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mammary gland

mammary gland, organ of the female mammal that produces and secretes milk for the nourishment of the young. A mammal may have from 1 to 11 pairs of mammary glands, depending on the species. Generally, those mammals that bear larger litters have more glands. The mammary gland of the cow and of some other mammals is known as the udder.

In humans, there is one pair of mammary glands, also known as mammae, or breasts. They are rudimentary in both sexes until the age of puberty when, in response to ovarian hormones, they begin to develop in the female. During pregnancy, they distend still further in preparation for nursing the infant. Pregnant women are prevented from lactating (producing milk) by the presence in the blood of high levels of estrogen and progesterone, secreted by the placenta until birth occurs.

After birth, response to prolactin, the milk-stimulating hormone, is no longer inhibited by placental hormones, and lactation begins. Mammary tissue contains between 15 and 20 compartments called lobes, each of which is divided into smaller compartments called lobules. The lobes and lobules are connected by a network of tubes whose cells manufacture the liquid and fatty substances that form milk. The tubes of each lobe connect with a duct, and all ducts lead to the nipple, where the milk is secreted when the nipple is sucked by the young. The letdown of milk during the nursing process is aided by oxytocin, a hormone secreted by the pituitary. The physical force of an infant's sucking on the breast is a major stimulus to milk production. Disorders of the mammary gland include mastitis and breast cancer.

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The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

Udder

 

the mammary glands of agricultural animals. In ruminants and mares the udder is located in the inguinal region, between the thighs. In swine udders are symmetrically placed right and left of the white line on the belly. The udder of the cow, camel, and reindeer consists of two fore, or belly, parts and two rear, or hip, parts. Milk is synthesized in the secreting epithelium of tiny sacs called alveoli. Each cell synthesizes milk with each of its constituent parts. Alveoli, the largest of which include up to 100 epithelium cells each, are placed radially around the milk ducts. These ducts unite to form larger ones and open into milk cisterns. Milk is retained in the udder because of capillary action, as well as the presence of circular closing muscles (sphincters) in the teats. The udder is well supplied with blood, because 500 liters of blood must pass through the udder in order to make 1 kg of milk.

In heifers the glandular tissues of the udder begin to grow with the onset of sexual maturity and develop very intensely not long before calving. (In pregnant cows this is in the second half of the dry period, a month before calving.) In dairy cows the udder is goblet-shaped and set forward. It is firmly attached to the body (not hanging), and its parts are even and symmetrically placed. This kind of udder is soft, pliant, and elastic to the touch; after milking it becomes smaller and has long, twisted, clearly visible veins. The udders of sheep, goats, and mares each consist of two complexes of glands and two teats.

REFERENCE

Zaks, M. G. Molochnaia zheleza. Moscow-Leningrad, 1964. Chapter 1. [5_1570_1]
The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.

udder

[′əd·ər]
(vertebrate zoology)
A pendulous organ consisting of several mammary glands enclosed in a single envelope; each gland has its own nipple; found in some mammals, such as the cow and goat.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.

udder

the large baglike mammary gland of cows, sheep, etc., having two or more teats
Collins Discovery Encyclopedia, 1st edition © HarperCollins Publishers 2005