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What is the primary function of sustained contractions (involution) after childbirth?
What is the primary function of sustained contractions (involution) after childbirth?
Which hormone is essential for initiating myometrium contractions during birth?
Which hormone is essential for initiating myometrium contractions during birth?
What role do glucocorticoids play in fetal development?
What role do glucocorticoids play in fetal development?
Which hormones are involved in cervical ripening during the first stage of labor?
Which hormones are involved in cervical ripening during the first stage of labor?
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During which stage of labor does the delivery of the neonate occur?
During which stage of labor does the delivery of the neonate occur?
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What occurs during Phase 1 of labor?
What occurs during Phase 1 of labor?
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What is produced during lactogenesis I after birth?
What is produced during lactogenesis I after birth?
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Which mechanism overrides the negative feedback of cortisol before birth?
Which mechanism overrides the negative feedback of cortisol before birth?
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Which statement correctly describes galactopoiesis?
Which statement correctly describes galactopoiesis?
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What is the role of DHEA in the hormonal changes during labor?
What is the role of DHEA in the hormonal changes during labor?
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What triggers the let-down reflex during breastfeeding?
What triggers the let-down reflex during breastfeeding?
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What effect do prostaglandins have in the context of labor?
What effect do prostaglandins have in the context of labor?
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During what phase of labor do myometrial contractions predominantly occur?
During what phase of labor do myometrial contractions predominantly occur?
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What occurs in women who breastfeed regarding menstrual cycles?
What occurs in women who breastfeed regarding menstrual cycles?
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Which of the following describes the change in the mammary epithelium during lactogenesis II?
Which of the following describes the change in the mammary epithelium during lactogenesis II?
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Which of the following changes occurs in the fetus just before birth?
Which of the following changes occurs in the fetus just before birth?
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Which element primarily contributes to the contraction of myoepithelial cells during breastfeeding?
Which element primarily contributes to the contraction of myoepithelial cells during breastfeeding?
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What happens to progesterone levels as labor approaches?
What happens to progesterone levels as labor approaches?
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How does progesterone influence lactation during pregnancy?
How does progesterone influence lactation during pregnancy?
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What is the primary role of the placenta in the context of cortisol during pregnancy?
What is the primary role of the placenta in the context of cortisol during pregnancy?
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Which process occurs in the fetus to prepare for birth, specifically in relation to lung maturity?
Which process occurs in the fetus to prepare for birth, specifically in relation to lung maturity?
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What role do glucocorticoids play in fetal development?
What role do glucocorticoids play in fetal development?
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Which hormone initiates contractions of the myometrium during the birth process?
Which hormone initiates contractions of the myometrium during the birth process?
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What is the primary change occurring in Phase 1 of labor?
What is the primary change occurring in Phase 1 of labor?
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Which of the following is a uterotonic that can induce labor?
Which of the following is a uterotonic that can induce labor?
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What is the effect of increased estrogen levels as labor approaches?
What is the effect of increased estrogen levels as labor approaches?
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Which statement correctly describes the action of prostaglandins during labor?
Which statement correctly describes the action of prostaglandins during labor?
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During which phase of labor are the inhibitory effects of progesterone predominant?
During which phase of labor are the inhibitory effects of progesterone predominant?
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What role does the fetal adrenal gland play as birth approaches?
What role does the fetal adrenal gland play as birth approaches?
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What physiological change assists with thermoregulation in the fetus before birth?
What physiological change assists with thermoregulation in the fetus before birth?
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What occurs to the lower uterine segment during the first stage of labor?
What occurs to the lower uterine segment during the first stage of labor?
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Which hormone primarily triggers the secretion of copious milk during lactation?
Which hormone primarily triggers the secretion of copious milk during lactation?
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What happens to tumor growth in the myometrium during the stages of labor?
What happens to tumor growth in the myometrium during the stages of labor?
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What is the primary physiological function of colostrum during lactation?
What is the primary physiological function of colostrum during lactation?
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What physiological changes occur to the cervix during the first stage of labor?
What physiological changes occur to the cervix during the first stage of labor?
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What is the role of suckling in milk production after childbirth?
What is the role of suckling in milk production after childbirth?
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Which condition occurs in breastfeeding women concerning menstrual cycles?
Which condition occurs in breastfeeding women concerning menstrual cycles?
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What causes the let-down reflex during breastfeeding?
What causes the let-down reflex during breastfeeding?
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During which stage of lactation is breast milk secretion at its peak?
During which stage of lactation is breast milk secretion at its peak?
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What effect does a decrease in progesterone have on lactation shortly after birth?
What effect does a decrease in progesterone have on lactation shortly after birth?
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What role does the closure of the foramen ovale serve in fetal development before birth?
What role does the closure of the foramen ovale serve in fetal development before birth?
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Which event is primarily triggered by the decrease in progesterone as labor approaches?
Which event is primarily triggered by the decrease in progesterone as labor approaches?
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What is the primary effect of increased cortisol levels toward the end of pregnancy?
What is the primary effect of increased cortisol levels toward the end of pregnancy?
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What is the primary function of uterotonins during the labor process?
What is the primary function of uterotonins during the labor process?
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Which effect does the administration of synthetic PGE2 have during labor?
Which effect does the administration of synthetic PGE2 have during labor?
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During Phase 0 of labor, which substances are primarily responsible for maintaining uterine quiescence?
During Phase 0 of labor, which substances are primarily responsible for maintaining uterine quiescence?
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In which phase of labor is the myometrium most actively contracting due to oxytocin and prostaglandins?
In which phase of labor is the myometrium most actively contracting due to oxytocin and prostaglandins?
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What physiological change assists with the fetal ability to generate heat in preparation for birth?
What physiological change assists with the fetal ability to generate heat in preparation for birth?
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How does rising estrogen influence the myometrium as labor approaches?
How does rising estrogen influence the myometrium as labor approaches?
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The transition of fetal hemoglobin to adult hemoglobin is crucial for which post-birth function?
The transition of fetal hemoglobin to adult hemoglobin is crucial for which post-birth function?
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What hormonal change primarily triggers the transition from lactogenesis I to lactogenesis II?
What hormonal change primarily triggers the transition from lactogenesis I to lactogenesis II?
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Which of the following is NOT a function of oxytocin during lactation?
Which of the following is NOT a function of oxytocin during lactation?
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Which factor primarily contributes to the suppression of GnRH in breastfeeding women?
Which factor primarily contributes to the suppression of GnRH in breastfeeding women?
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What physiological change occurs in the mammary epithelium during lactogenesis I?
What physiological change occurs in the mammary epithelium during lactogenesis I?
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Which statement accurately describes the role of the placenta during the stages of labor?
Which statement accurately describes the role of the placenta during the stages of labor?
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What role does suckling play in the regulation of prolactin and oxytocin?
What role does suckling play in the regulation of prolactin and oxytocin?
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Which condition best describes lactational amenorrhea?
Which condition best describes lactational amenorrhea?
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In which stage of labor does cervical dilation reach its maximum?
In which stage of labor does cervical dilation reach its maximum?
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What is the primary nutritional benefit of colostrum for newborns?
What is the primary nutritional benefit of colostrum for newborns?
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What triggers the detachment of the placenta during the third stage of labor?
What triggers the detachment of the placenta during the third stage of labor?
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Study Notes
Fetal Preparation for Birth
- The fetus needs to mature various systems before birth as the placenta will no longer be functioning:
- Lungs: Surfactant development
- Cardiovascular System (CVS): Closure of the foramen ovale, ductus arteriosus, and AV shunts
- Gut:
- Renal Function: Regulation of extracellular fluid and acid-base balance
- Thermoregulation: Generation of heat using brown fat and glycogen
- Hemoglobin: Change from fetal hemoglobin to adult hemoglobin
Role of Glucocorticoids
- Glucocorticoids are vital for:
- Fetal organ development
- Orchestrating the timing of birth
- Glucocorticoid-induced stress responses rise towards the end of pregnancy:
- Secreted by the fetal adrenal cortex
- Prepartum cortisol surge overrides the negative feedback mechanism before birth
- Glucocorticoid administration at risk of preterm delivery facilitates the early development of the fetus.
Labour - Hormonal Changes
- Exact mechanisms of labor initiation remain unknown, but several factors are implicated:
- Positive feedback loops with cortisol (fetal adrenal) and CRH (placenta)
- Rising levels of fetal adrenal DHEA contribute to an increase in estrogen
- Uterotropins: Preparing the myometrium for labor
- Increased estrogen: Stimulates contractile proteins, oxytocin/prostaglandin receptors, and gap junctions in myometrial cells.
- Decreased progesterone:
- Placental CRH:
- Uterotonins: Contractions of the myometrium during labor
-
Oxytocin:
- Released from the posterior pituitary gland and placenta
- Raises during stages 1 and 2, decreasing during stage 3.
- Contributes to Braxton-Hicks contractions and the Ferguson reflex (stretch-induced positive feedback with contractions)
-
Prostaglandins (PGF2α, PGE2):
- Synthesized locally in the placenta in response to increased estrogen which stimulates arachidonic acid synthesis.
- PGE2 can induce labor when administered.
- PGF2α acts as a physiological uterotonin.
-
Oxytocin:
Labour - Hormonal Phases
- Labor is characterized by four hormonal phases:
- Phase 0 (Quiescent): Inhibitory effects of progesterone, prostacyclin, and nitric oxide (NO)
-
Phase 1 (Activation): Towards the end of pregnancy, estrogen rises, stimulating:
- Production of contractile proteins within myometrial cells
- Production of receptors for prostaglandins and oxytocin
- Generation of gap junctions in myometrial cells
- Phase 2 (Stimulation): Myometrial contractions occur under the influence of oxytocin and prostaglandins
- Phase 3 (Involution): After the baby’s birth, sustained contractions reduce the size of the enlarged postpartum uterus.
Labour - Physical Changes
- Stages of Labor and their associated physical changes:
-
Stage 1:
- Regular painful contractions followed by periods of relaxation
- Decreasing uterine volume, shortening of muscle fibers, and thickening of the fundal musculature. The lower uterine segment remains passive and is pulled upwards.
- Dilation and shortening of the cervix until full dilation is achieved.
-
Stage 2:
- Full dilation of the cervix, pulled upwards.
- Delivery of the neonate due to contractions.
-
Stage 3:
- Placental detachment and expulsion.
-
Stage 1:
Cervical Ripening
- Occurs in the weeks or days preceding birth.
- Involves the breakdown of collagen tissue, increasing compliance.
- Pro-inflammatory changes and neutrophilic infiltration favor rapid tissue remodeling.
- Prostaglandins F2α and E2, relaxin, and NO contribute to cervical ripening.
Myometrial Changes
- Occur during labor:
- Regular, short contractions occur
- Increased estrogen leads to:
- Increased myometrial bulk - increase in myocyte size and number
- Increase in oxytocin receptors
- Decreased progesterone: Typically inhibits myometrial activity and reduces oxytocin receptors.
- Oxytocin and prostaglandins F2α and E2: Enhance myometrial activity.
Lactation: Stage I (Lactogenesis I)
- Mid-pregnancy to 2 days postpartum:
- Breast glands undergo differentiation, becoming competent in secreting small amounts of milk components (casein, lactose).
- Colostrum production occurs during the first two days after birth, rich in protein but low in lactose and fat.
- Progesterone inhibits lactation, with its decline triggering the onset of lactation.
Lactation: Stage II
- Secretion of abundant milk:
- Decreased progesterone and increased prolactin lead to milk secretion.
- Mammary epithelium transformation occurs:
- Altered permeability between epithelial cells
- Change in secretion of protective substances such as immunoglobulins, lactoferrin, and complex carbohydrates.
Suckling
- Suckling stimulates the release of prolactin (anterior pituitary) and oxytocin (posterior pituitary).
- Prolactin: Drives galactopoiesis (milk production)
- Oxytocin: Triggers the let-down reflex (milk ejection)
Galactopoiesis
- Sustained milk production:
- Requires prolactin, which acts on alveolar epithelial cells of mammary glands.
- Requires regular milk removal.
Let-Down Reflex
-
Milk ejection:
- Oxytocin acts on myoepithelial cells, causing contraction.
- Contractions distort nipple tissue, allowing pressurized milk to exit.
- Stimulation of mechanoreceptors in the nipple activates thoracic nerves and the spinal cord, leading to the release of oxytocin from the supraoptic nucleus (SON) and paraventricular nucleus (PVN) of the hypothalamus.
- These neurons can also be activated by higher brain centers, so even the sight or sound of the baby is sufficient to induce the reflex.
-
Breast milk provides essential nutrients for the baby and maternal immunoglobulins for passive immunity.
Lactational Amenorrhoea
- Menstrual cycles typically resume within six to eight weeks after childbirth in women who do not breastfeed.
- Lactational amenorrhoea (absence of a menstrual period) occurs in breastfeeding women due to high prolactin levels that suppress the GnRH pulse generator.
Fetal Development Before Birth
- Fetus needs to mature areas that the placenta was functioning for before birth
- Lungs: develop surfactant
- Cardiovascular System (CVS): closure of AV shunts, foramen ovale, ductus arteriosus
- Gut
- Renal function: regulation of ECF and acid-base balance
- Generate own heat for thermoregulation (brown fat and glycogen)
- Change of hemoglobin from fetal to adult type
- Glucocorticoids are essential for fetal organ development and orchestrating birth timing
- Rising output toward the end of pregnancy
- Secreted by the fetal adrenal cortex
- Prepartum cortisol surge - negative feedback mechanism overridden before birth
- Administration at risk of preterm delivery encourages early development of the fetus
- Rising output toward the end of pregnancy
Labor - Hormonal Changes
- Exact mechanisms of initiation are unknown
- Uterotropins prepare the myometrium for labor:
- Unsuppression of myometrial contractions and softening of the cervix
- Increased estrogen: stimulate contractile proteins, oxytocin/prostaglandin receptors, and gap junctions in myometrial cells
- Decreased progesterone
- Placental CRH
- Uterotonins contract the myometrium during birth
- Oxytocin:
- Released from the posterior pituitary gland and placenta
- Builds in the first two stages and falls during the third stage of labor
- Correlates with Braxton-Hicks contractions and is involved in the Ferguson reflex
- Prostaglandins (PGF2alpha, PGE2):
- Synthesized locally in the placenta in response to a rise in estrogen (as it stimulates synthesis of arachidonic acid)
- PGE2 can be administered to induce labor
- PGF2alpha is a physiological uterotonin
- Oxytocin:
Four Hormonal Phases of Labor
- Phase 0 (Quiescent): Inhibitory effects of progesterone, prostacyclin, NO
- Phase 1 (Activation): Toward the end of pregnancy, estrogen stimulates:
- Production of contractile proteins within myometrial cells
- Production of receptors for prostaglandins and oxytocin
- Production of gap junctions on myometrial cells
- Phase 2 (Stimulation): Myometrium contracts under the actions of oxytocin and prostaglandins
- Phase 3 (Involution): After the birth of the baby, sustained contractions reduce the size of the massively enlarged postpartum uterus
Labor - Physical Changes
- Stages of Labor and Physical Changes:
- Stage 1: Cervical ripening
- Regular painful contractions followed by a period of relaxation
- Uterine volume decreases - overall shortening of muscle fibers, fundal musculature thickens
- Lower uterine segment remains passive and is pulled upward
- Dilations and shortening of the cervix → full dilation of the cervix
- Stage 2:
- Full dilation of the cervix - pulled up
- Delivery of neonate - pushed down via contractions
- Stage 3:
- Placenta detaches and is expelled
- Stage 1: Cervical ripening
Lactation
- Stage I (Lactogenesis I): Midpregnancy - 2 days post-partum
- Glands in breasts become well differentiated
- Capable of secreting small quantities of specific milk components (casein, lactose)
- Colostrum is produced for 2 days after birth - rich in protein, poor in lactose and fat
- Progesterone inhibits lactation, its fall triggers onset
- Stage II: Secretion of copious milk
- Decreased progesterone and increased 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 (anterior pituitary) and oxytocin (posterior pituitary)
- 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 the nipple and allows pressurized milk to exit
- Stimulation of mechanoreceptors in the nipple → thoracic nerves and spinal cord → SON and PVN of the hypothalamus where neurons release oxytocin
- These neurons can also be activated by higher brain centers, so sight/sound of the baby is sufficient
- Breast milk provides all basic nutritional requirements of the baby + maternal immunoglobulins for passive immunity
Lactational Amenorrhea
- Menstrual cycles resume >6-8 weeks after parturition in women who do not breastfeed
- Lactational amenorrhea (no period) occurs in those who breastfeed - high levels of prolactin suppress GnRH pulse generator
Fetal Development Before Birth
- Fetal organs mature before birth to take over functions previously performed by the placenta.
- Lungs develop surfactant for proper gas exchange.
- Cardiovascular system (CVS) undergoes closure of fetal shunts like foramen ovale and ductus arteriosus.
- Gut prepares for digestion and nutrient absorption.
- Kidneys develop renal function for regulating electrolytes and acid-base balance.
- Thermoregulation develops with brown fat and glycogen for heat production.
- Hemoglobin switches from fetal to adult type.
-
Glucocorticoids (specifically cortisol) are crucial for fetal organ development and orchestrating the timing of birth.
- Cortisol levels rise towards the end of pregnancy, secreted by the fetal adrenal cortex.
- Prepartum cortisol surge overrides negative feedback mechanisms, triggering the birthing process.
- Glucocorticoid administration during potential preterm delivery encourages early fetal development.
Labour - Hormonal Changes
- Initiation of labour is complex and not fully understood.
-
Uterotropins prepare the myometrium for labor, including:
- Increasing estrogen levels stimulate contractile proteins, oxytocin/prostaglandin receptors, and gap junctions in myometrial cells.
- Decreasing progesterone levels.
- Placental corticotropin-releasing hormone (CRH) plays a role.
-
Uterotonins trigger myometrial contractions during birth, including:
-
Oxytocin is released from the posterior pituitary gland and placenta.
- Levels build during the first two stages of labor and decline during the third stage.
- Involved in Ferguson reflex (stretch positive feedback with contractions).
-
Prostaglandins (PGF2α and PGE2) are synthesized locally in the placenta in response to rising estrogen levels.
- PGE2 can be administered to induce labor.
- PGF2α is a physiological uterotonin.
-
Oxytocin is released from the posterior pituitary gland and placenta.
Stages of Labour
-
Four hormonal phases of labour:
- Phase 0 (quiescent): Progesterone, prostacyclin, and nitric oxide (NO) have inhibitory effects on labor.
-
Phase 1 (activation): Estrogen levels rise towards the end of pregnancy, stimulating:
- Production of contractile proteins within myometrial cells.
- Production of receptors for prostaglandins and oxytocin.
- Production of gap junctions on myometrial cells.
- Phase 2 (stimulation): The myometrium contracts under the influence of oxytocin and prostaglandins.
- Phase 3 (involution): After the baby's birth, sustained contractions reduce the size of the enlarged postpartum uterus.
Physical Changes During Labour
-
Stage 1:
- Regular, painful contractions followed by periods of relaxation.
- Uterine volume decreases, with muscle fibers shortening and fundal musculature thickening.
- The lower uterine segment remains passive and is pulled upwards.
- Cervical dilation and shortening leading to full dilation of the cervix.
-
Stage 2:
- Full dilation of the cervix.
- Delivery of the neonate, pushed downwards by contractions.
-
Stage 3:
- Placenta detaches and is expelled.
Lactation
-
Stage I (Lactogenesis I):
- Occurs from mid-pregnancy to two days postpartum.
- Breast glands become well differentiated.
- Capable of secreting small amounts of specific milk components (casein, lactose).
- Colostrum is produced for the first two days after birth, rich in protein, poor in lactose and fat.
- Progesterone inhibits lactation, and its decline triggers the onset of milk production.
-
Stage II:
- Declining progesterone and increasing prolactin lead to copious milk secretion.
- Transformation of mammary epithelium:
- Increased permeability between epithelial cells.
- Increased secretion of protective substances like immunoglobulins, lactoferrin, and complex carbohydrates.
Suckling and Milk Ejection
- Suckling stimulates prolactin (anterior pituitary) and oxytocin (posterior pituitary) release.
- Prolactin promotes galactopoiesis (milk production).
- Oxytocin triggers the let-down reflex (milk ejection).
- Galactopoiesis requires prolactin acting on alveolar epithelial cells of mammary glands and regular milk removal.
-
Let-down reflex: Oxytocin acts on myoepithelial cells, causing their contraction.
- This distorts tissue in the nipple, allowing pressurized milk to exit.
- Stimulation of mechanoreceptors in the nipple sends signals through thoracic nerves and the spinal cord to the supraoptic nucleus (SON) and paraventricular nucleus (PVN) of the hypothalamus, where neurons release oxytocin.
- These neurons can also be activated by higher brain centers (sight/sound of the baby).
- Breast milk provides the baby's basic nutritional needs and maternal immunoglobulins for passive immunity.
Lactational Amenorrhea
- Menstrual cycles resume approximately 6-8 weeks after parturition in women who don't breastfeed.
- Lactational amenorrhea (no period) occurs in breastfeeding women due to high prolactin levels suppressing the GnRH pulse generator.
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