The integument as an organ: The integument as an organ, and is an alternative name for skin. The integumentary system includes the skin and the skin derivatives hair, nails, and glands. The integument is the body’s largest organ and accounts for 15% of body weight.
The derivatives of the integument:
Hair: functions include protection & sensing light touch.
Functions of the skin:
Hair is composed of columns of dead, keratinized cells bound together by extracellular proteins. Hair has two main sections: The shaft- superficial portion that extends out of the skin and the root- portion that penetrates into the dermis. Surrounding the root of the hair is the hair follicle. At the base of the hair follicle is an onion-shaped structure called the bulb Papilla of the hair and the matrix within the bulb produce new hair.
Nails: participate in the grasp & handling of small things.
Nails are plates of tightly packed, hard, keratinized epidermal cells.
The nail consists of:
- nail root: -the portion of the nail under the skin,
- nail body: -the visible pink portion of the nail, the white crescent at the base of the nail is the lunula, the hyponychium secures the nail to the finger, the cuticle or eponychium is a narrow band around the proximal edge of the nail and
- free edge: -the white end that may extend past the finger.
Glands: participate in regulating body temperature.
There are three main types of glands associated with the integument:
- Sebaceous - Oil glands. Located in the dermis, and secrete sebum.
- Sudoriferous - Sweat glands. Divided into two main types:
- Eccrine - Most common, main function is regulation of body temperature by evaporation, and
- Apocrine - Responsible for “cold sweat” associated with stress.
- Ceruminous – Lie in subcutaneous tissue below the dermis, secrete cerumen (ear wax) into ear canal or sebaceous glands.
Thermoregulation - Evaporation of sweat & Regulation of blood flow to the dermis.
Cutaneous sensation - Sensations like touch, pressure, vibration, pain, warmth or coolness.
- Vitamin D production - UV sunlight & precursor molecule in skin make vitamin D.
- Protection – The sin acts as a physical barrier.
- Absorption & secretion – The skin is involved in the absorption of water-soluble molecules and excretion of water and sweat.
- Wound healing - When a minor burn or abrasion occurs basal cells of the epidermis break away from the basement membrane and migrate across the wound. They migrate as a sheet, when the sides meet the growth stops and this is called ‘contact inhibition’.
- In deep wound healing - A clot forms in the wound, blood flow increases and many cells move to the wound. The clot becomes a scab; granulation tissue fills the wound and intense growth of epithelial cells beneath the scab. The scab falls off and the skin returns to normal thickness.
The Two Layers of Skin:
Epidermis – The Epidermis is the thinner more superficial layer of the skin.
The epidermis is made up of 4 cell types:
- (A) Keratinocytes – Produce keratin protein a fibrous protein that helps protect the epidermis
- (B) Melanocytes - produces the brown pigment melanin
- (C) Langerhan Cells – participate in immune response and
- (D) Merkel cells - participates in the sense of touch.
There are five distinct sub-layers of the Epidermis:
- Stratum corneum: the outermost layer, made of 25-30 layers of dead flat keratinocytes. Lamellar granules provide water repellent action and are continuously shed & replaced.
- Stratum lucidum: Only found in the fingertips, palms of hands, & soles of feet. This layer is made up of 3-5 layers of flat dead keratinocytes.
- Stratum granulosum: made up of 3-5 layers of keratinocytes, site of keratin formation, keratohyalin gives the granular appearance.
- Stratum spinosum: appears covered in thornlike spikes, provide strength & flexibility to the skin.
- Stratum basale: The deepest layer, made up of a single layer of cuboidal or columnar cells. Cells produced here are constantly divide & move up to apical surface.
Dermis: is the deeper, thicker layer composed of connective tissue, blood vessels, nerves, glands and hair follicles.
The epidermis contains 3 cell types:
- Macrophages and
- There are two main divisions of the dermal layer:
- Papillary region - The superficial layer of the dermis, made up of loose areolar connective tissue with elastic fibers.
- Dermal papillae - Fingerlike structures invade the epidermis, contain capillaries or Meissner corpuscles which respond to touch.
- Reticular region of the Dermis – Made up of dense irregular connective & adipose tissue, contains sweat lands, sebaceous (oil) glands, & blood vessels.