Review of Key Concepts
Structure of the Skin and Subcutaneous
Tissue (p. 192)
- Dermatology is the study of the integumentary system. This system consists of the skin, hair, nails, and cutaneous glands.
- The skin is composed of the epidermis and dermis.
- The epidermis is a stratified squamous epithelium with four histological layers in most areas of the body, but five in the thick skin of the palms and soles: the stratum basale, stratum spinosum, stratum granulosum, stratum lucidum (missing in thin skin), and stratum corneum.
- There are four types of cells in the epidermis: keratinocytes (the most abundant), melanocytes, tactile cells, and dendritic cells.
- The dermis consists of a thin superficial papillary layer of areolar tissue and a thicker deep reticular layer of dense irregular connective tissue.
- The dermis is composed mainly of collagen but also has elastic fibers and a variety of cells. It contains blood vessels, nerves, glands, muscle, and the roots of the hair and nails.
- Between the skin and muscle is a connective tissue hypodermis. In many areas, it is predominantly adipose tissue (subcutaneous fat).
- Normal skin colors result from hemoglobin (in the blood), melanin, and carotene. Pathological skin colors include cyanosis, erythema, jaundice, bronzing, pallor, albinism, and hematomas.
- The skin is marked with hemangiomas (birthmarks), freckles, moles (nevi), friction ridges, and flexion creases.
Functions of the Skin (p. 198)
- The skin is a barrier to pathogenic organisms and ultraviolet radiation, and to the loss of water, although some water and small amounts of O2 and CO2 penetrate the skin, as do some vitamins, drugs, and poisons.
- Epidermal keratinocytes begin the synthesis of vitamin D.
- The skin is the body's most extensive sense organ, with receptors for touch, heat, cold, pressure, vibration, and tissue injury.
- Blood vessels and sweat glands of the skin are important in thermoregulation.
- The expressiveness of the facial skin and appearance of the integument in general are important in social communication.
Hair and Nails (p. 200)
- A hair is a filament of keratinized cells growing from an epidermal tube called the follicle.
- Fetuses have temporary hair called lanugo. After birth, the hair is a mixture of fine vellus and coarser terminal hair.
- A hair consists of a basal bulb, a root below the skin surface, and a shaft above the skin. It has a central, loose core called the medulla, surrounded by keratinized and pigmented cells of the cortex, and a surface layer of thin cells forming a cuticle.
- Variations in hair color result from various proportions of eumelanin to pheomelanin.
- A hair is supplied by a piloerector muscle that raises the hair in response to cold or fear, and a nerve ending called a hair receptor that detects hair movements.
- A hair has a life cycle consisting of anagen (growth), catagen (apoptosis), and telogen (resting) stages.
- The functions of hair vary from one region of the body to another and include heat retention on the scalp, sensation, signifying individual identity and sexual maturity, regulating dispersal of sex pheromones, protecting the eyes and ears from debris, and nonverbal communication.
- A nail is a clear plate of hard keratin that grows from a nail matrix under the skin fold.
- Nails serve for manipulation of objects, grooming, and digging.
Cutaneous Glands (p. 205)
- The most numerous glands of the skin are merocrine sweat glands, which release perspiration through pores in the skin surface. They function to cool the body.
- Apocrine sweat glands open into hair follicles of the groin, anal region, axilla, areola, and male beard. They produce a thicker form of sweat with probably pheromonal functions.
- Sebaceous glands open into hair follicles and produce an oily sebum that keeps the skin and hair from becoming dry, brittle, and cracked.
- Ceruminous glands secrete cerumen (earwax), which has waterproofing and antibacterial functions.
- Mammary glands develop in the breast during pregnancy and lactation, and produce milk.
Diseases of the Skin (p. 208)
- The three forms of skin cancer are defined by the types of cells in which they originate: basal cell carcinoma (the most common but least dangerous form), squamous cell carcinoma, and malignant melanoma (the least common but most dangerous form).
- Burns can be first-degree (epidermal damage only, as in a mild sunburn), second-degree (some dermal damage, as in a scald), or third-degree (complete penetration of the dermis, as in burns from fire).
- People with serious burns must be treated first with respect to fluid balance and second for infection control.
Saladin: Anatomy & I 6. The Integumentary I Text I I © The McGraw-Hill
Physiology: The Unity of System Companies, 2003 Form and Function, Third Edition
214 Part Two Support and Movement
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Rosacea and Eczema are two skin conditions that are fairly commonly found throughout the world. Each of them is characterized by different features, and can be both discomfiting as well as result in undesirable appearance features. In a nutshell, theyre problems that many would want to deal with.
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