The mammary gland in humans is located in the female breast. It produces and secretes milk to nourish the offspring under the influence of the hormones oxytocin and prolactin. Impaired milk production occurs mainly when there is a failure of the hormones involved.
What is the mammary gland?
Lactation in all mammals takes place with the help of the mammary gland. This is a skin gland of female mammals that specializes in milk production and secretion. These processes are relevant for the nutrition of offspring and are hormonally controlled. In humans, hormone secretion is stimulated by the interaction between mother and child. The most relevant lactation hormones are prolactin and oxytocin. The latter mainly stimulates the secretion of the milk produced. This production already begins during pregnancy. Mammary glands can be directed by tubular glands. During embryonic development, mammary glands are formed on the basis of the mammary crest. Because they are located directly in the mammary tissue in the human race, human mammary glands are referred to as mammary glands. Human mammary glands belong to the thoracic mammary glands due to their localization, which differs from, for example, the inguinal udders of a cow or the thoraco-inguinal mammary glands of a cat. The fine structure of the gland in humans depends on the menstrual cycle of the woman and thus changes, for example, during pregnancy or breastfeeding. The mammary gland secretes apocrine. This means that with each drop of milk, it discharges a strangulated cell dome into the lumen.
Anatomy and structure
The mammary gland of all higher mammals consists of individual glandular complexes called mammary complexes, each bearing a nipple. The number of complexes depends on the species and correlates with the average number of newborns. Each human mammary complex contains a completely isolated glandular system. In humans, up to 20 different stalk ducts open into each papilla. The mammary gland cavity system begins with blind-ending sacs, also known as alveoli, which correspond to the actual site of lactation. The alveoli are each connected to several draining ducts. All mammary ducts open into the so-called cistern, which leads from the inside to the outside through the dash duct. The fine structure of the mammary gland is determined by the menstrual cycle and also changes with pregnancy and the breastfeeding period. Within the lactation period, the human mammary gland is fully developed and the alveoli are equipped with a single-layered epithelium that varies between cylindrical and oblate shape depending on the filling state. A basket cell lies between each epithelial cell and the basement membrane in the human breast. Small milk ducts also have an epithelium. Larger milk ducts have a bilayered epithelium and bear smooth muscle in the wall. The cistern has a bilayered cuboidal epithelium and also bears smooth muscle fibers. Striated ducts exhibit cutaneous mucosa with strong keratinization.
Function and tasks
The function of the human mammary gland is to form, transport, and secrete milk to nourish the offspring. In the sacs of the mammary gland, milk is not only formed but also stored due to the hormonal influence of prolactin. Prolactin is already produced during pregnancy in the pituitary gland and stimulates milk production. The basket cells of the gland have special contractility, which in turn is stimulated by the hormone oxytocin. This hormone is increasingly produced in the pituitary gland from the birth of the child and has an effect mainly on secretion. Direct interaction with the child further stimulates the production of oxytocin and initiates the secretion of milk. The small milk ducts have a single-layered epithelium that produces additional milk. The larger milk ducts have smooth muscle in their wall that transports the milk. In addition, the smooth muscles form a sphincter that closes the gland along with its vascular plexuses and mucosal fold to prevent milk from draining. Human mammary glands engage in apocrine secretion and release strangulated cellular flakes with the droplets into the lumen during milk production.
Diseases
The mammary gland can cause problems in several ways.For example, underproduction or overproduction of milk in and after pregnancy is related to abnormal activity of the pituitary gland. When the pituitary gland produces too little prolactin or oxytocin, too little milk is produced or secreted. This phenomenon is known as hypolactation. The opposite is hyperlactation, which is due to increased production of hormones in the pituitary gland. The most common causes of lactation disorders are benign tumors on the pituitary gland that pathologically alter hormonal activity. The mammary gland itself is also frequently affected by tumors. Tumors in this area are the most frequent neoplasms in women and often correspond to mixed variants of benign and histologically malignant tumors. Another disease of the mammary gland is mastitis. This is an inflammation of the mammary gland. This pathological phenomenon is also common. Equally common is incontinentia lactis, which is a disorder of the milk-holding capacity. In this disease, the glandular duct closes insufficiently. In most cases, this phenomenon is preceded by an injury to the breast, which has caused damage to the glandular ducts. Most of the diseases mentioned here in relation to the mammary gland are common not only among humans but also among other mammals.
