Connective tissue typically consists mostly of fibers and ground substance, with widely separated cells. It is the most abundant, widely distributed, and histologically variable of the primary tissues. As the name implies, it often serves to connect organs to each other—for example, the way a tendon connects muscle to bone—or serves in other ways to support, bind, and protect organs. This category includes fibrous tissue, fat, cartilage, bone, and blood.
The functions of connective tissue include the following:
- Binding of organs. Tendons bind muscle to bone, ligaments bind one bone to another, fat holds the kidneys and eyes in place, and fibrous tissue binds the skin to underlying muscle.
- Support. Bones support the body, and cartilage supports the ears, nose, trachea, and bronchi.
- Physical protection. The cranium, ribs, and sternum protect delicate organs such as the brain, lungs, and heart; fatty cushions around the kidneys and eyes protect these organs.
- Immune protection. Connective tissue cells attack foreign invaders, and connective tissue fiber forms a "battlefield" under the skin and mucous membranes where immune cells can be quickly mobilized against disease agents.
- Movement. Bones provide the lever system for body movement, cartilages are involved in movement of the vocal cords, and cartilages on bone surfaces ease joint movements.
- Storage. Fat is the body's major energy reserve; bone is a reservoir of calcium and phosphorus that can be drawn upon when needed.
- Heat production. Brown fat generates heat in infants and children.
- Transport. Blood transports gases, nutrients, wastes, hormones, and blood cells.
The mesenchyme described earlier in this chapter is a form of embryonic connective tissue. The connective tissues present after birth fall into three broad categories: fibrous connective tissues, supportive connective tissues (cartilage and bone), and fluid connective tissue (blood).
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This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.
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