Chapter 5

Describe how the skin accomplishes at least five different functions

The 5 functions of the skin are protection, sensation, heat regulation, excretion, and absorption. The skin also synthesizes.

Explain how serious burns are life threatening. Describe how to determine the extent of a burn and differentiate first, second, and third degree burns

(1) A burn is tissue damage inflicted by intense heat, electricity, radiation, or certain chemicals, all of which denature cell proteins and cause cell death to infected areas (2) The most immediate threat to a burn patient is dehydration and electrolyte imbalance due to fluid loss (3) After the first 24 hours has passed, the threat to a burn patient becomes infection to the wound site (4) Burns are classified according to severity: (a) First-degree burns involve damage only to the epidermis (b) Second degree burns injure the epidermis and the upper region of the dermis (c) Third degree burns involve the entire thickness of the skin

Summarize the characteristics of the three major types of skin cancers

(1) Basal cell carcinoma is the least malignant and the most common skin cancer (2) Squamous cell carcinoma tends to grow rapidly and metastasize if not removed (3) Melanoma is the most dangerous of the skin cancers because it is highly metastatic and resistant to chemotherapy

List the parts of a hair follicle and explain the function of each part. Also describe the functional relationship of arrector pili muscles to the hair follicles.

(1) Hairs, or pili, are flexible strands produced by hair follicles that consist of dead, keratinized cells (a) The main regions of a hair are the shaft and the root (b) A hair has three layers of keratinized cells; the inner core is the medulla, the middle layer is the cortex, and the outer layer is the cuticle (c) Hair pigments (melanin of different colors) are made by melanocytes at the base of the hair follicle (2) Structure of a Hair Follicle (a) Hair follicles fold down from the epidermis into the dermis and occasionally into the hypodermis (b) The deep end of a hair follicle is expanded, forming a hair bulb, which is surrounded by a knot of sensory nerve endings called a hair follicle receptor, or root hair plexus (c) The wall of a hair follicle is composed of an outer connective tissue root sheath, a thickened basement membrane called a glossy membrane, and an inner epithelial root sheath (d) Associated with each hair follicle is a bundle of smooth muscle cells called an arrector pili muscle

Name the tissue types composing the epidermis and dermis. List the major layers of each and describe the functions of each layer

(1) The skin (integument) (A) Consists of three major regions (1) Epidermis-outermost superficial region (2) Dermis-middle region (3) Hypodermis (superficial fascia) - deepest region (B) Epidermis (1) Composed of keratinized stratified squamous epithelium (2) Consisting of four distinct cell types and four or five layers (3) Cell types (a) keratinocytes (b) melanocytes (c) Merkel cells (d) Langerhans' cells (4) Outer portion of the skin, exposed to the external environment functions in protection (C) Cells of the Epidermis (1) Keratinocytes-produce the fibrous protein keratin (2) Melanocytes-produce the brown pigment melanin (3) Merkel cells-function as touch receptors in association with sensory nerve endings (D) Layers of the Epidermis (1) Stratum Basale (Basal Layer) (a) Deepest epidermal layer firmly attached to the dermis (b) Consists of a single row of the youngest keratinocytes (c) Cells undergo rapid division, hence its alternate name, stratum germinativum (2) Stratum Spinosum (Prickly Layer) (a) cells contain a weblike system of intermediate filaments attached to desmosomes (b) Melanin granules and Langerhans' cells are abundant in this layer (3) Stratum Granulosome (Granular Layer) (a) Thin; three to five cell layers in which drastic changes in keratinocyte appearance occurs (4) Stratum Lucidum (Clear Layer) (a) Thin, transparent band superficial to the stratum granulosum (b) Consists of a few rows of flat, dead keratinocytes (c) Present only in thick skin (5) Stratum Corneum (Horny Layer) (a) Outermost layer of the keratinized cells (b) Accounts for three quarters of the epidermal thickness (c) Functions 1)Waterproofing 2) Protection from abrasion and penetration 3) Rendering the body relatively insensitive to biological, chemical, and physical assaults (E) Dermis (1) Second major skin region containing strong, flexible connective tissue (2) Cell Types (a) fibroblasts (b) macrophages (c) mast cells (d) white blood cells (3) Two Layers (a) papillary (b) reticular (F) Layers of the Dermis (1) Papillary Layer (a) Areolar connective tissue with collagen and elastic fibers (b) Superior surface contains peglike projections called dermal papillae (c) Dermal papillae contain (1) Capillary loops (2) Meissner's corpuscles (3) Free nerve endings (2) Reticular Layer (a) Accounts for approximately 80% of the thickness of the skin (b) Collagen fibers in this layer add strength and resiliency to the skin (c) Elastin fibers provide stretch-recoil properties (G) Hypodermis (1) Subcutaneous layer deep to the skin (2) Composed of adipose and areolar connective tissue

Describe the factors that normally contribute to skin color. Briefly describe how changes in skin color may be used as clinical signs of certain diseases

(1) Three pigments contribute to skin color (a) Melanin-yellow to reddish-brown to black pigment, responsible for dark skin colors (1) Freckles and pigmented moles-result from local accumulations of melanin (b) Carotene-yellow to orange pigment, most obvious in the palms and soles of the feet (c) Hemoglobin-reddish pigment responsible for the pinkish hue of the skin Diseases on page 156-157

Compare the structure and locations of sweat and oil glands. Also compare the composition and functions of their secretions Compare and Contrast Eccrine and Apocrine glands

(A) Sweat (Sudoriferous) Glands (1) Eccrine sweat glands, or merocrine sweat glands, produce true sweat, are the most numerous of the sweat glands, and are particularly abundant on the palms of the hands, soles of the feet, and forehead (2) Apocrine sweat glands are confined to the axillary and anogenital areas and produce true sweat with the addition of fatty substances and proteins (3) Ceruminous glands are modified sweat glands found lining the ear canal that secrete earwax, or cerumen (4) Mammary glands are modified sweat glands found in the breasts that secrete milk (B) Sebaceous (Oil) Glands (1) Sebaceous glands are simple alveolar glands found all over the body except the palms of the hands and soles of the feet that secrete sebum, an oily secretion (2) The sebaceous glands function as holocrine glands, secreting their product into a hair follicle or to a pore on the surface of the skin (3) Secretion by sebaceous glands is stimulated by hormones

Describe and attempt to explain the causes of changes that occur in the skin from birth to old age

(A) The epidermis develops from the embryonic ectoderm, and the dermis and the hypodermis develop from the mesoderm (B) By the end of the fourth month of development the skin is fairly well formed (C) During infancy and childhood, the skin thickens and more subcutaneous fat is deposited (D) During adolescence the skin and hair become oiler as sebaceous glands are activated (E) The skin reaches its optimal appearance when we reach our 20's and 30's; after that time the skin starts to show the effects of cumulative environmental exposures (F) As old age approaches, the rate of epidermal cell replacement slows and the skin thins, becoming more prone to bruising and other types of injuries

Name the regions of a hair and explain the basis of hair color. Describe the distribution, growth, replacement, and changing nature of hair during the life span

(a) Hairs come in various sizes and shapes, but can be classified as vellus or terminal (b) Hair growth and density are influenced by many factors, such as nutrition and hormones (c) The rate of hair growth varies from one body region to another and with sex and age (d) After age 40 hair is not replaced as quickly as it is lost, which leads to hair thinning and some degree of balding, or alopecia, in both sexes (e) Male pattern baldness, which is a type of true, or frank, balding, is a genetically determined, sex-influenced condition

Describe the structure of nails

A nail is a scalelike modification of the epidermis that forms a clear, protective covering Nails are made up of hard keratin and have a free edge, a body, and a proximal root