Urinary System

1. Urinary System Exercises 40 and 41

2. Organs of the Urinary System • 2 kidneys • Urinary bladder • 2 ureters • Urethra • Primary function is to filter blood, and reabsorb water and needed substances back into blood. Remaining water and wastes are removed in urine.

4. Regulate blood volume and composition • Regulate blood pH • Regulate blood pressure • Contribute to metabolism • Calcitriol • Erythropoietin • Gluconeogenesis

5. Location of kidneys • Between T12 and L3 • Partially protected by 11th and 12th ribs • Right kidney is lower than left • Kidneys and ureters are retroperitoneal • Protected by three layers: • Renal capsule • Adipose capsule • Renal fascia

7. Anatomy • Renal hilum – ureter, blood and lymphatic vessels • Renal sinus • Renal cortex • Renal medulla • Renal pyramids • Renal papilla • Renal columns

9. Nephron Functional unit of kidney Number constant from birth Can function on 2/3 of one kidney Forms the urine

12. Duct system • Minor calyces • Major calyces • Renal pelvis • Ureter • Urine is not changed after it leaves the collecting duct

13. Kidneys = 1% of body mass • Receive 15-30 % of blood flow • Blood supplied to kidney by renal artery • Afferent arteriole divides into ball shaped capillary network called the glomerulus. • Capillaries rejoin to form efferent arteriole, then peritubular capillaries • Vasa recta

17. Functions of the Nephron • Filtration • Tubular reabsorption • Tubular secretion

18. Structure of a nephron • Renal corpuscle • Glomerulus • Glomerular capsule or Bowman’s capsule • Renal tubule • Proximal convoluted tubule • Nephron loop or loop of Henle • Distal convoluted tubule • Collecting duct

20. Bowman’s capsule • Outer layer - simple squamous epithelium • Inner layer – modified simple squamous epi. • Cells called podocytes • Projections are pedicels • Endothelium of capillary and podocytes form the endothelial-capsular (filtration) membrane.

21. Filtration membrane • Fenestrated endothelium – prevents the passage of cells • Basement membrane of glomerulus – prevents passage of large proteins • Slit membrane (between pedicels) – prevents the passage of medium sized proteins

24. Wall of renal tubules made up of single layer of epithelial cells and a basement membrane. • Proximal convoluted tubule – cells are cuboidal and have microvilli. • About 65 % of water and 100 % of some solutes are reabsorbed here.

25. Renal Physiology • Glomerular filtration – most substances easily filtered • Filtrate = 180 L/ day but urine = 1-2 L /day • Filter is thin • Glomerular capillaries are long • Capillary blood pressure is high (afferent arteriole diameter > efferent arteriole)

28. Filtration fraction is the percentage of plasma that becomes filtrate, usually 16-20 %. • Glomerular Filtration Rate (GFR) is the amount of filtrate formed in both kidneys per minute; normally about 125 ml / min.

29. Renal autoregulation • JGA senses Na+, Cl- and water • When these ↓, JGA dilates afferent arteriole, ↑ blood pressure in glomerulus

30. Hormonal regulation • When BP ↓, JGA secretes renin which converts angiotensinogen to angiotensin I, angiotensin I is converted to angiotensin II in the lungs. Angiotensin II is a potent vasoconstrictor. It also stimulates the release of aldosterone, and stimulates the thirst center in the hypothalamus and release of ADH from the posterior pituitary gland.

32. Tubular reabsorption • Volume of fluid that enters the proximal convoluted tubule in ½ an hour > total plasma volume. • Reabsorb water, glucose, amino acids, urea and ions, esp. Na+, Cl- and K+ • Na+ diffuses into cells, but is actively pumped out into interstitial fluid • Promotes reabsorption of water

34. DCT and collecting ducts • By end of DCT 90 % of water and solutes reabsorbed. • Aldosterone causes principal cells to synthesize sodium pumps. Also causes potassium to be secreted into urine. • ADH stimulates cells to put water channels into membranes. ADH is responsible for facultative (responding to need) water reabsorption.

35. Tubular secretion • Two main functions: • Secretion of substances to eliminate them from body – ions, nitrogen-containing waste (urea, creatinine) and certain drugs • Secretion of H+ helps to maintain blood pH

37. Urinary bladder • Posterior to pubic symphysis • Stores urine prior to micturition • Trigone – between openings of ureters and internal urethral orifice – mucosa is firmly bound to muscularis. • Muscosa, submucosa, muscularis (detrusor muscle), and serous coat.

41. Evaluation of kidney function • Blood Urea Nitrogen (BUN) – urea is a breakdown product of proteins • Influenced by diet • Creatinine – end product of muscle metabolism • Normally constant • Can determine creatinine clearance

42. Normal urine • Transparent yellow • Contains ions : Na+, Cl-, K+ ; nitrogenous wastes: ammonia, creatinine, urea and uric acid; and foreign chemicals: drugs, pesticides, food additives, etc. • Suspended solids in trace amounts: bacteria, blood cells, casts.

43. Not normally present • Albumin • Glucose, Acetone– diabetes mellitus • Bile – liver disease, obstruction of bile ducts, hemolytic disease • pH 4.6 -8.0

44. Specific gravity • 1.001 -1.035 • Damage to tubules , s.g. fixed at 1.010 = filtrate • Diabetes insipidus (lack of ADH) - • 1.003 • Diabetes mellitus – “sugar diabetes” • 1.030 osmotic diuresis • Emesis or fever – • 1.040