Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Physiology > Lecture 17: Tubular Reabsorption And Secretion > Flashcards

Lecture 17: Tubular Reabsorption And Secretion Flashcards

1
Q

Describe the passive transport route

A
  • For a substance to be reabsorbed, it must first be transported:
  • Across the tubular epithelial membranes into the renal interstitial fluid.
  • Through the peritubular capillary membrane back into the blood.
  • Water is transported from the lumen through the tubular cells into the interstitium via both transcellular and paracellular routes by osmosis.
  • See Slide 5
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Describe ultrafiltration and bulk flow

A
  • Water is transported by way of specific water channels:
  • Aquaporins (AQP):
    • Aquaporin-1 is widespread, incl. renal tubules.
    • Aquaporin-2: Present in apical membranes of collecting tubule cells and Controlled by ADH
  • -Aquaporin-3: Present in basolateral membranes of collecting tubule cells.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Describe ATPases

A
  • ATPases establish ionic gradients across nephron cell membranes:
  • Gradients drive reabsorption or secretion of many other solutes.
  • These are then transported by way of “secondary” active transport.
  • Symport(cotransport):
    • Solute moves with Na+ gradient
  • Antiport (countertransport)
    • Solute moves opposite to Na+ gradient
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

Describe ATPases and their association with channel movement

A
  • ENaC channel
  • Found in apical membrane of nephron cells
  • Closed by drug amiloride
  • Opened by a number of hormones
  • CFTR (chloride) channels and K+ channels also found in apical membranes of some segments of nephron.
  • Uniporters are also found in cell membranes:
  • Driven by concentration gradient of substance concerned
  • Transport occurring through channels or uniporters
  • Facilitated transport
  • i.e.: glucose transport
  • Transport directly coupled to an energy source
  • = active transport
  • Transport that is coupled indirectly to an energy source (i.e., ion gradient)
  • = secondary active transport
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What enzymes are primary active transporters?

A
  • Na+K+ATPase
  • H+ATPase
  • H+K+ATPase
  • Calcium ATPase
  • Study Fig. 28-2
  • See Slide 12
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

Describe secondary active transport

A
  • Reabsorption of glucose or amino acids by renal tubule are examples of secondary active transport:
  • Sodium-glucose co-transporters on brush border of proximal tubule cells:
    • SGLT2: Reabsorbs 90% of glucose in early proximal tubule
    • SGLT1: Reabsorbs 10% of glucose in late proximal tubule
  • See Slide 14
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

List substances that are actively secreted into the renal tubules.

A
  • Creatinine

* Para-aminohippuric acid

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

Describe the transport maximum

A
  • Limit to the rate at which the solute can be transported:
  • Due to saturation of a specific transport system
  • Threshold for glucose reabsorption:
  • Transport max. for glucose = 375 mg/min
  • Filtered load for glucose = 125 mg/min
  • GFR x plasma glucose = 125 ml/min x 1 mg/ml
  • See Slide 18
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What are some reasons that some passively reabsorbed substances do not have a transport maximum

A
  • Rate of diffusion is determined by electrochemical gradient of the substance
  • Permeability of the membrane for the substance
  • Time that the fluid containing the substance remains within the tubule
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What is the Gradient-Time Transport

A
  • Rate of transport depends on:
  • The electrochemical gradient
  • Time the substance is in the tubule:
    • Depends on tubular flow rate
  • Characteristic of some passively reabsorbed substances
  • Includes some other substances that are actively transported
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What is solvent drag

A
  • Passive water reabsorption by osmosis is coupled mainly to sodium reabsorption.
  • Osmotic movement of water can also carry some solutes =
  • Solvent drag
  • See slide 22
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

Describe the proximal tubule

A
  • Highly metabolic w/large numbers of mitochondria
  • Extensive brush borders on luminal surfaces
  • Extensive intercellular and basal channels on interstitial surfaces
  • Reabsorb:
  • 65% of filtered sodium, chloride, bicarbonate and potassium
  • Reabsorb all filtered glucose and amino acids
  • See Slides 26-29
  • Secretes:
  • Organic acids, bases and hydrogen ions into tubular lumen
  • Sodium reabsorption:
  • In first half of proximal tubule:
    • Reabsorption is via co-transport along with glucose, amino acids, and other solutes.
  • In second half of proximal tubule:
    • Reabsorption is mainly with chloride ions
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

Describe sodium transport in the proximal tubule

A
  • Most Na+entry is via antiport with H+
  • Na+ is pumped out of cell via Na+K+ATPase pump
  • 3Na+: 2K+
  • K+ can easily diffuse back out of cell.
  • Electrical gradient:
  • Cytoplasm = -70 mV
  • Tubular lumen = -3 mV
  • Concentration gradient:
  • Luminal Na+ concentration = 140 mOsm
  • Cytoplasmic Na+ concentration = 30 mOsm
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

Describe Hydrogen and bicarbonate ions in the proximal tubule

A
  • [H+] increases in lumen due to antiport transport with Na+
  • H+combines with luminal bicarbonate
  • Forms carbonic acid
  • Carbonic anhydrase in lumen splits carbonic acid into carbon dioxide and water.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

Describe what occurs when carbon dioxide and water enter cell in the proximal tubule

A
  • Carbon dioxide and water combine to form carbonic acid.
  • Carbonic acid dissociates to form bicarbonate ion and H+
  • Bicarbonate ion diffuses out of cell into interstitial space.
  • H+removed from cell via:
  • Antiport with Na+
  • H+ATPase
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

Describe the Thin Descending Segment of the Loop Of Henle

A
  • Highly permeable to water and moderately permeable to most solutes, including urea and sodium
  • Reabsorbs about 20% of filtered water
  • Impermeable to water
17
Q

Describe the thick ascending segment of the Loop Of Henle

A
  • Na+K+ATPase pump in basolateral membranes:
  • Drives reabsorption of K+ into cell against concentration gradient.
  • Sodium, Potassium, Chloride co-transporter:
  • Moves 1-sodium, 2-chloride, 1 potassium into cell.
  • Slight back leak of K+ into lumen:
  • Creates positive charge of +8 mv.
  • Forces Mg++ and Ca++ to diffuse through tubular lumen through paracellular space into interstitial fluid.
  • Impermeable to water
  • Site of action of powerful “loop” diuretics:
  • Furosemide
  • Ethacrynic acid
  • Bumetanide
  • See Slide 34-35
18
Q

Describe the distal tubule

A
  • First portion forms macula densa.
  • Next part is highly convoluted and has characteristics similar to thick ascending segment of loop of Henle.
  • Reabsorbs most of the ions but is impermeable to water and urea:
  • Therefore, referred to as diluting segment.
  • Na+-Cl─ co-transporter (luminal membrane)
  • Na+K+ATPase pump (basolateral membrane)
  • See Slide 39-40
19
Q

Describe the principle cells of the Late Distal Tubule/Cortical Collecting Tubule

A
  • Reabsorb Na+ and water from tubular lumen.
  • Secrete K+ into tubular lumen.
  • Uses Na+K+ATPase pump.
  • Primary site of K+sparing diuretics:
  • Spironolactone, eplerenone, amiloride, triameterene
  • See Slide 42-43
20
Q

Describe the intercalated cells of the Late Distal Tubule/Cortical Collecting Tubule

A
  • Reabsorb K+ from tubular lumen.
  • Secrete H+ into tubular lumen:
  • Mediated by a H+ATPase transporter.
  • H+is generated through the action of carbonic anhydrase.
  • For each H+ secreted, a bicarbonate ion is reabsorbed across the basolateral membrane.

See Slide 45

21
Q

Describe the Medullary Collecting Duct

A
  • Epithelial cells are cuboidal:
  • Smooth surfaces
  • Few mitochondria
  • Permeability to water controlled by ADH.
  • Permeable to urea:
  • Urea transporters
  • Capable of secreting H+ against a large concentration gradient.

See Slides 47-52

22
Q

For aldosterone, describe the source, function, site of actin, and stimulus for secretion

A
  • Source:
  • Adrenal cortex
  • Function:
  • Increases sodium reabsorption and stimulates potassium secretion.
    • Stimulates Na+K+ATPase pump on basolateral side of cortical collecting tubule membrane.
  • Site of action:
  • Major site of action is on the principal cells of cortical collecting ducts.
  • Stimulus for secretion:
  • Increased extracellular potassium
  • Increased levels of angiotensin II
  • Absence of:
  • Addison’s disease
  • Results in marked loss of sodium and accumulation of potassium
  • Hypersecretion:
  • Conn’s syndrome
23
Q

Describe the function and effects of angiotensin II

A
  • Function:
  • Increased sodium and water reabsorption
  • Returns blood pressure and extracellular volume toward normal
  • Effects:
  • Stimulates aldosterone secretion
  • Constricts efferent arterioles
  • Directly stimulates sodium reabsorption in proximal tubules, loops of Henle, distal tubules, and collecting tubules
  • See Slide 57
24
Q

Describe the source, function, and effects of ADH

A
  • Source:
  • Posterior pituitary
  • Function:
  • Increases water reabsorption
  • Effects:
  • Binds to V2receptors in late distal tubules, collecting tubules, and collecting ducts
  • Increases formation of cAMP
    • Stimulates movement of aquaporin-2 proteins to luminal side of cell membranes (form clusters)
25
Q

Describe the source and function on ANP

A
  • Source:
  • Cardiac atrial cells in response to distension
  • Function:
  • Inhibits reabsorption of sodium and water
26
Q

Describe the source and function of parathyroid hormone

A
  • Source:
  • Parathyroid glands
  • Function:
  • Increases calcium reabsorption
27
Q

Define and give the equation for renal clearance

A
  • Renal clearance of a substance:
  • = volume of plasma that is completely cleared of the substance by the kidneys per unit time.
  • Example: If 1 ml of plasma contains 1 mg of a substance, and if 1 mg of this substance is excreted in the urine per minute:
    • Then 1 ml/min of the plasma is cleared of the substance.
  • Cs x Ps = Us x V
  • Cs = clearance rate of substance s
  • Ps = plasma concentration of substance s
  • Us = urine concentration of substance s
  • V = urine flow 63
  • Cs = (Us x V)Ps
28
Q

Describe the renal clearance of inulin

A
  • Inulin:
  • Polysaccharide (mol. Wt. = 5200)
  • Not produced in body
  • For a substance that is completely filtered but not reabsorbed or secreted:
  • The rate at which it is excreted in urine (Us x V) = filtration rate (GFR x Ps)

GFR x Ps = Us x V
GFR = (Us x V)/Ps = Cs

GFR = (Us x V)/Ps = Cs 
* Assume: 
 Ps = 1 mg/ml 
 Us = 125 mg/ml 
 V = 1 ml/min

GFR = (125 mg/ml x 1 ml/min)/1 mg/ml = 125 ml/min
- Thus, 125 ml of plasma flowing through the kidneys must be filtered to deliver the inulin that appears in the urine

Physiology (24 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions