W7L3 Thu lactation and breast feeding Flashcards
Role of lactation
- Extends the period of maternal protection (for example, in the elephant it lasts 3-5 years)
- Suckling frequency, via neuroendocrine feedback, controls birth spacing
- Provides immune protection against gastric diseases
- It enhances maternal-infant interactions and infant learning
- Protection against breast cancer*
Hormonal level before and afterbirth
§ ↑Progesterone + ↑oestrogen during pregnancy causes ↑prolactin + hPL which helps produce milk
-After birth, there is a sharp drop of oestrogen and progesterone which remain at basal until new cycle begin
-, no hPL, slow fall in PRL (requires nipple stimulation to maintain PRL + milk secretion)
Milk type and composition
- Colostrum: post-partum secretion high in protein, sodium and chloride. –also antibodies (IgG and IgA).
- Milk: large species differences in concentrations of milk fat, lactose, protein and water.
- Milk fat mixture of lipids: triglycerides, diglycerides, monoglycerides, free fatty acids, phospholipids and sterols.
- Arctic, aquatic, desert mammals produce milk with 75% energy in lipid fraction
experiment to show lactation is hormonally controlled
Mammary gland transplanted to neck of goat (separated from nerve supply) + continued milk secretion
Ø Control is hormonal, not neural – but milk removal necessary for continued lactation
Ø Denervated wallaby glands continue lactating, but neural inhibition of embryonic diapause is lost
Milk secreation and production
- Initiation of milk secretion begins in pregnancy
-Synthesis of milk constituents within alveolar cells → intracellular transport of milk components → discharge of constituents into alveolar lumen - Prolactin and other hormones required, depending on species
local control of milk secreation
feedback inhibitor of lactation - FIL: small protein secreted in alveolus – if not removed by emptying alveolus, acts to suppress further milk secretion
contributor to milk secreation
- Exocytosis: proteins made via RER + Golgi release vesicles into lumen
- Apocrine secretion of lipids: vesicle membranes → phospholipids
- Transmembrane: water; small molecules; drugs
- Trans-cytosis: immunoglobulins, some hormones + growth factors
- Paracellular: adjoining to next mammary gland cell; immune cells
THE ENTERO-MAMMARY CIRCULATION: protection from diarrhoeal diseases
mother ingests pathogen
→ activates beta cells in Peyer’s Patches in gut
→ beta cells migrate to breast + become plasma cells
→ secrete IgA to counteract pathogen (into milk)
Milk removal
§ Passive removal of milk from cisterns + large ducts
§ Milk ejection reflex: nipple stimulation → dorsal horn of spinal cord → medial forebrain bundle → hypothalamus (paraventricular nucleus + supraoptic nucleus)
Ø ↑oxytocin release from posterior pituitary causing milk ejection from alveoli
Ø Mesotocin in marsupials
Hormone in milk production for rat, sheep and rabbits
To maintain high milk production after removal of the pituitary gland:
Ø Rats: prolactin, adrenocorticotrophin (ACTH)
Ø Sheep/goats: growth hormone, prolactin, adrenocorticotrophin (ACTH), thyrotrophin (TSH)
Ø Rabbits: prolactin
Sucking inducing prolactin
-Sucking induced release of prolactin (key player in milk synthesis + insulin and cortisol)
-Nipple/teat stimulation – afferent signals to hypothalamus:
*Neuroendocrine reflex – increases VIP (vasoactive intestinal peptide) a potent PRL releasing factor
*Decrease dopamine from hypothalamic TIDA (Tubero-Infundibular Dopamine neurons), a PRL-releasing inhibitory factor
Milk Composition Changes in Marsupials
initial milk ↑carbohydrates, ↓lipids (like human milk) → as young ready to leave pouch, milk high in lipids + low in carbohydrates (like cow milk)
Ø Phase 2A: attached to teat; high in early lactation protein (ELP)
Ø Phase 2B: on + off teat in pouch; high in whey acidic protein (WAP)
Ø Phase 3: in + out of pouch, high in LLP-A + LLP-B
Ø Milk composition dictating growth of marsupial young
Concurrent Asynchronous Lactation
adjacent mammary glands produce milk of different compositions to support growth + development of 2 siblings of different ages
Ø Mammary glands have different sensitivities to hormones + different receptor concentrations
Ø Younger gland much more sensitive to exogenous oxytocin allowing milk ejection in gland with young attached
Ø Sucking by out of pouch young causes milk ejection in both glands; continuous sucking by small young does not cause milk ejection in older gland
Contraceptive effects of breastfeeding
Low monthly risk of pregnancy (<5%) up to 12 months of lactational amenorrhea
* Increased risk of pregnancy with increased period of lactational amenorrhea
* Risk of pregnancy is significantly variable after ~ 2 years of lactational amenorrhea
The Risks of Not Breastfeeding for Mothers
and Infants
- For infants, not being breastfed is associated with an increased incidence of infectious morbidity, as well aselevated risks of childhood obesity, type 1 and type 2 diabetes, leukaemia, and sudden infant death syndrome.
- For mothers, not breastfeeding is associated with a higher incidence of premenopausal breast cancer, ovarian cancer, retained gestational weight gain, type 2 diabetes, myocardialinfarction, and the metabolic syndrome
