Picture Of Collagenous Fibrous Tissue

Why would infants and children have more need for brown fat than adults do? (Hint: Smaller bodies have a higher ratio of surface area to volume than larger bodies do.)

Dense regular connective tissue is named for two properties: (1) the collagen fibers are closely packed and leave relatively little open space, and (2) the fibers are parallel to each other. It is found especially in tendons and ligaments. The parallel arrangement of fibers is an adaptation to the fact that tendons and ligaments are pulled in predictable directions. With some minor exceptions such as blood vessels and sensory nerve fibers, the only cells in this tissue are fibroblasts, visible by their slender, violet-staining nuclei squeezed between bundles of collagen. This type of tissue has few blood vessels, so injured tendons and ligaments are slow to heal.

The vocal cords, suspensory ligament of the penis, and some ligaments of the vertebral column are made of a type of dense regular connective tissue called yellow elastic tissue. In addition to the densely packed collagen fibers, it exhibits branching elastic fibers and more fibro-blasts. The fibroblasts have larger, more conspicuous nuclei than seen in most dense regular connective tissue.

Elastic tissue also takes the form of wavy sheets in the walls of the large and medium arteries. When the heart pumps blood into the arteries, these sheets enable them to expand and relieve some of the pressure on smaller vessels downstream. When the heart relaxes, the arterial wall springs back and keeps the blood pressure from dropping too low between heartbeats. The importance of this elastic tissue becomes especially clear when there is not enough of it—for example, in Marfan syndrome (see insight 5.1, p. 172)—or when it is stiffened by arteriosclerosis (see chapter 19).

Dense irregular connective tissue also has thick bundles of collagen and relatively little room for cells and ground substance, but the collagen bundles run in random directions. This arrangement enables the tissue to resist unpredictable stresses. This tissue constitutes most of the dermis, where it binds the skin to the underlying muscle and connective tissue. It forms a protective capsule around organs such as the kidneys, testes, and spleen and a tough fibrous sheath around the bones, nerves, and most cartilages.

It is sometimes difficult to judge whether a tissue is areolar or dense irregular. In the dermis, for example, these tissues occur side by side, and the transition from one to the other is not at all obvious. A relatively large amount of clear space suggests areolar tissue, and thicker bundles of collagen with relatively little clear space suggests dense irregular tissue. The dense connective tissues are summarized in table 5.5.

Saladin: Anatomy & I 5. Histology I Text I I © The McGraw-Hill

Physiology: The Unity of Companies, 2003 Form and Function, Third Edition

170 Part One Organization of the Body

Table 5.4 Loose Connective Tissues

Areolar Tissue

Reticular Tissue

Adipose Tissue

Areolar Tissue

Reticular Tissue

Adipose Tissue

Loose Fiberous
(a)

Fibroblasts^

Elastic Collagenous Ground fibers fibers substance

-Lipid in adipocyte

Fibroblasts^

Elastic Collagenous Ground fibers fibers substance

-Lipid in adipocyte

Adipose Tissue Amount Fibers

Figure 5.17 Adipose Tissue.

Figure 5.15 Spread of the Mesentery. Figure 5.16 Lymph Node.

Figure 5.17 Adipose Tissue.

Microscopic appearance: Loose arrangement of collagenous and elastic fibers; scattered cells of various types; abundant ground substance; numerous blood vessels Representative locations: Underlying nearly all epithelia; surrounding blood vessels, nerves, esophagus, and trachea; fascia between muscles; mesenteries; visceral layers of pericardium and pleura Functions: Loosely binds epithelia to deeper tissues; allows passage of nerves and blood vessels through other tissues; provides an arena for immune defense; blood vessels provide nutrients and waste removal for overlying epithelia

Microscopic appearance: Loose network of reticular fibers and cells, infiltrated with numerous lymphocytes and other blood cells Representative locations: Lymph nodes, spleen, thymus, bone marrow Functions: Supportive stroma (framework) for lymphatic organs

Microscopic appearance: Dominated by adipocytes—large, empty-looking cells with thin margins; tissue sections often very pale because of scarcity of stained cytoplasm; adipocytes shrunken; nucleus pressed against plasma membrane; blood vessels often present

Representative locations: Subcutaneous fat beneath skin; breast; heart surface; surrounding organs such as kidneys and eyes Functions: Energy storage; thermal insulation; heat production by brown fat; protective cushion for some organs; filling space, shaping body

Saladin: Anatomy & I 5. Histology I Text I I © The McGraw-Hill

Physiology: The Unity of Companies, 2003 Form and Function, Third Edition

Chapter 5 Histology 171

Table 5.5 Dense Connective Tissues

Dense Regular Connective Tissue

Collagen fibers —Ground substance

— Fibroblast nuclei

Collagen fibers —Ground substance

— Fibroblast nuclei

Microscopic Dense Connective

Figure 5.18 Tendon.

Figure 5.18 Tendon.

Microscopic appearance: Densely packed, parallel, often wavy collagen fibers; slender fibroblast nuclei compressed between collagen bundles; scanty open space (ground substance); scarcity of blood vessels Representative locations: Tendons and ligaments

Functions: Ligaments tightly bind bones together; resist stress; tendons attach muscle to bone and transfer muscular tension to bones Dense Irregular Connective Tissue

Ground Substance Muscle

Bundles of collagen fibers

Gland ducts

Figure 5.19 Dermis of the Skin.

Bundles of collagen fibers

Gland ducts

Fibroblast nuclei

Ground substance

Fibroblast nuclei

Ground substance

Figure 5.19 Dermis of the Skin.

Microscopic appearance: Densely packed collagen fibers running in random directions; scanty open space (ground substance); few visible cells; scarcity of blood vessels

Representative locations: Deeper portion of dermis of skin; capsules around viscera such as liver, kidney, spleen; fibrous sheaths around cartilages and bones

Functions: Durable, hard to tear; withstands stresses applied in unpredictable directions

Saladin: Anatomy & I 5. Histology I Text I I © The McGraw-Hill

Physiology: The Unity of Companies, 2003 Form and Function, Third Edition

172 Part One Organization of the Body

Insight 5.1 Clinical Application

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