SYSTEMIC HISTOLOGY URINARY SYSTEM II Mr. Babatunde

Home , Distal convoluted tubule, Efferent arteriole, Interlobar arteries, Interlobar veins, Loop of Henle, Macula densa

SYSTEMIC HISTOLOGY URINARY SYSTEM II

Mr. Babatunde, D.E Descending Pars Recta (straight portion) of Proximal Tubule

 Is also lined by a simple cuboidal epithelium having a prominent brush border.  Cells are shorter and less elaborate in shape than those of the proximal convoluted tubule, but they have the same general features.  This region of the nephron is often damaged in acute renal failure and mercury poisoning.  This segment constitutes the initial part (thick descending limb) of the loop of Henle. Proximal convoluted tubule and thick descending limb of Henle’s loop

Distal convuloted tubule and thick ascending limb of Henle’s loop

Thin limb of Henle’s loop

Collecting duct

 is composed of a descending limb, a loop, and an ascending limb, all of which are lined by a simple squamous epithelium.  cells in this epithelium have nuclei that bulge into the lumen, and their surfaces possess only a few short microvilli.  the thin limb has separated into four distinct segment based on shape of cells, their content of organelles, the depth of their tight junctions, and their water permeability.  is the region that forms the middle part of the loop Henle. Proximal convoluted tubule and thick descending limb of Henle’s loop

Distal convuloted tubule and thick ascending limb of Henle’s loop

Thin limb of Henle’s loop

Collecting duct

 Is the third (and final) component of the loop of Henle.  Is lined by a simple cuboidal epithelium containing only a few microvilli.  Its nuclei occupy an apical position in the cells.  Mitochondria are compartmentalized within the interdigitations formed by the basal and lateral infoldings.  Cells transport ions from the lumen into the interstitium, and since this part of the nephron has a impermeability to water, the luminal fluid becomes hypotonic to the blood. Proximal convoluted tubule and thick descending limb of Henle’s loop

Distal convuloted tubule and thick ascending limb of Henle’s loop

Thin limb of Henle’s loop

Ascending Thick Limb of Distal Tubule

Collecting duct

 Begins at the macula densa.  Has microvilli much shorter than the proximal microvilli, and their nuclei occupy an apical position in the cytoplasm.  Extensive lateral interdigitations compartmentalize mitochondria in basal cytoplasmic infoldings.  Cells actively transport sodium ions from the filtrate into the interstitium. Proximal convoluted tubule and thick descending limb of Henle’s loop

Distal convuloted tubule and thick ascending limb of Henle’s loop

Thin limb of Henle’s loop

Collecting duct

Figure 19–16. Cellular ultrastructure of the nephron, represented schematically. Cells of the thick ascending limb of Henle’s loop and the distal tubule are different in their ultrastructures and functions. Figure 19—19. Region of the kidney consisting mainly of distal convoluted tubules (DCT) and thin segments of Henle’s loop (asterisks). Capillaries filled with blood appear in red. PT stain. Medium magnification. Figure 19—13. Renal cortex showing proximal (P) and distal (D) convoluted tubules. One can see sections through the vascular pole of 3 renal corpuscles where juxtaglomerular renin-secreting cells appear well stained (broken lines). PT stain. Medium magnification. 1. Macula Densa

 Is a specific region of the distal tubule, lying near the afferent glomerular arteriole.  Is one component of the juxtaglomerular apparatus.  Cells are tall, narrow, and lined up closely together to form a row of nuclei that appear as a “dense spot” by light microscopy.  Cells are thought to monitor the fluid in the distal tubule and send a signal to the juxtaglomerular cells (modified smooth muscle cells) located in the afferent arteriole.  Signaling could occur via gap junctions present between these two cells types. Figure 19—3. The renal corpuscle. The upper part of the drawing shows the vascular pole, with afferent and efferent arterioles and the macula densa. Note the juxtaglomerular cells in the wall of the afferent arteriole. Podocyte processes cover the outer surfaces of the glomerular capillaries; the part of the podocyte containing the nucleus protrudes into the urinary space. Note the flattened cells of the parietal layer of Bowman’s capsule. The lower part of the drawing shows the urinary pole and the proximal convoluted tubule. Figure 19—9. Photomicrograph of a renal cortex showing parts of 2 renal corpuscles, macula densa, and distal and proximal convoluted tubules. The collagen type IV of the basement membrane of the glomerular capillaries is clearly visible (arrows). The collagen of the parietal layer of the Bowman’s capsule and basal membrane of a distal tubule are shown by the arrowhead. Picrosirius stain. Medium magnification. Figure 19—21. Photomicrograph of renal cortex. A macula densa is clearly seen (arrow) at the vascular pole of a renal corpuscle. Picrosirius-hematoxylin (PSH) stain. Medium magnification. 2. Juxtaglomerular (JG) Apparatus

 is located at the vascular pole of the renal corpuscle.  consists of four structures: modified smooth muscle cells of the afferent arteriole, of the efferent arteriole, the macula densa (of the distal tubule) and the extraglomerular mesangial cells.

Function of Juxtaglomerular Apparatus  in response to a decrease in extracellular fluid volume (perhaps detected by the macula densa) the JG cells release renin (an Enzyme). Figure 19—3. The renal corpuscle. The upper part of the drawing shows the vascular pole, with afferent and efferent arterioles and the macula densa. Note the juxtaglomerular cells in the wall of the afferent arteriole. Podocyte processes cover the outer surfaces of the glomerular capillaries; the part of the podocyte containing the nucleus protrudes into the urinary space. Note the flattened cells of the parietal layer of Bowman’s capsule. The lower part of the drawing shows the urinary pole and the proximal convoluted tubule. Figure 19—24. Photomicrograph of an afferent arteriole entering a renal corpuscle. The wall of this arteriole shows the renin-producing juxtaglomerular (JG) cells (broken line). At the upper right is a distal convoluted tubule (DCT) with many elongated mitochondria. PT stain. High magnification. Renin

 acts on angiotensinogen in the plasma, converting it to angiotensin I.  in capillaries of the lung, angiotensin I is converted to angiotensin II, which causes release of aldosterone from the zona glomerulosa cells in the adrenal cortex. Aldosterone

 stimulates distal tubule cells to retain sodium ions.  water follows the sodium, and the fluid volume is increased in the extracellular compartment (thus correcting the initial problem.

Angiotensin II

 is also a potent vasoconstrictor, which acts to elevate the blood pressure. Distal tubule

Macula densa Afferent arteriole Juxtaglomerular cells (modified smooth muscle) Juxtaglomerular cells Efferent arteriole Bowman’s capsule Vascular pole

(Parietal layer) Bownan’s capsule (Visceral layer Podocytes)

Parietal layer Urinary space Urinary pole

Brush border Proximal convoluted tubule Figure 19—24. Photomicrograph of an afferent arteriole entering a renal corpuscle. The wall of this arteriole shows the renin-producing juxtaglomerular (JG) cells (broken line). At the upper right is a distal convoluted tubule (DCT) with many elongated mitochondria. PT stain. High magnification.

3. Collecting Tubules

 have different functions, depending on their location in the kidney.  in the cortex and medulla they respond to antidiuretic hormone (ADH), also known as vasopressin.  in the medulla they play a primary role in producing a concentrated urine (by establishing a gradient due to the transport of urea from the tubular fluid into the renal interstitium). Figure 19—22. Photomicrograph of renal medulla with 2 collecting ducts consisting of cuboidal cells resting on a basement membrane. In this hypertonic region of the kidney, because of the action of the hypophyseal antidiuretic hormone, water is reabsorbed, controlling the water balance of the body. PT stain. Medium magnification. Figure 19—23. Electron micrograph of a collecting tubule wall. M, mitochondria; NU, nucleolus. x15,000. C

P Collecting tubule (C) Proximal tubule (P)

C P Cortical Collecting Tubules

 are located primarily within the medullary ray, although a few arched collecting tubules exist with the cortical labyrinth.  have two cell types, a light (principal) cell and a dark (intercalated) cell.

1) Light Cells  are simple cuboidal in shape and have round centrally located nuclei.  a single central cilium (flagellum) extends into the lumen from the surface of each light cell. 2) Dark Cells  are fewer in number and have microplicae (folds) on their surface.  apical cytoplasm of the dark cell contains many vesicles. Glomerulus Collecting tubule Medullary Collecting Tubule

 is similar in structure to the cortical collecting tubule.  dark cells are present in outer medulla but absent in inner medulla.  principal (light) cells increase in height, and in the inner medulla are the only cell type lining the collecting tubule. Papillary Collecting Tubule (duct of Bellini)

 large collecting tubule formed from converging collecting tubules.  consists only of principal cells and is a simple columnar epithelium.  lumen of the duct of Bellini measures 200 to 300 µm in diameter.  empties at the area cribrosa (a region having a sieve-like appearance) on the apex of a renal papilla. Renal pyramid Papillary collecting tubule (a) Minor calyce (c) 4. Renal Interstitium

 is the connective tissue compartment in the kidney.  in cortical interstitium are two main cell types: fibroblasts and mononuclear cells.  in interstitium of the medulla, pericytes are present along the descending vasa recta.  another cell type having long processes and containing many small lipid droplets (which probably contain a hormone that reduces blood pressure) is also common in medulla interstitium. 5. Blood Supply of Kidney

 is extensive (flow through both kidneys is about 1,200 ml/min.

Renal Artery

 its branches enter the hilus, giving rise to interlobar arteries that travel between the renal pyramids. Interlobar Arteries

 divide into several arcuate arteries that run along the corticomedullary junction, in a direction parallel with the surface of organ.  small interlobular arteries arise from the arcuate arteries and enter the cortical tissue to pass between lobules. Interlobular Arteries

 give rise to afferent (glomerular) arterioles, which supply the glomerular capillaries.

Efferent Glomerular Arterioles

 leave the glomerulus and give rise to an extensive peritubular capillary network that supplies the convoluted tubules.  from glomeruli of juxtamedullary nephrons form thin-walled vessels called vasa recta, which are long straight capillaries that extend into the medullary pyramids. Figure 19—3. The renal corpuscle. The upper part of the drawing shows the vascular pole, with afferent and efferent arterioles and the macula densa. Note the juxtaglomerular cells in the wall of the afferent arteriole. Podocyte processes cover the outer surfaces of the glomerular capillaries; the part of the podocyte containing the nucleus protrudes into the urinary space. Note the flattened cells of the parietal layer of Bowman’s capsule. The lower part of the drawing shows the urinary pole and the proximal convoluted tubule. Efferent arteriole

Glomerulus Afferent arteriole

Interlobular artery Vasa Rectae “juxtamedulary nephrons”

 form hairpin loops and ascend to form a countercurrent system of vessels called vascular bundle (rete mirabile).  these vessels drain into interlobular or arcuate veins, then into interlobar veins, which at the hilus form the renal vein.

Outermost Layers of Cortex

 are drained by superficial cortical veins, which join stellate veins and empty into interlobular and arcuate veins.

Deeper Regions of the Cortex

 are drained by deep cortical veins. Excretory Passages

Components  Include the minor and major calyces, the renal pelvis, ureter and urinary bladder.  Each of these passages has three layers, a mucosa (consisting of transitional epithelium lying on a subepithelial connective tissue), a muscularis, and an adventitia. 1. Ureter

 Is the conduit between the renal pelvis and the urinary bladder.  epithelium is thicker and has more cell layers than that in the calyces.  upper two-thirds of ureter has an inner longitudinal and an outer circular layer of smooth muscle.  lower one-third of ureter has an additional outer longitudinal layer of smooth muscle.  contraction of these muscle layers produces peristaltic waves, which propel urine along so that it enters the bladder in spurts. Figure 19—28. Photomicrograph showing the main components of the ureter, which consists of an inner layer of transitional epithelium, a highly vascularized connective tissue, a smooth muscle layer, and an outer layer of connective tissue. PT stain. Low magnification. Epithelium Outer longitudinal adventitia Sub epithelial muscularis connective tissue Middle circular muscularis Smooth muscle coat

Inner longitudinal muscularis Lumen

Adventitia Dome shaped cell

2. Urinary Bladder

 Is lined by a layer of transitional epithelium several cell layers thick.  Lumen of the bladder has a scalloped contour in the relaxed state, due to the domeshaped surface cells.  Lining cells have a thick asymmetrical plasmalemma, which displays a unique substructure (when viewed in the transmission electron microscope after freeze fracture).  Plaques in the form of hexagonally arranged subunits are observed, but their functional significance remains obscure.  cytoplasm of the surface cell has flattened elliptical vesicles, which insert themselves into the plasma membrane (to rapidly expand the area when the bladder is stretched).  epithelium has a remarkable ability to change its morphology in the relaxed versus the distended state.  a thin basal lamina underlies the transitional epithelium, and beneath it is fibroelastic connective tissue.  muscularis of the bladder is thick and consists of smooth muscle arranged in an inner longitudinal, middle circular and out longitudinal layer. Transitional epithelium

Lamina propria

Venule

Arteriole

Submucosa Transitional epithelium (relaxed) Transitional epithelium (stretched)

3. Male Urethra

 Conveys urine from the urinary bladder to the outside.  Also serves as a passageway for semen during ejaculation.  Is divided into prostatic, membranous and cavernous portions.  Transitional epithelium lines the prostatic portion, which pseudostratified or stratified columnar epithelium lines the remaining portions.  Beneath a thin basement membrane is the subepithelial connective tissue, where mucus-secreting glands (of Littre) may be found.  Muscularis has an inner longitudinal and an outer circular layer.  At distal end of the cavernous urethra is the fossa navicularis, lined by stratified squamous epithelium. 4. Female Urethra

 Is a short passageway from the urinary bladder to the outside.  Is lined primarily by stratified squamous epithelium, but has patches of pseudostratified columnar epithelium.  Mucus-secreting glands (of Littre) are located in the subepithelial connective tissue.  Muscularis is composed of an inner longitudinal and an outer circular layer of smooth muscle.