Urine Formation in the Nephron There are 4

Urine Formation in the Nephron There are 4 processes that are crucial to the formation of urine

Glomerular filtration moves water & solutes, except proteins, from blood plasma into the nephron (filtrate); 2 factors affect this. . . the permeability of the capillaries (many, many pores) and blood pressure (force of blood affects filtration)

Tubular reabsorption removes useful substances such as sodium from the filtrate & returns them into the blood for the reuse by the body systems Tubular Reabsorption (in depth); ~65% of filtrate that passes through proximal tubule is reabsorbed & returned to body. Requires both active (requires ATP) & passive transport

Tubular secretion moves additional wastes & excess substances from the blood into the filtrate active reabsorption of Na+ ions (from filtrate to capillaries) and passive reabsorption of Cl- ions (& others); K+ ions are actively secreted into distal tubule from bloodstream to capillaries; H+ ions actively secreted to maintain proper p. H

Water reabsorption removes water from the filtrate & returns it to the blood from re-use by body systems

The Loop of Henle reabsorbs water & ions from Glomerular filtrate; as loop enters deeper portion of medulla, higher salt content. Water diffuses from filtrate to capillaries by osmosis

Ascending Loop; less permeable than before; Na+ ions diffuse from filtrate & pass into nearby blood vessels (this makes filtrate less concentrated)

Reabsorption from Collecting Duct Filtrate entering collecting duct still contain a lot of water; collecting duct extends into medulla where concentration of ions is higher as a result of active transport of ions from ascending limb

Reabsorption from Collecting Duct Causes water to passively follow (osmosis); this causes the filtrate to become up to 4 x as concentrated (now is called urine)

Structure & Function Glomerulus Filtration Glomerular blood pressure forces some of the water & dissolved substances from the blood plasma through pores of the Glomerular walls

Structure & Functure Bowman’s Capsule Filtration Recieve’s filtrate from glomerulus

Structure & Function Proximal Tubule Reabsorption Active reabsorption of all nutrients, including glucose & amino acids Active reabsorption of +ve’lycharged ions (Na+, K+, Ca 2+) Passive reabsorption of water by osmosis Passive reabsorption of –ve’ly charged ions like Cl- & bicarbonate ions Secretion Active secretion of hydrogen ions

Structure & Function Descending of Henle Loop Reabsorption Passive reabsorption of water by osmosis

Structure & Function Ascending of Henle Loop Reabsorption Active reabsorption of sodium ions Passive reabsorption of Cl& K+ ions

Structure & Function Distal tube Reabsorption Active reabsorption of Na+ ions Passive reabsorption of water by osmosis Passive reabsorption of –ve’ly charged ions Secretion Active secretion of H+ ions Passive secretion of K+ ions (electrically attracted to Cl- ions)

Structure & Function Collecting tube Reabsorption Passive reabsorption of water by osmosis

Maintaining the Excretory System How do the kidneys know when to conserve water, and when not too? Osmoreceptors: cells that are sensitive to osmotic pressure (located in hypothalamus) If blood plasma becomes too concentrated (you’re dehydrated) osmotic pressure increases & brain releases ADH (antidiuretic hormone) which stimulates the increase of permeability of distal tube & collecting duct (allows more water to be reabsorbed)

Maintaining… Blood plasma too dilute? Osmoreceptors prevent release of ADH Alcohol stimulates urine production; dehydrates you.

Reabsorption of Salts Na+ (most abundant in blood plasma) but fluctuates depending on diet; a drop in [Na+] is compensated by the hormone, aldosterone, which stimulates distal tubules & collecting ducts to reabsorb Na+ (followed passively by chlorine) Also stimulates the secretion of K+ into distal tubes & collecting ducts if K+ in blood is too high

Maintaining Blood p. H

Blood p. H Changes in breathing rate (increased) causes the pulls reaction to right to generate CO 2 more quickly

Videos on Urine Formation www. youtube. com/watch? v=KINOArt De. Wg www. youtube. com/watch? v=cc 8 s. Uv 2 Sua. Y