12. Physiology of pregnancy

Question 1

What are the stages of pregnancy?

Answer 1

• Early pregnancy phase (1-2w) - Embryonic phase (2-8 weeks) - Fetus phase

Question 2

What occurs in the early pregnancy phase?

Answer 2

• Dividing zygote - Formation of blastocysts - Implantation - Endometrium is prepared and has become secretory, so that blastocytst can embed into it. ○ This triggers endocrine events that prevent the next ovulation ○ We suspend menstrual cycles via the conversion of corpus luteum to the corpus luteum of pregnancy. - Not susceptible to teratogen

Question 3

What occurs in the embryonic phase? (2w - 8)

Answer 3

• Organ system developing The red line indicate the major susceptibility point for each organ system, is there is a major effect you can have a major morphological abnormality. - Susceptible to teratogens

Question 4

What occurs in the Fetus phase? (8w +)

Answer 4

• Maturation of all organ systems - Still tiny! ○ At weeks 6 woman has just missed her first menstrual period, if she is not certain of her cycles she may not know she is pregnant until this point. - Any issues can result in functional deficit, organs not functional to the highest capability

Question 5

What is the normal duration of pregnancy?

Answer 5

• 280 days (40w) from last menstrual period or 38w from fertilisation.

Question 6

What are the physical signs of pregnancy?

Answer 6

• Cessation of menstruation (CL of pregnancy release oestrogen and progesteron) - Morning sickness - Inc frequency of urination (pressure against bladder + progesterone can increase urination) - Inc breast size - Fatigue - Darkening of areolae

Question 7

What test is done to determine pregnancy?

Answer 7

• Human chorionic gonadotropin (hCG) produced from the trophoblast detectible in blood and urine. - Highly reliable

Question 8

What are the adaptations required to maintain utero-placental perfusion & fetal demands?

Answer 8

• Anatomical, physiology, biochemistry, metabolism - Cardiovascular, blood, metabolic, renal, respiratory, endocrine

Question 9

Describe the process of implantation of Blastocysts into the placenta

Answer 9

Invading trophoblasts burrows into the endometrium and blastocytst
- Inner cell mass becomes the fetus
Tropoblast becomes the placenta

Question 10

What is the function of the placenta?

Answer 10

1. A major site of fluid transfer
2. Regulation of uroplacentral blood flow
3. Protects the vascular exchange
4. Substrutures for fetal organs
   
   1. Lungs
   2. Kidneys
   3. GI

Question 11

How is the placenta formed?

Answer 11

When trophoblast invade endometrium, it actually breaks down the blood vessels in the mother’s uterine arteries and arterioles to end up with blood lakes.

When the mother is exposed to vasoactive and vasocontricting agents we don’t want unique vasculature to construct (exercise, stress etc).

Maternal oxygenated blood comes in the blood lakes and the fetal capillaries pick up the nutrients and oxygen taking it through the to umbilical veins and into the fetus. This is how the fetus gets all the oxygen and nutrients.

Question 12

What are the Endocrine organ of pregnancy?

Answer 12

The placenta is an endocrine organ.
- Human chorionic gonadotropin (hCG)
○ Rescues corpus luteum
- Human placental lactogen (hPL)
○ Breast development, metabolic effects
- Estrogen and progesterone
○ Pregnancy maintenance and breast development
- Other factors = GH, CRH, ACTh

Question 13

How can you tell if twins are monozygotic or dizygotic before birth?

Answer 13

• Can see if they’ve implanted together
• Can share amniotic sack & placenta (clearly monozygotic)
• If divide early and implant at different sites wouldn’t know if monozygotic or dizygotic

Question 14

What is the process of parturition/birth?

Answer 14

• Prior to labor
  
  • Maturation of fetal organs (driven by hormone cortisol)
  • Softening of the cervix
• Labor
  
  • Rythmic uterine contraction
  • Once initiate sustained by positive feedback
  • Cervical dilation
• Delivery
• Placental release and expulsion

Question 15

What are the regulators of Parturition?

Answer 15

• Largely unknown trigger
• Corticotrophin releasing hormone; fetus; placenta role
• Stretch of cervix stimulates Uterine contraction and Oxytocin release

Question 16

Why is the head position important during birth?

Answer 16

Head down on cervix allows for cervical pressure and positive influence. If its bottom first you don’t get pressure so you need cesarean section because cervix doesn’t dilate sufficiently

Question 17

What is the role of Oxytoxin remaining after ejection of placenta?

Answer 17

Acts to contract the uterus to regain its original size

Question 18

What are the stages of mammary gland development?

Answer 18

• Puberty
  
  • Estrogen stimualte growth of ducts and fat desposition
• Pregnancy
  
  • Estrogen, GH and cortisol stimulate further gland development
• Late pregnancy
  
  • Progesterone stimulate conversion of ducts to secretory epithelium

Question 19

What are the stages of lactation?

Answer 19

• Before birth
  
  • Prolactin-inhibiting hormone (PIH) blocks prolactin
  • High sex steroid levels suppress milk production
• After birth
  
  • High prolactin & low estrogen –> lactation
  • Breast milk = nutrition + immunity
• SUckling
  
  • Inhibits PIH
  • Prolactin stimulates milk production
  • Oxytocin stimulate “let-down reflex” milk ejection
  • Inhibits GnRH and ovarian