Chapter 4: Tissues

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Tissues
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Types of tissues Epithelial tissue Connective tissue Membranes Muscular tissue Nervous tissue Tissue repair: restoring homeostasis Aging and tissues

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Types of Tissues
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A tissue is a group of similar cells that usually has a similar embryological origin and is specialized for a particular function. The various tissues of the body are classified into four basic types: epithelial tissue, connective tissue, muscular tissue, and nervous tissue. Epithelial tissue (eṕ -i-THĒ-lē-al) covers body surfaces; lines body cavities, hollow organs, and ducts (tubes); and forms glands. Connective tissue protects and supports the body and its organs, binds organs together, stores energy reserves as fat, and provides immunity. Muscular tissue generates the physical force needed to make body structures move. Nervous tissue detects changes inside and outside the body and initiates and transmits nerve impulses (action potentials) that coordinate body activities to help maintain homeostasis.

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1. 2. 3. 4.

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Epithelial Tissue

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Epithelial Tissue

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Epithelial Tissue

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Epithelial Tissue

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Epithelial Tissue

© 2013 John Wiley & Sons, Inc. All rights reserved.

Epithelial Tissue

© 2013 John Wiley & Sons, Inc. All rights reserved.

Epithelial Tissue

© 2013 John Wiley & Sons, Inc. All rights reserved.

Epithelial Tissue

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Epithelial Tissue

© 2013 John Wiley & Sons, Inc. All rights reserved.

Epithelial Tissue

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Epithelial Tissue

© 2013 John Wiley & Sons, Inc. All rights reserved.

Epithelial Tissue

© 2013 John Wiley & Sons, Inc. All rights reserved.

Epithelial Tissue

© 2013 John Wiley & Sons, Inc. All rights reserved.

Epithelial Tissue

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Epithelial Tissue

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Epithelial Tissue
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The general types of epithelial tissue (epithelium) include covering and lining epithelium and glandular epithelium. Epithelium has the following general characteristics: It consists mostly of cells with little extracellular material, is arranged in sheets, is attached to connective tissue by a basement membrane, is avascular (no blood vessels), has a nerve supply, and can replace itself. Epithelial layers can be simple (one layer) or stratified (several layers). The cell shapes may be squamous (flat), cuboidal (cubelike), columnar (rectangular), or transitional (variable). Simple squamous epithelium consists of a single layer of flat cells (Table 4.1A). It is found in parts of the body where filtration or diffusion are priority processes. One type, endothelium, lines the heart and blood vessels. Another type, mesothelium, forms the serous membranes that line the thoracic and abdominal cavities and cover the organs within them.

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Epithelial Tissue
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Simple cuboidal epithelium consists of a single layer of cube-shaped cells that function in secretion and absorption (Table 4.1B). It is found covering the ovaries, in the kidneys and eyes, and lining some glandular ducts. Nonciliated simple columnar epithelium consists of a single layer of nonciliated rectangular cells (Table 4.1C). It lines most of the gastrointestinal tract. Specialized cells containing microvilli perform absorption. Goblet cells secrete mucus. Ciliated simple columnar epithelium consists of a single layer of ciliated rectangular cells (Table 4.1D). It is found in a few portions of the upper respiratory tract, where it moves foreign particles trapped in mucus out of the respiratory tract.

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Epithelial Tissue
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Pseudostratified columnar epithelium has only one layer but gives the appearance of many (Table 4.1E). The ciliated variety moves mucus in the respiratory tract. The nonciliated variety functions in absorption and protection. Stratified squamous epithelium consists of several layers of cells; cells in the apical layer and several layers deep to it are flat (Table 4.1F). It is protective. A nonkeratinized variety lines the mouth; a keratinized variety forms the epidermis, the most superficial layer of the skin. Stratified cuboidal epithelium consists of several layers of cells; cells in the apical layer are cubeshaped (Table 4.1G). It is found in adult sweat glands and a portion of the male urethra. It protects and provides limited secretion and absorption.

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Epithelial Tissue
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Stratified columnar epithelium consists of several layers of cells; cells in the apical layer are column-shaped (Table 4.1H). It is found in a portion of the male urethra and large excretory ducts of some glands. It functions in protection and secretion. Transitional epithelium consists of several layers of cells whose appearance varies with the degree of stretching (Table 4.1I). It lines the urinary bladder. A gland is a single cell or a group of epithelial cells adapted for secretion. Endocrine glands secrete hormones into interstitial fluid and then the blood (Table 4.2A). Exocrine glands (mucous, sweat, oil, and digestive glands) secrete into ducts or directly onto a free surface (Table 4.2B).

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Anatomy Overview:
• Epithelial Tissues

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Connective Tissue
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Connective tissue, one of the most abundant body tissues, consists of cells and an extracellular matrix of ground substance and fibers; it has abundant matrix with relatively few cells. It does not usually occur on free surfaces, has a nerve supply (except for cartilage), and is highly vascular (except for cartilage, tendons, and ligaments). Cells in connective tissue include fibroblasts (secrete matrix), macrophages (perform phagocytosis), plasma cells (secrete antibodies), mast cells (produce histamine), and adipocytes (store fat). The ground substance and fibers make up the extracellular matrix. The ground substance supports and binds cells together, provides a medium for the exchange of materials, and is active in influencing cell functions.

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Connective Tissue
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The fibers in the extracellular matrix provide strength and support and are of three types:
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collagen fibers (composed of collagen) are found in large amounts in bone, tendons, and ligaments elastic fibers (composed of elastin, fibrillin, and other glycoproteins) are found in skin, blood vessel walls, and lungs reticular fibers (composed of collagen and glycoprotein) are found around fat cells, nerve fibers, and skeletal and smooth muscle cell.

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Connective tissue is subdivided into loose connective tissue, dense connective tissue, cartilage, bone, and liquid connective tissue (blood tissue and lymph).

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Connective Tissue
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Loose connective tissue includes areolar connective tissue, adipose tissue, and reticular connective tissue. Areolar connective tissue consists of the three types of fibers, several cells, and a semifluid ground substance (Table 4.3A). It is found in the subcutaneous layer; in mucous membranes; and around blood vessels, nerves, and body organs. Adipose tissue consists of adipocytes, which store triglycerides (Table 4.3 B). It is found in the subcutaneous layer, around organs, and in the yellow bone marrow. Reticular connective tissue consists of reticular fibers and reticular cells and is found in the liver, spleen, and lymph nodes (Table 4.3 C). Dense connective tissue includes dense regular connective tissue, dense irregular connective tissue, and elastic connective tissue. Dense regular connective tissue consists of parallel bundles of collagen fibers and fibroblasts (Table 4.4A). It forms tendons, most ligaments, and aponeuroses.
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Connective Tissue
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Dense irregular connective tissue consists of usually randomly arranged collagen fibers and a few fibroblasts (Table 4.4B). It is found in fasciae, the dermis of skin, and membrane capsules around organs. Elastic connective tissue consists of branching elastic fibers and fibroblasts (Table 4.4C). It is found in the walls of large arteries, lungs, trachea, and bronchial tubes. Cartilage contains chondrocytes and has a rubbery matrix (chondroitin sulfate) containing collagen and elastic fibers. Hyaline cartilage is found in the embryonic skeleton, at the ends of bones, in the nose, and in respiratory structures (Table 4.5A). It is flexible, allows movement, and provides support. Fibrocartilage is found in the pubic symphysis, intervertebral discs, and menisci (cartilage pads) of the knee joint (Table 4.5B). Elastic cartilage maintains the shape of organs such as the epiglottis of the larynx, auditory (eustachian) tubes, and external ear (Table 4.5C).

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Connective Tissue
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Bone or osseous tissue supports, protects, helps provide movement, stores minerals, and houses blood-forming tissue. Blood tissue is liquid connective tissue that consists of blood plasma in which red blood cells, white blood cells, and platelets are suspended. Its cells transport oxygen and carbon dioxide, carry on phagocytosis, participate in allergic reactions, provide immunity, and bring about blood clotting. Lymph, the extracellular fluid that flows in lymphatic vessels, is also a liquid connective tissue. It is a clear fluid similar to blood plasma but with less protein.

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Connective Tissue

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Connective Tissue
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Because of the diversity of cells and extracellular matrix and the differences in their relative proportions, the classification of connective tissues is not always clear-cut. We offer the following scheme: I. Loose connective tissue
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Areolar connective tissue Adipose tissue Reticular connective tissue Dense regular connective tissue Dense irregular connective tissue Elastic connective tissue Hyaline cartilage Fibrocartilage Elastic cartilage

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II. Dense connective tissue
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III. Cartilage
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IV. Bone tissue V. Liquid connective tissue (blood tissue and lymph)

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Loose Connective Tissue

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Loose Connective Tissue

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Loose Connective Tissue

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Dense Connective Tissue

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Dense Connective Tissue

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Dense Connective Tissue

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Connective Tissue – Cartilage

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Connective Tissue – Cartilage

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Connective Tissue – Cartilage

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Anatomy Overview:
• Connective Tissues

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Membranes
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An epithelial membrane consists of an epithelial layer overlying a connective tissue layer. Examples are mucous membranes, serous membranes, and synovial membranes. Mucous membranes line cavities that open to the exterior, such as the gastrointestinal tract. Serous membranes line closed cavities (pleura, pericardium, peritoneum) and cover the organs in the cavities. These membranes consist of a parietal layer and a visceral layer. Synovial membranes line joint cavities, bursae, and tendon sheaths. They consist of areolar connective tissue and do not have an epithelial layer.
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Membranes

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Muscular Tissue
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Muscular tissue consists of cells (called muscle fibers) that are specialized for contraction. It provides motion, maintenance of posture, heat production, and protection. Skeletal muscle tissue is attached to bones, cardiac muscle tissue forms most of the heart wall, and smooth muscle tissue is found in the walls of hollow internal structures (blood vessels and viscera).

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Anatomy Overview:
• Muscle Tissue

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Nervous Tissue
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The nervous system is composed of neurons (nerve cells) and neuroglia (protective and supporting cells). Neurons are sensitive to stimuli, convert stimuli into nerve impulses, and conduct nerve impulses.

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Anatomy Overview:
• Nervous Tissue

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Tissue Repair – Restoring Homeostasis
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Tissue repair is the replacement of worn-out, damaged, or dead cells by healthy ones. Stem cells may divide to replace lost or damaged cells. The formation of scar tissue is called fibrosis.

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Aging and Tissues
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Tissues heal faster and leave less obvious scars in the young than in the aged; surgery performed on fetuses leaves no scars. The extracellular components of tissues, such as collagen and elastic fibers, also change with age.

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End of Chapter 4
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