Lactation
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Lactation. Mammary gland development. Cyclic changes in ovarian steroid hormones Essential for mammary development Estradiol Development of mammary alveoli (secretory unit) Progesterone Development of mammary ducts. Final stage of mammary gland development Pregnancy

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Lactation

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Lactation

Lactation


Mammary gland development

Mammary gland development

  • Cyclic changes in ovarian steroid hormones

    • Essential for mammary development

      • Estradiol

        • Development of mammary alveoli (secretory unit)

      • Progesterone

        • Development of mammary ducts


Lactation

  • Final stage of mammary gland development

    • Pregnancy

      • Ovarian/placental steroid hormones

    • Periparturient period

      • GH and prolactin

        • Placental lactogen?

      • Glucocorticoids


Lactation1

Lactation

  • Parturition

    • Metabolic shift

      • Fetal growth to synthesis and secretion of milk

    • Mobilization of nutrients

      • Storage within the body

        • Fats

      • Triggered by changes in hormones


Lactation and re initiation of reproductive cycle

Lactation and re-initiation of reproductive cycle

  • Lactating women

    • High prolactin

    • Low LH and estradiol

      • No ovulation

        • Lactation-induced anovulation/amenorrhea (infertility)

    • Women remain anovulatory as long as they breast-feed their babies

      • Increased survivability of the infants


Lactation

  • Lactational anestrus in the domestic species

    • Divert nutrients for lactation

      • Ensure the survival of offspring

    • Lactation stimuli/physical contact between mother and offspring

    • Animals remain in anestrus (absence of estrus) until nutrient intake exceeds nutrient demand


Lactation2

Lactation

  • Critical for survival of newborn

    • Nutrients

    • Immune system

      • Passive immunity


Milk composition

Milk composition


Lactation

  • Milk composition

    • Varies greatly among species

      • Frequency of nursing

        • Increased frequency, lesser the concentrations of fats

    • Derived via synthesis or filtration

      • Alveolar epithelial cells

      • Components of blood


Lactation

  • Changes in milk composition during lactation

    • Colostrum

      • First week of lactation

        • High concentrations of proteins

        • Immunoglobulins

        • Low in fats and water-soluble vitamins

    • Concentrations of proteins

      • Decrease as lactation progresses

        • Increased fat and lactose content


Lactation

  • Milk fat

    • Major source of energy

      • Highly digestible

      • Carrier of fat-soluble vitamins

    • Synthesized by the smooth ER of alveolar epithelium


Lactation

  • Lactose

    • Promotion of bacterial growth in intestine

    • Provides component for myelin sheath in neurons

    • Synthesized by the Golgi apparatus


Milk ejection

Milk ejection

  • Process

    • Transport of milk from alveoli to ducts

      • Nipple or teats

    • Milk ejection reflex

      • Central nervous system

        • Regulation of prolactin and oxytocin release


Function of oxytocin

Function of oxytocin

  • Lactation

    • Critical for milk let-down

      • Oxytocin receptors

        • Grandular cells in the mammary alveoli

        • Myoepithelial layers in the mammary ducts

      • Contraction of myoepithelial layer

    • Secretion stimulated by suckling

      • Tactile response

      • Regulated by the CNS


Lactation

  • Suckling stimuli

    • Increased release of oxytocin

      • Increased synthesis

  • Release of oxytocin

    • Conditioned

      • Response to factors other than actual suckling stimuli


Lactation

  • Inhibition of milk ejection reflex

    • Stress

      • Physical

      • Psychological

    • Cause

      • Inhibition of oxytocin release

      • Release of catecholamines

        • Constriction of mammary gland blood supply


Ejection of milk

Ejection of milk

  • Combination of factors

    • Pressure within the nipple/teat from accumulating milk

      • Contraction of alveoli by oxytocin

    • Expression of milk by the infant

      • Stripping of milk from teat/nipple

      • Aided by suckling


Inhibition of lactation

Inhibition of lactation

  • Medical reason

    • Transmission of infectious agent

      • HIV

    • Unnecessary

      • Stillbirth

      • Abortion after the first trimester

  • Social issues

    • Returning to the workforce


Lactation

  • Inhibition of lactation

    • Inhibition of periparturient prolactin surge

      • Dopamine receptor agonists


Termination of lactation

Termination of lactation

  • Loss of suckling stimuli

    • Distension of alveoli and ducts

      • Mechanical atrophy

      • Physical destruction of alveolar epithelium

      • Loss of blood supply

        • Compression of vessels

        • Hypoxia and ischemia

    • Loss of alveolar epithelium

      • reduction of alveolar size


Termination of lactation1

Termination of lactation

  • Loss of suckling stimuli

    • Distension of alveoli and ducts

    • Loss of alveolar epithelium

    • Reduction of duct size

      • Reduced lumen diameter

  • Involution of mammary gland

    • 3 months after cessation of lactation


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