Preparing for Birth PDF

Preparing for Birth Before fetus is born it needs to mature areas that the placenta was functioning for: Lungs - develop surfactant CVS - closure of AV shunts, foramen ovale, ductus arteriosus Gut Renal function - regulation of ECF and acid base Generate own heat...

Preparing for Birth Before fetus is born it needs to mature areas that the placenta was functioning for: Lungs - develop surfactant CVS - closure of AV shunts, foramen ovale, ductus arteriosus Gut Renal function - regulation of ECF and acid base Generate own heat for thermoregulation (brown fat and glycogen) Change of haemoglobin from fetal to adult type Glucocorticoids are essential for development of fetal organs and orchestrating timing of birth Rising output toward end of pregnancy ○ Secreted by fetal adrenal cortex ○ Prepartum cortisol surge - negative feedback mechanism overridden before birth Administration at risk of pre-term delivery encourages early development of fetus  Labour - Hormonal Changes Exact mechanisms of initiation unknown Uterotropins: prepare myometrium for labour (un-suppression of Positive feedback loop with cortisol (fetal adrenal)/CRH myometrial contractions and softening of cervix) (placenta) Inc Oestrogen - stimulate contractile proteins, ○ Inc cortisol oxytocin/prostaglandin receptors and gap junctions in myometrial ○ Inc prostaglandins via direct/indirect actions cells Inc DHEA (fetal adrenal) → inc oestrogen Dec progesterone Placental CRH Uterotonins: contractions of myometrium during birth Oxytocin ○ From posterior pituitary gland and placenta ○ Builds in first 2 stages and falls during third stage of labour ○ Correlates with Braxton-Hicks contractions and is involved in ferguson reflex (see pic - stretch positive feedback w contractions) Prostaglandins - PGF2alpha, PGE2 ○ Both synthesised locally in placenta in response to rise in oestrogen (as it stimulates synthesis of arachidonic acid) ○ PGE2 can be administered to induce labour ○ PGF2alpha is a physiological uterotonin  Labour - Hormonal Changes 4 hormonal phases of labour Phase 0 Inhibitory effects of progesterone, (quiescent) prostacyclin, NO Phase 1 Toward end of pregnancy oestrogens (activation) stimulate: Production of contractile proteins within myometrial cells Production of receptors for prostaglandins and oxytocin Production of gap junctions on myometrial cells Phase 2 Myometrium contracts under actions (stimulation) of oxytocin and prostaglandins Phase 3 After birth of baby. Sustained contractions (involution) reduce size of massively enlarged postpartum uterus  Labour - Physical Changes Stages of Labour Physical Changes Stage 1: Cervical ripening Regular painful contractions followed by period of Weeks/days preceding birth relaxation Loss of collagen tissue and increase in compliance Uterine volume decreases - overall shortening of Pro-inflammatory changes and neutrophilic infiltrate muscle fibres, fundal musculature thickens favour rapid tissue modelling Lower uterine segment remains passive and is pulled Prostaglandins F2alpha and E2, relaxin, NO upward Dilations and shortening of cervix → full dilation of Myometrial changes cervix Regular and short contractions occur during labour Inc Oestrogen → increase myometrium bulc via inc Stage 2: number and size of myocytes, and increase in oxytocin Full dilation of cervix - pulled up receptors Delivery of neonate - pushed down via contractions Dec Progesterone → usually inhibits myometrial activity and decreases oxytocin receptors Stage 3: Oxytocin and prostaglandins F2alpha and E2 → Placenta detaches and is expelled increase myometrial activity  Lactation Stage I (Lactogenesis I): Midpregnancy - 2D post-partum Glands in breasts become well differentiated Capable of secreting small quantities of specific milk components (casein, lactose) Colostrum is produced for 2D after birth - rich in protein, poor in lactose and fat Progesterone inhibits lactation, fall triggers onset Stage II: Secretion of copious milk Dec progesterone and inc prolactin → milk secretion Transformation of mammary epithelium ○ Δ permeability between epithelial cells ○ Δ secretion of protective substances - immunoglobulins, lactoferrin, complex carbs  Suckling Suckling increases prolactin (ant pit) and oxytocin (post pit) Prolactin → galactopoiesis Oxytocin → let down reflex Galactopoiesis: maintenance of milk production Requires prolactin that acts on alveolar epithelial cells (of mammary glands) Requires milk to be removed regularly Let-down reflex: milk ejection Oxytocin acts on myoepithelial cells → contraction Distorts tissue in nipple and allows pressurised milk to exit Stimulation of mechanoreceptors in nipple → thoracic nerves and spinal cord → SON and PVN of hypothalamus where neurons release oxytocin ○ These neurons can also be activated by higher brain centres so sight/sound of baby is sufficient Breast milk provides all basic nutritional requirements of baby + maternal immunoglobulins for passive immunity Lactational Amenorrhoea Menstrual cycles resume >6-8W after parturition in women who do not breastfeed Lactational amenorrhoea (no period) occurs in those who breastfeed - high levels of prolactin suppresses GnRH pulse generator