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1 POINTS TO REMEMBER : Dwnladed frm Excretry Prducts and Their Eliminatin Ammntelic: eliminatin f nitrgenus waste in the frm f ammnia.(fish) Uretelic: eliminatin f nitrgenus waste in the frm f urea.(amphibia and mammalian) Urictelic: eliminatin nitrgenus waste in the frm f uric acid. (Reptilia, bird and insects) Excretry rgans : Prtnephridia r flame cells Platyhelminthes (Planaria), rtifers, sme annelids and cephalchrdates (Amphixus) Nephridia: annelid. Malpighian tubules insects Antennal gland r green glands crustacean like prawn. HUMAN EXCRETORY SYSTEM : Human excretry system cnsists f A pair f kidney A pair f ureters A urinary bladder A urethra Kidney is reddish brwn, bean shaped structure situated between the levels f last thracic vertebra clse t drsal inner wall f the abdminal cavity. Each kidney measures cm in length, 5-7 cm in width, 2-3 cm in thickness. Twards the centre f inner cncave surface is a ntch, called hilum thrugh which ureters, bld vessel and nerves enter int the kidney. Inner t hilum is a brad funnel shaped space called renal pelvis with prjectins called calyces. The uter wall f kidney is a tugh capsule. Internally the kidney is differentiated int uter crtex and inner medulla. The medulla is divided int a few cnical masses called medullary pyramids. Pyramids prjected int the calyces. The crtex extended in-between the medullary pyramids as renal clumns called clumns f Bertini. Each kidney has nearly ne millin cmplex tubular structures called nephrns. Structural and functinal unit f kidney is called nephrn r uriniferus tubule. Each nephrn has tw parts: Glmerulus Renal tubule. Glmerulus is a tuft f capillaries frmed by the afferent renal arterile (a branch f renal artery). Bld frm the Glmerulus is cllected by efferent renal arterile. The renal tubule begins with a duble walled cup-like structure called Bwman s capsule, which enclses the Glmerulus. Glmerulus alng with Bwman s capsule is called Malpighian bdy r renal crpuscles. Bwman s capsule fllwed by highly ciled prximal cnvluted tubule (PCT). Dwnladed frm

2 Dwnladed frm PCT fllwed by hairpin shaped Henle s lp with ascending and descending limb. The ascending limb fllwed by anther ciled tubular regin called distal cnvluted tubule (DCT). DCT f many nephrn pens int a straight tube called cllecting duct. All the cllecting duct cnverges and pens int renal pelvis thrugh medullary pyramids in the calyces. The malpighian crpuscles, PCT and DCT f the nephrn are lcated in the crtex but the lp f Henle dips int the upper medulla. In sme f the nephrn, the lp f the Henle is very lng and runs deep int the inner medulla. These nephrns are called juxta medullary nephrns. The efferent renal arterile emerging frm the Glmerulus frms a fine capillary netwrk arund the renal tubule called the peritubular capillaries. A minute vessel f this netwrk runs parallel t the lp f Henle frming U shaped vasa recta. Vasa recta are absent r reduced in crtical nephrn. The juxta medullary nephrn has juxta-glmerular apparatus, in which the DCT run clse t the afferent renal arterile. MECHANISM OF URINE FORMATION : Urine frmatin invlves three main prcesses Glmerular filtratin Selective reabsrptin Tubular secretin. Glmerular filtratin r ultra filtratin : On an average ml bld is filtered by the kidneys per minute. The glmerular capillary bld pressure caused filtratin f thrugh filtratin membrane. The filtratin membrane is frmed by Endthelium f glmerular bld vessel. The epithelium f Bwman s capsule (pdcytes) Basement membrane f these tw layers. The epithelial cells f Bwman s capsule called pdcytes are arranged in an intricate manner s as t leave sme minute spaces called filtratin slit r slit pres. All cnstituent f plasma pass the filtratin membrane except prtein, hence it is called ultra filtratin. The amunt f filtrate frmed by the kidneys per minute is called glmerular filtratin rate (GFR). GFR is abut 125 ml/min. i.e. 180 liters per day. Selective reabsrptin : Out f 180 liters f filtrate frmed every day liters alng with useful materials reabsrbed int the bld thrugh peritubular capillaries leaving 1.5 liters excreted in the frm f urine. The tubular epithelial cells f different segments f nephrn perfrm these either active r passive mechanisms. Substance like glucse, amin acids Na+ absrbed actively. Nitrgenus wastes are absrbed by passive transprt. Reabsrptin f water als ccurs passively in the initial segments f the nephrn. Tubular secretin : Dwnladed frm

3 Dwnladed frm The tubular cells adds substances like H +, K + and ammnia t the filtrate frm the peritubular capillaries. Tubular secretin maintains inic and acid base balance f the bdy fluids. FUNCTION OF THE TUBULES : Prximal cnvluted tubule (PCT) : PCT is lined by simple Cubidal brush brder epithelium which increases the surface area fr absrptin. All essential nutrients and 70-80% f the electrlytes and water are reabsrbed by this segment. PCT als maintain the ph and inic balance f the bdy fluids by selective secretin f H +, K + and ammnia int the filtrate and by absrptin f HCO3-. Henle s Lp : This regin plays imprtant rle in maintenance f high smlarity f medullary interstitial fluid. The descending limb is permeable t water but impermeable t electrlytes. This cncentrates the filtrates as it mves dwn. The ascending limb is permeable t electrlytes but impermeable t electrlytes. Therefre as the cncentrated filtrate pass upward, it gets diluted due t active r passive transprt f electrlytes t the medullary fluid. Distal cnvluted tubules : Selectable reabsrptin f Na+ and water takes place in this segment. DCT als capable f reabsrptin f HCO3- and selective secretin f H +, K +, and NH3 t maintain the ph and sdiumptassium level in bld. Cllecting duct : This duct extends frm crtex t inner part f the medulla. Large amunt f water culd be reabsrbed frm this regin t prduce cncentrated urine. This segment allw small amunt f urea int the medullary interstitium t keep up the smlarity. MECHANISM OF CONCENTRATION OF FILTRATE : Mammals have the ability t prduce cncentrated urine. The Henle s lp and vasa recta plays significant rle in cncentrating urine. The flw f filtrate in tw limb f Henle s lp and bld flw in tw limbs f vasa recta are in ppsite directin hence frm cunter current. The prximity between the Henle s lp and vasa recta, as well as the cunter current in them help in maintain an increasing smlarity twards the inner medullary interstitium, i.e. frm 300 mosmll-1 in the crtex t abut 1200 mosmll-1 in the inner medulla. The gradient is mainly due t NaCl and urea. The NaCl actively transprted frm the ascending limb f Henle s lp is exchanged by the ascending prtin f the vasa recta. NaCl is returned t the interstitium by the ascending prtin f vasa recta. Small amunt f urea enters the thin segment f ascending limb f Henle s lp which is transprted back t the interstitium by the cllecting tubule. This abve described transprt f substances facilitated by the special arrangement f Henle s lp and vasa recta is called the cunter current mechanism. Dwnladed frm

4 Dwnladed frm This mechanism helps t maintain a cncentratin gradient in the medullary interstitium, that prmte easy passage f water frm the cllecting duct, leads t frmatin f cncentrated urine. REGULATION OF KIDNEY FUNCTION : Regulatin by ADH : Osmreceptrs present in the hypthalamus are activated by the change f bld vlume, bdy fluid vlume and inic cncentratin. An excessive lss f bdy fluid activates the Osmreceptrs f hypthalamus t release antidiuretic hrmne (ADH) rvaspressin frm the neurhypphysis. ADH facilitates active reabsrptin f water frm the DCT, preventing dieresis. An increase in bdy fluid vlume can switch ff the Osmreceptrs and suppress the release f ADH, prmting dilute urine frmatin. ADH als cnstricts the afferent renal arterile in increase the bld pressure in the ther hand t maintain the GFR. Regulatin by JGA (Juxta Glmerular Apparatus) : A fall in glmerular bld flw/glmerular bld pressure/gfr can activate the Juxta Glmerular cells t releaserenin. Renin cnverts angitensingen in bld t angitensin I and further t angitensin II. Angitensin II cnstricts afferent renal arterile t increase glmerular bld pressure and thereby GFR. Angitensin II als stimulates adrenal crtex t release aldsterne. Aldsterne cause active reabsrptin f Na+ and water frm the distal part f the tubule, this increase in bld vlume and GFR. This cmplex mechanism is called RAAS (Renin angitensin aldsterne system). Regulatin by ANF : An increase in bld flw t the atria f the heart due RAAS cause the release f Atrial Natriuretic Factr (ANF). ANF can cause vasdilatin (afferent renal arterile) and thereby decrease the bld pressure. ANF als stp the release f renin hence stps RAAS. MICTURITION : The expulsin f urine frm the urinary bladder. It is a reflex prcess but can be cntrlled vluntarily t sme extent in grwn up children and adults. The CNS (Central Nervus System) sends the signal which causes the stretching f the urinary bladder when it gets filled with urine. In respnse, the stretch receptrs n the walls f the bladder send signals t the CNS. The CNS passes n mtr massage t initiate the cntractin f smth muscles f the bladder and simultaneus relaxatin f the urethral sphincter causing the release f urine. An adult human excretes n an average 1 t 1.5 liters f urine per day. On an average gram f urea is excreted ut per day. Presence f Glucse is called Glycsuria. Presence f Ketne bdies in urine called Ketneuria. Glycsuria and Ketneuria are the indicatin f Diabetes mellitus. Rle f ther rgans in excretin : Lungs - remves CO2 (18L/day) and water. Dwnladed frm

5 Dwnladed frm Liver - secretes bilirubin, biliverdin etc. helps t eliminate these substances alng with chlesterl, vitamins, drugs and degraded sterid hrmnes thrugh digestive wastes. Sweat and sebaceus glands - These glands f skin help t eliminate small amunt f urea, NaCl and lactic acid etc. thrugh sweat while sebaceus glands help t eliminate sme substances like sterids, hydrcarbns and waxes thrugh sebum. Saliva - It can help t eliminate small amunt f nitrgenus wastes. Disrders f Excretry system : Uremia - The accumulatin f urea in bld due t malfunctining f kidney. Hemdialysis - The prcess f remval f urea frm the bld artificially. In this prcess the bld frm an artery is passed int dialysing unit after adding an anticagulant like heparin. The bld passes thrugh ciled cellphane tube surrunding by dialysing fluid. The nitrgenus wastes frm the cncentratin gradient and the bld becme clear. This bld is pumped back t the bdy thrugh vein after adding anti-heparin t it. Renal calculi - The frmatin f insluble mass f crystallised salts (xalates r phsphates f calcium. Glmerulnephritis - Inflammatin f glmeruli f kidney. Dwnladed frm