Physiology Flashcards
How much of a male is water?
60%
How much of TBW is intracellular/extracellular?
67% = intracellular 33% = extracellular
What are tracers used for?
measuring sizes of fluid compartments
What is a good indicator for TBW?
3H20
What is a good indicator for plasma volume?
labelled aluminium
What is a good indicator for extracellular fluid volume?
inulin
Name 3 things which cause input of fluid throughout the day.
fluid
food
metabolism
Name 5 things which cause output of fluid throughout the day.
skin, lungs (insensible)
sweat, faeces, urine (sensible)
What are the ICF and ECF concentrations of sodium?
ICF - 10
ECF - 140
What are the ICF and ECF concentrations of potassium?
ICF- 140
ECF- 4.5
If there is a gain of water, what changes occur?
similar to both ECF and ICF
If there is a gain/loss of Na/Cl what changes occur?
opposite in ECF and ICF
e.g.
if NaCl ECF increases, ECF increases but ICF decreases
What happens if there is a gain or loss of isotonic fluid?
no change in fluid osmolarity
change in ECF only
Does water follow salt, or does salt follow water?
water follows SALT
How much of the body’s potassium is intracellar?
95%
What two things might small leakages or increase in cellular uptake of K cause?
muscle weakness - paralysis
cardiac irregularities - cardiac arrest
Does cell lysis occur if a cell is hypotonic or hypertonic?
hypotonic
What happens if a cell is hypertonic?
cell shrinkage
Which, tonicity or osmolarity takes into account the ability of a solute to cross the membrane?
tonicity
What is the major anion of ECF?
chloride
Major cation of ECF?
sodium
Are osmotic concentrations of ECF//ICF the same or different?
identical
What alters composition + volume of ECF?
kidney
What are the two types of nephron?
juxtamedullary
corticol
How much of plasma entering the glomerulus is filtered?
20%
What calculation is used for the filtration rate?
Filtration rate = concentration of plasma X GFR
What calculation is used for the Excretion rate?
Excretion rate = concentration of urine X urine flow rate
What calculation is used for the reabsorption rate?
rate of filtration - rate of excretion
What calculation is used for the secretion rate?
rate of excretion - filtration
Approx value for glomerular capillary blood pressure?
55
Approx value for Bowmans capsule oncotic pressure?
0
Approx value for hydrostatic pressure in Bowmans capsule?
15
capillary oncotic pressure approx value?
30
What is net filtration equal to?
(55 + 0) - (15+30) = 10mmHg
What is GFR equal to?
Kf x net filtration pressure = 125ml/min
What is GFR?
rate at which protein free plasma is filtered from glomeruli at Bowman’s capsule?
What is clearance of a substance equal to?
volume of plasma cleared for substance per minute
Is clearance of every substance the same?
no substance has different clearance values
What is used clinically to determine GFR?
inulin
What else can be used to determine GFR?
creatinine
What properties should a substance have to make it an indicator for GFR measurement?
freely filtered at glomerulus neither absorbed nor secreted not metabolised by kidney not toxic easily measured in urine and blood
What is the clearance for a substance which is completely reabsorbed and not secreted, and give an example of such a substance?
0
glucose
What is the clearance for a substance which is filtered, partly reabsorbed and not secreted, and give an example of such a substance?
more than GFR
urea
What is the clearance for a substance which is filtered, secreted but not reabsorbed, and give an example of such a substance?
less than GFR
H+
If clearance < GFR (inulin clearance) then substance is what?
reabsorbed
If clearance = GFR then substance is what?
neither reabsorbed or secreted
If clearance > GFR then substance is what?
secreted into tubule
What can be used to calculate RPF?
para-amino hippuric acid (PAH)
What happens to all the PAH in the plasma that escapes filtration?
it is secreted from the peritubular capillaries
What is creatinine?
Creatinine is a muscle metabolite produced at a near constant rate
What does measurement of inulin require?
does require constant infusion to ensure a constant [inulin]p not very convenient
Describe what a GRF marker should be.
should be filtered freely; NOT secreted or reabsorbed
Describe what a RPF marker should be.
marker should be filtered and completely secreted
What is filtration fraction?
fraction of plasma flowing through the glomeruli that is filtered into the tubules - 20%
20% of the plasma that enters the flomerulus is filtered. What happens to the other 80%?
it is not filtered and leaves through the efferent arteriole
Which is more specific, reabsorption or filtration?
reabsorption
Fluid reabsorbed in the proximal tubule is what with filtrate?
iso-osmotic with filtrate
What is reabsorbed in the proximal tubule?
Sugars Amino acids Phosphate Sulphate Lactate
What is secreted in the proximal tubule?
H+ Hippurates Neurotransmitters Bile pigments Uric acid Drugs Toxins
What type of active transport is this: Energy is directly required to operate the carrier and move the substrate against its concentration gradient
primary
What type of active transport is this: Passive carrier-mediated transport of a substance down its concentration gradient
facilitated diffusion
What type of active transport is this: The carrier molecule is transported coupled to the concentration gradient of an ion (usually Na+)
secondary
Normally, how much glucose is reabsorbed in the proximal tubule?
100%
Is clearance of reabsorbed or secreted substances is constant once Tm is reached?
NO
How much of all salt and water is reabsorbed in the PT?
~67%
What drives sodium reabsorption?
the basolateral Na+-K+-ATPase
How is water reabsorbed?
by osmosis
What is the function of the loop of henle?
Generates a cortico-medullary solute concentration gradient, enabling the formation of hypertonic urine
Is the ascending or descending limb permeable to water?
descending
Which side reabsorbs NaCl, ascending or descending ?
ascending
What do “Loop diuretics” block?
the triple co transporter
What is the purpose of countercurrent multiplication?
To concentrate the medullary interstitial fluid
What run alongside the long loop of Henle of juxtamedullary nephrons?
vasa recta
Is the residual load of NaCl after reabsorption important?
Yes very apparently
What are major sites for the regulation of ion and water balance?
The distal tubule and the collecting duct
What does Aldosterone do to regulate ion and water balance?
increases Na+ reabsorption
increases H+ / K+ secretion
What does Atrial natriuretic hormone do to regulate ion and water balance?
decreases Na+ reabsorption
What does PTH do to regulate ion and water balance?
increases Ca2+ reabsorption
decreases PO43- reabsorption
Does the distal tubule have high or low permeability to water and urea?
low
What two mechanisms control bladder emptying?
The micturation reflex
Voluntary control
What produces ADH and where is it stored?
hypothalamus
stored in POSTERIOR pituitary gland
What controls the release of ADH from the pituitary into the blood?
hypothalamus
WhWhat stimulates ADH secretion?
water deficit
When is ADH secretion stimulated and when is it inhibited?
Stimulated when hypertonic
inhibited when hypotonic
What are the main symptoms of diabetes insipidus?
large volumes of dilute urine
constant thirst
How is diabetes insipidus treated?
ADH replacement
ADH release is affected by activation of left atrial stretch receptors. If atrial pressure decreases, what happens to ADH release?
increases
How does salt imbalance manifest itself?
as changes in extracellular fluid volume
Is regulation of extracellular fluid volume important for short term regulation of blood pressure or also long term regulation?
also long term
What does sodium filtered minus sodium reabsorbed equal?
sodium excreted
What is aldosterone?
steroid hormone secreted by adrenal cortex
When is aldosterone secreted?
in response to rising potassium or falling sodium
AND
activation of Renin angiotensin system
WHat does aldosterone do to sodium?
stimulates reabsorption
WHat does italdosterone do to potassium?
stimulates secretion
What happens wto potassium reabsorption if aldosterone is absent?
all is reabsorbed in distal tubule, so no potassium is excreted in urine
What does a decrease in plasma sodium promote?
the indirect secretion of aldosterone via the juxtaglomerular apparatus
What are the 3 main ways of control of renin release from granular cells in the juxaglomerular apparatus?
- reduced pressure in afferent arteriole
- macula densa cells sense amount of NaCl in distal tubule
- increased sympathetic activity as a result of reduced arterial BP
How is fluid retention associated with congestive heart failure caused by RAAS problems treated?
low salt diet
diuretics (LOOP)
ACE Is
What does atrial natriuretic peptide do?
is released when atrial muscle cells are stretched
promotes eexcretion of sodium and diuresis, so causes:
1.a decrease in plasma volume
2. and in BP
What is the difference between water diuresis and osmotic diuresis?
Both have increased urine flow, but water does NOT have an increased solute excretion, osmotic does
What produces erthropoitin?
kidney
WHat does erytropoitin do?
stimulates stem cells in bone marrow to produce RBCs which increases O2 supply to tissues (if there is not enough O2 supply to tissue, kidney makes more!)
