Thermoregulation, Healing and Aging

Regulation of Body Temperature  Slight shifts in temperature can disrupt metabolic rates  Stable temperature is a balance between heat lost and heat produced Cellular metabolism produces heat ○ Skeletal and cardiac muscle and liver cells are very active  Skin is key to thermoregulation

Rise in Body Temperature  Nervous system signals organs to release heat Blood is warmed and reaches the brain  Signal sent to dermal blood vessels to relax (vasodilation) Vessels dilate Heat from blood escapes to outside  Deeper blood vessels signaled to contract (vasoconstriction) Blood diverted to surface Skin reddens  Heart stimulated to beat faster and move more blood out of deeper regions

 Radiation- heat radiates from warmer surfaces to cooler surroundings  Conduction- heat moves from body to a cooler object in contact  Convection- heated air moves way from body and is replaced with cooler air moving toward the body (circulates)  Evaporation- sweat is released onto skin surface and evaporates, carrying heat away

Drop in Body Temperature  Walls of dermal blood vessels contract (vasoconstriction) Flow of heat-carrying blood is decreased Reduces heat loss by radiation, conduction and convection  Sweat glands remain inactive  Muscles cells in skeletal muscles may begin to contract Increases cellular respiration and releases heat Rhythmic, strong contractions cause shivering

Problems in Regulation  High humidity limits or represses evaporation Sweating is ineffective  High air temperature Decreases heat loss by radiation Can also cause heat gain from surroundings  Hyperthermia- body temperature exceeds 106  F Weak, dizzy, nauseous, headache Rapid, irregular pulse Dry, hot, flushed skin

 Hypothermia- lowered body temperature Begins with shivering Mental confusion, lethargy, loss of reflexes, loss of consciousness Organs shut down  Core can only withstand a drop of a few degrees  Extremities can withstand drops of  F below normal  Must warm gradually to avoid disrupting respiratory and cardiovascular functioning

Wound Healing  Inflammation is a response to injury or stress Blood vessels dilate and become permeable ○ Fluids leak into damaged tissue ○ Tissue gets more nutrients and oxygen Skin becomes reddened, swollen, warm and painful  Shallow cuts Epithelial cells divide more rapidly Newly formed cells fill gap

 Deep cuts Blood vessels break and form clots Tissue fluids seep in and dry Clotted blot and dried fluids for a scab to protect wound Epithelial cells bridge the wound and fibroblasts secrete fibers to bind the wound Blood vessels extend beneath scab ○ Phagocytes remove deal cells ○ Damaged tissues replace ○ Scab falls off Scars form if excess collagenous fibers formed above the normal epidermal surface

Burns  1 st degree (superficial partial-thickness) burn Only affects epidermis Skin becomes warm and reddened Mild edema Tender Surface layer may peel No scarring

 2 nd degree (deep partial-thickness) burn Destroys epidermis and some underlying dermis Fluid accumulates beneath epidermal cells to form blisters Areas becomes moist and firm Color varies from dark red to waxy white Exposure to hot objects, liquids, flames, clothes Stem cells divide and differentiate during healing Low risk of scarring

 3 rd degree (full-thickness) burn Destroys epidermis, dermis and accessory structures of skin Skin is dry and leathery Red to black to white in color Results from immersion in hot liquids, prolonged exposure to hot objects, flames or chemicals Spontaneous healing of epithelial cells inward from burn margins May need grafting or temporary membrane covers Extensive scarring

Aging  Aging affects: skin appearance temperature regulation vitamin D formation  Epidermis thins over time Cell cycle slows Cells grow larger, more irregular in shape and fewer  Scaly skin results from changes in chemical bonding  Age spots result from oxidation of fats in apocrine and eccrine glands

 Wrinkling and sagging of skin Dermis reduces and shrinks Fat loss from subcutaneous layer  Wound healing is delayed Fewer fibroblasts  Drier skin Decreased oil from sebaceous glands

 Whitening/graying of hair Slowed melanin production  Thinning hair Slower hair growth Decrease in hair follicles  Hard, dull nails Decreased blood supply to nail bed  Decrease in pain and pressure sensitivity

 Decreased ability to control temperature Number of sweat glands decreases Ability to shiver declines Blood vessels in deeper layers decrease Decreased ability to direct blood flow to interior  Paler complexion Fewer vessels in skin  Pressure Sores Less blood vessels, different distribution Decreased circulation  Decreased absorption of calcium Less vitamin D production