BI0005 - Lecture 18 Physiology of Motherhood
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What is the structure of the uterus?
- • Endometrium
- – Inner layer good blood supply
- – Maternal contribution to placenta
- • Myometrium
- – Muscle layer
- – No contractions during pregnancy
- – Contractions for labour
What is parturition?
• 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
What are contractions?
• 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
What is the process of initiation of parturition
• 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
What are the hormonal initiators of labour?
- • Progesterone
- – Relatively less
• Other factors are involved in the regulation of these hormones
What causes the stimulation of oestrogen, and what are its actions?
- • 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
What is oxytocin?
• 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
What are prostaglandins?
• Synthesised by placenta and myometrium
• Can be used to induce labour
• Enhance contractions
• One role is release of calcium required for muscle contraction
What is the introduction to the events of labour?
• 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
What are the three stages of labour?
Dilation (6-12 hours)
Expulsion (minutes to hours)
Placental (5-30 mins)
What is dilation?
• 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
What is expulsion?
• 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
What is the umbilical cord?
• 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
What is the placental stage?
• 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
What is lactation?
• 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’
What hormones cause the stimulation of breast development ?
- • 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
What causes the stimulation of milk production?
- • 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
What are Prolactin and Oxytocin?
- • 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
How does milk production and ejection work?
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.
What is the composition of the Milk?
- • 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
What does breast milk contain?
- • 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
How much milk does the baby drink?
• 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
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