Inegumentary system

• The strong surface layer of the skin is the epidermis which consists of squamous (flattened) epithelial cells.
• An essential function of the skin is to act as a physical barrier to infection.
• The protein keratin helps to waterproof the epidermis and is the main component of hair and nails.
• Melanin protects against UV radiation by absorbing it.
• Another function of the integumentary system is to regulate temperature
• Regulation of body temperature is controlled and coordinated by the hypothalamus
• The skin is an important receptor and effector (detect stimuli and respond to it).
• Sweat glands -  release sweat when the body temperatures rises. Thermal energy from the skin and blood in capillaries close to the surface of the skin is transferred to the water in sweat, causing it to evaporate. This transfer of thermal energy cools the skin.
• Hairs - A fall in core body temperature causes the hypothalamus to send nerve impulses to the hair erector muscles. This causes them to contract, which raises the hairs. As a result, a thicker layer of air is trapped next to the skin and forms an insulating layer, reducing heat loss. If the core body temperature rises, nerve impulses from the hypothalamus cause the erector muscles to relax and so the hair lies flat, reducing the thickness of the insulating layer.
• Arterioles supplying the capillaries near the surface of the skin can constrict (vasoconstriction) or dilate (vasodilation).
• When the core body temperature rises, nerve impulses from the hypothalamus cause the muscles in the walls of the arterioles in the dermis to relax. This causes vasodilation – the diameter of the arterioles increases. As a result, more blood can flow through the capillaries close to the surface of the skin and so more thermal energy is transferred to the surroundings.
• When the core body temperature falls, nerve impulses from the hypothalamus cause contraction of the muscles in the walls of the same arterioles. This causes vasoconstriction – the diameter of the arterioles decreases. As a result, less blood flows through the capillaries close to the surface of the skin and is diverted through the shunt vessel to a venule. Less radiation lost to the capillaries at the surface so less heat lost.
• Another function of the integumentary system is Vitamin D synsthesis
• In the absence of sunlight, there can be a deficiency in vitamin D, meaning that it needs to be consumed in the diet.
• Vitamin D works together with PTH and calcitonin to regulate the calcium balance of the body.
• Another function of this sytem is cutaneous sensation
• Label the 4 types of receptors on skin

  A) Pacianin receptor

  B) Noncireceptor

  C) Meissner's corpuscle

  D) Thermoreceptor

  
• Another function is excretion
• Sweat glands are an example of exocrine glands because they secrete their products onto a surface rather than into the blood.
• Sebaceous glands are another exocrine gland that excrete the oily substance sebum. This helps to lubricate the skin and hair. Sebum also keeps the skin slightly acidic, which helps protect against microbes.
• sweat glands are found in epidermis
• sweat glands are a type of exocrine gland
• hair erector muscles contract to raise hair and trap air to insulate the skin
• sweat is secreted through tiny ducts onto the surface of the skin
• neurotransmitters can excite or inhibit the target neurone