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The Integumentary System is an organ system that protects the body from damage, comprising the skin and its appendages1(including hair, scales, and nails). This is usually anything that grows out of the skin like hair or nails (also includes skin). The integumentary system has a variety of functions; in animals, it may serve to waterproof, cushion and protect the deeper tissues, excrete wastes, regulate temperature and is the location of sensory receptors for pain, pressure and temperature. In humans, the functions of the integumentary system are: protection, sensation, excretion, vitamin D synthesis.
The integumentary system is the largest organ system. It distinguishes, separates, protects and informs the animal with regard to its surroundings. Small-bodied invertebrates of aquatic or continually moist habitats respire using the outer layer (integument). This gas exchange system, where gases simply diffuse into and out of the interstitial fluid, is called integumentary exchange.
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Layers
Epidermis
This is the top layer of the skin made up of epithelial cells. Its main job is protection. Structurally it consists of a keratinized stratified squamous epithelium which is comprised of four types of cells: keratinocytes, melanocytes, Merkel cells, and Langerhans' cells. The majority of the epidermis is the keratinocyte which produces keratin. Keratin is a fibrous protein that aid in protection. Millions of dead keratinocytes rub off everyday. A totally new epidermis is present every 25 to 45 days. Melanocytes create melanin, the substance that gives our skin color. These cells are found deep in the epidermis layer. Accumulations of melanin are packaged in melanosomes (membrane-bound granules). These granules form a pigment shield against UV radiation for the keratinocyte nuclei.
The Epidermis itself is made up of many layers. The basale stratum is the only layer capable of cell division 'pushing up' cells to replenish the outer layer which is constantly shedding dead cells. The Epidermis does not contain blood vessels (nonvascular). It contains the pigment melanin which gives skin colour and allows the skin to tan, uneven distrubtion of melanin causes 'freckles'.
The protein keratin stiffens epidermal tissue to form finger nails. Nails grows from thin area called the NAIL MATRIX, growth of nails is 1 mm per week on average. the lUNULA is the crescent shaped area at the base of the nail, this is a lighter colour as it mixes with the matrix cells.
The epidermis contains different types of cells, the most common are; sqamous cells which are flat, scaly cells on the surface of the skin, basal cells which are round cells, and melanocytes which give the skin its colour. The epidermis also contains Langerhan's cells, these are formed in the bone marrow and then migrate to the epidermis. They work in conjunction with other cells to fight foreign bodies as part of the body's immune defence system. Granstein cells play a similar role.
Dermis (Cutis)
The dermis is the mid layer of skin, thick inner layer of skin, which comprises blood vessels, connective tissue, nerves, lymph vessels, sweat glands and hair shafts. It has two main layers:
- Composed of two layers- papillary and reticular
- The upper layer for touch, pain and heat, which communicate with the central nervous system and is responsible for the folds of the fingerprints.
- The lower layer made of dense elastic fibers that house the hair follicles, nerves, gland, and gives the skin most of its stretchiness and strength.
Subdermis (Hypodermis/Superficial Fascia)
The subdermis is the layer of tissue directly underneath the dermis. It is mainly composed of areolar connective tissue and adipose tissue. Its physiological functions include insulation, the storage of energy and aiding in the anchoring of the skin. It also cushions the underlying body for extra protection against trauma.
Functions
The integumentary system has multiple roles in homeostasis. All body systems work in an interconnected manner to maintain the internal conditions essential to the function of the body. The skin has an important job of protecting the body and acts somewhat as the body’s first line of defense against infection, temperature change or other challenges to homeostasis. Functions include:
- Protects the body’s internal living tissues and organs
- Protects against invasion by infectious organisms
- Protects the body from dehydration
- Protects the body against abrupt changes in temperature
- Helps excrete waste materials through perspiration
- Acts as a receptor for touch, pressure, pain, heat, and cold (see Somatosensory system)
- Protects the body against sunburns
- Generates vitamin D through exposure to ultraviolet light
- Stores water, fat, and vitamin D
Diseases and injuries
Possible diseases and injuries to the human integumentary system include:
Integumentary System (additional info) The skin is the largest organ in the body and weighs 4.5-5kg(10-11 lb), about 16% of body weight, with a surface area of about 2 meters. Skin is continuous with, but structurally distinct from mucous membranes that line the mouth, anus, urethra, and vagina. Two distinct layers occur in the skin: the dermis and epidermis. The basic cell type of the epidermis is the keratinocyte, which contain keratin, a fibrous protein. Basal cells are the innermost layer of the epidermis. Melanocytes produce the pigment melanin, and are also in the inner layer of the epidermis. The dermis is a connective tissue layer under the epidermis, and contains nerve endings, sensory receptors, capillaries, and elastic fibers.
The integumentary system has multiple roles in homeostasis, including protection, temperature regulation, sensory reception, biochemical synthesis, and absorption. All body systems work in an interconnected manner to maintain the internal conditions essential to the function of the body. Follicles and Glands Hair follicles are lined with cells that synthesize the proteins that form hair. A sebaceous gland (that secretes the oily coating of the hair shaft), capillary bed, nerve ending, and small muscle are associated with each hair follicle. If the sebaceous glands becomes plugged and infected, it becomes a skin blemish (or pimple). The sweat glands open to the surface through the skin pores. Eccrine glands are a type of sweat gland linked to the sympathetic nervous system; they occur all over the body. Apocrine glands are the other type of sweat gland, and are larger and occur in the armpits and groin areas; these produce a solution that bacteria act upon to produce "body odor". Hair and Nails
Hair, scales, feathers, claws, horns, and nails are animal structures derived from skin. The hair shaft extends above the skin surface, the hair root extends from the surface to the base or hair bulb. Genetics controls several features of hair: baldness, color, texture.
Nails consist of highly keratinized, modified epidermal cells. The nail arises from the nail bed, which is thickened to form a lunula (or little moon). Cells forming the nail bed are linked together to form the nail. Skin and Homeostasis
Skin functions in homeostasis include protection, regulation of body temperature, sensory reception, water balance, synthesis of vitamins and hormones, and absorption of materials. The skin's primary functions are to serve as a barrier to the entry of microbes and viruses, and to prevent water and extracellular fluid loss. Acidic secretions from skin glands also retard the growth of fungi. Melanocytes form a second barrier: protection from the damaging effects of ultraviolet radiation. When a microbe penetrates the skin (or when the skin is breached by a cut) the inflammatory response occurs.
Heat and cold receptors are located in the skin. When the body temperature rises, the hypothalamus sends a nerve signal to the sweat-producing skin glands, causing them to release about 1-2 liters of water per hour, cooling the body. The hypothalamus also causes dilation of the blood vessels of the skin, allowing more blood to flow into those areas, causing heat to be convected away from the skin surface. When body temperature falls, the sweat glands constrict and sweat production decreases. If the body temperature continues to fall, the body will engage in thermiogenesis, or heat generation, by raising the body's metabolic rate and by shivering.
Water loss occurs in the skin by two routes.
1. evaporation 2. sweating
In hot weather up to 4 liters per hour can be lost by these mechanisms. Skin damaged by burns is less effective at preventing fluid loss, often resulting in a possibly life threatening problem if not treated. Skin and Sensory Reception Sensory receptors in the skin include those for pain, pressure (touch), and temperature. Deeper within the skin are Meissner's corpuscles, which are especially common in the tips of the fingers and lips, and are very sensitive to touch. Pacinian corpuscles respond to pressure. Temperature receptors: more cold ones than hot ones. Skin and Synthesis | Back to Top
Skin cells synthesize melanin and carotenes, which give the skin its color. The skin also assists in the synthesis of vitamin D. Children lacking sufficient vitamin D develop bone abnormalities known as rickets. Skin Is Selectively Permeable
The skin is selectively soluble to fat-soluble substances such as vitamins A, D, E, and K, as well as steroid hormones such as estrogen. These substances enter the bloodstream through the capillary networks in the skin. Patches have been used to deliver a number of therapeutic drugs in this manner. These include estrogen, scopolamine (motion sickness), nitroglycerin (heart problems), and nicotine (for those trying to quit smoking).
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