Skin and Temperature Regulation Flashcards
What does homeothermic mean?
Maintains stable internal body temperature regardless of external influence
What is normal core body temperature?
37 +/- 0.5oC
At what temperature do proteins start to denature?
41oC
At what temperature do you lose consciousness?
Below 30oC
What does core body temperature vary with?
- External temp
- Activity
- Circadian rhythm
- Menstrual cycle***
***basal body temperature (BBT) chart.
during ovulation body temperature drops and after 24hrs rises again and stays raised for 6-7 days.
How is core body temperature maintained?
By balancing heat loss and heat gain
What are the different methods that thermal balance is achieved?
Convection
Conduction
Evaporation
Radiation
Heat production
What is evaporation in terms of thermal balance?
****Evaporation is one way- heat loss only****
Respiration and sweating
About 600ml/day at rest
But 4L/hour at extremes and losses 600kcal/L
What is conduction in terms of thermal balance?
Heat transfer direct between touching objects
What is convection in terms of thermal balance?
When a fluid, such as air or a liquid, is heated and then travels away from the source, it carries the thermal energy along.
****Important in blood too*****
How is body temperature detected?
Cold and warm thermoreceptors
What are thermoreceptors divided into?
- Peripheral thermoreceptors
- Located in the skin, especially in face and scrotum
- Central thermoreceptors
- Located in spinal cord, abdominal organs and hypothalamus
Where are peripheral thermoreceptors located?
Skin, especially in face and scrotum
Where are central thermoreceptors located?
Spinal cord, abdominal organs and hypothalamus
How does an increases in temperature impact a warm receptor, and a decrease in temperature impact a cold receptor?
when temperature is raised, the warm thermoceptors increase their action potential firing and then settle in a new higher rate action potential, while the cold thermoceptors first stop firing their action potential and then settle on a new slower rate of action potential.
Where do peripheral and central thermoreceptors feed their sensory information into?
Hypothalamic thermoregulatory centre
What do peripheral receptors detect?
Change in environmental temperature
What do central receptors detect?
Change in core body temperature
What are different ways that heat is generated within the body in response to cold stress?
by increasing the fellowing:
- General metabolism
- Oxidative phosphorylation and other chemical reactions are not 100% efficient
- Voluntary muscular activity
- “Futile” muscular activity
- Shivering thermogenesis
- Involuntary muscular activity
- Nonshivering thermogenesis
- In humans is only significant in infants, due to brown adipose tissue
How is heat loss from the body reduced?
- Vasomotor control
- Sympathetic arteriolar constriction reduces delivery of blood to the skin
- Behavioural responses
- Reducing surface area, adding clothing, moving to warmer environment
How does vasomotor control reduce heat loss?
- Sympathetic arteriolar constriction reduces delivery of blood to the skin
What are some illnesses caused by cold stress?
- Hypothermia
- Frost bite
When does hypothermia occur?
when deep body temperature is below 35
Who is most at risk of hypothermia?
- Neonates
- Big SA:volume, not much fat, don’t shiver well, but do have brown adipose tissue (BAT)
- Elderly
- Do not detect temperature change so well, less shivering capacity, more immobile
- Vagrants
- Cold store workers
- Outdoor pursuits
- North sea workers
Why are neonates at risk of hypothermia?
- Big SA:volume, not much fat, don’t shiver well, but do have brown adipose tissue (BAT)
What does BAT stand for?
Brown adipose tissue
Why are the elderly at risk of hypothermia?
- Do not detect temperature change so well, less shivering capacity, more immobile
What is the treatment of hypothermia?
- insulation to prevent further heat loss
- Slow re-warming with bag/blankets
- Fast re-warming by immersion in water, extracorporeal circulation
- Internal re-warming with hot drinks and/or warm air
What is frostbite?
Injury caused by freezing of the skin and underlying tissues
What are the two changes that occur in Forst bit which causes tissue death?
Vascular changes: Vasoconstriction and Increased viscosity ( thickness of blood) due to cold blood causes thrombosis and anoxia (an absence of oxygen).
Cellular changes: extreme cold cause ice crystals to form in the extracellular space. This increases extracellular osmolarity, which causes movement of water from intracellular space leading to Cell death and dehydration
What is the percentage of excess deaths in winter due to cold stress?
40% excess in UK
Why does mortality due cold stress increases in the winter?
- Partially due to an increase in heart attacks and strokes caused by an increased vasoconstriction and increased blood viscosity due to the cold weather.
How the body reduce heat production in response to heat stress?
- By decreasing physical activity
- By decreasing food intake
How the body increases heat loss in response to heat stress?
-
Vasomotor control
- Arteriolar dilation increases delivery of blood to the skin
-
Sweating
- increases evaporation and heat loss
-
Behavioural responses
- Increasing surface area, removing clothing, moving to shaded area
What are some illnesses due to heat stress?
- Heat exhaustion (heat illness) Body temperture is between 37.5 - 40 C
- Heat stroke (heat injury) Body temperture is above 40 C
Which age group is at risk of heat stress?
- Neonates
- Elderly
- People doing physical work in hot humid environments
- Workers wearing non-breathable protective clothing
What is the treatment for heat stress?
Move to cool environment, Remove clothing, Fan, Give fluids (oral, IV)
When does heat exhaustion and heat stroke occur?
- Heat exhaustion: occurs when Body temperature is between 37.5-40 C
- Heat Stroke: occurs when body temperture is above 40 C
What are the clinical presentations of heat exhaustion?
- Headache
- Confusion
- Tachycardia
- Hypotension
- Fainting and collapse
What causes heat stroke?
Body’s temperature control mechanism fails
What is the clinical presentation of heat stroke?
- Hot dry skin (sweating ceased)
- Circulatory collapse due to the lack of central blood flow.
What is a fever? What produce fever?
- Is the body’s mechanism for fighting infection, because some pathogens don’t survive in high tempertures.
- Caused by endogenous pyrogens interleukin-1 and Interleukin-6 (IL-1, IL-6) which are produced by the immune cells.
Explain the concept of ‘set point’ controlled by hypothalamus?
- Interleukin-1 and interleukin-6 controlle the the “set point” of the hypothalamus. When infection is detected in the body by the immune cells, immune cells release IL-1 and IL-6. In the hypothalamus prostaglandins is produced by cyclo-oxygenase which h shifts or changes the “set point” of the Hypothalamus to high (i.e 40C)t
- Aspirin and Paracetamol inhibit cyclo-oxygenase which explains why aspirin and paracetamol reduce fever.
Are fevers beneficial?
- Mild fever is beneficial, sever fever is dangerous
