How do apocrine sweat glands differ from eccrine sweat glands in terms of location, secretion, and function?

Eccrine sweat glands are widely distributed and most abundant on the palms, soles, and forehead, opening through funnel-shaped pores at the skin surface, while apocrine glands are confined mainly to the axillary and anogenital areas and empty into hair follicles. Eccrine secretion is a watery, hypotonic filtrate of blood that is mostly water with salts and trace wastes; apocrine secretion contains the same basic components plus fatty substances and proteins, making it viscous and prone to bacterial decomposition that creates body odor. Eccrine glands primarily help regulate body temperature through evaporative cooling, whereas apocrine glands play little role in temperature control and are more related to pain, stress, and possible sexual signaling.

Both eccrine and apocrine sweat glands have secretory cells associated with myoepithelial cells and release their products by exocytosis. Eccrine glands are simple coiled tubular glands whose secretory part lies coiled in the dermis and whose duct opens at a funnel-shaped pore on the skin surface. Apocrine glands are larger, lie deeper in the dermis or even in the hypodermis, and their ducts empty into hair follicles. Eccrine sweat is a hypotonic filtrate of blood: about 99% water, with salts such as sodium chloride, vitamin C, antibodies, the microbe-killing peptide dermcidin, and traces of metabolic wastes such as urea, uric acid, and ammonia. It is normally acidic, with a pH of 4 to 6. Apocrine secretion contains the same basic components as true sweat plus fatty substances and proteins, so it is viscous and sometimes milky or yellowish; it is odorless when first secreted, but bacteria decomposing the organic molecules give it a musky, unpleasant odor. Functionally, eccrine glands are regulated by the sympathetic division of the autonomic nervous system and prevent overheating by producing sweat that evaporates and cools the body. Apocrine glands begin functioning at puberty under the influence of androgens, are activated by sympathetic nerve fibers during pain and stress, and may enlarge and become active with sexual foreplay and phases of the menstrual cycle, suggesting they may be the human equivalent of sexual scent glands. They have little role in maintaining constant body temperature.