Flashcards in Homeostasis Deck (31):
Where does the term 'homeostasis' come from?
Homeo - same
Stasis - standing still
Which parameters need to be maintained constant in the internal environment?
- Conc. of oxygen, carbon dioxide, salt and other electrolytes
- Conc. of nutrients and waste products
- Volume & pressure of body fluid compartments
Why is homeostasis important for enzyme function?
Enyzmes can be denatured by a pH change or too hot/cold temperature - prevents catalytic function.
Why is homeostasis important for energy generation?
Mitochondria require nutrients such as glucose to generate energy:
- extracellular fluid needs to contain right amount of glucose and oxygen
- tissues need correct BP to provide RBCs carrying oxygen
Why is the homeostatic control of water and electrolytes important?
- Too much water in extracellular fluid - cells swell.
- Too little water in extracellular environment - cells shrink.
- Electrolyte balance requires for generation of AP.
What is core temperature?
Temperature at which vital organs (e.g. Brain, heart) are maintained, as opposed to that or peripheral tissues.
What is normal body temperature?
37 C +/- 0.6 C
How is body temperature measured?
- Rectal, oral, auxiliary, tympanic, vaginal, bladder or skin on forehead over temporal artery.
- Produce different temperature results: rectal/vaginal > oral > skin.
How does the body generate heat?
As a byproduct of metabolism:
- Body breaks down food molecules - energy in chemical bonds of food is released - powers body.
- But human body only ~25% efficient so 75% of energy from food released as heat - some allowed to escape body, some conserved to maintain body temperature.
What is responsible for thermoregulation?
Sensors in CNS activate hypothalamus - sends signals to various effectors.
What are the mechanisms used by the body to cool down?
1. Sweating: sweat cools skin as it evaporates
2. Vasodilation: blood vessels under skin widen, increasing blood flow to the surface - heat release through radiation
What are the mechanisms used by the body to warm up?
1. Vasoconstriction: narrowing of blood vessels under the skin, decreasing blood flow - heat retained near warm inner body.
2. Thermogenesis: body muscles, organs and brain produce heat in a variety of ways inc. shivering.
3. Hormonal thermogenesis - thyroid gland releases hormones to increase metabolism.
What are the 4 mechanisms promoting body heat loss?
1. Evaporation of water from skin (sweating) - during intense exercise, body loses 85% of heat through sweating.
2. Radiation. Normal process of heat moving away from body, usually occurs in air temperatures lower than 20 C. 65% body heat loss.
3. Conduction: body conducts heat to whatever skin is in direct contact with. 2% body heat loss.
4. Convection: process of air or water flowing by the skin and carrying away body heat. 10-15% body heat loss.
What is hypothermia?
Body temperature drops below 35%.
Give examples of hypothermia-induced pathologies.
1. Prolonged regional vasoconstriction - acidosis (decreased blood and body tissue pH) - blunts response to catecholamines production.
2. Generalised slowing of heart rate.
3. Depressed respiratory rate and tidal volume - bronchiolar and alveolar oedema.
3. Impaired immune function.
4. Reduced oxygen tension - weakened wound repair: impaired collagen deposition at the wound as scar formation requires hydroxylation of abundant proline and lysine residues to form cross-links between collagen strands.
When is therapeutic hypothermia used?
- Comatose cardiac arrest survivors
- Head injury
- Neonatal encephalopathy
Allows prevention of cerebral reperfusion injury?
What are the main problems associated with the use of therapeutic hypothermia?
What are dangerously high temperature levels?
Temperatures exceeding 41.1 C are generally catastrophic and require immediate aggressive therapy.
What are the pathophysiological effects of hyperthermia at the cellular level?
1) Heat interferes with cellular process - denatures proteins and cellular membranes.
2) Inflammatory cytokines, interleukins and heat shock proteins produced (e.g. HSP-70).
3) Cell apoptosis.
4) Cardiovascular collapse & multi-organ failure.
When would therapeutic hyperthermia be used?
Type of cancer therapy in which body tissue is exposed to high temperatures (up to 45 C).
Why is cool temperature important during sleep?
- Allows better and faster sleep: body naturally cools during sleep, so isn't trying to regulate.
- Sleeping at 15-20C allows release of more melatonin (anti-ageing hormone).
- Sleeping at 19C increases the amount of brown fat - body burns more calories instead of storing them - lower risk of metabolic diseases.
Why are the testicles stored at 2 C less than body temperature?
Spermatogenesis depends on maintenance of lower temperature, e.g. For cell cycle - higher temperatures prevents transition from mitosis to meiosis (inhibits translation of cyclin B1 and p34^cdc2).
What is pyrexia?
Raised body temperature, fever
How is pyrexia triggered?
1) Hypothalamus activated by pyrogens (biochemical substances) from the 'danger' site.
2) Stimulates body to generate and retain more heat.
What are the benefits of pyrexia?
- Support the immune system
- Makes body less favourable as a host for replicating viruses and bacteria
What are the dangers of pyrexia?
- Temperature rising >40.5 C exposes proteins and body fats to direct temperature stressors.
- Prolonged severe fevers can cause:
Why are the elderly particularly at risk of pyrexia?
- Hypothalamus does not work as well - body temp can rise too much - heart problems & confusion.
What is rigor?
- Episode of shaking or exaggerated shivering which can occur with a high fever (extreme reflex response).
- With infection/inflammation, pyrogens "reset" the trigger temperature (at which shivering occurs) so that the body feels cold and shaking occurs to raise the temperature to the new hypothalamic temperature set point.
What is a febrile seizure?
- Seizure occurring in children aged 6 months - 5 years, associated with fever.
- Vast majority are not serious, occurring with common illnesses such as ear infections and colds.
What are antipyretics and how do they act?
- Substances that reduce fever.
- Cause hypothalamus to override a prostaglandin-induced increase in temperature - lower temperature - reduced fever.