Specialised connective tissue

There are two main types of specialised connective tissue - adipose and reticular tissues.

Adipose tissue is a metabolical tissue, which stores fat and provides several functions: 1) fat is the nutrition and energy store house, 2) provides insulation (protection) against heat (warmth) loss, 3) functions in mechanical support in certain regions of the body.

About 10 percent of the total body weight of an average man is fat, representing approximately 40 days reserve of energy.

Fat is an efficient form of calorie storage, because it has about twice the calorie density of carbohydrate and protein. The metabolism of fat can also be an essential source of water for the body in extreme conditions. In fact, the hump of a camel consists largely of fat and is a source of both energy and water for this animal in the desert.

There are two types of adipose tissue, which differ in their colour, distribution, vascularity and metabolic activity. One is white adipose tissue, which comprises the bulk of body fat. The other, called brown adipose tissue, is less abundant.

White adipose tissue (or unilocular). This type is made of assemblage of cells, a small amount of collagen fibers and is often subdivided into small lobules by loose connective tissue septa with vessels, especially capillaries. Adipose cells have a big lipid drop and a thin rim of cytoplasm with the flattened nucleus.

This type is widely distributed in the subcutaneous layer (punniculus adiposus) and especially under the skin of the abdomen, buttocks and thighs, where it exhibits regional differences in influenced by age and sex. And there are extensive accumulations in both sexes in the omentum, mesenteries and retroperitoneal areas, in the orbits, major joints, on the palms of the hands and soles of the feet. In those latter places the adipose tissue has the mechanical function of support or protection and as a cushion (pillow).

Brown adipose tissue (multilocular). This type has the brown colour. Its cells are smaller and are polygonal in cross section, their cytoplasm is more abundant and there are multiple lipid droplets of varying size. The numerous mitochondria occupy a large part of the cytoplasm, the nucleus is usually in an eccentric position, but it is not flattened in comparison with the cells of white adipose tissue For this type of adipose tissue is characteristically big amount of blood vessels between cells.

Brown adipose tissue arises in embryonic life and is only in fetus and first days after parturition and may be present in adult person in between muscles, along the spinal column.

This adipose tissue is present in large amount in hibernating animals (e.g. in bears) for production of heat due to the big vascularity and metabolic activity.

Reticular tissue is developed from mesenchyme and forms stroma of lymphoid and blood forming organs (immune, hemopoietic), forming the medium for the developing cells of the blood (spleen, lymph nodes, bone marrow). This tissue consists of small reticular cells - stellate cells with cell contacts between processes and the reticular fibers (or type collagen fibers No 1V), which are coloured with silver staining methods. Reticular tissue looks like network - reticulum.

CARTILAGE

Cartilage is a skeletal connective tissue characterized by firmness and resiliency. It forms most of the fetal skeleton and persists in sites where its mechanical properties are needed. Most fetal cartilage eventually becomes bone. Like all connective tissues, cartilage is composed of cells, fibers, and ground substance.

The extracellular matrix predominates and determines cartilage's mechanical properties. Type II collagen is a characteristic cartilage matrix component, and the abundant ground substance is firm and gel-like. Cartilage cells are termed chondroblasts and chondrocytes.

Under the light microscope, chondrocytes (mature cells) appear rounded, with an eccentric nucleus, a prominent nucleolus, and light stained cytoplasm. With Electron Microscopy, chondrocyte surfaces exhibit characteristic projections and infoldings. Some lipid droplets are typically found in the cytoplasm. Chondroblasts synthesize and secrete the fibers and ground substance of the extracellular matrix. Collagen is synthesized on the RER, and GAGs are assembled and sulfated in the Golgi complex. There are the 3 types of cartilage: hyaline cartilage, elastic cartilage, and fibrocartilage.