Human is a structure made up of many different parts. It can be likened to a house made of blocks, doors, windows and the roof. To the body, there is the muscle tissue, skeleton, and several internal organs. But what holds these different parts together? Are they floating loosely within the body? Just like a house whose blocks are held together by cement, the various parts of the body are held together in a tight package by a group of tissues called the connective tissue. Connective tissue is a matrix that connects, binds and supports other tissues and organs of the body as well as maintaining the form of the body. The connective tissue is primarily composed of the cells and the matrix. The matrix consists of the glycoproteins, protein fibres and proteoglycans. The types of cells found in connective tissues differ with the type of connective tissue. There are four types of specialized connective tissues. These are the bone, cartilage, blood, and fat. This paper discusses the bone and cartilage; composition and types.
Cartilage is a flexible, strong type of connective tissue that occupies the halfway point between muscles and the bones. Cartilage is not as rigid as the bone, neither is it too flexible. As a result, it is found in areas where support and structure, as well as flexibility, is required. Such areas include joints, ears and between spinal column.
Connective tissue is compost of living cells within an extracellular matrix. In cartilage, the extracellular matrix is produced by chondroblasts cells suspended by chondrocytes in the matrix (Halper & Kjaer, 2014). Chondrocytes determine the flexibility of the cartilage tissue. There are types of cartilage within the human body. These are elastic cartilage, hyaline cartilage, and fibrocartilage.
Elastic cartilage is compost of elastic fiber networks and collagen fiber. The standard protein is elastin. It is almost similar to hyaline cartilage, but it has yellow elastic fibers lying in a solid matrix. The fibers bundle together forming dark-like structures under the microscope view. Chondrocytes lie in between the fibres. The common areas where elastic cartilage is found include epiglottis and the pinnae (Hunter & Finlay, 2016).
Hyaline cartilage is the most common and widely spread type of cartilage in the body. In adults, it is the main content of the articular surfaces of long bones, the rings of the trachea, the rib tips and parts of the skull. In the embryo, bones develop as hyaline cartilage before hardening as the development process progresses. The hyaline cartilage is enclosed by perichondrium, a fibrous membrane, except when it occurs at the end of particular bones. Hyaline also occurs under the skin, for example, in the ears and nose (Palukuru, McGoverin & Pleshko, 2014).
Hyaline is also found on the joint surfaces without blood vessels or nerves. The structure is simple. When viewed under a microscope, the cells of hyaline cartilage would be found to be rounded or angular form, and they lie in groups of two or more in an almost homogenous matrix or granular form.
Fibrocartilage, on the other hand, is a fibrous cartilage mainly comprised of collagen fibers of type I and Type II. The collagen fibers show a tendency of grading into a dense ligament and tendon tissue. White fibrocartilage comprises a mixture of cartilaginous tissue and fibrous tissue in varying proportions. The flexibility and toughness of the fibrocartilage tissue are due to the fibrous tissue while its elasticity is derived from the cartilaginous tissue. It is the single type of cartilage containing type I collagen alongside the normal type II (Lane,& Amiel, 2017).
Fibrocartilage is located in the pubic symphysis, the temporal mandibular joint and intervertebral discs and menisci.
The bone connective tissue is highly hard, solid, calcified and rigid tissue. Its matrix is compost of an organic component called ossein. The bone forms the major part of the adult vertebrate endoskeleton. The firmness of the bone is derived from calcium phosphate which is the main mineral crystal making up the bone. Bone connective tissue provides support and structure to the mammalian body.
The bone is compost of calcium phosphate, calcium carbonate, sodium chloride and magnesium phosphate. These are the main salts of the bone and are collectively known as the hydroxyapatite. They constitute the major part of the body weight, about two-thirds (McClung et al., 2014). Bone matrix is made up of sixty-seven mineral salts and thirty-three percent of collagenous protein fibres.
Structurally, the bone connective tissue is rigid, hard, solid and calcified. Externally, it is covered with periosteum and internally coated with endosteum. To the tips, the bone is covered by smooth, soft and spongy bone. The middle part is long, solid, hard and elongated with haversian canal know as the compact bone. The periosteum is the outer most layer of the bone which is dense and hard and is compost of white fibrous connective tissue. Nerve fibres and blood vessels are present in the periosteum. Below the periosteum are osteoblast cells which divide to give rise to new bone cells (McClung et al., 2014).
The endosteum forms the lining of the center of the compact bone alongside the marrow cavity. The matrix of the bone, called ossein, is laid in concentric rings known as lamellae. Lamellae is situated between endosteum and periosteum. The space between lamellae is filled with small cavities called lacunae. Each lacuna covers a single osteocyte cell.
The haversian canal is tube-like central part of the compact bone. The harvesian canal comprises lymph vessels, blood vessels, and nerve fibres. The canaliculi, lamellae and osteocyte cell found in the lacunae are arranged in a concentric manner surrounding the haversian canal to form the haversian system. However, haversian spongy bones are not found in mammals (McClung et al., 2014).
There are two major types of bone connective tissue; spongy bone and compact bone. Spongy bone is located in the extended ends of long bones. They have a loose matrix, with many spaces and spongy. The main substance filling the spongy bone is the red colored fatty red bone marrow. On the other hand, compact bone is the hard, long, elongated and rigid part of the bone, called the compact bone. It is what constitutes the shaft of the long bone. Its matrix is solid, hard and dense with the absence of spaces. The central part is comprised of the haversian system. The main component of the matrix is the yellow fatty substance known as the yellow bone marrow (McClung et al., 2014).
The cartilage and bone connective tissues are essential building parts of the body. The cartilage connects structure and supports the joints for easy flexibility. Elastic cartilage is the one responsible for flexible organs such as the nose and the ears while Fibrocartilage is less flexible and is found in areas such as the knee where toughness is necessary. The bone is necessary for providing the shape to the body as well as firm support. The bones have salts that form the weight and strength of the body.
Halper, J., & Kjaer, M. (2014). Basic components of connective tissues and extracellular matrix: elastin, fibrillin, fibulins, fibrinogen, fibronectin, laminin, tenascins and thrombospondins. In Progress in Heritable Soft Connective Tissue Diseases (pp. 31-47). Springer Netherlands.
Hunter, J. A., & Finlay, B. (2016). of Connective Tissues in Health and Disease. International Review of Connective Tissue Research, 6, 217.
Lane, J. G., & Amiel, D. (2017). Ligament Histology, Composition, Anatomy, Injury, and Healing Mechanisms. In Bio-orthopaedics (pp. 291-312). Springer Berlin Heidelberg.
McClung, M. R., Grauer, A., Boonen, S., Bolognese, M. A., Brown, J. P., Diez-Perez, A., ... & Katz, L. (2014). Romosozumab in postmenopausal women with low bone mineral density. New England Journal of Medicine, 370(5), 412-420.
Palukuru, U. P., McGoverin, C. M., & Pleshko, N. (2014). Assessment of hyaline cartilage matrix composition using near infrared spectroscopy. Matrix Biology, 38, 3-11.
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