The Urinary System

1. The Urinary System Removingwaste, balancing blood pH, and maintaining water balance

2. The Importance of Removing Wastes • The cells of the body obtain energy by converting complex organic compounds into simpler compounds. • Many of these simpler compounds can be harmful and must be eliminated • The lungs eliminate carbon dioxide • Thelarge intestine removes toxic wastes from the digestive system

3. Removing Waste • The liver transforms ingested toxins, such as alcohol and heavy metals, and the hazardous products of protein metabolism into soluble compounds that can be eliminated by the kidneys • The kidneys play a crucial role in removing waste, balancing blood pH, and maintaining water balance

4. Metabolic Waste • When protein is used for energy, it is deaminated before it can enter the Krebs cycle • The byproduct of deamination is ammonia • Ammonia is extremely toxic— a buildup of as little as 0.005 mg can kill humans • In the liver, two molecules of ammonia combine with carbon dioxide, to form urea. • Urea is 100 000 times less toxic than ammonia.

7. The Kidney • Renal arteries branch from the aorta and carry blood to the kidneys. • Mass: about 0.5 kg • May hold as much as 25% of the body’s blood at any given time.

8. The Urinary System • Wastes are filtered from the blood and conducted to the urinary bladder by ureters. • A urinary sphincter muscle located at the base of the bladder acts as a valve, permitting the storage of urine. • Urine is voided through the urethra

10. http://www.dnatube.com/video/2754/Function-of-the-Nephron

11. Structure of the Kidney • The cross section of the kidney reveals three structures: • An outer layer of connective tissue: the cortex • An inner layer: the medulla, • A hollow chamber: the renal pelvis, joins the kidney with the ureter

12. Nephrons • Approximately one million slender tubules, called nephrons, are the functional units of the kidneys

13. Parts of the Nephron • Afferent arterioles: small branches that carry blood to the glomerulus • Glomerulus: high-pressure capillary bed that is the site of filtration • Efferent arterioles: small branches that carry blood away from the glomerulus to a capillary net • Peritubular capillaries: network of small blood vessels that surround the nephron

14. Parts of a Nephron • Bowman’s capsule: cuplike structure that surrounds the glomerulus • Proximal tubule: section of the nephron joining the Bowman’s capsule with the loop of Henle • Loop of Henle: carries filtrate from the proximal tubule to the distal tubule

15. Parts of the Nephron • Distal tubule: conducts urine from the loop of Henle to the collecting duct • Collecting duct: tube that carries urine from nephrons to the pelvis of a kidney

16. Nephron • Small branches from the renal artery, the afferent arterioles, supply the nephrons with blood. • The afferent arterioles branch into a capillary bed, called the glomerulus.

17. Nephrons • Blood leaves the glomerulus by way of the efferent arterioles. • Bloodis carried from the efferent arterioles to a net of capillaries called peritubular capillaries that wrap around the kidney tubule.

19. The Nephron • The glomerulus is surrounded by a funnel-like part of the nephron, called the Bowman’s capsule. • The Bowman’s capsule, the afferent arteriole, and the efferent arteriole are located in the cortex of the kidney.

20. The Nephron • Fluids to be processed into urine enter the Bowman’s capsule from the blood. • The capsule tapers to a thin tubule, called the proximal tubule. • Urine is carried from the proximal tubule to the loop of Henle, which descends into the medulla of the kidney.

21. The Nephron • Urine moves through the distal tubule, the last segment of the nephron, and into the collecting ducts. • As the name suggests, the collecting ducts collect urine from many nephrons that, in turn, merge in the pelvis of the kidney.

22. Nephrons

23. The Formation of Urine • Urine formation depends on three functions: • Filtration • Reabsorption • Secretion

24. Filtration • Each nephron of the kidney has an independent blood supply • Blood moves through the afferent arteriole into the glomerulus which is a high-pressure filter. • Normally, pressure in a capillary bed is about 25 mm Hg • The pressure in the glomerulus is about 65 mm Hg

25. Filtration • Dissolved solutes and water pass through the walls of the glomerulus into the Bowman’s capsule. • Plasma protein, blood cells, and platelets are too large to move through the walls of the glomerulus. • Smaller molecules such as Na+ , H+ glucose, amino acids, vitamins, minerals, urea, and uric acid pass through the cell membranes and enter the nephron.

27. Reabsorption • On average, about 600 mL of fluid flows through the kidneys every minute. • Approximately 20% of the fluid, or about 120 mL, is filtered into the nephrons. • Only 1 mL of urine is formed for every 120 mL of fluids filtered into the nephron. • The remaining 119 mL of fluids and solutes is reabsorbed.

28. Reabsorption in the Proximal Tubule • 85% of the water in the filtrate is reabsorbed here • Selective reabsorption of nutrients such as glucose and amino acids, vitamins and minerals occurs by active and passive transport. • pH is controlled by secretion of hydrogen ions (H+) and reabsorption of bicarbonate ions (HCO3- )

29. Reabsorption in the Descending Loop of Henle • Descending limb of loop of Henle is permeable to water, resulting in loss of water from filtrate by osmosis. • Salt (NaCl) becomes concentrated in filtrate as descending limb penetrates inner medulla

30. Reabsorption in the Ascending Loop of Henle • The ascendinglimb of loop of Henleis permeable to salt, resulting in diffusion of salt out of ascending limb.

31. Reabsorption in the Distal Tubule • Selective reabsorption of penicilin and other medications from blood into nephron occurs by active transport. • Distal tubule helps regulate potassium (K+) and salt (NaCl) concentration of body fluids.

32. Reabsorption in the Collecting Tubule • As water is reabsorbed from the nephron, the remaining solutes become more concentrated. • Molecules such as urea and uric acid will diffuse from the nephron back into the blood, although less is reabsorbed than was originally filtered.

34. Secretion • Secretion is the movement of wastes from the blood into the nephron. • Nitrogen-containingwastes, excess H+ ions, and minerals such as K+ ions are examples of substances secreted. • Even drugs such as penicillin can be secreted. • Tubular secretion occurs by active transport • Molecules are shuttled from the blood into the nephron

37. http://www.youtube.com/watch?v=cuc5KnnRpIM