The Functions of the Excretory SystemThe primary function of the excretory system is:• To get rid of wastes• Eliminates useless by-products excreted from cells• Eradicates harmful chemical build-ups• Maintains a steady, balanced chemical concentration
Organs Responsible for Excretion 1. LUNGSLungs are two-sponge like organs localized in each sideof the thorax. They are constituted by pulmonaryalveoli. They are responsible for maintaining lifesupporting levels of CO2 and O2 in blood stream byexcreting the extra carbon dioxide and keeping aregular supply of oxygen. Each and all organisms cellscan take the oxygen through passive diffusion from thebloodstream and use it in its own metabolism, thusproducing carbon dioxide that will be further excretedwhen passing through alveoli circulation. They alsoremove some water in the gaseous form (water vapor).
2. SKINThe skin is another part of the system, whichhelps regulate the concentration of fluids andminerals in one’s body while also keeping it cool.The salt helps evaporate the water, cooling offthe skin. Sweat is excreted through sweat glands.There are two types of sweat glands: eccrine (ormerocrine) sweat glands and apocrine sweatglands. The basic purpose of skin is to provide awaterproof, protective, covering for the bodyscomplex internal environment.
-The skin also plays a key role in helping tomaintain the circulatory and nervous system.The eccrine glands secrete mostly water andsalt and are used by the body for temperaturecontrol. These glands are located all aroundthe body but are most profuse around thesoles of the feet, palms of the hands, and theforehead. They look like coiled tubes, spiralingtowards the exterior of the skin.
3. LARGE INTESTINEThe large intestine, or the colon, is the organthat removes solid waste from the body. Itsfunction is not only to remove solid waste butto collect water from the waste that can bereused. It is part of the alimentary canal, achannel that flows through vertebrateanimals. It is about 6 to 7 meters long andprocesses, transports, and excretes solidwastes.
4. LIVERThe liver is a vital part of the excretorysystem, and the human body. It regulatesglycogen storage, plasma protein synthesis, anddrug detoxification. The liver secretes bile, a baseused for breaking down fats. Therefore, it helpsget rid of unneeded wastes in the body. Itchanges toxic ammonia, which is a poisonous gas, to urea, a harmless fluid. The kidney filters urea(a mix of sugar and waste) into a liquid calledurine. The liver is the largest gland in the body.
The Urinary System The Urinary System is a group of organs in the bodyconcerned with filtering out excess fluid and othersubstances from the bloodstream. The urinary systemacts as the regulator of extracellular products of thebody protein foods that we eat, which containcarbon, hydrogen and oxygen plus nitrogen and otherelements. The waste that is produced when proteinscombine with oxygen is called nitrogenous waste, andit is more difficult to excrete from the body than gaseslike carbon dioxide and water vapor. The substancesare filtered out from the body in the form of urine.
-Urine is a liquid produced by thekidneys, collected in the bladder and excretedthrough the urethra. Urine is used to extractexcess minerals or vitamins, urea, creatinine, aswell as blood corpuscles from the body. Theurinary organs include thekidneys, ureters, bladder, and urethra. Theurinary system works with the other systems ofthe body to help maintain homeostasis. Thekidneys are the main organs of homeostasisbecause they maintain the acid base balance andthe water salt balance of the blood.
Functions of the Urinary System One of the major functions of the Urinary systemis the process of excretion. Excretion is theprocess of eliminating, from an organism, wasteproducts of metabolism and other materials thatare of no use. The urinary system maintains anappropriate fluid volume by regulating theamount of water that is excreted in the urine.Other aspects of its function include regulatingthe concentrations of various electrolytes in thebody fluids and maintaining normal pH of theblood.
KidneysSeveral body organs carry out excretion, but thekidneys are the most important excretory organ.The primary function of the kidneys is to maintaina stable internal environment (homeostasis) foroptimal cell and tissue metabolism. They do thisby separating urea, mineral salts, toxins, andother waste products from the blood. They alsodo the job of conserving water, salts, andelectrolytes. At least one kidney must functionproperly for life to be maintained
Kidneys The kidneys are a pair of bean shaped, brownorgans about the size of a fist. A kidney measures10-12 cm in length. Kidneys are covered by therenal capsule, which is a tough capsule of fibrousconnective tissue. Adhering to the surface of eachkidney are two layers of fat to help cushion them.There is a concaved side of the kidney that has adepression where a renal artery enters, and arenal vein and a ureter exit the kidney. Thekidneys are located at the rear wall of theabdominal cavity just above the waistline, andare protected by the ribcage.
-They are considered retroperitoneal, which meansthey lie behind the peritoneum. There are threemajor regions of the kidney, renal cortex, renalmedulla and the renal pelvis. Theouter, granulated layer is the renal cortex. Thecortex stretches down in between a radiallystriated inner layer. The inner radially striatedlayer is the renal medulla. This contains pyramidshaped tissue called the renalpyramids, separated by renal columns. Theureters are continuous with the renalpelvis, which is the very center of the kidney.
Six Important Roles of the Kidneys(1) Regulation of plasma ionic composition. Ions such as sodium, potassium, calcium, magnesium, chl oride, bicarbonate, and phosphates are regulated by the amount that the kidney excretes.(2) Regulation of plasma osmolarity. The kidneys regulate osmolarity because they have direct control over how many ions and how much water a person excretes.
-(3) Regulation of plasma volume. The kidneys are so important they even have an effect on our blood pressure. The kidneys control plasma volume by controlling how much water a person excretes. The plasma volume has a direct effect on the total blood volume, which has a direct effect on our blood pressure. Salt (NaCl) will cause osmosis to happen; the diffusion of water into the blood.
-(4) Regulation of plasma hydrogen ion concentration (pH). The kidneys partner up with the lungs and they together control the pH. The kidneys have a major role because they control the amount of bicarbonate excreted or held onto. The kidneys help maintain the blood pH mainly by excreting hydrogen ions and reabsorbing bicarbonate ions as needed.
-(5) Removal of metabolic waste products and foreign substances from the plasma. One of the most important things the kidneys excrete is nitrogenous waste. As the liver breaks down amino acids it also releases ammonia. The liver then quickly combines that ammonia with carbon dioxide, creating urea which is the primary nitrogenous end product of metabolism in humans.
-The liver turns the ammonia into urea becauseit is much less toxic. We can also excrete someammonia, creatinine and uric acid. Thecreatinine comes from the metabolicbreakdown of creatine phospate (a high-energy phosphate in muscles). Uric acidcomes from the break down of nucleotides.Uric acid is insoluble and too much uric acid inthe blood will build up and form crystals thatcan collect in the joints and cause gout.
-(6) Secretion of Hormones. The endocrine system has assistance from the kidneys when releasing hormones. Renin is released by the kidneys. Renin leads to the secretion of aldosterone which is released from the adrenal cortex. Aldosterone promotes the kidneys to reabsorb the sodium (Na+) ions.
-The kidneys also secrete erythropoietin whenthe blood doesnt have the capacity to carryoxygen. Erythropoietin stimulates red bloodcell production. The Vitamin D from the skin isalso activated with help from the kidneys.Calcium (Ca+) absorption from the digestivetract is promoted by vitamin D.
Kidneys - StructureNephrons A nephron is the basic structural and functional unit of the kidney. The name nephron comes from the Greek word (nephros) meaning kidney. Its chief function is to regulate water and soluble substances by filtering the blood, reabsorbing what is needed and excreting the rest as urine. Nephrons eliminate wastes from the body, regulate blood volume and pressure, control levels of electrolytes and metabolites, and regulate blood pH. Their functions are vital to life and are regulated by the endocrine system by hormones such as antidiuretic hormone, aldosterone, and parathyroid hormone.
-Each nephron has its own supply of bloodfrom two capillary regions from the renalartery. Each nephron is composed of an initialfiltering component (the renal corpuscle) anda tubule specialized for reabsorption andsecretion (the renal tubule). The renalcorpuscle filters out large solutes from theblood, delivering water and small solutes tothe renal tubule for modification.
- Glomerulus The glomerulus is a capillary tuft that receives itsblood supply from an afferent arteriole of therenal circulation. The glomerular blood pressureprovides the driving force for fluid and solutes tobe filtered out of the blood and into the spacemade by Bowmans capsule. The remainder ofthe blood not filtered into the glomerulus passesinto the narrower efferent arteriole.
-It then moves into the vasa recta, which arecollecting capillaries intertwined with theconvoluted tubules through the interstitialspace, where the reabsorbed substances willalso enter. This then combines with efferentvenules from other nephrons into the renalvein, and rejoins with the main bloodstream.
-Afferent/Efferent Arterioles• The afferent arteriole supplies blood to the glomerulus. The efferent arteriole drains the glomerulus.Glomerular Capsule or Bowmans Capsule• Bowmans capsule (also called the glomerular capsule) surrounds the glomerulus and is composed of visceral (inner) and parietal (outer) layers. The visceral layer lies just beneath the thickened glomerular basement membrane.
Between the visceral and parietal layers isBowmans space, into which the filtrate entersafter passing through the filtration slits. Unlikethe visceral layer, the parietal layer does notfunction in filtration. 99% of glomerularfiltrate will ultimately be reabsorbed.
-• The process of filtration of the blood in the Bowmans capsule is ultrafiltration (or glomerular filtration). The filtrate leaving the Bowmans capsule is very similar to blood plasma in composition as it passes into the proximal convoluted tubule. Together, the glomerulus and Bowmans capsule are called the renal corpuscle.
-Proximal Convoluted Tubule (PCT) The proximal tubule can be anatomically divided into two segments: the proximal convoluted tubule and the proximal straight tubule. The proximal convoluted tubule has one layer of cuboidal cells in the lumen. This is the only place in the nephron that contains cuboidal cells. These cells are covered with millions of microvilli. The microvilli serve to increase surface area for reabsorption.
-• Fluid in the filtrate entering the proximal convoluted tubule is reabsorbed into the peritubular capillaries, including approximately two-thirds of the filtered salt and water and all filtered organic solutes (primarily glucose and amino acids).
• The solutes are absorbed isotonically, in that the osmotic potential of the fluid leaving the proximal tubule is the same as that of the initial glomerular filtrate. However, glucose, amino acids, inorganic phosphate, and some other solutes are reabsorbed via secondary active transport through co-transport channels driven by the sodium gradient out of the nephron.
-Loop of the Nephron or Loop of HenleThe loop of Henle (sometimes known as thenephron loop) is a U-shaped tube that consists ofa descending limb and ascending limb. It beginsin the cortex, receiving filtrate from the proximalconvoluted tubule, extends into the medulla, andthen returns to the cortex to empty into the distalconvoluted tubule. Its primary role is toconcentrate the salt in the interstitium, the tissuesurrounding the loop.
-Distal Convoluted Tubule (DCT)The distal convoluted tubule is similar to the proximalconvoluted tubule in structure and function. In thepresence of parathyroid hormone, the distalconvoluted tubule reabsorbs more calcium andexcretes more phosphate. When aldosterone ispresent, more sodium is reabsorbed and morepotassium excreted. After traveling the length of thedistal convoluted tubule, only 3% of waterremains, and the remaining salt content is negligible.97.9% of the water in the glomerular filtrate enters theconvoluted tubules and collecting ducts by osmosis.
- Collecting ducts• Each distal convoluted tubule delivers its filtrate to a system of collecting ducts, the first segment of which is the connecting tubule. The collecting duct system begins in the renal cortex and extends deep into the medulla.• Urine leaves the medullary collecting ducts through the renal papilla, emptying into the renal calyces, the renal pelvis, and finally into the bladder via the ureter.
Formation of UrineUrine is formed in three steps: Filtration, Reabsorption, and Secretion:(1) Filtration Blood enters the afferent arteriole and flows into the glomerulus. Blood in the glomerulus has both filterable blood components and non-filterable blood components. Filterable blood components move toward the inside of the glomerulus while non-filterable blood components bypass the filtration process by exiting through the efferent arteriole.
-• Filterable Blood components will then take a plasma like form called glomerular filtrate. A few of the filterable blood components are water, nitrogenous waste, nutrients and salts (ions). Nonfilterable blood components include formed elements such as blood cells and platelets along with plasma proteins. The glomerular filtrate is not the same consistency as urine, as much of it is reabsorbed into the blood as the filtrate passes through the tubules of the nephron.
-(2) Reabsorption - Within the peritubular capillary network, molecules and ions are reabsorbed back into the blood. Sodium Chloride reabsorbed into the system increases the osmolarity of blood in comparison to the glomerular filtrate. This reabsorption process allows water (H2O) to pass from the glomerular filtrate back into the circulatory system.
-- Glucose and various amino acids also are reabsorbed into the circulatory system. - Glomerular filtrate has now been separated into two forms: Reabsorbed Filtrate and Non- reabsorbed Filtrate. Non-reabsorbed filtrate is now known as tubular fluid as it passes through the collecting duct to be processed into urine.
-Secretion Some substances are removed from blood through the peritubular capillary network into the distal convoluted tubule or collecting duct. These substances are Hydrogen ions, creatinine, and drugs. Urine is a collection of substances that have not been reabsorbed during glomerular filtration or tubular reabsorbtion.
Ureters• The ureters are two tubes that drain urine from the kidneys to the bladder. Each ureter is a muscular tube about 10 inches (25 cm) long. Muscles in the walls of the ureters send the urine in small spurts into the bladder, (a collapsible sac found on the forward part of the cavity of the bony pelvis that allows temporary storage of urine).
-• After the urine enters the bladder from the ureters, small folds in the bladder mucosa act like valves preventing backward flow of the urine. The outlet of the bladder is controlled by a sphincter muscle. A full bladder stimulates sensory nerves in the bladder wall that relax the sphincter and allow release of the urine. However, relaxation of the sphincter is also in part a learned response under voluntary control. The released urine enters the urethra.
Urinray Bladder• The urinary bladder is a hollow, muscular and distensible or elastic organ that sits on the pelvic floor. The urinary bladder can hold approximately 17 to 18 ounces (500 to 530 ml) of urine, however the desire to micturate is usually experienced when it contains about 150 to 200 ml. When the bladder fills with urine (about half full), stretch receptors send nerve impulses to the spinal cord, which then sends a reflex nerve impulse back to the sphincter (muscular valve) at the neck of the bladder, causing it to relax and allow the flow of urine into the urethra.
-• The Internal urethral sphincter is involuntary. The ureters enter the bladder diagonally from its dorsolateral floor in an area called the trigone. The urethra exits at the lowest point of the triangle of the trigone. The urine in the bladder also helps regulate body temperature. If the bladder becomes completely void of fluid, it causes the patient to chill.
UrethraThe urethra is a muscular tube that connectsthe bladder with the outside of the body. Thefunction of the urethra is to remove urinefrom the body. It measures about 1.5 inches(3.8 cm) in a woman but up to 8 inches (20cm) in a man. Because the urethra is so muchshorter in a woman it makes it much easier fora woman to get harmful bacteria in herbladder this is commonly called a bladderinfection or a UTI.
-The urethral sphincter is a collective name forthe muscles used to control the flow of urinefrom the urinary bladder. These musclessurround the urethra, so that when theycontract, the urethra is closed.There are two distinct areas of muscle: theinternal sphincter, at the bladder neck and theexternal, or distal, sphincter.
-Human males have much stronger sphinctermuscles than females, meaning that they canretain a large amount of urine for twice aslong.The external urethral orifice is the externalopening or meatus of the urethra.The voiding of urine is called urination, alsoknown as micturition