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7/27/2019 Functional Organization of Mammary Gland
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Mammary gland
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http://en.wikivet.net/File:Suspensory_structure_of_udder.g7/27/2019 Functional Organization of Mammary Gland
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http://en.wikivet.net/File:Udder_lymphatics.g7/27/2019 Functional Organization of Mammary Gland
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Cross Section through the Teat Canal of the Mammary Gland
showing a Keratin Plug
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Mammary gland
Ectodermal in origin.
Modified sweat gland.
Tubulo-alveolar type in advancedmammals.
Wide species wise variation in the
appearance of mammary gland.
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Anatomical structure of mammary
gland
Located in inguinal region.
Mammary gland and teats together iscalled dder.
Cows udder has two halves, each half
has two teats. Each teat is joined with separate gland,
called quarter.
External structure
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Separate Mammary Glands-Quarters
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Each quarters are separated by
connective tissue.
There may be supernumery teats having
non-secretary functions.
Supernumery teatssheep,goaaat, swine
and mare.
Wt. of lactating bovine udder: 14-32kg.
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Udder can weigh anywhere from 7 to 165
pounds
May support up to 80 pounds of milk
Rear quarters secrete 60% of the milk
Udder continues to grow in size until cow
is 6 years of age.
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Mammary Gland Suspension
Skin
1. Minor role in support
Median suspensory ligament
1. Connects udder to abdominal wall
2. Elastic tissue which responds to weight of milk in udder.
Lateral suspensory ligament
1. Inflexible
2. Surround the outer wall of udder
3. Attached to prepubic and subpubic tendons
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Radiating upward from streak canal -opens
structure called Furstenbergs rosette.
Composed of 7-8 folds of mucus membrane,which helps to retain milk in the teat.
Sphincter muscle surrounding streak canal-
primary structure-retention of milk.
Above each teat, there is gland cistern to which
teat cistern is joined.
Numerous ducts of quarter are attached with
gland cistern.
These ducts branch profusely, ultimately ending
in the secretory units called alveoli or acini.
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Milk is formed in the epithelial cells of
alveoli. Alveoli grouped together in units called
lobules.
Lobules are grouped into larger unitscalled lobes.
Alveoli are surrounded by myoepithelial
cells that are involved in milk ejectionreflex.
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An alveolus surrounded by blood vessels and
myoepithelial cells in the mammary gland
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Skin epithelial of udder-stratified
squamous
Streak canal epithelium- transitional
epithelial
Teat and gland cisterns-two layers
epithelium-cuboidal (one layer), cylindrical
(another layer).
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Alveoli and Duct System
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Growth and development of
mammary gland
a) Pre-pubertal development:
At birth, bovine udder has distinct teatand gland cistern.
Muscular and lymphatic systems aredeveloped.
From birth to puberty, little development.
Increases in size due to increase inconnective tissue, fat and extension ofduct system.
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b) Growth during puberty and estrous cycle
Growth of duct-follicular phase
Lobulo-alveolar development-luteal phase
c) Development during pregnancy
Mammary gland develops rapidly.
Glandular tissue spread.
By 5th month, lobules are formed.
Development of duct system-completed atthe time of parturition.
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Hormonal control of mammary
gland (lecture no. 22)
1) Pituitary Gonadotropins (FSH, LH)
FSH- development of follicles-source of
estrogen causes duct development.
LH-causes ovulation and forms CL-source of
progesterone
Estrogen+ progesterone lobulo-alveolar
growth.
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2) Anterior pituitary hormones
GH, ACTH, TSH, Prolactin- optimum mammary
growth.3) Adrenal hormones-mammary growth
development by estrogen and progesterone
further stimulated by adrenocorticotropic
hormones.
Adrenal steroidsregulation of mammary gland.
4) Placenta: Partly plays the functional role of
hypophysis and ovary in enhancingdevelopment of mammary gland.
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Lactogenesis
Process by which the alveolar cells of
mammary gland are tuned with the ability
to secrete milk is k/a lactogenesis.
There are different stages involved in it:
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1st stage: enzymatic and cytologic change ofalveolar epithelial cells and a limited
secretion of milk before parturition occurs.
2nd stage: All milk constituents are secreted
just immediately before parturition and theprocess extends for several days.
3rd stage: Onset of milk secretion afterparturition occurs to supply nutrients tonew borns.
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Onset of milk secretion is under the control
of following hormones:
Prolactin
Glucocorticoids
Sudden fall in progesterone level at
parturition
Placental lactogen
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Galactopoiesis
Process of maintenance of milk secretion
Depends upon-alveolar cell number, their syntheticefficiency and let down of milk.
Hormones responsible for galactopoiesis are:
1. Oxytocin2. ACTH
3. GH
4. Glucocorticoids
5. Tsh
6. Prolactin
7. Insulin
L d f ilk
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Let down of milk Neuro-hormonal reflex
Mechanical stimulation of peripheral neural receptors in skin of teat
(during milking/suckling) neural stimulus.
Stimulus travels from teat to spinal cord and to the supraoptic and
paraventricular nuclei of hypothalamus.
Synthesize oxytocin hormone release through posterior pituitary.
Oxytocin-released to b/d-transported to target t/s (myoepithelial cells ofmammary gland).
Contraction of gland and ejection or let down of milk.
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Composition of milk
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Composition of milk
Milk
Water Total solid (Dry matter)
Fat Solid Not Fat (SNF)
True fat Associated substances(phospholipid, chlesterol)
Lactose Nitrogenous substances Minerals matter Other constituents
Non-protein Protein
AAs, Uric acids, NH3, creatinine Casein, lactoalbumin, lactoglobulin, protease
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