DR.Tazeen Hassan shah M.Phil physiology EXCRETORY SYSTEM DR.Tazeen Hassan shah M.Phil physiology

kidney Structural and functional unit of kidney is nephron glomerulus renal tubules:pct,loop of henle,dct,collecting tubule,collecting ducts(250 each draining 4000 nephrons)

FUNCTIONS OF KIDNEY Removal of metabolic waste Electrolyte balance Water balance Regulation of blood pressure Regulation of acid-base balance Erythropoiesis Vit D activation Release of renin

Gluconeogenesis Release of kinins VASCULAR BEDS OF KIDNEY GLOMERULUS:60 mm of hg PERITUBULAR CAPPILLARIES:13 mm of hg

TYPES OF NEPHRON Cortical nephron:present in renal cortex,short loop of henle,that is surrounded by tortuous peritubular cappillaries. Juxtra medullary nephron(30%):present near corticomedullary junction,long loop of henle,surrounded by straight pt cappillaries,k/as vasa recta,concerned with concentration of urine.

URINE FORMATION GLOMERULAR FILTRATION SELECTIVE REABSORPTION ACTIVE SEREATION

GLOMERULAR FILTRATION 125ml of plasma is filtered each min,or 180L/d Of which 178.5 lit are reabsorbed and 1.5 lit becomes urine/day Whole plasma is filtered 60 times /day

SELECTIVE REABSORPTION As filtrate passes via renal tubules ,nutrionally important subtances are reabsorbedto blood via peritubular cappillaries,e.g:glucose,amino acid,vitamins. Unwanted substances are not reabsorbed eg:urea,creatinine

Active secreation Some substances are actively secreated into renal tubules via peritubular cappillaries like H and K ions EXCRETION Substances not reabsorbed and those which are secreated together with water are finally excreted via kidney as urine.

GLOMERULAR FILTRATION Through high pressure bed of glomerulus 125ml/min or 180L/day No cells are filtered,no proteins are filtered Donnan’s effect:cat ions less and anions more filtered Plasma bound substances are less filtered

FILTRATION MEMBRANE Surface area: 0.8 msq Has three layers: Endothelium: fenestrated .large pores. Basement membrane:negatively charged proteoglycans,these repel and oppose the filtration of –vely charged plasma proteins. Epithelium:has podocyted with pores called slit pores.

FILTRATION PRESSURE Hydrostatic pressure:60mmof hg Plasma colloid osmotic pressure:32 Capsular pressure :18 Net filtration pressure:60-18-32=+10mm of hg Filtration coefficient:125/10=12.5/min/mm of hg

Factors affecting GFR Increase bp….increase GFR Inc gcp……inc GFR(glomerulonephritis) Inc bcp……dec GFR(UT obstruction) Dec filtration area…dec GFR Afferent arteriolar constriction… dec GFR Afferent arteriolar dilation…..inc GFR Efferent arteriolar constriction…inc GFR…long term dec GFR

Sympathetic stimulation-dec GFR Angiotensin 2 …..dec GFR FORCES FAVOURING FILTRATION GHP=60mm of hg bcop=0 mm of hg FORCES OPPOSING FILTRATION BHP=18mm of hg GCOP=32mm of hg

AUTOREGULATION OF GFR OCCURS VIA JGA(JUXTRA GLOMERULAR APPARATUS) MACULA DENSA:Proximal part of DCT,condensed cells in close contact with aff and eff arteriole,act as chemoreceptors and sense conc of Nacl reaching DCT. JG CELLS:modified smooth muscle cells of afferent arteriole,has renin containing granules,on signals from macula densa release renin.

LACIS CELL:present in mesangium,act by : afferent arterioler feedback mechanism efferent arterioler feedback mechanism When GFR dec less Nacl reaches macula densa in dct,It causes 2 reactions: afferent arteriole dilation JG cells relese more renin more angiotensin 2 formed

Constriction of efferent arteriole GFR inc toward normal