch, of the trachea (windpipe). The lower partcellulose, and complex sugars such as consists of the lower part of the trachea,sucrose (cane or beet sugar) and fructose bronchi, and lungs (which contain(fruit sugar). ATP is the compound used bronchioles and alveoli).by all cells to carry out their ordinary The nose and nasal cavity. The nosefunctions: growth, the production of newRespiratory System – Breathing Page 33is the only external part of the cavity, separating it from the mouth orrespiratory system. It is made of bone oral cavity below. Three flat, spongyand cartilage (tough connective tissue) folds or plates project toward the nasaland is covered with skin. The two septum from the sides of the nasalopenings to the outside, called nostrils, cavity. These plates, called nasalallow air to enter or leave the body conchae, help to slow down the passageduring breathing. The nostrils are lined of air, causing it to swirl in the nasalwith coarse hairs that prevent large cavity.particles such as dust, insects, and sand Alveoli, air sacs of the lungs.from entering. Breathing, process of inhaling and The nostrils open into a large exhaling air.cavity, the nasal cavity. This cavity is Bronchi, largest branch of the bronchialdivided into right and left cavities by a tree between the trachea andthin plate of bone and cartilage called bronchioles.the nasal septum. The hard portion of thepalate forms the floor of the entire nasal