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65 Cards in this Set
- Front
- Back
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What forms the filtration barrier in Bowman's capsule?
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1. Endothelial cells of glomerular capillaries
2. Basement membrane of endothelial cells 3. Filtration slits created by podocyte processes. |
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What special feature do the processes of podocytes have making them very effective?
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Electric charge which prevents negatively charged proteins from crossing.
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What its the compositional difference between plasma and ultrafiltrate?
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Ultrafiltrate is void of proteins.
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Why can't roughly half the calcium be included in ultrafiltrate?
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It's bound to proteins.
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What forces control the flow of fluid across the filtration barrier?
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1. Glomerular pressure (out)
2. Osmotic pressure (in) 3. Hydrostatic pressure in Bowman's capsule (in) |
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How does increasing the flow rate through the glomerulus affect the filtration rate?
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It increases filtration rate.
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How does the diameter of the afferent arteriole affect filtration rate?
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Constriction reduces filtration by decreasing glomerular pressure.
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How does the diameter of the efferent arteriole affect filtration rate?
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Moderate constriction will increase glomerular capillary pressure and increase filtration. Excessive constriction will decrease flow and decrease filtration.
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What is a method to measure glomerular filtration?
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Use inulin which is completely expelled and determine how much is urinated per unit volume per minute.
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What is autoregulation?
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Changes in afferent arteriole diameter to affect glomerular flow rate to maintain a constant filtration rate.
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What is the anatomy of the proximal convoluted tubule?
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Cuboidal epithelium with a brush border.
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What is reabsorbed in the proximal convoluted tubule?
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65% filtered water, sodium, chloride, potassium, bicarbonate, calcium, phosphate, magnesium.
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Where does parathyroid hormone act on the kidney?
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Acts to increase the amount of calcium absorbed in the distal convoluted tubule and collecting ducts.
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How much of the total amount of calcium excretion takes place in the kidney?
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10%
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How is sodium reabsorbed in the tubules?
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Leak/pump mechanism. Sodium leaks in and is pumped out of the other side.
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What is the function of the symporter proteins in the proximal convoluted tubule?
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Couple the inward leak of sodium with glucose, amino acids, phosphates.
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What is the function of anti porter proteins in the proximal convoluted tubule?
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Sodium uptake is tied to H+ excretion.
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How does water follow sodium in the tubules?
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Passes through aquaporin I.
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Once a substance is removed from the tubule where is it collected?
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In the peritubular capillaries which is facilitated by high osmality and low hydrostatic pressure in the capillaries.
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What does the proximal peritubular secrete?
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Bile salts, prostaglandins, creatinine, dopamine, and epinephrine, and certain drugs.
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Fluid that enters Henle's loop is _____ with interstitial fluid?
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Isotonic.
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Fluid that leaves Henle's loop is _____ with interstitial fluid?
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Hypotonic.
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What is the main osmotically active solute in filtrate passing through Henle's loop?
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Urea.
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What moves out of Henle's loop in the descending portion?
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Water only. This causes the fluid to become hypertonic.
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What moves out or in of Henle's loop in the ascending portion?
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Sodium, chloride, potassium, magnesium, and calcium are pumped out causing the fluid to become hypotonic.
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Is the ascending portion of Henle's loop permeable to water?
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No.
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Where does most hormonal control take place within a nephron?
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The distal convoluted tubule and the collecting duct.
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What are the main components fine-tuned in the distal convoluted tubule and collecting duct?
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Sodium, potassium, calcium, H+, water.
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Are sodium and water movements coupled in the distal convoluted tubule and collecting duct?
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No.
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What is the first portion of the distal convoluted tubule permeable to?
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Sodium, chloride, and calcium (via parathyroid hormone). It is not permeable to water.
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What is permeable in the last part of the distal convoluted tubule and collecting duct?
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Water. This is the fine tuning portion of the nephron.
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Where is the acidity of the filtrate fine tuned?
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In the collecting duct which can secrete H+ and absorb bicarbonate via an H+-ATP-ase.
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What is the main regulator of water permeability in the collecting duct?
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ADH increases water permeability by inserting aquaporin II into the apical surface and aquaporin III into the basal and lateral surfaces.
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What receptors does ADH bind to?
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V2 receptors.
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What is nephrogenic diabetes insipidus and what are the causes?
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Mutations in the V2 receptor or aquaporin II gene which leads to impermeability in the collecting duct and large urine volumes. Dehydration and excessive third follow.
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Can the presence of aquaporin I be regulated?
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No, it's a permanent channel.
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What is the largest factor in ADH levels?
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Osmoreceptors in the hypothalamus can detect rises in osmolarity of plasma and secrete ADH to correct.
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What is the condition where too much ADH is secreted?
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Syndrome of Inappropriate Secretion of ADH (SIADH). This can happen with various diseases including lung cancer, pneumonia, CNS disorders. This leads to very dilute blood (hypoosmolar). Treat with restricted fluids and drugs.
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What is another name for diabetes insipidus?
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Hypothalamic or Central diabetes insipidus.
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What is diabetes inspidus?
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A condition that inhibits ADH secretion and leads to hyperosmolar blood. This can be via head injury, hypothalamic or posterior pituitary pathologic state, or other unknown reasons. Treat with analog of vasopressin.
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What is the antagonistic action of sodium reabsorption?
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Potassium excretion is tied to sodium reabsorption.
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What stimulates atrial natriuretic factor and what is its effect?
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Increased atrial stretch leads to secretion which inhibits sodium reabsorption which ultimately leads to more dilute urine and decreased blood volume.
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Where does atrial natriuretic factor act?
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On the distal convoluted tubule and collecting ducts.
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What are the three functions of parathyroid hormone?
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1. Increase bone resorption via osteoclast stimulation
2. Increase calcium reabsorption by increasing permeability in the distal convoluted tubule and collecting duct 3. Stimulates conversion of vitamin D3 to calcitriol in the kidney, which increases calcium absorption in the gut |
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Why does water move out of the collecting duct?
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Because interstitial fluid is hypertonic to fluid in the duct.
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What creates the osmotic gradient found in the renal medulla?
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Loops of Henle pump osmotically active substances into the medulla and therefore set the gradient.
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Why can't animals lacking Loops of Henle produce a concentrated urine?
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Without loops, an osmotic gradient can't be established and therefore water won't be reabsorbed from the collecting ducts.
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What two substances generate the osmotic gradient in the medulla?
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Sodium chloride and urea.
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What is the osmolarity of filtrate at the tip of the Loop of Henle?
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Isotonic with the interstitia because only water is permeable in the descending loop so they will equilibrate.
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What is the osmolarity at the end of the collecting duct with maximum ADH activity?
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Isotonic with the interstitia because water is completely permeable so they will equilibrate.
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What happens to fluid as it moves through the ascending limb of the Loops of Henle?
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Pumps out ions and therefore becomes hypotonic (a decrease in osmolarity).
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Where is the absolute lowest osmolarity found in the tubule system?
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The early distal tubule because solutes will continue to be pumped into the interstitia.
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Describe and explain the flow through the Loops of Henle.
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It's a very slow rate because the Loops have a limited capacity to handle water and electrolytes. If the rate is too fast the osmotic gradient in the medulla will be ruined.
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What can cause destruction of the osmotic gradient?
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If too much remains in the filtrate upon entering the Loop of Henle (proximal convoluted tubule did not adequately reabsorb) the Loop can become overwhelmed and the gradient destroyed.
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What is the effect if the osmotic gradient is destroyed?
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ADH will be ineffective because there will be no osmotic pressure to drive water from the collecting duct into the interstitia. This will causes maximum urine volume and systemic dehydration.
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How does excess glucose in the filtrate leaving the proximal convoluted tubule overwhelm the Loops of Henle?
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Because glucose is osmotically active, it will cause the backwards diffusion of water and electrolytes into the filtrate. This will overwhelm the tubule and ruin the osmotic gradient.
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Where is the majority of bicarbonate reabsorbed?
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In the proximal tubule.
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Where is bicarbonate found in the body (major)?
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In the blood.
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What is the process of H+ extraction in the Loops of Henle?
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Carbon dioxide in the tubular epithelium becomes carbonic acid via carbonic anhydrase. The acid then dissociates into H+ and bicarbonate. A sodium-H+ antiporter then extracts H+ into the tubule as sodium is reabsorbed. Bicarbonate then enters the interstitia and into general circulation.
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How are vasa recta arranged so that they don't destroy the osmotic gradient.
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They descend and ascend almost perfectly vertically so that although they lose water to the interstitia upon descent they reabsorb water as they ascend.
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What is the purpose of the vasa recta?
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To supply oxygen, nutrients, remove waste, and carbon dioxide from the cells of the medulla.
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Why can the peritubular capillaries be highly convoluted while the vasa recta are so perfectly straight?
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There is no osmotic gradient set up in the renal cortex were peritubular capillaries are found and therefore, there orientation is not significant.
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How can sickle cell anemia pose a problem specifically for vasa recta?
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Because erythrocytes affected by mutated hemoglobin are not flexible like normal, they have a difficult time passing through the lower limb of the vasa recta as blood becomes highly concentrated. This can lead to blockage and ischemia in the medulla.
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Where are ammonium (NH4+) ions found?
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In urine but not plasma.
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Is bicarbonate found in urine?
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Not under normal conditions.
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