body temperature

• The skin consists of the outer, tinner epidermis, and the inner, thicker dermis. Underneath the dermis is a layer of subcutaneous fat.
• Epidermis layers:

  • Innermost layer = Malpighian layer where mitotic cell divisions occur to produce new cells. Vitamin D is produced here.
  • Middle layer contains cells produced by the Malpighian layer, with cell content gradually replaced by the fibrous protein keratin as they are pushed towards the skin surface (nuclei disappears and the cell dies)
  • Outermost layer = cornified layer consisting of flattened, dead cells
• Functions of the epidermis layers:

  • Some cells in the Malpighian layer produce pigment melanin which gives skin color and absorbs UV light
  • Cornified layer serves as a barrier preventing pathogen invasion and minor mechanical injuries
  • Cornified layer is waterproof to minimize water loss from the skin surface
• Dermis contains:

  1. hair follicles, hairs and erector muscles
  2. sebaceous glands
  3. sweat glands
  4. sensory receptors and nerves
  5. blood vessels
• Hair follicles, hairs and erector muscles:

  • hair follicles are sac-like structures that extend from the epidermis to the dermis. It is connected to the erector muscle.
  • hair roots are at the base of hair follicles and is the site where the hair develops
  • contraction of erector muscle is involuntary

  
• Sebaceous glands open into the hair follicles and produce an oily secretion called sebum.

  Sebum keeps skin soft and waterproof; and acts as antiseptic to inhibit the growth of bacteria and fungi on the skin.

  
• Sweat glands: coiled tubular glands

  Sweat: water + minerals + metabolic wastes (eg urea)

  sweat gland → sweat duct → sweat pore

  sweating helps cool the skin through evaporation and excretes metabolic waste

  
• Skin is a sense organ. Various types of sensory receptors are present in the dermis to detect stimuli such as temperature and pain.

  receptors → sensory neurones → CNS

  CNS → motor neurones → muscles and glands in the dermis
• Blood vessels supply living skin cells with oxygen and nutrients, and remove carbon dioxide and metabolic wastes from them.

  Shunt vessels connect arterioles and venules to bypass some capillaries. This allows amount of blood flowing through near skin surface and controls amount of heat loss.

  
• Subcutaneous fat:

  • Lies underneath dermis.
  • Thinkness vaies among different region of the body
  • Serves as insulating layer to reduce heat loss
  • Serves as a sourse of energy reserve
• Core body temerature is monitored and controlled by the thermoregulatory center in the hypothalamus of the brain.
• Thermoreceptors in the skin detect temperature of the skin.

  Thermoreceptors in the hypothalamus detects temperature of the blood flowing through the brain (ie core body temperature).
• Skin reducing heat loss:

  1. Vasoconstriction of the arterioles near the skin surface
  2. constriction of arterioles, reduces blood flow, less heat loss
  3. Reduced sweating
  4. Erector muscles contract, hairs become erect
  5. traps a thick layer of still air (in thick fur)
  6. Layer of subcutaneous fat becomes thicker (long-term)
• Skin promote heat loss:

  1. Vasodilation of the arterioles near the skin surface
  2. dilation of arterioles, blood flow increases, more heat lost
  3. Increased sweating
  4. only effective when sweat evaporates quickly (wind speed and relative humidity)
  5. Erector muscles relax, hairs lie flat
  6. Thinner layer of still air. Insulation is reduced.
  7. Layer of subcutaneous fat becomes thinner (long-term)
• Metabolism of skeletal muscles helps warm body. Heat gain center sends more frequent nerve impulses to the skeletal muscles causing them to contract in short bursts when fall in body temperature.

  (Involuntary action, generates extra heat from increased cellular respiration)
• Hormones in body temperature regulation:

  • long-term response to cold conditions
  • thyroid gland secretes more thyroxine
• Thyroxine:

  • transported in the blood
  • increases metabolic rate of body cells
  • secretion controlled by the pituitary gland (under control of hypothalamus)
• 1. lower body temerature detected by thermoreceptors in the hypothalamus
  2. hypothalamus signals pituitary gland to secrete a hormone
  3. hormone stimulates thyroid gland to secrete more thyroxine
  4. thyroxine increases metabolic rate of body cells