Physiology of Pregnant Mother

Question 1

What are the key stages during process of implantation of the blastocyst?

Answer 1

1. Free-floating blastocyst adheres to the endometrial lining, cords of trophoblastic cells begin to penetrate the endometrium
2. Advancing cords of trophoblastic cells tunnel deeper into the endometrium, carving out a hole for the blastocyst. The boundaries between the cells in the advancing trophoblastic tissue disintegrate. Inner cell mass begins to differentiate, giving rise to start of amniotic cavity
3. When implantation is finished, the blastocyst is completely buried in the endometrium - inner cell mass continues to divide and differentiate giving rise to developing embryo

Question 2

What are some functions of the placenta?

Answer 2

• forms function of the kidneys, digestive and respiratory systems for the fetus: nutrients and O2 brought to the fetus in maternal blood are acquired by mothers digestive and respiratory systems, and waste transferred into maternal blood are eliminated by the mothers kidneys and lungs (mothers kidneys, lungs and digestive tract serves fetus needs as well as her own)
• becomes a temporary endocrine gland during pregnancy (placental hormones, maternal hormones, fetal hormones): interact to support and enhance growth and development of fetus, to coordinate timing of birth and to prepare mammary glands for nourishing baby after birth

Question 3

How can materials move across the placenta?

Answer 3

Depends upon substance:

• simple diffusion: oxygen, CO2, water, electrolytes
• glucose by facilitated diffusion
• receptor mediated endocytosis - cholesterol
• many drugs, pollutants, chemical agents and microorganisms in mothers bloodstream can cross placental barrier
• pregnant woman should be very cautious about potentially harmful exposure from any source

Question 4

What are the most important placental hormones and their function?

Answer 4

Hormones secreted by the placenta play a critical role in maintaining pregnancy:

• human chorionic gonadotrophin (hCG)
• oestrogen
• progesterone

The placenta is unique among endocrine tissues:

• transient tissue
• secretion of hormones is not subject to extrinsic control - type and rate of placental hormone secretion depend primarily on the stage of pregnancy

Question 5

What is hCG and where is it secreted?

Answer 5

Human chorionic gonadotrophin:

• peptide placental hormone that acts to prolong life span of the corpus luteum
• CL of pregnancy is an ovarian endocrine unit that grows larger and produces increasingly greater amounts of oestrogen and progesterone for 10 weeks post implantation

Question 6

Maintenance of normal pregnancy depends upon which hormones?

What do these hormones do throughout pregnancy?

What happens in the male fetus with respect to hCG?

How is hCG eliminated? What is it useful for? What is it thought to cause?

Answer 6

Maintenance of normal pregnancy depends upon high concentrations of oestrogen and progesterone

• persistence of oestrogen and progesterone maintains the thick, pulpy endometrial tissue and menstruation ceases during pregnancy
• in a male fetus, hCG stimulates precursor Leydig cells in the fetal testes to secrete testosterone, which masculinises the developing reproductive tract

Urine, pregnancy diagnostic tests detect hCG in urine as early as in the first month of pregnancy, may be underlying trigger for morning sickness

Question 7

Why doesn’t the placenta secrete oestrogen in the first place instead of secreting hCG, which in turn stimulates the corpus luteum to secrete this hormone and progesterone?

Answer 7

• the placenta does not have all the enzymes needed for oestrogen synthesis in the first trimester
• oestrogen synthesis requires a complex interaction between the placenta and the fetus

Question 8

Give some facts about secretion of progesterone:

Answer 8

• the placenta can synthesise this hormone soon after implantation
• however, the amount of progesterone produced is proportional to placental weight
• the placenta is too small in the first 10 weeks to produce enough progesterone to maintain the endometrial tissue
• the increase in circulating progesterone in the last 7 months of gestation reflects placental growth during this period

Question 9

What are the roles of oestrogen and progesterone during pregnancy?

Answer 9

• high concentrations of both hormones are required to maintain pregnancy
• both hormones secreted by CL in the 1st trimester and by the placenta in the 2nd and 3rd trimesters

Oestrogen: stimulates growth of the myometrium, increases in size throughout pregnancy, the stronger uterine musculature is needed to expel the fetus during labour

• also promotes development of mammary gland ducts, through which milk will be ejected during lactation

Question 10

What are the 3 key roles for progesterone?

Answer 10

• prevent miscarriage by suppressing contractions of the uterine myometrium
• promotes formation of mucus plug in the cervical canal to prevent vaginal contaminants from reaching the fetus
• stimulates development of milk glands in the breasts in preparation for lactation