Connective tissue is the most abundant tissue in the body. Cells are scattered in an extracellular matrix composed of cells (collagen and/or elastin fibers) secreted by fibroblasts in a polysaccharide ground substance.
Loose connective tissue supports epithelia and organs and surrounds blood vessels and nerves. It contains more cells and fewer, thinner fibers.
Dense, irregular connective tissue has fewer cells and more fibers that are thick. It forms protective capsules around organs.
Dense, regular connective tissue has bundled parallel collagen fibers such as in ligaments (bone to bone) and tendons (muscle to bone).
This animation (Audio - Important) describes soft connective tissues.
Specialized Connective Tissues
Cartilage contains a dense array of fibers in a rubbery ground substance. It cushions and maintains the shape of body parts. It resists compression and is resilient. Cartilage is found in the ends of bones, parts of the nose, external ear, and disks between vertebrae.
Bone tissue is mineral-hardened with collagen fibers and a ground substance rich in calcium salts. Bones are organized as flat plates and cylinders, that support and protect body tissues and organs. Bones work with muscles to perform movement. Bone stores mineral salts, produces blood cells, and provides spaces for its own living osteocytes.
Adipose tissue cells are specialized for the storage of fat, which can be used as an energy reserve and cushions to pad organs.
Blood is classified as a connective tissue because blood cells arise in bone. Blood transports oxygen, wastes, hormones, and enzymes. Blood consists of red cells, white cells, and platelets dispersed in a fluid medium called plasma. Blood contains clotting factors to protect against bleeding. Blood also contains components to protect against foreign invaders.
Muscle tissue is composed of cells that contract when stimulated. Muscle helps move the body and specific body parts. Muscle tissue contracts in response to stimulation, then passively lengthens.
Nervous tissue detects stimuli, integrates information, and relays commands for response. It consists of excitable neurons and supporting neuroglial cells. Nervous tissue exerts greatest control over the body's responsiveness to changing conditions. Neurons, excitable cells, are organized as lines of communication throughout the body. When stimulated, an electrical impulse travels along the plasma membrane. Arrival of the impulse at the neuron endings triggers events that stimulate or inhibit adjacent neurons or other cells.
Neuroglia constitute more than half of the nervous tissue. It protects and supports the neurons, both structurally and metabolically.
This animation (Audio - Important) describes specialized connective tissues.