THE INTEGUMENTARY SYSTEM

Chapter 24AHUMAN 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 vessels4 yards of nerves25 nerve endings100 sweat glandsmore 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 15-20 minutes of sunlight 2-3 days a week will produce sufficient vitamin D.

ABSORPTION

The skin can absorb some chemicals, a fewdrugs, and asmall amountof 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.

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

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

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

Callusa thickened epidermis

which helps protect the

deeper layers of the skin

BlistersBlisters are not a form of protection, but a response to injury.

Friction causes layers of skin to separate and water collects in the space betweenthe separated layers.

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

BurnsBurns 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

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