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Unit 8 > Renal physiology 2 > Flashcards

Renal physiology 2 Flashcards

1
Q

What is the main ion determingin the movement of water?

A

Sodium ions

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2
Q

What are the two main processes that regulate the intake and output of water?

A

Thirst
ADH

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3
Q

Where does the majority of our body water come from?

A

60% drinks
30% foods
10% metabolism

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4
Q

How is the majority of out body water removed?

A

60% urine
28% insensible loss via skin and lungs
8% sweat
4% faeces

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5
Q

What is the average water input/output per day?

A

2500ml

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6
Q

What is the maximum amount of water the kidney can handle in a day?

A

15L - more than this overwhelms and damaged the kidney

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7
Q

What is osmolality?

A

The amount of solute dissolved in 1kg of solvent

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8
Q

What is tonicity?

A

The capcity of a solution to alter the volume of cells.
Isotonic
Hypotonic
Hypertonic

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9
Q

How is osmolarity related to water potential?

A

Lower osmolarity means less solute dissolved in the solvent, therefore a higher water potential
Inversely proportional

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10
Q

Explain how the urine output of the kidney will change if the output is ECF is hypotonic?

A

Lower concentration of solutes in the ECF = higher water potential
More water moves into cells
Excess water in cells, kidney secretes a larger volume of more dilute urine to return homeostasis

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11
Q

Explain how urine output of the kidney will change if the out of the ICF is hypertonic?

A

Higher concentration of solutes in the ECF = lower water potential
Water moves out of cells and cell shrinks
Shortage of water, kidney secretes a smaller volume of more concentrated urine to help restore homeostasis.

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12
Q

What is central pontine myelinolysis and how is it related to kidney function?

A

Typically occurs when patients with hyponnatremia has sodium volume replaced too quickly.
Results in a hypertonic blood, this pulls water from the cells including the schwann cells surrounding the brain
This results in damage to the brain, leading to demyelination.

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13
Q

What is the normal physiological range of plasma osmolality?

A

280-300mOsm/kg-1 H20

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14
Q

What is the normal range of urine volume in a day?

A

0.5 to 18L
Average is 1.5L

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15
Q

What is the normal range of urine osmalality?

A

1200-50mOsm/kg-1 H20
Average is 300-500mOsm/kg-1 H2O

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16
Q

Give an example of an osmoreceptor?

A

Macular densa cells

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17
Q

What is the main factor controlling osmolality in the ECF?

A

Regulating the amount of water in the body

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18
Q

What is the main factor controlling volume of the ECF?

A

Osmolality of the ECF

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19
Q

In physiological ‘healthy’ and pathological terms, is the regulation of osmolarity or volume more important?

A

Healthy - osmolarity
Pathological - volume

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20
Q

What is the effect on urine of a longer loop of henle?

A

More concentrated urine

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21
Q

What is the change of water movement in the loop of henle?

A

From the turn in the loh onwards the nephron is impermeable to the free movement of water, all water must be moved by channel protein rather than osmosis.

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22
Q

What is the purpose of the counter current mechanism in the loop of henle?

A

Create a steep concentration gradient from the cortex to the medulla
Maximise Na+ and water reabsoprtion

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23
Q

How does the osmolarity of fluid leaving the loop of henle compare to the plasma?

A

hypoosmolarity

24
Q

In the loop of Henle, describe the cellular process that transports substances from the lumen to the interstitial fluid?blood?

A

NKCC2 cell - transports Na+, 2Cl- and K+ into the cytoplasm of the epithelial cells down a concentration gradient
This concentration gradient is maintained by the Na+ K+ pump (ATPase) that transports Na+ out into the intersitium
K+ is recyled back into the lumen by ROMK channels
Cl- leaves the cytoplasm and enters the interstitial space down a concentration gradient through CIC-Ka channels
This movements creates a more negative environment in the interstitial fluid, this attracts Na+ Ca2+ and Mg2+ into the interstitium by paracellular transport down a chemical gradient

25
Q

Explain how the action in the ascending loop of henle affects the descending loop of henle?

A

Ascending loop - NKCC and other channel proteins and paracellular methods contribute to the active transport of sodium ions from the lumen of the nephron into the interstitium
Interstitial osmolarity increases, lower water potential
This same intersitial space surrounds the descending limb (as close proximity)
Ecnourages water the leave the descending limb down a concentration gradient and be reabsorbed into the blood stream
The filtrate within the des. then moves onwards and replaces the filtrate in the asc. allowing more Na+ transport continuing the process. (the counter current)

26
Q

What is the change in urine over the loop of henle?

A

Descending limb - concentration increases as water leaves
Ascending limb - concentration decreases as Na+ leaves
Overall concentration mildly decreases.

27
Q

What process in the collecting duct affects interstitial osmolarity?

A

Urea reabsorption

28
Q

What are some examples of loop diuretics?

A

Furosemide
Bumetanide

29
Q

What is the action of loop diuretics?

A

Act on NKCC to inhibit the reabsorption of Na+ K+ and Cl-
Less movement of Na+ into the interstitial space at the ascending loop of henle
reduces the water potential gradient between the descending limb and the interstitium, so less water is reabsorbed from the interstitial space
Increased osmolarity of urine (lower wp)
Leads to natiriuresis (more sodium is excreted), and diuresis (more urination)

30
Q

What stimulates urea trapping/cycling?

A

Low blood volume or less water being absorbed
results in ADH secretion

31
Q

Where does urea cycling occur? Why?

A

The collecting duct in the medulla
The rest of the tubule is impermeable to urea

32
Q

Describe the molecular mechanism by which ADH facilitated urea recycling?

A

ADH is released into circulation due to a low blood pressure
Binds to basolateral membrane receptor, activea adenylate cyclase, activating protein kinase A results in activation of UT-A1.
ADH stimulates apical urea transport by UT-A1 transport protein.
Urea leaves the epithelial cell and enters the intersitiu, by faciliated difussion (down a conc gradient) by UT transport proteins

33
Q

What is the consequence of urea recylcing on blood volume?

A

Higher conc of urea enters the nephron interstitium
Decreased the water potential of interstitium - more water is reabsorbed into the blood stream, this increases blood volume

34
Q

Describe the process of urea recycling?

A

Medullary urea concentration increases
Some urea diffuses into the loop of henle in the medulla by UT-Bs
urea is carried through back to the distal segment and CD
Urea once again leaves the nephron by ADH mechanisms
The process repeats
Function: Aid water reabsorption

35
Q

What is the basic direction of movement in the kidney which helps regulate acid base balance?

A

Bicarbonate moves from the urine into the blood
H+ moves from the blood into the urine

36
Q

What are the key protein channels found on the distal convoluted tubule epithelium?

A

The NCCT - apical side
The Na+ (in) H+ (out to urine) on the apical side
The Cl- (in) HCO3- (out to blood) on the basolateral side

37
Q

What are thiazide diurectics?

A

Inhibit NCCT
Prevents Na+ reabsorption into the epithelium from the filtrate
This decreases the concentration of Na+ in the epithelium
As a consequence also inhibits the Na+ K+ pump and can lead to hyperkalemia as less potassium is secreted.
increased secretion of sodium and chloride

38
Q

Give some examples of a thiazide diuretic.

A

Bendroflumethiazide
Indapamide

39
Q

How does Calcium ion reabosorption occur in the nephron?

A

Majority in the loop and PCT - by passive paracellular down a chemical gradient
10-15% then occurs in the Distal convoluted tubule under the influence of PTH and vitamin D by secondary active transport.

40
Q

How change happens to filtrate as it passess through the DCT?

A

Becomes more dilute as sodium reabsorbed

41
Q

What receptors are used in urea recycling int he collecting duct?

A

UT-A1 (apical - filtrate to cytosplasm)
UT-A3 (apical - filtrate to cytoplsam)
UT - basolateral cytoplasm to intersitium

42
Q

What is the main goal of urea recycling>

A

Decrease excretion of urea in urine
50% of urea is reabsorbed into the blood stream.

43
Q

What is the main process of absorption in the collecting duct?

A

Sodium ions are transported in to the epithelial cell from the filtrate ENaC
K+ are transported out of the epithelial cell into the filtrate
Both are passive through transport channels
The soidum potassium pump then pumps Na+ out into the interstitial space.

44
Q

What side of the collecting duct is impermeable to water?

A

THe apical side

45
Q

What is the mechanism of ADH when over hydrated?

A

Little ADH is released
Few/no aquaporins are released
water channels are internalised into vesicles for storage
Tubule is impermeable to water
water is lost with a high flow rate, dilute urine

46
Q

What is the mechanism of ADH when de-hydrated?

A

More ADH is secreted from the posterior pituitary gland
Insertion of water channels on the apical membrane
Vesicles fuse with the membrane
Water is reabsorbed back into the bloodstream
A small volume of concentrated urine is produced.

47
Q

What is the origin of ADH?

A

Posterior pituitary gland
Regulated by osmoreceptors and baroreceptors
Is synthesised and packaged into neurons in the hypothalamus
Transported down the axon and stored before release into the blood stream from the posterior pituitary gland.

48
Q

What is the plasma concentration at which ADH is released?

A

> 280mOsm/kg

49
Q

How are urine osmolarity and urine flow rate related?

A

As urine osmolarity increases flow rate decreases - are inversely proportional

50
Q

How is the total solute excertion in urine affected by urine osmolality and urine flow rate?

A

Remains constant always
Urine flow rate and urine osmolality have an inverse relationship to ensure this is true

51
Q

What is the effect of mineralocorticoid antagonists in the collecting duct?

A

Stop water and salt retention in the the distal nephron - resulting in a drop in BP
May cause hyperkaelemia’s
Inhibits ENaC

52
Q

What is Liddle’s syndrome? (relates to the kidney)

A

Overexpression of ENaC
- leads to increased reabsorption of Na+, leads to increased water retention and increase k+ excretion
Can cause hypotension and hypokalaemia

53
Q

How does diabetes inspidus relate to the water retention in the kidney?

A

Nephrogenic - no response of ADH to V2 receptors
Cranial diabetes inspidus - reduced production of ADH
Diabetes inspidus is a rare disorder that causes the body to produce too much urine up to 18L a day

54
Q

What is the effect of alcohol on renal function?

A

Inhibits ADH - hence need to pee more
Helps remove alcohol toxins to beat a hangover

55
Q

What is the clinical relevance of diabetes inspidus due to reduced ADH secretion?

A

Idiopathic - lack of degeneration of hypothalamic ADH secreting cells
Caused by head trauma, infection or brain surgery
Familial (ADH mutation)
Treatment with synthetic ADH

56
Q

What is the clinical relevance of diabetes insipidus due to failure to respond to ADH?

A

Kidney damage from certain drugs or inherited
Dietary management - dieuretics to reduce GFR, and NSAIDs

Unit 8 (22 decks)

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