11.13 Physiology of Pregnancy

Question 1

What are the critical periods of pregnancy?

Answer 1

• Periconceptual period, early pregnancy are critical that marternal health is good
• First 2 weeks of foetal life is where there is the most highest susceptibility to death
• Embryonic period weeks 3-8: risk of major formation abnormalities
• Foetal period (9 weeks onwards): risks for growth, function and physiological changes

Question 2

What is the duration of pregnancy?

Answer 2

280 days (40 weeks) from last menstrualperiod

Which is actually 266 days (38 weeks) from fertilisation but this is a lot harder to measure

Question 3

How do we estimate foetal age?

Answer 3

Length and ultrasound measurements of fetus

Question 4

What are the physical signs of the establishment of pregnancy? [6]

Answer 4

1. cessation of menstruation
2. morning sickness (this has some impact on maternal nutrition)
3. Increased 􏰀frequency of urination
4. 􏰀􏰁Increased size of breasts (Developing in preparation to provide nutrition after birth)
5. fatigue (due to energy use of physiological adaptations)
6. darkening of areolae

Question 5

Does the cessation of menstrual periods always mean pregnancy?

Answer 5

No

Many higher centres of the brain impact the HAO axis (eg. extreme stress can suppress ovulation and development of endometrium)

Other pathological sources can cause cessation of menstrual periods (eg. PCOS, drugs and alcohol, weight loss/gain, pituitary adenoma, thyroid, endocrine)

Question 6

What is the gold standard biochemical marker for pregnancy?

How is it measured?

Answer 6

human chorionic gonadotropin (hCG)

• Measured in the urine
• Measured as a blood test (this is definitive for pregnancy)

(beta HCG can also be secreted as a result of some cancers)

Question 7

Pregnancy adaptations occur in the mother during pregnancy, what body systems are involved and how do they change?

Answer 7

Dynamic process with maternal adaptations:

• Anatomy, physiology, biochemistry, metabolism
• Cardiovascular, blood, metabolic, renal, respiratory, endocrine

Question 8

Why are these physiological changes in the mother necessary in pregnancy?

Answer 8

• Maintain uteroplacental perfusion
• Maintain fetal demands

Question 9

What can impact or hinder the physiological changes that need to occur in the mother during pregnancy?

Answer 9

Pathological or already existing problems with these systems in the mother prior to conception (ie. chronic disease) undergo further stress during pregnancy and thus there can be failure or altered pregnancy development/adaptations

Question 10

Describe the process of implantation

Answer 10

Trophoblast cells invade into the endometrium (which is secretory and nourishes the structure and process). And allows for the boundary to be continuous.

Once the blastocyst is implanted, the endometrium is called the dicidua of pregnancy

Question 11

What are the major functions of the placenta?

Answer 11

An organ that connects the developing fetus to the uterine wall to allow nutrient uptake, waste elimination, and gas exchange via the mother’s blood supply, fight against internal infection and produce hormones to support pregnancy.

Question 12

How is the placenta connected to the mother’s blood flow?

Answer 12

• The maternal artery takes blood to the maternal side of the placenta and the maternal veins take deoxygenated blood out.

Maternal blood bathes chorionic vessels (blood lakes - for maximal efficiency in transferring blood) that become the source and drainage point for the umblical vein and artery to connect with the placenta.

• The umbilical vein carries oxygenated blood from the mother.
• Deoxygenated blood is carried back to the mother from the foetus in the 2 umbilical arteries.

Question 13

Why would the placenta structure contain the chorionic vessel/pool structure?

Answer 13

For maximal efficiency in transferring blood.

Another major reason is to prevent unwanted vessel constriction to occur to the foetus everytime there is a systemic peripheral change in maternal vasculature.

[Pathology: If invasion of placenta by the blastocyst is not appropriate then the plaecnta is exposed to peripheral vasoconstrictors then there is a problem with blood delivery to the foetus]

Question 14

The placenta acts as a substitute for foetal organs. How does it substitute for foetal lung functioning and why is this necessary?

Answer 14

The lungs are liquid filled at this point in time because the baby is free floating in the amniotic sac. They are making foetal breathing movements (practicing) but there is no air there.

Thus the placenta acts to deliver O2 and remove CO2 from the foetus

Question 15

The placenta acts as a substitute for foetal organs. How does it substitute for foetal kidney functioning and why is this necessary?

Answer 15

Amniotic fluid comes from liquid produced by foetal lungs and foetal urine.

The foetus is producing large volumes of dilute urine with amniotic fluid that is excreted into the amnioitic fluid.

It is thus important that this urine doesn’t contain waste products and toxic products normally found in urine. Thus the placenta filters out the bad stuff so it is not in the amniotic fluid

Question 16

The placenta acts as a substitute for foetal organs. How does it substitute for foetal gastrointestinal functioning and why is this necessary?

Answer 16

Swallowing amniotic fluid to facilitate gastrointestinal functioning and development.

The placenta also provides all the nutrients the baby requires

Question 17

What is the importance of the Human chorionic gonadotropin (hCG) hormone?

Answer 17

• Rescue” of corpus luteum
• Basis of pregnancy tests

hCG (not LH and FSH) maintain the corpus luteum of pregnancy. It rescues it and keeps it a functioning endocrine gland producing progesteron and oestrogen

Question 18

What is human chorionic gonadotropin (hCG) hormone?

Answer 18

A hormone produced by the cells that surround the growing human embryo (syncitiotrophoblasts - the outer layer of trophoblasts) from the implanting conceptus.

These cells will eventually go on to form the placenta.

Human chorionic gonadotrophin can be detected in the urine from 7-9 days post-fertilisation as the embryo attaches and implants in the womb

Question 19

The placenta produces Human placental lactogen (hPL)

What is this hormone responsible for?

Answer 19

Breast development and metabolic effects

Question 20

The placenta as an endocrine organ also acts as a source for two major hormones important for pregnancy. What are they and what is their significance?

Answer 20

Estrogen and progesterone

• Pregnancy maintenance
• breast development

Note: Several additional hormones are produced – maternal adaptations of pregnancy (Facilitate adaptations of mother and communications to foetus.)

Question 21

What are the 2 ways of multiple pregnancy?

Describe each one

Answer 21

Monozygotic

• genetically identical
• same sex
• single fertilised ovum (the ovum splits: started out as one individual)

Dizygotic

• 2 oocytes ovulated and fertilised by 2 separate sperm
• two completely separate individuals that are the same as being regular brothers/sisters

Question 22

What are the four major steps in partuition?

Describe them

Answer 22

1. Prior to labor
   
   • Maturation of fetal organs
   • Softening of the cervix (normally long thick and closed)
2. Labor
   
   • Rhythmic uterine contractions
   • Once initiated sustained by positive feedback -no way of stopping it once it starts; always leads to delivery
   • Cervical dilation
3. Delivery of the baby
4. Placental release and expulsion
   
   • Important to avoid haemorrhage of the mother

Question 23

What causes the onset of labour?

Answer 23

The Trigger complex & unknown

• Corticotrophin releasing hormone CRH
• Fetus
• Placenta role
• Stretch of cervix stimulus (eg. impact or baby’s head or breeching)

Question 24

What hormone is heavily involved in labour?

Describe this

Answer 24

Oxytocin released from the posterior pituitary

Stretch increases the levels of oxytocin which causes release of 􏰀prostaglandin release that causes contractions of the myometrium of the uterus to aid in labour and partiuition.

A Positive feedback loop (uterine contractions then induce stretch to induce more oxytocin release)

Question 25

How does the amount of amniotic fluid contained in the placenta affect the baby?

Answer 25

Important for lung and GIT growth and positioning of the baby

Question 26

What is placenta previa?

Answer 26

When the placenta is sitting on top of the cervix (where the baby is supposed to travel through in birth)

Ie. the placenta has implanted at the bottom of the uterus, over the cervix, and the baby can’t be born vaginally. Once the baby is old enough to be delivered, a caesarean section is usually performed.

Question 27

Compare and contrast mammary gland development:

• Puberty
• Early pregnany
• Late pregnancy

Answer 27

Puberty

Estrogen stimulates grow of ducts and fat deposition

Pregnancy
Estrogen, growth hormone and cortisol stimulate further gland development (architecture is preparing to be able to produce milk but no production yet)

Late pregnancy

Progesterone stimulates conversion of ducts to secretory epithelium to produce milk

Question 28

Breast milk is full of nutrients. What is the source of this?

Answer 28

Nutrients are extracted from the mother’s circulation to form milk

Question 29

Lactation doesn’t occur before birth of the baby but there is the architecture there to enable milk production.

What is the halting signal that is preventing milk production at this stage?

Answer 29

Prolactin‐inhibiting hormone (PIH) blocks prolactin. High levels of sex steroids (like oestrogen and progesterone that are high to support the placenta) also suppress milk production

Question 30

What is the switch that happens after birth to enable milk production?

Answer 30

High prolactin (overrides the PIH) & low estrogen (due to delivery of the placenta) lead to 􏰃lactation

Breast milk = nutrients + immunity

Question 31

Describe how suckling impacts lactation [3]

Answer 31

Suckling provides mechanical stimuli that Inhibits PIH, this enables prolactin to stimulate milk production

Suckling also provides the stimuli to increase levels of oxytocin from the posterior pituitary to stimulate “let‐down reflex”; milk ejection - ie. the contraction of myoepithelial cells

Suckling also inhibits GnRH (which inhibits LH and FSH) to act as a natural contraceptive to ensure no baby is fertilised during the energy demanding lactation phase.

Only works if exclusively and regularly breast feeding

Question 32

How can stress impact the lactation process?

Answer 32

Stress can have a negative impact on pituitary gland and suppresss lactation

Question 33

Draw the hormone axis for lactation

Answer 33

Question 34

Suckling during a feed produces the stimuli for milk production (prolactin hormone).

Is this milk used straight away or is it stored?

Answer 34

Milk ejection delivers milk to the baby and the milk secretion is making the milk for the next feed. Alveoli are already filled with milk from last feed. That is why regularity of breast feeding is important

Question 35

What are the benefits of lactation?

Answer 35

Nutrition, immunity (antibodies) protect the infant, bonding, maternal health (and returning to pre-pregnancy health)