mamary gland

internal anatomy

• 3 structure

• streak canal- functions to keep milk in udder and bacteria out of udder

• teat cistern- duct in teat with capacity of 30-45ml, separated from streak canal by folds of tissue called Furstenbergs rosette

• gland cistern- separated from teat cistern by cricoid fold, holds up ot 45 ml of milkand is the collecting area for hte mammary ducts. from this branches the mammary duct

stroma- what does it contain

contains fibroblasts, apidocytes, pasma cells and blood vessles

alveoli

• structure

• what is it lined with and what is secreted

• what it it surrounded with

• what is stimulated and how

• where do they empty and what does this form

• what does this now empty into and then where does that empty to

➢Alveoli- secreting epithelial cells

• Small bulb-shaped structure with hollow centre

• Lined with epithelial cells that secrete milk

• Each alveoli is surrounded by network of capillaries and myoepithelial cells

• Contraction of myoepithelial cell stimulates milk ejection

➢Groups of alveoli empty into a duct forming a unit called a lobule

• Several lobules create a lobe

• Ducts of lobe empty into a galatophore, which empties into the gland cistern

mammary gland suspension

• skin- minor role in support

• median suspensory ligament- separates r and l udder half, connects udder to abdominal wall by lamellae, elastic tissue which responds to weight of milk in udder

• lateral suspensory ligament- inflexible, surround the outer wall of udder, attached to the prepubic an dsuboubic tendons

• intermammary groove- formed where lateral suspensry ligament and median suspensory ligament meets

circulation

• how much blood does one gallon of milk need

• where does blood enter udder

• what does the mammary artery branch into

• where does blood exit

• One gallon of milk requires 400 gallons of blood being passed through udder- Ratio may increase in low producing cows

• Blood enters the udder through two external pudic arteries, one for each half of the udder;

• The mammary artery branches into cranial mammary artery and the caudal mammary artery

• Blood exiting udder from veins at the base of udder, blood can travel through two routes Via external pudic veins Via subcutaneous abdominal veins

mammogenesis

• what is it

• where does it penetrate

• what bud does this form

• how is the secondary bud form

• what happens to the secondary branch and what surrounds the newly formed structure

• when does it begin

• what is expressed in the mesenchyme and what receptors does it singla through and what does this do

• what does pthlh signals increase

wh

• it is the development of mammary tissue from paired mammary ridges (thickened epidermal tissue) on ventral surface of developing embryo

• ridges begin to develop inwards and penetrate into the mesoderm

• primary bud begins to send out branches that further penetrate dermis this is the secondary

• canalisation- secodnary branch out and form canals that form the duct system of the gland. myoepithelial cells surround the terminal portions of the developing gland

• begins during 7-8 wks gestation when primary and secondary ducts develop

• • Bone morphogenetic protein 4 (BMP4) expressed in the mesenchyme signals through its receptor BMPR1A to MSX2 and inhibits hair follicle formation at the developing nipple.

• • Parathyroid hormone-related protein (PTHLH) signals from the epithelium to the mesenchyme to increase the expression of BMPR1A

lactogenesis

• when is it

• what are the 2 stages

• onset of milk secretion

• ▪ During the second half of pregnancy, secretory activity accelerates, and colostrum is produced.

• ▪ The capacity of the breast to secrete milk during later pregnancy is called lactogenesis stage 1, or lactogenesis 1.

• ▪ Lactogenesis stage 2 occurs after birth (days two or three to eight postpartum) with the onset of copious milk secretion.

• ▪ During lactogenesis 2, milk volume increases rapidly from 36 to 96 hours postpartum and then abruptly levels off.

• 
  

galactopoeisis

• what is it

• what happens when milk is not removed

• what controls breast milk synthesis

• what is this reposnecalled

▪ Galactopoiesis, or the maintenance of a milk supply, requires removal of milk from the breast.

▪ When milk is not removed or not removed adequately, capillary blood flow decreases, and the lactation process can be inhibited.

▪ It is the quantity and quality of infant suckling or milk removals that controls breast milk synthesis. This can be mimicked by the use of milking machines.

▪ As long as milk is regularly removed, the alveolar cells will continue to secrete milk.

▪ This phenomenon, called the supply-demand response, is a feedback control that regulates the production of milk to match the infant of the infant.

oestrogen- purpose in

• udder

• growth of

• breast

• milk

• development of stromal tissue of udder

• growth of ductal system

• fat in breast

• inhibits milk secretion

progesterone

• role

• what does the concurrent elevation of e2 and p4 during later pregnancy do

• promotes dev of lobules and alveoli

• alveoli cell roliferation, enlarge and become seretory

• do not cause alveoli to secrete milk but inhibits, milk only secreted after prepared udder is further stimulated by prolatin

• concurrent elevation of e2 and p4 during later pregannacy establish conditions needed for geometri cell multiplication to occur resulting in lobuloalveolar growth

prolactin

• function

• what does it signal through

• milk production

• signals throug JAK/Stat to stimulate prolif of lobuloalveolar system in mammary growht

• 
  

what is prolactin inhibited by

PIH - dopamine (binding decreases cAMP levels)

suckling reposne inhibits PIH release

prolactin levels

• lactogenesis triggered following expulsion of placenta by fall in prog and estrogen and continued presence of prolactin

• as p ande drop anteriro pituitary is no longer inhibited and releases lots of prolactin

• they rise and fall in proportion to freq intesnity and duration of nipple stimulation

• if mother does not breastfeed prlactin levelsusually reach non pregnant levels by 7 days postpartum

what are other regulatory factors

GH

• acts synergically with oestrogen to develop mammary gland ducts

IGF 1

• primary mediator of GH

• during foetal development levels are low and graudally increase from birth o puberty where they reach to their highest levels

Glucocortcoids and ACTH

• mintaining tigh tjunction in breast parenhcyma

milk ejection reflex

• what does it ultimately lead to

• what do the nerve pathways lead to and what does this cause

• wher is this released from and what does this cause

• causes alveoli to reelase milk they have nade

• when the newborn suckles and stimulates a message is sent up the nerve pathways to the paraventricular and supraoptic nuclei in the hypothalamus causing the production of oxytocin

• oxytocin is relased from posterior pg and causes myoepithelia (musckes around the alveoli) to contract and push stored milk down the ducts through the collecting sinuses and out the nippple pores

cow involution

• mammary epithelial cells de differentiate during dry period

• become non secretory within 7 days of drying off

• ageing cells are lost by apoptosis and replaced by division of remaining cells

involution in rodents

• defoliation occurs- mammary epithelial cells fall off the basement membrane

• requires more extensive regeneration at the start of next lactation

what are mechanisms for secertion

• exocytosis

• lipid synthesis and secretion

• transmembrane secretion of ions and water

• trasncytosis of extra alveolar proteins from intersistial spae

• paracellular pathway - transfer of materials between milk space and intersitiial space

amino acid absorption

• through where

• what happens once they reach inside the cell and examples

• through basal membrane by transport systems

• once inside the cell they are covalently bound together to form proteins in the RER

  • eg milk proteins, casein, beta lactoglobulin and alpha lactoalbumin

• these proteins are transferred from the RER to the golgi

casein secretion

• what form and what is this formed from

• where is it transported and how

• as a micelle which is formed in the golgi from the casein molecules, calcium and phosphorus

• transported to apical membranes of cell via secretory vessels budding off of the golgi which are bounded by a lipid bilayer membrane

glucose to lactose

• where does glucose enter the cell from

• what is some converted into

• how is lactose formed

• what does this lead to

• glucose enters the cell via the basolateral membrane

• some converted into galactose

• both glucose and glactose enter golgi and enter a reaction forming lactose

• formation of lactose in the golgi results in drawing water into the cell, into th golgi and then becoming prt of milk

milk fat precursors to milk fat

• taken up by the epithelial cells at the basolateral membrane

• acetate and beta hydroxybutyrate

• preformed fatty acids, glycerol and MAG are absorbed at the basolateral membrane

• all enter into the synthesis of triglycerides of milk

• milk fat triglycerides are synthesised on SER and form small droplets

• small droplets fuse together as moving towards the apical membrane

• then forces out

transport of milk components not synthesised in the epithelial cells

• an example

• how are they taken into the cell

• where are they transported

• what happens once they are transported here

• where is it released

• eg immunoglobulins which bind to specific receptors on the basolaeral surface of cells

• taken into the cell in endocytic vesicles

• transported to the apical side of the cell via the vesicles

• membrane of transport vesicles fuses with inner surface of apical membrane of cell

• releases immunoglobulin into the lumen of the alveolus

paracellular pathway

• in which situations is it used

• what does this allow

• what does this lead to and what can this be used for

• when udder is inflamed eg mastitis or involution, or when oxytocin is causing milk ejection, the tight junctions open or some become leaky

• allows lactose and potassium to move from the lumen into the extracellular space

• and sodium and chlorine to move into the lumen from the extracellular space

• changes in electrical conductivity of the milk and this can be used for mastitis detection

• another example is leukocytes whuch pass between the epithelial cells breaking open the junctions and enter the paracellular

  • this allows other extracellular components to diffuse into lumen and milk components to diffuse out

stages of milk

colostrum

• 1-3 days

• first child immunisation

• protein, minerals, vitamins, immunoglobulins

transitional milk 2-4 days after birth

• breast milk with some colostrum

mature milk

• 7+ days

• 90 water, 10 carbs, proteins and fats

within species what does milk production vary with

• breed/genotype

• stage of lactation

• nutrition

• health/disease

• interval since last milk withdrawal

• litter size

• age