Chapter 4: The Tissue Level of Organization I. Tissues of the Body: An Introduction, p. 107 •
For our bodies to function, cells must work together as tissues. Tissues: collections of specialized cells with specific functions. Histology: the study of tissues.
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There are 4 basic types of tissues: 1. Epithelial tissue covers surfaces exposed to the environment (skin, airways, digestive tracts, glands) 2. Connective tissue fills internal spaces, supports other tissues, transports materials and stores energy. 3. Muscle tissue is specialized for contraction (skeletal muscle, heart muscle, walls of hollow organs). 4. Neural tissue carries electrical signals from one part of the body to another.
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(*) Tissues are collections of cells and cell products that perform specific, limited functions. Four tissue types form all the structures of the human body: epithelial, connective, muscle, and neural.
II. Epithelial Tissue, p. 107 •
Epithelial tissue includes: - epithelia: layers of cells that cover internal or external surfaces. - glands: structures that produce fluid secretions.
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Epithelia line digestive, respiratory, urinary and reproductive tracts. Also fluid or gas-filled internal cavities and passageways such as the chest cavity, inner surfaces of blood vessels and chambers of heart.
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Epithelia have 5 important characteristics: 1. Cellularity: cells are tightly bound together by cell junctions. 2. Polarity: the structural and functional differences between the exposed (apical) and attached (basal) surfaces of the tissue. 3. Attachment: the base of the epithelia is bound to a basal lamina or basement membrane. 4. Avascularity: epithelia are avascular (lacking blood vessels) 5. Regeneration: a high rate of cell replacement by stem cells in the epithelium.
Functions of Epithelial Tissue, p. 107 •
There are 4 basic functions of epithelial tissues:
1. Provide Physical Protection from abrasion, dehydration, biological and chemical agents. 2. Control Permeability to proteins, hormones, ions or nutrients. 3. Provide Sensation such as touch or pressure. - neuroepithelia are specialized for the sensations of smell, taste, sight, equilibrium, and hearing. 4. Produce Specialized Secretions for physical protection or chemical messengers. - gland cells are scattered among other epithelial cells. - in glandular epithelium, most cells produce secretions. Specializations of Epithelial Tissue, p. 108 •
Individual epithelial cells may be specialized for: 1. Movement of fluid over the epithelial surface (protection or lubrication). 2. Movement of fluid through the epithelium (permeability). 3. Production of secretions (protection or chemical messengers).
Figure 4-1 Polarity of Epithelial Cells • The apical surfaces of cells lining internal passageways (such as digestive and urinary tracts) have microvilli on their surfaces which increase surface area to aid in absorption, secretion and transport. • Longer epithelial extensions called cilia (ciliated epithelium) move fluids across the surface of the epithelium. Cilia in the respiratory tract move mucus, containing particles such as smoke, out of the lungs. Maintaining the Integrity of Epithelia, p. 108 •
Three factors make the epithelium an effective barrier: intercellular connections, attachment to basal lamina, and maintenance and repair.
Figure 4-2 •
I. Intercellular Connections: Cells can form permanent or temporary bonds with other cells or extracellular material. - Connections between large areas of opposing cell membranes are formed by transmembrane proteins called cell adhesion molecules (CAMs). - Adjacent cell membranes may be bonded by a thin layer of proteoglycans called intercellular cement (glycosaminoglycans such as hyaluronan). - Cell junctions are specialized areas of attachment between cells. The 3 types of cell junctions are: 1. Tight junctions: close enough to prevent water and solutes from passing through. Tight junctions can isolate destructive chemicals such as enzymes, acids and wastes inside tubular passageways called lumen. In tight junctions, the lipid portions of 2 cell membranes are tightly locked by
membrane proteins, forming an adhesion belt. 2. Gap junctions: allow rapid intercellular communications. Cells are held together by channel proteins (junctional proteins) call connexons. Small molecules and ions pass from cell to cell through the channels. Gap junctions in cardiac muscle tissue coordinate contractions. 3. Desmosomes: durable structural connections which allow tissues to stretch, bend and twist. CAMs and proteoglycans link cells, forming dense areas which connect to the cytoskeleton, providing mechanical strength. The 2 types of desmosomes are: Button desmosomes: discs connected to intermediate fibers, which stabilize cell shape. Hemidesmosomes: attach a cell to extracellular filaments in the basal lamina. •
II. Attachment to the Basal Lamina: The inner surface of the epithelium is attached to a 2-part basal lamina. 1. Lamina lucida, the thin layer closest to the epithelium, acts as a barrier to proteins and other large molecules. Contains glycoproteins and a layer of fine protein filaments. 2. Lamina densa, the deeper layer, gives the basement membrane its strength and filters substances entering from adjacent tissues. Contains bundles of coarse protein fibers.
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III. Maintenance and Repair: - Epithelial cells are exposed to toxic chemicals, pathogens and mechanical abrasion. - An epithelial cell of the small intestine may survive only a day or two before it is destroyed. - New epithelial cells are produced by division of stem cells (germinative cells) located near the basal lamina.
Classification of Epithelia, p. 111 Table 4-1 • Epithelia are sorted into categories by cell shape (squamous = flat, cuboidal = square, columnar = tall) and number of cell layers. - One cell layer is simple epithelium, more than one layer is stratified epithelium. • I. Squamous Epithelia Figure 4-3a 1. Simple squamous epithelium is thin and flat. Only 1 layer thick, it is the most delicate epithelium. It is found in smooth, protected areas where absorption or exchange takes place (linings of lungs, blood vessels). - Mesothelium: simple squamous epithelium lining ventral body cavities (pleura, peritoneum, pericardium).
- Endothelium: simple squamous epithelium lining heart and blood vessels. Figure 4-3b 2. Stratified squamous epithelium forms many layers which protect against chemical and physical attacks. It is found lining the mouth, esophagus and anus, and on exposed body surfaces. - Keratinized stratified squamous epithelium (packed with the fibrous protein keratin), found in apical layers of skin cells, is tough and water resistant. - Nonkeratinized stratified squamous epithelium resists abrasion but dries out and must be lubricated (e.g. oral cavity, pharynx, esophagus, anus, vagina). • II. Cuboidal Epithelia Figure 4-4a 1. Simple cuboidal epithelium occurs where secretion or absorption takes place (e.g. lining of kidney tubules). Figure 4-4b 2. Stratified cuboidal epithelia are relatively rare, found in ducts of sweat glands and mammary glands. Figure 4-4c • III. Transitional epithelia tolerate repeated cycles of stretching without damage (e.g. urinary bladder). It is called transitional because cell layers change appearance (from stratified to simple) as they stretch. • IV. Columnar Epithelia Figure 4-5a 1. Simple columnar epithelium is found where absorption or secretion occur (e.g. stomach, small intestine, large intestine). Secretions protect against chemical stress. Figure 4-5b 2. Pseudostratified columnar epithelium appears stratified but is actually simple. Cilia-bearing cells found in portions of the respiratory tract (e.g. nasal cavity, trachea and bronchi) and portions of the male reproductive tract. Figure 4-5c 3. Stratified columnar epithelia are relatively rare. They protect portions of the pharynx, epiglottis, anus and urethra. Glandular Epithelia, p. 114
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Glands are cells, or collections of cells, specialized for secretions ranging from sweat to hormones.
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Endocrine glands (endo = in) release hormonal secretions into interstitial fluids. - The blood stream carries hormones throughout the body. - Hormones control specific tissues, organs and organ systems. - Examples of endocrine glands are the thyroid gland and pituitary gland. - Endocrine glands have no ducts.
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Exocrine glands (exo = out) release secretions into ducts which carry the secretions onto an epithelial surface such as the skin, or an internal passageway that communicates with the outside environment. - Examples of exocrine secretions are digestive enzymes, sweat, tears and milk.
Figure 4-6 • There are 3 methods of glandular secretion: merocrine, apocrine and holocrine. 1. Merocrine secretion is the most common. - Merocrine secretions are released from secretory vesicles by exocytosis. - Examples are the mucus-producing secretion mucin, and merocrine sweat glands which produce the watery secretions that cool you when you are hot. 2. In apocrine secretion, part of the cell cytoplasm is released along with the secretory product. - Milk production involves both apocrine and merocrine secretions. 3. Holocrine secretion fills a gland cell and causes it to burst, killing the cell. - Holocrine cells must be replaced by stem-cell division. - An example of holocrine secretion is the sebaceous gland which produces oil in hair follicles. •
Exocrine glands can also be categorized by 3 types of secretions: 1. Serous glands produce watery secretions containing enzymes. - Example: parotid salivary glands 2. Mucous glands secrete mucins. - Examples: sublingual salivary glands, submucosal glands of small intestine 3. Mixed exocrine glands produce both serous and mucous secretions. - Example: submandibular salivary glands.
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Exocrine glands can also be classified by structure, either unicellular (one cell) or multicellular (many cells). 1. The only unicellular exocrine glands are goblet cells, which secrete mucins.
- Goblet cells are scattered among other epithelial cells. - Examples: linings of trachea, small and large intestines. Figure 4-7 2. All other exocrine glands are multicellular exocrine glands. •
Three characteristics describe the structure of multicellular exocrine glands: 1. Structure of the duct: - simple (undivided) - compound (divided) 2. Shape of secretory portion of the gland: - tubular (tube shaped) - alveolar (blind pockets) - acinar (chamber-like) 3. The relationship between ducts and glandular areas: - branched (several secretory areas sharing one duct)
III. Connective Tissues, p. 118 •
Connective tissue connects the epithelium to the rest of the body (via the reticular layer of the basal lamina). Other connective tissues provide structure (e.g. bone), store energy (e.g. fat), and transport materials throughout the body (e.g. blood).
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Unlike epithelial tissues, connective tissues are never exposed to the exterior environment.
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Though there are many different kinds of connective tissues, all have three basic characteristics: 1. Specialized cells 2. Extracellular protein fibers 3. A fluid, extracellular ground substance
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The extracellular components (protein fibers and ground substance) together form a matrix surrounding the cells. Connective cell matrix makes up most of the volume of connective tissue. Matrix is a connective cell’s specific product, and determines its specialized function.
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Some specialized functions of connective tissues include: - Structural framework of the body - Transporting fluids and dissolved materials - Protecting delicate organs - Supporting, surrounding and connecting other tissues - Storing lipids - Defense against invading microorganisms.
Classification of Connective Tissues, p. 118 •
There are three general categories of connective tissues: 1. Connective tissue proper can have many types of protein fibers and a syrupy ground substance. Connective tissue proper is divided into 2 categories determined by the proportion of ground substance to protein fibers in the matrix : (1) loose connective tissue - more ground substance, less fibers - e.g. fat (adipose tissue) (2) dense connective tissue - more fibers, less ground substance - e.g. tendons 2. Fluid connective tissues have a watery matrix of dissolved proteins, carrying specific cell types. There are 2 types of fluid connective tissues: (1) blood (2) lymph 3. Supportive connective tissues support soft tissues and the weight of the body. The 2 types of supportive connective tissues are: (1) cartilage: a gel-type ground substance with various fibers for shock absorption and protection. (2) bone: which is calcified (made rigid by heavy deposits of calcium salts and other minerals) for weight support.
Figure 4-8 Connective Tissue Proper, p. 119 •
There is a wide variety of connective tissues proper, with many different functions. All have extracellular fibers and a viscous (syrupy) ground substance.
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There are 8 basic types of cells in connective tissue proper: 1. Fibroblasts: The most abundant cell type, found in all connective tissues proper. - Fibroblasts secrete proteins and the polysaccharide derivative hyaluronan (the cement which locks cells together). 2. Macrophages (macro = large, phagein = eat): Large, amoeba-like cells of the immune system which eat pathogens and damaged cells. - fixed macrophages stay in the tissue. - free macrophages migrate through tissues. 3. Adipocytes (fat cells): Each cell stores a single, large fat droplet. 4. Mesenchymal cells: Stem cells that respond to injury or infection by differentiating into fibroblasts, macrophages or other types of cells. 5. Melanocytes: Synthesize and store the brown pigment melanin.
6. Mast cells: Release the chemicals histamine and heparin to stimulate inflammation after injury or infection. - basophils are mast cells carried by blood to damaged tissues. 7. Lymphocytes: Specialized immune cells carried by the lymphatic system. - including plasma cells which produce antibodies. 8. Microphages (neutrophils and eosinophils): Phagocytic blood cells responding to chemical signals from macrophages and mast cells. •
There are 3 types of fibers in connective tissue proper: 1. Collagen fibers: The most common fibers in connective tissue proper. - long, straight and unbranched - strong and flexible - resists force in one direction - examples: tendons and ligaments 2. Reticular fibers: Similar to collagen fibers but shaped differently. - network of branching, interwoven fibers (stroma) - strong and flexible - resists force in many directions - stabilizes the positions of functional cells (parenchyma) and structures 3. Elastic fibers: Contain the protein elastin. - branched and wavy - return to original length after stretching - example: elastic ligaments of vertebrae
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In connective tissue proper, the ground substance is clear, colorless and viscous. It fills spaces between cells and slows down pathogens.
Figure 4-9 • Embryonic connective tissues are mesenchyme or embryonic stem cells -- the first connective tissue to appear in embryos. - Mucous connective tissue is loose embryonic connective tissue. - Neither of these forms is found in adults. Figure 4-10 • Loose connective tissues are the packing materials of the body. - In embryos, it is mucous connective tissue. •
In adults, there are 3 types of loose connective tissue: areolar, adipose, and reticular. 1. Areolar tissue (areola = little space) is the least specialized. - open framework distorts without damage - viscous ground substance absorbs shock - elastic fibers return to original shape - holds blood vessels and capillary beds
- example: separates skin from deeper structures Figure 4-10a 2. Adipose tissue (fat) is similar to areolar tissue but contains many adipocytes (fat cells) which store fat. Adipose tissue also absorbs shocks and slows heat loss. - There are 2 types of adipose tissue: (1) white fat, the most common adipose tissue, and (2) brown fat, a more vascularized tissue with adipocytes containing many mitochondria. These cells are metabolically active, breaking down fat and producing heat. - Adipocytes in adults do not divide. They expand or shrink as fats are stored or released. If there are not enough fat cells to store available lipids, mesenchymal stem cells divide and differentiate to produce more fat cells. Figure 4-10b 3. Reticular tissue has a complex, 3-dimensional network of supportive fibers (stroma). - The stroma support functional cells (parenchyma). - Reticular organs include spleen, liver, lymph nodes and bone marrow. Figure 4-11 • Dense connective tissues (collagenous tissues) are the second type of connective tissue proper. They are dense because of their high numbers of collagen fibers. •
There are 3 kinds of dense connective tissue: 1. Dense regular connective tissue has tightly packed, parallel collagen fibers. - Tendons attach muscles to bones. - Ligaments connect one bone to another, or stabilize organs. - Large flat muscles have sheets of dense regular connective tissue called aponeuroses. 2. Dense irregular connective tissues have interwoven networks of strengthening fibers. - Examples: - layered in skin - around cartilages (perichondrium) - around bones (periosteum) - forms capsules around some organs (e.g. liver, kidneys) 3. Elastic tissue Though both dense regular and dense irregular connective tissues contain elastic fibers, elastic tissue is mostly elastic fibers.
- e.g. elastic ligaments of the spinal column Fluid Connective Tissues, p. 123 •
The fluid connective tissues, blood and lymph, are liquids carrying specialized cells and suspended proteins.
Figure 4-12 • Blood consists of solids (formed elements) and liquids (fluid elements). •
There are 3 types of formed elements in blood: 1. Red blood cells (erythrocytes) make up about half the volume of blood. Their main function is to transport oxygen to the cells. 2. White blood cells (leukocytes) include several types of immune system cells (neutrophils, eosinophils, basophils, lymphocytes and monocytes). 3. Platelets are cell fragments containing enzymes and proteins that aid clotting.
♣ The fluid element of blood is the watery matrix called plasma. Plasma is one of the 3 forms of extracellular fluid found in the body, which are regulated together by processes of homeostasis. - Extracellular fluid is called plasma as long as it stays within the cardiovascular system (veins, arteries and capillaries) as part of circulating blood. - When blood pressure forces plasma out of the blood through the thin walls of capillaries, it becomes interstitial fluid (fluid between cells) carrying nutrients to the cell and absorbing cellular products and wastes. - Interstitial fluid then drains into the lymphatic vessels, where it is called lymph. Immune system elements of the lymphatic system screen the fluid for infections before returning it to the blood where, once again, it is called plasma. Supportive Connective Tissues, p. 125 ♣ Two types of supportive connective tissues, cartilage and bone, provide a strong framework that supports the rest of the body. ♣ Cartilage - Cartilage matrix consists of proteoglycans derived from polysaccharides (chondroitin sulfates) and ground substance proteins. - Cartilage cells in the matrix (chondrocytes) are surrounded by chambers called lacunae. - Cartilage has no blood vessels because chondrocytes produce an antigrowth chemical (antiangiogenesis factor). - The perichondrium, or outer cover, consists of an outer, fibrous layer (for
strength) and an inner, cellular layer (for growth and maintenance). Figure 4-13 -Cartilage grows by 2 mechanisms: (1) Interstitial growth increases cartilage size from the inside. - Chondrocytes divide and produce new matrix. (2) Appositional growth increases the outer size of a cartilage by adding new layers. - Neither interstitial growth nor appositional growth normally occurs in adults. Figure 4-14 - There are 3 major types of cartilage: (1) Hyaline cartilage is translucent and has no prominent fibers. - provides stiff, flexible support. - reduces friction between bones. - is found in synovial joints, rib tips, sternum and trachea (2) Elastic cartilage has tightly packed elastic fibers. - is supportive but bends easily. - is found in the external ear and epiglottis. (3) Fibrocartilage has very dense collagen fibers. - limits movement and prevents bone-to-bone contact. - pads knee joints, pubic bones and intervertebral discs. Figure 4-15 ♣ Bone - Bone or osseous tissue is strong because of calcification (calcium salt deposits), and resists shattering due to its flexible collagen fibers. - Osteocytes are arranged around blood vessels in central canals within the matrix. Small channels through the matrix (canaliculi) allow osteocytes to exchange nutrients and wastes with their blood supply. - A periosteum (with a fibrous layer and a cellular layer) covers the surface of most bones. - Unlike cartilage, bone is metabolically active, and can repair itself or adapt to activity. Table 4-2 summarizes the differences between cartilage and bone. IV. Membranes, p. 129
♣ There are many different types of membranes in the body. Here we see how connective tissues combine with epithelial tissues to form membranes that line or cover body surfaces. Figure 4-16 ♣ Epithelial and connective tissues combine to form four types of membranes: 1. Mucous membranes (mucosae) line passageways that communicate with the outside environment (in digestive, respiratory, urinary and reproductive tracts). - The epithelial surfaces are moist (lubricated) to reduce friction, or facilitate absorption and excretion. - The areolar tissue in mucous membranes is the lamina propria. 2. Serous membranes line cavities that are not open to the outside environment. Serous membranes are thin but strong. They are lubricated with a fluid transudate to reduce friction. - Each serous membrane has a parietal portion covering the cavity surface, and a visceral portion (serosa) covering the organs. - pleural membrane lines pleural cavities and covers the lungs. - peritoneum lines the peritoneal cavity and covers abdominal organs. - pericardium lines the pericardial cavity and covers the heart. 3. Cutaneous membrane is the skin that covers the surface of the body. - It is thick, waterproof and dry. - It consists of stratified squamous epithelium, areolar tissue, and dense irregular connective tissue. 4. Synovial membranes line articulating (moving) joint cavities and produce the synovial fluid which lubricates the joint. - protect the ends of bones and allow free movement. - consist of areolar tissue, collagen fibers, proteoglycans and glycoproteins. - do not have a true epithelium. V. The Connective Tissue Framework of the Body, p. 131 ♣ Connective tissues: - provide strength and stability. - maintain positions of internal organs. - provide routes for blood vessels, lymphatic vessels and nerves.
Figure 4-17 ♣ Fasciae (fascia) are layers that surround and support organs. There are 3 types of these layers: 1. Superficial fascia or subcutaneous layer (sub = below, cutis = skin) is the areolar tissue and fat that separates the skin from underlying tissues. - allows independent movement. - pads and insulates deep tissues. 2. Deep fascia is a strong, fibrous network of dense irregular connective tissue which ties structural elements together. - internal organs are anchored to deep fascia. 3. Subserous fascia is areolar tissue that separates the deep fascia of muscles from serous membranes, allowing independent movement. VI. Muscle Tissue, p. 132 ♣ Muscle tissue is specialized for contraction. All body movement is produced by muscle tissue. ♣ There are three types of muscle tissues (skeletal, cardiac and smooth) each with its own special structures and functions. - Muscle cells can be striated (muscle cells with a banded appearance) or nonstriated (not banded). - Muscle cells can have a single nucleus or be multinucleate. - Muscle cells can be controlled voluntarily (consciously) or involuntarily (automatically). Figure 4-18a 1. Skeletal muscle tissue forms the large body muscles responsible for major body movements such as walking. Skeletal muscle cells: - are long and thin, and are usually called muscle fibers. - do not divide, new fibers are produced by stem cells called satellite cells. - are striated, voluntary, and multinucleated. Figure 4-18b 2. Cardiac muscle tissue is found only in the heart. Cardiac muscle cells: - are called cardiocytes. - form a branching network connected at intercalated disks. - are regulated by pacemaker cells. - are striated, involuntary, and have a single nucleus. Figure 4-18c 3. Smooth muscle tissue is found within the walls of hollow organs that contract (blood vessels; urinary bladder; respiratory, digestive and reproductive tracts). Smooth muscle cells: - are small and tapered. - can divide and regenerate.
- are nonstriated, involuntary, and have a single nucleus. VII. Neural Tissue, p. 134 Figure 4-19 ♣ Neural tissue (nervous or nerve tissue) is specialized for conducting electrical impulses that rapidly sense the internal or external environment, process information and control responses. ♣ Most neural tissue is concentrated in the brain and spinal cord, which make up the central nervous system. ♣ There are 2 kinds of neural cells: 1. neurons, the nerve cells that do the electrical communicating, and 2. neuroglia, the support cells that repair and supply nutrients to neurons. ♣ Neurons are made up of 3 parts: 1. the cell body contains the nucleus and nucleolus. 2. dendrites are short branches extending from the cell body to receive incoming signals. 3. the axon (nerve fiber) is a long, thin extension of the cell body that carries outgoing electrical signals to their destination. VIII. Tissue Injuries and Repair, p. 135 ♣ The restoration of homeostasis after a tissue has been injured involves 2 processes: inflammation and regeneration. Figure 4-20 1. Inflammation is the tissue’s first response to injury. Signs of inflammatory response include swelling, redness, heat, and pain at the site of the injury. The presence of harmful bacteria (pathogens) in a tissue (an infection) also causes an inflammatory response. The process of inflammation occurs in several stages: - Damaged cells release prostaglandins, protein and potassium ions into the surrounding interstitial fluid. - As the cell breaks down, lysosomes release enzymes that destroy the injured cell and attack surrounding tissues. Tissue destruction is called necrosis. - Necrotic tissues and cellular debris (pus) accumulate in the wound. (Pus trapped in an enclosed area is an abscess.) - The injury stimulates mast cells in the tissue to release histamine,
heparin, and prostaglandins, which trigger changes in the surrounding blood vessels. - Dilation (widening) of blood vessels increases blood circulation in the area, causing warmth and redness. - Plasma diffuses into the area, causing swelling and pain. - Increased blood flow brings more nutrients and oxygen to the area, and removes wastes. - Phagocytic white blood cells clean up the area. 2. When the injury or infection has been cleared up, the regeneration or healing phase begins. - Fibroblasts move into the necrotic area, laying down collagen fibers that bind the area together (scar tissue). - New cells migrate into the area, or are produced by mesenchymal stem cells. - Not all tissues can regenerate. Epithelia and connective tissues regenerate well. Cardiac cells and neurons do not regenerate. Aging and Tissue Structure, p.137 ♣ The speed and effectiveness of tissue repairs decreases as people age. Contributing factors include: - a slower rate of energy consumption (metabolism). - changes in hormonal activity. - reduced physical activity. ♣ The cumulative effects of chemical and structural tissue changes associated with age include: - thinning of epithelia and connective tissues. - increased bruising and bone brittleness. - joint pain and broken bones. - cardiovascular disease. - mental deterioration. Aging and Cancer Incidence, p. 137 ♣ ♣ ♣ ♣
Cancer rates increase with age. About 1 in 4 people in the United States develop cancer. Cancer is the #2 cause of death in the United States. Most cancers result from chemical exposure and environmental factors such as cigarette smoke.
SUMMARY In Chapter 4 we learned about: ♣ The organization of specialized cells into tissues:
epithelial tissue connective tissue muscular tissue nervous tissue ♣ The division of epithelial tissues into epithelia and glands. Epithelia as avascular barriers for protection Glands as secretory structures ♣ Specializations of epithelial cells for sensation or motion (microvilli and cilia) ♣ Attachments of epithelia to other cells and underlying tissues. Cell polarity (apical surface and basal lamina) Cell Adhesion Molecules (CAMs) Cell Junctions (tight junctions, gap junctions and desmosomes) ♣ Maintenance of epithelia (germinative cells, stem cells). ♣ Classification of cells by number of cell layers (simple or stratified) and shape of cells (squamous, columnar or cuboidal). ♣ Classification of glands by method of secretion (exocrine or endocrine), by type of secretions (merocrine, apocrine, holocrine), by organization (unicellular or multicellular) and by structure (related to branches and ducts). ♣ The functions of connective tissues: structure transport protection support connections energy storage ♣ The structure of connective tissues (matrix consisting of ground substance and protein fibers) ♣ The classification of connective tissues connective tissue proper (cell types, fiber types, embryonic connective tissues) fluid connective tissues (blood and lymph, fluid transport systems) supporting connective tissues (cartilage and bone) ♣ The 4 types of membranes that cover and protect organs Mucous membranes (containing lamina propria) Serous membranes (forming transudate) Cutaneous membrane (the skin)
Synovial membrane (encapsulating joints) ♣ The fascia (superficial, deep and subserous). ♣ The 3 types of muscle tissues ( skeletal, cardiac and smooth) ♣ The classification of muscle tissues by striation, nucleation and voluntary control. ♣ The 2 types of cells in neural tissue (neurons and neuroglia) ♣ The parts of a neuron (nerve cell): cell body, dendrites and axon (nerve fiber). ♣ Tissue injuries and repair systems (inflammation and regeneration). ♣ The relationship between aging, tissue structure and cancer.
