Exam #5 (Both cumulative and non-cumulative portions) Review Topics Listed below are some of the key topics discussed in class. This is not meant to be a comprehensive review of lessons 19-23 (for that, you should go over your notes). You are ultimately responsible for all of the information that was presented in class.Lesson 19-20: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)? • Nephrons – functional unit of the kidney• Microscopic, tubular structures in cortex of each renal lobe• Each kidney has approximately 1.25 million nephrons• Where urine production begins• Consists of renal tubule and renal corpuscle• Renal corpuscle - Spherical structure consisting of:• Glomerular capsule (Bowman’s capsule) forms outer wall of renal corpuscle, encapsulates glomerular capillaries• Cup-shaped chamber• Glomerulus knot of fenestrated capillaries• Capillaries are “enveloped” by podocytes (cells that have complex “feet” (pedicels) that wrap around the capillaries• Filtration slits – narrow gaps between pedicels, allows small substances to pass out of capillary• Renal tubule - Long tubular passageway• Begins at renal corpuscle • Segments of the Renal Tubule • Located in cortex• Proximal convoluted tubule (PCT)• Reabsorption of water, ions, and all organic nutrients• Nephron loop (loop of Henle) • U-shaped tube• Extends partially into medulla• In juxtamedullary nephrons, the nephron loop extends deeper into the medulla• Further reabsorption of water (descending limb) and both sodium and chloride ions (ascending limb)• Distal convoluted tubule (DCT)• Secretion of ions, acids, drugs, toxins• Variable reabsorption of water, sodium ions, and calcium ions (under hormonal control)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? • The Proximal Convoluted Tubule (PCT) - first segment of renal tubule• Epithelial Lining of PCT is simple cuboidal, has microvilli on apical surfaces, functions in reabsorption of:• Organic nutrients (99% of glucose, amino acids, etc.)• If glucose in blood is greater than 180 mg/dL, not all glucose reabsorbed, will appear in urine (glycosuria)• Amino acid common in urine after protein-rich meal (aminoaciduria)• Ions (Na+, K+, HCO3-)• H2O (by osmosis follows when solutes are reabsobed)• Reabsorbed substances enter peritubular fluid (interstitial fluid around renal tubule) and diffuse into surrounding peritubular capillaries• Note: PCT cells normally reabsorb 60%–70% of filtrate produced in renal corpuscle• Also some secretion of substances into tubular lumen• Secretion (by active transport - uses energy) of• H+, ammonium ions, drugs, toxins• The Nephron Loop (Loop of Henle) - renal tubule turns toward renal medulla, reabsorbs about 1/2 of H2O and 2/3 of Na+ and Cl- ions in tubular fluid• Parallel Segments, very close together, separated only by peritubular fluid• Have very different permeability characteristics• Descending limb (thin) – functions in H2O reabsorption • Permeable to water, impermeable to solutes• As tubular fluid flows along thin descending limb:• Osmosis moves H2O into peritubular fluid, leaving solutes behind (osmotic concentration of tubular fluid increases)• The further the descending loop travels into the medulla, the greater the concentration gradient the tubular fluid will experience. This allows for more H2O to be drawn out in juxtamedullary nephrons. The vasa recta prevents the drawn out H2O fluids from diluting the peritubular fluids• Ascending limb (thick) – functions in Na+ and Cl- reabsorption• Has highly effective pumping mechanism• 2/3 of Na+ and Cl- are pumped out of tubular fluid before it reaching DCT (solute concentration in tubular fluid declines)• Note: In juxtamedullary nephrons, the ascending limb creates high solute concentrations in the surrounding peritubular fluid (functions in concentrating urine)• The Distal Convoluted Tubule (DCT) - The third segment of the renal tubule• Has a smaller diameter than PCT, epithelial cells lack microvilli• Three Processes at the DCT: • 1. Selective reabsorption of water (depends on ADH )• Concentrates tubular fluid (which becomes urine)• 2. Selective reabsorption of Na+ (depends on aldosterone ) and Ca2+ (depends on PTH and calcitriol ) from tubular fluid• 3. Active secretion of ions (H+, K+, ammonium), drugs/toxins• The Collecting System • The distal convoluted tubule opens into the collecting system • Individual nephrons drain into a nearby collecting duct• Adjusts fluid composition - determines final osmotic concentration and volume of urine• Na+ reabsorbed in exchange for K + secreted (controlled by aldosterone), HCO3- reabsorbed in exchange for Cl-• H2O reabsorbed (controlled by ADH ), urea reabsorbed• H+ secreted in exchange for HCO3- if peritubular fluid too acidic• Several collecting ducts converge into a larger papillary duct• Which empties into a minor calyx then to the major calyx and into the renal pelvis.Which are affected by aldosterone? What is the effect of these two hormones on filtrate/tubular fluid composition? - The Distal Convoluted Tubules and Collecting Duct are affected by aldosteroneo Aldosterone - increases number of Na+/K+ exchange pump at DCT and collecting duct to reabsorb Na+ in exchange for K+ (H2O is reabsorbed by osmosis)o ADH - increases water channels (aquaporins) in apical cell membranes of DCT and collecting duct-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? - Filtration at renal corpuscle: o Blood pressure - Forces water and small solutes across membrane into capsular space Larger solutes, such as plasma proteins, are excluded (not filtered out of plasma so not found in filtrate) Passive process (no energy required) Solutes enter capsular space (filtered out). Solutes include:- Glucose, free
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