Body Fluid Compartments Flashcards
name the percentages of water gain
- Food 30%
- drink 60%
- Metabolism 10%
name the percentage of water losses
- Urine 60%
- Faeces 4%
- Insensible losses 28%
- sweat 8%
what is insensible losses of water
through SKIN Transepidermal diffusion & Lungs breath water
what is rate of fluid movement in the digestive system
- ingested water (2 liters)
- liver and pancreatic secretions ( 2 liters)
- salivary gland secretions (1.5 liters)
- secretions by glands of the stomach and small intestines (3.5 liters).
- Small intestines absorbs ~ 8.5 liters
- Colon (400ml)
- feces (100 ml)
what is the total body fluid
- total body fluid 42L which is 60% of body weigh
what is the total intracellular fluid
- intracellular fluid 28L (40%) (in the cell
what is the total extracellular fluid
- extracellular fluid 14L is (20%) (surrounds the cell)
what does extracellular fluid split into
- plasma
- interstitial fluid
- other ECF
how much does plasma make up of extracellular fluid
- plasma 3L
how much does interstitial fluid make up of extracellular fluid
- interstitial fluid is10.5L
what is the other extracellular fluid
- Other ECF is 0.5L this is lymph cerebrospinal fluid, eye humours, synovial fluid, serous fluid and GI secretions
what is serous fluid made up of
- Serous fluid is peritoneal fluid and pleural fluid
what ions are in intracellular fluid
- potassium and phosphate and protein anions is high
- sodium and chloride and bicarbonate is low
what ions are in extracellular fluid
sodium, chloride and bicarbonate is high
- potassium is little
what is water
- it is a universal solvent
what dissolves in water and why
- More substances dissolve in water than in any other chemical, this is to do with the polarity of water molecules
what are the major solutes that are contributing to osmolarity
- sodium
- chloride
- glucose
- urea
how does penicillin use osmosis
- pencilling creates a semi permeable membrane
- this prevents bacteria from forming a wall therefore they cannot sustain osmosis, this means that water enters the bacteria and the bacteria just explodes
describe osmotic diarrhoea
- this happens if glucose is not absorbed in the right place
what are solutes
- these are molecules in solutions
what are the 2 classification of solutes
electrolytes
non electrolytes
what are electrolytes
inorganic salts (ie: Na+, K+, Cl-) , all acids and bases and some proteins
what are non electrolytes
examples include glucose, lipids, creatinine, and urea
out of electrolytes and non electrolytes what has the greater osmotic power
Electrolytes – these have greater osmotic power than non electrolytes therefore electrolytes have the greater power to shift fluids
what is osmotic pressure
the process that controls the movement of solvents (water) across a membrane.
- Movement will occur when there are differences in osmotic pressure across a membrane.
what side does water move towards
- water migrates towards the side containing a more concentrated solute
define osmolarity
the measure of solute concentration expressed as the number of osmoles (Osm) of solute per litre (L) of solution = Osm/L or mOsm/L.
define osmolality
is the measure of the osmoles (Osm) of solute per kilogram (Kg) of solvent = Osm/Kg or mOsm/Kg.
what is used osmolality or osmolarity
osmolality
why is it better to use omsmolaltiy
- Kg does not change with temperature or pressure as much as a volume would
- Osmolality is per unit mass: not affected by changes in temperature or pressure
- Osmolality is used in preference. However, at low concentrations very little difference in values.
- Osmolality is used in clinical laboratories to assess electrolyte and acid base disorders
what is the normal range for plasma osmolality
- This is about 280-300 mOsm/Kg
what is the membrane between the interstitial fluid and intracellular fluid
plasma membrane
what is the membrane between the interstitial fluid and the plasma
capillary wall
what is the membrane between the plasma and the changing environment
kidney
skin
lungs
gut epithelium
what controls the balance between the plasma and interstitial fluid
- The balance between plasma and interstitial fluid is controlled by hydrostatic pressure(comes from the heart) and osmotic pressure (comes from protein that is made in the liver)
what is the major solute within the body
sodium
How does sodium influence water
- In the extracellular fluid mainly – it creates a pull on the water towards the blood vessels
- Sodium is the predominant extracellular cation and is a major determinant of plasma and ECF osmolality
- Where sodium goes water follows
what happens if plasma and ECF sodium are in equilibrium
- if plasma volume is regulated then ECF volume will follow
what happens if both plasma volume and osmolality are regulated
- this means then both total water and total sodium will be regulated
how is the water system regulated
- CNS
- Hormones
- Kidneys
what parts in the brain allow for linkage between CNS and peripheral blood flow
- Subfornical organ
- Organum vasculosum of lamina terminalis
- These structures in the brain are characterized by extensive vasculature and lack of a normal blood brain barrier (BBB).
- They allow for the linkage between the central nervous system and peripheral blood flow
How does the CNS help control water
- Increase in plasma osmolality – means there is a lot of solute but not enough water
- This triggers a dropin saliva and produces a dry mouth this is relayed to the hypothalamic thirst centre
- This is also relayed to the hypothalamic thirst centre by osmoreceptors in the hypothalamus
- Therefore, the person takes a drink
- Water moistens mouth, throat, stretches stomach, intestine
- Water is absorbed from the GI tract
- This decreases plasma osmolarity
- Or
- Plasma volume decreases
- This decreases blood pressure
- This triggers renin angiotensin mechanism
- Produces angiotensin II
- And ADH
what is the main stimulus for thirst sensation
- an increase in plasma osmolality
what percentages are needed to stimulate thirst sensation
- An increase in plasma osmolality of 1% - 2% (about 3 to 6 mOsm/Kg) or a decrease in plasma volume of 10% - 15% is required to stimulate the thirst sensation
where is the thirst centre located and what is it monitored by
- The thirst centre is located in the anterior hypothalamus & monitored by osmoreceptor. It relays impulses to the cerebral cortex making thirst a conscious sensation.
how is plasma volume regulated by the CNS
- Baroreceptors relayed to the hypothalamus
- Go to osmoreceptors
- Project into the pituitary gland
- Releases ADH from the posterior lobe of the pituitary
what is the effect of ADH on urine production
- Low ADH levels produce dilute urine and reduced volume of body fluids
- High ADH levels produce concentrated urine
water reabsorbed in the collecting duct is..
proportional to ADH release
what are factors that can trigger ADH release
- prolonged fever
- excessive sweating
- vomititng
- diarrhoea
- severe blood loss
- traumatic burns
what are the cellular targets of ADH
aquaporins
what is the hormonal regulation of plasma osmolarity
- aldosterone
how does hormonal regulation of plasma osmolarity take place
eleased from the adrenal cortex when there is reduced sodium or increased potassium
- Antiporter of sodium and potassium – go opposite directions to each other
- This is related to adrenal cortex
- Releases aldosterone
- Increases sodium absorption and potassium excretion
- Therefore water follows sodium
what does aldosterone do to the cell
- Binds to the cell
- Effects transcription
- Says we need to make sodium potassium ATPase
- Produces sodium channel as well
what is the hormonal regulation of high plasma volume
ANP
How does ANP work
- Released from the cardiac atria when – there is increased blood volume (this stretches the atria)
- This produces effects which bring blood volume back towards normal including increased sodium excretion
- There is increased juxtaglomerular apparatus
what are the 4 hormones that regulate osmolality and volume and what do they do
- Antidiuretic hormone (ADH) or vasopressin makes cells of collecting duct & distal tubule permeable to water.
- Angiotensin II and Aldosterone promote the urinary reabsorption of Na+ and Cl- (as well as water, by osmosis) when dehydrated.
- Atrial natriuretic peptide (ANP) promote excretion of Na+ and Cl- followed by water excretion to decrease blood volume.
how much water is reabsorbed in the proximal tubule
- 80% of the water is reabsorbed in the proximal tubule – this is through active reabsorption of solutes
what is variable reabsorption
- Variable reabsorption (collecting duct)– depending on individual water balance and status (aldosterone and ADH level) this is where the aquaporins are
- This is depending on relative presence or absence of aqauporins and Na+/H+ pumps in the kidneys (related to ADH/aldosterone levels)
what is the normal value for urine osmolarity
• 24 hour urine osmolality should average between 500
and 800 mOsm/Kg
• Random urine osmolality should be 50 to 1400 mOsm/Kg
• After 12-14 hours of fluid intake restriction, urine osmolality should be greater than 800mOsm/Kg= Base for water deprivation test
what are failures of body fluid balance
dehydration
water intoxication
oedema
when does dehydration happen
If the water intake is insufficient to cover water loss over a long period of time, water is lost from the plasma and the ISF. This can lead to weight loss, fever and confusion.
what is water intoxication
- this is when too much water is drunk too fast or complete blockage of urine production this leads to dilation of the body fluids
how does water intoxication lead to death
- the sodium in ECF is reduced
- this causes osmotic shift of water into the cell
- this leads to cell swelling
- this is dangerous in the brain where swelling can cause convulsions, coma and death
what are the 4 causes of oedema
- increased capillary hydrostatic pressure
- loss of plasma proteins - due to severe malnutrition
- obstruction to lymphatic system
- increased capillary permeability
