Chapter FIVE-225 - sheehan PDF

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CHAPTER FIVE TISSUES I. CELLS ARE ORGANIZED INTO TISSUES - tissues are layers or groups of similar cells with a common function - intercellular Junctions – connect cell membranes to each other Figure 5.1 a. tight junction – membranes of adjacent cells converge and fuse with the area of fusion surrounding the cells like a belt 1) e.g. lining the inside of digestive tract, linings of tiny blood vessels in brain b. desmosomes – rivets or “spot welds” adjacent skin cells, forming a reinforced structural unit c. gap junctions – these are tubular channels that allow ions, nutrients, and other small molecules to move between the cells 1) e.g. heart muscle and muscles of the digestive tract connected by these 5.2 EPITHELIAL TISSUES A. General Characteristics 1. Widespread throughout body. 2. Lines body cavities, covers organs. 3. Always have a free surface. The underside is anchored to connective tissue by a thin, nonliving layer called the basement membrane. 4. Generally lack blood vessels – nutrients diffuse from connective tissue. 5. Reproduce rapidly, so injuries heal quickly. 6. Tightly packed, with little intercellular material – form effective barriers. 7. Classified according to shape of cells and number of layers of cells: a. simple – one layer b. stratified – more than one layer c. squamous – thin, flattened cells. d. cuboidal – cells are cubelike e. columnar – cells are elongated – taller than wide 8. The free surface of epithelial cell are modified to reflect their specialized functions. B. Simple Squamous Epithelium Figure 5.3 1. Single layer of thin, flattened cells – fit tightly together like floor tiles; nuclei broad and thin. 2. Common at sites of diffusion and filtration – air sacs ( alveoli ) of the lungs, walls of capillaries, covers membranes that line body cavities. 3. Easily damaged because they are so thin. C. Simple Cuboidal Epithelium Figure 5.4 1. Single layer of cube-shaped cells with centrally located spherical nucleus. 2. Covers the ovaries, lines kidney tubules and ducts of certain glands ( pancreas, salivary glands, and liver ) – functions in secretion and absorption. D. Simple Columnar Epithelium Figure 5.5 1. Single layer of elongated cells with nuclei usually near the basement membrane.

2. Cells may be ciliated or nonciliated. a. cilia, which are 7-10 um in length, extend from the free surface of cells and move constantly 1) e.g. move egg cells through the oviducts to the uterus 3. Nonciliated epithelium lines the uterus and portions of the digestive tract. a. this tissue is thick, enabling it to protect underlying tissues b. cells of digestive tract secrete digestive fluids and absorb nutrients from digested food 4. Cells that are specialized for absorption often have many tiny, cylindrical processes extending from their surfaces. a. these processes are called microvilli and are from 0.5 to 1.0 um long – they increase the surface area of the cell membrane Figure 5.6 5. Goblet cells are typically scattered among the cells of this tissue. They secrete a protective fluid called mucus onto the free surface of the tissue. E. Pseudostratified Columnar Epithelium Figure 5.7 1. The cells appear stratified due to the nuclei being at different levels and the cells vary in shape – but it is only one layer. 2. Often fringed with cilia. Goblet cells secrete mucus, which the cilia sweep away. a. lines passages of respiratory system – mucus traps dust and microorganisms that enter with air, cilia moves mucus and trapped particles upward and out of the airways F. Stratified Squamous Epithelium Figure 5.8 1. Several layers of cells – the outermost layers have flattened cells while the deeper layers, where cell division occurs, consist of cuboidal or columnar cells. 2. The epidermis consists of this tissue type – as the older cells are pushed outward, they accumulate a protein called keratin, then harden and die – produces a dry, tough, protective material that prevents water from escaping and blocks chemicals and microorganisms entering. 3. Also lines oral cavity, throat, esophagus, vagina and anal canal. The tissue is not keratinized in these regions and the cells remain alive. G. Stratified Cuboidal Epithelium Figure 5.9 1. Consists of two or three layers of cuboidal cells that form the lining of a lumen. 2. Lines the ducts of mammary glands, sweat glands, salivary glands, and pancreas; also lining of developing ovarian follicles and seminiferous tubules. H. Stratified Columnar Epithelium Figure 5.10 1. Several layers of cells with the surface cells being elongated and the basal layers consisting of cube-shaped cells. 2. Found in the vas deferens, part of the male urethra, and in parts of pharynx. I. Transitional Epithelium Figure 5.11 1. Specialized to change in response to increased tension. 2. Inner linings of urinary bladder, ureters, and part of urethra. a. forms an expandable lining as these structures fill with urine – forms barriers

so that the contents can’t diffuse back into internal environment J. Glandular Epithelium Table 5.3 1. Cells specialized to produce or secrete substances – these cells usually found in cuboidal or columnar epithelium – one or more of these cells make up a gland. 2. Endocrine glands secrete their products into tissue fluid or blood. 3. Exocrine glands secrete their products into ducts that open onto some internal or external surface. a. unicellular gland – consists of a single epithelial cell – e.g. goblet cell b. multicellular gland – consists of many cells 4. Structure of multicellular glands: Figure 5.12 a. simple gland – communicates with the surface by an unbranched duct b. compound gland – has a branched duct c. these two types may also be further classified as to the shapes of their secretory portions: 1) tubular glands have epithelial-lined tubes 2) alveolar glands have saclike dilations at their terminal portion d. there may also be coiling and branching of the tubular and alveolar glands 5. Classification of exocrine glands according to method of secretion: Figure 5.13 a. merocrine glands – release fluid products by exocytosis 1) salivary glands, pancreatic glands, sweat glands 2) serous cells secrete watery fluids, usually has high concentration of enzymescalled serous fluid 3) mucous cells secrete a thicker fluid called mucus, a substance rich in the glycoprotein mucin b. apocrine glands lose small portions of their glandular cell bodies during secretion 1) mammary glands, ceruminous glands c. holocrine glands release entire cells during secretion – the cells then disintegrate, releasing their secretions 1) sebaceous glands of the skin Figure 5.14 5.3 CONNECTIVE TISSUES A. General Characteristics 1. Most abundant tissue type by weight. 2. Bind structures, provide support and protection, serve as frameworks, fill spaces, store fat, produce blood cells, protect against infections, and help repair tissue damage. 3. Cells are further apart than epithelial tissue cells; they have an abundance of intercellular material, or matrix, between them. a. consists of proteins fibers and a ground substance whose consistency varies from fluid to semisolid to solid 4. These tissue cells usually divide and most have a good blood supply and are well nourished.

B. Major Cell Types 1. Fixed cells – usually present in stable numbers. a. fibroblast is the most common – large, star-shaped cell; produces fibers by secreting protein into the matrix Figure 5.15 b. mast cells are large and widely distributed, located near blood vessels – release heparin, a compound that prevents blood clotting – also release histamine, a substance that is a vasodilator Figure 5.17 2. Wandering cells – appear temporarily in tissues, usually in response to an injury or infection. a. macrophages = histiocytes – originate as white blood cells and are very numerous – usually attached to fibers but can detach and actively move about 1) specialized to carry on phagocytosis – function as scavenger cells that can remove foreign particles from tissues – important defense against infection Figure 5.16 C. Connective Tissue Fibers 1. Collagenous fibers are thick threads of collagen ( the major structural protein of the body. Figure 5.18 a. grouped in long, parallel bundles b. flexible, but only slightly elastic c. great tensile strength – can resist considerable pulling force d. e.g. ligaments – connect bone to bone; tendons – connect bone to muscle e. dense connective tissue contains abundant collagenous fibers and appears white – sometimes called white fibers f. loose connective tissue has sparse collagenous fibers 2. Elastic fibers are composed of bundles of microfibrils embedded in a protein called elastin. a. fibers branch and form complex networks in various tissues b. very elastic, not as strong as collagenous c. e.g. vocal cords, air passages of respiratory system d. sometimes called yellow fibers 3. Reticular fibers are very thin collagenous fibers. a. highly branched, forming delicate supporting networks in a variety of tissues D. Loose Connective Tissue or Areolar Tissue Figure 5.19 1. Forms delicate, thin membranes. 2. Mainly fibroblasts widely scattered in a gel-like ground substance that contains many collagenous and elastic fibers that are secreted by the fibroblasts. 3. Binds skin to underlying organs and fills spaces between muscles. E. Adipose Tissue or Fat Figure 5.20 1. Adipocytes store fat droplets in cytoplasm. 2. Cushions joints and some organs ( kidneys ), lies beneath skin forming insulating layer, stores energy in fat molecules. F. Reticular Connective Tissue Figure 5.21 1. Composed of thin, collagenous fibers in a three-dimensional network.

2. Supports walls of certain internal organs, such as the liver, spleen, and lymphatic organs. G. Dense Connective Tissue 1. Consists of many closely packed, thick, collagenous fibers, a fine network of elastic fibers, and a few cells. a. regular – fibers are very strong, binds body parts together, as parts of tendons and ligaments – poor blood supply, so tissue repair is slow Fig. 5.22 b. irregular – thicker, interwoven, more randomly organized fibers – allows the tissue to sustain tension exerted from many different locations – found in the dermis Figure 5.23 H. Elastic Connective Tissue Figure 5.24 1. Consists of yellow, elastic fibers in parallel strands or in branching networks. a. collagenous fibers and fibroblasts between these fibers b. e.g. attachments between vertebrae ( ligamenta flava ), within the walls of some internal hollow organs such as larger arteries, some portions of heart, and the larger airways I. Cartilage 1. Rigid connective tissue that provides support, frameworks, attachments, protection of underlying tissues, and forms structural models for many developing bones. 2. Matrix composed of collagen fibers in gel-like ground substance rich in a protein-polysaccharide complex ( chondromucoprotein ) and contains a lot of water. 3. Chondrocytes ( cartilage cells ) occupy lacunae, small chambers. 4. A cartilaginous structure is enclosed in a covering called perichondrium. 5. Lacks a direct blood supply, blood vessels are in perichondrium, so cells receive nutrients by diffusion – cartilage heals slowly and chondrocytes do not divide frequently. 6. Three types of cartilage based on their different types of intercellular material: a. hyaline cartilage – most common type – very fine fibers in matrix, appears somewhat like white glass Figure 5.25 1) soft part of nose, supporting rings of respiratory system, on the ends of bones, parts of embryo’s skeleton begin as hyaline cartilage “models” b. elastic cartilage – more flexible than hyaline because of the elastic fibers in matrix Figure 5.26 1) framework for external ears and parts of the larynx c. fibrocartilage – very tough, containing many collagenous fibers Figure 5.27 1) shock absorber for structures subjected to pressure – intervertebral discs, pads in the knees, and between pelvic bones J. Bone 1. Most rigid of connective tissues – its hardness due to calcium phosphate and calcium carbonate in its matrix. Large amount of collagen in matrix, these fibers flexibly reinforce the mineral components.

2. Supports body structures, protects organs in thoracic and cranial cavities, forms blood cells, attachment for muscles, stores inorganic salts. 3. Matrix deposited by osteocytes ( bone cells ) in thin layers called lamellae, which form concentric circles around capillaries located in central, or Haversian canals. Figure 5.28 a. osteocytes are located in lacunae rather evenly spaced in lamellae 4. The lamellae around an osteonic canal make up an osteon – many of these cemented together form the substance of bone. 5. Every bone cell is fairly close to a nutrient source, since each central canal contains a blood vessel. a. bone cells have cytoplasmic extensions that extend outward and pass through canaliculi to receive nutrients K. Blood Figure 5.29 1. Composed of cells ( red blood cells, white blood cells, and cellular fragments called platelets ) that are suspended in a liquid matrix, plasma. 2. Most blood cells form in hematopoietic tissues located in red marrow. 5.4 TYPES OF MEMBRANES A. Membranes are actually organs since they are composed of two or more kinds of tissues grouped together and performing specialized functions. B. Epithelial Membranes 1. Serous membranes line the body cavities that lack openings to the outside and reduce friction between the organs and cavity walls. a. consist of a layer of simple squamous epithelium and a thin layer of connective tissue b. cells of the membrane secrete watery serous fluid, which helps lubricate the membrane surfaces 2. Mucous membranes line the cavities and tubes that open to the outside. a. consist of epithelium overlying a layer of loose connective tissue 1) the type of epithelium varies with the location of membrane b. goblet cells secrete mucus 3. Cutaneous membrane is an organ of the integumentary system – more commonly called skin. C. Synovial Membranes 1. Line joint cavities. 2. Cells secrete synovial fluid. 5.5 MUSCLE TISSUES A. General Characteristics 1. The cells are sometimes called muscle fibers. 2. The cells are contractile – can shorten and thicken; as they do so, they pull at their attached ends.

B. Skeletal Muscle Tissue Figure 5.30 1. Forms muscles usually attached to bones. 2. Voluntary muscle – controlled by conscious effort. 3. Long, narrow cells – up to more than 40 mm in length and less than 0.1 mm wide. 4. Have striations – alternating dark and light bands. 5. Multinucleate. C. Smooth Muscle Tissue Figure 5.31 1. The cells lack striations. 2. Cells shorter than skeletal muscle and are spindle-shaped. 3. Single nucleus in each cell. 4. Comprise the walls of hollow internal organs, such as the stomach, uterus, urinary bladder, intestines, and blood vessels. 5. Involuntary actions. D. Cardiac Muscle Tissue Figure 5.32 1. Found only in the heart. 2. Striated cells, joined end to end – cells are branched and interconnected in complex networks. 3. Junctions are called intercalated discs. 4. Involuntary control – can continue to function without being stimulated by nervous tissue. 5. Single nucleus in cell. 5.6 NERVOUS TISSUES A. General Characteristics 1. Found in brain, spinal cord, and peripheral nerves. B. Neurons Figure 5.33 1. These are the basic cells of nervous tissue. 2. Among the more highly specialized body cells. 3. Sense changes in surroundings and respond by transmitting nerve impulses. 4. Can coordinate, regulate, and integrate many body functions. C. Neuroglia Figure 5.33 1. These are supporting cells of the nervous system. 2. Support, bind, carry on phagocytosis, provide nutrients, communication....