Distal convoluted tubule (DCT) Highly coiled, ~ 5 mm in length Last part of the nephron. Wall; simple cuboidal epithelium Less metabolically active than the PCT no brush border light eosinophilic cytoplasm Restricted to the cortex. DCT is shorter than PCT Less convoluted and abundant than PCT cortex 1 Along its path, the DCT establishes contact with the wall of the afferent arteriole. This portion contains modified cells; the macula densa. Functions as a chemoreceptor Stimulated by a decrease in sodium ions. 2
Wall of the afferent arteriole next to the macula densa contains modified smooth muscle cells called juxtaglomerular cells. These cells are stimulated by a decrease in BP to produce renin. Juxtaglomerular apparatus (GA) = macula densa, + juxtaglomerular cells important in BP regulation. 3 GA has several functions If [Na + ] in the DCT is unusually high; inadequate Na + reabsorption from the PCT Danger of excessive Na + loss from the body Response is constriction of the afferent arteriole BP in the glomerular capillaries falls; filtration rate decreases. 4
Collecting tubule (CT) CT is a short and straight portion following the DCT Connecting to collecting duct little to no absorptive activity wall; light-staining simple cuboidal epithelium CTs are uncommon in sections of cortex--less common than DCT's. 5 Collecting duct (CD) Collecting tubules and ducts. Each collecting tubule descends in the cortex drains an increasing number of DCTS. CTs join and form larger, straight CDs which drain the urine into minor calyces. Mostly columnar epithelium. CD is important for final nephron H2O reabsorption 6
7 Histological appearance of zones of the medullary pyramid Outer zone Most common: thick portion of LH; Less common: thin portion of LH, CD, capillaries Rare: DCT. 8
Histological appearance of zones of the medullary pyramid, as seen in crosssection: Inner zone: Composed of CD's, thin portions of LH's, and capillaries. 9 Other histological features of the kidney Lumenal epithelium of minor calyces and major calyx: transitional epithelium AKA, urothelium 10
Kidney has a thin outer wall of dense C.T. Capsule of the kidney Surrounded by fat Kidneys are retroperitoneal -behind the peritoneum Not covered by a mesothelium (serosa) 11 Ureter Carries urine to the bladder small-diameter thick-walled tube Wall components Mucosa simple folds (unbranched); lumen is symmetrical Epithelium: urotehlium; no glands Lamina propria: thin;-dense C.T.; no vessels larger than venules or arterioles No muscularis mucosae Submucosa: thin; extends into folds 12
13 Ureter Muscularis: smooth muscle tissue; layers incomplete and/or indistinct. inner, longitudinal layer middle, circular layer inner outer, longitudinal layer only in lower ureter, near bladder middle 14
Ureter Tunica adventitia dense C.T. small muscular artery, etc. yellow adipose tissue loose CT Urine is moved by peristalsis. No serosa ureter is retroperitoneal TA 15 Urinary bladder Wall components (similar to ureter) Mucosa folded when relaxed, simple folds short compared to organ's diameter Epithelium: urothelium much thicker when relaxed. Unusually impermeable to small molecules e.g., H2O and urea 16
17 Urinary bladder LP: thin; as in ureter No muscularis mucosae Submucosa: thicker than ureter but similar Muscularis: very thick--more than ureter SMT layering pattern similar to ureter not as distinct; some remnant of fundamental 3-layered Tunica adventitia: relatively thin; similar to ureter. Serosa present Bladder is within the peritoneal cavity 18
Urethra General features Tubular organ; last organ of the system opens to outside Simple mucosal folds. Flattened to crescent-shaped (Ushaped) lumen 19 Urethra I. Urethra Three regions along the length of the organ :upper region, middle region, (4) and Three lower region; regions along the length of the organ Male urethra are designated: upper region, middle region, and much longer than female s as it passes through the penis lower Mucosa: region; transitional these to stratified regions squamous (urothelium) differ histologically between each other and between sexes. (5) The urethra of males is much longer than that of females due to the presence of the penis in males. 20
Urethra Muscularis SMT, 2 to 3 layers: inner, longitudinal middle, circ. outer, long. Some regions Crypts of Morgagni; lumenal tubular extensions to submucosal mucus glands Submucosa In some regions: composed partly of erectile tissue. Composed of venous sinuses surrounded by dense CT Erectile tissue has two names corpus cavernosum urethrae (translations: spongy body; cavernosa) corpus spongiosum 21 22