Homeostasis Flashcards
Normal plasma osmolality
275-295 mmol/kg
Normal plasma sodium range
135-145 mmol/L
Transudate
fluid pushes through the capillary due to high pressure within the capillary (low protein content)
Exudate
fluid that leaks around the cells of the capillary caused by inflammation and increased permeability of pleural capillaries to proteins (high protein content and may contain cells, bacteria, enzymes)
Diabetes insipidus
caused by the failure of the axons with cell bodies in the hypothalamus and synapses on blood vessels in the posterior pituitary to synthesize or release vasopressin (central diabetes insipidus) or the inability of the kidneys to respond to vasopressin (nephrogenic diabetes insipidus). Regardless of the type of diabetes insipidus, the permeability to water of the collecting ducts is low even if the patient is dehydrated.
Osmolality units
Concentration per kg
Osmolarity units
Concentration per L
Water distribution in a 70kg male: total body water
60% of body weight
42L
Water distribution in a 70kg male: intracellular fluid
40% of total
28L
Water distribution in a 70kg male: Extracellular fluid
20% of total
14L
Water distribution in a 70kg male: intravascular
3L
Water distribution in a 70kg male: Interstitial
11L
Extracellular fluid
• sodium is main contributor to osmolality and volume
• Anions = chloride and bicarbonate
• Glucose and urea
• Protein- colloid osmotic pressure (oncotic) eg albumin
Intracellular fluid
surrounds the cells but does not circulate
• predominant cation is potassium
Water intake
Drink
Diet
IV fluid
Water loss
Kidneys
Sweat
Breath
Vomiting
Faeces
Plasma osmolality
• largely determined by sodium and associated anions
• Estimated plasma osmolality= 2[Na] + 2[K] + urea + glucose mmol/L
• Intra- and extracellular osmolality are equal (isotonic)
• Change in plasma osmolality pulls or pushes water across cell membranes
How to estimate plasma osmolality
2[Na] + 2[K] + urea + glucose mmol/L
Why don’t we give water IV
it is hypo-osmolar/hypotonic vs cells
• Water enters blood cells causing them to expand an burst : haemolysis
• However, this only occurs in vicinity of the IV cannula
Extracellular fluid osmolality
very tightly regulates, changes lead to a rapid response.
Normal plasma osmolality 275-295 mmol/kg
Water deprivation or loss will led to a chain of events
Extracellular fluid volume
changes causes a slower response
Factors controlled by water homeostasis
ECF osmolality
ECF volume
Factors in calculated Osmolarity
• Na+
• K+
• urea
• glucose concentrations.
Dehydration causes…
- Movements of ICF to ECF
- Stimulation of thirst centre in hypothalamus
- Release of ADH from pituitary glands —>renal water retention
Causes of hypernatremia (water depletion)
• reduced intake
• Sweating
• Vomiting/diarrhoea/ diuretics/ diuresis
• drugs
• Sodium excess: mineralocorticoid (aldosterone) excess, salt poisoning
Symptoms of dehydration
Symptoms of dehydration:
• Thirst
• Dry mouth
• Inelastic skin
• Sunken eyes
• Raised haematocrit (proportion of blood made up of erythrocytes- less plasma)
• Weight loss
• Confusion – brain cells
• Hypotension
How much water is lost as a result of fever
Loose 500ml of water a day for every degree above 37
Where is ADH synthesised
Synthesised by the supraoptic and paraventricular nuclei of the hypothalamus.
Where is ADH stored
Posterior pituitary gland
What detects a low renal perfusion pressure due to low ECF volume
Juxtaglomerular in kidney
Renin-angiotensin-aldosterone system
Releases renin (kidney)
Renin cleaves angiotensinogen (liver) to form angiotensin I
Then cleaved by ACE (lungs) to form angiotensin II
Which enzyme cleaves angiotensinogen to form angiotensin I
Renin
Which enzyme cleaves angiotensin I to form angiotensin II
ACE
Where is renin produced
Kidney
Where is angiotensinogen produced
Liver
Where is ACE produced
Lungs