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Anatomy II > M24: Tubular Reabsorption & Regulation > Flashcards

M24: Tubular Reabsorption & Regulation Flashcards

1
Q

At what point does glomerular filtrate become tubular fluid?

A

once it enters the proximal convoluted fluid

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2
Q

Where does most reabsorption occur?

A

proximal convoluted tubule

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3
Q

purpose of tubular secretion

A

transfer of materials from blood into glomerular filtrate
- controls blood pH (H+ ions)
- eliminate substances (ammonia, creatinine, K+, some drugs)

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4
Q

transport mechanisms for tubular reabsoprtion

A

PRIMARY ACTIVE TRANSPORT
- ATP dependent (e.g. Na+/K+ pump)

SECONDARY ACTIVE TRANSPORT
- driven by ion’s electrochemical gradient
- SYMPORTERS move substances in same direction (e.g. Na+-glucose symporters move Na+ AND glucose into cell)
- ANTIPORTERS move substances in opposite directions

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5
Q

paracellular reabsorption

A

passive transport mechanism between cells

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6
Q

the 2 water reabsorption processes

A

OBLIGATORY WATER REABSORPTION
- 90% reabsorbed this way
- water follows solutes that are reabsorbed
- facilitated by AQUAPORIN-1: protein water channel found in apical and basolateral membranes of proximal convoluted tubule and descending limb

FACULTATIVE WATER REABSORPTION
- 10% reabsorbed this way
- water reabsorbed based on need
- regulated by anti-diruetic hormone (ADH)

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7
Q

Reabsorption in the first half of proximal convoluted tubule

A

Na+ SYMPORTERES
- help reabsorb materials from tubular fluid
- glucose, AAs, lactic acid, water soluble vitamins all reabsorbed in first half of PCT

Na+ ANTIPORTERS
- help reabsorb Na+
- also secrete H+ ions which aides bicarbonate reabsorption

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8
Q

Reabsorption in the second half of proximal convoluted tubule

A

PASSIVE REABSORPTION
- several different ions: Cl-, K+, Ca2+, Mg2+, urea
- water taken up via osmosis (making osmolality in this section of PCT same as blood)

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9
Q

cell type in descending nephron loop

A

simple squamous

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10
Q

reabsorption in nephron loop

A

Descending limb
- 15% of water reabsorbed
- small diffusion of solutes into tubule

Ascending limb
- water not reabsorbed, but solutes are (cells not permeable to water)
- thin region - PASSIVE ION DIFFUSION
- thick region - ACTIVE TRANSPORT (Na+, K+, Cl-)

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11
Q

why is reabsorption of water high in descending nephron loop?

A
  • solute concentration in interstitial fluid gets higher as loop descends into medulla
  • therefore, more water is reabsorbed as a result of osmosis
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12
Q

what end of nephron loops are solutes reabsorbed?

A

ascending
via active and passive transport

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13
Q

How much water and solutes are reabsorbed in proximal convoluted tubute?

A

65% of water
ALL glucose and amino acids

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14
Q

reabsorption in the early distal convoluted tubule

A
  • reabsorption of Na+ and Cl- continues via symporters
  • 10-15% water reabsorbed
  • PARATHYROID HORMONE (PTH) acts on cells to control Ca2+ reabsorption here
    DCT in cortex, so reabsorption happens into the PERITUBULAR CAPILLARIES
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15
Q

reabsorption and secretion in late distal convoluted tubule and collecting duct

A
  • By the end of DCT, 95% of water and solutes reabsorbed
  • Cells in collecting duct make final concentration adjustments for urine production

PRINCIPLE CELLS
- reabsorb Na+ and secrete K+
- controlled by ADH and Aldosterone

INTERCALATED CELLS
- reabsorb K+ and bicarbonate ions, secrete H+

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16
Q

name cells in collecting duct that make final adjustments to urine concentration

A

Principle cells
Intercalated cells

17
Q

name the 5 hormones that regulate Na+, Cl-, Ca2+ and water reabsorption and K+ secretion in renal tubules

A
  1. Angiotensin II
  2. Aldosterone
  3. Antidiuretic hormone (ADH)
  4. Atrial natriuretic hormone (ADH)
  5. Parathyroid hormone (PTH)
18
Q

Renin-Angiotensin system

A

Activated if blood volume and pressure decrease

Process
a) less stretch in afferent arterioles (increases SNS response)
b) juxtaglomerular cells secrete RENIN into blood
c) renin converts ANGIOTENSINOGEN (from liver) into ANGIOTENSION I (still not the active hormone)
d) ANGIOTENSIN CONVERTING ENZYME (ACE) (released from lungs) converts angiotensin I into ANGIOTENSIN II
- Angiotensin II ↓ GFR
- vasoconstriction of afferent arterioles
- Na+/Cl-/H20 reabsorption in PCT via Na+/H+ antiporters
- causes renal cortex to secrete ALDOSTERONE - targets principle cells to reabsorb Na+/Cl-/H20 and secrete K+ via Na+/K+ pump

19
Q

Role of Angiotensin II

A
  • ↓ GFR via vasoconstriction of afferent arterioles
  • ↑ Na+, Cl- and water reabsorption in PCT by stimulating Na+/H+ antiporters
  • causes adrenal cortex to secrete ALDOSTERONE - causes principle cells in collecting ducts to reabsorb more Na+, Cl- and water and secrete K+
20
Q

Role of Antidiuretic hormone (ADH)

A
  • Increases permeability of principle cells to water -> increased facultative water reabsorption
  • How? On demand water protein channels! Signals insertion of AQUAPORIN-2 channels into membrane (bring up to apical surface of principal cells)

Keys:
increased facultative water reabsorption in principle cells via aquaporin-2

21
Q

where is antidiuretic hormone (AHD) released

A

Pituitary gland

Receptors: osmoreceptors in to hypothalamus
Control centre: hypothalamus and posterior pituitary
Effectos: principle cells

22
Q

alcohol inhibits the release of which hormone? What are the effects?

A

Antidiruetic hormone (ADH)
- increases urine production because water is not reabsorbed int blood supply

23
Q

role of atrial natriuretic peptide (ANP)

A
  • helps regulate blood pressure: decreases water reabsorption
  • suppresses secretion of water reabsorption increasing hormones
  • released if high blood pressure/volume detected
  • inhibits reabsorption of Na+ and water in the proximal convoluted tubule and collecting ducts
  • suppresses secretion of aldosterone and antidiuretic hormone: therefore ↑ Na+ excretion in urine, ↓ blood volume
24
Q

role of parathyroid hormone (PTH)

A
  • regulates Ca2+ ion concentrations
  • released from parathyroid glands in response to low blood Ca2+
  • stimulates cells in early distal convoluted tubule to increases Ca2+ reabsorption
  • inhibits phosphate reabsorption in proximal convoluted tubule
25
Q

paracellular reabsorption

A

movement of solutes between the cells of the renal tubule

26
Q

what ion are solutes co-transported with in the kidney nephron cells?

A

Na+ ions

27
Q

Substances reabsorbed in PCT

A
  • water
  • solutes (glucose, AA, urea, ions: Na+, K+, Ca2+, bicarbonate, HPO4^2-)
  • small pr-
28
Q

By which mechanism is glucose reabsorbed in the PCT?

A

secondary active transport
- symporters

29
Q

Water reabsorption caused by the movement of solutes is called…

A

obligatory water reabsorption

30
Q

Water reabsorption on demand is called…

A

facultative water reabsorption

31
Q

once fluid passes through PCT, what has been removed?

A
  • 65% of water
  • all glucose and AA
32
Q

what causes a drop in blood volume?

A

dehydration
Na+ deficiency
hemmorage

Anatomy II (34 decks)

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