Internal and External features of mammary gland.pptx

Here are some the things that should be known about mammary gland of dairy animal while studying dairy science. The internal and external features of mammary gland are described briefly in this presentation slide.

1. Internal and External Feature of Mammary gland Presenter: Sristy Bhattarai Subject: Dairy Science and Technology Roll No.:93

2. Mammary Gland The mammary gland is a highly evolved and specialized organ whose primary function  is to secrete milk. It is an apocrine type of gland. In these glands, the apical part of the cells and a part of the cytoplasm are lost in the secretion . In calf, the development of the mammary gland starts early in the fetal life. Each mammary gland (also called quarters, of which cattle have 4) is formed by multiple lobules. Lobules are formed by a collection of alveoli. Milk, secreted by the alveoli, is carried by alveolar ducts into the lactiferous ducts. Those ducts carry the milk to the collecting ducts. A dozen of those ducts drain milk into the gland cistern (sinus). From there, the milk goes into the  teat  cistern and the papillary canal before being expressed by a suckling calf, by hand, or by a  milking machine. The junction between the gland and teat cisterns is called the annular folds.

3. External features of mammary gland Udder Teats Udder The bovine udder consists of 4 separate glands located in the inguinal region of the ventral side of the cow. We call each gland a quarter: Right fore Right rear Left fore Left rear

4. Udder development The udder of cattle is composed of 4 “quarters” or mammary glands. In lactating cows, its size is exceptionally large. Small mammary glands and teats are present at birth in both males and females. At this time, the collecting system is composed only of a small papillary canal and teat cistern. The udder remains in this stage until puberty when—under the influence of estrogen in heifers—connective tissue and fat invade the small primitive quarters. The epithelial buds proliferate, and small collecting ducts appear. During the first pregnancy, the epithelial buds continue growing and dividing, creating the lactiferous ducts. In the second half of gestation, fat within the udder is replaced by glandular tissue. As parturition (calving) approaches, a lumen appears—under the influence of progesterone and estrogen—within the alveoli. The lactocytes begin milk production under the influence of the hormone prolactin.

5. Intermammary groove Right and left halves are separated. Teat The only exit for the secretion from the mammary gland and the only means for the calf to receive milk are the teats. Teat size and shape are independent of the size, shape, or milk production of the udder. Average size for the fore teats is about 6.6 cm long and 2.9 cm (in diameter, and for the rear teats is 5.2 cm long and 2.6 cm in diameter. The teat consists of a sinus (or cistern), a teat canal, and surrounding tissues and skin. Teat canal is surrounded by bundles of smooth longitudinal and circular muscle fibers. Between milkings the smooth muscle ( sphincter muscles ) function to keep the teat canal closed. The teat canal is the single orifice in the gland between the internal milk secretory system and the external environment. The inner surface consists of a skin-like epidermis lined with keratin, a waxy antimicrobial material.

6. The mammary gland is densely innervated, especially in the teat. The skin of the teat has sensory nerves that are sensitive to the calf’s suckling, massaging by milker and machine milking. Milking is affected by applying enough pressure to the teat filled with milk to force open the sphincter muscles. I f the sphincter muscles are weak, the milk may leak out. Internal feature of mammary gland Internal structure of the udder can be simply discussed under following headings: Supporting structure Wall of teat Duct system: Teat cistern, Gland cistern, Milk duct, Alveoli, Lobes Blood supply and Vascular System Lymphatic system

7. Supporting structures of the udder Because of its weight, the udder has to be very well attached to the skeleton and muscles. The udder is held by two main ligaments: Median suspensory ligaments: Runs down the center. Elastic tissue that attaches the udder to the abdominal wall and stretch as udder fills with milk. Lateral suspensory ligaments Around the sides of the udder. Not elastic, and sends lamellae into udder, continuous with interstitial framework. When fibers in the supporting ligaments becomes stretched or broken, the udder breaks away from the body and becomes pendulous. Skin Skin stabilizes the udder

8.   Wall of teat Varies in the thickness. Consist of muscles and connective tissue as well as blood vessels. It is elastic and can contract. Wall become thicker when emptied of milk. Expand when filled with milk. Teat cistern: The teat cistern is joined with the streak canal that opens outside. It prevents the entrance of bacteria and other contaminants. Extend upward through the teat of gland cistern. Teat cistern and gland cistern are separated by a circular fold of the membrane lining the teat. Gland cistern: These are the sinus at the tip of udder. It is also called udder cistern or milk cistern. It is irregularly shaped chamber for collecting and storing milk(100-400ml).

9. Milk ducts: Ducts   are connective tissue by which milk drains from the alveoli down to the gland cistern. Radiating out from the cistern walls are large ducts which branch out until finally the branches become microscopic in size that are known as ductulus. At the ductulus ends are the secretory structure known as alveolus. Alveoli: It is sack-like structures where milk is synthesized and secreted. A single layer of secretory epithelial cells lines the lumen and contractile myoepithelial cells surround the epithelial lining. Outside of the myoepithelial cells the alveolus is surrounded by a connective tissue basement membrane. The outer walls of each alveolus (myoepithelial cells) relate to a fine network of blood vessels from which the cells get the milk-making materials(blood). The arrangement of alveoli, a small duct, and its branching ductulus resembles a bunch of grapes.

10. Blood supply and Vascular System All of the milk precursors come from blood. To produce 1 liter of milk 500 liters of blood have to pass through the udder. When a cow produces 60 liters of milk per day, 30,000 liters of blood are circulation through the mammary gland. This represents a blood flow of 1250 liters per hour. There is a 2-6 fold increase in blood flow in the mammary gland starting 2-3 days prepartum. The mammary gland is very well supported with blood vessels, arteries and veins. Each udder half is almost completely independent and has its own vascular system, nerve supply, and suspensory apparatus. Right and left udder halves have separate arterial supply, although there are some small arterial connections that pass from one half to the other. Pure oxygenated blood leaves to mammary gland from the heart via aorta and through a series of smaller arteries, then the blood conveyed to the udder from two external pubic arteries. Arteries enter the udder from abdominal cavity through inguinal ring and form a sigmoid flexure (allow for extension).

11. Lymphatic system Lymph is a clear, colorless liquid somewhat similar to blood plasma from which is derived. Lymph contain less red cells and numerous lymphocytes as well as inorganic salts, glucose, on protein nitrogenous substance, and some protein (about half than blood plasma). I t serves as a system for draining tissue fluid that assists in the control of the intercellular fluid pressure. There is one large node for each half of udder; supra-mammary lymph node, lies just posterior to inguinal canal. Lymph nodes filter and remove foreign material and add lymphocytes to lymph in response to antigen stimulates antibody formation in the vascular system. Nervous system The udder is supplied with two types of nervous fibers: Afferent (sensory) fibers, originate from the dorsal root of spinal cord another is efferent or motor (sympathetic) fibers which is originate from the ventral root of the spinal cord. The motor nerve to the udder regulate blood flow and innervate the smooth muscles which is surrounded the milk collecting ducts and teats sphincters.

12. THANK YOU