Renal function 2

Question 1

Describe the location and function of neuronal volume sensores in the heart
Type of receptor, location and function.

Answer 1

Type of receptor- Sensory nerve fibers

Location- Mostly right atrium, lesser extent left

Function- Act as Stretch receptors. When When the venous return increases, they become more stretched and signal to the medulla vasomotor centre about volume of blood returning to the heart per minute.

Question 2

Describe the location and function of hormonal sensors in the heart
Type of receptor, location and function.

Answer 2

Type of receptor- Specialised muscle cells

Location- right atrium and inferior vena cava

Function- Stretching of these cells is caused by increased preload which can indicate excess blood volume.
Stretch causes release of atrial natriuretic peptide.
Causing increased fluid and sodium loss in urine hence reduction in BP

Muscle cells in ventricles also release BNP. Usually very low but rises when ventricles are over stretched. Also increases sodium excretion

Question 3

Use of osmoreceptors in BP monitoring

Answer 3

Osmoreceptors- located in the supraoptic and paraventricular nuclei of hypothalamus, monitor osmotic stretch (pressure).
of the blood passing through them. Also obtain information from blood volume receptors via NTS.

Paraventricular and supraoptic nucleus send axons down the pituitary stalk to posterior pituitary.

These axons stimulate
ANTIDIURETIC HORMONE (ADH)secretion
And trigger thirst

Question 4

Name the two nuclei important for control of water balance? How do the work?

Answer 4

Supraoptic and Paraventricular nuclei located in the hypothalamus.
Detect osmotic pressure of blood which passes through them
Release ADH from posterior pituitary in responce to increased osmolarity. Prevents Na+ and water loss.

Question 5

Which has the higher osmolarity, renal medulla extracellular fluid or plasma

Answer 5

medulla extracellular fluid

Question 6

What condition must be met before concentrated urine can be formed?

Answer 6

There needs to be concentrated fluid in renal medulla extracellular space

Question 7

What is the name of the capillaries which surround the loop of henle? What is there function?

Answer 7

vasa reca

Supply oxygen

Question 8

Describe the process of urine production

Answer 8

1. Fluid flows from the proximal tubule go down into the thin descending loop of Henle, and up into the thick part of the ascending limb.
2. The initial (thin) part of the loop has special channels (aquaporins) and this allows water to leave the tubule.
3. As the fluid descends in the tubule it becomes more and more concentrated, because it is in equilibrium with the high concentration in the extracellular fluid of the renal medulla.
4. Fluid then enters distal tubules then collecting ducts

Question 9

What is special about the thick part of the ascending loop of henle?

Answer 9

IT IS IMPERMEABLE TO WATER. HERE MEMBRANE PUMPS MOVE SODIUM AND CHLORIDE IONS OUT INTO THE EXTRACELLULAR SPACE BY ACTIVE TRANSPORT.
This maintains the high extracellular fluid concentration in the renal medulla.

Question 10

How is the high osmolarity of the extracellular medulla maintained?

Answer 10

The thick part of the ascending look of henle containes membrane pumps which move sodium and cl- into the extracellular space of the medulla

Question 11

What is the potential difference between the lumen and the inside of the cell in the thick ascending loop of henle? How is this created? Why is it created?

Answer 11

PD- 80 mV.
A renal outer medullary potassium channel or ROMK
transports potassium out of the cells into the lumen. This creates a positive voltage (about 10 mV) in the tubular lumen.
The positive potential in lumen enhances inward flow of sodium, chloride & potassium

Question 12

How is sodium, K+ and Cl- transported from the lumen into the medulla extracellular space?

Answer 12

1. Na-K-Cl cotransporter channel NKCC2 in luminal walls of the epithelial cells allows sodium chloride & potassium to move passively together down their concentration gradient into the cells.
   Sodium is actively transported out
   Cl- moves out with the Na+
   into the renal medullary extracellular space (interstitial fluid). K+ is transported back to the lumen using ROMK

Question 13

Where does ADH actually exert its effect in the kidneys? How does it do so?

Answer 13

The collecting ducts
has aquaporin water channels that are opened by Antidiuretic Hormone (ADH).

Channels open- water reabsorbed into extracellular fluid
Consequently- less urine produced and at a high concentration (same as medullary extracellular fluid)

Question 14

How is dilute and concentrated urone produced?

Answer 14

Dilute-Absence of ADH no reabsorption of water

Concentrated- Presence of ADH; reabsorption of water via aquaporins at the collecting duct; urine as concentrated as the renal medullary fluid

Question 15

What is diabetes insipidus and water diuresis

Answer 15

Water diuresis occures when you to drinking too much water; blood becomes dilute; ADH release inhibited: result high volume of dilute urine.

This manifestation is diabetes insipidus

Question 16

What is diabetes mellitus and osmotic diuresis

Answer 16

osmotic diuresis occures when sugars are not competly rebasorbed into the proximal tubules due to excesses.
Glucose passing into the collecting ducts provides an osmotic force which pulls water into the urine, uposing the force of the medulla.

There for high volumes of sugary urine is produced- this is diabetes mellitus

Question 17

When you give blood your blood pressure does change, why?

Answer 17

1. Neuronal blood pressure control system causes immediate vasoconstriction (sympathetic)
2. Slight increase in heart rate
3. Increase in peripheral vascular resistance
4. Water moves from tissue to blood

5 renin-angiotesin system detects loss of water and reduces urine flow and increases thirst

Question 18

What is the effect ADH has when it is being secreted and when triggered by the sympathetic nervous system?

Answer 18

1. Decreases sodium excretion, less sodium lost in urine = less water lost in urine
2. Urine is diluted back to normal

When triggered by sympathetic arousal during fight or flight water is conserved in expectation of blood loss due to trauma

Question 19

Name all the locations where blood volume is sensed?

Answer 19

Blood volume is sensed by 1.neuronal and hormonal receptors in the atria

2. Blood sodium level is sensed by sodium detectors in the kidney
3. Blood osmolarity is sensed by osmoreceptors in the hypothalamus

Question 20

What happens if blood volume is too high but osmolarity and sodium levels are normal?

Answer 20

ADH & renin levels do not change. Stretch receptors in atria increase ANP secretion, allowing more sodium and water to be excreted in urine. Conversely if blood volume is too low, ANP secretion is inhibited.

Question 21

What happens if blood volume is too high and osmolarity & sodium levels are low

Answer 21

blood is too dilute. Antidiuretic hormone release from the posterior pituitary is inhibited, this causes an increased volume of urine to be excreted. Renin and aldosterone release increases and this retains sodium. Thus water but not sodium is excreted to bring volume and osmolarity back to normal

Question 22

What happens after haemorrhage when blood volume will be low

Answer 22

osmolarity and sodium will also be low due to water moving into blood from tissues. ADH secretion will be stimulated due to low osmolarity. This reduces water loss in urine. ANP secretion is reduced due to reduced preload. Sodium excretion is inhibited. Renin and aldosterone secretion are increased due to low sodium. Tthis increases sodium retention. Thus both water and sodium are retained in the body. Behavioural thirst is stimulated which will help restore blood volume.

Question 23

How do loop diuretics work? Name an example of this drug

Answer 23

block the transport of sodium and chloride out of the the loop of Henle. This abolishes the high concentration of solutes in the renal medulla and so prevents the formation of concentrated urine.

Drug-Furosemide

Question 24

Where in the kidneys is the sight of ADH action?

Answer 24

Collecting ducts

Question 25

What us the counter current multiplier mechanism?

Answer 25

process of pumping out salt into the extracellular fluid around the loop of Henle

Question 26

What is the purpose of the countercurrent exchange? What is responsible for establishing this?

Answer 26

Function- preserve the concentration gradient in extracellular fluid ensures adequate oxygen supply to the medulla without washout of the high concentration needed for concentration of urine.

Vasa recta