The Urinary System: Kidneys, Ureters, Bladder, and Urethra

1. Chapter 17The Urinary System

2. Structures we’ll talk about tonight… Kidneys Ureters Bladder Urethra

3. Kidneys • Location—under back muscles, behind parietal peritoneum, just above waistline; right kidney usually a little lower than left • Internal structure • Renal cortex—outer layer of kidney substance • Renal medulla—inner portion of kidney • Renal pyramids—triangular divisions of medulla • Renal papilla—narrow, innermost end of pyramid

4. Kidneys • Renal Microscopic structure—nephrons are microscopic units of kidneys • They help with the formation of urine • Cortical nephrons—85% of total • Juxtamedullary nephrons—specialized role in concentrating urine • They consist of: • Bowman’s capsule—the cup-shaped top • Glomerulus—network of blood capillaries surrounded by Bowman’s capsule

5. Kidneys • Nephron parts continued: • Proximal convoluted tubule—first segment • Loop of Henle—extension of proximal tubule; consists of descending limb, loop, and ascending limb • Distal convoluted tubule—extension of ascending limb of loop of Henle • Collecting tubule—straight extension of distal tubule

6. What are the functions of the kidneys? What happens when you only have 1?

7. Kidneys • Functions • Excretes toxins and nitrogenous wastes • Regulates levels of many chemicals in blood • Maintains water balance • Helps regulate blood pressure • Not much changes when you only have 1 kidney!

8. Formation of Urine • Occurs by a series of three processes that take place in successive parts of nephron • Filtration—goes on continually in renal corpuscles; glomerular blood pressure causes water and dissolved substances to filter out of glomeruli into Bowman’s capsule; normal glomerular filtration rate 125 ml per minute

9. Formation of Urine • Reabsorption—movement of substances out of renal tubules into blood in peritubular capillaries; water, nutrients, and ions are reabsorbed; water is reabsorbed by osmosis from proximal tubules • Secretion—movement of substances into urine in the distal and collecting tubules from blood in peritubular capillaries; hydrogen ions, potassium ions, and certain drugs are secreted by active transport; ammonia is secreted by diffusion

10. Formation of Urine • Control of urine volume – • Antidiuretic hormone (ADH) = “water-retaining hormone” or “urine-decreasing hormone” • Aldoesterone = “salt- and water-retaining hormone” • Atrial natriuretic hormone (ANH) = opposite effect of aldosterone

11. Influence of water on urine production • Predict the changes that would occur in the urine of a runner who had just completed a marathon. • Predict the changes that would occur in the urine production of a person who just ate a jumbo bag of popcorn with extra salt.

12. Practical Application Marathon runner Bag of salty popcorn Proteinuria will probably occur Probably dehydrated Urine production less than normal Salt loss via sweat – impact on hormone production? What if they drank a lot of water during the marathon? Sports drinks? Decreased salt reabsorption with the greatly increased salt intake. Larger amount of salt excreted through the urine.

13. What urine can tell us • Urinalysis—examination of the physical, chemical, and microscopic characteristics of urine; may help determine the presence and nature of a pathological condition • What sort of info can we obtain in doing a urinalysis?

14. Ureters • Structure—narrow long tubes with expanded upper end (renal pelvis) located inside kidney and lined with mucous membrane and muscular layer • Function—drain urine from renal pelvis to urinary bladder

15. Urinary Bladder • Structure • Elastic muscular organ, capable of great expansion • Lined with mucous membrane arranged in rugae, like stomach mucosa • Functions • Storage of urine before voiding • Voiding

16. Urethra • Structure • Narrow tube from urinary bladder to exterior • Lined with mucous membrane • Opening of urethra to the exterior called urinary meatus • Functions • Passage of urine from bladder to exterior of the body • Passage of male reproductive fluid (semen) from the body

17. Micturition • Passage of urine from body (also called urination or voiding) • Regulatory sphincters • Internal urethral sphincter (involuntary) • External urethral sphincter (voluntary) • Bladder wall permits storage of urine with little increase in pressure

18. Micturition • Emptying reflex • Initiated by stretch reflex in bladder wall • Bladder wall contracts • Internal sphincter relaxes • External sphincter relaxes, and urination • Enuresis—involuntary urination in young child

19. Micturition • Urinary retention—urine produced but not voided • Urinary suppression—no urine produced but bladder is normal • Incontinence—urine is voided involuntarily • May be caused by spinal injury or stroke • Neurogenic bladder—paralysis or abnormal function of the bladder, preventing normal flow of urine out of the body • Types include urge, stress, and reflex

20. Renal and Urinary Disorders • Obstructive disorders interfere with normal urine flow, possibly causing urine to back up and cause hydronephrosis or other kidney damage • Renal calculi (kidney stones) may block ureters, causing intense pain called renal colic • Tumors—renal cell carcinoma (kidney cancer) and bladder cancer are often characterized by hematuria (blood in the urine)

21. Renal and Urinary Disorders • Urinary tract infections (UTIs) are often caused by gram-negative bacteria • Urethritis—inflammation of the urethra • Cystitis—inflammation or infection of the urinary bladder • Pyelonephritis—inflammation of the renal pelvis and connective tissues of the kidney; may be acute (infectious) or chronic (autoimmune) • Hydronephrosis—enlargement of renal pelvis and calyces

22. Renal and Urinary Disorders • Glomerular disorders result from damage to the glomerular–capsular membrane of the renal corpuscles • Nephrotic syndrome accompanies many glomerular disorders • Proteinuria—protein in the urine • Hypoalbuminemia—low plasma protein (albumin) level; caused by loss of proteins to urine • Edema—tissue swelling caused by loss of water from plasma as a result of hypoalbuminemia

23. Renal and Urinary Disorders • Acute glomerulonephritis is caused by delayed immune response to a streptococcal infection • Chronic glomerulonephritis is a slow inflammatory condition caused by immune mechanisms and often leading to renal failure

24. Renal and Urinary Disorders • Kidney failure or renal failure occurs when the kidney fails to function • Acute renal failure—abrupt reduction in kidney function that is usually reversible • Chronic renal failure—slow, progressive loss of nephrons caused by a variety of underlying diseases • Early in this disorder, healthy nephrons often compensate for the loss of damaged nephrons

25. Renal and Urinary Disorders • Loss of kidney function ultimately results in uremia (high BUN levels) and its life-threatening consequences • Complete kidney failure results in death unless a new kidney is transplanted or an artificial kidney substitute is used