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30 Cards in this Set
- Front
- Back
What is urine? |
- excretion from the body consisting of urea, excess salt and water (sterile) |
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What are the stages of osmoregulation in the body? |
- ultrafiltration - reabsorption of glucose and water by PCT - maintain Na+ gradient in medulla by loop of Henle - reabsorption of water by DCT and collecting ducts |
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What is the overview of ultrafiltration? |
- small molecules/ions filtered out blood into the renal capsule due to pressure maintained by efferent/afferent arterioles - forms a glomerular filtrate |
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How is a glomerular filtrate formed by ultrafiltration? |
- blood enters kidney via renal artery/afferent arteriole/glomerulus/efferent arteriole - wall of glomerular capillaries are epithelial with pores between them - diameter of afferent>efferent arteriole=glomerulus hydrostatic pressure up - water/glucose in blood squeezed out glomerulus capillaries - glomerulus filtrate picked up by renal capsule |
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What is the movement of the filtrate from the glomerulus to the renal capsule resisted by? |
- connective tissue/epithelial cells of glomerulus capillaries - existing hydrostatic pressure in the renal capsule - low water potential of blood in glomerulus |
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What modifications are there to reduce the barrier to the flow of the filtrate? |
- inner layer of Bowman's capsule=podocytes=spaces between them=allows filtrate to pass between cells - spaces between endothelium of glomerular capillaries allow fluid to pass through |
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What is the result of the resistance of movement of the glomerular filtrate combined with the modifications? |
- hydrostatic pressure in glomerulus enough = filtrate passes from blood to rena (Bowman's) capsule |
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Which components make up the three-part filter which forms the glomerular filtrate? |
- endothelium of blood capillary - basement of membrane - epithelium of renal capsule (podocytes) |
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What are the features of the endothelium of the blood capillary as part of the three-part filter? |
- thin - perforated with 1000s of pores approx 10nm - barrier to cells, not plasma proteins |
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What are the features of the basement membrane as part of the three-part filter? |
- meshwork of collagen/glycoprotein fibres - water/small molecules pass through - proteins too large=repelled by negative charge on fibres |
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What are the features of the epithelium of the renal capsule (podocytes) as part of the three-part filter? |
- each cell has foot-like extensions from its surface - wrap around capillaries of the glomerulus/neighbouring cells - filtration slits 23nm wide - filtered fluid passes through filtration slits |
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What is the main role of the proximal convoluted tubule (PCT)? |
- absorbs 85% of the filtrate back into the blood - includes water, amino acids, Na+ and other ions |
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How are the epithelial cells which line the PCT adapted for absorption? |
Microvilli: large surface area for reabsorption Infoldings on base: large SA=transfer reabsorbed substances to capillary Lots of mitochondria: provide ATP for active transport |
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What is the process of reabsorption of glucose and water in the PCT? |
- Na+ active transport out PCT epithelial to capillaries=carried away (Na+ conc. down) - Na+ diffuse from lumen to epithelial (facilitated diffusion) - carrier protein co-transports glucose with Na+ to epithelial - NA+/glucose diffuse from epithelial to blood - changes filtrate conc.=water moves from PCT lumen to blood (osmosis) |
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What is the main role of the loop of Henle? |
- to increase the conc. of salts in the tubule fluid to allow the water to move out the filtrate by osmosis and be reabsorbed by the blood |
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What are the two regions of the loop of Henle? |
Descending limb: narrow, thin walls;highly permeable to water Ascending limb: wider, thick walls;impermeable to water |
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What is the 1st step of the loop of Henle? |
- the filtrate arrives from the PCT at the descending limb |
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What is the 2nd step of the loop of Henle? |
- as filtrate moves down the descending limb to the medulla, the water potential goes down - lowest water potential at hairpin curve |
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Why does the water potential of the filtrate decrease as the filtrate moves down the descending limb? |
- walls of the descending limb are permeable to water/Na+ - water leaves by osmosis to interstitial region to be carried away by blood capillaries - Na+ diffuses into descending limb, maintaining the concentration gradient |
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What is the 3rd step of the loop of Henle? |
- as the filtrate moves up the ascending limb to the cortex, the water potential increases |
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Why does the water potential of the filtrate increase as the filtrate moves up the ascending limb? |
- Na+ diffuses out filtrate at hairpin curve - higher up, Na+ actively transported to interstitial region *ATP from mitochondria in cells of AL walls* - AL wall impermeable to water=can't leave AL |
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What is the 4th step of the loop of Henle? |
- the interstitial regions now have a lower water potential |
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What is the 5th step of the loop of Henle? |
- At the top of the AL, the filtrate passes through the distal convoluted tubule (DCT) - salts selectively reabsorbed into the blood through active transport - controlled by hormones |
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What is the 6th step of the loop of Henle? |
- water potential gradient in the interstitial region between the AL and collecting duct - water potential up in cortex and down in medulla |
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What is the 7th step of the loop of Henle? |
- As filtrate moves down collecting duct (permeable), water moves out (osmosis) and is carried away by blood capillaries |
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What is the 8th step of the loop of Henle? |
- As you move from the cortex to the medulla, the water potential of the filtrate and the interstitial region decreases counter current multiplier: constant water potential gradient allowing water to move out the collecting duct by osmosis |
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What is the 9th step of the loop of Henle? |
- water not removed from the collecting duct enters the ureter and becomes urine |
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What affects the amount of water reabsorbed from the filtrate? |
- the permeability of the collecting duct walls Aquaporins: channel proteins that allow water to pass out of collecting duct (osmosis) ADH: alters the no. aquaporins=controls water loss |
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What is the main role of the distal convoluted tubule? |
- adjust water/salts reabsorbed=control pH of blood (select reabsorbed ions) - permeability of walls altered by hormones |
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How does the distal convoluted tubule carry out its main role? |
- cells of the DCT wall=microvilli/many mitochondria=reabsorb material rapidly by active transport |