Thursday, May 15, 2014
Definition
The cutaneous membrane also called the skin serves coats the body externally. The skin and its derivatives such as the sweat and oil glands, hair and nails are generally called the integumentary system. The cutaneous membrane is a dry membrane and is exposed to air.
Functions of the SKIN
The integument or the skin with its derivatives serves the following function:
- Covers the body.
- Protects the body from mechanical damage. This function is done by insulating and cushioning the deeper body organs. Examples of mechanical damage are bumps and cuts. When a person is bumped, the uppermost layer of the skin toughens or hardens the cells. The toughening of the cells is due to the presence of keratin in the upper layer of the skin. Pressure receptors in the skin send an impulse to the nervous system about a possible damage. These receptors alert an individual to bumps and provide a great deal of information about the external environment.
- 3. Protects the body from chemical damage. Acids and bases, when exposed to the body at high levels, can cause extreme damage to the internal organs. However, because of the presence of tough keratinized cells, damage to internal organs is prevented.
- Protects the body from bacterial damage. In preventing infection, one of the most important considerations to consider is an unbroken skin surface. The skin secretes urea, salt and water (acidic) when a person sweats, thus, inhibiting bacterial growth. Phagocytes are also located in the skin which is responsible for ingesting foreign substances and pathogens. Hence, bacterial penetration to deeper body tissues is prevented.
- Protects from ultraviolet radiation. The pigment or color of the skin depends on the presence of melanin. This melanin that is produced by the melanocytes is good at protecting the body from the damaging effects of the sunlight or UV damage.
- Protects the body from thermal damage. When the body is exposed to extreme heat or cold the heat and cold receptors located in the skin alerts the nervous system of the tissue-damaging factors. The brain, in response sends impulses to the site of damage or possible damage for the body’s compensatory mechanism.
- Protects the body from drying out. The skin’s outermost part, the epidermis, contains a waterproofing glycolipid and keratin in order to prevent water loss from the body surface.
- Regulation of heat loss and heat retention. The body must maintain a constant core temperature. Any change in the environmental temperatures could possibly alter the required core temperature. The skin contains a rich capillary network and sweat glands which are controlled by the nervous system. These mechanisms play an important role in regulating heat loss or retention in the body. When the body is needs to loss heat, the skin receptors alert the nervous system which in response activates the sweat glands (sweat helps cool the body in a hot environment). The blood is also flushed into the skin capillary beds, making heat loss possible. When the body needs to retain heat, the blood is NOT allowed to be flushed into the capillary skin beds. This is the main reason why during cold weather, the palms of the hands are pale.
- Acts as mini-excretory system. The perspiration contains urea, uric acid and salts.
- Synthesizes Vitamin D. The skin produces proteins that are vital for the synthesis of the Vitamin D. When a person is exposed to sunlight, modified cholesterol molecules in the skinare converted to Vitamin D.
EPIDERMIS
The epidermis is the uppermost part of the skin which is made up of stratified squamous epithelium that is capable of keratinizing (becoming hard and tough).
Characteristics of Epidermis:
- It is composed of five layers termed as STRATA.
- It has no blood supply (avascular).
- It contains keratinocytes (keratin cells) which is responsible for producing keratin. This keratin found in the epidermal skin layer is a fibrous protein that makes the epidermis a tough protective layer.
Five STRATA of the Skin (Arranged from inside out)
- Stratum basale – this is the deepest layer of the epidermis which lies closely to the dermis. The epidermal cells of stratum basale receive the most adequate nutrition through diffusion from the nutrient supply in the dermis. Also called stratum germinativum because epithelial cells in this layer are constantly undergoing cell division where a huge amount of new cells are produced per day. These cells move away from the said stratum and moves upward to the superficial epidermal layers. In this layer, melanin, the pigment of the skinis produced by melanocytes. Exposure to sunlight stimulates the melanocytes to produce more of the melanin pigment.
- Stratum Spinosum
- Stratum granulosum
- Stratum lucidum – this stratum is clear and when the cells move to this area, they become flat and contain a large amount of keratin. Eventually the cells die because they are now increasingly full of keratin. This layer is selectively found in the body. It is only seen in areas where the skin is hairless and extra thick (palms of the hands and soles of the foot).
- Stratum Corneum – the outermost epidermal layer that is approximately 20-30 cell layers thick. The tough protein, keratin, is abundant in this layer to provide protection through a durable “overcoat.” Stratum corneum flakes off steadily and is replaced by the newly produced cells from the stratum basale. The epidermis renews its cells every 25-45 days.
DERMIS
The dermis lies next to the epidermis, which is a strong and stretchable envelope holding the body together. This part of the skin is made up of the papillary and the reticular areas.
Characteristics of Dermis:
- It is made up of dense connective tissues.
- Collagen and elastic fibers are located in this part of the skin.
- Supplied with blood vessels that is vital in maintaining the normal body temperature.
Collagen fibers – gives the dermis its toughness. It helps the skin to be hydrated by attracting and binding to water.
Elastic fibers – provides elasticity to the skin.
Two Layers of the Dermis:
- Papillary Layer – this is the upper dermal layer that has dermal papillae, the fingerlike projections from the superior surface. The papillary layer has uneven surface and the dermal papillae are responsible for indenting the epidermis above. Dermal papillae is a very important part of the dermis as it is the one that house the capillary loops which provides nutrition to the epidermis and it also houses some of the pain receptors and touch receptors. The pain receptors are the free nerve endings and the touch receptors are called the Meissner’s corpuscles.
- Reticular layer – this is the deepest skin layer which contains the sweat glands, blood vessels and oil glands. It also houses the pressure receptors called the Pacinian corpuscles. The skin’s ability to fight infection is made possible because of the presence of phagocytes in this area that prevents bacteria which passed through the epidermis from penetrating deeper into the body.
Cutaneous glands
The cutaneous glands are exocrine glands that produce secretions to the skin through their ducts. These glands are the divided into two groups:
- Sebaceous glands – also call the oil glands. These glands are found all over the bodies except the palms of the hands and the soles of the feet. The secreted product is a mixture of oily substances and fragmented cells called SEBUM. Sebum plays a vital role in keeping the skin soft and moisturized. It also prevents the hair from being brittle. Aside from that, the mixture of oily substance and fragmented cells contains chemicals that KILLS bacteria. Thus, invading microorganisms are prevented from penetrating deep in the skin. Activity of the sebaceous glands is heightened during the adolescent period where the levels of male sex hormones are increased.
- Sweat glands – also termed as sudoriferous glands. These glands are extensively spread all over the body. There are two types of sweat glands which are the eccrine and the apocrine glands. Eccrine glands produce sweat which outnumbers the apocrine gland in terms of distribution all over the body. Sweat produced by the eccrine glands is clear and composed of primarily water, some salts, vitamin C, few traces of ammonia, urea and uric acid and lactic acid. The pH of sweat is acidic which helps in inhibiting bacterial growth. The apocrine glands on the other hand are largely found on the axillary and the genital areas only. Unlike the eccrine glands, these glands produce a secretion that contains fatty acids and proteins which may have a milky or yellowish color.
- Hair and hair follicles – the hair is produced by the hair follicles. It is formed by the adequately nourished stratum basale epithelial cells in the MATRIX (growth zone) of the hair bulb at the inferior end of the follicle.
- Nails– Each nail has a free edge, a body (visible attached portion) and a root.
| Difference Between Eccrine and Apocrine Glands | ||
| Criteria | Eccrine Glands | Apocrine Glands |
| Distribution | Widely distributed all over the body | Largely confined to the axillary and the genital areas only |
| Size | Smaller than apocrine glands | Larger than eccrine glands |
| Secreted Product Content | Sweat, a secretion that is primarily water added with some salts (sodium chloride), vitamin C, traces of metabolic wastes (ammonia, urea and uric acid) and lactic acid. | The secretion contains fatty acids and proteins as wells as all the substances present in the eccrine secretion. |
| Color of secreted product | Clear | Yellowish or milky |
| Secretion of product is activated by | Nerve endings that cause them to secrete sweat when the external temperature is high | Actuvated by nerve fibers during pain and stress and during sexual foreplay |
| Purpose or Function | An important and highly efficient part of the body’s heat regulating mechanism. | Apocrine glands play a minimal role in thermoregulation. Their exact function is unknown. |
