Subcutaneous tissue

The hypodermis, also called the hypoderm, subcutaneous tissue, or superficial fascia is the lowermost layer of the integumentary system in vertebrates. (Hypoderm and subcutaneous are from Greek and Latin words, respectively, for "beneath the skin."^[1])Types of cells that are found in the hypodermis are fibroblasts, adipose cells, and macrophages. It is derived from the mesoderm, but unlike the dermis, it is not derived from the dermatome region of the mesoderm. In arthropods, the hypodermis is an epidermal layer of cells that secretes the chitinous cuticle. The term also refers to a layer of cells lying immediately below the epidermis of plants.

This cell is also used to supervise the outer skin from burns and other such articulates.

The hypodermis is used mainly for fat storage.

A layer of tissue lies immediately below the dermis of vertebrate skin. It is often referred to as subcutaneous tissue though this is a less precise and anatomically inaccurate term. The hypodermis consists primarily of loose connective tissue and lobules of fat. It contains larger blood vessels and nerves than those found in the dermis.

Contents

Specifically, the hypodermis contains:

• Fibrous bands anchoring the skin to the deep fascia
• Fat, except in the eyelid, scrotum, penis, nipple and areola
• Blood vessels on route to the dermis
• Lymphatic vessels on route from dermis
• Hair follicle roots
• The glandular part of some sudiferous glands
• Nerves: free endings and Pacinian corpuscles
• 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.

According to the eighth edition of Developmental Biology by Scott F. Gilbert, the hypodermis of C. elegans is derived from ectoderm.

Subcutaneous fat

Subcutaneous fat is found just beneath the skin as opposed to visceral fat which is found in the peritoneal cavity. Subcutaneous fat can be measured using body fat calipers giving a rough estimate of total body adiposity. This fat aids in the process of homeostasis, by forming a layer of insulation to slow heat loss.

Hypothetical function during human evolution

Body fat is cited within the aquatic ape hypothesis as the result of adaptation to aquatic environments, as a means of streamlining and insulation.^[2] Others have pointed out in response that the subcutaneous fat distribution in humans is more similar to a domesticated animal than an aquatic one, and is nearly identical to that of other primates.^[3][4] The subcutaneous fat of aquatic mammals and humans also seems to serve different uses - it forms the streamlined shape of seals, while in humans it is used for sexual selection; humans display considerable sexual dimorphism in their fat distribution, which is not explained by the aquatic ape hypothesis.^[5][6]

Injection

Injection into the subcutaneous tissue is a route of administration used for, for example, insulin. Skin popping is a slang term that includes this method of administration, and is usually used in association with recreational drugs.

See also

• Epidermis
• Dermis

References