Chapter 4 Histology Chapter Outline

Chapter 4 Histology Chapter Outline Module 4.1 Introduction to Tissues (Figures 4.1, 4.2) A. Define histology. A tissue is a group of structurally and functionally related cells and their external environment that together perform common functions. All tissues share the following two basic components: 1. 2. B. Types of Tissues: Four primary tissue types are defined by the kind and number of cells, the amount and composition of ECM, and their specific functions: 1. tissues, or epithelia, are tightly packed sheets of cells with no visible ECM that cover and line all body surfaces and cavities. Specialized epithelia form glands that manufacture secretions such as sweat, saliva, or chemical messengers called hormones. 2. tissues connect all the other tissues in the body to one another. The ECM is a prominent feature for most connective tissue types with cells scattered throughout. These bind, support, protect, and allow for transportation of substances. 3. tissues, capable of generating force by contracting, have little ECM between cells. 4. tissues consist of cells capable of generating, sending, receiving messages, and cells that support this activity all within a unique ECM. C. The Extracellular Matrix, composed of substances in a liquid, thick gel, or solid that surround the cells of a tissue, consist of two main components: 1) and 2) (Figure 4.1). 1. ECM performs a variety of functions including the following: Copyright 2016 Pearson Education, Inc 45

a. ECM provides the tissue with strength to resist tensile (stretching) and compressive forces. b. ECM directs cells to their proper positions within a tissue and holds those cells in place. c. ECM regulates the development, mitotic activity, and survival of cells in a tissue. 2. Ground Substance makes up most of the ECM and consists of interstitial or extracellular fluid (ECF) and their components: water, nutrients, and ions. Three families of macromolecules, glycosaminoglycans (GAGs), proteoglycans, and cell-adhesion molecules (CAMs), are also found in ground substance. 3. Protein Fibers, embedded within the ground substance, are long molecules composed of multiple fibrous subunits with a ropelike structure with enormous tensile strength. The following three protein fibers are found within the ECM: a. fibers are composed of multiple repeating subunits that form a white fibrous protein that is resistant to tension (pulling and stretching forces) and pressure. b. fibers, composed of the protein elastin surrounded by glycoproteins, has the property of extensibility that allows the fiber to stretch up to one and a half times its resting length without breaking. Once stretched, these fibers return to their resting length, a property called elasticity. c. fibers, a thin, short collagen fiber, form a meshwork or scaffold that support the cells and ground substance of many tissues. They form a web-like structure in organs like the spleen that help trap foreign cells. D. Cell Junctions are another way cells bind to one another where neighboring cells, plasma membranes, are linked by integral proteins. Describe the functions of the three major types of cell junctions (Figure 4.2): 46 Copyright 2016 Pearson Education, Inc

1. Tight junctions, also known as occluding junctions: 2. Desmosomes: 3. Gap junctions: (Figure 4.2a) (Figure 4.2b) (Figure 4.2c) Module 4.2 Epithelial Tissues (Figures 4.3, 4.4, 4.5, 4.6, 4.7, 4.8, 4.9, 4.10, 4.11) A. Epithelial tissues, found on every internal and external body surface, are barriers between the body and external environment, or our organs and fluid-filled cavities. Describe the following additional functions of epithelia: 1. Protection: 2. Immune defenses: 3. Secretion: 4. Transport into other tissues: 5. Sensation: B. Components and Classification of Epithelia. Epithelial tissues consist of tightly packed cells linked together by tight junctions and desmosomes. This structural arrangement make these sheets of cells fairly impermeable and resistant to physical stresses and mechanical injury (Figure 4.3): Copyright 2016 Pearson Education, Inc 47

1. Epithelial tissues are avascular, meaning 2. There is little ECM between epithelial cells. ECM is found beneath the cells in a structure called the basement membrane that has the following two components: lamina and lamina. Together, these layers glue the epithelial tissue to the underlying connective tissue, anchor underlying blood vessels in place, and provide a barrier between the epithelia and underlying tissues. 3. Epithelial tissue is classified based on two criteria: a. b. 4. The number of layers and the shapes of the cells have functional significance (Figure 4.4). a. Simple epithelia consist of b. Stratified epithelia consist of c. Squamous cells are d. Cuboidal cells are e. Columnar cells are tall and C. Covering and Lining Epithelia are found on inner and outer body surfaces. Each cell shape can be found in varying thicknesses in broad, flat sheets often called membranes when the basement membrane is included (Figures 4.5, 4.6, 4.7, 4.8): 1. Simple Epithelia are one cell-layer thick, adapted for transportation of substances between different tissues; some have microvilli for increased surface area, and some cells are ciliated for moving substance through hollow organs. Four types of simple epithelia follow (Figure 4.5): a. Simple squamous epithelium, a very thin single layer of cells with a fried egg appearance, is adapted for rapid diffusion of substances like oxygen, carbon dioxide, fluids, and ions. Where is this tissue found? 48 Copyright 2016 Pearson Education, Inc

1), 2), and 3) (Figure 4.5a). b. Simple cuboidal epithelium, a single layer of cube-shaped cells with a large central nucleus, is thin enough for rapid substance diffusion. Where is this tissue found? 1), 2), 3), and 4) (Figure 4.5b). c. Simple columnar epithelium, a single layer of rectangular-shaped cells with their nuclei located in the basal portion of the cell, often has microvilli on their apical plasma membrane. What is the benefit of microvilli? These cells with microvilli are found in small intestine and ciliated cells are found in the uterine tubes and segments of the respiratory tract (Figure 4.5c). d. Pseudostratified columnar epithelium appears to be layered because their nuclei are found at various heights but is only one cell-layer thick with the basal plasma membrane firmly in contact with the basement membrane. These cells are found in segments of the respiratory tract and nasal cavity and are ciliated (Figure 4.5d). 2. Transport Across Simple Epithelia occurs via paracellular transportation or transcellular transportation (Figure 4.6). 3. Stratified Epithelium has more than one layer of cells, making them best suited as protective barriers in locations subjected to high degrees of mechanical stress. The following are types of stratified epithelium (Figure 4.7): a. In keratinized stratified squamous epithelium the apical cellular layers are dead, have lost their nuclei, and are filled with the protein keratin. What is the function of keratin? Copyright 2016 Pearson Education, Inc 49

b. In nonkeratinized stratified squamous epithelium the apical cellular layers their nuclei because they are still alive. This epithelial type is found in regions subjected to mechanical stress where the surface must remain moist, such as the,,,, and (Figure 4.7a). c. Stratified cuboidal epithelium, rare in humans, consists of two cell layers and lines the ducts of sweat glands (Figure 4.7b). d. Stratified columnar epithelium, also rare in humans, consists of only a few layers where the apical cell layer is columnar and the basal cell layer is cuboidal. Where is this tissue found? 1), 2), and 3) (Figure 4.7c). e. Transitional epithelium is only found in the system where it lines the interior of the,,, and. The basal cell layers are cuboidal, while the apical cell layers are dome-shaped when the tissue is relaxed. The ability of the apical cells to flatten out contributes to the ability of the urinary tissues to stretch (Figure 4.7d). 4. The types of epithelia are summarized in Figure 4.8. D. Glandular Epithelia. What is a gland? Glands arise from epithelial tissue that migrated into the deeper connective tissue instead remaining at the surface. Glands can be classified either by their shape or by how they release their products. Products are released by the following two mechanisms (Figure 4.9): 1. Endocrine glands secrete their products, usually, directly into the bloodstream without the use of ducts. This allows these 50 Copyright 2016 Pearson Education, Inc

products to have widespread systemic effects on distant cells in different areas of the body. 2. Exocrine glands release their products onto the apical surfaces of the epithelium, onto the external surface of the body, or into a hollow organ that opens to the outside of the body through an epithelial-lined. Multicellular glands are classified according to the structure of their ducts and the shape of the clusters of secretory cells (Figure 4.10). Describe the following two methods for secreting products used by exocrine glands (Figure 4.11): a. Merocrine secretion b. Holocrine secretion Module 4.3 Connective Tissues (Figures 4.12, 4.13, 4.14, 4.15, 4.16, 4.17, 4.18, 4.19, 4.20) A. Connective tissues are divided into two basic groups that differ in their cell-types and ECM components: connective tissue proper and specialized connective tissue. These tissues include the following functions: 1. Connecting and binding: connective tissues anchor tissue layers in organs and link organs together. 2. Support: and support the weight of the body. 3. Protection: bone tissue protects certain internal organs and cartilage and fat provide shock absorption. Components of the immune system are found throughout different connective tissues. 4. Transport: is a fluid connective tissue that is the main transport medium in the body. 5. Like all tissues, connective tissue consists of cells and ECM. B. Connective Tissue Proper, also known as general connective tissue, is widely distributed in the body. These tissues connect tissues and organs to one another Copyright 2016 Pearson Education, Inc 51

and are components of the internal architecture of the some organs. The different tissues in this group are composed of the following types of cells (Figure 4.12), followed by the four basic types of connective tissue proper: 1. Cells of Connective Tissue Proper: Resident cells permanently inhabit the tissue in which they are found and migrant cells migrate into different areas of the body depending on the situation. The different cells in connective tissue proper include the following: a. Fibroblasts, the most common resident cell, are mature cells that have the properties of an immature blast cell. What do fibroblasts make? (Figure 4.12a) b. Adipocytes, fat cells, are found in many different connective tissues. What does the cytoplasm of an adipocyte store? (Figure 4.12b) c. Mast cells are immune system cells filled with cytosolic inclusions or granules of inflammatory mediators such as histamine. These cells release these mediators or degranulate when stimulated, causing inflammation a protective response that activates the immune system (Figure 4.12c). d. Phagocytes, also immune system cells, can ingest foreign substances, microorganisms, and dead or damaged cells by phagocytosis (Figure 4.12d). 2. Loose connective tissue, also known as areolar tissue, is mostly ground substance, with all three types of protein fibers, fibroblasts, and occasionally adipocytes, all suspended in ground substance (Figure 4.13). a. Where is this tissue found? 52 Copyright 2016 Pearson Education, Inc

b. What does this tissue contain? 3. Dense connective tissue, also known as fibrous connective tissue, is mostly protein fibers, grouped into the following three classes (Figure 4.14): a. Dense, irregular connective tissue is predominantly disorganized fiber bundles. This tissue is strong, resists tension in all three planes of movement, and is found in high-tension areas like the dermis deep to the skin and surrounding organs and joints (Figure 4.14a). b. Dense connective tissue is predominantly organized into parallel fiber bundles that are resistant to tension in one plane. This tissue is found in tendons and ligament that are subject to tension in one plane of movement. Figure 4.14b). c. Dense regular elastic connective tissue, also known as elastic tissue, is mostly parallel-oriented fibers with randomly oriented fibers. This tissue is found in the walls of organs that must stretch to perform their function, such as large blood vessels and certain ligaments (Figure 4.14c). 4. Reticular tissue is composed mostly of reticular fibers produced by fibroblasts, called reticular cells that form fine networks that can support small structures like blood and lymphatic vessels (Figure 4.15). 5. Adipose tissue, also known as fat tissue, consists of fat-storing adipocytes and surrounding fibroblasts and ECM. Adipocytes can increase in size to the point where fibroblasts and ECM are scarcely visible. Besides fat storage, this tissue also provides,,, and. This tissue is the major energy reserve in the body (Figure 4.16). C. Specialized Connective Tissues have more specific functions and include the following three types of tissue: cartilage, bone or osseous tissue, and blood Copyright 2016 Pearson Education, Inc 53

(Figures 4.17, 4.18, 4.19). The types of connective tissue are summarized in Figure 4.20. 1. Cartilage is found in the joints between bones, in the ear, nose, and segments of the respiratory tract. This is a tough, flexible tissue that absorbs shock and resists tension, compression, and shearing forces. The ECM consists of collagen and elastic fibers, glycosaminoglycans, and proteoglycans. a. Cartilage is populated with two cell-types: 1) are immature cells that divide by mitosis and make most of the ECM. These cells eventually surround themselves in small cavities or lacunae in the ECM to become mature, largely inactive 2). b. Cartilage is essentially avascular, unlike most connective tissues, and its blood supply is limited to the outer sheath of dense, irregular, collagenous connective tissue called the. Oxygen and nutrients must diffuse from the blood vessels in the perichondrium through the ECM to supply the chondroblasts and chondrocytes, which limits the thickness of living cartilage. 2. Cartilage can be further divided into three classes based on ECM composition (Figure 4.17): a. Hyaline cartilage is the most abundant cartilage in the body. The ECM is mostly ground substance made of small bundles of a fine collagen type that give the tissue a glossy bluish-gray appearance. Where is this tissue found? (Figure 4.17a) b. Fibrocartilage is filled with bundles of collagen fibers with little room for ground substance in the ECM. Fibroblasts reside in the tissue in addition to chondroblasts and chondrocytes, and fill the ECM with collagen and some elastic fibers. The tissue has great tensile strength, 54 Copyright 2016 Pearson Education, Inc

with some degree of elasticity. Where is this tissue found? (Figure 4.17b) c. Elastic cartilage has mostly elastic fibers in its ECM, which allows this tissue to vibrate. Where is this tissue found? (Figure 4.17c) 3. Bone, or osseous, tissue supports the body, protects our vital organs, provides attachments for the muscles that allow for movement, stores calcium, and houses bone marrow, which produces blood cells and stores fat. Bone ECM is composed of about 35% organic components consisting of collagen fibers and ground substance called osteoid. The remaining 65% of ECM is inorganic calcium phosphate crystals, making bone one of the hardest substances in the body (Figure 4.18a). List and describe the three resident cells found in bone tissue (Figure 4.18): a. b. (Figure 4.18b) c. 4. Blood is a unique connective tissue with a liquid ECM called plasma, which consists of mostly water, dissolved solutes, and proteins. Plasma proteins are not like the fibers found in other connective tissues. Plasma proteins provide a variety of functions including transport and blood clotting. List and summarize the functions of the cells found in blood (Figure 4.19). Copyright 2016 Pearson Education, Inc 55

a. b. c. Module 4.4 Muscle Tissues (Figure 4.21) A. Muscle tissues are specialized for contraction. The three muscle tissue types share the common ability to turn the chemical energy of ATP into the mechanical energy of movement. Walking, breathing, beating of the heart, and propelling substances through hollow organs all result from the contractions of the different muscle tissues. B. Components of Muscle Tissue. The main component of muscle tissue is the muscle cell, or myocyte, which is excitable. Muscle cells have the ability to respond to electrical or chemical stimulation. There are two forms of muscle cells based on the arrangement of the myofilaments (protein bundles) in their cytoplasm. Describe each cell type: 1. Striated muscle cells 2. Smooth muscle cells C. There are three types of muscle tissue that feature different structural and functional characteristics. Skeletal and cardiac muscle tissue are striated while smooth muscle tissue is composed of smooth muscle (Figure 4.21): 1. Skeletal Muscle Tissue is found mostly attached to the skeleton where its contraction produces body movement (Figure 4.21a). a. Skeletal muscle must be stimulated by the nervous system to contract and is under, or conscious, control. Most skeletal muscle cells are long, extending nearly the length of the whole muscle, and are often called muscle fibers. b. Muscle cells form by the fusion of embryonic myoblasts resulting in cells with more than one nucleus, known as, which 56 Copyright 2016 Pearson Education, Inc

is useful for the nearly constant synthesis of enzymes, structural proteins, and contractile proteins. 2. Cardiac Muscle Tissue, found only in the heart, is composed of cardiac muscle cells. Although these cells are striated like skeletal muscle cell, many differences can be seen (Figure 4.21b). a. Cardiac muscle tissue is ; the brain does not have conscious control over its contraction. Cardiac muscle cells are short,, and usually have nucleus. b. There is a dark line separating individual cardiac muscle cells, not seen in skeletal muscle, called that contain gap junctions and modified tight junctions that allow the heart muscle to contract as a unit. 3. Smooth Muscle Tissue consists of smooth muscle cells whose contractions are like cardiac muscle cells. (Figure 4.21c). a. Smooth muscle cells are found in the walls of nearly every hollow organ: blood vessels, the eyes, the skin, and the ducts of certain glands b. Smooth muscle cells are flattened cells with one centrally located ovoid nucleus. Module 4.5 Nervous Tissues (Figure 4.22) A. Nervous tissue makes up the majority of the brain, spinal cord and nerves. Nervous tissue is composed of two main cell types and their surrounding ECM: 1. 2. B. Neurons are excitable cells. Once mature, neurons no longer divide by mitosis. List the three main components of neurons (Figure 4.22): 1. 2. Copyright 2016 Pearson Education, Inc 57

3. C. What are the functions of neuroglial cells? Neuroglial cells are able to divide by mitosis. Module 4.7 Membranes (Figures 4.24, 4.25) A. Membranes are thin sheets of one or more tissues that line a body surface or cavity. 1. Most membranes consist of a superficial layer and a tissue layer that sometimes contains smooth muscle. 2. Membranes serve the following functions:,,, and. a. True membranes include and membranes and fit the above structural and functional definitions. b. Membrane-like structures, including and membranes, don t fit the above structural and functional definitions but perform many of the same functions. B. True membranes do not open to the outside of the body and include the following two examples (Figure 4.24): 1. Serous membranes or serosae line the,, and body cavities and have the following structural and functional features (Figure 4.24a): a. Serous membranes consist of a (a thin layer of simple squamous epithelium), an associated basement membrane, and a layer of connective tissue. Mesothelial cells produce serous fluid to reduce friction created by organs moving within their respective membranes. 58 Copyright 2016 Pearson Education, Inc

b. Serous membranes fold over themselves giving the appearance of two layers; the outer layer is in contact with the body wall while the inner layer covers the organ within the body cavity. 2. Synovial membranes line the cavities surrounding freely moveable joints like the knee or shoulder. These membranes are made up of two connective tissue layers without a layer of epithelial cells (Figure 4.24b). Synoviocytes secrete synovial fluid, which primarily lubricates the joint. C. Cutaneous membranes line external surface of the body while mucous membranes line internal body surfaces and open to the outside of the body. Both are membrane-like structures, as they do not fit the full description of a true membrane (Figure 4.25). 1. Mucous membranes, also called mucosae, line all body passages as components of the walls of hollow organs that open to the outside of the body which includes the following structures:,,,, and (Figure 4.25a). Mucosae contain glands with goblet cells that produce and secrete mucous which primarily serves to protect. 2. The cutaneous membrane refers to the skin, which is the largest organ of the body (Figure 4.25b). The outer layer, known as the, consists of keratinized stratified squamous epithelium while the deeper layers of loose connective tissue and even dense irregular connective tissue form the. Module 4.7 Tissue Repair (Figures 4.26) A. Describe tissue repair. Tissue repair differs with different tissues (Figure 4.26). 1. Some tissues are capable of regeneration, where dead and damaged cells are replaced with cells of the same type. When the process is finished the tissue has returned to a normal functional level (Figure 4.26a). Copyright 2016 Pearson Education, Inc 59

2. Other tissues are not capable of full regeneration. Fibroblasts fill in the gaps left from injury by a process called fibrosis. The end result of fibrosis is formation, which is composed of dense connective tissue. B. The capacity of specific tissues for tissue repair is largely dependent on the tissue s resident cells ability to undergo mitosis. 1. Epithelial tissues typically undergo regeneration. Some tissues, especially the skin and digestive tract lining, are subjected to a great deal of stress so must have a mechanism for replacing dead and damaged cells. Stem cells are capable of replacing epithelial cells of the skin and digestive tract. 2. Most connective tissues heal by regeneration. Connective tissue proper, bone, and blood regenerate easily through the division of their resident immature cells. Cartilage is the exception as their resident cells have a limited capacity for regeneration so this tissue heals by fibrosis. 3. Smooth muscle tissue usually regenerates; cardiac and skeletal muscle tissues generally heal by fibrosis. 4. Nervous tissue generally undergoes fibrosis. Neurons have lost their ability to divide by mitosis so are incapable of regeneration while neuroglial cells retain the ability to divide by mitosis. C. Other Factors Affecting Tissue Repair beside the ability to undergo mitosis includes the following two factors: 1) and 2). 60 Copyright 2016 Pearson Education, Inc