Integumentary System Flashcards
Epidermis
The outer layer of skin is the epidermis. This layer is thinner than the inner layer (the dermis).
Dermis
The dermis is the inner, thicker layer of skin. It consists mainly of tough connective tissue, and is attached to the epidermis by collagen fibers. The main functions of the dermis are regulating body temperature, enabling the sense of touch, and eliminating wastes from the body.
Keratin
The epidermis consists mainly of epithelial cells, called keratinocytes, which produce the tough, fibrous protein keratin.
Hair
Hair is a fiber found only in mammals. It consists mainly of keratin-producing keratinocytes. Each hair grows out of a follicle in the dermis.
Fingernails and Toenails
Fingernails and toenails consist of dead keratinocytes filled with keratin. The keratin makes them hard but flexible, which is important for the functions they serve. Nails prevent injury by forming protective plates over the ends of the fingers and toes.
Keratinocytes
The epidermis consists mainly of stacks of keratin-producing epithelial cells called keratinocytes. These cells make up at least 90 percent of the epidermis. Near the top of the epidermis, these cells are also called squamous cells.
Melanocytes
Another eight percent of epidermal cells are melanocytes. These cells produce the pigment melanin that protects the dermis from UV light.
Langerhans Cells
About one percent of epidermal cells are Langerhans cells. These are immune system cells that detect and fight pathogens entering the skin.
Merkel Cells
Less than one percent of epidermal cells are Merkel cells, which respond to light touch and connect to nerve endings in the dermis.
Eccrine Sweat Glands
Eccrine sweat glands occur in skin all over the body. Their ducts empty through tiny openings called pores onto the skin surface. These sweat glands are involved in temperature regulation.
Apocrine Sweat Glands
Apocrine sweat glands are larger than eccrine glands, and occur only in the skin of the armpits and groin. The ducts of apocrine glands empty into hair follicles, and then the sweat travels along hairs to reach the surface. Apocrine glands are inactive until puberty, at which point they start producing an oily sweat that is consumed by bacteria living on the skin. The digestion of apocrine sweat by bacteria causes body odor.
Sebaceous Glands
Sebaceous glands are exocrine glands that produce a thick, fatty substance called sebum. Sebum is secreted into hair follicles and makes its way to the skin surface along hairs. It waterproofs the hair and skin, and helps prevent them from drying out. Sebum also has antibacterial properties, so it inhibits the growth of microorganisms on the skin. Sebaceous glands are found in every part of the skin — except for the palms of the hands and soles of the feet, where hair does not grow.
Hair Follicles
Hair follicles are the structures where hairs originate (see the diagram above). Hairs grow out of follicles, pass through the epidermis, and exit at the surface of the skin.
Cuticle
The cuticle (or outer coat) is the outermost zone of the hair shaft. It consists of several layers of flat, thin keratinocytes that overlap one another like shingles on a roof. This arrangement helps the cuticle repel water. The cuticle is also covered with a layer of lipids, just one molecule thick, which increases its ability to repel water. This is the zone of the hair shaft that is visible to the eye.
Cortex
The cortex is the middle zone of the hair shaft, and it is also the widest part. The cortex is highly structured and organized, consisting of keratin bundles in rod-like structures. These structures give hair its mechanical strength. The cortex also contains melanin, which gives hair its color.
