The Integumentary System

The dermis, or dermal layer, is found directly under the epidermis. This deep, thick layer is made of tough connective tissue. It is connected to the epidermis by collagen fibers. Unlike the epidermis, nerve endings and blood vessels flow through the dermis. This means the dermal layer is responsible for a person feeling the sensations associated with touch, pain, heat, and cold. There are two major regions of the dermis: papillary region and reticular region. Both these regions provide elasticity to the skin, enabling it to stretch. This is helpful during physiological events like pregnancy, during which the abdominal area must stretch.

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Did You Know?

The dermis layer of a young person is more elastic than that of an elderly person. This is because the dermis of elderly people has fewer elastic fibers. As the body ages, there is a reduction in physiological processes such as cell division, blood circulation, and muscle strength. These changes lead to a less elastic and thinner dermis.

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Hair follicles and glands are also part of the dermis. Hair follicles are the sites where hair strands originate before protruding from the epidermal layer and onto the skin’s surface. The two types of glands found in the dermis are detailed below:

1. Sweat glands: These glands produce a fluid that contains water, salts, and other waste products. They are made of ducts that extend through the epidermis and look like pores on the skin’s surface. There are two types of sweat glands:

   1. Apocrine: These glands are found primarily in the armpits and groin area, where hair follicles are abundant. These glands are attached to hair follicles and create a watery fluid that contains proteins and fats. Apocrine glands are typically inactive until a person reaches puberty. They produce sweat when the body is anxious or experiencing stress.
   2. Eccrine: These glands are found all over the body, primarily on the forehead, neck, palms, and soles of feet. They are not connected to hair follicles. They regulate body temperature with sweating if the body becomes too hot.

2. Sebaceous glands: These oil-producing glands are typically attached to hair follicles. They release sebum, which is a fatty, oily substance. It waterproofs the hair and skin, preventing both structures from drying out. Sebum also has antimicrobial properties, which help the skin fight off infections.

Right beneath the dermis is a third region of the integumentary system that contains subcutaneous tissue. This region is known as the hypodermis. It contains fat, or adipose tissue, that supplies energy for cells and provides insulation to regulate body temperature.

Did You Know?

Sebaceous glands are found all over the body, but they are not found on the palms of the hands or soles of feet. The face and head contain the most sebum.

Hair and Nails

Nails and hair are accessory organs of the integumentary system. Fingernails and toenails are made of keratin, which is also found in the hair and skin. In addition to mechanical functions such as grasping things and picking up objects, nails prevent injuries to the ends of fingers. As shown in the image, the nail is made of several parts.

The nail plate is the hard outer part of the nail. Adjoining the nail plate is the free edge, which overhangs the fingertip. This is the part of the nail that is commonly groomed and cut down. The nail bed is a layer of skin found under the nail plate. This layer of skin is comprised of epidermal cells. The white space between the nail bed and cuticle is called the lunula. The cuticle is a layer of dead skin cells that accumulate and form a thick overhang layer at the base of the nail and around the nail edge. During nail care, cuticles are removed. Beneath the cuticle is the matrix, which is a layer of tissue that contains blood vessels and nerves.

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For Example

Consider eyelashes and eyebrows. These structures protect the eyes from irritants like dirt and water. In the nose, there are tiny hairs that trap dust particles and microorganisms to keep the air entering the lungs clean.

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Hair

Hair consists of dead keratinized cells and grows from the dermis out of the epidermis and onto the surface of the body. This accessory organ provides insulation for the body, especially for the head.

Recall that within the dermis is the hair follicle. This is where hair strands in the epidermis originate. The hair shaft is not attached to the follicle. It consists of the hair that is exposed on the surface of the body. The hair root is attached to the follicles and found beneath the skin’s surface. Extending beyond the root, deep beneath the skin is the hair bulb, which contains actively dividing basal cells.

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Keep In Mind

Aging affects the accessory organs. It causes hair and nails to thin over time.

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Skin Cancer

Skin cancer is the most common type of cancer that affects the integumentary system. There are many causes of skin cancer, including as genetics, but the strongest risk factor is exposure to ultraviolet (UV) radiation. Sources of UV radiation include sunlight and tanning beds.

Overexposure to UV radiation damages DNA in the body’s cells. Exposure to UV radiation causes distinct mutations in skin cells. If the body does not repair the damage to these cells, the mutations accumulate. As a result, the cells can transform into cancerous cells and grow uncontrollably. The uncontrolled cell growth can lead to cancerous tumor formations. Most tumors are harmless, but some produce cells that can move away from the original site of DNA damage and establish new tumors in other organs. This process is called metastasis.

Did You Know?

There are different types of UV rays. UVA rays penetrate the dermis and can cause skin cancer. UVB rays penetrate the epidermis and cause damage to epidermal cells. UVB rays are responsible for sunburn and most skin cancers.

There are three types of skin cancer:

1. Basal cell carcinoma: This is the most common type of skin cancer that occurs in the basal cells of the epidermis. These cells are found in the stratum basale layer and divide to create keratinocytes. Basal cell carcinoma rarely spreads or undergoes metastasis.
2. Squamous cell carcinoma: This type of skin cancer occurs in the squamous cells of the epidermis. It affects the keratinocytes in the stratum spinosum. This is the second-most-common type of skin cancer. Because this type of skin cancer is more aggressive than basal cell carcinoma, if this carcinoma is not removed it can metastasize.
3. Malignant melanoma: This type of skin cancer occurs when there is an uncontrolled growth of melanocytes in the epidermis. Because melanocytes contribute to the pigmentation of the skin, melanoma is often associated with a dark patch on the body. It is the most dangerous and fatal type of skin cancer.

Use the chart below as a reference about each of the cancers outlined above.

Let’s Review

• The integumentary system is a body system composed of the skin, hair and nails.
• Skin is the largest organ of the body that primarily functions to protect the body and maintain homeostasis.
• The epidermis, dermis, and subcutaneous layer are the three layers of skin.
• The epidermis has four or five layers: the stratum basale, stratum granulosum, stratum lucidum, stratum spinosum, and stratum corneum.
• Two types of glands, sebaceous glands and sweat glands, are found in the dermis.
• Eccrine glands are found all over the body. Apocrine glands are found mainly in the armpits.
• Hair, nails, and skin all contain keratin, which hardens and toughens each structure.
• Exposure to UV radiation can cause three types of skin cancer.
• Aging affects the integrity and structure of the skin, hair, and nails.

Integumentary System Flashcards