Week 2 - Tissue - The Living Fabric PDF

Tissue: The Living Fabric Learning outcome • Overview of basic tissue types. List the steps involved in preparing tissue for microscopic viewing. • Understanding the structural and functional characteristics of epithelial tissue. Name, classify, and describe the various types of epithelia, and in...

Tissue: The Living Fabric Learning outcome • Overview of basic tissue types. List the steps involved in preparing tissue for microscopic viewing. • Understanding the structural and functional characteristics of epithelial tissue. Name, classify, and describe the various types of epithelia, and indicate their chief functions and locations. • Indicate common characteristics of connective tissue, and list and describe its structural elements. • Compare and contrast the structures and body locations of the types of muscle tissue. • Indicate the general characteristics of nervous tissue. Tissues • are groups of cells that are similar in structure and perform a common or related function. Four primary tissue types interweave to form the "fabric" of the body. These basic tissues are epithelial, connective, muscle, and nervous tissue. • If we summarized the role of each primary tissue in a single word, we could say that epithelial tissue covers, connective tissue supports, muscle tissue moves, and nervous tissue controls. • Most organs contain all four tissue types. How these tissues are arranged determines an organ's structure and capabilities. Overview of four basic tissue types: Epithelial, Connective, Muscle, and Nervous tissues Microscopic viewing • Light Microscopy, the stains are beautifully colored synthetic dyes. • Transmission Electron Microscopy (TEM), tissue sections are stained with heavy metal salts. • Scanning Electron Microscopy (SEM), provides three-dimensional pictures of an unsenctioned tissue surface Microscopic viewing The steps involved in preparing tissue for microscopic viewing. Microscopy allows us to study tissue structure. Before a specimen can be viewed through a microscope: • Must be fixed (preserved) • Cut into sections (slices) thin enough to transmit light (in light microscopy) or electrons (in electron microscopy). • Finally, the specimen must be stained to enhance contrast between structures. • Many dyes consist of negatively charged molecules (acidic stains) or positively charged molecules (basic stains) that bind within the tissue to macromolecules of the opposite charge. • Different parts of cells and tissues take up different dyes, distinguishing different anatomical structures. Epithelial tissue/epithelium Is a sheet of cells that covers a body surface or lines a body cavity (Two forms occur in the body: • Covering and lining epithelium, which forms the outer layer of the skin; dips into and lines the open cavities of the urogenital, digestive, and respiratory systems; and covers the walls and organs of the closed ventral body cavity. • Glandular epithelium, which fashions the glands of the body. Epithelium accomplishes many functions 1) 2) 3) 4) 5) 6) Protection Absorption Filtration Excretion Secretion Sensory reception Special Characteristics of Epithelium Epithelial tissues have five distinguishing characteristics: • Polarity: All epithelia have two surfaces that differ in structure and function. The apical surface is not attached to surrounding tissue and is exposed to either the outside of the body or the cavity of an internal organ. The basal surface is attached to the underlying connective tissue. For this reason, we say that epithelia exhibit apical-basal polarity. Special Characteristics of Epithelium • Apical surfaces are smooth and slick, most have microvilli, fingerlike extensions. • Some epithelia, such as that lining the trachea (windpipe), have motile cilia that propel substances along their free surface. • Adjacent to the basal surface of an epithelium is a thin supporting sheet called the basal lamina, this acts as a selective filter that determines which molecules diffusing from the underlying connective tissue are allowed to enter the epithelium. The basal lamina also acts as scaffolding along which epithelial cells can migrate to repair a wound. Special Characteristics of Epithelium • Specialized Contacts: Except for glandular epithelia, epithelial cells fit closely together to form continuous sheets. The sides of adjacent cells are tied together by tight junctions and desmosomes • Supported by Connective Tissue: All epithelial sheets rest upon and are supported by connective tissue. In between the epithelial and connective tissues is a basement membrane that reinforces the epithelial sheet, helps it resist stretching and tearing, and defines the epithelial boundary. The basement membrane consists of two layers: a basal lamina and a reticular lamina. The reticular lamina is deep to the basal lamina. It consists of a layer of extracellular material containing a fine network of collagen protein fibers that "belongs to" the underlying connective tissue. Special Characteristics of Epithelium • Avascular but Innervated: Although epithelium is avascular, it is innervated. Epithelial cells are nourished by substances diffusing from blood vessels in the underlying connective tissue. • Regeneration: Epithelium has a high regenerative capacity. Some epithelia are exposed to friction and their surface cells rub off. Classification of Epithelial Tissue • Simple epithelia consist of a single cell layer. They are typically found where absorption, secretion, and filtration occur. Classification of Epithelial Tissue • Stratified epithelia, composed of two or more cell layers stacked on top of each other, are common in high-abrasion areas where protection is important, such as the skin surface and the lining of the mouth. There are three common shapes of epithelial cells • Squamous cells: are flattened and scalelike • Cuboidal cells: are boxlike, approximately as tall as they are wide. • Columnar cells: are tall and column shaped. Simple Squamous epithelia Two simple squamous epithelia in the body have special names that reflect their location • Endothelium ("inner covering") provides a slick, friction-reducing lining in lymphatic vessels and in all hollow organs of the cardiovascular system (blood vessels and the heart). Capillaries consist exclusively of endothelium, and its exceptional thinness encourages the efficient exchange of nutrients and wastes between the bloodstream and surrounding tissue cells. • Mesothelium ("middle covering") is the epithelium found in serous membranes, the membranes lining the ventral body cavity and covering its organs. Simple Cuboidal epithelia Simple Columnar epithelia Pseudostratified Columnar Epithelium Stratified Epithelium Transitional epithelium Glandular Epithelia • A gland consists of one or more cells that make and secrete a particular product. • This product, called a secretion, is an aqueous (water-based) fluid that usually contains proteins. However, some glands release a lipid- or steroidrich secretion. Secretion is an active process. • Glandular cells obtain needed substances from the blood and transform them chemically into a product that is then discharged from the cell. Notice that the term secretion can refer to both the gland's product and the process of making and releasing that product. • Glands are classified according to two sets of traits: 1- Where they release their product-glands may be endocrine ("internally secreting") or exocrine ("externally secreting") 2- Number of cells-glands may be unicellular or multicellular Endocrine Glands • Because endocrine glands lose their ducts during development, they are often called ductless glands. • They produce hormones, chemical messengers that they secrete by Exocytosis directly into The Extracellular Space. From there the hormones enter the blood or lymphatic fluid and travel to specific target organs. Each hormone prompts its target organ(s) to respond in some characteristic way. • Endocrine glands are structurally diverse, Most are compact multicellular organs, but some individual hormone-producing cells are scattered in the digestive tract lining (mucosa) and in the brain, giving rise to their collective description as the diffuse endocrine system. • Endocrine secretions are also varied, ranging from modified amino acids to peptides, glycoproteins, and steroids. Not all endocrine glands arise from epithelial tissue. Exocrine Glands • All exocrine glands secrete their products onto body surfaces (skin) or into body cavities. The unicellular glands do so directly by Exocytosis, whereas the multicellular glands do so via an epitheliumwalled duct that transports the secretion to the epithelial surface. Exocrine glands are diverse. They include the liver (which secretes bile); the pancreas (which synthesizes digestive enzymes); mucous, sweat, oil, and salivary glands; and many others. Glandular Epithelia Glandular Epithelia Glandular Epithelia Simple glands have an unbranched duct, whereas compound glands have a branched duct. The glands are further categorized by their secretory units as: (1) tubular if the secretory cells form tubes; (2) alveolar if the secretory cells form small, flasklike (3) tubuloalveolar if they have both types of secretory units. Note that many anatomists use the term acinar interchangeably with alveolar Most are Merocrine glands, which secrete their products by Exocytosis as they are produced. The secretory cells are not altered in any way (so think "merely secrete" to remember their mode of secretion). Secretory cells of Holocrine glands, in contrast, accumulate their products within them until they rupture. (They are replaced by the division of underlying cells.) Because holocrine gland secretions include the synthesized product plus dead cell fragments (holo = whole, all), you could say that their cells "die for their cause." Sebaceous (oil) glands of the skin are the only true example of holocrine glands Connective tissue • Is the most abundant and widely distributed tissue in the body • While connective tissue is prevalent in the body, its amount in particular organs varies. For example, skin consists primarily of connective tissue, while the brain contains very little. • There are four main classes of connective tissue and several subclasses. These are connective tissue proper (which includes fat and the fibrous tissue of ligaments), cartilage, bone, and blood. The four main classes of connective tissue and several subclasses Connective tissue major functions include • (1) binding and supporting, • (2) protecting, • (3) insulating, • (4) storing reserve fuel, • (5) transporting substances within the body. Common Characteristics of Connective Tissue • Extracellular matrix. All other primary tissues are composed mainly of cells, but connective tissues consist largely of nonliving extracellular matrix, which separates, often widely, the living cells of the tissue. Because of its matrix, connective tissue can bear weight, withstand great tension, and endure abuses, such as physical trauma and abrasion, that no other tissue can tolerate. • Common origin. All connective tissues arise from mesenchyme (an embryonic tissue). **One noticeable difference between different types of connective tissue is how richly they are supplied by blood vessels. Cartilage is avascular. Dense connective tissue is poorly vascularized, and the other types of connective tissue have a rich supply of blood vessels. Structural Components of Connective Tissue • Connective tissues have three main components: ground substance, fibers, and cells • Together Ground Substance and Fibers make up the Extracellular Matrix. Ground Substance Is the unstructured material that fills the space between the cells and contains the fibers. It has three components: 1. Interstitial fluid. The ground substance consists of large amounts of fluid and functions as a molecular sieve through which nutrients and other dissolved substances can diffuse between the blood capillaries and the cells. 2. Cell adhesion proteins. These proteins serve mainly as a connective tissue glue that allows connective tissue cells to attach to the extracellular matrix. 3. Proteoglycans. consist of a protein core to which large polysaccharides called glycosaminoglycans (GAGs) are attached. The strand-like GAGs stick out from the protein core like the fibers of a bottle brush. The higher the GAG content, the more viscous the ground substance. Proteoglycans. consist of a protein core to which large polysaccharides called glycosaminoglycans (GAGs) are attached. Connective Tissue Fibers • The fibers of connective tissue are proteins that provide support. Three types of fibers are found in connective tissue matrix: Collagen, Elastic, and Reticular fibers. Of these, collagen fibers are by far the strongest and most abundant. Connective Tissue Fibers • Collagen Fibers These fibers are constructed primarily of the fibrous protein Collagen. Collagen molecules are secreted into the extracellular space, collagen fibers are extremely tough and provide high tensile strength to the matrix. Indeed, stress tests show that collagen fibers are stronger than steel fibers of the same size. • Elastic Fibers Long, thin, elastic fibers form branching networks in the extracellular matrix. These fibers contain a rubberlike protein, Elastin, that allows them to stretch and recoil like rubber bands. Connective tissue can stretch only so much before its thick, ropelike collagen fibers become stiff. Elastic fibers are found where greater elasticity is needed, for example, in the skin, lungs, and blood vessel walls. • Reticular Fibers These short, fine fibers are made of a different type of collagen than the more common, thicker collagen fibers. They connect to the coarser collagen fibers, but they branch extensively, forming delicate networks that surround small blood vessels and support the soft tissue of organs. They are particularly abundant where connective tissue is next to other tissue types, for example, in the basement membrane of epithelial tissues, and around capillaries, where they form fuzzy "nets" that allow more stretch than the larger collagen fibers. Connective Tissue Cells • Each major class of connective tissue has a resident cell type that exists in immature (-blast) and mature (-cyte) forms. For example: • Fibroblasts in connective tissue proper become fibrocytes. • Chondroblasts in cartilage become chondrocytes. • Osteoblasts in bone become osteocytes. *** Blood, the fourth major class of connective tissue, is an exception to the generalization that we have just made. Its immature blood cell-forming type (once called a hemocytoblast) is called a hematopoietic stem cell. In addition, it is not located in "its" tissue (blood) and does not make the fluid matrix (plasma) of that tissue. Connective tissue is also home to an assortment of other cell types, such as: • Adipocytes, commonly called adipose or fat cells, which store energy as fat. • White blood cells (WBCs or leukocytes, including neutrophils, eosinophils, and lymphocytes) and other cell types that are concerned with tissue response to injury. • Mast cells, which typically cluster along blood vessels. These oval cells detect foreign microorganisms (e.g., bacteria, fungi) and initiate local inflammatory responses against them. Mast cell cytoplasm contains secretory granules with chemicals that mediate inflammation, especially in severe allergies. These chemicals include: • Heparin an anticoagulant chemical that prevents blood clotting when free in the bloodstream • Histamine a substance that makes capillaries leaky • Proteases (protein-degrading enzymes). • Macrophages are large, irregularly shaped cells that avidly devour a broad variety of foreign materials, ranging from foreign molecules to entire bacteria to dust particles. Types of Connective Tissue Areolar Connective Tissue Adipose (Fat) Tissue Adipose tissue Reticular connective tissue Dense Connective Tissues- Regular Dense Connective Tissues- Irregular Elastic Connective Tissue Cartilages Bone Blood: Muscle tissue is responsible for body movement • Muscle tissues are well-vascularized tissues that are responsible for most types of body movement. • As in epithelial tissue, the cells in muscle tissue are all tightly packed together. • Muscle cells possess myofilaments, elaborate networks of the actin and myosin filaments that bring about movement or contraction in all cell types. • There are three kinds of muscle tissue: skeletal, cardiac, and smooth. • Because skeletal muscle contraction is under our conscious control, skeletal muscle is often referred to as voluntary muscle. • The other two types are called involuntary muscle because we do not consciously control them. Skeletal Cardiac Smooth Microscopic Appearance Muscle tissue types Long cylindrical fiber with many Peripherally located nuclei Striated Branched cylindrical fiber with one centrally located nucleus. Intercalated discs join adjacent fibres Striated Fiber is thickest in the middle with one centrally located nuclei Un-striated Properties Very large fibers 10-100m diameter Fiber length 100m – 30cm Large fibers 10-20m diameter Fiber length 50 - 100m Small fibers 3-8m diameter Fiber length 30 - 200m Location Most commonly attached by tendons to bones Heart Nervous control Voluntary Somatic Nervous System Involuntary Autonomic Nervous System Walls of hollow viscera, airways, blood vessels, iris, arrector pili muscles of hair follicles Involuntary Autonomic Nervous System Skeletal Cardiac Smooth Nervous tissue • Is the main component of the nervous system- the brain, spinal cord, and nerves-which regulates and controls body functions. • It contains two major cell types: neurons and supporting cells. • Neurons are highly specialized nerve cells that generate and conduct nerve impulses, typically, they are branching cells with cytoplasmic extensions or processes that enable them to: 1- Respond to stimuli (via processes called dendrites) 2-Transmit electrical impulses over substantial distances within the body (via processes called axons) • Supporting cells (known as glial cells or neuroglia) are non-conducting cells that support, insulate, and protect the neurons. Nervous tissue Cutaneous membrane • The cutaneous membrane is your skin. It is an organ system consisting of a keratinized stratified squamous epithelium (epidermis) firmly attached to a thick layer of connective tissue (dermis). Unlike other epithelial membranes, the cutaneous membrane is exposed to the air and is a dry membrane. Mucous Membranes • Mucous membranes, or mucosae: line all body cavities that open to the outside of the body, such as the hollow organs of the digestive, respiratory, and urogenital tracts. • In all cases, they are "wet," or moist, membranes bathed by secretions or, in the case of the urinary mucosa, urine. • Notice that the term mucosa refers to the location of the membrane, not its cell composition, which varies. • However, most mucosae contain either stratified squamous or simple columnar epithelia. • The epithelial sheet lies directly over a layer of areolar connective tissue called the lamina propria. • In some mucosae, the lamina propria rests on a third (deeper) layer of smooth muscle cells Serosa membranes, or serosa • Are the moist membranes found in closed ventral body cavities • serous membranes have a visceral layer and a parietal layer separated by serous fluid • The serosae are named according to their location and specific organ associations: The pleurae line the thoracic wall and cover the lungs; the pericardium encloses the heart; and the peritoneum encloses the abdominopelvic viscera. Tissue repair Tissue repair requires that cells divide and migrate, activities that are initiated by growth factors (wound hormones) released by injured cells. Repair occurs in two major ways: Tissue repair • Regeneration replaces destroyed tissue with the same kind of tissue • Fibrosis replaces destroyed tissue with scar tissue, which is dense connective tissue. • In the initial part of wound healing, a special tissue, called granulation tissue. Embryonic germ layers and the primary t issue types they produce: References and Further Reading • Elaine N. Marieb and Katja N. Hoehn (2019). Human Anatomy and Physiology. 11th Edition. Pearson Education. Chapter 4