Integumentary system

The integumentary system is the organ system that protects the body from damage, comprising the skin and its appendages(including hair, scales, and nails). The integumentary system has a variety of functions; it may serve to waterproof, cushion and protect the deeper tissues, excrete wastes, regulate temperature and is the location of receptors for pain, sensation, pressure and temperature. In humans the integumentary system additionally provides 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.

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 comprising 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 four to five layers. The stratum basale 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 (non vascular). It contains the pigment melanin which gives skin colour and allows the skin to tan, uneven distribution of melanin causes freckles. From the dermis to the epidermis the layers are named, stratum basale, stratum spinosum, stratum granulosum, stratum lucidum (the extra layer that occurs in places such as palms and soles of the feet), and the stratum corneum (the most superficial layer, made up of all dead cells, proteins, and glycolipids which keep the body waterproof)

The protein keratin stiffens epidermal tissue to form fingernails. 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: squamous 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, which 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:

1. Composed of two layers- papillary and reticular
2. The upper layer for touch, pain and heat, which communicate with the central nervous system and is responsible for the folds (called dermal papillae) of the fingerprints. The light touch sensors which are in the papillary section of the dermis are called Meissner's corpuscles.
3. 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. In this layer there are also touch receptors, these however are for sensing pressure, these sensors are called Pacinian Corpuscles.

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:

• Rash
• Blister
• Athlete's foot
• Infection
• Sunburn
• Skin cancer
• Albinism
• Acne
• Herpes
• Cold Sores

External links

• Berkeley anatomy lecture on the integumentary system