2. For humans, core temperature is
maintained at approximately 37°C (98–99°F).
skin plays a decisive role as both radiator
and insulator.
a temperature control center in the preoptic area
and anterior nucleus of the hypothalamus serves as
Neural thermo sensory impulse that arise in the skin.
3. Temperature regulation by the skin is
effected primarily through :
evaporative cooling after eccrine
sweating .
Cutaneous vascular supply.
4. Cutaneous vascular supply
constriction and dilatation of the cutaneous blood
Vessels will increase or decrease the blood flow at the
Periphery of the body leading to modify the thermal
Gradient to the environment depending upon the need
Is to conserve or loss heat.
5. Three main vascular plexuses:
1. First plexuses:
• Situated toward the base of the reticular dermis.
• consist of large, thick, walled arteries.
• each of which is closely associated with one or
Two veins.
• branches from this plexus link with the second
Plexus.
6. 2. Second plexuses:
• Situated at about the level of sebaceous glands.
• The hair follicles and sweat glands are supplied
Mainly by branches from this plexuses.
3. Third plexuses:
• Most superficial.
• Consist of capillaries which supply the epidermis.
The supply of palms, soles and nose via dermal
Papillae.
7. The close association between cutaneous arterioles and
Venules enables the body to operate a system of
Counter current heat exchange
When heat conservation is required in cold environment,
Vasoconstriction of venules occurs to reduce blood flow to the
Surface of skin.
On the other hand, blood directed to the deeper dilated
Venules accompanying the arterioles.
Thus the warm blood from the heart is partially cooled by adjacent
Venous blood in the opposite direction before reaching the skin
Surface.
8. Its thermal effect are most evident in the limbs and body extremities
Like ear which have numerous specialized
arteriovenous anastamoses
•Between dermal arterioles and venules.
• have a thick muscular wall .
• richly innervated by sympathetic system.
• capable of rabidly altering the blood flow to the skin surface.
• shunt blood to the superficial Venous plexuses.
9. 1. In hot environment:
• the deeper venules constrict and the peripheral vessels dilate.
• much of the blood passes close to the surface on its way throgh
The skin.
2. In warm condition:
• the arteriovenous anastamoses will remain open.
• Also large blood volumes reach the skin surface through dilated
capillaries to provide blood for heat loss.
10. Tissue damage by freezing and hypoxia is prevented by periodic
Reflex vasodilatation known as “ HUNTING REACTION” .
3. in cold conditions:
• the arteriovenous anastamoses reduce peripheral cooling
since They open reflexly when peripheral vessels contract
leading to lower Blood vessels flow to the surface.
11. Control of cutaneous blood flow
action of neural, physical and chemical stimuli on
Smooth muscle cells in the wall of arterial vessels.
under thermo neutral conditions, the arterioles
Are in partial constriction.
the basal tone of cutaneous vessels is dependent
On the action of vasoconstriction fibers by sympathetic
Nervous system.
12. vasoconstriction is induced also by:
1. increased transmural pressure.
2. hormonal effects by adrenalin and angiotensni.
vasodilatation is induced by:
1. local effects (histamine, bradykinin).
2. sympathetic nerve fibers with an active vasodilator action.
13. Eccrine sweat glands
the production of sweat cools the skin through evaporation.
minimum secretion per day is 0.5 L and maximum is 5_7 L.
maximum output is 2L/h.
Distributed over the entire cutaneous surface
(with the exception of the external auditory canals,
vermilion lips, clitoris and labia minora).
the glands on palm, soles, axillae and forehead respond
Mainly to emotional stimuli.
14. Composed of three sections:
o Acrosyringium :
intraepidermal spiral duct opening to surface of skin.
o Straight duct :
within dermis and consisting of double layer cuboidal
epithelium lined by eosinophilic cuticle on luminal side.
o Secretory eccrine coil :
within deep dermis/subcutaneous fat and consists of
two different cells which appear to fit together in one layer,
outer portion contains myoepithelial cells.
15. The secretory coils cell types:
(1) Large glycogen contaning pale or clear cells responsible
for the gland’s secretion of sweat.
(2) small mucopolysaccharide contaning dark cells,
of unknown function, with basophilic granules that are
thought to produce sialomucin.
16. The secretory coils cell types:
(1) Large glycogen contaning pale or clear cells.
(2) small mucopolysaccharide contaning dark cells with
basophilic.
17. Sweat production
its mainly produced by the pale clear cells of secretory portion
Of the eccrine gland.
energy requirements:
• numerous mitochondria.
• particles of glycogen.
intercellular canaliculi lined by micro villi serve as transporter for
Solution to the lumen of secretory coil.
the dark cells:
• contains granules the secrete mucoposacchrides the form the
Eosinophillic cuticle that lines the Lumina which facilitate the
reabsorption Of NA, K, HCO3 and others.
18. Sweat composition
watery isotonic sweat is modified in the excretory portion
Of the ducts so the fluid delivered to the skin surface:
• PH (4_6.8) hypotonic
• Na and Cl (30_70 mEq/l)
• K( up 5mEq/l)
• lactate (40_40 mEq/l)
•Urea
19. Sweat Production stimulation
predominant innervation through unmylinated cholinergic
Class C nerve fibers of sympathetic nervous system. Few
Unmyelinated adrenergic nerves also present.
in response to cholinergic stimuli is 5 times the adrenergic
stimuli.
other chemical stimuli: Acetylcholine, calcium, Prostaglandin E1
Epinephrine, norepinephrine and VIP.
thermal, emotional or exercise increases the rate of sweat
secretion.
20. How sweat is produced??
1. the previous mediators act on contra luminal plasma membrane
Of pale cells.
2. Increase there pearmbility and allowing Na, Cl and others to
Diffuse into the cytoplasm.
3. energy requiring Na pump located in canalicular plasma membrane
Of pale cells will transport Na actively into canaliculi followed by
Cl and water. The actual site of transport is intricately folded basolateral
Plasma membrane.
4. Aldosterone act upon the epithelium that lines the duct and stimulate
Na reabsorption in exchange for K.
21. Role of myoepithelium
respond to cholinergic stimuli only.
provide mechanical support for the wall of secretory coil
Against increased luminal hydrostatic pressure.
22. Major function of eccrine sweat
Gland
produce sweat during periods of stress induced by heat.
1L of evaporated sweat remove 585 kcal of heat.
it acts fast to the stress of heat by delivering sweat to the
Surface of the skin.
maximization of sweating response by exercise is mainly
By catecholamine.
23. during prolonged heat stress:
Eccrine glands become ACCLIMATIZED that is acquired
To secret more amounts of sweat at a greater rate in
Response to relatively smaller elevation in body temperature.
• at the same time the adrenal cortex secretes more aldosterone
To prevent excess Na loss from body.
