Fluid Distributions in the Body Flashcards
What proportion of a healthy man and woman is water?
- men: 60%
- women: 50%
What are the fluid compartments within the body and their values?
- intracellular fluid compartment: 25L
- extracellular fluid compartment (plasma (3L) and interstitial fluid (12L)): 15L
What is the difference between electrolytes and non-electrolytes?
non-electrolytes have bonds (usually covalent) that prevent them from dissociating in solution so no charged ion whereas electrolytes do dissociate into charged ions in water, and can conduct an electrical current
Why do electrolytes have greater osmotic power than non-electrolytes?
because each electrolyte molecule dissociated into at least 2 ions
What are the major differences between the ICF and ECF?
ICF:
- only contains small amounts of Na+ and Cl-
- most abundant cation is potassium and major anion is HPO4^2-
ECF:
- chief cation is sodium and major anion is chloride
- contains fewer chloride ions than ICF
What regulates fluid movement and what will cause water to shift between bodily compartments?
- osmotic and hydrostatic pressures regulate exchange and mixing of fluid
- solutes are unequally distributed between compartments due to size/electrical charge/need for active transport
- so anything that changes solute concentration in any compartment will lead to net water flow
What are the routes that the body gains and loses water?
- water intake is through ingested liquids and solid foods, it can also be produced by cellular metabolism called metabolic water/water of oxidation
- water output can vaporise out of lungs in expired air/diffuse out of skin/perspiration/faeces/urine
Describe the mechanism of ADH release
- osmoreceptors of hypothalamus sense ECF solute concentration and trigger/inhibit ADH release from posterior pituitary accordingly
- decrease in ECF osmolality inhibits ADH release allowing more water to be excreted in urine to restore normal Na levels in blood
- increase in ECF osmolality stimulates ADH release directly by stimulating hypothalamic osmoreceptors and indirectly through renin-angiotensin mechanism
- ADH secretion also influenced by large changes in blood volume or pressure by action of baroreceptors
What is dehydration and the symptoms of it?
- when water output exceeds intake over a period of time and body is in negative fluid balance
Symptoms:
- cottony/sticky oral mucosa
- thirst
- dry, flushed skin
- decreased urine output
- long term can cause weight loss, fever and mental confusion
What are the causes of dehydration?
- haemorrhage
- severe burns
- vomiting
- diarrhoea
- profuse sweating
- water deprivation
- diurectic abuse
- diabetes
Describe how dehydration disturbs the water balance
- water is lost from ECF
- results in osmotic movement of water from cells into ECF
- equalises osmolality even though total fluid volume has been reduced
What is hypotonic hydration?
- when ECF osmolality starts to drop, compensatory mechanisms are set into motion (ADH inhibited to decrease water reabsorption)
- but when there is renal insufficiency rr when a lot of water is drunk very quickly, hypotonic overhydration can occur
- ECF diluted, sodium content normal but excess water
- promotes net osmosis into tissue cells causing them to swell as they become abnormally hydrated
What are the symptoms of hypotonic hydration?
severe metabolic disturbances:
- nausea
- vomiting
- muscular cramping
- cerebral edema (if uncorrected can lead to convulsions, coma and death)
What is oedema?
- atypical accumulation of fluid in interstitial space leading to tissue swelling
What causes oedema?
- any event that steps up flow of fluid out of the blood or hinders its return
- increased BP (valve incompetence, blockage etc)/capillary permeability (inflammatory response)
