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115 Cards in this Set
- Front
- Back
when proximal tubule cells transport solutes out of lumen and water follows by osmosis, what do you have?
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reabsorption
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primary function of proximal tubule?
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bulk reabsorption of isosmotic fluid
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as fluid flows through proximal tubule, 70% gets reabsorbed leaving:
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54L in lumen
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filtrate passes through loop, more solute reabsorbed than water and becomes more hyposmotic to plasma
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true
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when fluid proceeds to loop of henle what is created:
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dilute urine
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secretion:
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moved from plasma to tubule lumen
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excretion:
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removal from body
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amount filtered=
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amount filtered- amount reabsorbed + amount secreted
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amount of substance excreted in urine reflects:
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how that substrate was handled during its passage through the nephron
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if reabsorption decreases to half the normal rate, what happens?
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the body would run out of plasma in under an hour
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filtration fraction=
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20% of plasma passing thru glomerulus (into nephron)
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what percent goes into efferent arteriole?
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80% ( peritubular capillaries)
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what percent of fluid is reabsorbed?
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19%
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what is the total percent of plasma that entered the kidney that returns to systemic circulation
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99%
1% excreted to outside environment |
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where are mesangial cells?
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they lie between and around the glomerular cap
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renal corpuscle contains filtration barriers (3 layers)
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1. glomerular capillary endothelium
2. basal lamina 3. Bowman's capsule epithelium |
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how do mesangial cells alter blood flow?
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with actin-like contractile filaments
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what to mesangial cells secrete?
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cytokines
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how do fenestrated capillaries form filtration barrier?
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no blood cells pass, (-) charged plasma proteins partially repelled by (-) charged protein on pore membrane
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what is the basal lamina
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acellular layer of extracellular matrix that separated capillary endothelium from epithelial lining of Bowman's capsule
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how does the basal lamina act as a filtration barrier?
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it acts like a sieve that excludes plasma proteins from fluid
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what are podocytes found in Bowman's capsule?
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extended foot processes that wrap around capillaries.
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what are foot processes in the kidney
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cytoplasmic extensions from podocytes that wrap around glomerular capillary and interlace with one another to form narrow filtration slits
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what are important proteins in podocyte filtration slit membranes
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nephrin and podocin
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what happens if nephrin and podocin are abnormal or absent
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proteins will leak across glomerular filtration barrier into urine
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what are filtration slits
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narrow- closed by semi-porous membrane
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what do filtered substances pass through?
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endothelial pores and filtration slits
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what is nephrin?
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zipper-like protein that forms a slit diaphragm
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what is CD2AP
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protein of the podocyte cytoskeleton
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what is the hydrostatic pressure of blood flowing through the glomerular capillaries that forces fluid thru leaky endothelium?
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55mmHg
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what happens to the pressure along the capillary resulting in filtration taking place throughout the capillary?
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it declines
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colloid osmotic pressure inside the glomerular capillary is greater than that of fluid in Bowman's capsule due to what?
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proteins in plasma
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what is the pressure gradient for colloid osmotic (pie) that favors fluid movement into the capillary
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30mmHg
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Bowman's capsule is an enclosed space, so fluid in capsule creates hydrostatic fluid (Pfluid) that :
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opposes fluid into the capsule
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what is the pressure gradient for hydrostatic fluid?
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15 mmHg
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what is the net driving force considering Ph- pie - Pfluid?
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10mmHg
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when you combine the net driving force with leaky fenestrated capillaries what do you get?
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rapid fluid filtration into tubules
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diabetic nephropathy disease progression:
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increased glomerular filtration
proteinuria later stages: filt rate decreases, thickening of basal lamina, changes in podocytes and mesangial cells mesangial cell proliferation increases and impedes blood flow dialysis required or even a transplant |
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GFR
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volume of fluid that filters into Bowman's capsule per unit time.
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what is the GFR
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125mL/min (180L/day)
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what is GFR influenced by?
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filtration pressure and filtration coefficient
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what are the components of filtration pressure?
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renal blood flow and blood pressure
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what are the components of filtration coefficient?
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capillary surface area available for filtration and permeability of interface between capillary and Bowman's capsule
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GFR is constant over a wide range of BP
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true
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what drives the hydrostatic pressure that drives glomerular filtration.
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BP
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what is GFR controlled by?
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regulation of blood flow through renal arteries
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what happens when there is increased renal artery pressure and decreased renal blood flow?
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blood diverted to other organs
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what happens when there is increase resistance in afferent arterioles?
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decreased GFR and RBF
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what happens when there is increase resistance in efferent arterioles?
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increase GFR and decreased RBF
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if there is an increased GFR what will happen to glomerular pressure
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increase
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why is it important to maintain constant GFR even when blood pressure varies?
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because hi GFR could damage filtration barriers
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how does it maintain constant GFR?
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myogenic response: vascular smooth muscle in afferent arteriole's response to pressure changes
tubuloglomerular feedback |
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how does the myogenic response work?
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Hi BP-- stretch activated ion channels open--voltage gated Ca channels open--vSM contracts-- flow decreases--GFR decreases
** but <80mmHg GFR also decreases |
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what is tubuloglomerular feedback?
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paracrine signalling where changes in fluid flow influence GFR
(juxtaglomerular apparatus) |
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what happens in the juxtaglomerular apparatus that controls GFR?
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GFR increase-- flow thru tubule increase- flow past macula densa increase- paracrine from macula densa to afferent arteriole--afferent arteriole constricts-- resistance in afferent arteriole increases-- hydrostatic pressure in glomerulus decreases-- GFR decreases
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what is renin?
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enzyme in salt and water balance
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how do sympathetic neurons work with GFR?
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via alpha receptors (vSM): there is a sharp BP drop - sympathetically induced vasocontriction decreases GFR to conserve fluid volume
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how do hormones work with GFR?
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Angiotensin II: potent vasoconstrictor
Prostoglandins: vasodilators Appear to act on: podocytes (change slit size), and megangial cells (contraction changes capillary surface area for filtration) |
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filtrate flowing out of Bowman's capsule into proximal tubule has:
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same solute concentration as ECF.
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To move solute out of lumen, tubule cells must:
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use active transport and water follows solute
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sodium is reabsorbed by:
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active transport
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electrochemical gradient drives:
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anion reabsorption
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water moves by :
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osmosis, following solute reabsorption
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concentration of other solutes increase as fluid volume in lumen decreases. Permeable solutes are reabsorbed by:
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diffusion
(K, Ca++, urea) |
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solutes moving down the gradient use:
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open leak channels or facilitated diffusion carrier
**Na involved |
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molecules that go against their gradient need :
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primary or secondary active transport
**Na involved |
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sodium linked secondary transport in the nephron is responsible for abs of many substances:
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glucose, AA, ions, and various organics
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steps in secondary transport: symport w/sodium
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1. Na moving down its electrochemical gradient using the SGLT protein pulls glucose into the cell against its concentration gradient.
2. glucose diffuses out the basolateral side of the cell using the GLUT protein 3. Na is pumped out by Na-K-ATPase (glucose and Na reabsorbed) |
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what is urea
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a nitrogenous waste product
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passive resorption of urea w/concentration gradient can move by diffusion
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true
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how does the passive resorption of urea work?
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initially equal--active transport of Na and other solutes in p.tubule creates a urea concentration gradient-- when Na and other solutes reab in p.t. transfer of osmotically active particles makes ECF more concentrated than filtrate remaining in lumen-- in response to osmotic gradient water moves across epithelium-- urea hasn't move yet=no gradient-- when water leaves, filtrate conc of urea increases-- urea moves b/c of gradient
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excretion=
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filtration - reabsorption
(inc) (constant) |
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glucose is not secreted so:
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glucose excreated
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Tm
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transport saturation
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see slides of graph on pg 8
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??
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secretion
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enables the nephron to enhance excretion of a substance.
ECF to nephron lumen |
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if a substance is filtered and not reabsorbed it is:
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excreted very efficiently
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if more secreted into tubule from peritubular capillary:
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excretion more efficient
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what is secreted that is important for homeostasis?
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K+ and H+
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Secretion depends mostly on membrane transport systems. what are most organic compounds carried by?
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secondary active transport: moving substances against their gradient
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Penicillin and probenecid
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when penicillin given it would be 80% excreted in 3 to 4 hrs. when given with probenecid, it would remove it and leave penicillin alone so it would stay in the body longer.
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excretion
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removed from the body.
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excretion=
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filtration- resorption + secretion
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excretion depends on:
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1.filtration rate
2. whether the substance is reabsorbed, secreted or both as it passes thru the tubule. |
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renal processing and GFR is clinically important because:
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GFR is an indicator of overall kidney function and the FDA needs info on kidney processing of every drug
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what is clearance?
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1. a noninvasive way to measure GFR
2. the rate of removal of a solute from the body by excretion or metabolism 3. is the volume of plasma passing thru the kidneys that is totally cleared of the solute in a given time |
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inulin
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polysaccharide isolated from tuberons roots of a variety of plants
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inulin clearance =
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GFR
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how much inulin that has been filtered into tubule is excreted?
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100%
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As filtered inulin and filtered plasma pass along nephron, what happens?
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all plasma reabsorbed but inulin remains
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what it is called when plasma has no inulin
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cleared
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inulin clearance is:
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100mL of plasma cleared / min
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inulin is equal to GFR because?
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any substance that is freely filtered but neither reabsorbed or secreted, clearance is equal to GFR
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equation 1
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filtered load of X = [X]plasma * GFR
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equation 2
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filtered load of inulin= excretion of inulin
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equation 3
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excretion rate of inulin = [inulin]plasma * GFR
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equation 4
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GFR= excretion rate of inulin
------------------------------------------------- [inulin]plasma |
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equation 5
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clearance rate of X= excretion rate of X (mg/min)
------------------------------------------- [X]plasma (mg/ml plasma) |
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equation 6
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inulin clearance = excretion rate of inulin
----------------------------------------------- inulin |
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equation 7
see examples pg 10 slides |
GFR = inulin clearance
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what is used in the clinical setting to estimate GFR?
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creatine
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creatine
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breakdown product of phosphocreatinine, an energy-storage compound found primarily in muscles
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are phosphocreatine production rate and breakdown rates relatively constant?
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yes
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why is creatine not perfect
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some secreted in urine
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renal handling of solutes:
filtration is greater than excretion |
net reabsorption of X
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renal handling of solutes:
excretion is greater than filtration |
net secretion of X
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renal handling of solutes:
filtration and excretion are the same |
no net reabsorption or secretion
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renal handling of solutes:
clearance of X is less than unulin clearance |
net reabsorption of X
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renal handling of solutes:
clearance of X is equal to inulin |
X is neither reabsorbed nor secreted
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renal handling of solutes:
clearance of X is greater than inulin clearance |
net secretion of X
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micturation
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urine-renal pelvis- ureter (smooth mus)-bladder- (micturation) urethra
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bladder holds
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500 mL
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internal sphincter
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smooth muscle, continuation of bladder wall
passively controlled |
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external sphincter
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ring of skeletal muscle, controlled by somatic motor neurons
stays contracted |
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steps in micturation
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1. stretch receptors fire
2. parasympathetic neurons fire. motor neurons stop firing 3. smooth muscle contracts. internal sphincter passively pulled open. external sphincter releases |