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psl201: physiology > 3 week 17 > Flashcards

3 week 17 Flashcards

1
Q

whats the diff bw reabsorption and secretion?

A
  • reabsorption: movement of water and solutes from tubular lumen into peritubular capillaries (returned to blood).
  • secretion: movement of solute from peritubular capillaries into tubular lumen.
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2
Q

what is the diff bw apical membrane vs basolateral membrane?

A
  • apical: plasma membrane of the epithelial cells facing the tubule lumen, has microvilli.
  • basolateral: plasma membrane facing the interstitial fluid.
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3
Q

which parts of the nephron…
a) reabsorb the MOST substances
b) reabsorb ONLY water
c) reabsorb ONLY ions
d) secrete ions

A

a) proximal tube
b) loop of henle (descending limb)
c) loop of henle (ascending limb)
d) proximal tube, distal tube, collecting duct

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4
Q

describe the role of the proximal tubule in reabsorption (4)

A
  • nonregulated reabsorption
  • mass reabsorber (ex 70% sodium/water, 100% glucose)
  • brush border = large surface area
  • leaky tight junctions = paracellular transport
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5
Q

why is lots of mitochondria found in the proximal tubule?

A

bc energy is needed for primary active transport

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6
Q

whats the diff bw…
a) active solute reabsorption
b) water reabsorption (passive)
c) passive solute reabsorption via diffusion

A

a) uses pumps. pumped into peritubular fluid then enters endothelial cells via pores.
b) via aquaporins
c) solutes move from higher to lower concentration. can be through ion channel/transporters (facilitated), EC gradient…

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7
Q

how is glucose reabsorbed?

A
  • actively transported across apical membrane via sodium from tubular fluid to epithelial cell.
  • carrier protein for glucose is located on basolateral membrane; high concentration inside the epithelial cell = down concentration gradient into the peritubular fluid via carrier, where it can diffuse into the plasma (facilitated diffusion).
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8
Q

what is transport maximum? renal threshold?

A
  • transport maximum: rate of transport when carriers are saturated.
  • renal threshold: the plasma concentration at which the amount of ___ in the filtrate exceeds the transport maximum, and at which ___ appears in the urine.
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9
Q

what is the descending limb of the loop of henle permeable to vs the ascending limb?

A
  • descending: permeable to water, no Na+, K+ or Cl- transport
  • ascending: permeable to Na+, Cl-, K+, impermeable to water
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10
Q

describe the role of the distal tubule and collecting ducts in reabsorption

A
  • regulated reabsorption and secretion (see slides 13-14)
  • transport is regulated across epithelium
  • tight junctions limit paracellular transport
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11
Q

what are the three factors that determine the rate of excretion of a substance?

A
  • filtered load
  • secretion rate
  • reabsorption rate
  • in other words: amount excreted = amount filtered + amount secreted – amount reabsorbed
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12
Q

what is clearance?

A
  • volume of plasma that contains the amount of a substance that has been excreted per unit time
  • can be used to estimate GFR
  • see slide 18 for how to calculate
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13
Q

describe creatinine

A
  • by-product of muscle metabolism
  • freely filtered
  • not reabsorbed
  • small amount secreted
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14
Q

how is renal plasma estimated?

A
  • via the clearance of para-aminohippuric acid (PAH) (freely filtered, fully secreted, and not reabsorbed)
  • amount excreted = amount contained in volume of plasma that entered the kidneys
  • normal value = 625 mL/min
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15
Q

how is renal blood flow estimated?

A

clearance PAH / 1 - hematocrit

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16
Q

how do you determine the fate of solutes in renal tubules?

A

If Cx > GFR (125mL/min), then substance was secreted
If Cx < GFR (125mL/min), then substance was reabsorbed

17
Q

how is micturition regulated?

A
  • +volume of bladder = wall expands and stretch receptors activate. at spinal cord…
  • -sympa activity = internal urethral sphincter relaxes, so it opens
  • +parasympa activity = detrusor muscle contracts, also opens internal urethral sphincter
  • -somatic motor activity = external urethral sphincter relaxes, so it opens
  • micturition occurs (urination)
18
Q

reabsorption of solutes increases the ____ of peritubular fluid and plasma.

A

osmolarity

19
Q

how is water reabsorbed via osmosis (3)

A
  • through aquaporins
  • by paracellular transport (proximal tubule)
  • across the lipid portion of plasma membranes
20
Q

where does water reabsorption take place?

A
  • 70% at proximal tubule
  • 15% loop of henle (descending limb)
  • 8% distal convoluted tubule and collecting duct
21
Q

what is needed for the regulated reabsorption of water? (2)

A
  • medullary osmotic gradient
  • ADH
22
Q

T or F: the medullary osmotic gradient decreases as we go down

A
  • FALSE
  • increases*
23
Q

describe how the medullary osmotic gradient is established (7)

A
  1. all fluids are at 300 mOsm. active transport of Na+, Cl-, K+ from ascending limb > medullary interstitial fluid = +osmolarity of interstitial fluid and -osmolarity of tubular fluid in ascending limb.
  2. +osmolarity of medullary interstitial fluid draws water from lumen of the descending limb > interstitial fluid.
  3. +osmolarity of tubular fluid in descending limb.
  4. +tubular fluid enters loop of Henle, pushing fluid farther into renal tubules. process of solute transport from ascending limb…
  5. …followed by water movement from descending limb,
  6. +osmolarity of tubular fluid in descending limb, followed by +tubular fluid entering loop of Henle, repeats until…
  7. medullary osmotic gradient is established.
24
Q

how does urea contribute to the medullary osmotic gradient?

A
  • transport of urea from collecting duct > medullary space is what helps establish gradient.
  • contributes approximately 40% of the osmolarity of the gradient.
  • moves from high urea to low urea.
25
Q

how does the vasa recta maintain the medullary osmotic gradient?

A
  • anatomical arrangement of vasa recta capillaries prevents the diffusion of water and solutes from dissipating the medullary osmotic gradient.
  • blood picks up salt as it moves down.
  • as it comes back up, it picks up water.
  • this counter-mechanism means that gradient is maintained.
26
Q

which nucleus contains cells that secrete ADH?

A

paraventricular nucleus

27
Q

how does ADH regulate water reabsorption?

A
  • increases permeability of collecting duct by putting aquaporins on surface of apical membrane.
  • makes urine have high osmolarity (1400 mOsm) and low volume.
28
Q

how does ADH increase water permeability?

A
  • binds to receptor + activates g protein
  • activates adenylate cyclase > ATP to cAMP > PKA > phosphorylation of targets, triggers aquaporins to membrane
29
Q

what stimulates ADH release? (2)

A

1) increase in plasma osmolarity (osmoreceptors detect, +neurosecretory cell activity, conservation of body water)
2) decrease in blood pressure (baroreceptors detect, +neurosecretory cell activity, conservation of blood volume)

30
Q

define hypernatremia and hyponatremia

A
  • hypernatremia: high plasma sodium
  • hyponatremia: low plasma sodium
31
Q

where does renal sodium reabsorption take place?

A
  • freely filtered at the glomerulus and actively reabsorbed from the renal tubule
  • 60-70% proximal tubule
  • 25-30% descending limb (via NaKCl transporter)
  • 10% distal tubules and collecting ducts (regulated)
32
Q

how does sodium reabsorption work at the distal vs proximal tubule?

A
  • distal: sodium and chloride channels + ATPase still moves sodium out of cell and into blood
  • proximal: pumps 3 sodiums out for every 2 potassiums in, chloride follows sodium
33
Q

what hormones regulate the reabsorption of sodium?

A
  • aldosterone (increases sodium reabsorption and potassium secretion)
  • atrial natriuretic peptide (increases sodium excretion)
34
Q

where is aldosterone released from? what is its mechanism of action?

A
  • adrenal glands on kidneys (lipid soluble)
  • moves into nucleus, triggers gene transcription
  • genes make sodium channels, potassium channels, NaK ATPase
  • more sodium and potassium channels on apical side
  • more NaK ATPase on basolateral side
  • result: reabsorption of sodium into blood stream and potassium exits into urine
35
Q

what stimulates the release of aldosterone?

A
  1. renin-angiotensin-aldosterone system
  2. high plasma K+ concentrations
36
Q

how does the renin-angiotensin-aldosterone system work?

A
  • angiotensin II acts as hormone to trigger release of aldosterone
  • angiotensinogen circulates in blood, made by liver
  • renin cleaves it to produce angiotensin I which is converted into II by ACE
  • key thing = renin
37
Q

what are stimuli for renin release? (3)

A
  • decreased pressure in afferent arteriole
  • renal sympathetic nerve activity
  • decreases in Na+ and Cl– in distal tubule filtrate (makes macula densa secrete paracrines)
38
Q

what is the function of atrial natriuretic peptide?

A
  • increases GFR
  • decreases Na+ reabsorption by closing Na+ channels in apical membrane
  • overall effect: increased Na+ excretion
39
Q

what stimulates the release of atrial natriuretic peptide?

A

secreted by atrial cells of the heart in response to distension of atrial wall caused by +plasma volume

psl201: physiology (21 decks)

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