Lecture 54: Pregnancy, Labour and Lactation

Question 1

what maternal physiological changes result from gestation

Answer 1

• ^ CO and BV
• ^ O2 consumption and CO2 production
• ^ ventilation
• ^ BMR
• ^ GFR/ Na+ and H2O reabsorption (net fluid retention)
• ^ nutritional demands
• maternal weight gain
• morning sickness

Question 2

what are the 3 stages of parturition (birth)/labour

Answer 2

• dilation of cervix
• expulsion of foetus
• delivery of placenta

Question 3

describe what happens in parturition before birth

Answer 3

relaxin:
- cervix softens and dilates
- pubic symphysis become more flexible

oestrogen stimulates uterine muscle:

• more excitable
• more connected by gap junctions
• ^ in prostaglandins and oxytocin receptors

foetal CRH prod ^ driving up placental CRH:

• foetal ACTH and cortisol ^
• cortisol vital to final maturity of foetal resp system
• foetus decides when to be born by ^ CRH

Question 4

describe the first stage of labour

Answer 4

dilation (8-24hr)

• cervix dilated by action of baby’s head pushing down on it by myompetrial contractions
• stretch causes reflex release of oxytocin from post pit
• acts on myometrium (already very sensitive to oxytocin) to further ^ contraction, ^ cervical stretch, +ve feedback
• prostaglandins also stim myometrial contraction

Question 5

describe the second stage of labour

Answer 5

expulsion (30-90mins)

• begins when cervix fully dilated to 10cm
• head exiting cervix triggers reflexes which contract abdominal muscles to help expel baby through vagina
• reflex contractions can be reinforced voluntarily

Question 6

describe the third stage of labour

Answer 6

delivery of placenta (15-30mins)

• shears off wall of contracted uterine
• risk of blood loss but normally quite minimal
• following delivery, dramatic drop in maternal oestrogen and progesterone
• leads to regression of decidual endometrium giving discharge post birth termed lochia

Question 7

what is lochia

Answer 7

discharge post birth as a result of regression of decidual endometrium after delivery of placenta

Question 8

outline the process of lactation

Answer 8

• during pregnancy, breasts develop into milk secreting organs
• under influence of oestrogen and progesterone from placenta
• oestrogen promotes duct development, progesterone enlarges terminal secretory portions of glands
• prolactin from maternal ant pit and human chorionic somatomammotropin from placenta act to develop enzymes necessary for successful milk production
• female fully capable of producing milk at 20 weeks into pregnancy
• this is prevented by high levels of oestrogen and progesterone before birth (drop after birth)

Question 9

what is human chorionic somatomammotropin

Answer 9

general anabolic hormone described as maternal growth hormone of pregnancy

Question 10

outline the process of suckling and milk ejection

Answer 10

• after delivery oestrogen and progesterone levels fall allowing lactation and suckling to proceed
• both processes are neuroendocrine (depend on both nervous afferents and endocrine effectors)
• mechanical stimulation of the nipple causes secretion of prolactin by dec. secretion of prolactin inhibitory hormone (PIH); PRH may also be involved to lesser extent
• initiates and maintains milk production
• nipple stim ^ oxytocin output from hypothalamus and release from post pit
• causes contraction of in smooth muscle surrounding secretory alveoli and expels milk into mouth of expectant infant

Question 11

explain how breast feeding can act as a slightly unreliable contraceptive

Answer 11

prolactin (secreted as a result of mechanical stim of nipple) inhibits GnRH production

Question 12

outline the components of breast milk

Answer 12

• triglycerides
• carbs (lactose)
• protein
• vitamins
• calcium
• phosphate
• for first few days after birth humans secrete colostrum which has more protein and less fat and lactose
• colostrum also contains lactoferrin (antibacterial) and maternal IgA antibodies providing passive immunity