Structural components of the dermis
The functions of the skin are heavily dependent on various structural components embedded inside the reticular region of the dermis - blood vessels, nerves, glands, and hair follicles.
Figure 1. Cross section of a skin sample showing basic skin layers and their internal structures.
Hair is present in most skin surfaces; however most heavily distributed across the scalp, in the eyebrows, in the armpits, and around genitalia. Their initial role was to protect the body from heat loss; however, during evolution that role was reduced to particular areas of the body, for example, the scalp. Eyebrows and eyelashes have an additional function to protect the eyes from foreign particles.
Oil (sebaceous) glands
The oil glands are mostly connected to hair follicles, except in some locations (lips, eyelids) where they open directly onto the skin surface. The glands secrete sebum - a mixture of triglycerides, cholesterol, proteins, and inorganic salts. Sebum covers the hair and prevents them from drying and becoming brittle. Sebum also prevents excessive water evaporation and keeps skin soft and pliable. It also has some antibacterial properties.
Sweat (sudoriferous) glands
Sweat glands release sweat into hair follicles or the skin surface through pores. There are two types of sweat glands - eccrine and apocrine.
Eccrine sweat glands are present in most regions of the body. The sweat produced by these glands is primarily water with small amounts of ions, urea, uric acid, ammonia, amino acids, glucose, and lactic acid. The main function of eccrine sweat glands is the regulation of body temperature. It also helps eliminate wastes; however, that function is mainly covered by kidneys.
Apocrine sweat glands are found mainly in the skin of the armpit, groin, around nipples, and bearded regions of the face in adult males. They do not function until puberty, and the sweat released from apocrine glands is more milky and yellowish in color. Their exact function is not known.
Nerves embedded in the skin are responsible for sensations that arise in the skin, which we call cutaneous sensations. These sensations can be tactile, like touch, pressure, vibration, and tickling - as well as thermal sensations such as warmth and coolness. The skin has a variety of nerve endings and receptors distributed throughout the whole body.
Blood and lymph vessels
The main function of blood and lymph vessels embedded inside the dermis is to provide nutrients for deeper layers of epidermis - mainly cells present in stratum basale and spinosum. They ensure that these cells are rich in nutrients. In some parts of the skin (lips and under our nails) the red color results from visible blood vessels. The vessels in the dermis carry 8-10% of the total blood flow, which acts as a blood reservoir. Blood reservoirs consist of systemic veins and venules that contain a large volume of blood that can be quickly transported to body parts requiring fast blood delivery.