Renal System PDF

KIDNEY Dr. Sally Salem Assistant professor of Histology & Cell Biology Suez Canal University, FOM Objectives Renal cortex, medulla, interstitium Uriniferous tubules Podocyte …..GFB JGA  Kidneys are paired bean-shaped organs enveloped by a thi...

KIDNEY Dr. Sally Salem Assistant professor of Histology & Cell Biology Suez Canal University, FOM Objectives Renal cortex, medulla, interstitium Uriniferous tubules Podocyte …..GFB JGA  Kidneys are paired bean-shaped organs enveloped by a thin capsule of connective tissue Each kidney is divided into an outer cortex and an inner medulla. Each kidney contains about 2 million nephrons. Each part has its own microcrtructure plus renal interstitium.  Renal Medulla Deep to the cortex, sends extensions into the cortex …… …………Medullary Rays Renal (medullary) pyramids: pyramidal-shaped structures that compose the bulk of the renal medulla. The bases of the pyramids establish the corticomedullary junction. The apex of each pyramid forms the deepest portion of the medulla. Each kidney contains 10 to 18 renal pyramids.  Renal Medulla Each pyramid: thin limbs of loops of Henle, blood vessels, and collecting tubules. The renal papilla at the apex of each renal pyramid. Area cribrosa projects into the lumen of a minor calyx.  Renal Cortex The renal cortex: renal corpuscles and convoluted tubules. 1. Renal columns of Bertin are extensions of cortical tissue between adjacent renal pyramids. 2. Medullary rays are groups of tubules that extend from the base of each renal (medullary) pyramid into the cortex. These tubules are the straight portions of the proximal and distal tubules as well as the collecting ducts that drain nephrons.  Renal Interstitium Scanty connective tissue compartment of the kidney, less than 10% of the cortical volume, 20% of the medullary volume. Fibroblasts and mononuclear cells. In the medulla, it consists of two additional cell types: 1. Pericytes are located along the blood vessels that supply the loops of Henle. 2. Interstitial cells have long processes that extend toward (and perhaps encircle) capillaries and tubules in the medulla. These cells manufacture medullipin I, converted to medullipin II in the liver. Medullipin II is a vasodilator.  Uriniferous Tubule Nephron and collecting tubule  Uriniferous Tubule Nephron Renal corpuscle, proximal tubule (composed of the proximal convoluted tubule and the pars recta of the proximal tubule), thin descending limb of Henle loop, Henle loop, thin ascending limb of Henle loop, and distal tubule (composed of the pars recta of the distal tubule, the very short macula densa, and the distal convoluted tubule). Pars recta of the proximal tubule is known as descending thick limb of Henle loop, and the pars recta of the distal tubule is known as the ascending thick limb of Henle loop.  Uriniferous Tubule Nephron, renal corpuscle Glomerulus and Bowman capsule. a. Bowman capsule (1) parietal layer. (2) visceral layer….. podocytes. The (3) Urinary space and leaves the renal corpuscle at (4) Urinary pole & vascular pole  Uriniferous Tubule Nephron renal corpuscle Bowman capsule…..Podocytes possess several primary processes that give rise to many secondary processes called pedicels. Pedicels encircle the glomerular capillaries and interdigitate with pedicels from other primary processes spaced with filtration slits (40 nm). A filtration slit diaphragm bridges each filtration slit is the principal structure responsible for the filtration of proteins.  Uriniferous Tubule Nephron renal corpuscle Glomerular filtration barrier (1) fenestrated endothelium of the glomerular capillaries (2) basal lamina (laminae rarae and lamina densa) (3) filtration slit diaphragm bridging the filtration slits between adjacent pedicels.  Uriniferous Tubule Nephron renal corpuscle Glomerular filtration barrier Function. The renal filtration barrier permits passage of water, ions, and small molecules from the bloodstream into the capsular space but prevents passage of large and most negatively charged proteins (a) The laminae rarae contain heparan sulfate, a polyanionic glycosaminoglycan restricting the passage of negatively charged proteins into the Bowman space. (b) The lamina densa contains type IV collagen  Uriniferous Tubule Nephron renal corpuscle b. Glomerulus. (1) Glomerular endothelial cells (2) The basal lamina (3) The mesangium  Uriniferous Tubule Nephron renal corpuscle b. Glomerulus. (1) Glomerular endothelial cells possess large fenestrae (60–90 nm in diameter) but lack the thin diaphragms that typically span the openings in other fenestrated capillaries  Uriniferous Tubule Nephron renal corpuscle b. Glomerulus……The basal lamina (a) The lamina rara externa, an electron- lucent zone adjacent to the podocyte epithelium. (b) The lamina densa, a thicker, electron- dense intermediate zone of amorphous material. (c) The lamina rara interna, an electron- lucent zone adjacent to the capillary endothelium  Uriniferous Tubule Nephron renal corpuscle b. Glomerulus……The mesangium mesangial cells and matrix. (a) Mesangial cells 1. phagocytose large protein molecules and debris. 2. contract decreasing the surface area available for filtration. 3. possess receptors for angiotensin II and atrial natriuretic peptide. 4. manufacture platelet-derived growth factor, endothelins... (b) The mesangial matrix, manufactured by mesangial cells, type IV collagen, laminin, and proteoglycans and helps support glomerular capillaries  Uriniferous Tubule Nephron and collecting tubule Proximal convoluted tubule  Uriniferous Tubule Nephron, Proximal convoluted tubule LM Cuboidal to columnar, microvilli forming a prominent brush border, deep acidophilic cytoplasm. EM (1) Apical canaliculi, vesicles, and vacuoles (endocytic complex), which function in protein absorption. (2) Prominent interdigitations along their lateral borders, which interlock adjacent cells with one another.  Uriniferous Tubule Nephron, Proximal convoluted tubule EM 3) Numerous mitochondria compartmentalized in the basal region by extensive infoldings of the basal plasma membrane, which supply energy for the active transport of Na+ out of the tubule.  Uriniferous Tubule Nephron, Thin limb of the Henle loop The thin limb of the Henle loop is composed of a descending segment, a loop, and an ascending segment, all of which are lined by simple squamous epithelial cells possessing a few short microvilli.  Uriniferous Tubule Nephron, distal convoluted LM It is much shorter and has a wider lumen than the proximal tubule and lacks a brush border. Cells are smaller and less acidophilic.  Uriniferous Tubule Nephron, juxtaglomerular apparatus At the vascular pole of the renal corpuscle Components of the JG apparatus (1) JG cells (juxtaglomerular cells) (2) Macula densa cells (3) Extraglomerular mesangial cells  Uriniferous Tubule Nephron, juxtaglomerular apparatus At the vascular pole of the renal corpuscle 1) JG cells (juxtaglomerular cells) (a) are modified smooth muscle cells, characters of protein-secreting cells. (b) primarily in the wall of the afferent arteriole, few may in the wall of the efferent arteriole. (c) synthesize renin (a proteolytic enzyme) and store it in secretory granules.  Uriniferous Tubule Nephron, juxtaglomerular apparatus At the vascular pole of the renal corpuscle (2) Macula densa cells (a) are tall, narrow, closely packed epithelial cells of the distal tubule. (b) have elongated, closely packed nuclei that appear as a dense spot (macula densa) by light microscopy. (c) monitor the osmolarity and volume of the fluid in the distal tubule and transmit this information to JG cells via the gap When the sodium concentration or the volume of the junctions between the two cell types. ultrafiltrate is reduced, the macula densa cells direct the JG cells to release their renin.  Uriniferous Tubule Nephron, juxtaglomerular apparatus At the vascular pole of the renal corpuscle (3) Extraglomerular mesangial cells (a) are also known as polkissen (pole cushion) or lacis cells. (b) lie between the afferent and efferent glomerular arterioles, but their functions are not understood. Uriniferous Tubule Nephron, juxtaglomerular apparatus  Uriniferous Tubule Nephron and collecting tubule Collecting tubule  Uriniferous Tubule Nephron and collecting tubule 1. Cortical collecting tubules are located primarily within medullary rays. Simple epithelium containing two types of cuboidal cells. a. Principal (light) cells possess a round central nucleus and a single primary cilium. Responsible for urine concentration b. b. Intercalated (dark) cells are less numerous than principal cells and possess microplicae (folds) on their apical surface and numerous apical cytoplasmic vesicles.