Integumentary System

Integumentary System

1. SKIN

   • skin is an organ of the integumentary system made up of a layer of tissues that guard underlying muscles and organs. As the interface with the surroundings, it plays the most important role in protecting against pathogens. 
   • LAYERS
     • The skin has two major layers which are made of different tissues and have very different functions. Skin is composed of the epidermis and the dermis. Below these layers lies the hypodermis or subcutaneous adipose layer, which is not usually classified as a layer of skin.
     • Epidermis
       • consists of stratified squamous keratinizing epithelium with an underlying basement membrane. It contains no blood vessels, and is nourished by diffusion from the dermis. The main type of cells which make up the epidermis are keratinocytes, with melanocytes and Langerhans cells also present. 
     • Dermis
       •  lies below the epidermis and contains a number of structures including blood vessels, nerves, hair follicles, smooth muscle, glands and lymphatic tissue. It consists of loose connective tissue otherwise called areolar connective tissue – collagen, elastin and reticular fibers are present. 
     • Hypodermis
       •  is not part of the skin, and lies below the dermis. Its purpose is to attach the skin to underlying bone and muscle as well as supplying it with blood vessels and nerves. It consists of loose connective tissue and elastin.
   • FUNCTIONS
     • Protection, sensation, and Heat regulation
       • Protection: Skin gives an anatomical barrier between the internal and external environment in bodily defense; Langerhans cells in the skin are part of the immune systemSensation: Skin contains a variety of nerve endings that react to heat, cold, touch, pressure, vibration, and tissue injuryHeat regulation: The skin contains a blood supply far greater than its requirements which allows precise control of energy loss by radiation, convection and conduction. 

2. types of glands in the integumentary system

   • sudoriferous (sweat) glands, sebaceous glands, ceruminous glands, and mammary glands.
     •  These are all exocrine glands, secreting materials outside the cells and body.

3. HAIR

   • Lanugo
     • unpigmented hair that covers nearly the entire body of a fetus, although most has been replaced with vellus by the time of the baby’s birth
   • Vellus hair
     •  body hair (also unpigmented) that grows in most places on the human body. While it occurs in both sexes, and makes up much of the hair in children, men have a much smaller percentage (around 10%) vellus whereas 2/3 of a female’s hair is vellus.
   • Terminal hair
     • the fully developed hair, which is generally longer, coarser, thicker, and darker than vellus hair, and often is found in regions such as the axillary, male beard, and pubic.

4. NAILS

   • The fingernail is an important structure made of keratin. The fingernail generally serve two purposes. It serves as a protective plate and enhances sensation of the fingertip. The protection function of the fingernail is commonly known, but the sensation function is equally important. 
   • Nail structure
     • Root, nail bed, nail plate, Eponychium, Perionychium, and Hyponychium

5. GLANDS

   • Sweat glands
     • Eccrine
       • are exocrine glands distributed over the entire body surface but are particularly abundant on the palms of hands, soles of feet, and on the forehead.
     • Apocrine
       • develop during early- to mid-puberty (approximately age 15) and release more than normal amounts of sweat for approximately a month and subsequently regulate and release normal amounts of sweat after a certain period of time. Apocrine sweat glands produce sweat that contains fatty materials.
     • Sebacious
       • are glands found in the skin of mammals. They secrete an oily substance called sebum (Latin, meaning fat or tallow) that is made of fat (lipids) and the debris of dead fat-producing cells.
     • Ceruminous
       • Earwax, also known by the medical term cerumen, is a yellowish, waxy substance secreted in the ear canal of humans and many other mammals. It plays a vital role in the human ear canal, assisting in cleaning and lubrication, and also provides some protection from bacteria, fungus, and insects. 
       • Function
     • Mammary glands
       • are the organs that, in the female mammal, produce milk for the sustenance of the young. These exocrine glands are enlarged and modified sweat glands and are the characteristic of mammals which gave the class its name.
       • Structure
         • The basic components of the mammary gland are the alveoli (hollow cavities, a few millimetres large) lined with milk-secreting epithelial cells and surrounded by myoepithelial cells. These alveoli join up to form groups known as lobules, and each lobule has a lactiferous duct that drains into openings in the nipple.