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Exam Prep Tutorials (Physiology) > Renal Physiology 3 > Flashcards

Renal Physiology 3 Flashcards

1
Q

Where is renin released from?

A

Juxtaglomerular cells

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2
Q

What controls renin release?

A

The macula densa, detecting low sodium flux

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3
Q

What effect does hypotension have on renin release?

A

Increased renin release

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4
Q

What effect do beta blockers have on renin release?

A

Inhibits renin release

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5
Q

How is the renin-angiotensin system activated?

A

In response to hypotension, and thus a fall in renal blood flow:

  • low BP detected by juxtaglomerular apparatus
  • JGA secretes renin
  • renin stimulates production of angiotension
  • angiotension vasoconstricts and also causes aldosterone release from the adrenal cortex
  • vasocontriction increases BP
  • aldosterone causes sodium and water reabsorption also increasing BP
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6
Q

What is the juxtaglomerular apparatus?

A

It’s the intrarenal baroreceptor.

Composed of the:

  • macula dena
  • JG cells
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7
Q

What is the macula densa? Where is it?

A

Specialized epithelial cells. They increase renin release in response to low levels of delivered sodium, due to a fall in GFR or increase in PCT reabsorption.

Situated in the wall of the 1st part of the DCT. It abuts the afferent and efferent arterioles.

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8
Q

What are the juxtaglomerular cells?

A

They secrete renin in response to hypovolaemia, increased Na concentration in blood and sympathetic stimulation.

Located in the wall of the afferent arteriole (in the media). Just before the arteriole enters the glomerulus.

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9
Q

What is renin?

A
  • A glyocoprotein hormone, synthesised and secreted by the JGA
  • formed from pro-renin and pre-pro-renin with a 1/2 life of 80mins
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10
Q

What are the actions of renin?

A
  • acts on circulating angiotensinogen, a large liver protein
  • cleaves a 10 amino acid peptide, Angiotensin I from angiotensinogen, in the plasma
  • Angiotensin I is converted to Angiotensin II in lungs, by angiotensin converting enzyme (ACE)
  • ACE is found in the capillary endothelium
  • Angiotensin II has multiple effects
  • Angiotensin II is converted to angiotensin III in many tissues by aminopeptidase
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11
Q

What is renin secretion controlled by?

A
  • renal sympathetic nerves
  • intrarenal baroreceptors
  • antiontension II
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12
Q

What increases renin secretion?

A
  • hypovolaemia
  • cardiac failure
  • cirrhosis
  • renal artery stenosis
  • catecholamines acting on beta-1 receptors
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13
Q

What is renin secretion decreased by?

A
  • angiotensin II
  • vasopressin
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14
Q

What are the actions of angiontensin II?

A
  • powerful vasoconstrictor, constricts afferent and efferent arterioles in the kidney
  • effect on efferent arteriole is greater, increasing GFR
  • causes aldosterone release
  • potentiates sympathetic activity
  • stimulates thirst by direct effect on hypothalamus
  • causes release of vasopressin (ADH)
  • acts directly on renal tubules, esp the PCT to cause Na+ and water retention, by stimulation of Na+/H+ antiporters
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15
Q

Where is aldosterone produced and secreted by?

A

It’s a mineralocorticoid. Secreted by the zona glomerulosa of the adrenal cortex in response to:

  • reduced renal blood flow (via RAS-angiotensin II)
  • stress and trauma via adrenocorticotrophin (ACTH) release
  • hyperkalaemia - small changes in plasma K+ are important
  • hyponatraemia
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16
Q

What are the actions of aldosterone?

A
  • acts on the DCT and renal cortical collecting ducts
  • increases Na reabsorption, thus Na and H2O are retained
  • potassium and H+ lost in exchange for Na
  • (Also increases production of distal nephron transport mechanisms
  • works via protein synthesis so effect takes hours)
17
Q

What does the adrenal cortex produce?

A

Aldosterone (glomerulosa)

Cortisol (fasiculata)

Androgens (reticularis)

Catecholamines (medulla - the rest are all cortex)

18
Q

Where is ADH synthesised?

A

Hypothalamus

19
Q

Where is ADH secreted from?

A

Posterior pituitary

20
Q

What does ADH do?

A
  • under control of baro and osmoreceptor reflexes
  • inactivated in liver and kidney
  • half life of 18 minutes
  • causes water retention due to an increase in water permeability of collecting duct membrane
  • inserts protein channels for water into luminal membrane via cyclic AMP (aquaporins)
  • at high concentrations, can act on arteriolar smooth muscle - reducing renal blood flow and GFR
  • also stimulates sodium reabsorption and K+ excretion from collecting ducts
21
Q

What do baroreceptors do?

A
  • can be arterial, venous, cardiac
  • detect fall in plasma volume
  • afferent firing rate to hypothalamus falls
  • ADH release from posterior pituitary increased
22
Q

What do osmoreceptors do?

A
  • osmoreceptors detect changes in plasma osmotic pressure
  • fall in plasma osmotic pressure reduces ADH secretion
  • rise in plasma osmotic pressure increases ADH secretion
23
Q

What is ANP?

A

Atrial natriuretic peptide - secreted in response to atrial stretch. Increases renal excretion of sodium and water. Potent vasodilator. Improves renal blood flow.

  • afferent arteriolar dilatation and efferent arteriolar constriction - increases net filtration pressure (increased filtration coefficient)
  • released from atrial myocytes
  • inhibits renin secretion
  • inhibits aldosterone release
  • direct action on collecting ducts to decrease sodium reabsorption
24
Q

What is the normal GFR of an adult?

A

125ml/min or 180L/day

25
Q

What is clearance?

A

The renal clearance of a substance is the volume of plasma completely cleared of that substance per unit time (ml/min).

Clearance is helped to quantify:

  • excretory function of the kidney
  • rate at which blood flows through the kidney
  • basic functions of the kidney
26
Q

What substances can be used to measure GFR?

A

Inulin

Creatinine

27
Q

What is inulin?

A
  • polysaccharide
  • molecular weight 5200 daltons
  • freely filtered, not reabsorbed or secreted
  • not toxic, metabolised or plasma protein bound
  • rate of excretion = filtration rate
  • not endogenous, must be administerd IV
28
Q

What is creatinine?

A
  • a by-product of muscle metabolism
  • no need for infusion
  • almost entirely cleared from the body by glomerular filtration
  • small amount is secreted so the amount excreted slightly exceeds the amount filtered - therefore overestimates GFR
  • under steady state conditions amount of creatinine excreted = rate of creatinine production
29
Q

How is renal plasma flow estimated?

A
  • if a substance is completely cleared from plasma, clearance should equal renal plasma flow
  • GFR is only 20% of renal plasma flow
  • for a substance to be completely cleared from plasma, some secretion must also occur
  • PAH (Para-aminohippuric acid) is 90% cleared by the kidneys from the plasma
  • PAH clearance is therefore used to estimate RPF
30
Q

How can renal blood flow be calculated?

A

You need to know renal plasma flow. You can calculate renal blood flow from this, provided the haematocrit is known.

Renal plasma flow = renal blood flow x (1 - haematocrit)

RBF = RPF / (1 - hct)

31
Q

What GFR would sodium as an indicator produce?

A

An underestimate of GFR because sodium is reabsorbed so urine concentration would be decreased.

32
Q

What is the calculation for clearance?

A

Clearance of a substance = renal excretion / plasma concentration

33
Q
A

Exam Prep Tutorials (Physiology) (10 decks)

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