The Integumentary System - Skin Anatomy and Function

CHAPTER 5-THE INTEGUMENTARY SYSTEM I. THE INTEGUMENTARY SYSTEM-includes the skin and its derivatives (hair, nails and glands). The skin accounts for about 7% of our total body weight and varies in thickness throughout the body. A. Dermatology-area of science that focuses on the diag...

CHAPTER 5-THE INTEGUMENTARY SYSTEM I. THE INTEGUMENTARY SYSTEM-includes the skin and its derivatives (hair, nails and glands). The skin accounts for about 7% of our total body weight and varies in thickness throughout the body. A. Dermatology-area of science that focuses on the diagnosis and treatment of skin disorders. II. FUNCTIONS OF THE SKIN: A. Protection-Resistance to Trauma and Infection 1. Provides a physical barrier to prevent bacterial and viral invasion of the body. 2. Provides chemical protection by secreting melanin and natural antibiotics (like dermcidin and defensin). 3. Provides biological protection by producing cells (like Langerhan’s cells) that are involved in immune responses. B. Regulation of Body Temperature (Thermoregulation) 1. Can occur via sweat production when the body is too hot. 2. In cold conditions, blood can be removed from the skin, thus reducing heat loss at the surface of the body. C. Cutaneous Sensation 1. Cutaneous Sensory Receptors-are located throughout the skin. These are actually a part of the Nervous System and they function by detecting and responding to stimuli on the surface of the skin and stimuli external to the skin. D. Vitamin D Production-this begins when UV light strikes special molecules in the skin. This molecule travels to the kidneys and liver where it is converted into the active form of Vitamin D (Calcitrol). E. Blood Reservoir-the skin can store large supplies of blood. F. Immunity G. Excretion-of waste materials via sweat production. Sweat is composed of salts and ammonia. H. Absorption-of the fat-soluble vitamins (A, D, E, K). III. The skin is composed of two distinct layers: the epidermis and the dermis. IV. THE EPIDERMIS-the outer layer of the skin. Is composed of keratinized stratified squamous  epithelial tissue. A. 4 Types of Cells in the Epidermis: 1. Melanocytes-synthesize and store melanin. Are found in the deepest layers of the skin. a. Melanin is stored in special storage structures called melanosomes. b. Melanosomes accumulate on the sunny side of keratinocytes to protect them from UV light. 2. Keratinocytes-produce the protein keratin which forms a protective layer over the skin. a. These are the most numerous types of cells in the epidermis. Millions of these rub off the skin every day. We replace our epidermis every 25-45 days. b. These cells are dead at maturity. c. These cells store keratohyalin, the precursor molecule to keratin. 3. Langerhan’s Cells-arise from bone marrow and migrate to the epidermis. These act as macrophages that help to activate our immune system. These are easily damaged by UV light. These are also referred to as Dendritic Cells. 4. Merkel Cells-are located deep in the epidermis and are involved in detecting tactile (touch) stimuli. a. These tend to be more common in areas of the skin that do not contain hair. b. Merkel Cells are always associated with a nerve ending known as a Merkel Disc. B. Layers of the Epidermis (from deep to superficial) 1. Stratum basale-1 cell layer thick. This layer contains stem cells which can divide to produce the above 4 types of cells as well as the major epidermal derivatives nails, hair and glands). 2. Stratum spinosum-8-10 cell layers thick. The cells in this layer are tightly packed together. 3. Stratum granulosum-3-5 cell layers thick. Cells here store keratohyalin which is  used in the production of keratin. 4. Stratum lucidum-very thin layer of cells found only in thick skin. The cells in this layer are dead-they are too far away from a blood supply to survive. This layer is commonly found in areas such as the palms of the hands and the soles of the feet. 5. Stratum corneum-25 cell layers thick. Is the most superficial layer of the epidermis. a. This layer is composed entirely of dead cells. Is often referred to as the horny layer. b. The stratum corneum plays a major role in protecting the body from foreign invaders. c. Dead keratinocytes flake off the epidermis as tiny specks known as dander. Dandruff on the scalp is composed of dead keratinocytes and sebum (oil). C. Keratinization-the process in which cells develop in the Stratum Basale and migrate upwards over time. 1. This process is what allows for the formation of new cells throughout the epidermis. 2. Typically, it takes 2-4 weeks for new cells to reach the stratum corneum. 3. This process is regulated by the hormone Epidermal Growth Factor (EGF). V. THE DERMIS-the deeper portion of the skin. Is composed of flexible, strong connective tissue (including collagen fibers). A. The dermis contains an extensive nerve and blood supply. B. Layers of the Dermis: 1. The Papillary Layer-composed of areolar connective tissue with numerous collagen fibers. a. Dermal Papillae-projections associated with the papillary region. These extend upward into the epidermis. Dermal papillae contain nerve endings, and capillaries. 1) When capillaries in this layer are damaged by friction or burns, fluid  can leak out of the capillaries to form blisters. 2) On the palms of the hands and the soles of the feet, the dermal papillae form upward projections known as dermal ridges. Together, the dermal papillae and dermal ridges produce what are known as friction ridges (fingerprints). The arrangement of these ridges is genetically determined and it is thought that these ridges help us grip objects. 3) Meissner’s Corpuscles-located in this region of the dermis. These are involved in detecting touch stimuli. 2. The Reticular Layer-makes up the bulk of the dermis. This layer provides the skin with extensibility (the ability to stretch) and elasticity. a. Striae-small tears in this layer of the skin. These are known as stretch marks. b. Pacinian Corpuscles-nerve endings here; these are sensitive to pressure changes. C. The Subcutaneous Layer-a layer composed of areolar and adipose tissue that sits between the dermis and the underlying muscles and tissue. This layer is also referred to as The Hypodermis. VI. PIGMENTS THAT PROVIDE US WITH OUR SKIN COLOR PATTERNS: A. Melanin-brown or black pigment. Is stored in melanocytes. 1. All individuals have about the same number of melanocytes; however, differences in skin color patterns are caused by differences in the amount of melanin in the melanocytes. Melanin production is genetically determined. 2. Melanin protects the skin and the body from high levels of ultraviolet sunlight. 3. Freckles-form when melanin accumulates in patches. 4. Albinism-inherited inability of an individual to produce melanin. 5. Vitiligo-partial loss of melanocytes from a small portion of the skin. B. Carotene-yellow-orange pigment. This can be converted to vitamin A which aids in vision and proper skin growth and development. C. Hemoglobin-red pigment in blood.  D. Skin Color Clues: 1. Cyanosis 2. Jaundice 3. Erythema 4. Pallor or blanching 5. Bronzing 6. Bruises E. Hemangiomas-birth marks. Their color is the result of the accumulation of numerous blood vessels. VII. EPIDERMAL DERIVATIVES-all develop from the embryonic epidermis, and they all play a role in maintaining body homeostasis. A. Glands-2 Types Associated with the Skin: 1. Sudoriferous (Sweat) Glands-2.5 million of these distributed over the entire surface of the human body. a. Two Types of Sudoriferous Glands: 1) Eccrine Sweat Glands-most numerous type of sweat gland. Are more numerous on the palms of the hands, soles of the feet and the forehead. 2) Apocrine Sweat Glands-located in the axillary region and they open directly into hair follicles. These are activated by nerves during pain and stress. The exact function of these glands is unclear. b. Perspiration (Sweat)-cools the body and removes nitrogenous wastes from the body. 1) It is about 99% water but sweat may include salt, urea, uric acid. 2) Sweat production and release is regulated by the hypothalamus. c. Specialized Sweat Glands: 1) Ceruminous Glands-modified apocrine sweat glands that line the external ear canal. These produce cerumen (earwax) which serves as a protective barrier in the ear. 2) Mammary Glands-secrete milk after childbirth. 2. Sebaceous (Oil) Glands-located all over the body except for on the palms of the  hands and the soles of the feet. These glands open into hair follicles. a. Sebum-oil secreted by these glands. The functions of sebum include: softening and lubricating the hair and skin, reducing water loss from the skin and preventing bacterial growth on the surface of the skin. b. The secretion of sebum is stimulated by hormones (especially the sex hormones). c. Acne-inflammation of sebaceous glands that leads to the formation of pimples. d. Blackheads-occur when some bacteria begin feeding on sebum. e. Seborrhea-overactive sebaceous glands on the skull of an infant. This is known as “cradle cap.” B. Nails-located at the ends of the fingers and toes. 1. The major parts of nails include: the body, the root, the lunula, the cuticle, the free edge. C. Hair (Pili)-mostly composed of dead, keratinized cells. 1. Hair Anatomy: a. Shaft b. Hair Root c. Hair follicle d. Bulb-enlarged region at the base of the hair follicle. This contains the Papilla of the Hair which houses blood vessels and oil glands. 2. Arrector pili muscle-smooth muscle fibers that connects the follicle to the underside of the epidermis. This muscle pulls the hair upright to form dimples on the skin. 3. Hair growth is most influenced by nutrition and hormones (especially testosterone). 4. Alopecia-hair thinning or balding. 5. Male Pattern Baldness VIII. SKIN CANCER A. Basal cell carcinoma-least malignant and most common type of skin cancer. Is most common in areas exposed to direct sunlight. This is easily treated.  B. Squamous cell carcinoma-arises from keratinocytes in the stratum spinosum. Can grown and spread quickly. Early detection, surgical removal and radiation all are effective ways to cure this cancer. C. Melanoma-cancer of melanocytes. Is rare but its incidence is increasing. Early detection is a key here. D. ABCD Rule-Asymmetrical, Border, Color, Diameter. IX. BURNS A. First degree burns B. Second degree burns C. Third degree burns XI. SKIN DISORDERS A. Albinism-genetic inability to produce melanin. B. Boils and Carbuncles-bacterial infection of the skin that extends into the subcutaneous layer. C. Cold sores-herpes infection that accumulates around moist or mucus regions of the body. D. Contact dermatitis-redness and itching of the skin due to chemicals that come in contact with the skin. E. Decubitis (Bed Sores)-reduced blood flow to regions over a bony prominence. This often leads to tissue death. F. Impetigo-light red rash that is bacterial in nature.