Urinary System Dr. Bolfa PDF

Urinary System Dr. Bolfa 1. Overview of urinary system a. Kidney → ureters → urinary bladder → urethra b. Kidney - excrete nitrogenous waste, conserve body fluids and electrolytes, reabsorb solutes and water c. Ureters - convey urine to bladder d. Urin...

Urinary System Dr. Bolfa 1. Overview of urinary system a. Kidney → ureters → urinary bladder → urethra b. Kidney - excrete nitrogenous waste, conserve body fluids and electrolytes, reabsorb solutes and water c. Ureters - convey urine to bladder d. Urinary bladder - store urine e. Urethra - expel urine 2. Functions a. Water and electrolyte homeostasis i. Filtration of cellular wastes ii. Selective reabsorption of water and solutes iii. Regulation of fluid balance iv. Maintain electrolyte homeostasis/ acid base balance b. Excretion of metabolic waste products, bioactive substances (drugs), and excess water c. Production of hormones such as renin and erythropoietin d. Regulation of blood pressure i. Juxtaglomerular apparatus e. Activation of vitamin D 3. Cat kidneys a. Appear on the paler side because of the lipid concentration b. This is NORMAL but makes it harder to recognize disease in cat kidneys 4. Structure of the kidney a. Located retroperitoneal 5. Lobes of kidneys a. Unilobular - carnivores b. Multilobular (with deep grooves) - large ruminants c. Multilobar (smooth) - pigs 6. Important tissues of the kidney a. Capsule i. Collagen fibers ii. Smooth muscle iii. Blood vessels b. Cortex i. Renal corpuscles ii. Convoluted tubules c. Medulla i. Loop of Henle ii. Collecting duct d. Pelvis i. Urothelium ii. Submucosa iii. Smooth muscle iv. Adventitia e. MAKE UP THE NEPHRON i. Renal corpuscles ii. Convoluted tubules iii. Loop of Henle 7. Nephron a. The functional unit of the kidney is the nephron b. Nephrons are the site of osmoregulation via i. Filtration of water and small molecules from blood plasma to form a filtrate ii. Selective reabsorption of most of the water and other molecules from the filtrate 8. Important structures in the regions of the kidney a. Cortex i. Renal corpuscles ii. Proximal tubules iii. Distal convoluted tubules iv. Collecting tubules  v. Peritubular capillary plexuses b. Medulla i. Loops of Henle ii. Collecting ducts iii. Vasa recta 9. Renal corpuscle is composed of the glomerulus and Bowman's capsule a. Glomerulus - loops (tuft) of capillaries with fenestrated endothelium within the Bowman’s capsule b. Bowman’s capsule i. Visceral epithelium - podocyte ii. Glomerular basement membrane iii. Urinary space iv. Parietal epithelium - squamous cells v. Vascular pole vi. Urinary (tubular) pole c. Mesangial cells lie between fenestrated capillaries i. Support cells that function to phagocytes d. PROTEIN CONSERVATION i. If there is protein in the urine, suspect renal corpuscle 10. Ultrafiltration at the glomerulus a. Vascular pole → ultrafiltration → urinary pole i. Vascular pole - blood enters at the glomerular capillaries via the afferent arteriole 1. Blood exits at the efferent arteriole (main) ii. Ultrafiltration - blood pushed through filtration barrier 1. Fenestrated endothelium 2. Glomerular basement membrane 3. Podocyte foot processes 4. Ultrafiltrate enters the urinary space iii. Urinary pole - ultrafiltrate enters proximal convoluted tubule 11. Filtration barrier is formed from 3 components a. Endothelium - of glomerular capillary loops (CL) with fenestrations b. Glomerular basement membrane (GBM) - fused basal laminae of capillaries and podocytes c. Podocytes with pedicels (foot processes) d. Outcome - albumin and larger molecules are retained; all smaller molecules cross freely with ultrafiltrate  i. Lamina densa of the basement membrane retains albumin and other molecules the size of IgG 12. Filtration slits are 25nm - 60nm 13. Formation of urine a. primary/glomerular filtrate is produced by ultrafiltration of blood in renal corpuscle b. The composition of ultrafiltrate is similar to blood plasma. It does not contain most proteins c. Reabsorption of most of substances: 98% of filtrate is reabsorbed i. Most of water and sodium, all glucose and all amino acids from ultrafiltrate are reabsorbed d. Tubular secretion - potassium, hydrogen, NH4, bile salts, drug metabolites e. Waste molecules + some water remain in the tubular system and eventually will empty into the ureter; urine is stored in the bladder pending voiding/micturition 14. Mesangial cells - macrophages!! a. Phagocytic b. Contractile c. Support d. Mesangial cells and matrix = mesangium 15. Fish do not have a glomerulus 16. Renal tubules a. Proximal tubule b. Thin descending and thick ascending limb of nephron (loop of henle) c. Distal convoluted tubule 17. Proximal convoluted tubule a. Begins at urinary pole of renal corpuscle b. Only in the cortex c. Single layer of cuboidal epithelial cells with microvilli “brush border” d. Basement membrane e. Highly metabolically active cells with many mitochondria i. Na+/K+ pumps ii. Aquaporins iii. Peroxisomes  iv. Endosomes v. Lysosomes f. Reabsorb glucose, Na+/H2O, amino acids, peptides and low molecular weight proteins g. Selectively reabsorbed anions, cations, urea h. Activate vitamin D 18. Loop of Henle a. Continues from proximal convoluted tubule b. U-shaped with segments/portions/limbs i. Thick descending - cuboidal epithelium ii. Thick ascending - cuboidal epithelium iii. Thin segment - squamous epithelium c. In medulla only! 19. Distal convoluted tubule a. Continues from the thick ascending segment of the Loop of Henle b. Single layer of cuboidal epithelial cells with basal striations c. No microvilli! d. Only in cortex e. Site of action of aldosterone f. Contain specialized chemoreceptor cells of macula densa 20. Collecting ducts a. Connect the DCT to the renal papillae/crest b. Lumen contains primitive urine c. Cuboidal to low columnar epithelium d. Site of action of antidiuretic hormone (ADH) via aquaporin receptors i. ADH (vasopressin) is secreted by neurons in the hypothalamus - reabsorbs solute-free water and returns it to the circulation e. Not part of the nephron f. Principal cells reabsorb sodium and water g. Intercalated cells participate in acid-base balance 21. Renal papilla (canine) - papillary ducts a. Terminal portion of collecting ducts are papillary ducts → which empty at the area cribrosa (AC) of the renal crest (renal papilla) b. Vasa recta take away water passing through collecting and papillary ducts c. The papilla is the terminal portion of the inner medulla, which extends into the renal pelvis or calices 22. Vasculature a. High blood supply (25% cardiac output) b. Terminal (end) artery system c. Renal artery i. Interlobar artery 1. Arcuate artery a. Interlobular artery i. Interlobular artery ii. Afferent arteriole - glomerulus (capillaries) iii. Efferent arteriole - peritubular capillaries (surround tubules) 1. Vasa recta (surrounds loop of Henle) 23. Interstitium - sparse especially in the cortex a. More interstitium is present in the inner medulla b. Interstitial cells: fibroblasts, bone-marrow-derived cells, and a unique lipid-laden interstitial cell that is prominent in the inner medulla - produce prostaglandin E2 24. Lymphatics - are found in the interstitium surrounding arteries a. The kidney has efferent innervation to the smooth muscle of arteries, afferent and efferent arterioles, and descending vasa recta 25. Juxtaglomerular apparatus a. The DCT is intimately associated with the renal vasculature (JA) b. Two components i. Macula densa cells are part of the DCT wall are chemoreceptors that sense sodium concentrations in filtrate - SODIUM CHEMORECEPTOR ii. Modified smooth muscles of manly afferent and to a lesser degree efferent arteriole - BARORECEPTOR 1. These cell detect variations in blood pressure (baroreceptors) and secrete renin into vessel lumen iii. Will secrete the hormone renin in response to low sodium or low blood pressure 26. What 3 structures have urothelium (transitional epithelium) a. Ureters b. Urinary bladder c. Urethra 27. Layers a. Mucosa b. Submucosa - lamina propria c. T. muscularis d. T. serosa/adventitia 28. Ureters a. Urine → renal pelvis → bladder b. Tunic mucosa - UROTHELIUM c. Tunica submucosa - lamina propria d. Tunica muscularis - i. 3 layers of smooth muscle ii. Outer and inner longitudinal iii. Middle circular layer iv. Autonomic innervation → peristalsis e. Tunica adventitia 29. Urinary bladder a. Stores urine b. Tunica mucosa - urothelium i. Lamina propria present ii. Lamina muscularis c. Tunica submucosa d. Tunica muscularis i. 3 layers 1. Outer and inner longitudinal 2. Middle circular layer ii. Smooth muscle (detrusor muscle) iii. Skeletal muscle sphincter near urethra e. Tunica serosa/adventitia 30. Urethra a. Lined initially with transitional epithelium, then stratified squamous b. Similar to ureters and urinary bladder c. Accessory sex glands i. Diffuse prostate in ruminants, boar and cats d. Male i. Vascular stratum (corpus spongiosum) ii. Tunica muscularis 1. Smooth muscle proximally (close to bladder)  2. Skeletal muscle distally e. Female i. Shorter 31. The kidney develops from intermediate mesoderm 32. Renal development a. Pronephros - regresses in mammals b. Mesonephros i. Forms nephros that secrete fluid into amnion early in development; regresses later ii. Mesonephric duct (wolffian duct) - retained in males forming epididymis, vas deferens, seminal vesicles c. Metanephros i. Ureteric bud - outgrowth of mesonephric duct ii. Collecting tubules form, bifurcate (leading to lobular architecture), and nephrons begin to develop iii. Metanephros duct becomes ureter d. Urinary bladder and urethra are derived from endoderm 33. Kidneys are smiling organs