Functions of the Urinary System

1. Functions of the Urinary System • Elimination of N wastes, toxins, drugs • Regulate aspects of homeostasis • Water, electrolytes, pH • Blood pressure • Red blood cell production • Activation of vitamin D

2. Organs of the Urinary system • Kidneys • Ureters • Urinary bladder • Urethra Figure 15.1a

3. Nephron • Basic unit that forms urine • Filters fluid and reabsorbs needed substances • Bowman’s capsule • Tubule: proximal, loop of Henle, distal, collecting

4. Tubular and Vascular Nephron Components • Blood vessels associated with tubules: • Arterioles: afferent, efferent • Capillaries: glomerular, peritubular, vasa recta Figure 15.5

5. Formation of Urine 1. Filtration - passive, nonselective 2. Reabsorption - water, glucose, amino acids 3. Secretion - active; H+, NH4+, K+, drugs Figure 15.6

6. Tubular Reabsorption • Overall: returns water and solutes to blood capillaries • 1. Na+ moved by active transport from tubule cells to interstitial fluid and diffuses to capillaries • 2. Cl- passively follows Na+ (balanced charge) • 3. Water reabsorbed with salts • 4. glucose and amino acids are cotransported with Na+ into tubule cells; then they diffuse into the interstitial fluid • ONLY energy input is to move Na+ out of tubule cell (step 1)

7. Tubular Secretion • Tubular secretion: removes other substances from blood • Purposes: regulate chemical levels in body, excrete harmful chemicals • Substances secreted: penicillin, cocaine, marijuana, pesticides, preservatives, H+, NH4+, potassium

8. Formation of Dilute Urine Figure 15.10

9. Regulation of Water and Electrolyte Reabsorption • Regulation is primarily by hormones • Antidiuretic hormone (ADH) prevents excessive water loss in urine • Aldosterone regulates Na+ content of extracellular fluid • Triggered by the renin-angiotensin mechanism • Cells in the kidneys (juxtaglomerular apparatus) and hypothalamus are active monitors

10. Regulation of Blood Solutes, Volume

11. Maintaining Water Balance • Water intake must equal water output • Sources for water intake • Ingested foods and fluids • Water produced from metabolic processes • Sources for water output • Vaporization out of the lungs • Lost in perspiration • Leaves the body in the feces • Urine production

12. Blood Buffers - Review • Blood pH must remain between 7.35 and 7.45 to maintain homeostasis • Buffer molecules react to prevent changes in H+ concentration • Bind to H+ when pH drops • Release H+ when pH rises • Three major chemical buffer systems • bicarbonate, phosphate, protein • Respiratory buffer system

13. Renal Mechanisms of Acid-Base Balance • Slower than chemical regulation, but effective at maintaining blood pH 1. Reabsorption of bicarbonate ions 2. Excretion of H+ (as NH4+) • Urine pH varies from 4.5 to 8.0

14. Urinary Bladder • Smooth, collapsible, muscular sac • Temporarily stores urine Figure 15.6

15. Urethra • Thin-walled tube that carries urine from the bladder to the outside of the body by peristalsis • Release of urine is controlled by two sphincters • Internal urethral sphincter (involuntary) • External urethral sphincter (voluntary)

16. Characteristics of Urine Used for Medical Diagnosis • Colored yellow due to the pigment urochrome and solutes • Sterile • Slightly aromatic • Normal pH of around 6 • Specific gravity of 1.001 to 1.035

17. Disorders of the Urinary System • Kidney stones • Acute and chronic renal failure • Therapies: • Dialysis • Kidney transplant