Skin is the layer of usually soft, flexible outer tissue covering the body of a vertebrate animal, with three main functions: protection, regulation, and sensation.
The integumentary system is the set of organs forming the outermost layer of an animal's body. It comprises the skin and its appendages, acting as a physical barrier between the external environment and the internal environment that it serves to protect and maintain.
Connective tissue is one of the four basic types of animal tissue, along with epithelial tissue, muscle tissue, and nervous tissue. It develops from the mesoderm. Connective tissue is found in between other tissues everywhere in the body, including the nervous system. In the central nervous system, the three outer membranes that envelop the brain and spinal cord are composed of connective tissue. All connective tissue consists of three main components: fibers, ground substance and cells. Not all authorities include blood or lymph as connective tissue because they lack the fiber component. All are immersed in the body water. The cells of connective tissue include fibroblasts, adipocytes, macrophages, mast cells and leucocytes.
A fascia is a band or sheet of connective tissue, primarily collagen, beneath the skin that attaches, stabilizes, encloses, and separates muscles and other internal organs. Fascia is classified by layer, as superficial fascia, deep fascia, and visceral or parietal fascia, or by its function and anatomical location.
The dermis or corium is a layer of skin between the epidermis and subcutaneous tissues, that primarily consists of dense irregular connective tissue and cushions the body from stress and strain. It is divided into two layers, the superficial area adjacent to the epidermis called the papillary region and a deep thicker area known as the reticular dermis. The dermis is tightly connected to the epidermis through a basement membrane. Structural components of the dermis are collagen, elastic fibers, and extrafibrillar matrix. It also contains mechanoreceptors that provide the sense of touch and thermoreceptors that provide the sense of heat. In addition, hair follicles, sweat glands, sebaceous glands, apocrine glands, lymphatic vessels, nerves and blood vessels are present in the dermis. Those blood vessels provide nourishment and waste removal for both dermal and epidermal cells.
The subcutaneous tissue, also called the hypodermis, hypoderm, subcutis, superficial fascia, is the lowermost layer of the integumentary system in vertebrates. The types of cells found in the layer are fibroblasts, adipose cells, and macrophages. The subcutaneous tissue is derived from the mesoderm, but unlike the dermis, it is not derived from the mesoderm's dermatome region. It consists primarily of loose connective tissue, and contains larger blood vessels and nerves than those found in the dermis. It is a major site of fat storage in the body.
Loose connective tissue is a category of connective tissue which includes areolar tissue, reticular tissue, and adipose tissue. Loose connective tissue is the most common type of connective tissue in vertebrates. It holds organs in place and attaches epithelial tissue to other underlying tissues. For example, it forms telae, such as the tela submucosa and tela subserosa, which connect mucous and serous membranes to the muscular layer. It also surrounds the blood vessels and nerves. Cells called fibroblasts are widely dispersed in this tissue; they are irregular branching cells that secrete strong fibrous proteins and proteoglycans as an extracellular matrix. The cells of this type of tissue are generally separated by quite some distance by a gelatinous substance primarily made up of collagenous and elastic fibers.
A reticular cell is a type of fibroblast that synthesizes collagen alpha-1(III) and uses it to produce reticular fibers. The cell surrounds the fibers with its cytoplasm, isolating it from other tissue components and cells. Reticular cells provide structural support, since they produce and maintain the thin networks of fibres that are a framework for most lymphoid organs.
The basement membrane is a thin, pliable sheet-like type of extracellular matrix, that provides cell and tissue support and acts as a platform for complex signalling. The basement membrane sits between epithelial tissues including mesothelium and endothelium, and the underlying connective tissue.
Reticular fibers, reticular fibres or reticulin is a type of fiber in connective tissue composed of type III collagen secreted by reticular cells. Reticular fibers crosslink to form a fine meshwork (reticulin). This network acts as a supporting mesh in soft tissues such as liver, bone marrow, and the tissues and organs of the lymphatic system.
Reticular connective tissue is a type of connective tissue with a network of reticular fibers, made of type III collagen. Reticular fibers are not unique to reticular connective tissue, but only in this type they are dominant.
Dense connective tissue, also called dense fibrous tissue, is a type of connective tissue with fibers as its main matrix element. The fibers are mainly composed of type I collagen. Crowded between the collagen fibers are rows of fibroblasts, fiber-forming cells, that generate the fibers. Dense connective tissue forms strong, rope-like structures such as tendons and ligaments. Tendons attach skeletal muscles to bones; ligaments connect bones to bones at joints. Ligaments are more stretchy and contain more elastic fibers than tendons. Dense connective tissue also make up the lower layers of the skin (dermis), where it is arranged in sheets.
Lymphangiomas are malformations of the lymphatic system characterized by lesions that are thin-walled cysts; these cysts can be macroscopic, as in a cystic hygroma, or microscopic. The lymphatic system is the network of vessels responsible for returning to the venous system excess fluid from tissues as well as the lymph nodes that filter this fluid for signs of pathogens. These malformations can occur at any age and may involve any part of the body, but 90% occur in children less than 2 years of age and involve the head and neck. These malformations are either congenital or acquired. Congenital lymphangiomas are often associated with chromosomal abnormalities such as Turner syndrome, although they can also exist in isolation. Lymphangiomas are commonly diagnosed before birth using fetal ultrasonography. Acquired lymphangiomas may result from trauma, inflammation, or lymphatic obstruction.
Stroma is the part of a tissue or organ with a structural or connective role. It is made up of all the parts without specific functions of the organ - for example, connective tissue, blood vessels, ducts, etc. The other part, the parenchyma, consists of the cells that perform the function of the tissue or organ.
The stroma of the ovary is a unique type of connective tissue abundantly supplied with blood vessels, consisting for the most part of spindle-shaped stroma cells. These appear similar to fibroblasts. The stroma also contains ordinary connective tissue such as reticular fibers and collagen. Ovarian stroma differs from typical connective tissue in that it contains a high number of cells. The stoma cells are distributed in such a way that the tissue appears to be whorled. Stromal cells associated with maturing follicles may acquire endocrine function and secrete estrogens. The entire ovarian stroma is highly vascular.
In anatomy and histology, the term wandering cell is used to describe cells that are found in connective tissue, but are not fixed in place. This term is used occasionally and usually refers to blood leukocytes in particular mononuclear phagocytes. Frequently, the term refers to circulating macrophages and has been used also for stationary macrophages fixed in tissues (histiocytes), which are sometimes referred to as "resting wandering cells".
The human skin is the outer covering of the body and is the largest organ of the integumentary system. The skin has up to seven layers of ectodermal tissue and guards the underlying muscles, bones, ligaments and internal organs. Human skin is similar to most of the other mammals' skin, and it is very similar to pig skin. Though nearly all human skin is covered with hair follicles, it can appear hairless. There are two general types of skin, hairy and glabrous skin (hairless). The adjective cutaneous literally means "of the skin".
Dense irregular connective tissue has fibers that are not arranged in parallel bundles as in dense regular connective tissue.
Anchoring fibrils extend from the basal lamina of epithelial cells and attach to the lamina reticularis by wrapping around the reticular fiber bundles. The basal lamina and lamina reticularis together make up the basement membrane. Anchoring fibrils are essential to the functional integrity of the dermoepidermal junction.
Elaunin is a component of elastic fibers formed from a deposition of elastin between oxytalan fibers. It is found in the periodontal ligament and in the connective tissue of the dermis, particularly in association with sweat glands.
