Integumentary System
system of the body composed of the epidermis/dermis and the underlying subcutaneous tissue
How much of the total weight of the body does the skin take up?
15%
Functions
- Protection of underlying tissues (barrier to UV light, bacteria, radiation, water)
- Acts as a site of sensory reception (pain, heat, cold, touch, pressure)
- Regulation of body temperature (erect hairs, sweat-500mL a day)
- Salt excretion (sweat)
- Formation of Vitamin D, which is essential for calcium absorption from the foods we eat
Layers
- The skin is composed of 2 layers: the epidermis and the dermis
- Both of these laters lie on an underlying layer called the subcutaneous tissue (sub, below; cutis, skin)
- The thickest skin is on the back (1/2 cm), whereas the thinnest skin is on the eyelids (1/2 cm)
Epidermis
- It is the outermost layer of skin composed of stratified squamous keratinized epithelium
- The epidermis is avascular but does contain nervier and nerve endings
- The deepest layers of epidermis have cells that undergo mitosis and migrate to the outermost layers, where they become desiccated, convert to keratin and eventually slough off
- It takes about 30 days for a cell to go from birth to slough
a. thus, the epidermis (not total skin) is constantly being replaced - Deeper layers also contain melanocytes that produce the dark pigment melanin
a. this pigment is responsible for skin color and also protects the individual from the harmful effects of uv radiation - The keratin is very thick on the palms and soles and forms papillary ridges that occur in characteristic patterns (fingerprints, toe prints)_
Dermis
- It is the layer deep to the epidermis composed of a dense irregular connective tissue, which does contain both blood vessels and nerves
- It is 80% of the thickness of the skin (epidermis is 20%)
- It has many collagen fibers, hair follicles, and sweat glands
Subcutaneous tissue (hypodermis)
- It lies deep to the dermis and is made of loose connective tissue w an abundance of adipose cells
- Blood vessels and nerves course through it on their way to the dermis
- The adipose tissue is more abundant in females than in males and provides insulation, conserves body temperature and acts a shock absorber
Associated structures
structures that are part of the integument that have specific functions
Hair follicle
derived from the epidermis and growing down into the dermis and subcutaneous tissue
- they contain hairs, which form by the papillae undergoing mitosis
- when a follicle becomes inactive, the hair it produces becomes lost
Sebacious gland
oil-producing glands that result from disintegration of some gland cells
1. a duct passes the oily secretion, called sebum into the neck of hair follicle
pylorus muscles
smooth muscles attached to the hair follicle and the epidermal-dermal junction
1. contraction due to cold weather causes the hairs to stand erect and traps a layer of air within the hairs, which acts as an insulator to keep warmth inside the body
Sweat glands
have their secretion part in the dermis and their ducts passing through the epidermis to open at PORES on the skin surface
1. sweat is water and salt and cools the body as it evaporates
Nails
protective structures of hard keratin located at the tips of fingers and toes
