Skin & Body Membranes
Epithelial MembranesEpithelial Membranes, also called covering and lining membranes, include the cutaneous membrane (skin), the mucous membranes, and the serous membrane. These membranes are called "epithelial," but that is often misleading and not accurate. They all contain an epithelial sheet, but it is always combined with an underlying layer of connective tissue.
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Connective Tissue MembranesSynovial membranes are composed of soft areolar connective tissue and contain no epithelial cells at all. Synovial membranes are the ones that line fibrous capsules surrounding joins when they produce a smooth surface and secrete lubricating fluid. These membranes also line small sacs of connective tissue called bursae and the tubelike tendon sheaths. These structures cushion organs moving against each other during muscle activity -- such as the movement of a tendon across a bone's surface.
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Cutaneous Membrane
The cutaneous membrane is your skin. Its superficial epidermis is made up of a keratinizing stratified squamous epithelium. The underlying dermis is made up of mostly dense connective tissue. This membrane is exposed to air and is a dry membrane, which is different from the other membranes.
Mucous Membrane
Mucous membranes are composed of epithelium resting on a loose connective tissue membrane called a lamina propria. This type of membrane lines all body cavities that open to the exterior, such as those of the hollow organs of the respiratory, digestive, urinary, and reproductive tacts. Most mucosae contain either stratified squamous epithelium or simple columnar epithelium. They are "wet," or moist membranes that are almost continuously bathed in secretions. The epithelium of mucosae is often adapted for absorption or secretion.
Serous Membrane
This membrane is composed of a layer of simple squamous epithelium resting on a thin layer of areolar connective tissue. Serous membranes line body cavities that are closed to the exterior. These membranes occur in pairs. The parietal layer lines a specific portion of the wall of the ventral body cavity. It fold in on itself to form the visceral layer, which covers the outside of the organs in that cavity. The serosa lining the abdominal cavity and covering its organs is the peritoneum. Serous membrane isolate the lungs and hear from one another in the thorax. The membrane that surrounds the lungs is the pleura and the membrane that surrounds the heart is the pericardium.
Function of the Integumentary System
Structures of the Skin
The skin is made up of two different kinds of tissue; the outer epidermis and the underlying dermis.
Epidermis |
Dermis |
Skin Color
Three pigments contribute to skin color:
- The amount and kind of melanin in the epidermis. (yellow, reddish brown, or black)
- The amount of carotene deposited in the stratum corneum and subcutaneous tissue. Skin tends to take on a yellow-orange cast when the person eats large amounts of carotene-rich foods.
- The amount of oxygen-rich hemoglobin in the dermal blood vessels.
People with brown toned skin produce a lot of melanin. In light-skinned people, who have less melanin, the crimson color of oxygen-rich hemoglobin in the dermal blood supply flushes through transparent cell layers about and gives the skin a rosy glow.
Emotions influence skin color in the following ways:
- When the skin reddens skin may indicate embarrassment, fever, hypertension, inflammation, or allergy.
- When the skin becomes pale, a person may be under a certain type of emotional stress.
- If a person's skin becomes an abnormal yellow color it usually signifies a liver disorder.
- When a person's skin bruises, their skin is black and blue in certain spots. The black and blue marks reveal sites where blood has escaped from the circulation and has clotted in the tissue spaces.
Appendages of the Skin
Cutaneous Glands
The cutaneous glands are all exocrine glands that release their secretions to the skin surface via ducts. There are two groups that these glands fall into: sweat glands and sebaceous glands. Sebaceous glands are also called oil glands. They are found all over the skin except on the palms of hands and the soles of feet. Normally, their ducts empty into a hair follicle, but some open directly onto the skin surface. The product of the sebaceous glands is a mixture of oily substances and fragmented cells. Sebum is a lubricant that keeps the skin soft and moist and prevents hair from becoming brittle. Sweat glands are widely distributed in the skin. There are two types of sweat glands; eccrine and apocrine. Eccrine glands are more numerous and they are found all over the body. They produce sweat and are an important and highly efficient part of the body's heat-regulating equipment. Apocrine glands are largely confined to the armpit and genital areas. Although they are larger than eccrine glands, their ducts empty into hair follicles. They begin to function during puberty under the influence of male sex hormones.
Another appendage of the skin is hair and hair follicles. A hair, which is produced by a hair follicle, is a flexible epithelial structure. The part of the hair that is enclosed in the follicle is called the root. The part that projects from the surface of the scalp or skin is called the shaft. A hair is formed by the division of the well-nourished stratum basale epithelial cells in the matrix of the hair bulb at the inferior of the follicle. As the daughter cells are pushed away from the growing region, they become keratinized and die. Hair follicles are compound structures. The inner epidermal sheath is composed of epithelial tissue and that is what forms the hair. The out dermal sheath is actually dermal connective tissue. This region supplies blood vessels to the epidermal portion and reinforces it.
Nails are scalelike modifications of the epidermis that correspond to the hoof or claw of other animals. Each nail is made up of a free edge, a body, and a root. Nails folds are the boarders of the nail that are overlapped by skin folds. The edge of the thick proximal nail fold is commonly called the cuticle.
Another appendage of the skin is hair and hair follicles. A hair, which is produced by a hair follicle, is a flexible epithelial structure. The part of the hair that is enclosed in the follicle is called the root. The part that projects from the surface of the scalp or skin is called the shaft. A hair is formed by the division of the well-nourished stratum basale epithelial cells in the matrix of the hair bulb at the inferior of the follicle. As the daughter cells are pushed away from the growing region, they become keratinized and die. Hair follicles are compound structures. The inner epidermal sheath is composed of epithelial tissue and that is what forms the hair. The out dermal sheath is actually dermal connective tissue. This region supplies blood vessels to the epidermal portion and reinforces it.
Nails are scalelike modifications of the epidermis that correspond to the hoof or claw of other animals. Each nail is made up of a free edge, a body, and a root. Nails folds are the boarders of the nail that are overlapped by skin folds. The edge of the thick proximal nail fold is commonly called the cuticle.
Homeostatic Imbalances of the Skin
Burns |
Infections and Allergies |
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Skin Cancer
- Basal Cell Carcinoma; least malignant and most common skin cancer -- cells of the stratum basale, altered so that they cannot form keratin, no longer honor the boundary between epidermis and dermis
- Squamous Cell Carcinoma; arises from the cells of the stratum spinosum -- the lesion appears as a scale, reddened papule, that gradually forms a shallow ulcer with a firm, raised boarder
- Malignant Melanoma; cancer of the melanocytes; accounts for only about 5 percent of skin cancers, but its incidene is increasing rapidly and it is often deadly
- Melanoma can begin wherever this is pigment; most such cancers appear spontaneously, but some develop from pigmented moles -- arises from accumulated DNAdamage in a skin cell and usually appears as a spreading brown to black patch that metastasizes rapidly to surrounding lymph and blood vessels