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Core Temperature It is the temp. of body structures under the skin and subcutaneous tissue. Skin Temperature It is the temp. of the skin and subcutaneous tissue. Normal Body Temperatures

Body temperture -Normal 37 ºC. (range +/- 0.5) - core temp. - Skin temp (shell temp) is lower than core temp. -Circadian rhythm.(0.5) or diurnal variation: *low (0.5)→during sleep & early morning. * high (0.5)→ during afternoon. -Variable according to site (oral,rectal,skin). *oral temp →37 ºC. * rectal temp is higher by 0.5 ºC. *axillary temp is lower by 0.5ºC.

 1- Diurnal rhythm  2- Age  3- Sex  4- Emotions  5- Daily activities

Estimated range of body "core" temperature in normal people.

Vertebrate animals are divided into:- *Homeothermic:- (warm blooded) animal. Its body temp. regulated to remain constant. *Poikilothermic:- (cold blooded) animal. its body temp. varies with that of the medium.

Heat balance: Heat gain=Heat loss. Heat gain by: -Basic metabolic processes (BMR):- Metabolic activity of all cells. -Food intake :- - especially protein → specific dynamic action (SDA). -Muscular activity (voluntary or involuntary). -voluntary muscular contraction. -shivering(involuntary rhythmic contraction of skeletal muscle) → large amount of heat..

Heat loss by: *Radiation (60%):- -In form of infrared from hot to cold objects not in contact to each. * Conduction (3%) and convection (15%): -Conduction :From hot objects to surrounding objects in- direct contact. - Convection: Heat must be conducted to air and water and then carried away by convection current as wind. *Evaporation of sweating(22%). -As water in perspiration evaporates from the surface of skin,the skin is cooled:

Mechanisms of heat loss from the body.

 1- Thermo receptors.  2- Thermoregulatory center.  3- Effector organ system.

*Thermoregulatory system is composed of Receptors: cold and warm receptors in skin & hypothalamus.. Control center: hypothalamus. It receives impulses from the thermoreceptors and compares it with its set –point, which almost 37°c -if body temp. > set point → stimulation heat losing center → ↑ heat loss &↓ heat production. -if body temp. < set point → stimulation heat promoting center → ↑heat production &↓ heat loss. Effectors: sweat glands, skeletal muscles, blood vessels of skin etc

-The thermoregulatory mechanisms act to: -Increase heat production (gain). -Decrease heat loss.

Increase heat production: -Shivering. -Non shivering thermogenesis (brown fat). -Hunger|(increase appetite). -Increased voluntary muscular activity. -Endocrine :increased Epinephrine(adrenaline) & norepinephrine( noradrenaline) → from adrenal medulla and throxine. Decrease heat loss by: -Cutaneous vasoconstriction. -Curling up -Horripilation (erection of hair as an insulator for cold)

The thermoregulatory mechanisms act to: -Increase heat loss (Vasodilatation). -Decrease heat production (gain). Increase heat loss:- - Cutaneous vasodilation. -Sweating. -Increased respiration. Decrease heat production: -Anorexia (loss of appetite). -Inertia (decreased voluntary activity).

Fever Heat stroke Hypothermia

-Rise in body temperature due to pathological cause. Mechanism (pathogenesis): -Bacterial toxins and inflammatory mediators act on monocytes, macrophages( kupffer cells) to produce cytokines (endogenous pyrogens IL1,6 IFN,TNF). Endogenous pyrogens PG (Prostaglandin) synthesis in hypothalamus raise set point Fever. N.B. IL=Interleukin INF=Interferon TNF=Tissue necrosing factor

Body temperatures under different conditions.