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CardioRespiratory Year 1 > Renal Structure and function part 2 > Flashcards

Renal Structure and function part 2 Flashcards

1
Q

what is osmosis

A

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

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2
Q

what is the osmotic pressure of a solution

A

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

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3
Q

what is an Osmol

A

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.

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4
Q

what is the osmolarity of blood plasma

A

Blood plasma has an osmolarity of about 300 mOsm.

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5
Q

what happens to a persons blood pressure when they give blood

A
  • 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
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6
Q

how much bloodies the systemic veins and venues contain

A

65% of the blood

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7
Q

what can constrict the veins do

A

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

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8
Q

what senses regulate the blood volume

A

volume sensors (neuronal) and sodium sensors (hormonal)

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9
Q

describe how neuronal volume sensors in the heart works

A
  • 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.
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10
Q

how do the hormonal volume sensors work in the heart

A
  • 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
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11
Q

what do ANP and BNP do to sodium excretion

A

they increase sodium excretion

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12
Q

what does aldosterone do to sodium excretion

A

it decreases sodium excretion

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13
Q

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

A
  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
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14
Q

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

A
  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
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15
Q

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

A

these are osmoreceptors

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16
Q

where are the osmoreceptors

A

are in cells lining capillaries in the hypothalamus of the brain

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17
Q

what is the hypothalamus

A

a series of tiny nuclei packed closely together

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18
Q

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

A
  • supraoptic nuclei

- paraventricular nuclei

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19
Q

what do the supraoptic and paraventricular nuclei do

A
  • 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
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20
Q

where do the supraoptic and paraventricular nuclei project into

A

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

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21
Q

what do the axons of the supraoptic and paraventricular nuclei secrete

A

they secrete antidiuretic hormone (ADH)

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22
Q

describe the structure of ADH

A
  • it is a peptide hormone
  • contains 9 amino acids
  • Cys-Tyr-Phe-Gln-Asn-Cys-Pro-Arg-Gly
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23
Q

what happens if the osmoreceptors detect higher than normal osmolarity

A
  • 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
24
Q

what happens if osmoreceptors detect lower than normal osmoalrity

A
  • ADH secretion is inhibited from the posterior pituitary
  • water is inhibited from being reabsorbed in the blood
  • increased water loss in the urine
25
Q

what stimulates release of ADH

A
  • 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
26
Q

what are the receptors that sense blood volume

A
  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
27
Q

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

A
  • 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
28
Q

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

A
  • 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
29
Q

what happens after haemorrhage

A
  • 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
30
Q

concentration urine can only be formed….

A

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
31
Q

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

A

found in the renal medulla

32
Q

what neurones surround the loop of Henle

A
  • it is surrounded by juxtamedullary neurones that are surrounded by a capillary network called the vasa recta
33
Q

Describe the flow of fluid in the loop of Henle

A
  1. Fluid flows from the proximal tubule down into the thin descending loop of Henle
    • 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
34
Q

describe the structure of the descending limb

A
  • it has specialised channels called aquaporins which allow water to leave the tubule
35
Q

describe the structure of the ascending limb

A
  • 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
36
Q

describe the oxygen supply of the loop of Henle

A
  • oxygen is supplied by the capillaries of the vasa recta
37
Q

describe the mechanism that pumps sodium and chloride out

A
  • 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
38
Q

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

A

renal outer medullary potassium channel

39
Q

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

A

80mV

40
Q

what is the protein channel in the ascending limb called

A

Na-K-Cl cotransporter channel NKCC2

41
Q

what does the Na-K-Cl cotransporter channel do

A
  • 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
42
Q

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

A
  • 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
43
Q

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

A
  • Some diuretics block the transport of sodium and chloride out of the the loop of Henle
44
Q

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

A

Loop diuretics

45
Q

what is an example of a loop diuretic

A

furosemide

46
Q

what is the mechanism of action of furosemide

A
  • 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)
47
Q

what is a side effect of furosemide

A
  • 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.
48
Q

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

A
  • the dilute fluid passes through the distal tubule and enters the collecting duct
  • then passes to the ureter
  • then passes to the bladder
49
Q

describe the action of ADH on the collecting duct

A
  • 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
50
Q

what happens to urea in the loop of Henle

A
  • 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
51
Q

what is the countercurrent multiplier system

A

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

52
Q

what provides the countercurrent exchange

A
  • the vasa recta provide a countercurrent exchange mechanism to preserve the concentration gradient despite a blood flow through the vasa recta capillaries
53
Q

what is countercurrent flow

A

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

54
Q

how do artic animals use the countercurrent heat exchange

A
  • 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
55
Q

how do the vasa recta work

A
  • 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
56
Q

what is water diuresis due to and caused by

A
  • due to drinking too much water;
  • blood becomes dilute;
  • ADH release inhibited: result high volume of dilute urine.
  • This condition is called diabetes insipidus
57
Q

what is osmotic diuresis due to and caused by

A
  • 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

CardioRespiratory Year 1 (28 decks)

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