Kidney Function 3

Question 1

Urine is always hypotonic to plasma - true or false?

Answer 1

False - can be hypertonic too

Question 2

Where are osmoreceptors located?

Answer 2

In the brain

Question 3

What does water deprivation lead to?

Answer 3

Increased extra-cellular fluid osmolarity. ADH release from posterior pituitary so water retention by kidney. Preoptic area makes you feel thirsty so you drink.
Two types of osmoreceptors: supraoptic&paraventricular nuclei (of the hypothalamus), lateral preoptic area.

Question 4

What do osmoreceptors then communicate?

Answer 4

Release of signals then release ADH.

This molecule is 9 amino acids and secreted from the posterior pituitary.

Question 5

What does excessive fluid ingestion lead to?

Answer 5

Decreased ECF osmolarity.
Hypothalamus - ADH release suppressed, collecting duct water impermeable, water excretion by kidney.

Lateral optical: thirst suppressed

Question 6

Volume regulation:

Give details on this

Answer 6

Since the osmolarity of ECF is tightly controlled.
The volume of the ECF is determined by the total quantity of solute (mainly NaCl).
Regulation of ECF volume is all about sodium balance.

Question 7

What does the volume of ECF contain?

Answer 7

Total amount of sodium in ECF.

Question 8

What happens when salt concentration is increased?

Answer 8

Cells are more permeable to water than solutes so must take up more water rather than lose the solute.

Question 9

What is plasma volume an important determinant of?

Answer 9

Determinant of blood pressure in veins, cardiac chambers and arteries. Low total body sodium leads to low plasma volume which leads to low cardiovascular pressures.

Question 10

What is the main solute inside cells?

Answer 10

Potassium

Question 11

What are key points about osmolarity?

Answer 11

• Body directly controls osmolarity and volume of ECF in vascular system.
• This affects the osmolarity and volume of the other compartments
• Normally osmolarity is maintained at expense of volume
• Osmoreceptors control water (renel excretion by controlling ADH release, intake by altering thirst)

Question 12

Sodium excreted in urine = ? - ?

Why is sodium freely filtered?

Answer 12

Sodium filtered - sodium reabsorbed

It does not bind to proteins.

Question 13

Na+ content is largely regulated by kidney by controlling what?

Answer 13

GFR

Sodium Reabsorption

Question 14

What are the three things that GFR depends on?

Answer 14

1) Starlings forces
2) Hydraulic permeability
3) Surface area

Question 15

Explain extrinsic control on the kidney

Answer 15

It maintains arterial blood pressure by controlling GFR.

Activation of sympathetic nervous system (baroreceptor response).. these nerves innovate the renal arterioles which then have a constriction.
*Vasoconstricts afferent arteriole decreases GFR. Reduces surface area of filtration barrier via mesangial cells decreases GFR.
(also increases renin release. NB: linked to (ii)regulation of sodium reabsorption slides).

Reduction in GFR will conserve sodium and water
and increase blood volume/pressure.

Question 16

Explain intrinsic control of GFR - local control mechanisms within the kidney

Answer 16

(protects renal capillaries from hypertensive damage and maintains a healthy GFR) Autoregulation (within kidney)
Can control afferent arteriole constriction.

Mechanisms include:
Myogenic response by the renal smooth muscle cells that surround arterioles. (Vasoconstriction in response to stretch when there is a sudden increase in blood pressure). Tubuloglomerular feedback by the juxtaglomerular apparatus.
(Controls vasoconstriction and renin release#)
#Renin linked to (ii)sodium reabsorption

Question 17

Give the example of an autoregulation-intrinsic mechanism

Answer 17

Afferent arterioles constrict when BP is raised and dilate when BP is lowered, thus maintaining constant capillary pressure and glomerular blood flow.
Purpose: to protect glomerular capillaries from hypertensive damage and maintain a healthy GFR.

Question 18

Explain the sensors in sodium reabsorption

Answer 18

Tubular fluid NaCl concentration receptors within macula densa. Pressure receptors in central arterial tree.
Pressure receptors in renal afferent arterioles (intrarenal baroreceptors). Volume receptors in cardiac atria and intrathoracic veins.

Question 19

Explain the effector pathways in sodium reabsorption

Answer 19

Renal sympathetic nerves (stimulate renin release)
Renin/angiotensin II/aldosterone (stimulate Na+ reabsorption)
Atrial Natriuretic Peptide (causes natriuresis, inhibits Na+ reabsorption) Direct pressure effect on kidney
Dopamine (causes natriuresis, inhibits Na + reabsorption)

Question 20

What does the activation of the sympathetic nervous system do to the kidney?

Answer 20

Vasoconstricts afferent arteriole which decreases GFR.
Reduces surface area of filtration barrier via mesengial cells which decreases GFR.

Stimulates renin release

Question 21

Where do mesengial cells sit in relation to the kidney?

Answer 21

Over the top of the kidney

Question 22

Explain the extrinsic control of renin release:

Answer 22

Sympathetic nerves of granular cells receive signals from baroreceptors in central arteriole tree via cardiovascular centre.

Cells in the distal tubes are mascular densa are parallel to the juxta glomerular cells. These together form the juxta glomerular apparatus.
The granular cells between the two can secrete renin. This is where sympathetic nerve innovate.

Question 23

What type of control is tubuloglomerular feedback?

Explain how this works

Answer 23

Intrinsic control

ATP is hydrolysed to ADP and more adenosine moves into the intra cellular fluid.
This interacts with A1 receptor on the arteriole cells.
Calcium concentration increases and smooth muscle cells are in contact with this undergo vasoconstriction causing a reduction in GFR and a decrease in renin release

Question 24

What are 3 reasons why renin may be released?

Answer 24

1) Decrease in sodium delivery to Macula Densa
2) Decrease in wall tension in afferent arteriole (intra renal baroreceptor)
3) Sympathetic activity

Question 25

What is the role of angiotensin?

Answer 25

Causes vasoconstriction and an increase in blood pressure. Stimulates release of aldosterone from the adrenal cortex to promote sodium retention.

Question 26

Give the flow chart from once plasma angiotensin is released into the blood system

What is the rate limiting factor?

Answer 26

• renin increase
• angiotensin 1 (a plasma converting enzyme) is released
• angiotensin 2 released

This leads to 5 effects:
Stimulates proximal tubule NA+ reabsorption, stimulates ADH release, causes aldosterone secretion, causes thirst, vasoconstricts small arterioles.

Rate limiting is the presence of renin

Question 27

What are the affects of angiotensin 2 on the proximal tubule?

Answer 27

Stimulates Na+ reabsorption by binding to AT1 receptors. This increases the activity of the sodium-potassium pump for more reabsorption to occur.

Question 28

What is the peptide number of angiotensin 1 and angiotensin 2?

Answer 28

1 = 10 peptides
2 = 8 peptides

Question 29

What region of the adrenal cortex is aldosterone released?

In what places in the nephron does aldoesterone increase sodium reabsorption?
What happens after?

Answer 29

Outer region called the zona glomerulosa

Distal convoluted tubule and collecting duct.

Leads to expansion of the extra cellular fluid and then restoration of volume.

Question 30

Give the places outside the nephron where sodium reabsorption is increased

Answer 30

• sweat glands
• salivary glands
• in the gut

Question 31

Apart from angiotensin 2, why else is aldosterone released from the adrenal cortex?

Answer 31

Increased plasma K+ concentration.

Question 32

Which works faster and why? ADH or aldoesterone

Answer 32

Aldosterone because ADH is a steroid and binds to receptors.

Question 33

Explain what happens when plasma volume decreases

Answer 33

• Increase in activity of renal sympathetic nerves
• Decrease in arterial pressure
• Decrease in GFR, which causes a decrease in flow to macula densa (decrease in NaCl delivery to macula densa).

Due to these…

• renin secretion
• increase in angiotensin 2
• increase in aldosterone secretion
• increase in sodium and water reabsorption

Question 34

Other than Na+ reabsorption, what can angiotensin 2 cause?

Answer 34

Increased plasma K+ concentration. (acts on the principal cells of the collecting duct to stimulate K+ secretion.

Question 35

Natriuretic Peptides (NP) released when the heart stretched (due to high blood volume).
Where are the A and B types secreted from?

Answer 35

A type = atrial myocardium

B type = ventricular myocardium

Question 36

How do natruietics work?

Diuretics?

Answer 36

Acts on collecting duct cells to inhibit Na+ entry through epithelial sodium channels.
Inhibits renin release and aldosterone production.

Inhibits ADH release

Question 37

What percentage of calcium plasma bound to proteins?

Will this be filtered at the renal corpuscle?

Answer 37

45%

No

Question 38

What stimulates parathyroid hormone release?

What does this act on?

Answer 38

Free calcium ++ plasma stimulates parathyroid hormone release.

Acts on the kidney

Question 39

What does parathyroid hormone promote in the kidney?

Answer 39

• Phosphate excretion in the urine

- Calcium reabsorption in kidney

Question 40

How are calcium and magnesium ions mainly reabsorbed?

How about phosphate?

What are the reabsorption of these linked to?

Answer 40

Mainly passively and via the paracellular route in the proximal tubule and thick ascending limb.

Phosphate reabsorption involves transporters in proximal and distal tubules.

Linked to water