Control Of Body Fluid Volume + Osmolality

Question 1

Action of angiotensin II

Answer 1

• vasoconstriction of EA
• releases ADH
• stimulates thirst
• causes aldosterone to be released from adrenal cortex > increases Na+ reabsorption from DCT (ENaC)

Question 2

How do prostaglandins affect Na+ reabsorption?

Answer 2

Decrease in circulating volume stimulates PG synthesis which results in:

• vasodilators > preventing excessive vasoconstriction
• renin release > Na+ reabsorption due to increased aldosterone

Question 3

How does atrial natriuretic peptide affect Na+ reabsorption

Answer 3

Produced by cardiac atrial cells in response to increased circulating volume > results in:

• inhibit NaK ATPase + closes ENaC channels > reduced Na+ reabsorption
• vasodilation of AE > increases GFR
• inhibit aldosterone secretion
• inhibit ADH release
• decrease renin release

Question 4

Renal responses to a increase in BP

Answer 4

• Release of ANP: inhibit NaK ATPase + reduced ENaC expression > decreases Na+ reabsorption > increased Na+ + H2O excretion
• increase in hydrostatic pressure of peritubular capillaries: pressure natriuresis + diuresis

Question 5

Renal responses to decrease in BP

Answer 5

• prostaglandin release
• RAAS activated: AngII > constriction of EA + release of aldosterone > stimulates ADH + thirst | increased expression of ENaC

Question 6

Renal response in congestive cardiac failure -

Answer 6

• cardiac output falls
• hypotension > Na+ and H2O retention > oedema
• renal hypotension after a fall in CO is sensed by kidneys as hypovolaemia > compensation by retaining NaCl + H2O to increase fluid volume
• increased pulmonary venous pressure > pulmonary oedema

Question 7

Management of pulmonary oedema due to congestive cardiac failure

Answer 7

Loop diuretics
ACE inhibitors
Vasodilators
Nitrates

Question 8

Presentation of hypervolemia

Answer 8

• ascites > swelling in abdomen
• pleural effusion
• pulmonary oedema
• peripheral oedema in legs
• coughing
• shortness of breath
• pumping action of heart grows weaker

Question 9

Causes of hypervolemia

Answer 9

• kidney rotation of sodium + water
• reduced effective arterial volume e.g. congestive cardiac failure
• excessive sodium or fluid intake
• cirrhosis
• hyperaldosteronism

Question 10

Treatment of hypovolemic shock

Answer 10

Isotonic fluid replacement - saline solution

Question 11

What is hypertensive renal disease?

Answer 11

High BP caused by narrowing of arteries to kidney

Question 12

What are hypertensive changes in the kidney

Answer 12

• arteriosclerosis of major renal arteries
• hyalinisation of small vessels with intimal thickening
  .
• causes chronic ENaC damage + reduced kidney size

Question 13

Outline the regulation of osmolality

Answer 13

• changes in plasma osmolarity sensed by hypothalamic osmoreceptors
  Two pathways initiated:
  -ADH in kidneys > affects renal water excretion
  -thirst > affects water intake

Question 14

Where are osmoreceptors located?

Answer 14

Hypothalamus

Question 15

Actions of ADH when plasma osmolality increases

Answer 15

• blood vessel vasoconstriction: V1 receptor mediated response
• increased water reabsorption: V2 receptor mediated response

Question 16

What stimulates the thirst response?

Answer 16

Increase in plasma osmolarity

Question 17

If plasma osmolality decreases, what type of urine is made?
How is this done?

Answer 17

hypoosmotic urine
- decrease ADH conc > decreased aquaporins > decreases H2O reabsorption
- loss of large amounts of dilute urine

Question 18

If plasma osmolality increases, what type of urine is made?
How is this done?

Answer 18

Hyperosmotic urine
- increase in ADH > increased aquaporins > increased H2O reabsorption in collecting duct
- concentrated urine

Question 19

What causes a release of renin?

Answer 19

• increased sympathetic innervation
• decrease in BP
• decreased Na+ to macula densa cells

Question 20

How does a decrease in Na+ activate renin release?

Answer 20

• less Na+ to macula dense
• MD stimulated > secrete prostaglandins
• prostaglandins act on granular cells
• renin released

Question 21

How do prostaglandins affect Na+ reabsorption?

Answer 21

• vasodilator effect (prevents excessive Vasoconsition)
• act on granular cells to release renin > activates RAAS > increases Na+ reabsorption from DCT

Question 22

Where does prostaglandin synthesis occur in the kidney?

Answer 22

Cortex
Medullary interstitial cells
Collecting duct epithelial cells

Question 23

Where are atrial natriuretic peptides produced by?
In response to what?

Answer 23

Caridac atrial cells
In response to increase in ECF volume

Question 24

How does angiotensin II maintain GFR?

Answer 24

Constricts efferent article > increases pressure in glomerulus

Question 25

What is SIADH?

Answer 25

Syndrome of inappropriate ADH secretion

Question 26

Presentation of SIADH

Answer 26

• fluid overload
• weight gain
• low urinary output
• conc. urine
• hyponatremia

Question 27

What is antidiuresis?

Answer 27

Reduction in renal water excretion