Chapter 6

Skin and the Integumentary System

PowerPoint Presentation to accompany Hole’s Human Anatomy and Physiology, 10th edition, edited by S.C. Wache for Biol2064.01

You are responsible for the following figures and tables:

Fig. 6.1 - skin consists of CT and ET.ET - stratified squamous epitheliumCT - irregular dense connective tissueET - glandular epitheliumCT - adipose tissueRead TB, p.159-164 on 'epidermis', 'dermis', 'subcutaneous layer'.Tab. 6.1 - Layers of the EpidermisFig. 6.2 - Skin.Fig. 6.4 - Melanocytes.Fig. 6.7 - Nails.Fig. 6.9 - Eccrine and apocrine sweat glands. Hair.Read on cuts and burns, TB, pp. 173-175. Which epidermal layer has regenerative function ?Fig. 6.13 - Wound Healing.Fig. 6.14 - Extent of skin damage.

Epithelial Membranes (EM)

• There are three types of EM:

Serous / Mucous / Cutaneous

• The skin or cutaneous epithelial membrane, consisting of layers of ET called the epidermis and a layer of CT called the dermis, is an organ of the integumentary system.

Cutaneous Membrane = Skin

• Skin contains two layers, the epidermis and the dermis.

• The hypodermis is the layer underneath the skin.

Figure 6.2

Cutaneous Membrane

• Beneath the dermis is loose connective and adipose tissue that binds the skin to underlying organs. This is the hypodermis / subcutaneous layer.

Cutaneous Membrane Function• Skin is a protective covering that prevents

harmful substances from entering the body.

• It helps regulate body temperature and water loss.

• It houses sensory receptors and contains immune system cells.

• It synthesizes chemicals and excretes some wastes.

Epidermis

• It is composed of stratified squamous epithelium (ET).

Figure 6.3

Epidermis

• It is composed of stratified squamous epithelium (ET) and a simple basal layer of cuboidal cells.

• It lacks blood vessels, but the deepest layer, the stratum basale, is close to the dermis and receives nutrients.

• The thickness of the epidermis varies with region of the body.

Layers of the Epidermis from deepest to top layer

• Stratum basale: deepest layer, single row of cells that divide and grow

• Stratum spinosum: flat cells specialize and synthesize keratin

• Stratum granulosum: flat keratinized cells mature and nuclei appear shriveled

• Stratum lucidum: clear cells• Stratum corneum: many layers of flat, dead, keratinized,

nonnucleated cells that are shed

* The epidermis, like most epithelial tissues, regenerates. Epidermal cells exhibit high mitotic activity. They divide, grow, and die, while the new cells are already progressing through the same process.

Melanin – A Pigment• It is a dark

pigment produced by melanocytes in the basal layer.

• Melanin absorbs UV light and prevents mutations and damage to cells. Figure 6.4

basal layer

Skin CancersClinical Applications 6.1 (textbook p. 163)

Problem: Need balance between too much UV and

skin cancer and too little UV and Vit. D deficiency

due to lack of Vit. D synthesis in the absence of

sunlight.

Types of Skin Cancers:

Squamous cell carcinoma

Basal cell carcinoma

Malignant melanoma

Carcinoma: a malignant tumor of epithelial origin

Melanoma: a benign or malignant skin tumor containing dark pigment;sometimes it is a tumor of high malignancy that starts in melanocytes of normal skin or moles and metastasizes rapidly and widely -- called also malignant melanoma, melanocarcinoma, melanoepithelioma, melanosarcoma

Sarcoma: a malignant neoplasm arising from connective tissue, bone, cartilage, or striated muscle that spreads by extension into neighboring tissue or by way of the bloodstream

From: http://www.nlm.nih.gov/medlineplus/mplusdictionary.html

Skin Cancers and Other Cancers

Dermis Structure• The dermis is separated from the epidermis by the

basement membrane.• Epidermal ridges = dermal papillae project into the

dermis. These dermal papillae are responsible for fingerprints.

• The dermis binds the epidermis to the underlying tissues.

• The dermis is composed of irregular dense connective tissue with collagen and elastin in a gel-like ground substance.

Dermis Function• Dermis contains muscle fibers. Smooth

muscles are associated with follicles and glands.

• Motor and sensory nerves and sensory receptors are found throughout the dermis.

• The dermis contains blood vessels, hair follicles, sebaceous and sweat glands.

Subcutaneous Layer • The subcutaneous layer or hypodermis is made up

of loose connective tissue and adipose tissue.

• Collagenous and elastic fibers are continuous with those in the dermis.

• The adipose tissue conserves body heat.

• The subcutaneous layer contains the major blood vessels that supply the skin with oxygen, nutrients, and immune cells.

Accessory Organs: Hair Follicles• Hair develops

from epidermal cells at the base of the hair follicle.

• Epidermal cells keep dividing continuously, grow, and die. Figure 6.6

Hair Follicles

• Hair develops from epidermal cells at the base of the hair follicle.

• Epidermal cells keep dividing continuously, grow, and die.

• The dead cells make up the shaft of the hair.

• The arrector pili muscle is a smooth muscle attached to the follicle.

• It causes hair to stand upright on the skin.

Accessory Organ: Nails

• consist of nail plate over a growing epithelium of the nail bed on the skin surface.

Figure 6.8

Nails

• Nails consist of a nail plate over a growing epithelium of the nail bed on the skin surface.

• The white lunula at the base of the nail is the region of most active growth.

• Epithelial cells divide and become keratinized.

Sweat Glands

• These glands respond to increased body temperature and

function in evaporative cooling.

Figure 6.10 – Eccrine Sweat Gland

Sweat Glands

• Sweat or sudoriferous glands are epithelial glands widespread in the skin.

• Eccrine sweat glands respond to increased body temperature and function in evaporative cooling.

• Apocrine sweat glands become active at puberty and secrete sweat that produces body odor when metabolized by bacteria.

They can respond to pain, fear, and emotions.

• Modified sweat glands:

Ceruminous glands secrete ear wax.

Mammary glands secrete breast milk.

Sebaceous Glands

• Sebaceous glands are holocrine glands associated with hair follicles.

• Sebum , a mixture of fatty material and cellular debris, is secreted to keep hair and skin soft and waterproof.

• Acne results from excess sebum secretion.

Figure 6.11

Problems in Temperature Regulation

• Hypothermia or lowered body temperature is a dangerous condition resulting from cold exposure.

• Hyperthermia or increased body temperature can result from inadequate body cooling during exercise or in extreme heat.

* Clinical Application 6.4

Skin Color

• Heredity and environment determine skin color.

• The number of melanocytes is the same in all races, but more melanin is released in darker skinned individuals.

• People who inherit mutant melanin genes do not produce this pigment and have nonpigmented skin and hair, albinism.

Other Factors Influencing Skin Color

• Ultraviolet light and X-rays stimulate melanocytes to synthesize melanin.

• Oxygenated blood creates a pink tint to skin while lack of oxygen results in cyanosis where the skin appears bluish.

• Carotene, found in yellow vegetables, can create a yellow or sallow tint to skin.

• Jaundice due to liver malfunction can create a bright yellow color in the skin.

Skin Healing

• Superficial cuts heal due to increased epithelial cell division.

• Dermal cuts involve clotting and scab formation. Growth factors stimulate cell division and growth and scars may form.

Skin Healing - Burns

• Superficial partial-thickness (first degree) burns involve redness of the epidermis.

• Deep partial-thickness (second degree) burns destroy the epidermis and some of the dermis. Fluid escapes causing blisters.

• Full-thickness (third degree) burns destroy the epidermis, dermis, and accessory skin organs.

• Treatment of burns involves estimating the burn surface area by the “rule of nines” (Fig. 6.14)