T3 L10 Regulation of homeostasis by the kidney: fluid balance

Question 1

What is the role of the kidney in volume regulation?

Answer 1

Fluid balance

Electrolyte balance

Question 2

What is fluid balance?

Answer 2

The amount of water gained by the body each day equals the amount lost

Question 3

What is electrolyte balance?

Answer 3

The ion gain each day equals the ion loss

Question 4

What increases the permeability of the collecting duct?

Answer 4

ADH

Question 5

What is ADH?

Answer 5

Most important hormone that regulates water balance
Nonapeptide with Mw of over 1000
Known as vasopressin or 8-arginine vasopressin (AVP)
Plasma half life is 10-15 minutes

Question 6

What does ADH act on?

Answer 6

On V2 receptors on the basal membrane of principal cells in the collecting duct.
This leads to the inserted of AQP 2 into the apical surface

Question 7

What happens when there is maximal ADH release?

Answer 7

There is the production of low amounts of concentrated urine

Question 8

When causes ADH to be released?

Answer 8

Changes in plasma osmolality and effective circulating volume

Question 9

What are changes in plasma osmolality detected by?

Answer 9

Osmoreceptors in hypothalamus

Question 10

What are changes in effective circulating volume detected by?

Answer 10

Baroreceptors

Question 11

What happens in dehydration?

Answer 11

1) There is an increase in plasma osmolality
2) Stimulates osmoreceptors in hypothalamus
3) Triggers ADH release
4) More water reabsorbed from collecting ducts back into circulation
5) Increases effective circulating volume

Question 12

What happens if there is increased osmolality?

Answer 12

Stimulates a group of osmoreceptors in hypothalamus
Triggers thirst
Promotes water intake which enters circulation
Increases effective circulating volume

Question 13

Describe the efferent pathway affected by plasma osmolality

Answer 13

ADH - effector is the kidney. Causes renal excretion of water
Thirst - effector is the brain. Causes water intake

Question 14

Where are baroreceptors found?

Answer 14

Carotid sinus
Aortic arch
Renal afferent arteriole
Atria of heart

Question 15

What are the efferent pathways affected by ECV?

Answer 15

ADH
RAAS
ANP
Sympathetic nervous system

Question 16

What is the effector for ECV in the short term?

Answer 16

Heart & blood vessels

Affects blood pressure

Question 17

What is the effector for ECV in the long term?

Answer 17

Kidney

Affects sodium excretion

Question 18

Where are low pressure blood volume baroreceptors found?

Answer 18

Large systemic veins
Cardiac atria
Pulmonary vasculature

Question 19

Where are high pressure blood volume baroreceptors found?

Answer 19

Carotid sinus
Aortic arch
Renal afferent arteriole

Question 20

What is the renal baroreceptor?

Answer 20

The renal afferent arteriole

Question 21

What is feedback control of ECV mediated by?

Answer 21

Baroreceptor stimulation

Question 22

What 4 parallel effector pathways are triggered by changes in ECV?

Answer 22

RAAS
Sympathetic nervous system
ADH release
ANP release

Question 23

What do the 4 parallel effector pathways change when triggered by ECV?

Answer 23

They change renal haemodynamics & sodium transport by renal tubule cells

Question 24

What is RAAS?

Answer 24

The principal factor controlling plasma Ang II levels is renin release from the juxtaglomerular cells

Question 25

How does a decreased ECV stimulate renin release?

Answer 25

Decrease renal perfusion pressure detected in the afferent arteriole - renal baroreceptor Decreased sodium concentration in the distal tubule detected by the macula dense cells Decreased systemic blood pressure triggers effects of the sympathetic nervous system supplying JGA

Question 26

What are the important actions of angiotensin II?

Answer 26

All of the actions designed to increase ECV 1) Enhances tubular sodium transport in the kidney 2) Stimulation of aldosterone release from adrenal cortex 3) Acts on hypothalamus to stimulate thirst & ADH release into circulation 4) Vasoconstriction of renal & other systemic vessels

Question 27

What does the stimulation of aldosterone release from the adrenal cortex lead to?

Answer 27

More sodium & water is reabsorbed from the distal tubule / collecting duct

Question 28

What does vasoconstriction of renal & other systemic vessels do?

Answer 28

Increase systemic blood pressure

Question 29

What are the longer term effects of angiotensin II?

Answer 29

Causes renal cell hypertrophy | More protein synthesis of sodium transporters & channels

Question 30

What are the important actions of aldosterone?

Answer 30

All the actions are designed to increase ECV in collaboration with angiotensin II Stimulates sodium reabsorption & potassium excretion in distal tubule & collecting duct Exerts indirect negative feedback on RAAS by increasing ECV & lowering plasma K+ concentration Important to conserve sodium & water & prevent large variations in plasma K+ levels

Question 31

What is the volume regulation pathway for RAAS?

Answer 31

1) Decrease in ECV 2) Detected by renal baroreceptors & renal sodium sensors 3) Activation of RAAS - angiotensin II & aldosterone 4) Reduced sodium excretion by kidney Increased renal sodium reabsorption 5) Increase in ECV

Question 32

What is the volume regulation pathway for ANS?

Answer 32

1) Decrease in ECV 2) Detected by peripheral baroreceptors 3) Signals to hypothalamus in brain 4) Activation of autonomic sympathetic NS 5) Reduced sodium excretion by kidney Increased renal sodium reabsorption 6) Increase in ECV

Question 33

What is the volume regulation pathway for ADH?

Answer 33

1) Decrease in ECV 2) Detected by peripheral baroreceptors 3) Signals to hypothalamus in brain 4) Release of ADH into circulation 5) Increased water consumption in the kidney 6) Increase in ECV 1) Decrease in ECV = increase in plasma osmolality 2) Detected by osmoreceptors in hypothalamus 3) Release of ADH into circulation 4) Increased water reabsorption in the kidney 5) Increase in ECV

Question 34

What are the actions of ANP?

Answer 34

All actions designed to lower ECV Atrial myocytes synthesis & store ANP Increased ECV causes atrial stretch leading to ANP release into circulation ANP promotes natriuresis Renal vasodilation --> increased blood flow --> increase in GFR -> more Na+ excreted More Na+ reaches macula dense --> renin release by JGA is reduced --> reduces effect of Any II Overall effect is to inhibit the actions of renin & oppose effects of Ang II