body fluids Flashcards
from what methods can our bodies gain water?
food - 30%
drink - 60%
metabolism - 10%
what is the total body fluid of a 70kg man?
42L - 60% of body weight
what percentage of body fluid is the ECF and ICF?
ECF - 20%
ICF - 40%
what ions are mainly found in the ECF and ICF?
ECF - Na+, Cl- and HCO3-
ICF - K+ and PO4^3-
what are the major solutes contributing to osmolality?
Na+, Cl-, Glucose & urea
what are solutes?
inorganic salts
how can solutes be classified?
o Electrolytes – inorganic salts (ie: Na+, K+, Cl-)
o Non electrolytes
which has more osmotic power; electrolytes or non-electrolytes?
electrolytes
what is osmotic pressure?
the process that controls movement of solvents (water) across a membrane
define osmolarity
measure of solute concentration expressed as the number of osmoles (Osm) of solute per litre of solution
what factors affect osmolarity and why?
pressure and temperature bc these can affect volume
define osmolality
the measure of osmoles of solute per kilogram of solvent – Osm/kg
what is the normal range for plasma osmolality?
280-300mOsm/Kg
which is used in clinical labs; osmolality or osmolarity?
osmolality
what are the two forces that control the equilibrium int he ECF and how are these generated?
hydrostatic pressure - force produced by the heart pumping
oncotic pressure - proteins in the plasma
what are the main forms of transport in a cell?
simple diffusion
facilitated diffusion
active transport
what is the major determinant of plasma and ECF osmolality?
sodium
what parts of the brain control the CNS and the thirst mechanism?
Subfornical Organ (SFO) and the Organum Vasculosum of the lamina terminalis (OVLT
where is ADH released from?
posterior pituitary gland
when is ADH released?
increased plasma osmolality
decreased plasma volume
what receptor detects plasma osmolality?
osmoreceptors of the hypothalamus
what receptors detect plasma volume?
baroreceptors of the great veins and right atrium
what effect does ADH have on collecting ducts?
makes collecting duct cells more permeable to water –> increases water reabsorption
what effect does ADH have on urine output?
Low ADH levels dilute urine and reduced volume of body fluids
High ADH levels concentrated urine
what factors can trigger ADH release?
prolonged fever, excessive sweating, vomiting, or diarrhea, severe blood loss and traumatic burns
what cells do ADH target?
aquaporins
where is aldosterone released from?
adrenal cortex
what triggers aldosterone release?
reduced sodium
increased potassium
what cells are the target of aldosterone?
• Na+/K+ ATPase and epithelial Na+ channel (ENaC)
what hormone is released in response to low plasma volume?
ADH
what hormone is released in response to plasma osmolality changes?
aldosterone
what hormone is released when there is high plasma volume?
atrial natriuretic peptide (ANP)
where is ANP released from?
cardiac atria
what triggers the release of ANP?
increased blood volume which stretches the atria
what hormones control plasma osmolality and volume?
ADH
angiotensin II
aldosterone
ANP
how much water is reabsorbed in the PCT?
80%
in a healthy individual, what should the 24 hour urine osmolality be?
500 and 800 mOsm/kg
after 12-14 hours of fluid intake restriction, what should the urine osmolality be?
over 800mOsm/kg
what conditions arise as a result of failures of body fluid balance?
dehydration
water intoxication
oedema
in what people is dehydration common?
very young and elderly people
what causes water intoxication?
too much water too quickly
urine blockage
what is an oedema?
Swelling of the tissue due to accumulation of fluid in ECF
what are the four main causes of oedema?
- Increased capillary hydrostatic pressure - capillary hydrostatic pressure > Osmotic pressure = fluid leave the capillary.
- Loss of plasma proteins
- Obstruction of lymphatic circulation
- Increased capillary permeability (inflammation)
