1. Urinary System

2. Food, water Water, salt Water Digestive tract Skin Respiratory system Nutrients, water Water, salt Waste Circulatory system Water, solutes, wastes Urinary system Metabolic products, toxins Waste Liver Elimination of food residues Elimination of waste, excess solutes, and water

3. Urinary System Kidneys regulate water levels – Excess water excreted – Output varies from 2-1/2 liter/day to 1 liter/hour Kidneys regulate nitrogenous wastes and other solutes – Urea from protein metabolism – Other solutes regulated by kidneys Sodium, chloride, potassium, calcium, hydrogen ions, creatinine

4. Organs of Urinary System Kidneys – Principal organ of urinary system – Cortex: outer portion of the kidney – Medulla: inner region of the kidney

5. Organs of Urinary System Ureters – Transport urine from kidneys to bladder Urinary bladder – Stores urine (600–1,000 ml) Urethra – Carries urine from body – Two sphincters control urination

6. Nephrons Produce Urine Nephron: functional unit of the kidney 1 million nephrons per kidney Remove approximately 180 liters of fluid from the blood daily – return most of it, minus wastes that are excreted

7. Nephron Nephron structure Glomerulus: ball of capillaries – where filtration occurs Glomerular capsule: cuplike structure surrounding glomerulus Proximal tubule: comes off capsule Loop of Henle: located in renal medulla Distal tubule: connects to collecting duct Collecting duct: shared by several nephrons, empties into renal pelvis

8. Nephron Blood Supply Renal artery supplies kidney Blood vessels associated with nephron – Afferent arteriole: enters glomerulus – Efferent arteriole: leaves glomerulus – Peritubular capillaries: surround proximal and distal tubule – Vasa recta: parallels loop of Henle

9. Formation of Urine 1.Glomerular filtration: movement of fluid and solutes from blood into glomerular capsule – No proteins or cells 2. Tubular reabsorption: return of fluid and solutes into blood – Stuff we want to keep 3. Tubular secretion: addition of solutes from blood into the tubule – Throwing out extra junk

10. Figure 15.7 a) The outer surface of several glomerular capillaries. Podocyte Filtrate Proximal tubuleCapillary wall Glomerular capsule Glomerular space Glomerulus Blood flow Movement of glomerular filtrate Afferent arteriole Efferent arteriole b)A highly magnified view of the inner surface of a single glomerular capillary, revealing its porous sievelike structure.

11. Glomerular filtration: Water, ions, glucose, amino acids, bicarbonate, and waste products (urea, creatinine) are filtered from the glomerular capillaries into the space within the glomerular capsule. Tubular secretion: Some drugs, waste products, and ions (primarily hydrogen, ammonium, and potassium) are actively secreted from the peritubular capillaries primarily into the distal tubule but also in other nephron segments. Tubular reabsorption: Water, amino acids, glucose, most ions (including bicarbonate), and some urea are reabsorbed back into the peritubular capillaries, primarily in the proximal tubule but also in other nephron segments. Glomerular capsule Glomerulus Afferent arteriole Efferent arteriole ArteryVein Proximal tubule Distal tubule Collecting duct Urine 1 3 2 Figure 15.6

12. Tubular Reabsorption 100% of filtered glucose, amino acids, and bicarbonate (buffer) 65% of water reabsorbed Most tubular reabsorption occurs in proximal tubule

13. Tubular Secretion Movement of materials from peritubular capillaries or vasa recta into the tubule Purpose – Regulation of chemical levels in body – Excretion of harmful chemicals Substances secreted – Penicillin, cocaine, marijuana, pesticides, preservatives, hydrogen ions, ammonium, potassium

14. Producing Concentrated Urine Too little water can lead to: – lower blood volume – declining blood pressure – dehydration of body cells Kidneys can conserve water and produce a more concentrated urine Mechanism – ADH (antidiuretic hormone) secreted from posterior pituitary gland – ADH increases permeability of collecting ducts to water More water reabsorbed

15. Producing Dilute Urine Excess water can: – Elevate blood pressure – Cause cells to swell and/or burst Kidneys respond to excess water by excreting it Mechanism – Distal tubule is impermeable to water except when ADH is present – Large volume of water is excreted

16. Micturition Reflex Stretch receptors in bladder wall Internal urethral sphincter – Smooth muscle, involuntary External urethral sphincter – Skeletal muscle, under voluntary control Brain can override the micturition reflex – Voluntary control becomes increasingly difficult as bladder gets very full

17. Kidneys Maintain Homeostasis in Many Ways Maintain water balance – Adjust blood volume and blood pressure Aldosterone, renin, ANH help maintain salt balance in order to control blood volume Maintain acid-base balance and blood pH Regulate red blood cell production via erythropoietin Activate an inactive form of vitamin D

18. Water Balance Determines Blood Volume and Blood Pressure Involves the kidneys, hypothalamus, and posterior pituitary gland – Involves increasing or reducing ADH secretion – Involves increasing or decreasing thirst Diruretic: increases formation and excretion of urine – Lasix (furosemide): medication that reduces blood volume and blood pressure – Caffeine: inhibits sodium reabsorption – Alcohol: inhibits ADH release

19. ADH Save water Kidneys Save salt Blood volume Increase Set point Decrease Adrenal cortex Angiotensin- converting enzyme Kidneys Vasoconstriction, blood pressure Liver Angiotensinogen Lungs Renin Figure 15.15

20. Kidneys Help Maintain Acid-Base Balance and Blood pH Blood pH must stay between 7.35 and 7.45 pH regulated by kidneys, buffers, lungs Role of kidneys in pH maintenance – Reabsorption of filtered bicarbonate – Excretion of acid as ammonium

21. Disorders of the Urinary System Kidney stones – Crystallized minerals – Block urine flow Urinary tract infections (UTI) – Usually caused by bacteria – More common in women than men because of shorter urethra – If untreated, bladder infections may ascend to involve kidneys

23. Disorders of the Urinary System Acute renal failure – Short-term impairment, may be reversible – Potential causes: sustained very low blood pressure, large kidney stones within renal pelvis, infections, transfusion reactions, severe injury, toxin exposure, drug reactions

24. Disorders of the Urinary System Chronic renal failure – Also known as end stage renal disease (ESRD) – >70% reduction in functioning nephrons – Causes: Diabetes (40% will develop CRF) Uncontrolled high BP Glomerulonephritis Polycystic kidney disease Overuse of acetaminophen or ibuprofen

25. Treatment of Irreversible Kidney Failure Dialysis Problems: – Dialysis cannot achieve complete homeostasis of ions and wastes – Dialysis does not replace renal hormones

26. Treatment of Irreversible Kidney Failure Kidney transplant

27. Kidney Transplants Best hope for many CRF patients >65,000 people on waiting list for kidneys Improvements in transplant protocols/processes have improved outcomes – Better tissue-matching techniques – Improved anti-rejection medications – National data banks