EXCRETORY SYSTEM DR Tazeen Hassan shah M Phil

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 125 ml of plasma is filtered each min, or 180 L/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 125 ml/min or 180 L/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: 60 mmof hg Plasma colloid osmotic pressure: 32 Capsular pressure : 18 Net filtration pressure: 60 -18 -32=+10 mm 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=60 mm of hg bcop=0 mm of hg FORCES OPPOSING FILTRATION BHP=18 mm of hg GCOP=32 mm 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