The integumentary system consists of the skin and its accessory structures, including the hair, nails, sebaceous glands, and sweat glands
Skin
It weighs more than 6 pounds in the average adult, and covers more than 3,000 square inches
It is the largest organ of the body
It is supplied with blood vessels and nerves
Functions of skin
It inhibits excessive loss of water and electrolytes
It produces a protective pigmentation to protect the body against excessive exposure from the sun
It helps produce the body's supply of Vitamin D
It protects against invasion by bacteria and other harmful agents
It protects delicate cells beneath the surface from injury
Skin regulates body temperature
1. When the body is too hot, the blood vessels in the skin dilate to bring more blood to the surface for cooling by radiation, and sweat glands secrete more sweat that cools the body when it evaporates
2. When the body is too cold, the skin's blood vessels constrict to allow more heat-carrying blood to circulate to the muscles and organs
Skin provides sensations
It contains millions of nerve endings that act as sensory receptors for pain, heat, cold, and pressure
Layers of the epidermis
Stratum corneum
Stratum lucidum
Stratum granulosum
Stratum germinativum
Stratum corneum
It is the outermost strata of the epidermis, mostly dead cells filled with a protein substance called keratin, thicker on the soles of the feet than on the eyelids
Stratum lucidum
It is a translucent layer lying directly beneath the corneum, may not even exist in thinner skin, cells are also dead or are in the process of dying
Stratum granulosum
It is one or more layers of cells starting to die and become hard, in the process of keratinization (becoming fibrous protein similar to that in hair and nails)
Stratum germinativum
It is the innermost layer of the epidermis, composed of several layers of living cells capable of cell division, contains melanin (the pigment that gives color to the skin), damage to this layer requires skin grafts
Dermis
It contains the lymphatics, nerves, nerve endings, blood vessels, sebaceous and sweat glands, elastic fibers, and hair follicles, it is beneath the epidermis and is composed of connective tissue
Layers of the dermis
Papillary layer (arranged into microscopic structures that form ridges, the finger- and footprints)
Reticular layer (beneath the papillary layer, a white fibrous tissue that supports the blood vessels)
Hypodermis
The subcutaneous tissue or hypodermis is composed of adipose and connective tissue, it supports, nourishes, insulates, and cushions the skin
Hair
It is a threadlike structure formed by a group of cells that develop within a hair follicle or socket, each hair has a shaft that is visible and a root that is embedded in the follicle
Pilomotor muscle
It is attached to the side of each hair follicle, stimulated by skin irritants, emotional arousal, or cold temperatures, and reacts by contracting to cause goose flesh or goose pimples
Hair papilla
It is at the base of each hair follicle, enclosing a loop of capillaries, provides nourishment to the hair, one of the few living parts of the hair, responsible for hair growth
Parts of the hair
Cuticle (covers the hair shaft like shingles, protects it from the elements and chemicals, and from losing moisture)
Cortex (provides most of the hair's weight, contains melanin which provides color, stores oils, provides flexibility and elasticity, and adds shape)
Medulla (inner hollow core that runs the length of the shaft)
Sebaceous glands
They are oil glands, have tiny ducts that open into each hair follicle, each gland secretes sebum which lubricates the hair and skin
Parts of the nail
Nail root (also called the germinal matrix or nailbed, begins several millimeters into the finger and extends to the edge of the white, crescent-shaped lunula, where the growth occurs at approximately 1 mm per week)
Nail plate (body of the nail, has grooves that help anchor it)
Cuticle (also called the eponychium, fuses the nail plate and the skin of the finger together to form a waterproof barrier)
Hyponychium (under the free edge of the nail, also creates a waterproof barrier, fusing the skin of the finger to the underside of the nail plate)
A lost finger- or toenail will regenerate
Ingrown nail
They are simply those that have curled down or around and are growing into the skin, may become swollen and inflamed
Trim toenails straight across to avoid ingrown nail growth pattern
Sudoriferous glands
They are sweat glands, about 2 million are distributed over the surface of the body, more numerous on the palms of the hands, soles of the feet, forehead, and axillae (underarms)
Functions of sweat glands
They produce sweat or perspiration, as sweat collects on the skin surface it evaporates and creates a cooling effect
Sweat also rids the body of waste through the pores of the skin
As sweat accumulates, it may become odorous by the action of bacteria
The average person loses approximately 1/2 liter of fluid through sweating each day