BSC 2086 1st EditionFinal Exam Study Guide1. What are the components of the nephron? What are the different regions of the renal tubule? Where does filtration occur? Where does reabsorption occur (what gets reabsorbed)? Where does secretion occur (what gets secreted)?a. The nephron is made up of:i. Renal corpuscle 1. Spherical structure made of a. Bowman’s capsule (glomerular capsule)b. Cup shaped chamberc. Glomerulus (capillary network)ii. Renal tubule1. Long tubular passageway that begins at the renal corpuscle 2. Located in cortex3. Made up of:a. Proximal convoluted tubule (PCT)b. Nephron loop (loop of Henle)c. Distal convoluted tubule (DCT)b. Filtration i. Blood pressure pushes water and small solutes across the membrane intocapsular space1. Larger solutes not found in filtrate because they aren’t filtered outof the plasmaa. Includes plasma proteins2. No energy required, passive process3. Solutes that enter capsular space include:a. Glucoseb. Fatty acidsc. Amino acidsd. Vitaminse. Metabolic wastesf. Excess ionsc. Reabsorption i. Useful materials are captured before the filtrate leaves the kidneysii. Takes place in proximal convoluted tube, loop of Henle, and distal convoluted tubed. Secretioni. Material that was undesirable and not filtered out is transported from theperitubular fluid into the tubular fluid1. Peritubular fluid originates from the peritubular capillaries 2. Secretion happens in proximal convoluted tubule, distal convoluted tubule, and collecting duct 2. What processes occur at the proximal convoluted tubule, loop of Henle, distal convoluted tubule, and collecting duct? What type of cells do you find lining the proximal convoluted tubule? What is this important? Which regions of the renal tubule and collecting duct are affected by ADH?a. Proximal convoluted tubule (PCT)i. Epithelial lining is simple cuboidal, has microvilli on apical surfacesii. Functions in reabsorption of:1. Organic nutrients a. 99% of glucose, amino acids, etc.b. Not all glucose is reabsorbed if glucose in blood is more than 180 mg/dLi. Glycosuria: glucose in urine c. After a protein rich meal, amino acid common in urineAminoaciduria 2. Ions (Na+, K+, HCO3-)3. H2O a. By osmosis follows when solutes are reabsorbed 4. These reabsorbed substances enter the peritubular fluid (IF around renal tubule) and diffuse into the surrounding peritubularcapillaries a. PCT cells usually reabsorb 60%-70% of the filtrate made in the renal corpuscle 5. There is some secretion of substances into tubular lumen a. Active transport secretion of H+, ammonium ions, drugs and toxins b. Nephron loop (Loop of Henle)i. Reabsorbs about ½ of H2O and 2/3 of Na+ and Cl- ions in tubular fluid ii. Very close parallel segments that are separated only by peritubular fluid 1. Very different permeability characteristicsiii. Descending limb: H2O reabsorption 1. Thin, permeable to water but impermeable to solutes2. As tubular fluid flows through, osmosis moves water into peritubular fluid leaving solutes behind 3. Osmotic concentration of tubular fluid increasesiv. Ascending limb: Na+ and Cl- reabsorption 1. Thick, highly effective pump2. 2/3 of Na+ and Cl- are pumped out of tubular fluid before reaching DCT3. solute concentration declines 4. In juxtamedullary nephrons the ascending limb will create high solute concentrations in the surrounding peritubular fluid a. Concentrates urine c. Distal convoluted tubule (DCT)i. Epithelial cells lack microvilliii. Three processes1. Selective reabsorption of water depending on ADHa. Concentrate the tubular fluid which eventually becomes urine2. Selective reabsorption of sodium depending on aldosterone and calcium depending on PTH and calcitriol from tubular fluid 3. Active secretion of ions including H+, K+ and ammonium, drugs andtoxins d. Collecting ducti. Collecting ducts receive the fluid from many nephronsii. Each collecting duct starts in the cortex and descends into the medulla1. Carries fluid to the papillary ducts 2. Papillary ducts drains into minor calyx iii. Found at the opening of DCTiv. Individual nephrons drain into nearby collecting duct 1. Adjustment of fluid composition a. Determines final osmotic concentration and urine volume2. Na+ reabsorbed in exchange for K+ secreted a. Controlled by aldosterone3. HCO3- reabsorbed in exchange for Cl-4. H2O reabsorbed controlled by ADHa. Urea reabsorbed5. H+ secreted in exchange for HCO3- if the peritubular fluid is too acidic3. Which are affected by aldosterone? What is the effect of these two hormones on filtrate/tubular fluid composition?a. Their secretion increases urine osmolarityb. Aldosterone i. Increases the number of Na+/K+ exchange pump at DCT and collecting ductsii. Promotes the reabsorption of Na+ in exchange for K+iii. Water is reabsorbed by osmosisc. ADH i. Increases the aquaporins, or water channels, in apical cell membranes of DCT and collecting ductii. Concentrates 100 mOsm/L tubular fluid arriving at DCT to be concentrated to 1200 mOsm/L when it reaches the minor calyxd. Absence of ADHi. All fluid arriving at DCT is lost in urine since water is not reabsorbedii. As seen in diabetes insipidus, large amounts of dilute (20-400 mOsm/L) urine (24 L/day)iii. Posterior pituitary normally is continuously secreting low levels of ADH1. DCT and collecting system are both always permeable to water2. Collecting system reabsorbs 16.8 L/day (9.3% of filtrate) 3. produces 1200 mL per day (0.6% of filtrate) of urine (800–1000 mOsm/L)e.4. How does filtration occur at the glomerulus? What properties of the glomerulus allows for filtration? Is everything filtered out during filtration? What substances are filtered and what substances are not filtered out?a. Filtration i. Blood pressure pushes water and small solutes across the membrane of the glomerulus and into capsular space1. Larger solutes not found in filtrate because they aren’t filtered outof the plasmaa. Includes plasma proteins2. No energy required, passive process3. Solutes that enter capsular space include:a. Glucoseb. Fatty acidsc. Amino acidsd. Vitaminse. Metabolic wastesf. Excess ionsii. The glomerulus is a capillary network, which is governed by the balance between hydrostatic pressure and colloid osmotic pressure. 5. How are cortical nephrons different from juxtamedullary nephrons? Why are these differences important in urine formation? Where is the vasa recta located and what role does it play?a. Cortical nephronsi. 85% of all nephrons ii. Efferent
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