1.1 Homeostasis Flashcards
What is homeostasis?
Ability of a living organism, cell, or tissue to keep the conditons inside it the same despite any changes in the conditions around it or maintaining a state of internal balance.
What percentage of water is in a standard 70kg man?
60% water
So 42L
2/3 Intracellular water: 28L
1/3 Extracellular water: 14L
3/4 interstitial fluid: 10.5L (+0.5L transmembrane water)
1/4 plasma: 3L (+2L red blood cells)
5L of blood.
State the body compartments where fluid accumalates.
ankles, legs, feet, abdomen.
Compare and contrast the water balance in males and females, including in early life and for older populations.
Infants have the highest total body water.
Males have more total body water than females.
Lean people have more water than average sized people.
Outline the physiological differences between dehydration and water toxicity, and the subsequent effect on osmality.
2.5L of water needed each day for a healthy adult.
Have to maintain a water balance - intake = output.
Dehydration:
- cells, tissue & organ death.
- initally absorb water from interstitial space, before absorbing from other cells.
- water absorbed from brain/liver etc as organs fail.
Too much:
- toxicity, leading to metabolic failure, cell, tissue & organ death.
- osmotic presssure high (large pressure from all the water), so cells swell and burst.
Explain the concepts behind positive and negative feedback loops.
Stimulus –> Sensor –> Control Centre –> Effector
Negative - returns back to the optimum.
Postiive - reinforces the deviation from the optimum.
Explain the importance of the acid-base balance for normal human physiology.
Very narrow range (7.35-7.45), so acid-base balance has to be tightly controlled.
Tissues are limited to 6.8-7.8.
Death is likely outside of these limits, despite only a small change in H+ ions.
State the normal range for core body temperature.
37
36.5 - 37.5
Recall the mechanisms (in broad terms) that regulate pH.
Metabolic & respiratory acidosis/alkosis.
Breathing rate increases, removing CO2, so pH falls.
More bicarbonate buffer is produced, to increase pH.
Recall the mechanisms (in broad terms) that regulate core body temperature.
Stimulus (temperature) –> Sensor (Skin, hypothalamus) –> control centre (hypothalamus) –> effector (muscles, blood vessels, hair, fat, sweat glands).
Too hot:
- vasodilation
- sweating
- pilorelaxation (hairs sit flat)
- stretching out (increases SA)
Too cold:
- vasoconstriction
- shivering
- piloerection (hairs stand up)
- curling up (reduces SA)
This mechanism is less effective in young/older people. High SA:V with kids and receptors/arterioles less receptive in
Fun fact: pyrogens cause the temperature to increase during infection, so the body uses shivering (rigors when hot) to reach the higher temperature.
Describe the process of oedema.
Hydrostatic pressure: pressure exerted by fluid on the vessel wall.
Osmotic pressure = force applied by solute to prevent osmotic movement across the membrane.
Oncontic pressure = force applied by large molecules (e.g. albumin).
Oedema occurs when:
1. High hydrostatic pressure (hypertension, heart failure, DVT).
2. Decreased oncontic pressure (less albumin –> liver disease, malnutrition or malabsorption, renal disease).
3. Endothelial wall integrity (burns & trauma).
4. Lymphatic damage (affecting interstitial fluid drainage).
What is the difference between osmolarity and osmolality?
Osmolarity: concentration of solution (solute per litre of solution).
Osmolality: concentration of solution (solute particles per kilogram).
Osmolality is used to look at serum osmolality with conc. of sodium, potassium, glucose and urea.
What is tonicity?
A measure of how a solution’s osmotic pressure affects the volume of cells. Compares solution osmolarity with cell osmolarity.
Links to hypotonic solutions (water moves into cells), isotonic (no net change), hypertonic solutions (water moves out of cells).
