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sem 2 renal > An introduction to kidneys and body fluid > Flashcards

An introduction to kidneys and body fluid Flashcards

1
Q

what does osmosis determine?

A

the movement of water between ICFV and ECFV

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2
Q

why might we want to prevent large fluid shifts between ICFV and ECFV?

A

too much water into cells will make them burst, causing tissue damage

too much water out causes them to shrink massively

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3
Q

ECFV

A

The ECFV consists of two sub-compartments:

Plasma (3L) - usually 20% of ECV

Interstitial fluid (11L)

Starling forces determine fluid and solute movement between plasma and interstitial fluid

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4
Q

how much of the body weight is ICV?

A

40%

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5
Q

what is osmolarity?

A

the total concentration of osmotically active solutes

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6
Q

what is the major determinant of ECV osmolarity and why?

A

sodium, because it is the principal electrolyte of ECF

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7
Q

Why is the control of body fluids important ?

A

Cell structure and function
-large shifts between ECFV and ICFV will disrupt tissue structure and function

Tissue perfusion
-depends on balance between circulating volume (plasma) and interstitial volume

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8
Q

what determine fluid and solute movement between plasma and interstitial fluid?

A

Starling forces

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9
Q

what do salt and water balance depend on?

A

Osmoregulation: maintain osmotic equilibrium between ICFV and ECFV

Volume regulation: maintain adequate ECFV to support plasma volume

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10
Q

why do we control ECFV osmolarity?

A

in order to maintain osmotic equilibrium between ICFV and ECFV

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11
Q

how can plasma osmolarity be estimated?

A

2[Na] + 2[K] + [glucose] + [urea]

(Why do we double sodium and potassium but not glucose and urea? Balance the charges, if you have a certain amount of sodium there is positive charge which needs to be balanced out with anions (most of the anions will be made up of chloride, but it also includes bicarbonate and other molecules). Glucose is not charged so isn’t doubled

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12
Q

give a difference between interstitial fluid and plasma fluid?

A

plasma proteins (cannot cross the plasma membrane)

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13
Q

how does the body achieve osmoregulation?

A

by adding or removing water (not sodium) through controlling by controlling ADH levels

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14
Q

when plasma osmolarity rises how do the kidneys respond?

A

by producing small volume of concentrated urine (water retention)

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15
Q

a rise in plasma osmolarity indicates what?

A

that solute concentration has gone up (so more water is needed)

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16
Q

what does volume regulation refer to?

A

the control of the circulating (plasma) volume

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17
Q

what are changes in plasma volume detected by?

A

stretch and pressure receptors in the CVS

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18
Q

what is a fall in blood volume opposed by?

A

sodium retention - water follows osmotically, restoring volume

(although the total amount of body sodium may be increased, osmolarity is barely changed because the retained sodium brings water with it)

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19
Q

function of the kidney?

A

salt and water balance

  • Osmoregulation
  • Volume regulation
  • Acid-base balance
  • Regulation of electrolytes balance (eg potassium, calcium, phosphate)
  • Removal of metabolic waste products from blood
  • Removal of foreign chemicals in the blood (e.g. drugs)
  • Regulation of red blood cell production (erythropoietin)
  • endocrine organ (EPO, renin, Vit D)
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20
Q

what is urine production?

A

a by-product of kidney function

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21
Q

urinary tract

A

important for temporary storage, then removes urine from the body

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22
Q

what is a nephron?

A 
functional unit of the kidney
-consists of special blood vessels and elaborate tubules (tiny tubes)
-where urine production begins 
-consists of several major structures:
  Blood vessels
  The glomerulus
  Bowman capsule
  The renal tubule
23
Q

what are the outer and inner sections of the kidney called?

A

outer - cortex

inner - medulla

24
Q

explain how the kidney (and nephrons) are supplied with blood

A

The whole kidney is supplied by a major artery called the renal artery

This subdivides many times into fine arterioles supplying each nephron, the afferent arteriole

Drained by the renal vein, which is supplied by venules coming away from each nephron, joining together into larger veins which merge into the renal vein.

In between there are complex capillary networks

25
Q

what does the collecting duct form?

A

the ureter, which drains into the bladder.

26
Q

what does a kidney tubule begin with?

A

Bowman’s capsule

27
Q

The Four Basic Processes

of Urine Formation

A
  1. Glomerular Filtration
  2. Tubular Reabsorption
  3. Tubular Secretion
  4. Excretion of water and solutes in the urine
28
Q

Glomerular Filtration

A

Hydrostatic pressure in the afferent arteriole forces fluids and solutes through the glomerular capillary membrane

Small molecules pass readily- large ones (proteins) and cells cannot pass

This leads to a plasma ultra filtrate in the Bowman’s capsule

29
Q

what can be used as an index of GFR?

A

Plasma creatinine

  • breakdown product of creatine phosphate in muscle
  • excreted unchanged
30
Q

what is Glomerular filtration rate (GFR)?

A

the amount of filtrate kidneys produce each minute

-averages 125 ml/min (approx 20% of renal plasma flow)

31
Q

when is GFR reduced?

A

renal failure

32
Q

Reabsorption

A

many substances are filtered and then reabsorbed from the tubular lumen into the peritubular capillaries

33
Q

importance of secretion

A

eliminating undesirable substances (urea/ uric acid)

getting rid of excess potassium ions

controlling blood pH

34
Q

what determines that amount of solute present in the urine?

A

the amount filtered out of the plasma MINUS the amount reabsorbed

35
Q

the control of water balance (osmoregulation) is based on the control of?

A

the osmolality of the ECFV

36
Q

how are changes in ECF osmolality sensed?

A

via sensory cells in the hypothalamus, and effectors ( in this case, the kidneys) are then needed to adjust the volume of water excreted or contained

37
Q

how is total body water balance calculated?

A

input vs output

38
Q

what should total body water balance be?

A

zero - otherwise there will be a change in osmolality

39
Q

insensible water loss

A

evaporation of water through the skin and the lungs

40
Q

give an example of uncontrollable water loss?

A

water loss via the GI tract

41
Q

Physiological response to water restriction (thirsty, but no water available to drink)

A
  • Plasma osmolality rises
  • Response is increased secretion of hormone, ADH/vasopressin

Results in:
Decreased urine volume
Increased urine osmolality

42
Q

Physiological response to increase in water intake

A

Increase in water absorption through GIT

Plasma osmolality falls
Response is reduced secretion of ADH

Results in:
Urine volume increases
Urine osmolality decreases

43
Q

what is a good indicator of ADH status?

A

osmolarity of the urine

44
Q

what happens when you drink TOO much water?

A
  • can be fatal
  • you will start to dilate the ECF, reducing the osmolarity
  • decreased osmolarity of ECF but ICF will have the same as normal, so water will move into the cells
  • shifts of fluid from EC to IC causes brain damage
45
Q

why must sodium intake and excretion be balances?

A

to maintain a constant ECF volume

46
Q

how do you calculate [Total body Na+]?

A

intake minus elimination (elimination is through sweat, diarrhoea and vomit)

47
Q

how do we expand the ECF volume?

A

sodium reabsorption in kidneys is increased, and water follows osmotically (so concentration is constant)

48
Q

what detectors detect changes in blood pressure/volume?

A

changes in pressure and volume are sensed in the CVS by baroreceptors, atrial stretch receptors

49
Q

Sodium retaining system

A

The Renin-angiotensin-aldosterone system (RAAS)

50
Q

Sodium eliminating pathways

A

Cardiac natriuretic peptides (ANP)

sodium eliminating pathways depend on ANP’s which are released from cells in the atria in response to increased stretch due to increased volume.

51
Q

a decrease in ECFV means what in terms of these sodium pathways?

A

decrease in ANP pathway, increase in RAAS pathway - overall decrease in sodium excretion

52
Q

example of when there in a decrease in ECFV?

A

haemorrhage

53
Q

increase in amount of body sodium means what?

A

increase in ECV

54
Q

how does the kidney act as an endocrine organ?

A

produces EPO, renin and Vitamin D

sem 2 renal (10 decks)

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