Lesson 1, Topic 1
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Anatomy of the Integumentary System

April 11, 2024

Anatomy of the Integumentary System

Learning Objective: Examine the anatomy of the integumentary system.

The most important function of the skin (or integument) is protecting the body from disease. The skin provides a physical barrier that is our first line of defense against pathogens. It is the largest organ of the body, and, in addition to physically protecting the body, it also helps to do the following:

• Regulate the body temperature
• Provide information about the environment through sensory activity
• Assist in the synthesis of vitamin D
• Eliminate waste products from the body

The skin functions together with accessory structures that include the hair, nails, sebaceous glands or oil glands, and sudoriferous glands or sweat glands. Any damage or injury to the skin has the potential to lessen its ability to carry out these functions, which can lead to disease.
The skin is considered a cutaneous membrane, made up of epithelial cells that cover the entire body. The skin is composed of two layers: the epidermis, which forms the outermost layer, and the dermis, which forms the inner layer (FIGURE 17.1). The dermis is attached to a layer of connective tissue called the subcutaneous layer, or hypodermis, which is mainly composed of fat or adipose tissue.

Epidermis

Learning Objective: Describe the anatomy of the epidermis.

The epidermis is the top layer of the skin and is composed of several different strata of epithelial tissue. This type of tissue covers many of the external and internal surfaces of the body and has a microscopic scaly appearance.

FIGURE 17.1  Diagram of the skin.

The epidermis is avascular, which means it contains no blood vessels. New skin cells are formed in the basal layer of the epidermis, called the stratum germinativum. This layer is also where melanin, which is a pigment, is produced by melanocytes. When the skin is exposed to ultraviolet (UV) light, the melanocytes secrete more melanin. Birthmarks, age spots, and freckles result from clumps of melanin. Individuals have different skin colors because of varying numbers of melanocytes in the stratum germinativum of the skin.
New cells produced in the stratum germinativum move upward toward the top layer, the stratum corneum. During the transition from the basal layer to the upper layer, the cell’s cytoplasm is replaced with keratin. Once this process is complete, the cells are called keratinocytes. Keratin is a hard protein material that enhances the skin by making it waterproof, abrasion resistant, and able to retain moisture in the body. These properties add to the protective nature of the skin.
A variety of microorganisms are normally found on the skin. These organisms are referred to as normal flora. Healthcare workers are taught to wash their hands or use hand sanitizer before and after each procedure. Good hand hygiene helps prevent the spread of microorganisms, reduces the likelihood of transferring possible pathogens, and decreases the risk of skin infections for our patients.

Dermal-Epidermal Junction

Learning Objective: Describe the dermal-epidermal junction.

The dermal-epidermal junction is where the two layers of the skin meet. The top layer of the dermis contains dermal papillae, which are peglike projections that help fasten the dermis and epidermis together. This unique junction not only uses dermal papillae to create a bond but also uses a specialized gel that acts as a glue to keep the two layers of the skin connected.
If the dermal-epidermal junction is damaged by a burn, irritation, abrasion, or friction, a blister may occur. If the dermal-epidermal junction is destroyed, the skin will fall apart. If this happens in a small area, the body can heal the damage. If a large area of the junction is destroyed, it results in an overwhelming infection that could be serious and possibly fatal.

17.1

Critical Thinking Application

Yesterday Mai wore a new pair of shoes to work and developed a little blister on the heel of her right foot. What skin layers are affected by the formation of a blister? How should Mai properly care for her blister over the next few days?

Dermis

Learning Objective: Describe the anatomy of the dermis.

The dermis is the thick, underlying layer of the skin that is composed of vascular connective tissue arranged in two layers. The dermis gives the skin strength and stretch that the epidermis does not possess. The thin upper layer of the dermis is composed of fibers made from loose connective tissue, collagen, and some elastin. The lower, thicker layer of the dermis is composed of dense collagen. Collagen gives the skin toughness, and elastin fibers help the skin stretch and have flexibility. Distributed throughout the dermis are hair follicles, sweat glands, and old glands.
There are two types of sweat glands: eccrine and apocrine. Eccrine sweat glands are dispersed throughout the body and help maintain a constant body temperature by releasing sweat through pores in the skin. Apocrine sweat glands open into hair follicles and are concentrated in the axillae (armpits), scalp, face, and the pigmented skin around the genitals. Apocrine sweat glands release a fatty sweat in response to stress. They enlarge and become more active at puberty.
The dermis contains many small blood vessels that supply the skin with nutrients and oxygen and take away waste products and carbon dioxide. Sensory receptors for the nervous system (pain, temperature, and pressure) are also located in the dermis.

Subcutaneous Tissue

Learning Objective: Describe the anatomy of the subcutaneous tissue.

The subcutaneous tissue is not a layer of the skin. It lies below the dermis and creates a connection between the skin and the structures that are below the skin, such as muscle or bone. Subcutaneous tissue is made up of loose connective tissue and adipose (fat) tissue. This tissue is not rigid but rather movable and pliable. The subcutaneous tissue can slip over underlying structures. Without subcutaneous tissue, our skin would tear with movement.
The subcutaneous tissue provides insulation for the body and serves as a calorie reserve in the adipose tissue. It also contains blood vessels, nerves, and the base of hair follicles. Subcutaneous tissue is distributed unevenly, and as the body ages, it thins. This can make administering injections or drawing blood on older adult patients more challenging. Also, the loss of subcutaneous tissue makes it more difficult for older adults to regulate body temperature; they are hotter when temperatures rise and colder when temperatures drop. Aging skin can be fragile and easily traumatized or damaged. The medical assistant must be careful to avoid injuring the skin of older patients.

17.2

Critical Thinking Application

Mai goes to the waiting area and calls back Casey Hernandez. She introduces herself and shows Casey back to the exam room. After vital signs are completed, Mai asks Casey the reason for her visit. Casey looks down and is a bit shy as she talks. Mai notices that the palms of Casey’s hands are sweaty. What types of glands produce sweat in the integumentary system? Where are they concentrated in the body?