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29 Cards in this Set
- Front
- Back
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What is the nephron doing when it filters, reabsorbs and secretes fluid?
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By filtering, reabsorbing and secreting, nephrons help maintain homeostasis of the blood's volume and composition.
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How much blood passes through the glomeruli each minute?
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1200ml of blood pass through the glomeruli each minute.
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What is glomerular filtration?
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Glomerular filtration is a passive nonselective process in which hydrostatic pressure forces fluids and solutes through a membrane.
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Why is the glomerulus a much more efficient filter than other capillary beds?
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(1). Its filtration membrane has a large surface area and is thousands of times more permeable to water than solutes and (2). glomerular blood pressure is much higher than in other capillary beds (~55mmHg as opposed to 18mmHg or less), which results in a much higher net filtration pressure.
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How much filtrate do the kidneys produce each day?
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The kidneys produce about 180 L of filtrate daily, in contrast to the 3 to 4 L formed daily by all other capillary beds of the body combined.
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What molecules can pass freely from the blood into the renal tubule in glomerular filtration?
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Molecules smaller than 3nm in diamter--such as water, glucose, amino acids and nitrogenous wastes.
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Why is it important to keep the plasma proteins in the capillaries?
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Keeping the plasma proteins in the capillaries maintains the colloid osmotic (oncotic) pressure of the glomerular blood, preventing the loss of all its waters to the renal tubules.
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What does GFR stand for? What does it mean?
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The glomerular filtration rate or GFR is the volume of filtrate formed each minute by the combined activity of all 2 million glomeruli of the kidneys.
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How is the GFR held relatively constant?
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The GFR is held relatively constant by both intrinsic (renal autoregulation) and extrinsic (neural and hormonal) controls, which regulate renal blood flow.
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What is tubular reabsorption?
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Tubular reabsoprtion, a reclamation process, is a transepithelial process that begins as soon as the filtrate enters the proximal tubule.
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Depending on the substances transported, the reabsorption process may be?
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(1). Passive (no ATP required) or (2). Active (at least one of its steps is driven by ATP directly or indirectly).
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What is the single most abundant cation in the filtrate?
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Sodium ions are the single most abundant cation in the filtrate, and about 80% of the energy used for active transport is devoted to their reabsorption.
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Sodium reabsorption is almost always active and occurs via the...
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Transcellular (transepithelial) route.
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What are the two basic processes that occur promoting active sodium resorption?
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(1). Sodium enters the tubule cells from the filtrate at the luminal membrane, and (2). is actively transported out of the tubule by a Na+-K+ ATPase located in the basolateral membrane.
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What occurs as a result of active pumping of sodium from the tubule cells?
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Active pumping of Na+ from the tubule cells results in a strong electrochemical gradient that favors its passive entry at the luminal face via cotransport or antitransport carriers or via facilitated diffusion through channels.
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What process provides the energy and the means for reabsorbing most other solutes?
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Sodium reabsorption by primary active transport provides the energy and the means for reabsorbing most other solutes.
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What movement establishes a strong osmotic gradient?
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Sodium movement establishes a strong osmotic gradient.
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How does water move from one region to the other and what aids this process in the peritubular capillaries?
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Water moves by osmosis into the peritubular capillaries, a process aided by water-filled pores called "aquaporins."
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In which regions of the tubule are aquaporins virtually absent?
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Aquaporins are virtually absent in the DISTAL TUBULE and COLLECTING DUCT membranes.
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What will increase aquaporin presences in the collecting duct and distal tubule?
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An increase in ADH.
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What substances are reabsorbed by secondary active transport (the "push" comes from the gradient created by N+-K+ pumping at the basolateral membrane)?
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Glucose, amino acids, lactate, vitamins and most cations.
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How, if possible, are plasma proteins that squeeze through the filtration membrane removed?
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Plasma proteins that squeeze through the filtration membrane are removed from the filtrate in the proximal tubule by endocytosis, digested to their amino acids, and moved into the pertitubular blood.
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What are three reasons why substances are either not reabsorbed or are reabsorbed incompletely?
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(1). Lack a carrier. (2). NOT lipid soluble. (3). Too large to pass through the plasma membrane pores of the tubular cells.
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Where is uric acid reabsorbed before being secreted back into the filtrate?
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Proximal Tubule.
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The reabsorption of more water depends on the presence of what hormone?
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Anitdiuretic Hormone (ADH).
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How does ADH aid in increasing the reabsorption of water?
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ADH makes the collecting ducts more permeable to water by inserting aquaporin subunits in the collecting duct apical membranes.
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How does aldosterone increase sodium retention?
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Aldosterone targets the principal cells of the collecting ducts, which prevent little to no sodium from leaving the body in urine, if possible.
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How does aldosterone increase water retention?
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A second affect of aldosterone is to facilitate water absorption b/c as sodium is reabsorbed, water follows it back into the blood (if it can)
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How does aldosterone reduce potassium concentrations?
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Aldosterone also reduces postassium concentrations because aldosterone-induced reabsorption of sodium is coupled to potassium secretion in the principal cells.
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