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Renal Physiology
Kyle's Renal Lecture
| Question | Answer |
|---|---|
| how many nephrons are in the kidney? | 1 million in each kidney or 2 million in the body |
| Name the 6 major functions of the kidney | 1.) Fluid/Electrolyte Balance 2.) Control of pH, 3.) Maintainance of blood volume 4.) Rid of waste products 5.) Control RBC production 6.) Formation of Vitamin D |
| How does the kidney control pH | It controls excretion and reabsorbtion of H+ and HCO3- |
| What kidney function is important in maintaining blood volume | Renin Angiotensin Aldosterone System |
| What is the kidney's role in RBC production? | It secretes EPO which stimulates Erythropoeisis in bone marrow. |
| What is the outter layer of the kidney called? | Renal Cortex |
| What structures are found in the cortex? | Cortical Nephrons, PCT, DCT, Capillaries, Glomeruli of ALL nephrons |
| Where does most renal blood flow occur? | The Renal Cortex |
| Which part of the kidney is most effected by Ischemic conditions? | The Cortex |
| What is the inner layer of the kidney called? | Medulla |
| Name the Structures of the renal Medulla | Juxtamedullary nephron LOH, Many tubules and vessels (vasa recta), Pyramids & Columns |
| Describe the Renal Pelvis | Innermost area where urine collects |
| What is the funtional unit of the kidney? | Nephron (cortical and juxtamedullary) |
| Describe Bowman's Capsule | It surrounds the glomerular capillary bed and collects filtrate |
| Order of Filtrate Travel through kidney | Bowman's Capsule, PCT, LOH, DCT, CD |
| Renal Arterial Supply | Renal Artery, Segmental Artery, interlobar artery, arcuate artery, interlobular artery, afferent arteriole, Glomerular cap bed, efferent arteriole, peritubular capillary bed |
| Renal Veins | Interlobular vein, Arcuate vein, interlobar vein, segmental vein, renal vein |
| Basic order of renal urine excretion | Filtration, Reabsorption, Secretion |
| What mechanism drives filtration in glomerular capillary beds? | Pressure |
| Describe net filtration pressure (equation) | Hydrostatic Capillary Pressure - (Capillary Oncotic Pressure + Bowman's Capsule Pressure) |
| Hydrostatic Pressure | The desire of a solution to push on a membrane |
| Oncotic Pressure | The desire of a solution to pull other stuff across a membrane |
| Normal Hydrostatic Pressure of glomerular capillary bed | 60mmHg |
| Normal Glomerular Oncotic Pressure of Glomerular Capillary Bed | 32 mmHg |
| Normal Bowman's Capsule Pressure | 18 mmHg |
| Normal Net Filtration Pressure | 10 mmHg |
| What mechanism creates the pressure in the capillary bed? | The efferent arteriole is more narrow than the afferent arteriole |
| How do you increase glomerular filtration rate? | Clamp down efferent arteriold (angiotensin II) |
| What characteristic of glomerular capillaries allows fluids to pass more easily into bowman's capsule? | They are fenestrated |
| What type of molecules are filtered the easiest? | Small positively charged molecules |
| Why to proteins not enter filtrate? | They are too big; They carry a negative charge which is repeled by the negatively charged protiens in the basement membrane of the glomerular capillaries |
| What are the names of the vessels that surround the LOH in both types of Nephrons? | Cortical -> Peritubular Capillaries, Juxtamedullary -> Vasa Recta |
| Where is blood flow the slowest in the kidney? | The Vasa Recta |
| Where does reabsorption occur? | Fluid/Electrolytes are reabsorbed into peritubular capillaries from PCT mostly |
| How much water is reabsorbed? | 99% |
| How much Na+ is reabsorbed? | 99.5% |
| How much glucose is reabsorbed? | 100% |
| How much urea is reabsorbed and why | 50% (It's a small molecule, but still a negatively charged protien, so some of it is cleared) |
| What mechanism does water use in reabsorption? | Osmosis |
| When will water reabsorption take place in the DCT and CD? | In th presence of increased levels of ADH |
| How does ADH Work? | Osmoreceptors detect a decrease in BV or increase in serum osmol, & cause the hypothalmus to secrete ADH. ADH increases the DCT and CD's permeability to H2O allowing it to move from DCT and CD back into circulation |
| Does ADH have a direct or indirect effect on H2O reabsorption? | Direct |
| How does aldosterone work to increase H2O reabsorption? | It causes Na+ retention and K+ excretion. The H2O follows Na+ |
| Does Aldosterone have a direct or indirect effect on H2O reabsorption? | Indirect |
| Describe tubular Secretion and Where it Ocuurs | Occurs mainly in the DCT and CD; It is the last chance for the kidneys to get rid of waste from peritubular capillaries to the DCT and CD |
| What mechanisms are used in tubular secretion? | Active Transport (Na+/K+ pump), Co-Transport, Counter Transport |
| Co-Transport | 1 carrier for 2 different types of molecules |
| Counter Transport | Ions flow in opposite directions (Ex. Na+ in and H+ out) |
| Renal Plasma Clearance | Volume of plasma that is cleared of a substance per minute |
| If a substance is not reabsorbed then the clearance rate will be ______________ to GFR | EQUAL |
| If a substance is filtered and tubular secretion occurs the clearance will be ________ GFR | Greater |
| If a substance is filtered and partially reabsorbed, the clearance rate will be ______ than GFR | Less |
| What substance is completely filtered with no reabsorption | Inulin, Mannitol, Creatine |
| What is the clearance rate of inulin, Mannitol, Creatinine? | 125 mL/min |
| What substance is filtered and secreted? | PAH |
| What percentage of PAH is cleared? | 91% |
| What is the clearance rate of PAH | 600 mL/min |
| What is the clearance rate of PAH? | 600 mL/min |
| Why is urea clearance less than GFR? | Some urea (50%) is reabsorbed back into pericapillary tubules |
| What is the normal GFR? | 120 mL/min |
| What is normal Renal Blood Flow? | 1200 mL/min |
| What percentage of CO goes to Kidneys? | 21% |
| Describe Renal Cortex Blood Flow? | Most blood flow occurs here, Rapid Circulation because of high pressures in the capillary beds |
| Medulla blood flow | Less Blood Flow; slow blood flow because of low pressures (slowest in vasa recta) |
| How much BF does the papilla recieve? | 1-2% |
| What kind of molecule is Renin? | Functional Protein |
| Where is Renin Synthesized and Stored? | Juxtaglomerular Cells (JG Apparatus) |
| Describe JG apparatus | Specialized smooth muscle cells in the walls of the Afferent arteriold that synthesized & store renin when stimulated by low arteriole BP |
| What factors can stimulate the release of Renin? | Decreased afferent arteriold BP detected by barrowreceptors (JG Apparatus); Decreased Na+ and Cl- concentration in DCT as detected by macula densa |
| What factors can inhibit the release of Renini? | Increased BP in Afferent arteriole detected by barrowreceptors (JG Apparatus); Increased Na+/Cl- concentration in DCT as detected by the macula densa |
| What is angiotensinogin's substrate? | Renin |
| How does Angiotensin II work to increase urine out put? | It clamps down the efferent arteriole causing increased hydrostatic pressure in the glomerular capillary bed, which increases GFR and urine output |
| What are the 3 main effects of angiotensin II? | Contrict Efferent Arteriole to increased GFR; Systemic Vasoconstriction; Simulated aldosterone released from the adrenal Cortex |
| Vasoconstriction = Increased or Decreased in Renal Blood Flow | Decrease |
| What hormones can caused a decrease in RBF? | Epi/NE, Endothelin, ADH, RAA system |
| Endothelin | Vasoconstrictor that is a peptited released with endothelial cell damage. |
| Vasodilation = Increase or Decrease in RBF? | Increase |
| What factors can cause an increase in RBF? | Saline load, Increased CO, Prostaglandins, Pyrogens, Renal Hypertrophy, Increased Cortisol, Increased TSH, Increased GH |
| What MAP is required to maintain renal autoregulation? | 75-160 |
| What areas of the kidney are responsible for autoregulation of RBF and GFR? | JG Conplex and or Macula Densa |
| What is the tubular reabsoption rate | 178.5 L/day |
| What variables affect GRF? | Permeability of the glomerular capillaries; hydrostateic pressure of capillaries; oncotic pressure of capillaries; pressure of Bowman's Capsule |
| What is the primary mechanism of transport for tubular reabsorption? | Active - (Na+ pump) |
| What types of passive transports are used in tubular reabsorption | Osmosis and diffusion through zona occludens |
| What are zona occludens | Small openings in tubule lumen that allow ions and small partiecles (urea) to diffuse through to the capillary |
| Tubular Load | Total amount of substance filtered into the tubule |
| Describe transport maxaimum | When a substance's carriers are saturated, the substance cannot be transported back to capillary (reabsorbed) so, it ends up in the urine |
| Threshold concentration | If substance exceeds a certain threshold in the plasma, it will end up in the urine |
| What mechanisms are involved in tubular secretion? | Active transport (K+ & H+) in DCT; Secondary Active Transport (K+ & H+, uric acid in PCT); Passive (Creatinine & Urea) |
| PCT Characteristics | 65% of flitrate is reabsorbed before LOH; Highly metabolic (microvilli to increase the surface area and reabsorption); Co-Transport of Glucose, AA, Vitamins; Countertransport secretion of H+ and Creatine |
| Desending LOH Characteristics | Thin Segment; Increased H2O permeability; Increased H2O permeability and decreased permeability to solutes (Urine Concentration); mOsm increases as filtrated desends through LOH |
| Asending LOH Characteristics | Thick Segment; Impermeable to H2O and Urea; Concentration decreased by active transport of Na+/Cl-; Few Microvilli |
| DCT Characteristics | Dilution ocurs here through active transport of Ions; Tubule filtrate is dilute compared to plasma |
| Where does aldosterone act and what does it cause? | It acts on the DCT and CD to allow Ca+ to be reabsorbed and K+ to be secreted causing increased blood volume |
| What controlls H2O permeability in the collecting Duct? | ADH |
| If ADH is increased, then the collecting duct H2O permeability is __________ | Increased |
| Where does H+ Ion Secretion occur? | Collecting Duct |
| Where is the Counter-Current Multipier Located | LOH |
| What is the Counter Current Multiplier? | Active Na+ & Cl- transport out of ascending LOH. Na+ is reabsorbed into interstium and diffuses into vasa recta carrying ions deep into the medulla; Larger reabsorption here than CD; ADH acts here |
| Where is the Counter-Current Exchange Located? | Vasa Recta |
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