1 - Homeostasis & Fluid Balance Flashcards
What is the meaning of the word homeostasis?
Homeo - the same
Stasis - standing still
The process by which cells, tissues and organisms maintain a state of internal balance
Give some examples of different factors that are maintained under homeostasis?
- Oxygen, carbon dioxide, salts etc.
- Nutrients and waste products
- pH, temperature, volume and pressure
What is negative feedback? Give an example.
The output from the effector acts to reduce the stimulus back to baseline
E.g. blood glucose levels
When does a negative feedback loop stop?
When the effector ceases
What is positive feedback? Give an example.
The output of the effector enhances or exaggerates the original stimulus
E.g. regulation of blood clotting, oxytocin release in childbirth
When does a positive feedback loop stop?
When the initiator ceases
What is the core body temperature maintained at?
36.5 to 37.5 degrees
What feedback mechanisms occur in response to hot temperatures?
- Vasodilation - heat radiates from the skin
- Sweating - evaporative cooling
- Pilorelaxation
- Stretching out
What feedback mechanisms occur in response to cold temperatures?
- Vasoconstriction - diverts blood to the deeper tissues
- Shivering - generates heat
- Piloerection - traps air close to the skin
- Curling up
What can influence the body’s set temperature (the temperature it is maintained at)?
- Pyrogens - released by immune cells in response to infection
- Exercise training and heat acclimation
- Biological rhythms
Below what temperature is hypothermia? What are the symptoms?
- Below 36.5 (mild) or below 32 (severe)
- Mild - shivering, fatigue, confusion
- Severe - no shivering, rigid muscles, weak pulse
What happens to the body below 28 degrees?
Appearance of death (no vital signs) but not dead until warm and dead!
At what temperature is a fever? What are the symptoms?
- 5 to 40 degrees
- Pale sweaty skin, cramps
At what temperature does heat stroke occur? What are the symptoms?
40-46 degrees
- Flushed dry skin, hot to the touch, strong bounding pulse
At what temperature does heat exhaustion occur? What are the symptoms?
Above 46 degrees
- Unconsciousness, seizures, confusion, headache, dizziness
What is normal pH in the body?
7.35 - 7.45
What two organs are responsible for regulating pH?
Lungs - respiratory balance
Kidneys - metabolic balance
What are the terms used for:
- high pH?
- low pH?
- High - alkalosis
- Low - acidosis
What is the pH of the stomach acid?
What can happen if the stomach acid enters the oesophagus? What happens if the stomach loses its protection?
1.5 to 3.5
- Oesophagus - oesophagitis
- Stomach - ulceration and perforation
What buffering systems exist in the body?
- Carbonic acid - bicarbonate (blood)
- Sodium phosphate buffering
What is the composition of water in the ICF and ECF?
Within the ECF how is the fluid distributed?
2/3 ICF
1/3 ECF
Within the ECF:
- 80% interstitial fluid
- 20% plasma
What is the total volume of blood?
5 litres
What is hypertonicity?
When there is less water inside the cell (more water outside) - cell shrinks
What is hypotonicity?
When there is more water inside the cell (less water outside) - cell swells
Bulk water flow can occur through ………..
aquaporins
What is osmolality? What is the normal range?
How does it differ from osmolarity?
Number of solute particles per kilogram. 280 - 300 mOsm/kg
Does not depend on temperature and pressure
What is oedema? Why does this occur?
- Fluid retention, commonly peripheral oedema in the ankles
- Occurs when hydrostatic pressure > osmotic pressure
