Functional Organization of Mammary Gland

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.g


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http://en.wikivet.net/File:Udder_lymphatics.g


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Cross Section through the Teat Canal of the Mammary Gland

showing a Keratin Plug
http://en.wikivet.net/File:Mammary_Gland_teat_canal_keratin_plug.j


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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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Functional Organization of Mammary Gland

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