The subcutaneous tissue (), also called the hypodermis, hypoderm (), subcutis, superficial fascia, is the lowermost layer of the

integumentary system The integumentary system is the set of organs forming the outermost layer of an animal's body. It comprises the skin and its appendages, which act as a physical barrier between the external environment and the internal environment that it serves ...

vertebrate Vertebrates () comprise all animal taxon, taxa within the subphylum Vertebrata () (chordates with vertebral column, backbones), including all mammals, birds, reptiles, amphibians, and fish. Vertebrates represent the overwhelming majority of the ...

s. 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. In arthropods, a hypodermis can refer to an epidermal layer of cells that secretes the chitinous cuticle. The term also refers to a layer of cells lying immediately below the

epidermis The epidermis is the outermost of the three layers that comprise the skin, the inner layers being the dermis and Subcutaneous tissue, hypodermis. The epidermis layer provides a barrier to infection from environmental pathogens and regulates the ...

of plants.

Structure

* Fibrous bands anchoring the skin to the deep fascia * Collagen and elastin fibers attaching it to the dermis * Fat is absent from the eyelids, clitoris, penis, much of pinna, and scrotum * Blood vessels on route to the dermis * Lymphatic vessels on route from the dermis * The glandular part of some sweat glands;

mammary glands A mammary gland is an exocrine gland in humans and other mammals that produces milk to feed young offspring. Mammals get their name from the Latin word ''mamma'', "breast". The mammary glands are arranged in organs such as the breasts in ...

lie entirely within the subcutaneous tissue (which are modified

apocrine sweat glands An apocrine sweat gland (; from Greek ''apo'' 'away' and ''krinein'' 'to separate') is composed of a coiled secretory portion located at the junction of the dermis and subcutaneous fat, from which a straight portion inserts and secretes into the ...

) * Cutaneous nerves and free endings * Hair follicle roots *

Ruffini Ruffini is an Italian surname. Notable people with the surname include: * Alessandro "Sandro" Ruffini (1889–1954), Italian actor and voice actor * Angelo Ruffini (1864–1929), Italian histologist and embryologist *Attilio Ruffini (1924–2011), ...

and Pacinian corpuscles *

Mast cells A mast cell (also known as a mastocyte or a labrocyte) is a resident cell of connective tissue that contains many granule (cell biology), granules rich in histamine and heparin. Specifically, it is a type of granulocyte derived from the CFU-GEMM, ...

* Bursae, in the space overlying joints in order to facilitate smooth passage of overlying skin * Fine, flat sheets of muscle, in certain locations, including the scalp, face, hand, nipple, and scrotum, called the panniculus carnosus In some animals, such as whales and hibernating mammals, the hypodermis forms an important insulating layer and/or food store. In some plants, the hypodermis is a layer of cells immediately below the epidermis of leaves. It is often mechanically strengthened, for example, in pine leaves, forming an extra protective layer or a water storage tissue.

Subcutaneous fat

Subcutaneous fat is the layer of subcutaneous tissue that is most widely distributed. It is composed of adipocytes, which are grouped together in lobules separated by

connective tissue Connective tissue is one of the four primary types of animal tissue, along with epithelial tissue, muscle tissue, and nervous tissue. It develops from the mesenchyme derived from the mesoderm the middle embryonic germ layer. Connective tissue ...

. The number of adipocytes varies among different areas of the body, while their size varies according to the body's nutritional state. It acts as padding and as an energy reserve, as well as providing some minor thermoregulation via insulation. Subcutaneous fat is found just beneath the skin, as opposed to visceral fat, which is found in the peritoneal cavity, and can be measured using body fat calipers to give a rough estimate of total body adiposity.

Clinical significance

Injection

Injection into the subcutaneous tissue is a route of administration used for drugs such as insulin: because it is highly vascular, the tissue absorbs drugs quickly. Subcutaneous injection is believed to be the most effective manner to administer some drugs, such as human growth hormones. Just as the subcutaneous tissue can store fat, it can also provide good storage space for drugs that need to be released gradually because there is limited blood flow. " Skin popping" is a slang term that includes this method of administration, and is usually used in association with recreational drugs.

Disease

Subcutaneous abscess A subcutaneous abscess is an abscess located in the subcutaneous tissue (also hypodermis). The abscess is formed due to a hypodermal infection by a bacterium, a fungus or a parasite. Typically, this kind of abscess needs drainage, usually for a mini ...

* Subcutaneous tumor

References