Control, volume and composition of ECF Flashcards
Influencers on diffusion
Concentration difference, electrical difference and pressure difference
What is osmotic pressure influenced by
molar concentration of a solution - number of active particles per unit volume, not their size
What is oncotic pressure?
fluid movement between plasma and interstitial fluid
Difference between osmolarity and tonicity
- Osmolarity: starting osmotic pressure with all solutes
- Tonicity: final osmotic pressure after solute removal
How does water move between compartments?
Aquaporins - allow movement through all compartments
Between which compartments can glucose move?
Between interstitial fluid, intracellular fluid and RBCS
How do proteins move between compartments?
Pinocytosis
Process of pinocytosis
- On surface of cell are clathrin molecules
- proteins binds to receptor
- coated put has protein bind to
- Invagination generated by actin and myosin
- Causes vesicle to form
- Energy dependent
Where is ADH secreted?
Osmoreceptors
- Polypeptide released from posterior pituitary
- Controlled by hypothalamic osmoreceptors
- 3 receptors - all g-protein
Site and role of V1a
Site: peripheral circulation
Role: vasoconstriction
Site and role of V2
Site: CD endothelium
Role: AQP2 insertion, clotting factor release
Site and role of V3
Site: CNS
Role: ACTH release
VOLT
- Vascular Organ of Lamina Terminalis - lies outside BB and contains AQP4
- When plasma osmolarity rises, water leaves these cells = shrinkage, triggers ion channels to generate AP and release ADH from pituitary
What happens when osmolality increases?
Hypothalamic osmoreceptors stimulated
Lateral pre-optic area = thirst
Paraventricular and supra-optic area = ADH release
What happens when osmolality decreases?
Hypothalamic osmoreceptors inhibited
ADh stimulation
Nicotine
ADH inhibition
ANP, alcohol
Function of junta-glomerular apparatus
- Between afferent arteriole and DCT
- Senses decrease in pressure in granular cells
- Senses decreased tubular sodium flow
- Triggering JGA leads to dilation of afferent arteriole, release of renin from granular cells
- Renin release stimulated by B1 stimulation
Function of aldosterone
- Aldosterone causes gene expression which activates sodium/potassium portal
- Drives sodium from tubule to blood
- Aldosterone release stimulated by angiotensin ii, increased plasma potassium concentration, ACTH
- Decreased blood volume = decreased renin
- Increased blood volume = increased NaCl and water excretion
What inhibits aldosterone
ANP (released to stretch heart)
Causes increased GFR, decreased aldosterone, decreased renin and decreased ADH
How is sodium retention encouraged
- Water retention = ADH agonist e.g. terlipressin and antagonist e.g. tolvaptan
How is water retention encouraged
ADH agonist e.g. terlipressin and antagonist e.g. tolvaptan
What happens to correct high osmolarity
Increased ADH so retain water
What happens to correct low osmolarity
Decreased ADH so excrete water
What happens to correct hypovolaemia
Increased aldosterone and decreased ANP = retain Na+
What happens to correct hypervolaemia
Decreased aldosterone and increased ANP = Na+ excretion
Causes of fluid retention
HF, no ADH, intake excess
Causes of sodium loss
Diuretics, vomiting/diarrhoea, Addison’s
Danger of hyponatraemia
water moving into brain by osmosis (cerebral oedema), increases ICP, worse in children
SIAD
- Syndrome of in-appropriate SDH secretion
- Caused by tumours (small cell lung cancer)
- Infections - pneumonia, meningitis
- Drugs (SSRIs)
- Hypothyroidism
- Fluid retention - sodium levels drops
- Cut back on fluid intake
What is used during endoscopic resection to irrigate
Glycine
Hyponatraemia treatment
- Restrict water
- Use hypertonic saline in crisis byt not used routinely - over correction
- CPM = damage to myelin in pons
- After exercise: sweat to lose heat, normal sodium in sweat = 40 mmol/l
- Relative to ECF more NaCl in sweat
How is ECF volume determined
Aldosterone regulating Na+
How is ECF osmolarity determined
ADh regulated water
