Anatomy/Integumentary System

The integumentary system or integument is a focus topic of the event Anatomy. It came into rotation for the 2014, 2015, and 2016 seasons. It will once again be a focus for the 2020 season, and rotates concurrently with the skeletal and muscular systems. The integumentary system is composed of skin, hair, nails, and glands.

Functions

The major functions of the integumentary system are:

1. Protection. The integumentary system's main focus is to protect your body from injury and pathogens. For example, the stratum germinativum repairs minor injuries. Additionally, the skin acts as a barrier to protect from pathogens. Keratin and glycolipids in the skin help waterproof it and the continuity of the skin protects from bacterial invasion. There are also chemical barriers such as skin secretions of sebum, human defensins, and cathelicidins . The acid mantle of the skin causes the skin to have a low pH which slows bacterial growth on the skin's surface. Melanin protects the body from UV damage. Additionally, Langerhans' cells and dermal macrophages are located in the skin and activate the immune system. The structure of DNA in the skin allows its electrons to absorb UV radiation and convert it into heat.
2. Temperature maintenance. The integumentary system also regulates heat exchange with environment and keeps body at an average of 98.6 degrees F or 36.0 degrees C. Sweat, secreted by sudoriferous glands, helps cool the body. Dilation and constriction of blood vessels in the skin also helps to regulate the body temperature.
3. Synthesis and storage of nutrients. Synthesizes Vitamin D3 and stores lipids in adipose (fat) tissue.
4. Sensory reception. There are touch, pressure, pain, and temperature receptors in the skin which interact with the nervous system. Meissner's corpuscles and Merkel disks sense light touch while Pacinian receptors, located deeper in the dermis, detect deep pressure. Hair follicle receptors sense movement of hairs. Nocireceptors and bare nerve endings sense pain. Thermoreceptors sense heat and cold.
5. Excretion and secretion. The skin excretes salt water and organic wastes. In postpubescent females, modified glands called mammary glands secrete milk. Sudoriferous (sweat) glands are identified into two types- apocrine and eccrine. Eccrine sweat glands secrete cooling sweat and apocrine sweat glands secrete during emotional stress or excitement. Ceruminous glands are modified sweat glands that produce ear wax.
6. Protects the body from dehydration.

Structure of the Skin

• 3 Major Layers of the Skin
  • Epidermis - outer, thinner layer that consists of epithelial tissue
  • Dermis - The inner, thicker layer that consists of connective tissue
  • Subcutaneous (subQ) - also called the hypodermis. Located underneath the dermis, however not necessarily part of skin but shares some functions. Composed of areolar/adipose connective tissues that anchors skin to the underlying structures -mostly muscles - and insulates/absorbs shock

Epidermis

• The epidermis is composed primarily of keratinized stratified squamous epithelium.
  • Contains four major types of cells:
    • Keratinocytes - produce keratin - a tough insoluble fibrous protein that provides protection and helps contribute to the strength and water resistance displayed by the epidermis, hair and nails)
    • Melanocytes - produce pigment melanin
    • Langerhans (dendritic) cells - Macrophages that originated in the red bone marrow. Involved in the immune responses
    • Merkel cells - function in the sensation of touch along with the other adjacent tactile discs (receptors)

• Types of Epidermis
  • Thin (hairy) skin - covers all body regions except the palms, palmar surface of digits, and soles of the feet. Usually 1-2 mm thick. Thin skin has fewer skin receptors and sudoriferous glands and more sebaceous glands.

• • Thick (hairless) skin - covers the palms, palmar surfaces of digits and soles.Thick skin has more skin receptors and sudoriferous glands and fewer sebaceous glands. Skin ridges (e.g., fingerprints) are found due to well-developed dermal papillae. Skin ridges aid in grip and object manipulation.

Epidermal Layers

• The epidermis is composed of four layers in thin skin, and five layers in thick skin. Moving from deep to superficial:

• Stratum basale, or stratum germinativum
  • Deepest epidermal layers. The stratum germinativum is also known as the "growing layer of the skin" or the "base of it" (hence its other name, stratum basale).
  • It is attached by hemidesmosomes, which are special disc-shaped proteins, to the basement membrane, which is a network of protein fibers separating the epidermis from the dermis below.
  • The Stratum Germinativum, as pictured above, descends into the dermis in what are called Epidermal ridges. The areas where the dermis projects upward are called "'dermal papillae'". These are required because there are no blood vessels in the epidermis, so all nutrients must be obtained through diffusion from the dermis.
  • These ridges are what cause the elaborate patterns in the epidermis of areas with thick skin, such as fingertips.
  • Present in this layer:
    • germinative cells, which are large stem cells that replace shed cells in the surface.
    • melanocytes, which are the cells that produce melanin, a brownish-yellow pigment. These melanocytes have processes which extend throughout this layer in order to distribute the melanin.
    • nervous receptors, which provide information about external stimuli to the brain.

A diagram depicting the layers of the epidermis in thick skin

• Stratum Spinosum
  • A layer of keratinocytes 8-10 cells deep. Also abundant in melanosomes and dendritic cells. Here cells divide rapidly.
• Stratum granulosum
  • Keratinocyte cell appearance changes. Cells flatten while nuclei and organelles disintegrate.
  • Keratinization begins and helps form keratin in upper layers
  • Cells above this layer die due to being too far from dermal capillaries
• Stratum lucidum
  • The 4th layer that is only present in thick skin the skin of the fingertips, palms, and soles
  • Thin, translucent band superficial to the stratum granulosum
• Stratum corneum
  • outermost layer composed of approximately 20 layers of flat cell-remnants (dead keratinocytes with no cellular organelles filled with only keratin protein.) They are continuously shed and replaced by cells from deeper strata.
  • After the cells of the stratum granulosum or of the stratum lucidum die, which is a total of around 2-4 weeks after they are born in the stratum germinativum, they are pushed up to the most superficial layer, the stratum corneum. This consists of 15-30 layers of densely packed, flattened dead cells that have accrued large amounts of keratin. They are considered keratinized or cornified cells. This is useful because keratin is very strong, and it protects the deeper and more vulnerable dermis. They are very tightly attached to each other by desmosomes, which are special proteins that join two cells and are very difficult to break. These desmosomes are why one's skin peels off in sheets after a bad sunburn instead of in individual cells.

The Dermis

An Image of Stained Skin With Layers of the Dermis Labeled

The dermis, which is beneath the Epidermis, consists of two layers. Collagen fibers comprise 70% of the dermis and give structural toughness and strength. From most superficial to deepest, they are the papillary layer and the reticular layer.

Papillary Layer

The papillary layer is named after the dermal papillae. It is a very loose connective tissue whose purpose is to supply the epidermis with nutrients. It is filled with capillaries and nerves to reach this end.

Reticular Layer

The reticular layer is made up of very dense irregular connective tissue. It is filled with densely packed elastin fibers, which give the skin its elasticity. This layer is also filled with collagen fibers, which resist that elasticity, in order to keep the skin rigid. One of the major causes of wrinkles is the degradation of collagen fibers due to UV light.

Skin Color

Pigmentation

Pigmentation is one of the two major methods of skin coloration

There are two major pigments which can influence skin color: carotene, which is orangey yellow and found in carrots and squashes, and melanin, which is brown, yellow-brown, or black and produced by melanocytes. Two types of melanin are eumelanin and pheomelanin. Eumelanin is brownish-black and pheomelanin is reddish-yellow. The number of melanocytes is about the same for all races, and there is about one melanocyte in every 10 keratinocytes. In albinism, melanocytes are present but experience interference with melanin production.

Carotene can be synthesized into Vitamin A, which is needed for the maintenance of epithelial cells. Eating large amounts of carotene can also cause the skin of light-skinned individuals to turn orange.

Melanin is transferred into the stratum germinativum and stratum spinosum by intracellular vesicles arising from melanocytes. Melanocytes are typically in a 1:20-1:4 ratio with basal stem cells depending on the area. Because cells rise through the strata, this colors the entire epidermis. When exposed to sunlight, melanocytes will gradually increase their production of melanin with the maximum occurring about 10 days after the initial exposure. Freckles appear due to increased melanocyte activity in an area. They occur mostly on surfaces exposed it the sun, such as the face.

UV radiation, while beneficial in small amounts to the synthesis of Vitamin D3, can cause serious damage in large doses. Melanin protects the body by absorbing the UV rays, and it clusters around the nuclei of epidermal cells to protect the DNA. Unfortunately, melanin cannot protect us from 100% of the UV light and some is bound to get through. Long periods of exposure can cause premature wrinkling and skin cancer even in dark-skinned individuals. A minimum of SPF 15 is recommended in sunscreen, and for fair-skinned individuals, it is better to have a 20-30 SPF sunscreen.

Dermal Circulation

The other major method of skin coloration is dermal circulation.

In times of vasoconstriction, such as fright, the skin will pale and in some cases turn blue. If the skin turns blue, it is called cyanosis.

In times of vasodilation, such as embarrassment, the skin will turn red.

Vitamin D3 Synthesis

One of the main functions of the integumentary system is the synthesis of Vitamin D3 from a cholesterol-based steroid, which is required for the uptake of calcium into our bones. This function is carried out by the two deepest layers, the stratum germinativum and the stratum spinosum. A low amount of UV radiation is required for this process.

Nails

Nails are made of tightly packed keratin. The nails help us grip things with our fingers.

The main parts of the nail are the hyponychium, eponychium (the cuticle), nail matrix, lunula, nail plate, nail root, free margin, and the paronychium.

Diagram of a human nail

Hair

Hair is comprised of keratin, and hair follicles develop before birth. Whether someone has straight, curly/kinky or wavy hair depends on the shape of the follicle. No new follicles develop after birth. The three main types of body hair are terminal hair, lanugo, and vellus hair.

Lanugo

Lanugo, colloquially referred to as "peach fuzz", is very fine, soft hair often found on infants. If lanugo grows on the body of an adult, it is typically a sign of anorexia nervosa.

Terminal Hair

Terminal hairs are thick, coarse hairs that grow during puberty.

Vellus Hair

Vellus hair is short, fine downy hair found all over the body except for the palms of the hands and soles of the feet. It is thinner than lanugo.

Vellus hair (via Wikipedia)

Glands

The two main types of glands in the integumentary system are sebaceous glands, which produce oil, and sudoriferous glands, which produce sweat. There are more sebaceous glands and less sudoriferous glands in thin skin. In thick skin, there are more sudoriferous glands and less sebaceous glands. Acne is caused by the inflammation of sebaceous (oil-producing) gland ducts.

Sebaceous Glands

Sebaceous glands secrete sebum, an oily substance which lubricates hair and skin. Sebaceous glands are present everywhere except for areas with thick skin, i.e. the palms of the hands and soles of the feet. Sebaceous glands are located in the dermis layer and are generally connected to hair follicles, except for in hairless areas such as the eyelids.

Sudoriferous Glands

Sudoriferous glands typically secrete sweat. Sudoriferous glands are found mostly on areas of thick skin. There are two types of sudoriferous glands: apocrine and eccrine.

Apocrine Glands

Apocrine glands develop during puberty. These glands are located in the ear canal, around the eyes and nose, under the arms, on the areola of the breasts, and in the pubic regions. Mammary (milk) glands are one type of modified apocrine gland. Earwax, or cerumen, is secreted by ceruminous glands, the other type of modified apocrine gland. The appearance of cerumen can differ depnding on genetic factors. Typical apocrine glands secrete sweat.

Eccrine Glands

Eccrine glands are found everywhere without thick skin. Eccrine glands are present at birth and continue to secrete sweat from then on. The sweat secretion produced by eccrine glands is made of water and sodium chloride.

Membranes

• Serous Membrane: Lines body cavities that have no opening to the outside. Secretes a watery fluid called serous fluid that lubricates surfaces.
• Mucous Membrane: Lines cavities and tubes that open to the outside.
• Synovial Membrane: Forms the inner lining of joint cavities. Secretes a thick fluid called synovial fluid.
• Cutaneous Membrane: Also known as skin.

Diseases of the Integument

Burns

Burns are disorders of the integument caused by exposure to intense heat, radiation, electricity, or friction. Burn appearance and treatment varies greatly depending on how deeply the skin was burned. Burns are classified into degrees.

First Degree Burns

These burns are the most superficial. First degree burns affect the epidermis to the papillary layer of the dermis. First degree burns give the skin a dry red appearance, sometimes with small white blisters.

Second Degree Burns

These burns destroy most or all of the epidermis, and involve all layers of the dermis. Second degree burns are pink or red, and cause the involved skin to look shiny and wet. The sensation in tissue with a second-degree burn is weakened.

Third Degree Burns

These burns involve all of the layers of the skin. Third-degree burns permanently damage tissue. These burns have a charred black or brown appearance. The tissue involved in a third degree burn often must be amputated.

Allergies and Allergens

An allergen is an antigen which produces a rapid response from the immune system when introduced to the skin.

Infections

An infection is an invasion of dermal tissue by disease-causing agents.

Dermatitis

Dermatitis is an inflammation of the skin due to a variety of factors.

Eczema

Eczema refers to any condition in which the skin becomes itchy or inflamed, but it is most often used to refer to atopic dermatitis. This condition typically begins in infancy or childhood and the skin becomes dry, flaky, and irritated near creases in the skin. Areas include the elbows, the knees, and at the back of the neck. The disorder is likely hereditary. Hot, cold, or dry conditions, as well as stress and certain allergens, can exacerbate eczema symptoms.

Treatment involves preventing infection and soothing itching or discomfort.

Contact Dermatitis

Contact dermatitis produces red, burning, itching, or stinging rashes in response to allergens or other topical irritants. Common causes include poison ivy or heavy metals.

Seborrheic Dermatitis

Seborrheic dermatitis (known as cradle cap in infants) produces scaly patches, dandruff, and incessant itching.

Psoriasis

Psoriasis is a condition resulting in red, flaky patches on the skin. There are five primary types: plaque, guttate, inverse, pustular, and erythrodermic. Psoriatic arthritis can also be considered a variation of this disorder. Many cases of psoriasis are hereditary, but other risk factors include weight or obesity, smoking, medications, infections, alcohol consumption, vitamin D deficiency, and stress.

Plaque Psoriasis

The most common type of psoriasis, plaque psoriasis appears as raised, red, scaly patches on the skin. These scales have well-defined edges and are most often found on the outsides of knees and elbows, the scalp, the lower back, the face, and the palms of the hands and soles of the feet. Topical creams and ointments with and without steroids (i.e. calcipotriene) are the main method of treatment for plaque psoriasis, but it can also be treated by medications or ultraviolet phototherapy.

Guttate Psoriasis

Rather than large scales, guttate psoriasis manifests as tiny lesions or teardrops on the skin. They mainly appear on the abdomen and upper extremities, and they do not appear on the palms or soles like other forms of the disorder. This form of psoriasis is most common in young adults or children, and less than a third of psoriasis patients have it. Dry air is a catalyst in flareups, especially in winter. Severity is determined by the amount of coverage: mild is approximately 3 percent, moderate is 3 to 10 percent, and severe is more than 10 percent coverage or adversely impacts the patient's livelihood and appearance.

Inverse Psoriasis

Also known as flexural or intertriginous psoriasis, inverse psoriasis manifests on "flexor surfaces" or in skin folds. Common sites of inverse psoriasis include the navel, groin folds or genitalia, the lips, the ears, the axillae (armpit region), under the breasts (inframammary folds), and between the buttocks (intergluteal cleft). Because these red patches occur in sensitive areas, patients may experience bleeding, pain, or irritation at the sites. They may also experience discomfort and fungal or bacterial infections. Many inverse psoriasis patients have another comorbid form of psoriasis.

Pustular Psoriasis

As the name suggests, raised bumps filled with pus (pustules) accompany the telltale psoriatic scales. This form of psoriasis is uncommon and can have acute flareups associated with fever or manifest chronically. Other skin disorders can be considered variations of pustular psoriasis, such as pregnancy-associated impetigo herpetiformis.

Erythrodermic Psoriasis

Erythrodermic psoriasis is described as aggressive and is considered the most severe form of psoriasis. It involves a full body rash that can spread quickly from the initial site of inflammation. The rash peels and itches or burns intensely.

Psoriatic Arthritis

Arthritis is an inflammation of the joints, and psoriatic arthritis involves scaly rashes along with joint stiffness and pain. Sometimes joint problems can start before the first rash appears.

Skin Cancer

Skin cancer is the most common type of cancer in the US. The three major types of skin cancer are basal cell carcinoma, squamous cell carcinoma, and melanoma. Skin cancer occurs when DNA of epithelial cells is damaged, causing the cells to grow out of control. The most common cause of skin cancer is excessive exposure to sunlight.

Basal Cell Carcinoma

Basal cell carcinoma is the most common type of skin cancer. It is curable if found early, especially because it rarely metastasizes (spreads to other organs). BCCs look like smooth, pearly bumps which are mostly found on the face, neck, and back.

Squamous Cell Carcinoma

Squamous cell carcinoma occurs on parts exposed to the sun. SCC often develops on areas with actinic keratoses, which are crusty red sores caused by UV exposure. SCC looks like firm red bumps susceptible to bleeding and crusting.

Melanoma

Melanoma is deadly if not found early because it metastasizes quickly. It is most common in the southern hemisphere where the ozone layer is thin. Melanoma looks like irregular dark spots with a different appearance than a patient's moles.

ABCD Test

You can separate skin cancer with other skin disorders by using the ABCD of skin cancers.

1. Asymmetry- the area is not symmetrical
2. Borders- the borders are not even
3. Color- different shades and varieties can signal skin cancer
4. Diameter- if the diameter is larger than 1/4 inch or 6 mm, it is likely it is melanoma.