The Urinary System

1. The Urinary System 0 15

2. Urinary System Contributes to Homeostasis Excretion: processes that remove wastes and excess materials from the body Digestive system: excretes food residues and wastes produced by the liver Respiratory system (lungs): excretes carbon dioxide Integumentary system (skin): excretes water, salt Urinary system (kidneys): excretes nitrogenous wastes, excess solutes, and water

3. Figure 15.1 Food,water Water,salt O2 Water CO2 Digestive tract Skin Respiratory system Nutrients,water Water,salt O2 CO2 Water, solutes,wastes Waste Circulatory system Urinarysystem cells Transport all to Metabolicproducts, toxins Waste Liver Elimination of foodresidues Elimination ofwaste, excesssolutes, andwater

4. The Kidneys Regulate Water Levels To maintain homeostasis, Water Intake  Water Output Kidneys adjust water output as necessary Water input: food, drink, metabolism Water output: lungs, skin, feces Kidneys modify output based on intake and loss Output varies from 1/2 liter/day to 1 liter/hour

5. Table 15.1

6. The Kidneys Regulate Nitrogenous Wastes and Other Solutes Protein metabolism produces nitrogenous wastes Initially, NH3 (ammonia) is produced during breakdown of amino acids Liver detoxifies NH3, producing urea Urea is transported from liver to kidneys for disposal Other solutes regulated by kidneys Sodium, chloride, potassium, calcium, hydrogen ions, creatinine

7. Table 15.2

8. Organs of the Urinary System Kidneys Principal organ of urinary system Cortex: outer portion of the kidney Medulla: inner region of the kidney Renal pelvis: hollow space in center of kidney where urine collects

9. Figure 15.2 Cortex Kidney Renal artery Renal vein Nephrons Aorta Cortex Medulla Inferiorvena cava Renalpelvis Medulla Collectingduct Ureter Bladder Ureter Urethra The components of theurinary system. The cortex and medulla ofthe kidney are composedof numerous nephrons. Internal structure of thekidney.

10. Organs of the Urinary System Ureters Muscular tube that transports urine from kidneys to bladder Urinary bladder Three layers of smooth muscle, lined with epithelial cells Stores urine (600–1,000 ml) Urethra Carries urine from bladder to outside of body Two sphincters control urination

11. Figure 15.3 Urinarybladder Rectum Internalurethralsphincter Uterus Prostategland Vagina Externalurethralsphincter Penis Rectum Urethra Testis The male. The female.

12. Nephrons Produce Urine Nephron: functional unit of the kidney Two functional parts: Tubule Associated blood supply 1 million nephrons per kidney Each nephron consists of a long thin hollow tube (tubule) plus associated blood supply Role of nephrons: remove approximately 180 liters of fluid from the blood daily, and return most of it, minus the wastes that are excreted

13. Figure 15.4 Distal tubule Efferent arteriole Glomerularcapsule Glomerulus Proximal tubule Afferent arteriole Cortex Descendinglimb Medulla Loop ofHenle Ascendinglimb Collectingduct Renal pelvis

14. The Tubule Filters Fluid and Reabsorbs Substances Nephron structure Glomerular capsule: cuplike end of nephron tubule surrounding glomerulus (network of capillaries)—this is where filtration occurs Four distinct regions of tubule 1. Proximal tubule: extends from glomerular capsule to renal medulla 2.Loop of Henle: extends into medulla then back into cortex 3.Distal tubule 4. Collecting duct: shared by several nephrons, empties into renal pelvis

15. Special Blood Vessels Supply the Tubule Renal artery supplies the kidney Blood vessels associated with tubules Arterioles Afferent: enters the glomerular capsule Efferent: leaves the glomerular capsule Capillaries Glomerular: network within the glomerular capsule Peritubular: surround proximal and distal tubule Vasa recta: parallels the loop of Henle Renal vein: collects filtered blood from kidneys

16. Figure 15.5 Collectingduct Efferent arteriole Glomerulus Afferent arteriole Afferentarteriole Peritubularcapillaries Cortex Efferentarteriole Renalvein Medulla Renalartery Vasa recta Pelvis Main blood vessels in thekidney. The renal artery andrenal vein branch many timesto deliver blood to eachglomerulus. Post-glomerular blood vessels. The efferent arteriole of most nephrons,such as the one shown here on the left, divides to become the peritubularcapillaries, which supply proximal and distal tubules in the cortex. In a fewnephrons, such as the one on the right, the efferent arteriole descends intothe medulla to become the vasa recta,which supply loops of Henle.

17. Formation of Urine: Filtration, Reabsorption, and Secretion 1.Glomerular filtration: movement of protein-free solution of fluid and solutes from blood into the glomerular capsule 2.Tubular reabsorption: return of most of the fluid and solutes into the blood 3.Tubular secretion: addition of certain solutes from the blood into the tubule

18. Figure 15.6 3 Tubular secretion:Some drugs, waste products,and ions (primarily hydrogen,ammonium, and potassium)are actively secreted from theperitubular capillaries primarilyinto the distal tubule but alsoin other nephron segments. Efferentarteriole Afferentarteriole Glomerularcapsule Glomerulus 1 Glomerular filtration:Water, ions, glucose,amino acids, bicarbonate,and waste products(urea, creatinine) arefiltered from theglomerular capillariesinto the space withinthe glomerular capsule. Proximal tubule Distal tubule Collectingduct 2 Tubular reabsorption:Water, amino acids,glucose, most ions(including bicarbonate),and some urea arereabsorbed back into theperitubular capillaries,primarily in the proximaltubule but also in other nephron segments. Artery Vein Urine

19. Glomerular Filtration Filters Fluid from Capillaries Filters protein-free plasma fluid from capillaries into glomerular capsule Large volume filtration, yet highly selective Impermeable to large proteins and cells Filtration is driven by high blood pressure in glomerular capillaries Rate of filtration Resting rate under local chemical control Stress causes sympathetic nervous system to reduce blood flow to kidneys

20. Figure 15.7 Blood flow Movement ofglomerular filtrate Glomerularcapsule Glomerulus Glomerularspace Afferent arteriole Efferent arteriole The outersurface ofseveral glomerularcapillaries. Podocyte Filtrate Proximal tubule Capillary wall A highly magnified view of theinner surface of a singleglomerular capillary, revealingits porous sievelike structure.

21. Tubular Reabsorption Returns Filtered Water and Solutes to Blood 100% of filtered glucose, amino acids, and bicarbonate and 50% of urea are reabsorbed Most tubular reabsorption occurs in proximal tubule Reabsorption of sodium begins the process Sodium moved by active transport from tubule cells to interstitial fluid and diffuses to capillaries Chloride passively accompanies sodium (balanced charge) Water reabsorbed with salts Water moves through aquaporins (water channels) Movement of sodium provides energy to transport glucose and amino acids from tubule into surrounding cells Glucose, amino acids then diffuse to the interstitial fluid

22. Figure 15.9 Capillary Interstitialfluid Proximal tubule cell Glucose,amino acids Na ATP Na Glucose,amino acids ADP  Pi Cl Tubulelumen H2O Active transport Diffusion

23. Tubular Secretion Removes Other Substances from Blood Involves the movement of materials from the peritubular capillaries or vasa recta to the tubule Purpose Regulation of chemical levels in body Excretion of harmful chemicals Substances secreted Penicillin, cocaine, marijuana, pesticides, preservatives, hydrogen ions, ammonium, potassium

24. Producing Dilute Urine: Excreting Excess Water Kidneys respond to excess water by excreting it Mechanism Distal tubule is impermeable to water so water is not reabsorbed here NaCl is reabsorbed without the concurrent reabsorption of water High volume dilute urine is produced

25. Figure 15.10 NaCl NaCl Cortex Isotonic Medulla NaCl NaCl NaCl NaCl NaCl H2O H2O H2O H2O NaCl H2O Urea Veryconcentrated Large volumeof dilute urine

26. Producing Concentrated Urine: Conserving Water Too little water can lead to lower blood volume, declining blood pressure, risk of dehydration of body cells Kidneys respond by conserving water and producing a more concentrated urine Mechanism Mediated by ADH (antidiuretic hormone) from the posterior pituitary gland ADH increases permeability of the collecting ducts to water and increases conservation of water Counter-current exchange mechanism

27. Figure 15.11 NaCl NaCl Cortex Isotonic Medulla NaCl H2O NaCl NaCl NaCl H2O NaCl H2O H2O H2O H2O H2O H2O NaCl H2O H2O Urea Veryconcentrated Low volume of concentrated urine

28. Figure 15.12 Kidney surface Blood fromefferentarteriole To vein Cortex Isotonic Solutes Solutes Medulla H2O H2O Counter-currentflow ofblood Solutes Solutes H2O H2O Solutes Solutes H2O H2O Veryconcentrated Renal pelvis Position of the vasa rectarelative to the tubule Movement of water and solutesacross the walls of the vasa recta

29. Urination Depends on a Reflex Micturition reflex: neural reflex that enables emptying of the bladder Responds to stretch receptors in bladder wall Internal urethral sphincter Smooth muscle External urethral sphincter Skeletal muscle, under voluntary control Brain can override the micturition reflex and control the timing of urination Voluntary control becomes increasingly difficult as the bladder gets very full

30. Kidneys Maintain Homeostasis in Many Ways Contribute to maintenance of water balance Contribute to maintenance of salt balance Secrete an enzyme involved in the control of blood volume and blood pressure Maintain acid-base balance and blood pH Regulate red blood cell production via erythropoietin Activate an inactive form of vitamin D

31. ADH (Antidiuretic Hormone) Regulates Water Balance Involves the following organs; Hypothalamus: synthesizes ADH Posterior pituitary gland: releases ADH Kidneys: respond to ADH Negative feedback loop regulates solute concentration of the blood Involves increasing or reducing ADH secretion, which will modify water reabsorption by kidneys Involves increasing or decreasing thirst

32. ADH Regulates Water Balance If blood solute concentration is too high (water concentration too low): ADH released ADH causes: Increase in permeability of collecting duct to water Increase in water reabsorbed by kidney Decrease in urine production Increase in thirst

33. ADH Regulates Water Balance • If blood solute concentration is too low (water concentration too high): ADH secretion is reduced • Decrease in permeability of collecting duct to water • Decrease in water reabsorbed by kidney • Increase in urine production • Decrease in thirst

34. ADH Regulates Water Balance Diuresis: high urine flow rate Diuretic: any substance that increases the formation and excretion of urine Lasix (furosemide): medication that reduces blood volume and blood pressure Used in treatment of congestive heart failure and hypertension Caffeine: inhibits sodium reabsorption Alcohol: inhibits ADH release

35. Figure 15.13 Blood solute concentration Increase Set point Decrease Hypothalamus Rate of Posteriorpituitary Water renal intake Thirst water loss ADH Kidneys: collectingduct permeabilityto water

36. Aldosterone Regulates Salt Balance Blood volume control is dependent on salt balance Aldosterone: adrenal hormone that regulates sodium excretion Mechanism: increases Na reabsorption from distal tubule and collecting duct Aldosterone secretion is controlled by the renin-angiotensin system

37. The Renin-Angiotensin System Controls Blood Volume and Blood Pressure Aldosterone release is stimulated indirectly by decreased blood volume or blood pressure Decreased blood volume/blood pressure causes release of renin (enzyme) from juxtaglomerular apparatus (region where afferent and efferent arterioles are in close contact with distal tubule) Renin cleaves inactive angiotensinogen (produced by liver), releasing angiotensin I Angiotensin converting enzyme (ACE) in lungs converts antiotensin I (inactive peptide) to angiotensin II (biologically active peptide)

38. The Renin-Angiotensin System Controls Blood Volume and Blood Pressure Effects of angiotensin II Constricts arterioles which raises blood pressure Stimulates release of aldosterone from adrenal glands Aldosterone: increases sodium reabsorption by distal tubules and collection ducts ANH (atrial natriuretic hormone), released by atria in response to stretching due to high blood volume, inhibits Na reabsorption

39. Figure 15.14 Distaltubule Afferentarteriole Glomerulus Glomerularcapsule Juxtaglomerularapparatus Efferentarteriole Proximal tubule Renin-secretingcells

40. Figure 15.15 ADH Blood volume Increase Set point Save water Decrease Savesalt Kidneys Kidneys Aldosterone Adrenalcortex Angiotensin-convertingenzyme Renin Lungs Angiotensin II Angiotensin I Angiotensinogen Vasoconstriction, blood pressure Liver

41. Atrial Natriuretic Hormone Protects Against Blood Volume Excess High blood volume stretches atria of heart Atria secrete ANH (atrial natriuretic hormone) in response to stretching ANH inhibits Na reabsorption in distal tubules and collecting ducts Na excretion increases Water follows the Na Effect of ANH is opposite to that of aldosterone

42. 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 (NH4)

43. Figure 15.16 Tubule cell Capillary Interstitialfluid Cellularmetabolism Tubulelumen HCO3  H H HCO3 HCO3 NH4 HCO3 HCO3 NH4 (excretedin urine) H2O  CO2 H2O  CO2 Reabsorption of filtered bicarbonate.Hydrogen ions within the cell are secretedinto the lumen, where they combine withfiltered bicarbonate to form CO2 and water.The CO2 and water diffuse into the cell anddissociate back into a hydrogen ion andbicarbonate. The hydrogen ion is secretedagain, but the bicarbonate diffuses fromthe cell back into the blood. Excretion of ammonium. Kidney cellsproduce ammonium and bicarbonate during cellular metabolism of glutamine.The ammonium is secreted into the tubuleand is excreted in the urine, but the newbicarbonate diffuses into the blood.

44. Erythropoietin Stimulates Production of Red Blood Cells Decrease in amount of oxygen is detected by certain cells throughout the kidney O2 sensitive cells in kidney secrete hormone, erythropoietin, in response to decrease in oxygen Erythropoietin triggers increase in red blood cell production in the bone marrow

45. Figure 7.6 O2 availability Increase Set point Decrease O2-sensitive cells in kidneys respond to a decline in O2 availability by increasing erythropoietin production Increased number of RBCs returns O2 availability to normal Erythropoietin stimulates increased RBC production by stem cells in bone marrow

46. Kidneys Activate Vitamin D Exposure of skin to sunlight causes production of an inactive form of vitamin D from a precursor found in the skin Inactive form of vitamin D is transported to liver, where it is modified Inactive form of vitamin D is then converted to active form by kidneys Conversion to active vitamin D in kidneys is influenced by activity of PTH (parathyroid hormone)

47. 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

48. 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

49. Disorders of the Urinary System • Chronic renal failure • Also known as end stage renal disease (ESRD) • ESRD: long term, irreversible damage • 60% reduction in functioning nephrons • See causes of acute renal failure above • 40% of people with type I diabetes will develop renal failure

50. Dialysis Cleanses Blood Artificially Dialysis: attempts to duplicate function of healthy kidneys CAPD: continuous ambulatory peritoneal dialysis Can be done at home Uses peritoneal cavity for waste, ion removal Risk of infection Hemodialysis Requires several visits/week to a dialysis center Blood is circulated through a kidney machine