BODY TEMP
Significance of thermoregulation
Why do we need to regulate internal body temperature?
− Homeostatic mechanisms that keep body temperature within acceptable limits
o Regardless of environmental conditions
− NB = enzymes operate over a relatively narrow temperature range
Factors influencing the body temp:
1. Age
• infants vary according to environment
• In children ↑(0.5°C) than adult
• Old age ↓the body temperature
2. Sex/Gender
• Females ↓than males
3. Diurnal variation
• min values in am
• max values pm
4. Meals
• ↑after meals
5. Exercise
• heat production from skeletal muscles can ↑
6. Menstrual cycle
• ↑during ovulation
7. Sleep
• ↓by 0.5°C
8. Emotions
• body temp↑
MICAELA DE JAGER 1
,FLG 332 Copyright Micaela de Jager
Body temperature range is narrow, within 1 degree
36.°C –37.5 °C
Temp influences metabolic processes:
↑temp : destroys protein Corrected by homeostasis
↓temp : inhibits enzymatic reactions = prevent biochemical process
Body is divided into a warm internal core and a cooler outer shell:
Core T Shell T
temp of deeper tissues temp of skin
o relatively constant o fluctuates substantially
- 36.5 °C–37.5 °C - 20 °C–40 °C
o metabolism works optimum o depends on surroundings
o shell insulates heat within the core
• Various parts of the body are at different T
• The extremities are generally cooler than the rest of the body
• T of scrotum is carefully regulated at 32°C
• Rectal T is representative of temp at core of the body and varies least with changes in environmental T
• Oral T < rectal T (normally 0.5°C ↓)
Affected by: ingestion of hot/cold fluids
gum chewing
smoking
mouth breathing
THERMOREGULATION
Skin plays major role
Maintenance of a constant body T
Balance between heat gain and heat loss in body:
More heat gain than loss = T↑
Less heat gain than loss = T↓
MICAELA DE JAGER 2
,FLG 332 Copyright Micaela de Jager
Temp regulation
Heat gain Heat loss
Gained by: Lost by:
- Radiation and conduction - Radiation, conduction and convection
- Muscular exercise - Vaporization of water in the respiratory
- Assimilation of food passages and on the skin (sweat)
- Thermogenic effect of hormone - Evaporative cooling
- All vital processes that contribute to BMR - Small # are removed in urine and faeces
HEAT GAIN MECHANISMS
Biochemical reactions contribute to body heat production
Ingestion of food ↑heat production – sympathetic discharge ↓during fasting and is ↑by feeding
Skeletal muscle contraction e.g. during exercise
Heat production can be varied by endocrine mechanisms in the absence of food intake or muscular exertion:
a) Epinephrine and NE - produce rapid but short-lived ↑in heat production
b) Thyroid hormones - produce slowly developing but prolonged ↑
Brown fat (infants) – highly metabolic and has a thermogenic function
Metabolism: Major source of internal heat generation
7% increase in metabolic rate ⇒ 0.55°C ↑in body temp
metabolic heat production by muscle contractions
↓body temp ⇒ somatic motor neurons
skeletal muscle contractions (agonist and antagonist muscles)
metabolism in muscles
heat production (↑body T )
degree of stimulation varies with demand
if heat-gain center is extremely active, you begin to shiver
shivering ↑rate of heat generation up to 400%
2. Non-shivering thermogenesis
metabolic heat production by fat
↓body temp ⇒ sympathetic neurons & hormones
metabolism in brown fat
heat production (↑body T )
MICAELA DE JAGER 4
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