LECTURE 4b URINARY SYSTEM (DR. B.M. KAVOI)
Main components of this system- 1. Kidneys, 2. Ureter, 3. Urinary bladder and 4. Urethra1. KIDNEY Parenchyma organized into cortex (F) and medulla (E) Within parenchyma occur nephrones, collecting ducts, blood vessels, lymphatics and nerves Parenchyma organized into lobes and lobules
Lobes and lobules
At the cortex, the collecting duct lies at the axis of lobule, being surrounded by corticolabyrinth or network comprising of renal corpuscles, PCT and DCTLobules are centered on "medullary rays“, which are bundles of straight tubules (collecting ducts and loops of Henle)Within the cortex, peripheral limits of a lobule are the interlobular blood vessels while in medulla, limits of lobules are not definedNephron
Tubules in which urine is formed (functional unit of the kidney Form the most abundant tissue of renal parenchyma Consist of 5 parts; i. Renal corposule, ii. Proximal convoluted tubule iii. Medullary loop (loop of Henle) iv. Distal convoluted tubule v. Collecting ducti. Renal corpuscle
Produces glomerular ultrafiltrateIs a spherical structure comprising of a) cluster of blood vessels= glomerulus b) double walled envelope= glomerular or Bowman’s capsuleEfferent arterioles enter while the afferent arterioles leave the glomerulus at vascular pole while ultrafiltrate leave corpuscle at renal poleCapillaries forming glomerulus are fenestrated and their endothelium rests on a thick basal laminaBowman’s capsule comprise of inner visceral and outer parietal layers and Bowmans space in btw the layersParietal layer is formed by simple squamous cells while visceral is formed by podocytes, whose foot processes (pedicels) contact glomerular blood capillariesThe connective tissue stroma of the glomerulus is constituted by mesangial cells, which support the glomerular capillaries
ii.Proximal convoluted tubule
Reabsorption of water, nutrients and solids (obligatory) Lined by simple cuboidal epithithelium resting on a thin b. lamina Tubule cells have microvilli on their luminal surfaces (typical brush border) Tubule cells appear striated due to numerous basal infoldings & plenty of mitochondria
iii.Medullary loop
Functions as a counter-current multiplier system to determines osmolarity of urine; blood flow in the loop is counter to that in medullary vasa recta. Extends from corticomedullary junction to medulla Consists of an descending limb, a thin segment and a ascending limb The thin part is lined by simple squamous epithelium resting on a thin BL; the sq cells sq. cells bulge into the lumen of tubuleiv.Distal convoluted tubule
Reabsorbs most of substances contained in ultrafiltrate especially glucosa and amino acids (mainly facultative) Reabsorption regulated by ADH and aldosterone Continues from the m. loop and extends to collecting tubule within cortex Lined by low simple cuboidal epithelium resting on a thin BL The cells lack microvilli but are striated, with basal infoldings and but less mitochondria Its epithelial cells stain less osmophilic compared to those of PCTJuxtaglomerular apparatus
Formed where the DCT contacts the afferent arteriole of parent r. corpuscle Constituted by 3 cell types; i. macular densa cells of DCT (t. cells that become columnar & closely packed) ii.Juxtaglomerular cells of afferent arteriole (smooth muscle cells of tunica media that become spherical and contain renin granules) iii. Extraglomerular mesangial cells (similar to those within glomerulus and surrounded by thick BL) Produce renin which converts angiotensinogen to angiotensin, (a vasoconstricter which raises bld pressure thus flow of ultrafiltrate)v. Collecting tubule
Drain urine from nephron to renal pelvis Lie on medullary ray within cortex Progressively increase in diameter towards medullar In inner medullar, CD from different renal lobes unite to form large papillary ducts, which open into renal pelvisDrain urine from nephron to r. pelvisProgressively increase in diameter towards medullar In inner medullar, unite with other CDs to form large papillary ducts, which open into renal pelvisCD are lined by epithelium that has 2 cell types 1. collecting duct cells – cuboidal in cortical part, columnar in medullary 2. intercalated /dark cells- resemble those of DCT but bulge into lumen of the CDBoth cell types rest on a thin BM and lack basal infoldingsPermeability of CD to water and ions is regulated by ADH