Mammary Gland and Lactation Flashcards
1
Q
Internal Anatomy
A
Streak canal- Functions to keep milk in udder & bacteria out of udder
Teat cistern- Duct in teat with capacity of 30-45 millilitres
- Separated from streak canal by folds of tissue called Furstenberg’s rosette
Gland cistern- Separated from teat cistern by the cricoid fold
- Holds up to 400 millilitres of milk- collecting area for the mammary ducts which branch from this
Stroma- ‘structural part’- CT containing fibroblasts, adipocytes, plasma cells & blood vessels
Parenchyma- ‘functional part’- Glandular, secreting tissue (consists of alveoli & ducts)
- Alveoli- Small bulb-shaped structure with hollow centre, lined with epithelial cells that secrete milk
-Each alveoli is surrounded by network of capillaries & myoepithelial cells
Contraction of myoepithelial cell stimulates milk ejection
- Groups of alveoli empty–> duct, forming a unit called a lobule, several lobules create a lobe
- Ducts of lobe empty–> galatophore, which empties gland cistern
- Number of mammary glands & position varies between species, may be
thoracic, abdominal and/or inguinal. No. of canals per teat may also vary.
2
Q
Mammary Gland Suspension
A
- *Skin- Minor role in support**
1. Median suspensory ligament- Divides right & left halves of udder & connects udder to abdominal wall - Contains lamellae fibres= elastic tissue which responds to weight of milk in udder
2. Lateral suspensory ligament- Inflexible - Surrounds the outer wall of udder & attaches to the prepubic & subpubic tendons
3. Intermammary groove formed where lateral suspensory ligament & median suspensory
ligament meets
3
Q
Circulation
A
- 1 gallon of milk produced per 400 gallons of blood passed through udder - Ratio may increase in low producing cows
- Blood enters udder via 2 external pudic arteries, 1 for each 1⁄2 of udder
- The mammary artery branches–> cranial & caudal mammary arteries
- Artery has sigmoid flexure- prevents blood supply damage when tissue stretches
- Blood exiting udder from veins at the base of udder, blood can travel through two routes:
- Via external pudic veins (parallel to arteries)
- Via subcutaneous abdominal veins (‘milk’ vein, very prominent)
- Blood flow to & from the mammary gland determines milk producing capability of the cow
4
Q
Cellular Mechanisms of Milk Synthesis
A
- Exocytosis of small proteins (made in RER, packaged in golgi) –>alveoli lumen
- Lipid synthesis & secretion- cholesterol + FAs–> triglycerides, surrounded by membrane stops the fat globules merging together
- Transmembrane secretion of ions & water
- Transcytosis of extra-alveolar proteins such as immunoglobulins, hormones & albumin from the interstitial space
- Paracellular pathway, the direct transfer of materials between themilk space and the interstitial space- usually during inflammation
5
Q
- Mammogenesis
(mammary gland dev.)
A
the development of mammary tissue
- Paired mammary ridges of thickened epidermal tissue develop on ventral surface of developing embryo-> during weeks 7-8 of gestation these develop inwards & penetrate the mesenchyme, forming primary mammary buds–> branching occurs–> secondary mammary buds–> canalisation occurs
- Control of mammary gland formation: PTH related protein–> ↑BMP4 (proliferatory cytokine)–> ↑mammary tissue growth & ↑MSX2–> inhibits hair follicle formation
6
Q
- Lactogenesis
(mammary gland dev.)
A
the onset of milk secretion
- During the second half of pregnancy, secretory activity accelerates & colostrum is produced.
- Lactogenesis stage 1: capacity of breast to secrete milk during later pregnancy
- Lactogenesis stage 2: occurs after birth (days 2/3 to 8 postpartum) with onset of copious milk secretion
- During this stage, milk volume ↑ rapidly from 36-96 hours postpartum & then abruptly levels off.
7
Q
- Glactopoeisis
(mammary glnad dev.)
A
the maintenance of lactation
- Requires removal of milk from the breast: When milk is not removed/ not removed adequately, capillary blood flow ↓ & the lactation process can be inhibited.
- Quantity & quality of infant suckling/ milk removals that controls breast milk synthesis. milking machines can mimic this. As long as milk is regularly removed, the alveoli will continue to secrete it.
- This supply-demand response, regulates production of milk to match the infant’s needs
- If animal is milked upto parturition can –>metabolic diseases e.g. milk fever (calcium deficiency)
8
Q
Milk Ejection reflex
(mammary gland dev.)
A
expulsion of milk from the alveoli
- Newborn suckles at breast & stimulates the nipple, impulse is sent –>paraventricular & supraoptic nuclei in the hypothalamus –>oxytocin production, which is released from p. pituitary –>contraction of the myoepithelia around the alveoli pushes stored milk into ducts collecting sinuses nipple pores
- Oxytocin is secreted- every time nipple is groomed by offspring/ newborn is heard crying
9
Q
Involution
(mammary gland dev.)
A
termination of milk secretion and mammary gland regression
- Large animals (Cow)- Mammary epithelial cells de-differntiate during the dry period
- Become non- secretory within 7 days of drying off
- Ageing cells (few) are lost by apoptosis & replaced by division of remaining cells
- Rodents- Defoliation occurs- mammary epithelial cells fall off basement membrane
- Requires more extensive regeneration at start of next lactation
10
Q
Oestrogen
A
produced by follicles
- Development of stromal tissue (structure) of udder
- Growth of an extensive ductal system
- Deposition of fat in the breasts
- Inhibits the actual secretion of milk
11
Q
Progesterone
A
- Promotes development of lobules & alveoli
- Causes alveolar cells to proliferate, enlarge & become secretory in nature
- Does not cause alveoli to secrete milk (actually inhibits the secretion of milk), milk is secreted only after the prepared udder is further stimulated by prolactin.
- P4= ↑ throughout gestation, while E2 is particularly ↑ during the 2nd half of gestation.
- Concurrent elevation of E2 & P4 during later stages of pregnancy, establish the conditions needed for geometric cell multiplication to occur lobuloalveolar growth.
12
Q
Prolactin
A
Major function is milk production
- Release is inhibited by PIH (dopamine)- Suckling response inhibits PIH release
- PRL acts via JAKSTAT receptor–> causes alveoli cells differentiate, proliferate & become secretory
- Lactogenesis is triggered by abrupt ↓ in progesterone & oestrogen levels after parturition–> anterior pituitary gland, no longer inhibited by these two hormones, releases very large amounts of prolactin.
- Prolactin levels rise & fall in proportion to the frequency, intensity, and duration of nipple stimulation & the suckling stimulus.
- PRL levels ↓ 50% during 1st week PP, reaches non-pregnant levels in 7 days if she doesn’t breastfeed
13
Q
Other Regulatory Factors
A
- Growth Hormone (GH) from A.pituitary acts synergically with oestrogen to develop mammary gland ducts
- Insulin-like growth factor 1 (IGF-1) is the primary mediator of GH.
- IGF-1 mammary implant restores duct development in hypophysectomised rats
- Although GH regulates IGF-1 production from liver, stromal cells of mammary gland (fibroblasts and adipocytes) also produce IGF-1.
- During embryonic development, IGF-1 levels are low, and gradually ↑ from birth to puberty.
- Glucocorticoids (adrenal cortex & medulla) & ACTH (pituitary)- are involved in maintaining tight junctions in breast parenchyma- important in maintaining the integrity of mammary gland
14
Q
Stages of Breast Milk Content
A
- Colostrum, “first milk” 1- 3 days- Creamy yellow liquid. Considered the “first” child immunization - Rich in 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, fats
15
Q
Factors affecting milk production
A
- Milk composition & volume produced= variable both between & within species
- Within species they vary with: Breed/ genotype, Stage of lactation, Nutrition (↑ glucose–> ↑milk),
Health/ disease, Interval since last milk withdrawal, Litter Size
