Understanding Connective Tissue: Types and Functions

1. Connective Tissue

2. 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

3. 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

4. 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

5. 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

6. 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

7. 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)

8. 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

9. 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.

10. 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

11. Dense Connective Tissue • also called dense fibrous tissue • has collagen fibers as its main matrix elements • crowded between the collagen fibers are rows of fibroblaststhat 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)

12. 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

13. 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

14. 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

15. Muscle Tissue • contract in response to specific stimuli • muscle fibers shorten during contraction • three types of muscle tissue: skeletal, smooth, cardiac

16. 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

17. 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

18. 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

19. 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