L118: Kidney 3 Flashcards

1
Q

The primary function of the kidneys is to filter blood however, what else do they regulate?

A
  • Fluid and electrolytes: blood volume ~ blood pressure;
  • Acid-base blood balance;
  • Calcium and vitamin D metabolism;
  • Erythropoietin.
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2
Q

What is the series of events upon excess fluid levels?

A
  • Excess fluid;
  • Elevated blood volume;
  • Elevated blood pressure;
  • Large volume of dilute urine;
  • Reduced blood pressure.
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3
Q

What is the series of events upon reduced fluid levels?

A
  • Reduced fluid;
  • Reduced blood volume;
  • Reduced blood pressure;
  • Small volume of conc. urine;
  • Elevated BP.
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4
Q

What is glomerular filtration rate (GFR)?

A

The rate at which blood is filtered through the glomerulus into the Bowman’s capsule

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5
Q

What are the three main factors that influence GFR?

A
  • Hydrostatic pressure;
  • Osmotic pressure;
  • Blood pressure.
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6
Q

What is the main driver of hydrostatic pressure in the glomerulus?

A

The afferent arteriole is larger than the efferent arteriole

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7
Q

How do the kidneys estimate GFR?

A

Blood pressure

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8
Q

If blood pressure increases, and the kidneys are unable to adjust (CKD) the GFR, GFR will…

A

increase

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9
Q

An increase in GFR leads to…

A

less time to reabsorb sodium and more sodium entering the DCT

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10
Q

What is the juxta-glomerulus apparatus (JGA) and what is its purpose?

A
  • Connects the glomerulus with the DCT;
  • Measures the [Na+] of the filtrate;
  • Adjusts the diameter of the afferent arteriole.
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11
Q

What is the macula densa?

A
  • A component of the JGA;
  • An area of closely packed specialised cells;
  • Detect the [Na+].
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12
Q

What are juxtaglomerular cells?

A
  • A component of the JGA;
  • Modified smooth muscle cells around the afferent arteriole (some on efferent);
  • Synthesise, store and secrete the enzyme, renin;
  • Adjust the diameter of the arterioles.
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13
Q

How do macula densa cells respond to an increase in blood pressure and why?

A
  • Increased BP;
  • Increased glomerular hydrostatic pressure;
  • Increasder GFR;
  • Increased Na+ in filtrate;
  • Detected by macula densa;
  • Macula densa release adenosine.
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14
Q

What does the release of adenosine from macula densa cells cause?

A
  • Paracrine signal to juxtaglomerular cells;
  • Juxtaglomerular cells constrict afferent arteriole;
  • Tubular-glomerular feedback.
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15
Q

How does the constriction of the afferent arteriole lead to restored homeostasis?

A
  • Reduces glomerular hydrostatic pressure (less blood can flow in);
  • Reduced GFR;
  • Homeostasis restored.
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16
Q

How do macula densa cells respond to a decrease in blood pressure and why?

A
  • Decreased BP;
  • Decreased glomerular hydrostatic pressure;
  • Decreasd GFR;
  • Decreased Na+ in filtrate;
  • Detected by macula densa;
  • Macula densa release prostaglandins.
17
Q

What does the release of prostaglandins from macula densa cells cause?

A
  • Paracrine signal to juxtaglomerular cells;
  • Juxtaglomerular cells release renin;
  • Activates renin-angiotensin system.
18
Q

Why is the renin-angiotensin system necessary to restore homeostasis?

A

The afferent arteriole is already relaxed (dilated) so further relaxation would not have an effect

19
Q

How does RAAS restore blood pressure?

A

(Through rapid vasoconstriction!)

  • Angiotensinogen is released into circulation (from liver);
  • Renin (enzyme from kidneys) converts angiotensinogen into angiotensin I;
  • Angiontensin converting enzyme converts angiotensin I into angiotensin II;
  • Angiotensin II is a potent vasoconstrictor - rapidly increases BP.
20
Q

How does RAAS restore blood volume?

A

(via action of aldosterone and ADH!)

  • Angiotensin II is detected by:
  • The adrenal medulla - aldosterone;
  • Hypothalamus - ADH.
21
Q

In RAAS, where is aldosterone released from?

A

The adrenal medulla

22
Q

In RAAS, where is ADH released from?

A

The hypothalamus

23
Q

What hormone counteracts RAAS?

A

ANP: atrial natriuretic peptide

24
Q

How does ANP counteract RAAS?

A
  • Acts to reduce blood pressure;
  • Works to reduce plasma volume through excretion of Na+ and water;
  • i.e. the opposite of RAAS, which works to increase plasma volume and resulting BP.
25
Q

What feedback system maintains GFR?

A

Tubularglomerular feedback

26
Q

What molecules do the macula densa signal to the juxtaglomerular cells via?

A
  • Adenosine (high BP, high Na+, high GFR);

- Prostaglandins (low BP, low Na+, low GFR);

27
Q

How do juxtaglomerular cells respond to high GFR (due to high blood pressure)?

A
  • Signalled by adenosine from macula densa;
  • Dilate to constrict afferent arteriole;
  • Reduced flow of blood into the glomerulus
28
Q

How do juxtaglomerular cells respond to low GFR (due to low blood pressure)?

A
  • Signalled by prostaglandins from macula densa;
  • Contract to dilate afferent arteriole;
  • Secrete renin to activate RAAS.
29
Q

What is the primary molecule through RAAS that restores blood pressure?

A

Angiotensin II (vasoconstrictor)

30
Q

What are the primary molecules through RAAS that restores blood volume?

A
  • Aldosterone (adrenal medulla);

- ADH (hypothalamus).

31
Q

How is GFR effected with CKD?

A

It decreases

32
Q

List some symptoms of CKD:

A
  • Oedema;
  • Anaemia;
  • Blood/ protein in urine;
  • Weak/ painful bones.
33
Q

List some causes of CKD:

A
  • Hypertension;
  • Diabetes;
  • High cholesterol.