the human body is constantly at work it is never completely at rest for example we are sleeping are busy inhaling oxygen and exhaling carbon dioxide oxide is a waste product generated by our body like carbon dioxide there is other waste products such as ammonia yuria uric acid water and excess ions like phosphate sulfate sodium potassium and chloride are produced in our body as a result of different metabolic activities like ingestion digestion and respiration these wastes or excretory products tained in the body may prove fatal so must be totally or partially removed from our body the process of elimination of metabolic waste products from the animal body is called excretion among the different waste products ammonia urea and uric acid known as nitrogenous wastes of these ammonia is the most toxic and requires a lot of water for its elimination and is thus excreted only by those organisms that can compensate the loss of water generally bony fishes aquatic amphibians and aquatic insects excrete ammonia in the form of readily soluble ammonium ions through their gills or body surface by the process of diffusion that excrete ammonia are called a mono telic while the process is called a mono tell ism as excretion of ammonia requires a lot of water terrestrial animals have evolved a mechanism to convert ammonia into less toxic forms of urea and uric acid which help conserve water mammals including humans and many marine fish and terrestrial amphibians excrete urea the excretion of nitrogenous wastes in the form of urea is called urea tell ISM and such animals are called urea chalak animals in these animals the liver converts ammonia into urea by the on Athene cycle and releases it into the blood the urea in the blood is then filtered by the kidneys and excreted however in some animals the small amount of urea is retained in the matrix of the kidney to maintain the required osmolarity the least toxic form of nitrogenous waste is uric acid though excretion of uric acid involves a lot of energy it helps conserve water considerably as it is excreted in the form of pellets or paste involving very little water some animals excreting acid are reptiles insects land snails and birds such animals that excrete nitrogenous waste in the form of uric acid are called URI cotellic animals and the process is called URI Kotel ISM did you know that in mammals uric acid is formed by the degradation of nucleic acids and is excreted as a part of urine as animals excrete nitrogenous wastes in different forms structure of their exquisitely system also varies the study of phylogeny of the exclusively system reveals that primitive animals such as invertebrates possessed simple organs like progeny Freedia or flame cells which in the course of time evolved into complex organs such as the kidneys in vertebrates flame cells or protein if Rydia are the excretory structures and animals like platyhelminthes rotifers cephalo chordates and certain annelids from performing the function of excretion cells help in osmoregulation or the regulation of the fluid volume and ionic balance in the body another excrete restructure is the new Phrygia found in many annelids like the earthworm Nvidia are tubular structures that help remove nitrogenous waste and maintain the fluid and ionic balance well Phrygian tubules are exclusively structures found in arthropod ons such as insects and arachnids these tubules along with removing nitrogenous wastes perform the function of osmoregulation the internal gland or Greenland is the exclusively structure in crustaceans such as the crab and crayfish and performs the function of excretion and osmoregulation the kidneys perform the main function of excretion in highly evolved mammals such as men along with the kidneys the skin liver and lungs also help in the removal of certain wastes from our body our skin has sebaceous glands that secrete sebum through which substances like hydrocarbons sterols and waxes are excreted this secretion however protective oily covering for the body like the sebaceous glands the sweat glands on our skin also help in the removal of excretory wastes these glands produce sweat a watery fluid containing sodium chloride and small amounts of substances such as urea and lactic acid moreover it also helps to cool the body's surface another organ that plays an important role in excretion is the liver the largest gland in our body drugs and reduces their toxicity by drug metabolism it also detoxifies ammonia and converts it into urea which is eliminated by the kidneys moreover it degrades hemoglobin moans drugs and vitamins and adds it to bile as by pigments bilirubin and Bella Verdun which are then excreted through the feces so excuse ryoga's that help in the removal of large amounts of carbon dioxide a byproduct of cellular respiration from our body the lungs also help in the removal of water besides the kidneys the skin liver and lungs saliva to helps in the removal of small amounts of nitrogenous wastes from our body therefore excretion is an important process which is vital for all living organisms the exclusive organelles may differ from animal to animal and have evolved from simple to complex structures based on the needs of the organism the excretory system is a biological system that helps in the removal of metabolic waste products from an organism much of the excretion in man is executed by the urinary system which constitutes a pair of kidneys a pair of ureters the urinary bladder and the urethra oh these the kidneys play a very vital role the filter blood by removing nitrogenous wastes regulates blood pressure and the the production of red blood cells the kidneys are compact bean-shaped organs on either side of the spinal cord in the lower back more precisely situated between the last thoracic and third lumbar vertebra in close proximity to the dorsal inner wall of the abdominal cavity the 11th and 12th ribs partially protect the upper part of the kidneys right kidney the other liver is slightly lower than the left one which is adjacent to the spleen the kidneys are reddish-brown in color adult each kidney measures about 10 to 12 centimeters in length five to seven centimeters in breadth and two to three centimeters in thickness kidney weighs about 120 to 170 grams the kidneys have an outer convex surface and an indentation or a notch on the inner concave surface called the hilum through which blood vessels nerves and the ureter spaz the kidney has a tough fibrous outer layer called a capsule and section shows that it's inside is differentiated into two main regions and outer cortex and an inner medulla there are about eight to 18 cone-shaped structures in the medulla called medullary pyramids which project into the calluses the tip of each middle era pyramid is called a papilla the cortex protrudes or extends between the pyramids as renal columns called the columns of botany the middle area pyramids project into the calluses which lead to a wide funnel shaped space called the renal pelvis each kidney contains about a million nephrons in the cortical region which are the basic functional units of the kidney the nephrons filter nitrogenous wastes and excess salts from the blood and help in body fluid regulation and urine formation each nephron has two parts the glomerulus and the renal [Music] the glomerulus is a ball-shaped network of capillaries formed by the efferent arteriole which is a fine branch of the renal artery it performs the first step in filtering blood from the glomerulus exits through the efferent arteriole the other part of the nephron the renal tubules in the reabsorption of salts and water as the urine passes through it thereby concentrating the urine the renal tubular begins with the Bowman's capsule and consists of proximal convoluted tubule PCT Henley's loop and distal convoluted tubule or DCT the Bowman's capsule is a double-walled funnel shaped structure that encloses the glomerulus it collects the glomerular filtrate the Bowman's capsule together with the glomerulus is called the Malthusian body or renal corpuscle the Bowman's capsule opens into the proximal convoluted tubule a highly coiled structure and is followed by a helping shaped loop called Henley's loop Henley's loop has a descending limb and an ascending limb the ascending limb opens into the distal convoluted tubule is also a highly coiled tubular structure the distal convoluted tubules of several netherlands open into a collecting duct several collecting ducts converge and pass through the medulla into the renal pelvis which leads to the ureter the collecting ducts along with Henley's loop lie in the medulla while the male Fijian body convoluted fuel and distal convoluted tubules of the nephron lie in the cortex of the kidney the nephrons in the kidney are also distinguished as cortical nephrons and Huxter medullary nephrons based on the length of Henley's loop cortical nephrons constitute the majority of nephrons and have a very short Henley's loop that just about extends into the medulla while the juxta medullary nephrons have a very long Henley's loop that runs deep into the medulla each nephron also has a fine network of capillaries called very tubular capillaries which is formed from the efferent arterial leaving the glomerulus from minut vessel from this network of capillaries forms a u-shaped structure called the Vasa recta lies parallel to the loop of Henle they are greatly reduced or absent in cortical nephrons the capillaries of many such efferent arterioles unite to form the renal vein which joins the inferior vena cava let's now study the other parts of the urinary system the kidney opens into the ureters through the renal pelvis et Rita is about 25 centimeters long and carries urine from the pelvis of the kidneys to the urinary bladder the urinary bladder is a hollow muscular and elastic organ that temporarily stores urine till it is released from body urine leaves the urinary bladder by the urethra a tube through which urine is discharged the urethra is undiluted by the urethral sphincter the flow of urine from the bladder to the outside hence the urethra along with the urinary bladder and kidneys constitute the human excreta system the kidney is the major excretory organ in humans and one of its primary functions is urine formation each kidney contains about a million nephrons which are the basic functional units of the kidney and help in urine formation urine formation involves three major processes namely glomerular filtration or ultra filtration reabsorption and secretion first step in urine formation is the filtration of blood which takes place in the glomerulus and hence the name glomerular filtration pressure of blood in the glomerular capillaries forces the blood to pass through three layers namely the endothelium of the blood vessel hook the capillary the basement membrane of the glomerulus and the epithelium of Bowman's capsule epithelial cells in Bowman's capsule also known as butter sites in secretly arranged a few minut openings called slit pause or filtration slits these slits or membranes help in the filtration of blood and almost all the constituents of the plasma except the proteins bars into the lumen of Bowman's capsule the reason why glomerular filtration is known as ultra filtration did you know that on average the human kidney filters about 1100 to 1200 milliliters of blood per minute which is about 1/5 of the blood pumped out by each ventricle of the heart in a minute the amount of filtrate formed in the Bowman's capsule of a nephron due to glomerular filtration in the kidneys every minute is called the glomerular filtration rate or GFR which in a healthy individual is about 125 milliliters per minute or 180 liters per day the blood pressure in the capillaries acts as a major force in glomerular filtration besides certain intrinsic mechanisms in the kidneys that ought to regulate the GFR the juxtaglomerular apparatus or JGA is one such microscopic structure that regulates the GFR the jja is formed by cellular modifications between the afferent and to some extent the efferent arteriole and the distal convoluted tubule or DCT of the same leaf Ron at their point of contact the juxtaglomerular cells release renin whenever there is a drop in the GFR which stimulates glomerular blood flow and normalizes the GFR did you know that of the 180 liters of glomerular filtrate formed per day the amount of urine released is just 1.5 liters this is because about 99% of the filtrate is reabsorbed in the renal tubules during the process of reabsorption reabsorption is performed by the tubular epithelial cells present in the different parts of the renal tubules through active or passive mechanisms while substances in the filtrate such as sodium amino acids and glucose are absorbed by active transport nitrogenous wastes are absorbed by passive transport water is also reabsorbed passively in the initial segments of the nephron from absorption the cells in the renal tubules also selectively secrete substances such as potassium and hydrogen ions and ammonia into the filtrate to maintain the pH and ionic balance in body fluids process of reabsorption and secretion occurs in different parts of the renal tubules namely the proximal convoluted tubule or PCT Henley's loop and distal convoluted tubules the collecting duct also takes part in the process the proximal convoluted tubule is the section of the nephron situated between Bowman's capsule and Henley's loop the glomerular filtrate from Bowman's capsule enters this tube you'll which is lined by cuboidal brush border epithelial cells that help to increase the surface area for reabsorption the proximal convoluted tubule reabsorbs about 70 to 80% of the electrolytes and water and almost all the essential nutrients and vitamins it also selectively secretes ammonia hydrogen ions and potassium ions into the filtrate and absorbs bicarbonate to maintain the pH and ionic balance of body fluids the proximal convoluted tubule is followed by Henley's loop where minimal reabsorption takes place however the region plays a vital role in maintaining the high osmolarity of medullary interstitial fluid the descending limb of Henley's loop is permeable to water and almost impermeable to electrolytes which helps concentrate the filtrate as it moves down the ascending limb is permeable to electrolytes actively or passively and is impermeable to water therefore electrolytes pass into the medullary fluid and dilutes the concentrated filtrate as it passes upwards Henley's loop is followed by the distal convoluted tubule where conditional reabsorption of water and sodium occurs this region helps maintain the sodium potassium balance and pH level in the blood by reabsorbing bicarbonate and selectively secreting potassium and hydrogen ions and ammonia the distal convoluted tubules of several nephrons open into a straight tube called the collecting duct which extends from the cortex of the kidney to the inner parts of the medulla the duct helps to reabsorb water thereby increasing the concentration of urine according to the body's state of hydration it also maintains osmolarity by enabling small amounts of urea to pass into the medullary interstitial further it selectively secretes hydrogen and potassium ions and maintains the ionic and pH balance of blood for the nephron filters blood by reabsorbing substances that are needed and excreting the rest as urine the yuvan produced by our body is around four times more concentrated than the initial filtrate which reflects the conservation of water in the nephrons Henley's loop and the vasa recta are the parts of the kidney that help concentrate the urine the counter current is created in both these parts this is because the direction of the flow of filtrate in the two limbs of Henry's loop and the flow of blood in the two limbs of the Vasa recta are opposite the counter current along with the proximity of Henley's loop to the Vasa recta maintains an increasing osmolarity in the inner medullary interstitial the difference in osmolarity between the cortex and the medulla is pronounced as we can see that the osmolarity in the cortex is 300 milliosmoles per liter while it is as high as 1200 milliosmoles per liter in the inner medulla this difference in osmolarity is caused by the difference in the concentration of urea and sodium chloride the sodium chloride that is transported through the ascending limb of Henley's loop is exchanged with the descending limb of the Vasa recta then the ascending limb of the Vasa recta returns the sodium chloride to the interstitium in the same way small amounts of urea entering the thin segment of the ascending limb of Henley's loop are transported back to the interstitial by the collecting tubule unique arrangement of the Henley's loop and the Vasa recta together with the counter current mechanism help maintain the concentration gradient in the medulla which aids the easy passage of water from the collecting duct into the medulla due to osmosis thus concentrating the urine yeren thus helps to eliminate the numerous waste compounds generated by our body your information is vital for human health and it is difficult to survive without producing and eliminating it kidney functions are monitored and regulated by the hormonal feedback mechanisms of the hypothalamus juxtaglomerular apparatus or JGA and heart our body has several ozma receptors that are activated by changes in the volume of body fluids volume of blood and ionic concentration and Osmo receptor is a sensory receptor that detects changes in osmotic pressure for example a decrease in the level of body fluids activates the ozma receptors which stimulate the hypothalamus which in turn nearly stimulates the neural hypothesis of the pituitary to release the antidiuretic hormone or ADH or vasopressin ADH prompts the distal convoluted tubules or DC tees and the collecting ducts to reabsorb more water thereby preventing diuresis on the other hand if the fluid volume in the body increases the ozma receptors suppress the release of ADH leading to increased excretion of water in urine adh also has the ability to constrict the blood vessels this increases blood pressure thereby increasing the glomerular blood flow in the kidney and consequently the glomerular filtration rate or GFR like the hypothalamus the JGA also plays a vital role in regulating kidney functions the juxtaglomerular cells detect a fall in the glomerular blood pressure or GFR and release a peptide hormone called renin renin converts angiotensinogen in the blood into angiotensin 1 which is further converted into angiotensin 2 angiotensin 2 a powerful vasoconstrictor fix the blood vessels thereby increasing blood pressure which stimulates the cortex of the adrenal gland to secrete aldosterone aldosterone increases the reabsorption of sodium and water from the distal parts of the renal tubule resulting in an increase in blood volume which increases blood pressure and GFR this complex mechanism is commonly known as the renin-angiotensin mechanism apart from the hypothalamus and JGA the heart also regulates the functioning of the kidneys to a certain extent the muscles of the heart release atrial natriuretic factor or ANF when the blood pressure in the atria increases anf a peptide hormone is a vasodilator and also a diuretic that dilates the blood vessels and helps to decrease the blood sodium and water levels it exhibits an inhibitory effect on the renin-angiotensin mechanism hence hormonal feedback mechanisms efficiently monitor and control the functioning of the kidneys leading to the formation of urine which passes into the urinary bladder where it is stored until a signal is received by the central nervous system or CNS as the urinary bladder gets filled with urine the bladder is stretched and causes the stretch receptors on its walls to send a signal to the CNS in turn sends motor messages that make the smooth bladder muscles contract and the urethral sphincter relaxed resulting in the release of urine this process of disposing urine is called micturition and the new mechanism responsible for the process is known as the micturition reflex on average an adult human releases about 1 to 1.5 liters of urine every day the urine released is a watery fluid that is light yellowish in color moreover it has a characteristic odor and is slightly acidic with a pH value of 6 the characteristics of urine can change according to different body conditions in fact a urine test helps to diagnose many metabolic disorders in the body and any malfunction in the kidneys instance the business of glucose in urine which is called glycosuria is indicative of diabetes mellitus moreover the urine of diabetic patients sometimes shows ketone bodies which is called ketonuria the malfunctioning of the kidneys can also cause uremia a condition where large amounts of urea accumulate in the blood uremia can even lead to kidney failure the life-saving process for uremic patients is hemodialysis we're in excess urea in the blood is removed in this process blood a convenient artery is drained into a dial izing unit after adding an anticoagulant like heparin in the dialyzer of the unit a coiled cellophane tube surrounded by a dilating fluid with a composition similar to plasma except for the nitrogenous waste is placed the membrane of the cellophane tube is porous and allows molecules to pass through it based on the concentration gradient these molecules are the nitrogenous wastes to be removed from the blood the absence of nitrogenous wastes in the dialyzer fluid helps urea to easily move out there by clearing the blood anteye heparin is added to this cleared blood and it is pumped back into the body through a vein however in cases of acute renal or kidney failure the only option is kidney transplantation in this process a functioning kidney from a donor is transplanted in the patient usually a close relative of the patient is the preferred donor to minimize the chances of the patient's immune system rejecting the kidney other disorders due to the malfunctioning of the kidneys include the formation of stones or insoluble masses of crystallized salts within the kidney a condition known as renal calculi these stones are usually salts of calcium mainly calcium oxalate or calcium phosphate such stones are also formed in the ureter and the urinary bladder another disorder affecting the kidneys is glomerulonephritis wearin the glomeruli of the kidneys get inflamed therefore the functioning of the kidneys is efficiently monitored and controlled by hormonal feedback mechanisms and even a slight dysfunction or disorder may lead to severe diseases of the kidneys