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renal physiology Flashcards

1
Q

What is osmolality?

A

Particles per kilo of solution

-a high osmolality is a highly concentrated solution

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2
Q

What is osmolarity?

A

proportional to the number of particles per litre of solution; it is expressed as mmol/L.
-a high osmolarity is a highly concentrated solution

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3
Q

What is:

  • hypotonic
  • hypertonic
  • isotonic
A

hypotonic: solution has a lower conc. than cell
Hypertonic: solution has a higher conc. than cell
isotonic: solution has the same conc. as cell

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4
Q

what compartments make up total body water?

A

Intracellular fluid: 67%

Extracellular fluid: 33%

  • plasma 20%
  • interstitial fluid 80%
  • lymph and transcellular fluid
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5
Q

How are body fluid compartments measured?

A

using tracers - obtain distribution volume from tracer

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6
Q

What are the tracers for:

  • total body water
  • extracellular fluid
  • plasma
A

TBW: 3H2O
ECF: inulin
Plasma: labelled albumin

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7
Q

How are body water compartments measured?

A

Volume in litres = dose (D) / sample conc

e.g. 42mg/1mg per litre = 42litres

e.g. for tracer X
distribution volume = quantity X (mol)/ equilbrium of X in body (mol/l)

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8
Q

what are the main ions in extracellular fluid?

A

Na+ CL- HCO3-

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9
Q

what are the main ions in intracellular fluid?

A

K+ Mg2+ and -vely charged proteins

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10
Q

Describe the four ways that fluid homeostasis is challenged? how does it affect intracellular vs extracellular fluid?

A

1: gain or loss of water - change to both ICF and ECF similarly
2: NaCl gain - water is drawn out of cells into the extracellular fluid
3: NaCl loss - water is drawn into cells out of the extracellular fluid
4: gain or loss of isotonic solution - ECF changes only as this does not affect tonicity

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11
Q

Which electrolyte is the main determinant of extracellular fluid?

A

Na+, therefore it is vital that this is regulated

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12
Q

Which electrolyte plays a key role in establishing membrane potential?

A

Potassium: more than 95% K+ is intracellular and small leakages or increased cellular uptake may affect conc. plasma K+
=muscle weakness
=cardiac irregulations

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13
Q

what are the ten kidney functions?

A 
1 - water balance
2 - salt balance
3 - plasma vol. maintenance
4 - plasma osmolarity balance
5 - acid-base balance
6 - excretion metabolic waste products
7 - excretion exogenous foreign compounds
8 - secretion renin
9 - secretion EPO
10 - activated vit D
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14
Q

What is the functional unit of the kidney? what are their 3 functions? what two different types do you get and what is the difference? which is the most common type?

A

Nephron

functions:
1 - filtration
2 - reabsorption
3 - secretion

Juxtamedullary nephrons (20%) have a longer loop of henle which dips far into the medulla

Cortical nephrons (80%) only have a small loop of henle

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15
Q

what are the three basic renal processes?

A

1: glomerular filtration (20% of plasma that enters the glomerulus is filtrated
2: Tubular reabsorption
3: Tubular secretion

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16
Q

How is rate of excretion calculated?

A

Rate of excretion = rate of filtration + rate of secretion - rate of absorption

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17
Q

how is filtation rate calculated?

A

Rate of filtration of X = mass of X filtered into bowmans capsule per unit time

Rate of filtation of X = [X]plasma X GFR

18
Q

How is excretion rate calculated?

A

rate of excretion of X = mass X excreted per unit time

= [X]urine X urine flow rate

19
Q

How is reabsorption rate measured?

A

=rate filtration of X - rate excretion X

if so much X has been filtrated but only a smaller amount has been excreted - must have been reabsorbed

20
Q

How is secretion rate measured?

A

= rate of excretion X - rate of filtration X

more X has been excreted than filtrated and therefore it must have been secreted

21
Q

Describe the 3 filtration barriers in the glomerulus that prevent RBCs/plasma proteins from being filtrated??

A

glomerular capillary endothelium provides a barrier to RBCs

Basement membrane and slit processes of podocyte provides a barrier to plasma proteins

22
Q

What two factors are involved in net filtration rate in the capillary?

A

hydrostatic and oncotic pressures in the capillary and in bowmans capsule (although no oncotic pressure in bowmans capsule as no plasma proteins here)
- usually this is about 10mmHg

23
Q

What is GFR and how is this calculated?

A

rate at which protein free plasma is filtrated to bowmans capsule per unit time
-Kf X net filtration rate

(Kf is filtation coefficient: how holey is glomerular membrane?)

24
Q

How is GFR regulated in the body?

A

Extrinsic: baroreceptor reflex
Intrinsic: autoregulation in the kidney

25
Q

Describe autoregulation in the kidney?

A

Myogenic:
-if vascular smooth muscle is stretched it contracts and constricts arteriole

Tubuloglomerular fneedback
-if GFR rises, more NaCl flows through which is detected by the macula densa in the juxtaglomerular apparatus
=constriction of afferent arteriole

=this ensures renal blood flow is maintained over a wide range of MAP to protect GFR

26
Q

how could:

  • renal stone
  • diarrhoea
  • severe burns
  • change in surface area avail. for filtration

affect GFR

A

Renal stone:
-increase the hydrostatic pressure in the bowmans capsule = GFR decreased

Diarrhoea:
-increases capillary oncotic pressure (dehydration)
=GFR decreased

Severe burns:
-decreases the oncotic pressure of capillary = increases GFR

change in surface area avail. for filtration:
-decreases the filtration coefficient = decreases GFR

27
Q

what is plasma clearance?

A

volume of plasma that is cleared of a particular substance per min
=rate of excretion/plasma conc.

=[X]urine + volume urine produced ml/min / [X] plasma

28
Q

What substance is used as a clearance marker? what qualities does a substance have to have to be a clearance marker?

A

Creatinine clearance = GFR
-endogeous

(inulin can be used too)

Qualities: freely filtered but no secreted or reabsorbed

29
Q 
What is the clearance of:
-glucose
-urea
-H+
-PAH (what can this be used for)
compared to GFR
A

Glucose: all is reabsorbed and none is secreted (clearance = zero)

Urea: clearance < GFR (is partly reabs. and none secreted)

H+: clearance > GFR (not reabsorbed and some secreted)

PAH: freely filtered and is all secreted
(can use this to calculate renal plasma flow as this is the rate of clearance of PAH)

30
Q

what is the filtration fraction of the kidney?

A

amount (% or fraction) of plasma that is filtered at the glomerulus
=GFR/renal plasma flow

31
Q

Where in the nephron is the main site for water and ion balance regulation?

A

distal tubule and collecting duct

32
Q

what regulates water and ion balance in the distal tubule and collecting ducts?

A

mainly hormones:

aldosterone - increases sodium reabsorption and increases H+/K+ secretion in the late distal tubule

ADH - increases the number of aquaporins in the luminal membrane of the late collecting duct to allow more water reabsorption

ANP: decreases sodium reabsorption

PTH: Ca2+ reabsorption increases, PO43- reabsorption decreases

33
Q 
How is:
Filtration
Secretion/Reabsorption
Excretion
Regulated?
A

Filtration: changes in blood pressure/changes in size of filtration slits

Secretion/reabsorption: changes in solute concentration e.g. ADH/Aldosterone

Excretion: bladder function under neural control

34
Q

Describe how ADH is regulated, what does ADH cause

A

ADH is stimulated by: Hypertonic ECF, decrease in left atrial pressure, nicotine

ADH is inhibited by: hypotonic ECF, stretch receptors in upper GI tract, alcohol

ADH increases thirst, causes arteriolar constriction and increases water reabsorption in the late distal tubule

35
Q

Describe salt balance in the body:

A

Amount of sodium reabsorbed is regulated by RAAS

Renin released from granular cells in the juxtaglomerular apparatus due to:

  • decreased pressure in the afferent arteriole
  • macula densa cells sense a decrease NaCl
  • increased sympathetic activity due to a decrease in arteriolar BP

Aldosterone - stimulated by high potassium or low sodium in the blood or RAAS, acts to reabsorb sodium and and pump out potassium

36
Q

Describe how RAAS is stimulated in heart failure?

A

Failing heart leads to a decreased cardiac output and decreased blood pressure which causes an increase in salt retention and water

37
Q

What hormone inhibits RAAS? where is this produced and stored?

A

ANP - causes excretion of sodium

Produced by the heart and stored in the atria: if heart stretched (e.g. by high BP due to high salt) ANP is released

38
Q

what is the difference between water diuresis and osmotic diuresis?

A

Water diuresis: this is an increased urine flow but no increased solute excretion

Osmotic diuresis: this is a primary increase in sodium excretion which causes a diuresis

39
Q

How does the kidney regulate acid base balance by regulating H+ ions in plasma?

A
  • in the proximal tubule HCO3- is reabsorbed
  • if there is a lot of H+ ions in tubular fluid, kidneys make more HCO3- to regenerate buffer stores depleted by acid load
40
Q

If the concentration of H+ ions in the tubular fluid increases - what does this cause?

A
  • drives reabsorption of HCO3
  • Forms acid phosphatase
  • forms NH4+ (ammonium ion)
41
Q

What is the difference between nephrogenic vs neurogenic diabetes insipidus?

A

Nephrogenic: inability of nephron to respond to ADH

Neurogenic: lack of vasopressin release from posterior pituitary - treat with desmopressin

Renal (20 decks)

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