Connective Tissue

General Characteristics most abundant and widely distributed of all the tissue types binds structures, provides support and protection, serves as frameworks, fills spaces, stores fat, produces blood cells, protects against infection, and helps repair tissue damage farther apart than epithelial cells

General Characteristics—cont. variations in blood supply most are well vascularized tendons and ligaments have a poor blood supply cartilages are avascular have an abundance of extracellular matrix produced by the connective tissue and then secreted to the exterior could be liquid, semisolid or gel-like, or very hard various types and amounts of fibers are deposited in the matrix

Major Cell Types in Connective Tissue Fibroblasts most common type of fixed cell in connective tissue large, star-shaped produce fibers by secreting proteins into the extracellular matrix produce three types of fibers: collagenous fibers, elastic fibers, and reticular fibers Before 1st bullet—Connective tissue contain a variety of cell types. Some are called fixed cells b/c they reside in the tissue for an extended period of time (fibroblasts and mast cells). Some are called wandering cells b/c they move through and appear in the tissues temporarily, usually in response to injury or infection (macrophages).

Major Cell Types in Connective Tissue Macrophages wandering cells that originate as white blood cells specialized to carry on phagocytosis can move about and function as scavenger and defensive cells that clear foreign particles from tissues After 1st bullet—almost as numerous as fibroblasts in some connective tissues After 2nd bullet—process by which a cell engulfs and digests solids Pic—shows several macrophages starting to engulf a cell

Major Cell Types in Connective Tissue Mast cells large and widely distributed usually located near blood vessels release heparin, which prevents blood clotting, and histamine, which promotes some of the reactions associated with inflammation and allergies After 1st bullet—fixed cell

Connective Tissue Fibers Collageneous fibers thick threads of the protein collagen flexible, but only slightly elastic great tensile strength important parts of ligaments (which connect bone to bone) and tendons (which connect muscles to bone) Before 1st bullet—Remember these are secreted by fibroblast cells. After 3rd bullet—they resist considerable force After 4th bullet—b/c of their tensile strength, they are found in body parts that hold structures together Bonus Question: Why are collagenous fibers called white fibers? (found in dense connective tissue and such tissue appears white)

Connective Tissue Fibers Elastic fibers composed of the protein elastin thin fibers that branch forming complex networks weaker than collageneous fibers but can stretch easily and resume original length and shape common in body parts that are frequently stretched, like the vocal cords Reticular fibers very thin collagenous fibers highly branched and form delicate supporting networks found in a variety of tissues, including the spleen Bonus Question: Why are they called yellow fibers? (tissues supplied with them appear yellowish) Read blue box on page 100. See Table 5.4 on page 100 for Review

Loose Connective Tissue also called areolar tissue soft, pliable tissue that cushions and protects the body organs it wraps considered a connective tissue “glue” lies beneath most layers of epithelium, where its many blood vessels nourish nearby epithelial cells When a body region is inflamed, the areolar tissue in the area soaks up the excess fluid like a sponge. The area swells and becomes puffy, a condition called edema. Before 1st bullet—There are six types of connective tissue: loose connective tissue, adipose tissue, dense connective tissue, cartilage, bone, and blood. After 3rd bullet—binds the skin to the underlying organs and fills spaces between muscles After pictures—What are fibroblast cells? (cells that produce fibers) collagenous fibers are the thick threads of protein collagen; the elastic fibers are the thin, branching fibers that are made of elastin See Figure 5.13 on page 101.

Adipose Tissue also called fat specialized form of loose connective tissue that develop when certain cells store fat in droplets within their cytoplasm and enlarge lies beneath the skin where it insulates and stores energy cushions joints and some organs Read under Adipose Tissue on page 101. About pictures—Adipose tissue cells contain large fat droplets that push the nuclei close to the cell membranes. See Figure 5.14 on page 101.

Dense Connective Tissue also called dense fibrous tissue has collagen fibers as its main matrix elements crowded between the collagen fibers are rows of fibroblasts that manufacture the fibers form strong, ropelike structures such as tendons and ligaments blood supply is low also makes up the lower layers of skin (dermis) After 4th bullet—enables tissue to withstand pulling forces After 4th bullet—where they bind bone to bone or muscle to bone After 6th bullet—tissue repair is slow See Figure 5.15 on page 102.

Cartilages less hard and more flexible than bone only found in a few places in the body several types in the body hyaline cartilage—most widespread; attaches ribs to breastbone, and covers the ends of bones where joints are formed elastic cartilage—found where a structure with elasticity is desired, such as the external ear fibrocartilage—very tough tissue; forms the cushionlike disks between the vertebrae of the spinal column; shock absorber See Figures 5.16 on page 102 and Figures 5.17 and 5.18 on page 103. Read box on page 103.

Bone most rigid connective tissue sometimes called osseous tissue composed of bone cells sitting in cavities called lacunae and surrounded by layers of a very hard matrix has an exceptional ability to protect and support other body organs See Figure 5.19 on page 104.

Blood considered a connective tissue because it consists of blood cells, surrounded by a nonliving, fluid matrix called blood plasma “fibers” of blood are soluble protein molecules that become visible only during blood clotting transport vehicle for the cardiovascular system See Figure 5.20 on page 105. See Table 5.5 on page 105. Have students complete questions 1-4 on page 102 and 1-3 on page 105.

Muscle Tissue contract in response to specific stimuli muscle fibers shorten during contraction three types of muscle tissue: skeletal, smooth, cardiac After 3rd bullet—About 40% of the body is skeletal muscle, and almost another is smooth or cardiac muscle.

Skeletal Muscle found in muscles that attach to bones form the flesh of the body can be controlled voluntarily pull on bones or skin when they contract which results in gross body movements or changes in facial expressions cells are long, cylindrical and multinucleate with obvious striations See Figure 5.21 on page 107.

Smooth Muscle Tissue no striations are visible individual cells have a single nucleus and are spindle shaped found in the walls of hollow organs such as the stomach, bladder, uterus and blood vessels When smooth muscle contracts, the cavity of an organ alternately constricts and dilates so that substances are propelled through the organ along a specific pathway. contracts more slowly than the other two muscles involuntary movement See Figure 5.22 on page 107.

Cardiac Muscle Tissue found only in the heart As it contracts, the heart acts as a pump and propels blood through the blood vessels. has striations like skeletal muscle, but cardiac cells are uninucleate and fit together tightly at junctions called intercalated disks under involuntary control See Figure 5.23 on page 108.

Nervous Tissue cells are called neurons All neurons receive and conduct electrochemical impulses from one part of the body to another. have a unique structure—drawn out cytoplasm into long extensions make up the structures of the nervous system See Figure 5.24 on page 109. See Table 5.6 on page 108. Read “Types of Membranes” on page 109—defining the four types of membranes.