regulation of ECF volume

Question 1

What are the major ECF osmoles

Answer 1

sodium and chloride ions

Question 2

What are the major ICF osmoles

Answer 2

Potassium

Question 3

What is the total body water in the body and the distribution

Answer 3

42L
14L ECF (3L plasma and 11L interstitial fluid)
28L ICF

Question 4

What happens when there is a change of sodium content in the ECF

Answer 4

There is a change in ECF volume - the volume of blood perfusing tissues is affected therefore circulating volume is effected and therefore blood pressure is impacted

Question 5

What happens when there is increased salt and water loss from the body (e.g in vomiting or diarrhoea) what happens with the baroreceptors as well

Answer 5

Loss of salt and water which reduces plasma volume which leads to a decreased venous pressure, this decreases venous return and atrial pressure which eventually leads to decreased blood pressure - the carotid sinus baroreceptor becomes inhibited which increases sympathetic discharge which increases vasoconstriction and total peripheral resistance which raises the blood pressure to normal - ADH also becomes stimulated to increase reabsorption of water

Question 6

What is the function of carotid sinus baroreceptors (high pressure)

Answer 6

Inhibit sympathetic discharge

Question 7

What is the function of angiotensin II

Answer 7

causes the re uptake of sodium chloride and water reabsorption at the proximal tubule - it also increases alddosterone - angiotensin II is also a potent vasoconstrictor

Question 8

What is the function of aldosterone

Answer 8

Increases NaCl reabsorption at the distal tubule

Question 9

What causes an increase in renin release

Answer 9

Increased renal vasoconstrictory nerve activity which increases arteriolar constriction

Question 10

WHat is the effect of angiotensin II on the peritubullar capillary with regards to hydrostatic and oncotic pressure and what does this cause

Answer 10

decreases hydrostatic pressure and increases oncotic pressure and this pressure difference created makes the conditions specific for reabsorption at the proximal tubule so more sodium is reabsorbed

Question 11

What mantains the GFR

Answer 11

Constriction of the afferent arteriole due to sympathetic vasoconstrictors and angiotensin II causing constriction of the efferent arteriole

Question 12

What are juxtaglomerular cells

Answer 12

Large epithelial cells with plentiful granules

Question 13

What is the macula densa

Answer 13

Specialised loop of the distal tubule

Question 14

What makes up the juxtaglomerular apparatus

Answer 14

Juxtaglomerular cells and Macula densa

Question 15

Describe the renin-angiotensin-aldosterone production

Answer 15

Renin causes angiotensinogen to be converted into angiotensin I - ACE then converts angiotensin I to angiotensin II - Angiotensin II stimulates the aldosterone secreting cells on the zona glomerulosa of the the adrenal cortex to release aldosterone

Question 16

What produces renin

Answer 16

juxtaglomerular cells

Question 17

Where is angiotensin converting enzyme found within the body

Answer 17

Found throughout the vascular endothelium but is in its greatest abundance at the pulmonary circuit

Question 18

What is the rate limiting step in the renin-angiotensin-aldosterone system

Answer 18

Renin - angiotensinogen is always in the plasma but renin is required to convert it into angiotensin I to be begin the sequence

Question 19

What causes renin release

Answer 19

A pressure drop in the afferent arterioles which act as baroreceptors sense less distension which causes an increase in renin secretion

Increase in sympathetic nerve activity can increase renin release via beta1 effect

Decreased sodium chloride delivery at the macula densa causes increased renin release

Question 20

What causes renin inhibition

Answer 20

Angiotensin II feedback inhibits renin

ADH inhibits renin

Question 21

How do the juxtaglomerular cells detect changes at the afferent arterioles

Answer 21

The granular cells of the juxtaglomerular cells are very close to the afferent arteriole and can detect pressure changes

Question 22

What is the function of Angiotensin II

Answer 22

Potent vasoconstrictor which increases total peripheral resistance

Stimulates aldosterone release so increases NaCl and water uptake at distal tubule

It acts on the hypothalamus to release ADH and increase water re uptake collecting duct

It stimulates thirst and salt appetite in the hypothalamus

Question 23

How does the juxtaglomerular filtration system control GFR

Answer 23

If there is high blood flow past the macula densa it releases vasoconstrictory signalling molecules which increase afferent arteriole constriction which decreases the blood flow

Question 24

What happens in the case where both water and electrolytes are lost where ADH would be conflicted

Answer 24

Volume has primacy over osmolarity therefore ADH will increase causing more water reabsorption

Question 25

What is the function of atrial natriuretic peptide (ANP)

Answer 25

Promotes sodium excretion

Question 26

What happens when aldosterone is given to normal patients with normal sodium values

Answer 26

There will be weight gain due to the increased sodium but then ANP will respond to the increased water retention causing the ‘aldosterone escape’ where there is increased excretion of water and salt

Question 27

What cells release ANP

Answer 27

atrial cells

Question 28

What happens to potassium during the aldosterone escape

Answer 28

It continues it’s effect of secreting potassium, even when ANP is active and therefore large amounts of potassium are being excreted

Question 29

What is Conn’s syndrome

Answer 29

Hyperaldosteronism due to a tumour in the adrenal cortex

Question 30

What happens in uncontrolled diabetes when the plasma glucose exceeds the maximum reabsorptive capacity in the proximal tubule

Answer 30

The excess glucose remains in the proximal tubule which will have an osmotic effect, keeping the water in the proximal tubule which leads to less water reabsorption - this results in a less osmotic fluid in the tubule so the sodium doesn’t have the correct concentration gradient to be reabsorbed - sodium and glucose reabsorption are linked so when sodium reabsorption decreases, the glucose reabsorption decreases

Question 31

What happens in the descending and ascending limb of the loop of Henle due to uncontrolled diabetes

Answer 31

The glucose and excess sodium in will draw water to stay in the lumen so the fluid does not become concentrated but instead is diluted - this abolishes the horizontal concentration gradient and therefore less sodium chloride is reabsorbed at the ascending limb and a larger volume of NaCl and water is delivered to the distal tubule

Question 32

What happens with the macula densa in uncontrolled diabetes

Answer 32

The macula densa senses detects the high delivery rate of sodium chloride so decreases renin secretion which will lead to even less reavsorption

Question 33

What is a hypoglycaemic coma

Answer 33

inadequate blood flow to the brain due to severe hypotension which leads to inadequate glucose for the brain