Integumentary System (Skin)

Integumentary refers to skin which has several functions.

Vertebrate skin has two main regions the epidermis and the dermis. The thin, outermost layers of cells are called epidermis. It is composed of stratified epithelium that grows from the bottom upwards. Keratinization of epidermal cells turns them into waterproof tissue. Three pigments. melanin, hemoglobin, and carotene contribute to skin color.

The underlying dermis is mostly dense connective tissue with many elastin and collagen fibers. It cushions the body against everyday stretching and mechanical stresses. Blood and lymph vessels, and nerve endings are located here. Sweat glands control skin temperature. Oil glands lubricate and soften the skin. Hair grows from follicles embedded in the dermis.

Sweat glands arise from epidermal cells. The composition of sweat is 99% water, with dissolved salts, and a trace of ammonia (waste product). Sweat glands are controlled by sympathetic nerves.

Oil glands, also called sebaceous glands, are derived from epidermal cells. Secretions lubricate and soften hair and skin. They also kill many surface bacteria. Acne occurs when bacteria infect oil gland ducts.

Hair roots are embedded in skin. Cells near the base of the root divide and push cells above them upward. Hair follicles are nourished by the dermis. As cells move upward away from the dermis they die.

Vitamin D is a steroid-like compound that helps the body absorb calcium from food. It is produced in the skin from a precursor molecule in a reaction that requires sunlight. In cooler climates, dietary vitamin D is required to supplement that produced by skin.

The skin is anchored to an underlying hypodermis, which also stores fat.

This animation (Audio - Important) describes the regions of the skin.

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