body balance Flashcards
body fluid distirbution
-lean adults contain between 55-60% fluids
-comprised of
-intracellular fluid 2/3rd of total fluid
-extracellular fluid 1/3rd of total fluid
-80% interstitial fluid
-20% plasma
[Na+ and Cl- main extracellular solutes]
what is the bodies primary source of water
ingested fluids [1600ml/day] and food [700ml/day]
what is metabolic water
water ‘made’ by electron acceptance and H+ binding by 02 during oxidative phosphorylation [during dehydration synthesis -formation of covalent bonds]
water loss
-urine production by kidneys
[1500ml/day]
-evaporation from skin [600ml/day]
-exhalation of water vapour from lungs [300ml/day]
-water content of faeces
[100ml/day]
osmolality
measure of the concentration of a solution by expressing the total number of solutes per 1Kg of tissue - mOsm/Kg
osmolarity
Measure of the concentration of a solution by expressing the total number of solutes per 1L of solvent - mOsm/L
2% loss of body mass due to water loss triggers thirst
-detected by osmoreceptors in the thirst centre of hypothalamus
-also neurons triggered by a dry mouth/low saliva flow
diuretics
-xanthines
-caffeine, theophylline [tea], and theobromine [chocolate]
-inhibits Na+ reabsorption and promoting water loss
-alcohol [ethanol]
-inhibits ADH secretion
-reduces water resorption and increases water loss
RAAS
-renin-angiotensin-aldosterone system
-the loss of water reduces blood volume and pressure [detected by baroreceptors]
-kidneys respond to this by releasing the enzyme renin
fluid and solute relationship
Na+ and Cl- regulation plays a key role in body fluid volume
need to maintain a constant Na+ and Cl- concentration [increased consumption results in higher fluid volume and increased blood pressure] the more we excrete the more water we lose due to osmosis
3 major hormones dictate Na+ concentration
Angiotensin 2
Aldosterone [increase Na+ reabsorption]
Atrial natriuretic peptide [reduces Na+ reabsorption]
ADH regulation of water loss
-primary regulator
-secreted from posterior pituitary
-acts to promote insertion of water channels in the collecting ducts [aquaporins]
-also reduces water lost in sweat and is a vasoconstrictor
osmolality in the kidney
-varies on location
-lowest in renal cortex [300 mOsm/kg or iso-osmotic]
-greater towards inner medullary region [up to 1200 mOsm/kg or hyper-osmotic]
dilute urine formation
osmolality changes in nephron loop
-increases in descending limb
-decreases a solutes are removed in ascending limb
we are usually slightly over-hydrated, ADH secretion will be low, lack of ADH means little water reabsorbed in late DCT and collecting duct
concentrated urine formation
-juxtamedullary nephrons utilised when dehydrated [very long nephron loop passes deep into hyper-osmotic renal medulla]
-tubular fluid osmolality increases to around 1200 mOsm/kg [due to more water leaving the tubules]
water intoxication
-when fluid intake is high and constant kidneys cannot match removal to intake. [also occurs if blood loss or excessive sweating followed by consumption of large quantities of plain water]
-cells swell to dangerous levels, hazardous in CNS, neurons contained in cranium, swelling increases intracranial pressure
-result in confusion, headache, drowsiness, cerebral oedema and death
function of minerals
-can be a part of enzymes that catalyse biochemical reactions
-plays an important role in immunity
-essential for muscle contraction and cell activation
2 groups of minerals based on daily requirement
-macrominerals
->100 mg per day
-microminerals
-<20 mg per day
calcium
-most abundant mineral
-present in blood as either free calcium, bound to plasma proteins
-daily requirement 100mg/day
-makes up inorganic component of bone [form extracellular matrix of bone together with collagen], very hard but brittle structure [extremely tough when combined with collagen]
functions of calcium -signalling
release of neurotransmitter across neuron synapses
-ca2+ enter axon terminal and trigger exocytosis of synaptic vesicles containing neurotransmitter [Ca+ flow into synaptic end bulb due to concentration gradient]
functions of calcium -muscle contraction
Ca2+ released from terminal cisterns in skeletal muscle bind to troponin
-causes tropomyosin to move from binding site on actin filament
-myosin heads can now bind to actin
-muscle can contract
functions of calcium - blood clotting
helps catalyse conversion of prothrombin to thrombin, thrombin converts fibrinogen to insoluble fibrin [forms the network of the clot]
phosphate
-most of phosphate in body [85%] in combined with calcium and used in bones and teeth
-15% left is in form of phosphate ions
-ions are dihydrogen phosphate [H2PO4-], hydrogen phosphate [HPO4^2-], phosphate [PO4^3-]
function of phosphate
-all three phosphate ions act as buffers [mainly in cells but also in extracellular fluid]
-most [phosphate ions are bound to other substrates]
-lipids to form phospholipids
-proteins
-CHO
-nucleic acid
-ATP
