Physiology of skin

1. Systemic Physiology
The Skin and Thermoregulation

2. Mechanisms of body temperature
regulation
 The core temperature stays constant in spite variations in heat production
and changes in environmental temperature.
 The body temperature has physiological diurnal rhythm being highest in the
afternoon and lowest in early morning, however it stays between 1-2 ⁰C
throughout the day.
 The maintenance of bodily temperature is mediated mainly by the
hypothalamus ( anterior → heat, posterior → cold).
 Sensory receptors come either:
 central thermoreceptors: monitoring blood temperature
 skin thermoreceptors: changes in temperature of environment

3. Neuronal mechanisms
 Neural mechanisms which control heat production depend on
integrated signals form central and peripheral thermoreceptors.
 Effects of exposure to heat:
1. Vasodilation of skin blood vessels. This dilation is caused by
inhibition of the sympathetic centers in the posterior hypothalamus
that cause vasoconstriction. Full vasodilation can increase the rate
of heat transfer to the skin as much as eightfold
2. Sweating. An additional 1°C increase in body temperature
causes enough sweating to remove 10 times the basal rate of body
heat production.
3. Decrease in heat production. Th mechanisms that cause excess
heat production, such as shivering and chemical thermogenesis, are
strongly inhibited.

4.  Effects of exposure to cold:
1. vasoconstriction throughout the body. This vasoconstriction is
caused by stimulation of the posterior hypothalamic sympathetic
centers.
2. shivering:
 Heat gain by increasing tension of skeletal muscles, by somatic
nerves
 Initiated by posterior hypothalamus. Starts at 25 ⁰C.
 The rigors of fiver is due to intense cutaneous vasoconstriction
with rapid fall of skin temperature.
3. Non-shivering thermogenesis: by the brown fat of children.

5. 4. Hormonal and chemical mechanisms
 Adrenergic stimulation results in release adrenaline setting of
profound calorinergic effect through uncoupling of oxidative
phosphorylation
 Sympatethic stimulation is responsible for the non-shivering
thermogenesis.
 Thyroid function increases slowly on prolonged exposure increasing
BMR, but this mechanism is uncertain in humans.

6. Adaptation
 Long term exposure to heat and cold causes variety of changes
which leads to more efficient maintenance of the thermal
balance under extreme environmentel conditions.
 Adaptation is by means of clothing or by means of behavioral
patterns.
Acclimatization to heat:
 Getting used to changes in thermal conditions.
 Main feature is by increase in sweating.
 The concentration of NaCl depends on the rate of sweating.
 In hot humid areas, convention becomes more important.

7. Acclimatization to cold
 In animals there’s an increase in TRH, but in humans this is unclear.
 However BMR increases in individuals exposed to cold.
 There is also increase in CRH stimulating ACTH release thus cortisol.
 And by behavioral patterns like avoiding cool surroundings.

8. Abnormalities of thermal regulation
I. Disturbance due to heat
 This can be caused by excessive exposure to hot
environment at work or any muscular activity.
 This results in heat load beyond the capacity of heat
losing mechanisms.
 Exposure to such heat leads to variety of heat syndromes;
broadly classified as heat stroke and heat exhaustion.

9. 1. Heat stroke:
 May be brought by failure to sweating or by inadequate sweat response.
 The symptoms include dizziness; abdominal distress sometimes accompanied
by vomiting; sometimes delirium; and eventually loss of consciousness if the
body temperature is not soon decreased, and exacerbated by circulatory
shock.
 Hyperpyrexia is also exceedingly damaging to the body tissues, especially the
brain.
 Also certain pyrogens lead to failure in sweating e.g in malaria.
 Insufficiency to heat response is seen in some cases of heat stroke.

10. 2. Heat exhaustion
 This can be caused by: circulatory deficiency, dehydration and salt
deficiency ( most prominent ).
 the patient feels giddy with head ache and may faint, nausea and
vomiting, low blood pressure and high HR.
 Some patients may proceed to exertional heatstroke (EHS).
3. Heat syncope
4. Dehydration
5. Salt deficiency

11. II. Disturbance due to cold
1. Hypothermia:
 It’s clinically defined as drop of body temperature to 35 ⁰C or
less.
 The dangers of hypothermia is much less than heat stroke.
 The elderly and newborn are particularly prone to suffer from
it.
 Hypothermia causes mental confusion and visual hallucinations,
and skeletal muscle weakness.
 At 33 ⁰C or below shivering ceases, and at 30 ⁰C consciousness is
lost.

12. 2. Cold injury:
 Freezing extremities (ear lobes,
fingers and toes) occurs below
zero, this is due to high salt in
cell.
 This is know as frostbite; fall in
vasomotor control of
extremities.

13. III. Fever
 Elevation of core body temperature by 1-4 ⁰C due to infection.
 It may be fast or slow, intermittent or continuous.
 If the rise of temperature is rapid, a sensation of cold or chill is experienced.
And actual rigors and shivering may occur.
 Both peripheral and central thermoreceptors contribute to rigors.
 The mechanism of fever production is associated with pyrogens which are
either; exogenous (LPS) or endogenous (IL-1, PGE2 )