THE INTEGUMENTARY SYSTEM Chapter 24A HUMAN SKIN

Skin Stats … Approx 1.9 square meters (about 18 sq. feet) of skin cover the body Average thickness is 1/8 inch (1-2 mm) Weighs 9 pounds (6% of the body weight) Skin is the largest organ of the human body

A piece of skin the size of a quarter contains: 1 yard of blood vessels 4 yards of nerves 25 nerve endings 100 sweat glands more than 3 million cells

FUNCTIONS OF THE SKIN Protection Sensation Heat Control Excretion Manufacture Absorption

Protection (a mechanical shield) Your skin is one of your body’s major defenses. The skin does not permit significant amounts of substances like water in or out of the body. Bacteria, viruses, and many common chemicals that you constantly touch would be very harmful if they penetrated into the body. Skin is an effective barrier to most of them.

Protection (a mechanical shield) Perspiration and oils secreted by the skin provide a form of chemical protection which is acidic and sometimes has enzymes that inhibit the growth of certain mircroorganisms.

SENSATION (Communication) Nerve receptors for touch, pressure, temperature, and pain are in the skin. Communication between your body and the outside world.

HEAT CONTROL The amount of blood being carried to the surface of the skin is regulated to control the amount of heat lost to the atmosphere. Blood vessels in skin dilate when you need to cool off and constrict when you need to conserve heat. Also evaporation of sweat cools the body.

EXCRETION (Secretion) A small amount of body wastes is excreted with sweat. sweat glands – move moisture to the surface to cool, also give off certain wastes to help keep the body clean oil glands (sebaceous) – coat the skin with oils to keep it from drying out.

VITAMIN MANUFACTURE The skin produces small amounts of vitamin D. As little as minutes of sunlight 2-3 days a week will produce sufficient vitamin D.

ABSORPTION The skin can absorb some chemicals, a few drugs, and a small amount of oxygen.

Layers of the Skin Epidermis (1) Dermis (2)

Epidermis the outermost layer of the skin has dead cells at the surface and living cells underneath contains nerve endings (example: pain receptors) the older cells of the epidermis fill with a waxy substance called keratin and die approximately every 25 days (faster for some people and in some areas of the body) a completely new epidermis covers the body

Dermis the inner, much thicker layer of the skin contains: connective tissues blood vessels nerve endings sweat glands hair follicles oil glands

Nerve Receptors Cold Heat Touch pressure

Subcutaneous layer not actually a part of the skin consists of loosely arranged fat cells and fibers the fat cells help to cushion and insulate you body the fibers attach the skin to the muscles under it

Skin Color dark pigment - melanin yellowish pigment - carotene Pink color of a person's skin is his blood showing through. Other colors are the results of pigments.

Melanin Melanin is produced by special cells (melanocytes) in the skin.

Freckles Freckles are clumps of cells that contain more melanin that the rest of the skin.

Albinism People with albinism do not have the ability to make melanin and thus cannot tan.

Callus a thickened epidermis which helps protect the deeper layers of the skin

Blisters Blisters are not a form of protection, but a response to injury. Friction causes layers of skin to separate and water collects in the space between the separated layers.

Boils Boils are bacterial infections (the raised portion of skin is filled with pus)

Burns Burns are classified by how deeply they penetrate the skin’s surface. First Degree Second Degree Third Degree

First Degree (superfiecial) involves only the epidermis

Second Degree (partial thickness) involves the epidermis and some of the dermis

Third Degree (full thickness) destroys the epidermis, dermis, and into the subcutaneous tissues

Burns Burns are classified by how deeply they penetrate the skin’s surface.