Integumentary System Part 2 - Bio40A Ch05 Notes PDF

Integumentary System part2 I) DERMIS A) The dermis is composed of connective tissue containing collagen and elastic fibers. A) The papillary layer is areolar connective tissue containing fine elastic fibers, dermal papillae, corpuscles of touch (Meissner’s corpuscles), and f...

Integumentary System part2 I) DERMIS A) The dermis is composed of connective tissue containing collagen and elastic fibers. A) The papillary layer is areolar connective tissue containing fine elastic fibers, dermal papillae, corpuscles of touch (Meissner’s corpuscles), and free nerve endings for sensations of heat, cold, pain, tickle, and itch. B) The reticular layer is the deeper part of the dermis consisting of dense, irregular connective tissue containing bundles of collagen fibers and some elastic fibers. (a) Spaces between the fibers may contain adipose cells, hair follicles, sebaceous glands, and sudoriferous glands. (b) The collagen and elastic fibers provide strength, extensibility (ability to stretch), and elasticity (ability to return to original shape after stretching) to skin. B) Epidermal ridges increase friction for better grasping ability and provide the basis for fingerprints and footprints. The ridges typically reflect contours of the underlying dermis. II) ACCESSORY STRUCTURES OF THE SKIN A) General Characteristics A) Accessory structures of the skin develop from the embryonic epidermis and include hair, glands, and nails. B) Hair A) Hairs, or pili, are present on most skin surfaces except the palms, palmar surfaces of the digits, soles, and plantar surfaces of the digits. B) Anatomy of Hair (a) Hair consists of a shaft above the surface, a root that penetrates the dermis and subcutaneous layer, the cuticle, and a hair follicle. (1) There are three concentric layers of cells: medulla, cortex, and cuticle of the hair. (a) The medulla, which may be lacking in thinner hair, is composed of two or three rows of irregularly shaped cells that contain large amounts of pigment granules. (b) The cortex forms the major part of the shaft and consists of elongated cells. (c) The cuticle of the hair, the outermost layer, consists of a single layer of thin, flat cells that are the most heavily keratinized. (2) The external root sheath is a downward continuation of the epidermis. (3) The internal root sheath is produced by the matrix.  (a) The hair matrix cells arise from the stratum basale 1. New hairs develop from cell division of the matrix in the bulb. (b) The base of each hair follicle is surrounded by the dermal root sheath. (b) Associated with hairs are sebaceous (oil) glands, arrector pili muscles, and root plexuses. C) Skin Glands A) Sebaceous (oil) glands are usually connected to hair follicles; absent in palms and soles. (a) Sebaceous glands produce sebum, which moistens hairs, waterproofs and softens the skin, and inhibits bacterial growth. B) Sudoriferous (sweat) glands are divided into apocrine and eccrine types. C) Eccrine sweat glands have an extensive distribution; their ducts terminate at pores at the surface of the epidermis. (a) The main function of eccrine sweat glands is to help regulate body temperature through evaporation. (b) They also help eliminate wastes such as urea. D) Apocrine sweat glands are limited in distribution to the skin of the axilla, pubis, and areolae; their duct open into hair follicles. E) Ceruminous glands are modified sudoriferous glands that produce a waxy substance called cerumen. These glands are found in the external auditory meatus. D) Nails A) Nails are hard, keratinized epidermal cells over the dorsal surfaces of the terminal portions of the fingers and toes. B) The principal parts of a nail are the body, free edge, root, lunula, eponychium, and matrix. C) Cell division of the matrix cells produces new nails. D) Functionally, nails help in grasping and manipulating small objects in various ways and provide protection against trauma to the ends of the digits.  Integumentary System I) INTRODUCTION A) The skin and its accessory structures make up the integumentary system. B) The integumentary system functions to guard the body’s physical and biochemical integrity, maintain a constant body temperature, and provide sensory information about the surrounding environment. II) FUNCTIONS OF SKIN A) Thermoregulation, the homeostatic control of body temperature, is due to the skin liberating sweat at its surface and by adjusting the flow of blood in the dermis. B) Blood Reservoir, The dermis houses an extensive network of blood vessels that carry 8–10% of the total blood flow in a resting adult. C) The skin provides protection through physical, chemical and biological barriers. D) Cutaneous sensations, including touch, pressure, vibration, tickle, heat, cold, and pain arise in the skin. E) The skin plays minor roles in excretion, the elimination of wastes from the body, and absorption, the passage of material from the external environment into body cells. F) Synthesis of Vitamin D requires activation of a precursor molecule in the skin by UV light, with enzymes in the liver and kidneys modifying the activated molecule to produce calcitriol, the most active form of vitamin D. III) STRUCTURE OF THE SKIN A) The skin consists of different tissues that are joined together to perform specific functions and is the largest organ of the body. Structurally the skin consists of two parts. A) The superficial portion of the skin is the epidermis and is composed of epitethelial tissue. B) The deeper layer of the skin is the dermis and is primarily composed of connective tissue. C) Deep to the dermis is the subcutaneous layer or hypodermis. (a) It consists of mostly areolar and adipose tissue. (b) It serves as a fat storage area, an area for blood vessel passage, and an area of pressure nerve endings. IV) EPIDERMIS A) The epidermis is composed of stratified squamous epithelium and contains four principal types of cells: keratinocytes, melanocytes, Langerhans cells, and Merkel cells.  (a) Keratinocytes produce the protein keratin, which helps protect the skin and underlying tissue from heat, microbes, and chemicals, and lamellar granules, which release a waterproof sealant. (b) Melanocytes produce the pigment melanin which contributes to skin color and absorbs damaging ultraviolet (UV) light. (c) Langerhans cells participate in immune responses. (d) Merkel cells contact a sensory structure called a tactile (Merkel) disc and function in the sensation of touch. B) Layers of the Epidermis (a) There are four or five layers of the epidermis, depending upon the degree of friction and mechanical pressure applied to the skin. From deepest to most superficial the layers of the epidermis are stratum basale (stratum germinativum), stratum spinosum, stratum granulosum, stratum lucidum (only in palms and soles), and stratum corneum. (b) The stratum basale is the deepest layer of the epidermis and contains some stem cells capable of undergoing cell division to form new cells. (1) Keratinocytes and melanocytes are found in this layer. (2) This layer is sometimes called the stratum germinativum to indicate its role in the formation of new cells. C) The stratum spinosum provides strength and flexibility to the skin. It contains keratinocytes. D) The stratum granulosum marks the transition between the deeper, metabolically active strata and the dead cells of the more superficial strata. This layer also shows the formation of a water repellent sealant between the cells. (1) This layer consists of keratinocytes that are undergoing apoptosis. (2) This layer is characterized by the presence of keratohyalin which converts tonofilaments into keratin. (b) The stratum lucidum is present only in the fingers, palms, and soles. (c) The stratum corneum is the most superficial layer and consists of dead cells. (1) Lamellar granules in this layer make it water-repellent. (2) Constant exposure to friction will cause this layer to increase in depth with the formation of a callus, an abnormal thickening of the epidermis. V) TYPES OF SKIN A) Thin skin covers all parts of the body except for the palms, palmar surfaces of the digits, and soles. A) Thin skin lacks epidermal ridges.  B) It has a sparser distribution of sensory receptors than thick skin. B) Thick skin covers the palms, palmer surfaces of the digits, and soles. A) It features a stratum lucidum and thick epidermal ridges. B) It lacks hair follicles, arrector pili muscles, and sebaceous glands, and has more sweat glands than thin skin. VI) STRUCTURE AND BASIS OF SKIN COLOR A) Melanin, hemoglobin, and carotene are three pigments that impart a wide variety of colors to skin B) Melanocytes synthesize melanin from the amino acid tyrosine using the enzyme tyrosinase.  Bone Tissue part 1 I. INTRODUCTION A. Bone is made up of several different tissues working together: bone, cartilage, dense connective tissue, epithelium, blood forming tissues, adipose, and nervous tissue. B. Each individual bone is an organ; the bones, along with their cartilages, make up the skeletal system. II. FUNCTIONS OF THE SKELETAL SYSTEM A. Bones support the soft tissues and provide attachment sites for muscles, thereby serving as the structural framework for the body. B. Many of the body’s internal organs are physically protected by bony coverings. C. Bones assist skeletal muscles to produce movement of body parts. D. Bones store and release several minerals, especially calcium and phosphorus, to help maintain mineral homeostasis. E. Hemopoiesis, blood cell formation, occurs in the red marrow of bones. F. Yellow marrow of adult bones serves as a site of triglyceride storage. III. STURCTURE OF BONE A. The structure of bone can be analyzed by studying a long bone. B. A typical long bone consists of numerous parts. 1. The diaphysis is the shaft of the long bone. 2. The epiphyses are the ends of the bone that articulate with adjacent bones. 3. The metaphyses are the areas between the epiphysis and diaphysis. It includes the epiphyseal plate, the site of bone elongation in growing bones. 4. Hyaline cartilage (articular cartilage) at the ends of the bones reduces friction and absorbs shock at freely moveable joints.  5. The periosteum is a connective tissue covering of the surface of the bone which contains osteogenic cells which promote bone growth in width, assists in fracture repair, helps nourish bone tissue, and serves as an attachment point for ligaments and tendons. 6. The space within the diaphysis is the marrow cavity which contains yellow marrow (adipose connective tissue). 7. The endosteum is the lining of the medullary cavity. IV. HISTOLOGY OF BONE TISSUE A. Bone (osseous) tissue consists of widely separated cells surrounded by large amounts of matrix. B. There are four principal types of bone cells. 1. Osteogenic cells undergo cell division and develop into osteoblasts. 2. Osteoblasts are bone-building cells, promoting bone deposition. 3. Osteocytes are mature bone cells, derived from osteoblasts, that maintain bone tissue. 4. Osteoclasts are derived from monocytes and serve to break down, or resorb, bone tissue. C. The matrix of bone contains inorganic salts, primarily hydroxyapatite and some calcium carbonate, and collagen fibers. 1. These and a few other salts are deposited in a framework of collagen fibers, a process called calcification or mineralization. 2. Mineral salts confer hardness on bone while collagen fibers give bone its great tensile strength. 3. The process of calcification occurs only in the presence of collagen fibers.