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Urinary System > Lecture 4.1: Control of Osmolarity > Flashcards

Lecture 4.1: Control of Osmolarity Flashcards

1
Q

What is Osmolarity?

A

Concentration of osmotically active
particles in a solution

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2
Q

What Osmolarity of Extracellular Fluid determined by? What ion accounts most of ECF osmolarity?

A
  • Determined by the total concentration
    of solutes that cannot cross cell membranes
  • Na+ accounts for 90% of the ECF
    osmolarity
  • Urea = An ‘ineffective osmole’
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3
Q

Plasma Osmolarity (Equation)

A

2 Na (mEq/L) + (Urea [mg/dL])/2.8 + (Glucose [mg/dL])/18

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4
Q

What are 4 Starling’s Forces?

A
  • Hydrostatic pressure in the capillary
    (Pc)
  • Hydrostatic pressure in the interstitium
    (Pi)
  • Oncotic pressure in the capillary (pc )
  • Oncotic pressure in the interstitium (pi )
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5
Q

How does [Na+] determines ECF volume?

A

Slide 6

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6
Q

Controlling Osmolarity: ECF is Hypertonic

A
  • Respond if the ECF is hypertonic by
    conserving water (thereby producing
    concentrated urine) achieved by
    release of vasopressin to promote anti-
    diuresis
  • Another response is the stimulation of
    thirst
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7
Q

Controlling Osmolarity: ECF is Hypotonic

A

Excrete water to produce dilute urine (diuresis) and restore ECF osmolarity

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8
Q

What is amount of water reabsorbed
from the tubular fluid is dependent on?

A

The permeability of the epithelial cells lining the connecting tubule and collecting duct

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9
Q

What is Arginine vasopressin?

A
  • Peptide hormone released from
    posterior pituitary
  • Release controlled by osmoreceptors
    in hypothalamus
  • Also called antidiuretic hormone
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10
Q

What is the Action of Antidiuretics?

A
  • An antidiuretic is a substance that
    helps to control fluid balance in an
    animal’s body by reducing urination,
    opposing diuresis
  • Increased water uptake from kidneys
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11
Q

Vasopressin and AQP2

A
  • Vasopressin stimulates the exocytic
    insertion of aquaporin-2 (AQP2)
    channels into the luminal membranes
    of the principal cells of the connecting
    tubule and collecting duct
  • When vasopressin is released,
    aquaporin 2 (AQP2) channels are
    inserted into the apical
    membranes of the cuboidal
    epithelium in the connecting
    tubules and the collecting ducts
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12
Q

Where is AQP1 found? Function?

A
  • Kidney (apically)
  • PCT
  • PST
  • tDLH
  • Water Absorption
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13
Q

Where is AQP2 found? Function?

A
  • Kidney (apically)
  • ICT
  • CCT
  • OMCD
  • IMCD
  • Water Reabsorption in response to
    arginine vasopressin
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14
Q

Where is AQP3 found? Function?

A
  • Kidney (basolaterally)
  • Medullary Collecting Duct
  • Water Reabsorption and glycerol
    permeability
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15
Q

Where is AQP4 found? Function?

A
  • Kidney (basolaterally)
  • Medullary Collecting Duct
  • Water Absorption
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16
Q

Via what AQPs does water enter and leave the cells of the kidney?

A
  • Water can then enter the cells via
    the AQP2 channels
  • And water can exit the cell through
    AQP3 and AQP4 channels (which are
    constitutively-expressed in the
    basolateral membrane)
17
Q

What happens to AQP2 is vasopressin is removed?

A
  • With the removal of vasopressin, the
    AQP2 channel is retrieved from the
    apical membrane by endocytosis
18
Q

What does the basolateral membrane
always contain?

A
  • The basolateral membrane always
    contains AQP-3 &4, and so is always
    permeable to water
  • Any water that enters across the apical
    membrane is thus able to pass into the
    peritubular capillaries
19
Q

Mechanism for Detection of Plasma Osmolarity

A

Hypothalamic osmoreceptors present in the supraoptic nuclei (SON) and organum vasculosum of the lamina terminalis (OVLT) of the hypothalamus detects increases in ECF osmolarity to induce thirst

20
Q

What happens to Mechanism for Detection of Plasma Osmolarity if BBB is disturbed?

A
  • The lack of a normal blood-brain barrier
    in the subfornical organ (SFO) and OVLT allows
    direct exposure of neurones to blood plasma
  • Elevations of 1-2% above normal plasma
    osmolarity levels, cause the cell bodies of the
    osmoreceptors to shrink, and fire an action
    potential
21
Q

What are Hypothalamic osmoreceptors stimulated by?

A

Hypertonic plasma

22
Q

Cycle of Vasopressin Release (6 rough steps)

A
  • Hypothalamic osmoreceptors are stimulated by
    hypertonic plasma
  • Which makes the hypothalmic osmoreceptors
    shrink
  • Mechanical stretch TRPV cation channels are
    activated
  • Allows the influx of positive charges from the
    ECF and consequent cell depolarisation
  • Action potentials fire to the posterior pituitary
    causing release of preformed vasopressin
  • Osmoreceptors can also stimulate thirst to
    induce a behavioural response to drink and
    replace water
23
Q

How is osmolarity primarily regulated?

A

Primarily regulated by adjusting output/urine production

24
Q

What neurones produce vaspressin? Where is it contained?

A
  • Vasopressin is produced by neurones located in
    the supraoptic and paraventricular
    nuclei of the hypothalamus
  • Vasopressin contained within secretory vesicles
25
Q

Vasopressin regulates the permeability
of the……..to water

A

Collecting Duct

26
Q

Production of DILUTE Urine

A
  • Production of dilute urine involves the
    active removal of solute from the.
    tubular fluid (e.g. via the NaK2Cl co-
    transporters)
  • This occurs in the thick ascending limb
    (TAL) of the Loop of Henle
  • The TAL dilutes the filtrate leaving the
    loop of Henle tubular fluid in TAL
  • Tubular fluid is further diluted in by
    reabsorption of Na+in the DCT
27
Q

Osmolarity of the Renal Medulla (outer to inner)

A
  • The osmolarity of the interstitial fluid in
    the renal medulla increases from the
    outer renal medulla to the inner renal
    medulla
  • Reaching 1200 mosm/l in the inner
    renal medulla
28
Q

What does high osmolarity mean?

A

Means you have more particles in your serum

29
Q

What does low osmolarity mean?

A

Means the particles are more diluted

30
Q

How is hypertonicity created in the renal
medulla? (2 Mechanisms)

A
  • Accumulation of solutes in the ISF of
    the renal medulla is required
    1) Countercurrent multiplication in loop
    of Henle (the ‘countercurrent.
    arrangement’ of the descending and
    ascending limbs, and the differential
    permeability of these two limbs to
    water and ions)
    2) Accumulation of urea in the renal
    medulla interstitium by recycling urea
    from the collecting duct
31
Q

What is the Descending Limb of the Loop of Henle permeable to?

A
  • Water via AQP1
  • Impermeable to solutes
32
Q

What is the Thick Ascending Limb of the Loop of Henle permeable to?

A
  • Impermeable to water
  • Actively transfers solute from the tubular
    lumen to the interstitial fluid via the Na+
    /K+/2Cl- co-transporter
33
Q

Blockade of the NaK2Cl co-transporters with ‘loop diuretics’, causes…?

A

The medullary interstitium to become isosmotic, and copious dilute urine is produced

34
Q

Ascending limb of LoH: What is the effect of gain of NaCl in the medullary interstitial fluid on osmotic pressure?

A
  • The gain of NaCl in the medullary interstitium
    raises the osmotic pressure in the interstitium * While the osmotic pressure in the ascending
    limb decreases
35
Q

What happens to water in the descending tubule of LoH? Osmotic Pressure?

A
  • Water flows out of the descending tubule by
    osmosis
  • Thus osmotic pressure is raised in the to 400
    mOsm/L
36
Q

Fresh tubular fluid enters….?

A

From the PCT, pushing the newly-concentrated fluid (400 mOsm/L) towards the tip of the loop, and into the ascending limb

37
Q

What transporters re-establishes a 200mosm/l gradient between the ascending limb and the interstitium?

A

The NaK2Cl pump

38
Q

More concentrated tubular fluid in the thick ascending limb (TAL), allows the interstitum osmolarity to rise to…?

A

500 mosm/l

Urinary System (15 decks)

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