Chapter 15 The Urinary System

1. Chapter 15 The Urinary System Biology 112 Tri-County Technical College Pendleton, SC

2. Functions of Urinary System • Regulating blood volume and blood pressure • adjusting volume of water lost in urine, releasing erythropoietin and renin • Regulating plasma [ ]s of Na+, K+, Cl-, and other ions by controlling quantities lost in urine and controlling Ca+2 ion levels by synthesis of calcitriol • Stabilizing blood pH by controlling loss of hydrogen ions and bicarbonate ions in urine

3. Functions, cont. • Conserving valuable nutrients while eliminating organic waste products, especially nitrogenous products like urea and uric acid • Assisting liver in detoxifying poisons and during starvation, deaminating amino acids so can broken down by other tissue • PERFORMS vital excretory functions and eliminates organic wastes generated by cells throughout the body

4. Location is everything…almost • Kidneys, ureters, urinary bladder, and urethra • Pair of kidneys located retroperitoneal (beneath parietal peritoneum) in superior lumbar region (T12-L3 vertebra) • Each kidney drained by ureter into urinary bladder located in lower pelvic region • Urinary bladder is drained by the urethra

5. Organs of the System, Visual

6. Kidney Structure • Medial indention called HILUS where ureters, renal blood vessels, and nerves enter/exit the kidney • Renal cortex=outer layer (light colored) • Renal medulla=beneath cortex with many triangular regions (striped) which are the renal pyramids • Medulla is darker, reddish brown area • Broader base of each pyramid faces cortex with tip facing inner region of kidney • Pyramids separated by renal columns

7. Structure, cont. • Medial to hilus is flat, basinlike cavity called renal pelvis • Pelvis continuous with ureter leaving hilus • Extensions of the pelvis, the calyces (minor and major) form cup-shaped areas that enclose tips of the pyramids • Calyces collect urine with drains from tips of pyramids into renal pelvis • Urine flows from pelvis into ureterbladder for temporary storage

8. Kidney Structure, Visual

9. Nephron Structure • Are structural and functional unit of kidney • Responsible for urine production • Each nephron has 2 main structures—Glomerulus and Renal Tubule • Glomerulus is knot of capillaries • Renal tubule is cup-shaped and closed end completely surrounds glomerulus • Enlarged portion of renal tubule called GLOMERULAR (Bowman’s) CAPSULE

10. Nephron Structure, cont. • Inner layer of capsule composed of highly modified cells called podocytes • Podocytes have long branching processes that intertwine with each other and cling to glomerulus • Openings (slits) exist between extensions to form porous membrane around glomerulus • Rest of tubule coils and twists (Proximal) before forming hairpin curve (Loop of Henle) and then Distal Convoluted tubule before entering Collecting Duct

11. Nephron Structure, cont. • Glomerular capsuleproximal convoluted tubuleLoop of Henledistal convoluted tubulecollecting duct • All tubules cells have microvilli (proximal has the most) • Cortical nephrons most numerous—located almost entirely within cortex • Juxtamedullary nephrons-situated close to cortex-medulla junction and their loops of Henle extend deep into the medulla

12. Nephron Structure, cont. • Collecting ducts receive urine from many nephrons • Ducts run downward through medullary pyramids giving them a striped appearance • Collecting ducts deliver final urine product into the calyces and renal pelvis

13. Nephron Visual

14. Nephron Blood Flow • Every nephron associated with two capillary beds: glomerulus and peritubular capillary bed • Glomerulus fed and drained by arterioles • Afferent (from interlobular artery) is feeder vessel and efferent arteriole receives blood that has passed through the glomerulus • Glomerulus specialized for FILTRATION

15. Nephron Blood Flow, cont. • Afferent arteriole has larger diameter than efferent so BP in glomerulus very HIGH • This high pressure forces fluid and solutes (smaller than proteins) OUT of blood into glomerular capsule • Peritubular capillaries arise from efferent arteriole that drains glomerulus • These capillaires are LOW pressure porous vessels adapted for ABSORPTION rather than filtration

16. Nephron Blood Flow, cont. • Peritubular capillaries cling closely to whole length of renal tubule • Ideal position to receive solutes and water from tubule cells as these substances are “reabsorbed from filtrate moving through tubule • Peritubular capillaries drain into interlobular veins leaving the cortex

17. Blood Flow Visual

18. Processes of Urine Formation • Filtration, reabsorption, and secretion • FILTRATION is nonselective, passive process • Glomerulus acts as filter and filtrate formed essentially blood plasma w/o proteins • Blood proteins and blood cells too large to pass through filtration membrane • When either appear in urine=problem with glomerular filters

19. Urine Formation, cont. • Systemic BP normal, filtrate WILL be formed • Arterial BP < too low, glomerular pressure becomes inadequate to force substances out of blood into tubules and filtrate formation STOPS • Oliguria=abnormally low urinary output (100-400 ml/day) • Anuria=urine output < 100 ml/day • Low urine output=low blood pressure, transfusion reactions, acute inflammation, or crush injuries of kidneys

20. Reabsorption • Designed to reclaim useful substances • Filtrate contains wastes/excess ions that must be removed but also contains water, glucose, amino acids, and ions that must be reclaimed and returned to blood • Tubular reabsorption begins as soon as filtrate enters proximal convoluted tubule • Water by osmosis, most others by active transport • Uses membrane carriers and is VERY selective

21. Reabsorption, cont. • Carrier numbers are the KEY • Glucose & AAs completely retained and nitrogenous wastes almost completely excreted • Various ions reabsorbed/excreted to maintain proper pH/electrolyte balance of blood • Most reabsorption occurs in proximal tubules, but under certain conditions, distal CT/collecting duct also active

22. Secretion • Tubular secretion essentially reabsorption in reverse • H+; K+; and creatinine removed from blood and moved through tubule cells into filtrate • Absolutely essential for ridding body of substances NOT in filtrate (certain drugs) and as additional means of controlling pH

23. Processes Visual

24. More Processes Visual

25. Nitrogenous Wastes • Most important are urea, uric acid, and creatinine • Urea product of deamination of AAs • Uric acid = nucleic acid metabolism • Tubule cells have few membrane carriers to reabsorb these substances and usually found in high [ ]s in urine • Creatinine actively secreted into filtrate

26. Water and Electrolyte Balance • Water occupies 3 main locations in body (fluid compartments) • Intracellular fluid (about 2/3 of body fluid) • Extracellular fluid (80% interstitial or tissue fluid and 20% is blood plasma) • More to fluid balance than just water-types and amounts of electrolytes (Na+, Ca++, K+) also very important to body homeostasis

27. Body Fluids Visual

28. Balance, cont. • Water and electrolyte balance linked as kidneys process blood • Body cannot afford to lose more water than it takes in • Most water intake is from fluids/foods consumed-about 10% comes from metabolism • Water leaves via vaporization from lungs, perspiration, and defecation

29. More Balancing… • Reabsorption of water/electrolytes by kidneys regulated primarily by hormones • Blood volume dropsBP dropsdecreases filtrate formedosmoreceptors in hypothalamus direct posterior pituitary to release ADH (kidney tubule cells) reabsorb more waterblood volume & BP increase • Only small amount of very [ ]ed urine produced

30. Balancing the balancing • ADH not released (injury/destruction of hypothalamus/posterior pituitary) huge amts of very dilute urine flush from body daily • Diabetes insipidus can lead to severe dehydration and electrolyte imbalance • Aldosterone (adrenal cortex) major factor regulating Na+ content of ECF and helps regulate [ ] of other ions (Cl-, K+, Mg++) • Secretion of aldosterone influenced by falling BP or low levels of Na+ in blood

31. OMG, more balancing… • Na+ MOST responsible for water flow • W/WO aldosterone, about 80% of Na+ in filtrate reabsorbed in proximal CT • If aldosterone [ ]s high, most of remaining Na+ reabsorbed in distal CT • Sodium chloride actually reabsorbed because Cl- follows Na+ • For each Na+ reabsorbed, a K+ is secreted into filtrate = back to normal balance in blood • As Na+ reclaimed, water follows passively

32. Please, no more balancing • Most important trigger for aldosterone release is renin-angiotensin mechanism • Juxtaglomerular apparatus (consists of modified smooth muscle cells in afferent arteriole + modified epithelial cells in part of DCT) stimulated by low BP or changes in solute content in filtraterelease renin into bloodcatalyzes production of antiotensin IIvasoconstriction of blood vessels and release of aldosterone by adrenal cortex cellsblood volume and BP >

33. The end of balancing..for now!! • Renin-angiotensin mechanism EXTREMELY important for regulating BP • Individuals with Addison’s disease (hypoaldosteronism) have polypuria • Excrete large volumes of urine and lose tremendous amounts of salt and water in urine

34. Blood Pressure Homeostasis

35. Acid-Base Blood Balance • Blood pH must be maintained ~ 7.35-7.45 • Alkalosis=pH above 7.45; acidosis= <7.35 • 7.35 represents higher than optimal H+ [ ] for functioning of most body cells • Any arterial pH between 7.35 and 7.00 called physiological acidosis • Small amounts of acidic substances in ingested foods but most H+s originate as by-products of cellular metabolismadds substances to blood that tend to disturb its acid-base balance

36. Not the same balancing… • Metabolism produces many acids (phosphoric, lactic, types of fatty acids) • Carbon dioxide released by metabolism forms carbonic acid • Cells also release ammonia and other basic substances as they go about their business • Blood buffers can tie up excess acids and bases (temporarily) and lungs have chief responsibility of eliminating carbon dioxide

37. Who is on first? • Kidneys assume most of load for acid-base balance of blood • Buffers first line of defense in resisting pH changes • Bicarbonate, phosphate, and protein buffer systems are 3 major buffer systems of body • All work essentially in the same way….

38. Bicarbonate Buffering • Mixture of carbonic acid (H2CO3) and its salt, sodium bicarbonate (NaHCO3) • Bicarbonate ion (HCO3-) act as base to tie up H+s if blood becoming acidic • Carbonic acid (H2CO3) dissociates in presence of rising OH- (blood becoming more basic) and releases H+s to bind with OH-s • Buffers can tie up excess acids/bases temporarily but CANNOT eliminate them from the body • Lungs can dispose of carbonic acid by eliminating carbon dioxide

39. Buffer me up…Scotty!!! • ONLY kidneys can rid body of other acids (from metabolism) and ONLY kidneys have power to regulate blood levels of alkaline substances • Most IMPORTANT for kidneys are excreting bicarbonate ions and by conserving (reabsorbing) or generating new bicarbonate ions

40. I Can’t Do It, Captain…. • Losing a HCO3- from body has same effect of gaining a H+ since it leaves a free hydrogen ion • Reabsorbing or generating an new HCO3- is same a losing a H+ because it tens to combine with a H+ • Urine pH ranges from 4.0 to 6.5 reflecting ability of renal tubules to excrete basic or acid ions to maintain blood pH homeostasis

41. The Urinary Bladder • Smooth, collapsible, muscular sac • Three openings: 2 ureter and 1 urethra (drains the bladder) • Smooth triangular region of bladder base outlined by three openings called the trigone (infections tend to persist in this region) • Bladder wall contains 3 layers of smooth muscle (detrusor muscle) and its mucosa is special type of epithelium called transitional epithelium

42. Bladder Visual

43. But Mommy, I really have to go.. • When empty, bladder is collapsed and its walls are thick and folded • Urine accumulates, its muscular walls stretch and transitional epithelium thins allowing bladder to store more urine w/o increasing its internal pressure • Urine formed continually by kidneys and usually stored in bladder until its release is convenient (or NOT)

44. Micturition • Act of emptying the bladder • Two sphincters (valves) control flow from bladder (internal and external urethral sphincter) • About 200 mls of urinestretch receptors activatedimpulses to sacral region of spinal cordback to bladder via pelvic splanchnic nervesbladder goes into reflex contractions

45. Micturition, cont. • Contractions force stored urine past internal sphincter (smooth muscle-involuntary) into upper part of urethra • Person feels urge to void • Lower external sphincter is skeletal muscle and subject to voluntary control so “going” can be delayed • Eventually, micturition occurs whether one wills it or not!!!

46. Some Key Terms • Incontinence occurs when one is unable to voluntarily control external sphincter • Normal in children less than 2 YOA; those who sleep too soundly, & emotional problems, pressure, and/or nervous system problems (stroke/spinal cord injury) • Retention is condition in which bladder is unable to expel contained urine • General anesthesia surgery; hypertrophy

47. Key Terms, cont. • Hypertrophy: enlargement of prostate gland which surrounds neck of bladder • Urethritis: inflammation of urethra • more common in females • Cystitis: inflammation of urinary bladder • Symptoms include dysuria, urinary urgency and frequency, fever, cloudy/blood-tinged urine • If kidneys involved; back pain and severe headache common

48. Key Terms, III • Escherichia coli normal flora of intestinal tract • pathogenic in sterile urinary tract • Glomerulonephritis: glomerular filters become clogged with antigen-antibody complexes resulting from streptococcal infections • Occurs most often in children with strep throat or scarlet fever that was not treated promptly or properly

49. Key Terms IV • Urgency describes feeling that it is necessary to void • Frequency describes frequent voiding of small amounts of urine • Both are generally consequences of aging process which causes bladder shrinkage and loss of bladder tone