Renal Structure and function part 2

Question 1

what is osmosis

Answer 1

Osmosis is the tendency of water to move from a more dilute solution to a more concentrated solution.

Question 2

what is the osmotic pressure of a solution

Answer 2

The osmotic pressure of a solution is the tendency of a solution to take in water by osmosis

Question 3

what is an Osmol

Answer 3

The Osmol is the unit defining the osmotic strength of a solution, i.e. the number of moles of solute that contribute to the osmotic pressure of a solution.

Question 4

what is the osmolarity of blood plasma

Answer 4

Blood plasma has an osmolarity of about 300 mOsm.

Question 5

what happens to a persons blood pressure when they give blood

Answer 5

• no change in their blood pressure
• neuronal blood pressure control causes venoconstriction via the sympathetic nervous system which compensates for the loss of volume
• also a increase in heart rate and rise in peripheral vascular resistance
• volume needs to be replaced, the renin angiote

Question 6

how much bloodies the systemic veins and venues contain

Answer 6

65% of the blood

Question 7

what can constrict the veins do

Answer 7

by constricting the veins, the sympathetic nervous system can restore preload after haemorrhage

Question 8

what senses regulate the blood volume

Answer 8

volume sensors (neuronal) and sodium sensors (hormonal)

Question 9

describe how neuronal volume sensors in the heart works

Answer 9

• Sensory nerve fibres are found in the tissues of the right atrium, and to a lesser extent the left atrium.
• These act as stretch receptors in an exactly analogous way to the stretch receptors on the carotid sinus.
• When the venous return increases, they become more stretched.
• They therefore signal the volume of blood returning to the heart per minute.

Question 10

how do the hormonal volume sensors work in the heart

Answer 10

• there are specialised muscle cells that exist in the tissue of the right atrium and IVC
• stretching of these cells is caused by increased preload this indicates excess blood voume
• stretch causes cells to release atrial natriuretic peptide (ANP_
• ANP decreases sodium reabosorption in the distal tubule of the kidney
• there is an increase sodium loss in the urine and also increased water loss by osmosis
• the increased fluid and sodium loss reduces the blood volume making it normal
• muscle cells in the ventricles can release bNP
• BNP normally low in a healthy person but is released when the ventricles are overstretched in heart filaure

Question 11

what do ANP and BNP do to sodium excretion

Answer 11

they increase sodium excretion

Question 12

what does aldosterone do to sodium excretion

Answer 12

it decreases sodium excretion

Question 13

describe the negative feedback pathway that happens when blood volume is increased to high

Answer 13

1. increased blood volume
2. causes an excessive preload
3. over stretching of atrial
4. ANP (BNP) causes an increased release
5. sodium diuresis
6. water diuresis
7. blood volume decreases

Question 14

describe the negative feedback pathway that happens when blood volume is decreased below normal

Answer 14

1. decreased blood volume
2. low blood pressure in veins
3. water moves from tissues into Venus blood
4. decreased blood sodium
5. renin and aldosterone release
6. sodium and water retention
7. blood volume increases

Question 15

what are the sensors that measure the osmotic strength of the blood

Answer 15

these are osmoreceptors

Question 16

where are the osmoreceptors

Answer 16

are in cells lining capillaries in the hypothalamus of the brain

Question 17

what is the hypothalamus

Answer 17

a series of tiny nuclei packed closely together

Question 18

what are the nucleic in the hypothalamus that is important in controlling water balance

Answer 18

• supraoptic nuclei

- paraventricular nuclei

Question 19

what do the supraoptic and paraventricular nuclei do

Answer 19

• contains receptors that measure the osmotic pressure of water that passes through them
• receive information from the blood volume receptors via relays in the brainstem NTS

Question 20

where do the supraoptic and paraventricular nuclei project into

Answer 20

they project into the pituitary
- they send the axons into the pituitary stalks and the axons end as secretory terminals on capillaries within the posterior pituitary

Question 21

what do the axons of the supraoptic and paraventricular nuclei secrete

Answer 21

they secrete antidiuretic hormone (ADH)

Question 22

describe the structure of ADH

Answer 22

• it is a peptide hormone
• contains 9 amino acids
• Cys-Tyr-Phe-Gln-Asn-Cys-Pro-Arg-Gly

Question 23

what happens if the osmoreceptors detect higher than normal osmolarity

Answer 23

• increase production of ADH and release from the posterior pituitary
• stops water form being lost in the urine
• increases the amount of water to normal in the blood
• osmoreceptor cells trigger thirst so you are stimulated to drink
• this increases amount of water in the blood

Question 24

what happens if osmoreceptors detect lower than normal osmoalrity

Answer 24

• ADH secretion is inhibited from the posterior pituitary
• water is inhibited from being reabsorbed in the blood
• increased water loss in the urine

Question 25

what stimulates release of ADH

Answer 25

- when osmoreceptors detect higher than normal osmolarity in the blood - sympathetic arousal from the hypothalamus, w went he sympathetic nervous system is aroused it sends a signal to the hypothalamus as the body wants to conserve water in expectation of blood loss through haemorrhage

Question 26

what are the receptors that sense blood volume

Answer 26

1. Blood volume is sensed by 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 27

what happens if the blood volume is too high but osmolarity and sodium levels are normal

Answer 27

- ADH and renin levels do not change - stretch receptors int he atria increase ANP secretion this allows more sodium and water to be excreted into the urine - on the other hand if blood volume is too low, ANP secretion is inhibited

Question 28

what happens if the blood volume is too high and osmolarity and sodium levels are low

Answer 28

- the blood is too dilute - ADH reeled from the posterior pituitary is inhibited, this causes an increased volume of urine to be excreted - Renin and aldosterone release increases and retains sodium - therefore water and not sodium is excreted to bring volume and osmolarity back to normal

Question 29

what happens after haemorrhage

Answer 29

- blood volume will be low - osmolarity and sodium will also be low due to water moving into the blood from the 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 - this increases sodium retention - therefore both water and sodium are retained in the body - behavioural thirst is stimulated this helps restore blood volume

Question 30

concentration urine can only be formed....

Answer 30

if there is concentrated fluid in the extracellular space in the renal medulla - in a normal kidney the omoslarity of the extracellular fluid in the renal medulla is much higher than that of the plasma therefore the kidney makes urine that is more concentrated than plasma

Question 31

what part of the kidney is the loop of Henle found in

Answer 31

found in the renal medulla

Question 32

what neurones surround the loop of Henle

Answer 32

- it is surrounded by juxtamedullary neurones that are surrounded by a capillary network called the vasa recta

Question 33

Describe the flow of fluid in the loop of Henle

Answer 33

1. Fluid flows from the proximal tubule down into the thin descending loop of Henle 2. - as the fluid descends in the tubule it becomes more concentration because it is in equilibrium with the high concentration in the extracellular fluid in the renal medulla 3. this then goes up into the thick part of the ascending limb 4. the thick part is impermeable to water but it has membrane pumps that move sodium and chloride ions out into the extracellular space by active transport 5. this maintains the high extracellular fluid concentration in the renal medulla 6. when the fluid leaves the loop of Henle it enters the distal tubule 7. the fluid entering the distal tubule is more dilute than the plasma due to the removal of sodium and chloride

Question 34

describe the structure of the descending limb

Answer 34

- it has specialised channels called aquaporins which allow water to leave the tubule

Question 35

describe the structure of the ascending limb

Answer 35

- the thick part of the ascending limb is impermeable to water - it has membrane pumps that move sodium and chloride ions out into the extracellular space by active transport

Question 36

describe the oxygen supply of the loop of Henle

Answer 36

- oxygen is supplied by the capillaries of the vasa recta

Question 37

describe the mechanism that pumps sodium and chloride out

Answer 37

- it is helped by a potassium transporter - ATP dependent potassium channel called the renal outer medullary potassium channel - this transports potassium out of the cells into the lumen - this generates a positive voltage in the tubular lumen - this allows the protein channel NKCC2 to allow sodium, chloride and potassium to move passively down there concentration gradient

Question 38

what is the ATP dependent potassium channel called in the ascending limb

Answer 38

renal outer medullary potassium channel

Question 39

what is the potential difference between the lumen and inside the cell in the ascending limb

Answer 39

80mV

Question 40

what is the protein channel in the ascending limb called

Answer 40

Na-K-Cl cotransporter channel NKCC2

Question 41

what does the Na-K-Cl cotransporter channel do

Answer 41

- it is a protein channel in the luminal walls of the epithelial cells allowing sodium, chloride and potassium to move passively down the concentration gradient into the cells - they are allowed to do this due to the positive gradient that is created by the potassium ROMK channel

Question 42

how is sodium transported out of the base of the epithelial cell

Answer 42

- actively transported out of the bae of the epithelial cell by a sodium potassium a ATPase - chloride moves out passively with sodium - therefore sodium and chloride are transported into the renal medullary extracellular space

Question 43

what is the mechanism of action of diuretics to the loop of Henle

Answer 43

- Some diuretics block the transport of sodium and chloride out of the the loop of Henle

Question 44

what are the diuretics called that act on the loop of Henle

Answer 44

Loop diuretics

Question 45

what is an example of a loop diuretic

Answer 45

furosemide

Question 46

what is the mechanism of action of furosemide

Answer 46

- inhibits NKCC2 - By blocking this transporter it prevents the high concentration of solutes in the renal medulla and so prevents the formation of concentrated urine - (acts independnely of ADH)

Question 47

what is a side effect of furosemide

Answer 47

- A similar NKCC2 transporter exists in the cochlea of the ear therefore Prolonged high doses of furosemide can lead to irreversible hearing loss. - low blood pressure with standing - ringing in the ears - sensitivity to the sun.

Question 48

where does the fluid go after it has entered the distal tubule

Answer 48

- the dilute fluid passes through the distal tubule and enters the collecting duct - then passes to the ureter - then passes to the bladder

Question 49

describe the action of ADH on the collecting duct

Answer 49

- collecting duct has aquaporin water channels that are opened by ADH - the collecting duct is the site of ADH action in the kidney - if the channel is open then most of the water is reabsorbed down the concentration gradient into the concentration extracellular fluid - this results in a small volume of concentrated urine produced with the same osmolarity as the renal medullary fluid - if the channel is closed there is no reabsorption of water and dilute urine is produced

Question 50

what happens to urea in the loop of Henle

Answer 50

- urea is actively pumped out of the collecting dust and into the interstitial fluid by urea transport proteins in the collecting duct - this increases solute concentration in the renal medulla and therefore makes urine more concentrated - some urea passes into the ascending limb and therefore creates a urea cycle between the collecting duct and ascending limbs - some urea is not pumped out and is lost in the urine

Question 51

what is the countercurrent multiplier system

Answer 51

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

Question 52

what provides the countercurrent exchange

Answer 52

- the vasa recta provide a countercurrent exchange mechanism to preserve the concentration gradient despite a blood flow through the vasa recta capillaries

Question 53

what is countercurrent flow

Answer 53

when there is an exchange of temperature when the flow is in opposite directions - doesn't just have to be heat exchanged can exchange solutes

Question 54

how do artic animals use the countercurrent heat exchange

Answer 54

- use this between arteries and veins - allows them to supply blood to their feet without freezing to death - exchange allows heat between the arteries and veins in their legs and feet

Question 55

how do the vasa recta work

Answer 55

- countercurrent exchange - blood goes in at a normal osmolarity and gets concentrated in the medulla and then gets dilute as it comes out again - ensures that there is an adequate oxygen supply to the medulla without washout of the high concentration needed for urine

Question 56

what is water diuresis due to and caused by

Answer 56

- due to drinking too much water; - blood becomes dilute; - ADH release inhibited: result high volume of dilute urine. - This condition is called diabetes insipidus

Question 57

what is osmotic diuresis due to and caused by

Answer 57

- Sugars like glucose are normally completely reabsorbed in the proximal tubule; if they are not, due to excess glucose in the blood, then the glucose passing through the collecting duct provides an osmotic force tending to pull water into the urine, opposing the osmotic force of the medulla which is tending to pull water out. - Result; high volume of sugary urine. This condition is diabetes mellitus