The hypodermis acts as a shock absorber because it is composed of fat cells. According to For Dummies, fat cells protect organs from falls in order to prevent injury to vital areas of the body. The hypodermis is composed mostly of fat, blood vessels and connective tissue called white adipose tissue.
The hypodermis is the layer in between actual skin and muscles. This layer of the body attaches skin to muscles and contains roughly half of the body's stores of fat cells. Cells in the hypodermis are bound together by collagen and elastin, two substances that make the skin flexible. The hypodermis lets skin and muscles move easily throughout the body. Thickness of this layer varies based upon the individual and the area of the body. The hypodermis also stores additional fatty acids brought there by the digestive system.
The hypodermis is not technically a layer of skin. Because it contains numerous blood vessels, the hypodermis helps insulate the body by regulating the temperature of the layer. This part of the body is beneath the deepest layer of skin and above muscle walls. Hair follicles can reach into the hypodermis. This part of the human body is part of the integumentary system that includes the skin, hair and nails protecting and covering the body.