Chapter 2.
Integumentary system (skin)
Note: The skin is also called integument. The skin system is integumentary system. You cannot pass the test if you don’t know how to spell integument or integumentary.
The skin (or integument, from the Latin integer, which means “to cover”) is the outer coverage of the body, the organ with the largest surface area. The skin and its derivatives, such as hair, nails, sweat and oil glands, form the integumentary system.
Skin is a tissue membrane, and it contains two basic regions: the epidermis and dermis.
The epidermis is composed mainly of stratified squamous epithelial tissue.
There are five layers of cells in the epidermis: stratum corneum, stratum lucidum, stratum granulosum, stratum spinosum, and stratum basale.
The outmost cells of at the epidermis are dead and continually slough off. They are replaced by cells from the deeper epidermal layers. The principal function of the epidermis is to provide protection from everyday wear and tear on underlying body tissues.
The primary feature of the dermis is the fibers: collagen, elastic, and reticular fibers embedded in a ground substance.
The fibers allow the skin to stretch when we move, and they give it strength to resist abrasion and tearing. As we age, our skin becomes less flexible and more wrinkled because the number of fibers in the dermis the creases.
Hair follicle cells – the hair is formed at the root of hair cells, and the shaft piece pushes upwards towards the skin surface. The longer the hair, the older and less maintain it is, so the ends of long hair may show up as split ends.
Smooth muscle contracts when one is frightened or cold, causing the hair to become more erect.
Oil glands (sebaceous glands) produce the oily fluid which serves to moist and soften the hair and skin. If the oil is trapped and accumulates, it causes pimples.
Sweat glands contain the salt the watery fluid with dissolved ions and metabolic wastes. The evaporation of sweat on the outer body surfaces serves to remove body heat and help lower our body temperature.
Blood vessels supply both the epidermis and dermis with nutrients and remove their wastes. They also regulate body temperature through dilation (when one is too hot) and constriction (when one is too cold).
Sensory nerve endings are specialized receptors which detect heat, cold, light touch, deep pressure, and vibration. These sensations enable a person to feel the wind, the corners for table, the quickness of a cold drink, the heat of a cup of tea, or the onset of an earthquake.
Nails form at the fingers and toes, to protect and strengthen the tips. Nails are clear and colorless, but they appear pink because of the blood supply in the underlying skin, except for a white crescent shaped area called the lunula.
The nails consist of a nail body, which is primarily composed of dead keratinized cells. It covers the nail bed, which is the skin underneath the nail. There is a free edge at the most distal portion of the nail body and the nail route at the most proximal portion, which is the site of nail production. An epithelial skinfold (cuticle) projects onto the nail body.
The nail matrix, which is a portion of the skin underneath the nail, produces the modified tissue we call nails. As the nail cells grow out and extend from the base of the nails, they become keratinized and die. Thus, like hairs, nails are mostly non-living material.
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Back to Introduction Ch. 1 – Cells, Tissue, Organs Ch. 3 – Skeletal System