The duct portion of apocrine glands is lined by stratified cuboidal epithelium and lacks myoepithelial cells.
The duct of the apocrine gland is similar to that of the eccrine duct; it has a narrow lumen. However, it continues from the secretory portion of the gland in a relatively straight path to empty into the follicle canal. Because of its straight course, the probability of viewing both the duct and the secretory portion of an apocrine gland in the same histologic section is reduced. Also in contrast to the eccrine duct, resorption does not take place in the apocrine duct. The secretory product is not altered in its passage through the duct.
The duct epithelium is stratified cuboidal, usually two but sometimes three cell layers thick. The apical cytoplasm of the luminal cells appears hyalinized, a consequence of the aggregated tonofilaments in the apical cytoplasm. In this aspect, they resemble the luminal cells of the eccrine duct.
Apocrine glands produce a protein-rich secretion containing pheromones.
Apocrine glands produce a secretion that contains protein, carbohydrate, ammonia, lipid, and certain organic compounds that may color the secretion. However, the secretions vary with the anatomic location. In the axilla, the secretion is milky and slightly viscous. When secreted, the fluid is odorless; through bacterial action on the skin surface, it develops an acrid odor.
Apocrine glands become functional at puberty; as with axillary and pubic hair, their development depends on sex hormones. In the female, both axillary and areolar apocrine glands undergo morphologic and secretory changes that parallel the menstrual cycle.
In many mammals, similar glands secrete pheromones, chemical signals used in marking territory, in courtship behavior, and in certain maternal and social behaviors. It is generally believed that apocrine secretions may function as pheromones in humans. Male pheromones (androstenol and androstenone) in the secretion of apocrine glands have a direct effect on the female menstruation cycle. Furthermore, female pheromones (copulins) inﬂuence male perception of females and may also induce hormonal changes in males.
Innervation of sweat glands
Both eccrine and apocrine sweat glands are innervated by the sympathetic portion of the autonomic nervous system. Eccrine sweat glands are stimulated by cholinergic transmitters (usually identified with the parasympathetic component of the autonomic system), whereas apocrine glands are stimulated by adrenergic transmitters. As described above, eccrine glands respond to heat and stress. Apocrine glands respond to emotional and sensory stimuli but not to heat.
Nails are plates of keratinized cells containing hard keratin.
The slightly arched fingernails and toenails, more properly referred to as nail plates, rest on nail beds. The nail bed consists of epithelial cells that are continuous with the stratum basale and stratum spinosum of the epidermis (Fig. 15.18 and Plate 47, page 525).