structure/function
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- What are the 3 general kidney functions?
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1. Regulation of Body's internal environmnt - H2O conc., inorganic ion compstn, ECF
2. Removal of metabolic waste, drugs, foreign chemicals.
3. Activation of hormones. - What 4 ways does the kidney regulate internal environment?
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1. By diluting/conc. urine
2. By regulating Na output
3. By regulating K+ output
4. By regulating acid/base balance - What 3 major wasteproducts do the kidneys remove from plasma?
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1. Urea
2. Uric acid
3. Creatinine - What 3 hormones are released from the kidneys?
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1. Renin
2. Erythropoietin
3. Vitamin D - IN general, what structures does urine flow when being formed/eliminated?
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Kidneys -> ureters -> bladder ->
urethra -> outside. - what are the functional subunits of the kidney? how many are there per kidney?
- Nephrons --> app. 1 million per kidney.
- What are the 2 main components of a nephron?
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1. Renal corpuscle
2. Tubule - What is a glomerulus?
- a tuft of interconnected capillary loops, supplied by the afferent arteriole and relieved by the efferent arteriole.
- what do the glomeruli reside in?
- Bowman's capsule
- how much blood plasma is filtered from the glomeruli into bowman's capsule?
- 20%
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What is filtration?
What's another thing filtrate is sometimes called? -
the removal of plasma (w/ no cells or proteins) from the blood of the glomeruli into the tubule.
-Ultrafiltrate. -
What are the two types of nephrons in a kidney?
What is the ratio of the two? -
1. Superficial, cortical = 85%
2. Juxtamedullary - 15% - What is the order of fluid flow through the various components of a nephron tubule?
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1. Bowman's capsule/capill tuft
2. Proximal tubule
3. Loope of henle (asc/desc)
4. Distal tubule
5. Collecting duct
-Out the renal pelvis, etc. -
What characterizes juxtamedullary nephrons?
What is their purpose? -
They reach into the inner medulla, not just the cortex.
Purpose: to concentrate urine. - How far into the kidney do cortical nephrons reach?
- to the outer medulla (despite their being called CORTICAL)
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Where are macula densa cells?
What is their function? -
In the ascending limb wall.
Function: to detect increased Na+ in filtrate. - what are juxtaglomerular cells?
- secretory cells in the wall of the afferent arteriole that secrete renin.
- where exactly are the macula densa and juxtaglom. cells?
- as the asc. limb becomes the distal convuluted tubule; it passes right close to the afferent arteriole bringing these cells into close proxim.
- what is the juxtaglomerular apparatus?
- the combination of macula densa cells and juxtaglomerular cells.
- what does dr. lobner call juxtaglomerular cells?
- granular cells.
- How do macula densa cells respond to increased sodium in the filtrate?
- Release something(?) that constricts the Afferent Arteriole.
- What is the result of constricting the Aff. arteriole?
- Decrease in filtration, Na+ filtratn, Na+ in filtrate --> decreased Sodium loss!!!
- How do the granular cells operate?
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1. Detect decreased BP; stimulates Renin release.
2. Activates Angiotensinogen -> angiotensin 1
3. Activates Angiotensin II in lungs.
4. Activates general vasoconstriction.
5. Increases BP - What is the purpose of granular (juxtamedullary) cells in a nutshell?
- to increase bp when it is decreased.
- How many arterioles/capillary beds are in each nephron?
- 2 of each - 2 arterioles in series, with 2 capillary beds in between.
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What are:
-Filtration
-Reabsorption
-Secretion
-Excretion -
Filt: glomerulus -> nephron
Reab: Nephron -> blood
Secr: Blood -> nephron
Excr: removing filtrate waste. - What is the equation for total excretion?
- Excretion = (filt + secr) - Reab
- What 2 factors determine what/howmuch is filtered by the glomerulus?
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1. Permeability
2. Starling forces - What are the 3 barriers to glomerular filtration?
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1. RBCs
2. Podocytes (nonbarrier?)
3. Basement membrane - the main barrier - How does the basement membrane of bowman's capsule prevent filtration?
- it is negatively charged, and therefore prevents large negatively charged (plasma proteins) from passing through.
- what 7 things are filtered by bowman's capsule?
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20% of:
Glucose
amino acids
Na Cl K Ca H2O - what 3 forces determine glomerular filtration?
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-Glomerular Capillary Hydrostatic pressure
-Bowman's space Hydrostatic pressure
-Osmotic force of plasma protein -
Pgc
Pbs
Pi-gc -
Glomerular and bowman's space hydrostatic pressure
and osmotic pressure (Pi) - how does bowman's space oppose filtration?
- it has higher water concentration than the glomerulus because plasma proteins don't filter into bowman's capsule.
- the osmotic pressure of glomerular capillaries is 29; in normal capill its 24; why?
- so much plasma flows out, the remaining blood is concentrated.
- What is the net glomerular filtration pressure?
- GFP = Pgc - Pbs - Pi-gc
- What regulates filtration/absptn in a normal systemic capillary?
- Capillary hydrostatic minus oncotic pressure - which one is larger determines direction of fluid flow.
- How can filtration occur if ther's always bs hydrostatic pressure and glomerular oncotic pressure opposing it?
- the glomerular hydrostatic pressure is always greater than the sum of the other two, so net filtration pressure is positive.
- how does increasing renal blood flow change GFR?
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it increases GFR, thence urinary output too.
B/c they are directly ppnl. - what is the GFR equation?
- GFR = Kf x net filtr pressure
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how much plasma is filtered per minute and per cay?
how often is the body's plasma filtered? -
125 ml/min
180 L/day
the 3 liters of body plasma is filtered 60 x per day - what does autoregulation refer to?
- the fact that the renal blood flow is relatively constant despite changes in MAP. If cardiac output increases, blood flows ELSEWHERE.
- what would happen if autoregulation didn't occur?
- If MAP increased, so would cardiac output and RBF; thus urine output too and you'd pee everytime you exercised.
- What happens if MAP decreases?
- autoregulation maintains GFR, which is good b/c blood will continue to be filtered.
- How, mechanically, does autoregulation change blood flow?
- by changing RESISTANCE of renal arterioles.
- what are 2 hypotheses regarding increased resistance for autoregulation?
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1. Myogenic hypothesis
2. Tubuloglomerular feedback hypothesis - what does the myogenic hypothesis propose?
- when MAP increases, it stretches renal arteries; this causes vasoconstriction which increases resistance.
- what does the tubuloglomerular feedback hypothesis propose?
- that the juxtaglomerular apparatus is involved.
- How does the juxtaglomerular apparatus alter RBF in response to increased MAP for autoreg?
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1. Incr MAP causes two things: a)increased glomerular blood flow, b)incr. glom hydrostat pressure
2. both increase GFR, thus Na filtration.
3. Mac densa detects Na+ incr. and release SOMETHING
4. Afferent arterioles constrict.
5. Pgc decreases, thus RBF decreases. - Other than autoregulation, what factors influence RBF?
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Sympathetic nervous system constricts the afferent art'ole -> decr. RBF and GFR and urine formation.
(which is good, don't want to pee while fighting/flighting)