The Mammary Gland The milk secreting organ Modified sweat gland Exocrine gland

MAMMARY GLANDS thoracic inguinal abdominal

MAMMARY GLANDS 4 abdominal; 15 openings / teat

MAMMARY GLANDS 2 thoracic, 6 abdominal, ; 3-7 openings / teat

MAMMARY GLANDS 2 thor., 6 abdom. 2 ing., ; 8-10 openings/ teat

MAMMARY GLANDS 4 thor., 2 abdom. 4 ing., ; 1 opening/ teat

MAMMARY GLANDS 2 inguinal ; 1 opening/ teat

MAMMARY GLANDS 2 inguinal ; 2 openings/ teat

MAMMARY GLANDS 4 thor., 6 abdom. 2 ing., ; 2 openings/ teat

MAMMARY GLANDS 4 inguinal ; 1 opening/ teat

Anatomy of the Mammary Gland Mammary gland - milk secreting structure including teats, duct system, lobes, lobules, and secretory tissue Modified sweat gland Exocrine gland Cow Large & in inguinal region 4 teats/quarters = 4 separate glands No mixing of ducts across quarters

Anatomy of the Mammary Gland Rear quartes produce approx. 60% of the milk and the fore quarters produce the remaining 40% The size and shape of udders vary with the 1) producing ability, 2) age, and 3) genetic of the cow

Anatomy of the Mammary Gland Cow Front & rear quarters separated by fine membrane Left and right separated by median suspensory ligament Supernumerary teats (some with duct and secretory system)

How much support is enough? High producing Holstein cow Empty Udder = 25 kg. Milk = 30 kg 25 + 30 = 55 kg !!!

Udder Support in Cow Skin Fine connective tissue below skin Connective tissue attaches front quarters to abdominal wall Lateral suspensory ligaments (LSL) Median suspensory ligament (MSL) The subpelvic tendon

Udder Support in Cow LSL Sling around udder 2 layers Inelastic, more fibrous than MSL

Lateral Suspensory Ligaments Like a “hammock” around the udder From the pelvis to the median suspensory ligament Mostly fibrous tissue Collagen Attaches to the alveolar tissue Provides internal framework

Udder Support in Cow MSL Primary support Relatively elastic 2 layers Broken MSL – pendulous udder

Median Suspensory Ligament Primary support of the udder Two adjacent heavy sheets of tissue Mostly elastic, some fibrous tissue Attaches to the abdominal wall Divides the udder into halves Glands on each half are divided by sheets of tissue © Biology of Lactation, Schmidt

Udder Support in Cow Lamella septa Connective tissue Runs between LSL & MSL Divides parenchyma into lobes and lobules

Duct System Teat meatus, the small canal located in the end of each teat is .5 to 1 cm long and is the only sphincter in each gland Seven or eight loose folds of membrane known as furstenburg rosette are located above the teat meatus The teat cistern, the cavity within the teat hold 30 to 90 ml of milk.

The Secretory Tissue A Lobe: group of lobules A Lobule: group of alveoli Alveoli: cluster of alveolus Alveolus: a single layer of epithelial cells surrounding a central lumen

Blood Supply to Mammary Gland 400 kg blood to produce 1 kg of milk 2 major arteries Front ½ of udder Rear ½ of udder 4 major veins 2 follow same path as arteries 2 mammary veins

© Biology of Lactation, Schmidt Nervous System Sensory (afferent) nerves in skin and teats Positive stimulation of teats and surrounding area initiates milk let-down reflex via oxytocin © Biology of Lactation, Schmidt

Nervous System Sympathetic (efferent) (involuntary) nerves associated with arteries in the gland Control blood flow to the gland Innervation of sphincters muscles in teats Stress causes vasoconstriction decreasing milk secretion and let-down No parasympathetic innervation No nerves to myoepithelial cells or alveolar cells

Lymph System of Mammary Gland What is lymph & what does it do? Supramammary lymph nodes Lymph vessels Factors that influence edema Age Diet (especially NaCl) Exercise Genetics

Mammary Gland Development Five phases of mammary development Prenatal (teats & cisterns dev.) Prepubertal (limited growth) Postpubertal Pregnancy (most growth) Early lactation

Mammary Gland Development Major development occurs at puberty and during gestation Hormones Estrogen (growth of duct system) Progesterone (development of alveolar tissue in combination with other hormones) GH (growth of duct system) Prolactin (initiation and continuity of lactation)

Mammary Gland Development

Mammary Gland Development

Anatomy of the Mammary Gland Goats and sheep 2 teats/ 2 halves (glands) Pig 12-14 teats – 2 glands and duct systems per teat Mare 4 quarters/duct systems but 2 teats

Mammary Duct System

Epithelial Cell Lumen of alveolus Fat Droplet Fat Droplet migrating Golgi Body Lysosome Nucleus Mitochondria Mitochondria E.R. Blood Vessel