Lecture 20 - Anatomy (Breast) Week 16.pdf

IMED3003 (Lecture 30) Anatomy and Histology of the Breast Dr Kathy Sanders School of Human Sciences [email protected] Learning outcomes Describe the gross anatomy and histology of the human breast Relate structure to function Explain the development of the breast across the l...

IMED3003 (Lecture 30) Anatomy and Histology of the Breast Dr Kathy Sanders School of Human Sciences [email protected] Learning outcomes Describe the gross anatomy and histology of the human breast Relate structure to function Explain the development of the breast across the life course and the changes that occur with pregnancy and lactation Explain the hormonal control of milk secretion, the milk ejection reflect and the endocrinology of lactational amenorrhoea Breast Mammary glands are a defining feature of mammals Lactation is crucial to health, growth and (in most mammals) survival of the newborn Lactation is important for maternal health (e.g. birth spacing, cancer risk, weight control, osteoporosis etc)  Anatomy of the human breast (lactating state) deep fascia ↓ Rib retromamma se Intercostal · Suspensory ligaments muscles S Lactiferous Areolar ducts Pectoralis minor muscle Lobe Nipple Pectoralis major muscle Lobule Adipose tissue Sagittal section Anterior view  Anatomy of the human breast (lactating state) Text book image  Reality…. Lactiferous sinuses do not Suspensory exist ligaments The ductal network is more complex and branching than Areolar Lactiferous shown ducts Glandular tissue is closer to the nipple than shown (65% of glandular tissue is in a Nipple Lobe 30mm radius of base of nipple) Remember not all breasts Lobule are lactating….inactive Adipose tissue breasts comprise mainly ducts and CT; little gland development Ramsay,D.T., Kent,J.C., Hartmann,R.A., & Hartmann,P.E. Anatomy of the lactating human breast redefined with ultrasound imaging. J Anat 206, 525-534 (2005). Vessels, lymphatics and nerves Arterial supply Lateral: branches from axillary a. Medial: branches from internal thoracic a. ↳ come through 2nd 4th intercostal spaces Venous drainage veins parallel the arteries Lymphatics Superior & lateral: axillary nodes (75% of drainage) Medial: parasternal nodes Inferior: may be some drainage into abdomen Innervation Breast: 2nd to 6th intercostal n (ant. & lateral cutaneous br.) Nipple: 4th intercostal n. Cross section through part of nipple Stratified squamous Stratified squamous epithelium epithelium (keratinized) Sebaceous glands not associated with hair follicles sebum secreted onto epidermal Sebaceous surface gland Dense CT protect from chaffing and cracking during nursing Dense CT with smooth Lactiferous duct muscle bundles SM contract in response to cold, touch and sexual arousal X 02 Histology of the human breast (inactive state) Mainly duct elements & connective tissue Adipose Cyclic changes in non- pregnant women (E & P stimulation) Duct Lobule Some duct growth Some limited lobulo- alveolar development Fluid accumulation in CT (= heavy sensation Dense CT premenstrually) X 80 Histology of the human breast (lactating state) Lobule of alveoli Less CT (than inactive) Lobulo-alveolar development Lobules separated by septa of dense CT CT Lactiferous duct X 90 Histology of the human breast (lactating state) Myoepithelial cell (nucleus of) Myoepithelial cells (contractile cells – imp. In milk ejection reflex) Alveolar cells (milk synthesis) High magnification through part of an Electron micrograph alveolus x 560 of alveolus  Breast development Embryologically derived from ectoderm; visible ~4 weeks (both sexes) Paired epidermal thickenings extending from mid-axilla to inguinal region  “milk line” Human  pair of breasts Supernumery breast / nipple in 1% of females Birth rudimentary ducts May be some secretory activity “witches milk” as consequence of exposure to mother’s hormones – normal! Puberty  increase in breast size (fat), proliferation of ducts, cyclical changes (growth in size at puberty unique to humans!) Pubertal stages of breast development (external) 1. Preadolescent 2. Breast bud stage – breast and papilla elevated; areolar area 3. pigmentation 4. Areolar and papilla form secondary mound above the level of the breast 5. Mature stage; erect papilla projecting above areolar, classification is independent of breast size  (1) Proliferation Begins at puberty Adipose ) Lactiferous duct growth Duct Lobule (oestrogen, growth hormone, adrenal steroids) Alveoli Rudimentary lobules of Dense CT alveoli (progesterone) Adipose (1) Proliferation continued during gestation… (2) Lactogenesis (milk secretion) Secretory activation - occurs ~40-48 hours post birth ↓ progesterone & oestrogen at parturition releases inhibition of prolactin on secretory alveolar cells ↑ milk volume 50ml/day on day 2 to 500ml/day on day 4 post-partum (3) Lactation Maximal milk yield (~850ml / day or more!) Maintained by milk removal – infant demand Prolactin (milk production) Oxytocin (milk ejection) (4) Involution After weaning Induced by accumulation of milk (mechanical atrophy) Distension also compresses capillaries  nutrients, oxygen to breast tissue Loss of epithelial cells (apoptosis) Gradual replacement of ducts and alveoli with stromal and fat tissue Involution process takes ~ 3 months After menopause Structural atrophy of breast Hormonal control of milk secretion Nipple stimulation due to suckling Spinal nerves Secretion of prolactin from ant. pituitary Milk synthesis by alveolar cells Milk ejection (letdown) reflex Nipple stimulation due to suckling Spinal nerves Release of oxytocin from post. pituitary Contraction of myoepithelial cells around alveoli Reflex can be conditioned Lactational amenorrhoea Temporary suppression of ovarian activity (and therefore menstrual cycling) during breast feeding Mean duration of lactational amenorrhoea by duration of breastfeeding **Population level data Less predictable for individual women Type and intensity of breast feeding most important From: Bongaarts & Potter 1983 Fertility, Biology and Behavior Academic Press Lactation disrupts pattern of GnRH release During pregnancy high oestrogen (E) and progesterone (P)  ↓ GnRH and LH secretion  inhibits follicular development and ovulation Birth - decline in E & P Non-breast feeding woman pulsatile secretion of GnRH and LH within ~2-3 weeks; ovulation within 6 weeks During lactation erratic release of GnRH → LH (as opposed to normal 60-90 minute pulse frequency) Crucial in preventing return to normal ovarian activity Related to strength of sucking stimulus – likely through prolactin? Useful references Ross, M.H. and Pawlina, W (2016). Histology: a Text and Atlas with Correlated Cell and Molecular Biology. 7th Ed. Wolters Kluwer Health Chapter 23 Johnson MH (2018) Essential Reproduction. 8th ed. Wiley Blackwell. Chapter 19. Available online via Ebook Central via Library website https://www.medela.us/breastfeeding- professionals/professional-resources/research- literature The End Thank you  Lactiferous duct Alveoli Alveoli Fat B Lactiferous duct Resting Lactating