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SUGER Physiology > Renal Physiology > Flashcards

Renal Physiology Flashcards

1
Q

Give the 5 segments of a nephron and their functions.

A
  1. Renal corpuscle (glomerulus + Bowman’s capsule): filter
  2. Proximal convoluted tubule: reabsorbs solutes
  3. Loop of Henle: concentrates urine
  4. Distal convoluted tubule: reabsorbs more water and solutes; fine regulation
  5. Collecting duct: reabsorbs water, controls acid base & ion balance.
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2
Q

Give the two types of arteriole found in the glomerulus.

A 
Afferent = coming IN
Efferent = going OUT
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3
Q

Give the three major functions of the kidney.

A
  1. Endocrine function
  2. Maintains balance of salt, water, PH
  3. Excretes waste products
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4
Q

How much cardiac output does EACH kidney receive?

A

20%

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5
Q

What is total renal blood flow?

A

1L/min

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6
Q

What is total urine flow?

A

1ml/min

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7
Q

Give the branches of bloody supply to the kidney.

A

Abdominal aorta >
Renal artery > Segmental artery > Interlobar artery > Arcuate artery > Interlobular artery > Afferent arteriole > Glomerular capillaries

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8
Q

Give the branches of venous drainage of the kidneys.

A

Efferent arteriole > Peritubular capillaries > Vasa recta > Renal veins > Inferior vena cava

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9
Q

Why is a good blood supply to the nephron essential?

A

Tubular processes are ACTIVE - they require oxygen & energy

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10
Q

What percentage of blood manages to filter into the Bowman’s capsule?

A

20%. The rest leaves the glomerulus via the efferent arteriole.

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11
Q

Give the three layers of the filtration barrier.

A
  1. Single-celled capillary endothelium
  2. Basement membrane
  3. Single-celled epithelial lining of Bowman’s capsule: podocytes
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12
Q

What structure is found on podocytes?

A

Foot processes

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13
Q

Which part of the kidney contains all the renal corpuscles?

A

Cortex

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14
Q

Which part of the kidney is the Loop of Henle found?

A

Extends from cortex down into the medulla

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15
Q

What are the two types of nephron?

A

15% = juxtamedullary nephrons. Renal corpuscle lies closest to cortical-medullary junction, loop of Henle plunges deep into medulla

85% = cortical nephrons. Renal corpuscle lies in outer cortex, loop of Henle does not enter medulla.

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16
Q

Which cells make up the juxtaglomerular apparatus?

A

Macula densa and granular cells.

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17
Q

What is the function of granular cells?

A

Secrete renin into blood to initiate renin-angiotensin-aldosterone system

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18
Q

What is the function of macula densa cells?

A

Detect how much NaCl passes through the DCT. Release prostaglandins to trigger granular cells to produce renin.

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19
Q

What is the surface area of the glomerulus?

A

1m^2

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20
Q

Briefly describe the path of glomerular filtrate.

A
  1. Renal corpuscle
  2. PCT
  3. Loop of Henle
  4. DCT
  5. Collecting duct
  6. Papillary duct
  7. Minor calyx
  8. Major calyx
  9. Renal pelvis
  10. Ureter
  11. Urinary bladder
  12. Urethra
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21
Q

Which molecules can pass through the filtration barrier?

A

Molecules and ions up to 10kDa e.g. glucose.

Negative charge of basement membrane replies negatively charged ions e.g. albumin

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22
Q

Which is the only normal protein to be found in urine?

A

Uromodulin/Tamm Horsfall protein

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23
Q

What is nephrotic syndrome?

A

Damage to filtration barrier, leading to protein leak

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24
Q

What can be found in the urine to detect early diabetes?

A

Low levels of albumin

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25
Q

Crossing the filtration barrier is determined by…

A

Size of molecule
Charge of molecule
Rate of blood flow
Binding to plasma proteins

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26
Q

Is hydrostatic pressure along the capillary constant?

A

Yes

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27
Q

What is GFR?

A

The volume of fluid filtered from the glomeruli into Bowman’s space per minute.

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28
Q

How do you calculate GFR?

A

GFR = KF (PGC - PBS - πGC)

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29
Q

In a 70kg person, what is the average GFR?

A

125ml/min

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30
Q

Which three factors determine GFR?

A
  1. Net filtration pressure
  2. Permeability of corpuscular membranes
  3. Surface area
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31
Q

What happens to GFR when afferent arterioles are constricted?

A

Decreases GFR as hydrostatic pressure decreases.

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32
Q

What happens to GFR when efferent arterioles are constricted?

A

Increases GFR as hydrostatic pressure increases. This is due to the blood being ‘dammed back’ in the capillaries.

33
Q

What happens to GFR when afferent arterioles are dilated?

A

GFR increases as hydrostatic pressure increases.

34
Q

What happens to GFR when efferent arterioles are dilated?

A

GFR decreases as hydrostatic pressure decreases.

35
Q

How is GFR measured? Give an equation also.

A

By measuring excretion of a marker substance. The marker substance must be:
Freely filtered
Not secreted or absorbed in the tubules
Not metabolised

GFR = Um x urine flow rate / Pm

36
Q

Give an example of a marker substance.

A

Creatinine

37
Q

What is filtration fraction?

A

Proportion of renal blood flow that gets filtered.

Filtration fraction = GFR/ renal plasma flow (600ml/min)

38
Q

What is renal clearance?

A

The volume of plasma from which a substance is completely removed by the kidney per minute.

Glucose has a clearance of 0 as it is completely reabsorbed. M has a clearance of 125ml/min (= to GFR) as all plasma that is filtered is cleared of M.

39
Q

Give the equation for renal clearance.

A

Clearance = (urine concentration x urine volume) / plasma concentration

40
Q

Which substances does the PCT reabsorb?

A

Na, Cl, glucose, amino acids, HCO3

41
Q

How permeable is the PCT to water?

A

High permeability

42
Q

What mechanism re-uptakes glucose, amino acids & lactate in the PCT?

A

Secondary active transport. Na+ is actively transported and the other substances are co-transported along.

43
Q

What causes a high concentration of Na+ to be out of the PCT cells in order to diffuse back in whilst co-transporting other substances?

A

The NaKATPase pump. Pumps 3Na+ out for every 2K+ in via active transport. Creates a concentration gradient.

44
Q

As Na+, glucose and phosphate are reabsorbed, which substance follows through passively?

A

Water, passes through by osmosis. Reabsorbed substances increase osmolarity in the cell (water concentration decreases in the cell) so water moves via osmosis from the tubular lumen into the interstitial fluid.

45
Q

As Na+ moves back into the PCT cells, which substance is secreted out?

A

H+

46
Q

How is H+ generated in the PCT?

A

CO2 + H2O combine to form H2CO3 in the tubular cells under the action of carbonic anhydrase > H2CO3 rapidly dissociates into H+ and HCO3- > HCO3- moves down its concentration gradient into the blood > H+ is secreted into the lumen to combine with HCO3- to generate H2CO3 > This is converted to CO2 + H2O and the cycle begins again

47
Q

What is the transport maximum?

A

The concept that reabsorptive systems in the tubule have a limit to the amount of material they can transport per minute. Due to binding sites on transport proteins becoming saturated.

48
Q

Give the permeabilities to water of the limbs of the Loop of Henle.

A

Descending limb: Water permeable

Ascending limb: Water impermeable

49
Q

Where does solute reabsorption occur in the Loop of Henle?

A

Thick ascending limb

50
Q

What is osmolality?

A

The concentration of a solution measured as the number of solutes per kg.

51
Q

What is osmolarity?

A

The concentration of a solution measured as the number of solutes per litre.

52
Q

What does it mean for the interstitial fluid to be hyperosmotic?

A

Having a higher osmolality than the fluid inside the tubules

53
Q

What is the effect of vasopressin/ADH on the Loop of Henle?

A

Causes water to diffuse out of the loop, into the interstitial fluid of the medulla. Water enters the blood vessels of the medulla to be carried away.

54
Q

What is countercurrent flow in the Loop of Henle?

A

Fluid flows down the descending limb and up the ascending limb. Opposing flows create countercurrent flow.

55
Q

What is the function of the countercurrent system?

A

Creates a hyperosmotic interstitial fluid. This enables water to be drawn out of the collecting ducts by ADH which concentrates the urine.

56
Q

How is a hyperosmotic interstitial fluid created?

A

Along the ascending limb, Na+ and Cl- are actively pumped (e.g. by NKCC2) from the lumen into the interstitial fluid. In the lower ascending limb, there are no cotransporters so simple diffusion takes place. Ascending limb is impermeable to water, and as the solutes are reabsorbed into the interstitial fluid without water, the interstitial fluid becomes hyperosmotic

57
Q

What are the capillaries in the medulla called?

A

Vasa recta

58
Q

What is the role of the vasa recta?

A

Carries away reabsorbed salt & water by bulk flow to maintain a steady countercurrent gradient

59
Q

How much urea actually reaches the Loop of Henle?

A

50%. The other 50% is reabsorbed back into the PCT and carried away by blood

60
Q

Is the DCT permeable to water?

A

It is impermeable to water. Under the action of ADH, it becomes more permeable to reabsorb more water and make urine concentrated.

61
Q

Is the collecting duct permeable to water?

A

No, it is highly impermeable

62
Q

Name 2 cell types found in the collecting duct.

A

Principal cells

Intercalated cell

63
Q

What is the effect of aldosterone on the principal cells?

A

Increases transcription of ENaC (epithelial sodium channel).
This increases Na+ influx which causes K+ efflux
Acts slower than ADH as it induces changes in gene expression

64
Q

What is the effect of ADH on the principal cells?

A

Binds to the V2R receptor
Results in insertion of vesicles containing aquaporin 2 into the apical membrane
Increases water permeability + results in more concentrated urine as more water is reabsorbed

65
Q

What is the function of intercalated cells?

A

Secrete acid into the collecting duct

66
Q

What type of hormone is ADH? Where is it synthesised and released?

A

It is a peptide hormone. Synthesised in the hypothalamus and secreted by the posterior pituitary.

67
Q

Which receptors detect changes in osmolarity?

A

Osmoreceptors

68
Q

What is the effect of ADH?

A
  1. Anti-pee. If you drink lots of water, ADH secretion will be inhibited. If you are dehydrated, ADH secretion will be stimulated.
  2. Causes widespread arteriolar constriction to control blood pressure
69
Q

Give the affects of alcohol, MDMA and nicotine on ADH secretion.

A

Alcohol: Inhibits secretion - results in dehydration
MDMA: Increases secretion - results in dilute blood, seizures and fits
Nicotine: Increases secretion

70
Q

Give the percentage reabsorption of Na+ in each part of the nephron.

A

PCT = 60%
Loop of Henle = 25%
DCT = 10%
Collecting duct = 4%

71
Q

Why would Na+ be reabsorbed into the blood stream?

A

To increase blood pressure

72
Q

Briefly describe the renin-angiotensin system in relation to the kidney.

A
  1. Cells of the macula densa detect low NaCl
  2. Juxtaglomerular cells in afferent arterioles are stimulated to release renin
  3. Renin cleaves angiotensinogen into angiotensin 1
  4. ACE converts the inactive angiotensin 1 into the active angiotensin 2
  5. Angiotensin 2 stimulates the cells of the zona glomerulosa in the adrenal cortex to secrete aldosterone
  6. Aldosterone vasoconstricts efferent arterioles
  7. There is increased pressure resulting in increased GFR
  8. This increases Na+ reabsorption in the PCT
  9. This stimulates thirst which stimulates ADH release resulting in water retention
73
Q

What are the effects of ANP (atrial natriuretic peptide)?

A
  1. ANP inhibits Na+ reabsorption by blocking ENaCs in the collecting duct.
  2. Vasodilates afferent arterioles which increases GFR
  3. Inhibits aldosterone secretion, leading to increased Na+ excretion
74
Q

Which cells synthesise and secrete ANP?

A

Cells in the cardiac atria

75
Q

When does secretion of ANP increase?

A

When there is an excess of Na+ in the body. This means there is more water in the blood vessels, increasing blood volume. This stretches the atria which stimulates ANP secretion.

76
Q

What percentage of filtered K+ is reabsorbed back into the PCT?

A

90%

77
Q

What can a deficit in K+ (hyperkalemia) lead to?

A

Arrhythmia, abnormalities in skeletal muscle contraction and neuronal action potential conduction

78
Q

Where is parathyroid hormone released from?

A

Parathyroid glands

79
Q

When is parathyroid hormone released and what are its effects?

A

It is released in response to decreased levels of Ca2+ plasma concentrations. It directly increases Ca2+ reabsorption, decreasing Ca2+ excretion.

SUGER Physiology (11 decks)

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