Histology is the study of tissues. Tissues are groups of cells that are similar in structure and function. There are four tissue types associated with animals such as humans. They are:
Each of these tissue categories has distinctive cell shapes and functions.
Connective tissue is the most abundant and variable of the human tissues. It is designed for supporting, protecting and binding the tissues of the body. Most CT's are well vascularized (except for tendons, ligaments and cartilage). Connective tissues all consist of three elements: (1) CT cells, (2) matrix produced by the CT cells and (3) fibers produced by the CT cells. There are many types of cells associated with CT, but the generic "CT precursor" is the fibroblast.
Matrix is produced by the CT cells, then released from the cells. It is noncellular and nonliving. It provides extracellular support for the CT cells that produced it. There are several types of fibers in CT. The three major types are collagen, elastic and reticular.
(1) Bone CT is mostly matrix, with scattered cells called osteoblasts.
(2) Osteoblasts mature to become osteocytes. The matrix of bone undergoes ossification to become a hard, calcified material.
(3) The osteocytes remain alive inside small "chambers" called lacunae (sing: lacuna) that are positioned in a ring arrangement around a central_canal, which contains blood vessels. Another, older term for the central canal is Haversian_canal.
(4) The rings are called lamellae (sing: lamella).
(5) The lamellae are connected to one another by tiny canals called canaliculi. This access system allows the cells to remain alive, despite the fact that their matrix calcifies.
(6) Perforating_canals can be seen at various locations. Perforating canals are often referred to as Volkmanns or transverse_canals.
(7) Perforating canals connect the central canal of one osteon with the central canal of a different osteon.