L1) Homeostasis, pH, core body temperature any body fluids ✔ Flashcards
what is homeostasis?
homeo = sameness
stasis = standing still
phsiological process of maintaining the internal environment of the body in a state of dynamic equilibrium
what needs to be maintained constant in the internal environment?
temperature
pH
water
what technique does the body use to maintain homeostasis?
feedback loops
negative and positive
what does a feedback loop consist of?
stimulus
sensor
control centre
effector
what is a negative feedback?
when the effector ceases
what is a positive feedback?
when the stimulus ceases
what is an example of negative feedback?
regulation of blood glucose
what is an example of a positive feedback?
regulation of blood clotting
birth
what is the core body temperature?
37 ± 0.5 degrees celsius
but this fluctuates throughout day = circadian rhythm
how do we measure temperature?
infra-red skin thermometer
tympanic thermometer
temporal film
oral/rectal/axillary thermometer
traditional (mercury)
what is the body response to being too hot?
vasodilation
sweating
pilorelaxation
stretching out (large SA)
how does vasodilation help heat loss?
arterioles dilate
allows more blood to enter the skin capillaries
heat is lost
how does sweating help heat loss?
sudorific glands secrete sweat
removes heat
when water changes state
what is the body response to being too cold?
vasoconstriction
shivering
piloerection
curling up (small SA)
how does vasoconstriction help maintain heat?
arterioles get smaller
reduce blood going to skin
keeps core temp warm
how does shivering help maintain heat?
rapid contraction & relaxation of the skeletal muscles
heat produced by respiration
Briefly describe an overview of temperature control in the body
stimulus: low/high temperature
sensor: skin, hypothalamus
control centre: hypothalamus
effector: muscles, blood vessels, hairs on the skin, fat, sweat glands
what is the normal plasma pH?
7.35-7.45
what are the two major organs responsible for maintaining acid base balance?
lungs - respiratory balance
kidneys - metabolic balance
what is the gastric pH?
1.5-3.5
what are the limits of human tissue survival?
6.8-7.8
how do we measure for plasma pH?
Arteriole blood gases
what are the two extremes of pH trouble?
acidosis (pH<7.35)
alkalosis (pH>7.45
what are the body’s buffering systems?
for blood pH: bicarbonate buffering system
for intracellular pH: sodium phosphate buffering system
additional : calcium (alkali)
all systems also regulate water levels in cells due to presence of ions
briefly describe the blood pH buffering system
uses erythrocyte as an intermediate
carbonic anhydrase in RBC converts the CO2 into carbonic acid (H2O + CO2 ⇆ H2CO3)
this carbonic acid travels to the lungs where it dissociates into CO2 + H2O)
How do antacids work?
weak basic alkali salts
neutralise the acidic pH by binding to free H+ ions
and cannot dissociate back into acid (passed through the rectum)
what is a clinically relevant antacid?
aluminium hydroxide
preferred as insoluble
hence it is milder, long acting and fewer side effects
why do we need fluid balance?
not enough - dehydration and cell, tissue and organism death
too much - toxicity, metabolic failure and cell tissue, organism death
how much fluid is needed each day to maintain a healthy adult?
2.5L
briefly describe the distribution of water in the body of a 70kg man
of total body mass: 60% is fluids
of fluids: 2/3 is Intracellular & 1/3 is Extracellular
of extracellular: 3/4 is Interstitial & 1/4 is plasma
How does total body water (TBW) differentiate between different patient groups?
the higher the percentage of body fat, the lower the percentage of TBW
hence, different ECF, ICF, plasma and blood volumes
what is the order of TBW (most to least)?
Infants, Males, Females
what are the three different types of tonicity?
isotonic
hypotonic
hypertonic
what does isotonic mean?
same amount of water on both sides of the plasma membrane
solute conc. is same on both sides
what does hypotonic mean?
more water outside cell
solute conc. higher inside cell
(hypo indicates condition inside cell)
what does hypertonic mean?
less water outside the cell
solute conc. is lower in cell
(hyper indicates condition inside cell)
what is osmosis?
movement of water downiest concentration gradient by diffusion
what is osmolality?
concentration of a solution
the total number of solute particles per kilogram
expressed in milliOsmoles → most/kg
How does osmolality differ for solutes that ionise?
solutes that ionise can dissociate into independently active solutes (NaCl → Na+ and Cl-)
hence, each milliosmole in solution would provide 2 mOsm
what happens if there is not enough water?
initially, cells and tissues absorb water from the interstitial space
then from neighbouring cells (cell sacrifice)
then as tissues die, water absorbed from organs
then as organs die, water absorbed from brain, liver, kidney and heart
briefly describe bulk water flow
presence of aquaporin exist on different sides of cells
different aquaporin isoforms have different affinities for water (slow/fast)
this allows for discrete water flow
what is bulk water flow regulated by?
amount of glycerol in cell
what is oedema?
fluid retention
‘dropsy’
what causes oedema?
hydrostatic pressure > osmotic pressure
what is hydrostatic pressure?
force exerted by the fluid on the vessel wall
what is osmotic pressure?
force applied by the solute/colloid to prevent osmotic movement across the membrane
colloid osmotic pressure = oncotic pressure
how is the osmotic pressure measured?
measured from the number (concentration) of solute molecules present in a solution
what is peripheral oedema?
retention of fluids in the peripheries - i.e. ankles
how does oedema occur?
oedema occurs when the lymphatics get blocked or damaged and fluid retains in the interstitial fluid
