Human Anatomy and Physiology (dermis)

Have you ever wondered what structures lied in the dermis layer, or what was responsible for the stimulus reaction behind your involuntary response? Inside this vascularized layer lies microscopic structures. These structures carry out specific functions inside your dermis. These functions could be sweating, secreting, or an involuntary stimulus-response.

Among these structures are the arrector pilli muscles. These Little collections of smooth muscle cells bring your hair to attention and create dimples or if preferable “goosebumps.” For animals, this involuntary response could mean life or death. Not only can this help regulate temperature by trapping a layer of heat between fur and the body, but it may ward off a predator or an aggressive opponent. Arrector pilli muscles also bring aid in secreting sebum, an oily substance produced by sebaceous glands. Sebaceous glands are found all over the body and function as holocrine glands. The central cells become overfilled with oily fat molecules and explode. The shrapnel of the explosion and the lipids make up sebum. Sebum has some antibacterial properties, but it also aids in reducing water loss and lubricates hair and skin.

Like the arrector pilli muscle, the sweat glands are also involuntary and can be activated by fight or flight response. These tiny coiled tubular glands can be categorized into two different groups: the apocrine or the eccrine glands. Apocrine sweat glands not as dispersed as the eccrine sweat glands are believed to function as sexual scent glands. The eccrine gland secretes a hypotonic filtrate of blood plasma. Its function is multipurpose; to regulate temperature and the secretion also has somewhat of antibacterial property.

Next, let’s discuss a network of nerve fibers and nerve receptors located in the dermal layer. Bundled around the bulb of hair follicles is a network of sensory nerve endings identified as hair follicle receptors; also known as root hair plexus. You may be able to identify its function by brushing your hand gently across the hair on your arm, or by lightly touching the hair on your head. If you can feel the sensation of the stimulation your root hair plexus is responding. The dermis also contains cutaneous sensory receptors. These receptors are associated with the nervous system and categorized as exteroceptors because they involuntarily react to stimuli coming from outside the body. These receptors are located throughout the body and react to wide varieties of stimulus, such as a light touch; a deeper pressured bump on a chair; stimulus as light as a feather across the skin; hair sensation from a light stroke to a ripping tug; all the way to free nerve endings dispersed through the skin that react to unpleasant stimuli (boiling water, chemical burn, ice).

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