Topic 6: Human Health and Physiology


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This is topic 6 for IBSL biology. Last topic that IB students need to know for their SL biology tests.

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Topic 6: Human Health and Physiology

  1. 1. Topic 6Human Health and Physiology
  2. 2. Taking in Food• Absorption: food passes through a layer ofcells into the body’s tissues– Takes place in the small intestines– Uses villi: small finger-like projections fromthe wall of the small intestine• Assimilated: after food is absorbed itbecomes part of the tissues of the body
  3. 3. The Need for Digestion• Some substances are not suitable for absorptioninto human tissues and so must be broken downand reassembled into another form• Many molecules are too large to be absorbed bythe villi and so must be broken down in size• Three main types of food molecule that need to bedigested:1. Starch2. Protein3. Triglycerides (fats and oils)
  4. 4. Enzymes of DigestionEnzyme Amylase Protease LipaseExample Salivary amylase Pepsin Pancreatic lipaseLocation Salivary glands Wall of stomach PancreasSubstrate (whatit breaks down)Starch Proteins Triglycerides (fatsand oils)Products Maltose SmallpolypeptidesFatty Acids andGlycerolOptimum pHlevelpH 7 Ph 1.5 Ph 7
  5. 5. Human Digestive System
  6. 6. Structure of Villi and their Functions• Villi increase the surface area over which food isabsorbed• Have only one thin layer of cells (the epithelium)that foods have to pass through– Small distance for diffusion of foods• Have microvilli to increase the surface area of thevilli• In microvilli, protein channels allow facilitateddiffusion and pumps allow active transport– Mitochondria in the epithelium provide the ATP for thisactive transport• Lacteal branch in the villi’s center carries awayfats after absorption
  7. 7. Stomach and Intestines Functions• Pepsin in the stomach digests proteins inthe stomach• Acidity of the stomach kills most bacteria• Villi in the small intestine absorb finishedproducts of digestion• Ingestible parts of food are made solid aswater is absorbed by the large intestine• Egested through the anus
  8. 8. Heart Structure• Double pump: right side pumps blood to thelungs; left side pumps blood to all otherorgans• Myogenic: the cardiac muscle of the heartcontracts on its own w/o nerve stimulus• There are many capillaries in the muscularwall of the heart (blood in capillaries issupplied by coronary arteries)• Blood brought by coronary arteries bringnutrients and oxygen for aerobic cellrespiration (which produces energy forcardiac muscle contraction)
  9. 9. Heart Diagram• Always draw the leftventricle on the right• Draw the left ventriclevisibly thicker than theright ventricle
  10. 10. Arteries• Arteries: carry blood from the heart– Thick wall to withstand high pressures– Thick outer layer to avoid bulges and leaks– Thick layers of elastic and muscle to helppump the blood on after each heart beat– Narrow lumen to help maintain high pressure
  11. 11. Veins• Veins: carry blood to the heart– Thin layers with thin elastic and muscle; blooddoes not need to be pumped– Wide lumen is needed to accommodate theslow-flowing blood– Thin walls let the veins be pressed flat byadjacent muscles; help moves the blood– Thin outer layer because there is little dangerof bursting– Some have valves to prevent back-flow
  12. 12. Capillaries• Capillaries: connect arteries to veins– Wall is a single layer of thin cells so diffusionhas a small distance– Pores between cells in the wall allow somephagocytes and some plasma to leak outwhich forms tissue fluid– Very narrow lumen; can fit into small spaces
  13. 13. The Action of the Heart1. Walls of the atria contract, pushing blood into theopen atrioventricular valves and into theventricles, which have closed semilunar valves2. The ventricles fill and blood pressure rises. Theatrioventricular valves close and the semilunarvalves open, so blood is pumped out of thearteries. Meanwhile, more blood is filling into theatria.3. The ventricles stop contracting and the semilunarvalve closes. The atrioventricular valves reopenwhen the ventricles have lower pressure than theatria.4. Process repeats
  14. 14. Control of the Heart Beat• Pacemaker: region located in the wall ofthe right atrium; its signal causes the heartto contract (beat)• Nerves and hormones can transmitmessages to the pacemaker– Nerves carry messages to the pacemaker tospeed up or slow down the contractions– Adrenalin (carried by the blood stream) tellsthe pacemaker to speed up
  15. 15. Composition of Blood• Blood is composed of plasma,erythrocytes (red blood cells), leukocytes(white blood cells), and platelets• Two types of leukocytes: lymphocytes andphagocytes
  16. 16. Functions of Blood• Two main functions of blood:1. Transportation2. Defense against infectious disease• Red blood cells transport oxygen from the lungs tocells• Blood plasma transports– Nutrients– Carbon dioxide– Hormones– Antibodies– Urea• Blood also transports heat• Leukocytes defend the body against infectiousdiseases
  17. 17. Phagocytes• Phagocytes: white blood cells that canidentify pathogens and ingest them byendocytosis• Pathogens: organism or virus that causesdisease
  18. 18. Antibodies• Antibodies: proteins that recognized andbind to specific antigens• Antigens: foreign substances thatstimulate the production of antibodies• Antibodies defend the body againstpathogens by binding to antigens on thesurface of a pathogen
  19. 19. Barriers to Infection• Skin and mucous membranes form abarrier that prevents most pathogens fromentering the body– The skin is acidic– Mucus found in nose, trachea, vagina, andurethra• Contains an enzyme that kills bacteria
  20. 20. Antibiotics• Antibiotics: chemicals produced bymicroorganisms to kill or control thegrowth of other microorganisms• Most bacterial diseases can be treatedsuccessfully with antibiotics• Virus diseases can not be treated withantibiotics
  21. 21. Production of Antibodies1. Antibodies are made by lymphocytes (typeof white blood cell)1. Lymphocytes can only make specific types ofantibodies2. Antibodies form on the surface oflymphocytes3. When antigens come in contact with theseantibodies, the lymphocite divides by mitosisto produce clones of itself4. These clones also produce the antibodies toattack the antigen
  22. 22. AIDS• AIDS is a syndrome: group of symptomsthat are found together• Those with AIDS have low numbers of onetype of lymphocyte, weight loss, anddiseases• These diseases weaken the body andeventually cause death
  23. 23. Cause of AIDS• HIV causes Aids• Infects a type of lymphocyte andeventually destroys these lymphocytes—stopping production of these antibodies• This leaves the body vulnerable topathogens that would normally becontrolled easily
  24. 24. Transmission of AIDS• HIV can’t pass through skin and does notsurvive long outside of the body• Transmission involves the transfer of bodyfluids from an infected person to anuninfected person
  25. 25. Need for Gas Exchange/Ventilation• Humans must take in oxygen for cellrespiration and release carbon dioxide• Gas exchange: swapping one gas foranother in the alveoli of the human lungs• Ventilation: the process of bringing freshair to the alveoli and removing stale air tomaintain concentration gradientsnecessary for gas exchange
  26. 26. Ventilation System Diagram
  27. 27. Adaptations of the Alveolus to Gas Exchange• Millions of alveoli create a huge overallsurface area for gas exchange• Alveolus walls are a single layer of cells;gases only have to diffuse a short distance• Alveolus is covered by blood capillariesthat oxygen diffuses into in place of CO2• Alveolus is moist inside and the sides areprevented from sticking together
  28. 28. Ventilation of the LungsInhaling ExhalingExternal intercostal muscles contract,moving the ribcage up and outInternal intercostal muscles contract,moving the ribcage down and inDiaphragm contracts, becoming flatterand moving downAbdominal muscles contract, pushingthe diaphragm up into a dome shapeMuscle movements increase thevolume of the thoraxMuscle movements decrease thevolume of the thoraxPressure inside the thorax is lowerthan the pressure outsidePressure inside the thorax is higherthan the pressure outsideAir flows from outside the body intothe lungs until the pressure risesAir flows from inside the body outsideuntil the pressure falls
  29. 29. Organization of Nervous System• Neurons: cells that carry messages at highspeed in the form of electrical impulses• Two parts of the Nervous System:1. Central Nervous System (CNS): Brain andspinal cord2. Peripheral Nervous System: nerves thatconnect all parts of the body to the CNS
  30. 30. Sensory and Motor Neurons• Sensory neurons carry nerve impulsesfrom receptors (sensory cells) to the CNS• Motor neurons carry impulses from theCNS to effectors (muscle and gland cells)• Relay neurons carry impulses within theCNS from one neuron to another
  31. 31. Structure of Motor Neuron
  32. 32. Synaptic Transmission1. Nerve impulse reaches the end of the pre-synaptic neuron2. Calcium diffuses in through calcium channels into the pre-synaptic neuron3. Vesicles of neurotransmitters fuse with the pre-synapticmembrane and release their neurotransmitters4. Neurotransmitters diffuse across the synaptic cleft andbinds to receptors5. Sodium and other positively charge ions diffuse into thepost-synaptic neuron; causing depolarization of the post-synaptic membrane6. Depolarization causes action potential7. Calcium is pumped out. Neurotransmitter is broken downin the cleft and reabsorbed into the veins.
  33. 33. Resting/Action Potentials• Resting Potential: electrical potentialacross the plasma membrane of a cell thatis not conducting an impulse• Acting Potential: reversal and restorationof the electrical potential across theplasma membrane of a cell, as anelectrical impulse passes along it(depolarization and repolarization)
  34. 34. Passage of Nerve Impulse1. Action potentials develop and reduce the restingpotential; causes voltage-gated channels to open2. Sodium channels open, reduces membranepotential, causing more channels to open.Positively charged Sodium ions cause a netpositive charge to develop; reversing themembrane potential (this is depolarization)3. Potassium channels open and positive potassiumions leave causing the membrane potential to fallback to a negative charge (this is repolarization)4. Potassium and sodium levels are balanced andresting potential returns; waiting for the nextimpulse
  35. 35. Homeostasis• Homeostasis: maintaining the internalenvironment of the body between limits• Nervous system and Endocrine systemare both involved in controlling:– Body temperature– Blood pH– Carbon dioxide concentration– Blood glucose concentration– Water balance
  36. 36. Endocrine System
  37. 37. Controlling Levels• Feedback system: level of a product feedsback to control the rate of its ownproduction• Negative Feedback system: change inlevel causes the opposite change;increase in product leads to decrease inproduction and vice versa
  38. 38. Responses to Overheating• Skin arterioles become wider so moreblood flows through the skin; temperatureof skin rises so more heat is lost to theenvironment• Skeletal muscles remain relaxed andresting so they do not generate heat• Sweat glands secrete seat to make thesurface of the skin damp; waterevaporates from the skin for a coolingeffect
  39. 39. Response to Chilling• Skin arterioles become narrower and bringless blood to the skin, so less heat is lostto the environment• Skeletal muscles shiver to generate heat(small rapid muscle contractions)• Sweat glands do not secrete sweat tokeep the skin dry
  40. 40. Responses to High Blood Glucose Levels• Beta cells in the pancreatic islets produceinsulin• Insulin stimulates the liver and musclecells to convert glucose to glycogen• Glycogen is stored in the cytoplasm• Cells use the glucose for cell respiration• This lowers the blood glucose level
  41. 41. Responses to Low Blood Glucose Levels• Alpha cells in the pancreatic islets produceglucagon• Glucagon stimulates liver cells to breakdown glycogen into glucose• Glucose is released it to the blood• Blood glucose level rises
  42. 42. DiabetesType 1 Diabetes Type 2 DiabetesThe onset is usually during childhood The onset is usually after childhoodBeta cells do not produce enoughinsulinTarget cells become insensitive toinsulinInsulin injections are used to controlblood glucose levelsInsulin injections are not usuallyneededDiet cannot by itself control theconditionLow carbohydrate diets usually controlthe condition
  43. 43. Female Reproductive System
  44. 44. Female Sex Hormones• The pituitary gland produces FSH and LH• FSH stimulates the development of follicles(contain egg cell)• LH stimulates follicles to mature and releaseeggs (ovulation) and develop into the corpusluteum• Estrogen and Progesterone stimulate creationof secondary sexual characteristics anddevelopment of uterus lining for pregnancy
  45. 45. Male Reproductive System
  46. 46. Testosterone• Testosterone is responsible for:– Development of genitalia on fetus– Development of secondary sexualcharacteristics during puberty (example: pubichair)– Maintenance of the sex drive in adulthood topass on genes to offspring
  47. 47. Menstrual Cycle
  48. 48. Infertility• Infertility: couples do not achievefertilization for a temporary or permanenttime span• Some problems can be solved with in vitrofertilization
  49. 49. In Vitro Fertilization1. Woman’s normal cycle is stopped using drugs2. FSH is injected to stimulate ovaries to developmany follicles3. HGG matures and loosens eggs in the follicles4. Sperm is collected and processed5. Eggs are extracted from the follicles6. Eggs are mixed with sperm and incubated7. Two or three embryos are selected and placed intothe uterus8. Pregnancy test is used to see if any embryos haveimplanted
  50. 50. Ethical Issues of IVFEthical arguments against IVF Ethical arguments for IVFInherited forms of infertility might bepassed onto the children, spreadingthe suffering of the parentsMany forms of infertility are due to theenvironment and so will not be passedonto the offspringSpare embryos are sometimes killed;they deserve a chance at lifeEmbryos killed during IVF feel nothingand do not sufferHumans are deciding whether newindividuals survive or dieGenetic diseases could be reduceddue to screening of embryosIVF is unnatural; not an act of love Parents willing to endure the processare likely to be loving parentsInfertility is an act of God Infertility brings uphappiness andloneliness. This makes people happy.