Integumentary system

• • The skin is the largest organ in the body, with a total area of about 2m2.
  • The skin comprises 15% of the total adult body weight.Its thickness ranges from <0.1mm at its thinnest part(eyelids) to 1.5mm at its thickest part (palms of the hands and soles of the feet)
• Epidermis

  • The epidermis is the strong surface layer of the skin which consists of squamous (flattened) epithelial cells. These cells are continually worn away and so the epidermis is regenerated by division of stem cells in the lowest layer of the epidermis.
  • There are no blood vessels in the epidermis, so it obtains nutrients from the underlying dermis.

  * The protein keratin (the main fibrous protein of hair and nails) helps skin to be waterproof.
• Its 3 main roles are:

  • To make new skin cells
  • To give skin its colour. Melanin protects the skin from UV rays
  • To protect the body from the external environment
• Function of the integumentary system

  • Protection
  • Temperature regulation
  • Vitamin D synthesis
  • Cutaneous sensation
  • Excretion
• Protection

  • The skin acts as a barrier to infection.
  • Antimicrobial peptides are produced by skin cells and exocrine glands and help to protect against infection by bacteria and fungi.
  • We have a population of benign bacteria that live on our skin and also help to prevent infection.
• Temperature regulation

  • Regulation of body temperature is controlled by the hypothalamus, but the skin is an important receptor and effector.
  • The main temperature receptors are in the hypothalamus itself and monitor core body temperature (the temperature of internal organs, which is often higher than the temperature of the body surface)
  • Peripheral temperature receptors are located in the skin and monitor the external temperature.
  • The hypothalamus uses inputs from both types of receptor.
• temperature regulation

  The hypothalamus controls the three main mechanisms that helps the skin maintain an almost constant body temperature.

  -Sweat glands

  -Arterioles

  -Hairs
• Sweat glands

  • The sweat glands release sweat when the body temperature rises
  • Thermal energy from the skin and blood in the capillaries close to the surface is transferred to the water in the sweat, causing it to evaporate taking heat with it, therefore cooling the skin.
• Arterioles 


  Arterioles supplying the capillaries near the surface of the skin can dilate (vasodilation) or constrict (vasoconstriction).
• 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 (they get wider).
  • As a result, more blood can flow through the capillaries close to the skin and so more thermal energy is transferred to the surroundings (heat I lost through the skin through radiation) that's why our skin goes pink when we are hot.
• Vasoconstrictions 


  • When the core body temperature drops, nerve impulses from the hypothalamus cause contraction of the muscles in the walls of the same arterioles. This causesvasoconstriction - the arterioles get narrower.
  • 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.
  • A shunt vessel is a small vessel connecting the arteriole to the venule, bypassing the capillaries. This means that less thermal energy is transferred by radiation (less heat is lost through the skin)
• Hairs 


  • A fall in core temperature causes the hypothalamus to send nerve impulses to the 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 temperature rises, nerve impulses from the hypothalamus cause the erector muscles to relax and so the hairs lie flat.
• Vitamin D synthesis

  • Vitamin D or cholecalciferol is strictly not a vitamin. This is because it is made in the lower layers of the skin epidermis.
  • This reaction is dependent on sunlight. Therefore 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 is fat soluble and relatively few foods contain significant levels of the vitamin.
  •  vitamin D is added to some foods such as milk and breakfast cereals.
  • Vitamin D works together with PTH and calcitonin to regulate the calcium balance of the body.
• Nails

  • They are derived from the same cells as the epidermis and hair and consists of a hard, horny keratin plate. They protect the tips of fingers and toes.
  • The root of the nail is embedded in the skin, is covered by the cuticle and forms the hemispherical pale area called the lunula
  • the nail plate of the nail is the exposed part that has grown out from the germinative zone of the epidermis called the nail bed.
  • Finger nails grow more quickly than toe nails and growth is quicker when the environmental temperature is high