The integumentary system or integument is a focus topic of the event Anatomy. It came into rotation for the 2014 and continued for the 2015 season. It will once again be a focus for the 2016 season. The integumentary system is composed of skin, hair, nails, and glands.
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- 1 Functions
- 2 Strucuture of the Skin
- 3 Nails
- 4 Glands
- 5 Diseases of the Integument
The major functions of the integumentary system are:
- 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.
- 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.
- Synthesis and storage of nutrients. Synthesizes Vitamin D3 and stores lipids in adipose (fat) tissue.
- 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.
- 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.
- Protects the body from dehydration.
Strucuture 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
- 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)
- Contains four major types of cells:
- Types of Epidermis
- Thin (hairy) skin - covers all body regions except the palms, palmar surface of digits, and soles.sually 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.
- 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 the outside world to the brain.
- 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.
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 are about the same for all races, and 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.
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.
The dermis, which is beneath the Epidermis, consists of two layers. Collagen fibers make up 70% of the dermis and give structural toughness and strength. From most superficial to deepest, they are the papillary layer and the reticular 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.
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.
Nails are made of tightly packed keratin. The nails help us grip things with our fingers.
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 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 typically secrete sweat. Sudoriferous glands are found anywhere on the body without thick skin. There are two types of sudoriferous glands: apocrine and eccrine.
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 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.
Diseases of the Integument
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.
An infection is an invasion of dermal tissue by disease-causing agents.
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 damages, 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 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.
You can separate skin cancer with other skin disorders by using the ABCD of skin cancers.
Asymmetry- the area is not symmetrical
Borders- the borders are not even
Color- different shades and varieties can signal skin cancer
Diameter- if the diameter is larger than 1/4 inch or 6 mm, it is likely it is melanoma.