Basic Water And Electrolyte Homeostasis Flashcards
Where is water stored in the body?
Outline to distribution in a 70kg man
Intracellular compartment - cytosines and organelles
Extra cellular compartment - vascular, extravascular, plasma, interstitial, CSF, vitreous humour, GI, pleural and pericardial
28L in intracellular compartment
14L in extracellular: 10.5 in interstitial and 3.5 in plasma
What electrolytes are found in the body?
Cations (+ve): sodium, potassium, magnesium, calcium and hydrogen
Anions(-ve): chloride, bicarbonate, phosphate, sulphate, organic acids and proteins
How can electrolytes move between compartments?
Across cell membrane by passive diffusion or active transport
Across capillary membranes civil size exclusion passive diffusion
What is the anion gap?
(Na + K) - (Cl + Bicarbonate)
Should be 10-16
What is electroneutrality?
State of net charge of 0 achieved in any compartment
What three forces control water and solute movement?
Oncotic pressure (colloid osmotic pressure) Osmotic pressure Hydrostatic pressure
What is oncotic pressure?
Form of osmotic pressure exerted by proteins that determines distribution of fluid between blood vessels and intersitial fluid
What is osmotic pressure?
Ability of a solution to causes osmosis
Controls water movement between compartments speared by semi-permeable membranes
Water moves from dilute compartment( low osmotic pressure) to concentrated compartment (high osmotic pressure)
What is difference between osmolality and osmolarity?
Osmolality : amount of solute in 1Kg of water (mmol/Kg)
Osmolarity : amount of solute in 1L of water (mmol/L), is temperature dependent
In water osmolality=osmolarity
In plasma some of the volume taken up by substances : and water volume 6% less then total volume.
Major solutes that contribute: Na, Cl, K, PO4, urea and glucose
What is the calculation of osmolality?
2*(Na+K) + urea + glucose
What is the osmolar gap?
Osmolality - osmolarity
Increased gal suggested presence of other osmotically active solutes in plasma
What is hydrostatic pressure?
Mechanical pressure generated by heart against the fluid membrane
What are the three IV fluids, which compartments do they enter?
5% dextrose crystalloid : plasma, interstitial fluid and intracellular
0.9% saline: plasma and interstitial fluid
Plasma/blood: plasma
How are changes to water balance detected?
1) osmolality : osmoreceptors detect changed in ECF. Sensitive to 1-2% changes to osmolality
2) volume : changes to intravascular column detected by baroreceptors. Low volume = right atrium and veins. High pressure = carotid sinus. Input to hypothalamus. 8-10% changes
What is produced due to changes in water balance?
ADH
Made by hypothalamus
