BI0005 - Lecture 18 Physiology of Motherhood

• • Endometrium
•     – Inner layer good blood supply
•     – Maternal contribution to placenta

• • Myometrium
•     – Muscle layer
•     – No contractions during pregnancy
•     – Contractions for labour

• Labour

• Delivery of the baby, placenta and associated membranes

• Initiated by chemical and physical factors

• Physically associated with regular, painful, uterine contractions

• Physiologically with cervical ‘ripening’– Cervix softens, shortens and dilates

• Contractions occur in the myometrium

• During pregnancy progesterone inhibits contractions

• • Smooth muscle
•     – So is involuntary control

• • In last few weeks practise contractions
•     – Braxton-Hicks contractions
•     – Painless, last few seconds
•     – Due to increase in level of oestrogen

• Not well understood

• Complex interplay of local regulators, hormones and physical factors

• Physical factors associated with enlargement of placenta

• • Chemical factors changes in hormone levels & possibly other bioactive factors
•     – Hormonal changes in mother and foetus

• • Progesterone
•     – Relatively less

• Oestrogen

• Prostaglandins

• Oxytocin

• Other factors are involved in the regulation of these hormones

• • Corticotropin-releasing hormone (CRH)
•     – From placenta and pituitary gland
•     – Releases oestrogen building blocks

• • Cortisol 
•     – From foetal adrenal gland
•     – Increases the oestrogen to progesterone ratio
•     – Removal of inhibitory effect on myometrium by progesterone

• • Oestrogen (large increase towards end of pregnancy):
•     – Increases sensitivity of uterus to contractile stimuli
•     – Increases number of receptors for oxytocin in the uterus
•     – Stimulates release of prostaglandins

• Oxytocin produced by foetus and mother’s posterior pituitary gland

• Oxytocin receptors increase at end of pregnancy

• Stimulates powerful contractions of uterus

• Stimulates production of prostaglandins by placenta

• Following delivery reduces blood loss

• Lipids

• Synthesised by placenta and myometrium

• Can be used to induce labour

• Enhance contractions

• One role is release of calcium required for muscle contraction

• For normal pregnancy the baby has rotated, dropped low in the pelvis and head “engaged” with cervix before labour can begin

• Results in stretching of cervix

• Stretch receptors “send” message to release oxytocin

Dilation (6-12 hours)

Expulsion (minutes to hours)

Placental (5-30 mins)

• From onset of labour until full cervical dilatation (10cm)

• Opening up and thinning of cervix

• Cervix stretches round engaged head

• Uterine contractions increase in strength and frequency

• Time from full cervical dilatation until birth

• Usually lasts less than 2 hours

• Rotation to make birth easier

• Continuous strong contractions force foetus down and out of the uterus and vagina

•Contractions alone sufficient for delivery

• Blood continues to pass for short period following birth

• Blood pressure drops & blood flow stops

• Only cut umbilical cord once flow stopped

• Useful nutrients pass to baby in this short period

• From birth until delivery of placenta and membranes

• • Powerful contractions result in:
•     – Expulsion of placenta and membranes
•     – Closure of uterine blood vessels to reduces blood loss

• Supply of milk to feed baby

• From the mammary glands

• Hormonal induced changes in mammary glands during pregnancy

• Stimulation to deliver milk part hormonal and part suckling

• Milk initially secreted as colostrum before milk ‘proper’

• • During pregnancy breasts enlarge as
•     – ducts proliferate, increasing cell number for milk secretion
•     – fat deposited between lobules

• • Stimulated by combination of hormones:
•     – progesterone
•     – oestrogen
•     – placental lactogen

• • During pregnancy inhibited by high levels of oestrogen and progesterone
•   – decrease at birth
•   – no negative feedback

• Prolactin secreted

• Milk production stimulated by rise in prolactin and oxytocin

• Suckling further stimulates oxytocin & prolactin

• • Prolactin
•    – From anterior pituitary
•    – Initiate milk production by milk-producing epithelial cells
•    – Need to maintain high levels to continue milk production

• • Oxytocin
•    – From posterior pituitary
•    – Stimulates milk-ejecting epithelial cells

Suckling acts as a sensory input.

The hypothalmus stimulates the anterior pituitary to produce prolactin, resulting in milk production.

The hypothalmus stimulates the posterior pituitary gland to produce oxytocin, resulting in milk ejection.

• • Colostrum (to 4th day)
•    – Yellow fluid
•    – High protein
•    – Low fat
•    – Rich in immune molecules, especially IgA
•    – Rich in some vitamins A, D, E and K
•    – Plenty of minerals

• • Milk
•    – Fat main source of energy
•    – Sugar: high level of lactose
•    – Casein main milk protein; other proteins relatively low • Makes sure essential amino acids provided
•    – Calcium and other minerals and vitamins

• • Cells
•    – White blood cells against infection

• • Molecules
•    – IgA antibody
•    – Interferon & lysozyme are anti-bacterial

• • Affects on disease later in life
•    – Slight reduction in lymphoma, heart disease, allergies, respiratory & GI infections
•    – Breast feeding protects mother against osteoporosis & breast cancer

• Baby weighing 5-6kg consumes 0.8-1 litre per day

• Each litre of milk contains 3MJ (750kcal)

• • Mother needs to have nutrient in-take for this extra energy expenditure
•    – Especially calcium and phosphate