BODY TEMPERATURE REGULATION AND FEVER

There is no single body temperature because temperature varies from organ to organ. Outer body temperature Outer shell Skin & subcutaneous tissues Central core Core temperature Abdominal ,thoracic organs, CNS &Skeletal muscles

Outer body temperature Outer shell May vary. Fluctuate Central core Core temperature Precise regulation. 98-98.6F when measured orally.

DEPEND UPON BALANCE BETWEEN HEAT PRODUCTION AND HEAT LOSS CONTROL OF BODY TEMPERATURE  DEPEND UPON BALANCE BETWEEN HEAT PRODUCTION AND HEAT LOSS Heat production Heat loss

Heat production depends upon rate of metabolism by; All body cells Thyroxin, GH, testosterone. Epinephrine, norepinephrine and sympathetic stimulation. Increase chemical activity  

How rapidly heat can be conducted from body core to skin. Heat loss How rapidly heat can be conducted from body core to skin. How rapidly heat can be conducted from skin to surrounding.  

How rapidly heat can be conducted from body core to skin. Profuse blood supply beneath skin. Large numbers of vessels are present beneath the skin. These are responsible for increase in rate of blood flow Thus increase rate of conduction from body core to skin. Sympathetic stimulation of arterio-venous anastomosis and arteries This stimulation cause vasoconstriction of all vessels other than that to heart, brain and working muscle. Thus there is decrease in rate of blood flow. Decrease in rate of heat conduction from body core to skin.

2. How rapidly heat can be conducted from skin to surrounding. Radiation /infrared heat rays Conduction Convection Evaporation

Radiation /infrared heat rays (60%) Human body radiates heat in all directions. Heat is also radiated from walls of room and other objects toward body. But if body temperature is more than environment then greater quantity of heat is radiated from body.

Conduction Direct Loss of heat from surface of body to solid objects (chair/bed 3%). Direct loss of heat from body surface to air (15%)

Convection Molecules of skin are in constant vibratory motion. This energy of motion transfer only when air is cooler than skin. When temperature of air =temperature of skin→ no heat loss.

So heated air should continuously move away from skin and new air should bring in contact with skin→ air movement (air convection/air current). In case of wind→ increase air convection→ increase heat loss.

Evaporation (22%) Sweating from skin and loss of water from lungs. When temperature of surrounding is more than skin→ body gain heat by conduction and convection→ now only mean of losing heat is by evaporation.

Local skin temperature reflexes REGULATION OF BODY TEMPERATURE  Behavioral control Local skin temperature reflexes Increase in internal body temperature→ signals from temperature controlling area of brain→ give person a psychic sensation of feeling overheated. Conversely in severe cold→ receptors from skin and deep tissues detect cold→ person make appropriate environmental and cloth adjustment. When a person places foot under a hot lamp for short time→ local vasodilation and local sweating occur. Conversely placing the foot in cold water→ local vasoconstriction and cessation of sweating occur. Role of hypothalamus

REGULATION OF BODY TEMPERATURE ROLE OF HYPOTHALAMUS ROLE OF ANTERIOR HYPOTHALAMUS ROLE OF POSTERIOR HYPOTHALAMUS

ROLE OF ANTERIOR HYPOTHALAMUS   Increase in body temperature Stimulation of pre-optic area of anterior hypothalamus Send nerve impulse to spinal cord through autonomic pathways Inhibition of sympathetic center in posterior hypothalamus that cause vasoconstriction Inhibition of shivering Then through sympathetic outflow to skin Vasodilation of skin blood vessels Release of epinephrine/norepinephrine Increase heat transfer from core to skin Stimulate sweat glands Sweating INCREASE HEAT LOSS

ROLE OF POSTERIOR HYPOTHALAMUS Cold Signal from skin & deep tissues   ROLE OF POSTERIOR HYPOTHALAMUS Cold Signal from skin & deep tissues Decrease in body temperature Stimulation of dorsomedial portion of posterior hypothalamus/primary motor center of hypothalamus Stimulation of sympathetic center in posterior hypothalamus Cooling of ant. hypothalamic pre-optic area Vaso- constricti on of skin blood vessels Arrector pili muscles attached to the hair follicles contract Release of norepinephri ne ↑ TRH from hypothalamus Stimulate brown fat in animals/neo nate which contain large number of mitochondri a Transmit signals through lateral column of spinal cord Decrease heat transfer from body core to skin Upright projection of hairs allows them to trap heat Stimulate release of TSH from anterior pituitary gland Stimulation of anterior motor neurons Increase tissue expression of thermogenin (mitochondri al coupling protein)→↑ heat production Increase muscle tone Stimulate release of thyroxin by thyroid gland →↑ metabolic rate Shivering Increase heat production DECREASE HEAT LOSS

ROLE OF POSTERIOR HYPOTHALAMUS   Decrease in body temperature Stimulation of sympathetic center in posterior hypothalamus Vaso- constriction of skin blood vessels Arrector pili muscles attached to the hair follicles contract Release of norepinephrine Stimulate brown fat in animals/neonate which contain large number of mitochondria Decrease heat transfer from body core to skin Upright projection of hairs allows them to trap heat Increase tissue expression of thermogenin (mitochondrial coupling protein)→↑heat production DECREASE HEAT LOSS

ROLE OF POSTERIOR HYPOTHALAMUS   ROLE OF POSTERIOR HYPOTHALAMUS Cold Signal from skin & deep tissues Decrease in body temperature Stimulation of dorsomedial portion of posterior hypothalamus/primary motor center of hypothalamus Stimulation of sympathetic center in posterior hypothalamus Cooling of ant. hypothalamic pre-optic area Vaso- constricti on of skin blood vessels Arrector pili muscles attached to the hair follicles contract Release of norepinephri ne Stimulate brown fat in animals/neo nate which contain large number of mitochondri a ↑ TRH from hypothalamus Transmit signals through lateral column of spinal cord Decrease heat transfer from body core to skin Upright projection of hairs allows them to trap heat Stimulate release of TSH from anterior pituitary gland Stimulation of anterior motor neurons Increase tissue expression of thermogenin (mitochondri al coupling protein)→↑ heat production Increase muscle tone Stimulate release of thyroxin by thyroid gland →↑ metabolic rate Shivering Increase heat production DECREASE HEAT LOSS

Fever is defined as body temperature above usual normal range. Caused by any brain abnormality or by toxic substances (pyrogens ) that effect the temperature regulating center.

FEVER Bacteria or breakdown product of bacteria→ phagocytized by leuckocytes,tissue macrophages or granular killer lymphocytes→ digest bacterial products→ release cytokines (interleukin-1)→ cause formation of prostaglandins E2→ act on hypothalamus→ Cause set point to raise→ FEVER

Chills If set point of hypothalamic control raise to high value→ body temperature rise in response→ during this period ,person experience extremely cold ,chills and shivers.

Crisis/Flush When the factor causing high temperature is removed→ set point reduced to low level→ now body temperature is at high level ,so body try to lower its temperature→during this period person experience intense sweating→these change of events is known as crisis or flush.

Circulatory shock due to excessive loss of fluid and electrolytes. Heatstroke   When body temperature rises beyond a critical temperature into the range of 105 0F to 1080F, Heatstroke develops. Symptoms include dizziness, abdominal distress and loss of consciousness. Circulatory shock due to excessive loss of fluid and electrolytes. Damage to brain and body tissues.

Reason: At this very high temperature, temperature regulating mechanism often fail. Increase body temperature doubles the rate of all intracellular chemical reactions, thus liberating more heat.

Treatment: Remove all clothing. Cool water spray Cool water sponging Immersion of body in chilled water if available.

Exposure of body to extreme cold When body temperature falls below 940C, the ability of hypothalamus to regulate body temperature is lost. Reason: decrease rate of chemical reactions. Decrease activity of central nervous system to control heat mechanism and prevent shivering.  

FROSTBITE When body is exposed to extremely low temperature, surface area freeze. Occur in lobes of ear and in digits of hand and feet. Ice crystal form in the cells, local tissue damage and permanent circulatory impairments + gangrene

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