Pregnancy

Question 1

Describe the hormonal changes during pregnancy

Answer 1

• Thoughout pregnancy oestrogen and progesterone continually increase (in first two months supplied by corpus lutenum, then trophoblasts secrete more after death of CL)
• Oestrogen stimulates the growth of muscle mass - this is eventually supplies the contractile force needed to deliver the featus
• Human chorionic gonadotrophin rises and reaches peak at 60-80 days, then decreases rapidly

Question 2

What is the effect of estrogen during pregnancy?

Answer 2

-Oestrogen stimulates the growth of muscle mass - this is eventually supplies the contractile force needed to deliver the featus

Question 3

What is the effect of progestrogen during pregnancy?

Answer 3

-Progesterone inhibits uterine contractility so that the fetus is not expelled prematurely

Question 4

What secretes human chorionic gonadotrophin (hCG) What is its role in pregnancy?

Answer 4

• hCG is secreted by trophoblast cells
• hCG is the hormone that allows the corpus luteum to persist
• hCG is detected in pregnancy test
• Stimulates steroid secretion from maternal ovaries
• reaches a peak at 60-80 days after last menstruation, it then decreases rapidly
• at 3 months reaches very low levels and corpus lutenum regresses

Question 5

What do the mother’s ovaries and adrenal glands supply to the placenta?

Answer 5

Supplies androgens to placenta so that progesterone can be synthesized and secreted.

Question 6

Describe placenta formation

Answer 6

1. Placenta forms after a few weeks, supplied by chorion (outermost layer of trophoblast cells), the maternal section is underlying and is from the endometrium
2. Chronic vili extend from the chorion to endometrium
3. Villi contain rich network of capillaries
4. Enzymes are other paracrine molecules are secreted so that each vili is surrounded by a sinus of maternal blood supplied by maternal arterioles
5. Maternal blood enters via uterine artery, blood then flows through the sinuses and exits via the uterine veins
6. Simultaneously blood flows from featus into capillaries of the chorionic vilia via umbilical arteries and out of the capillaries back to the featus via umbilical vein
7. All of these vessels are contained in the umbilical cord
8. Five weeks after implantation the placenta is well established - the fetal heart begins to pump blood and nutrition and excretion of waste is transported and supplied via the placenta

Question 7

How are molecules transported across placenta?

1. O2 and CO2
2. Glucose
3. (Amino acids and hormones)

Answer 7

1. Diffusion
2. Transport membranes
3. Some aminoacids and hormones are produced by the trophoblast layer and added to featal and maternal blood

There is NO mixing of blood.

Question 8

What do umbilical veins carry?

Answer 8

Carry O2 and nutrient rich blood to featus from the placenta

Question 9

What do umbilical arteries carry?

Answer 9

blood with waste products and low O2 to the placenta

Question 10

What is the function of amniotic fluid?

Answer 10

Amniotic fluid - resembles fetal ECF and buffers mechanical disturbance and temp variations (this is the fluid that is tested during amniocentesis)

Question 11

How does the amnotic cavity form?

Answer 11

Forms between the inner cell mass and chorion, the epithelial layer lining the cavity is derived from the inner cell mass and is called the amnion or amniotic sac
It eventually fuses with the inner surface or chorion so only a single combined membrane surrounds the featus

Question 12

What is tested in chorionic villus sampling?

Answer 12

Obtain tissue from a chronic villus of the placenta, this is then tested
(higher risk of miscarriage than amniocentesis)

Question 13

Describe the process of fertilisation from egg transport to ejaculation and capacitation

Answer 13

Egg transport

1. At ovulation the egg is extruded on ovary surface
2. The fimbriae pass over ovary and the cilia beat in waves towards the interior of duct
3. This sweeps the egg into the fallopian tube
4. The cilia of the fallopian tube drive egg movement (very slow)

Ejaculation

1. The sperm enters the uterus, this is dependent on mucus consistency
2. Sperm propulsions and uterine contractions propel sperm into fallopian tubes

Capacitation

1. The sperm is affected by secretions in the female reproductive tract this means that
   a) perviously wave-like motion of tail is replaced by a more whip-like motion that propels the sperm forward in strong surges
   b) sperm plasma membrane is altered so it can fuse with egg surface membrane

Fertilzation

1. Occurs in fallopian tube a few hours after ovulation
2. Sperm undergoes acrosomal reaction, this digests a pthway through zona pellucida
3. Cortical reaction occurs when sperm enters the egg to prevent polyspermy
4. Sperm is drawn into egg and the egg undergoes 2nd meiotic division
5. Nuclei of sperm and egg unite and egg enzymes are activated
6. Zygote undergoes embryogenesis (Pronuclei migrate to centre, DNA replicates, membrane breaks down, mitotic division, fertilization is complete)

Question 14

What hormones do trophoblast cells secrete?

Answer 14

• hCG
• Inhibin
• Human placental lactogen

Question 15

What is human placental lactogen?

Answer 15

• Similar to prolactin and growth hormone
• mobilizes fats from maternal adipose tissue and stimulates glucose production in the liver
• also stimulates lactation in breast development

Question 16

Describe what occurs in parturition

Answer 16

Parturition occurs in the last few weeks, delivery of baby and placenta

1. In the last few weeks ever increasing levels of estogen results in smooth muscles synthesizing connexins
2. Connexins are proteins that form gap junctions between smooth muscle cells so myometrium can undergo contractions
3. Simultaneously the cervix becomes soft and flexible due to enzymatically mediated breakdown of collagen fibres (estrogen stimulates synthesis of enzymes)
4. Weak infrequent contractions begin at 30wks, these gradually increase in frequency and strength
5. In the last month the entire uterine contents shifts downwards so that the featus is in contact with the cervix
6. Amnotic sac rupture and fluids flow through vagina
7. Contractions occur at 10-15 min intervals, they begin in the upper portion of uterus and sweep down
8. The cervix is forced open - dilates to 10cm 4inch
9. Contractions move the featus out of the uterus, then cervix and vagina
10. The mother adds to uterine contractions to deliver the baby
11. Placental vessels constrict and placeta becomes separated from underlying uterine wall
12. Wall of uterine contractions deliver the placenta as after birth

Question 17

What is the role of relaxin? What is it secreted by?

Answer 17

Relaxin

• secreted by ovaries, placenta and uterus
• softens cartilaginous joints in pelvis

Question 18

What is the role of oxytocin? What is it secreted by?

Answer 18

• Oxytocin is a strong stimulator of uterine smooth muscle contraction
• Produced by posterior pituitary gland
• Oestrogen induces synthesis of receptors

Question 19

Lactogenesis

Answer 19

1. During late pregnancy the mammary glands undergo an increase in size and cell number
2. At birth milk is produced and secreted (lactation)
3. Each breast contains numerous mammary glands, each with ducts that branch through the tissue and converge at the nipple
4. Alveoli - site of milk secretion
5. The alveoli and ducts are surrounded by myoepithelial cells (contractile cells)

Question 20

What hormones affects the breasts during pregnancy?

Answer 20

Oestrogen, progesterone, prolactin, human placental lactogen

• dopamine (hypothalamus) inhibits prolactin secretion (ant. pit. gland)
• Prolactin releasing factor (PRF-hypothalamus) stimulates prolactin
• large amounts of progesterone and oestrogen inhibit action of prolactin to induce milk production (delivery removes placenta and therefore source of hormones, so production is no longer inhibited)

All secreted from the placenta except prolactin (from maternal anterior pit. gland)

Question 21

What controls parturition?

Answer 21

1. Smooth muscle cells - autonomous contraction
2. Pregnant uterus secretes PGE2 and PGF 2alpha - this stimulates uterine smooth muscle contraction
3. Oxytocin - uterine muscle stimulant (also synthesizes PGE2 and PGF 2 alpha)
4. (progesterone secretion inhibits the contraction until delivery, however conc does not always decrease)

Question 22

What is the milk ejection reflex? - milk let down

Answer 22

This is the movement of milk to the alveoli and ducts

• Occurs due to the contraction of myoepithelial cells
• Controlled by oxytoxin - this is released in response of nipple mechanoreceptor stimulation and higher brain centres
• suckling also prevents ovulation, this “natural birth control” is not always effective

Question 23

What occurs during suckling to cause milk ejection and milk synthesis?

Answer 23

Suckling leads to;

1a) Decrease in dopamine in hypothalamus (increase in PRF?)
b) increased prolactin secretion from anterior pituitary
c) stimulates the gland cells in the breasts to increase milk synthesis

2a) Posterior pit increases oxytocin release
b) contraction of myoepithelial cells
c) Milk ejection

Question 24

What is in maternal milk?

Answer 24

• Water, proteins, lipids, lactose, minerals, vitamins
• antibodies, leukocytes and other components of immune system
• growth factors and hormones
• neuropeptides and endogenous opioids (may shape infants brain and behaviour)

Question 25

Why can babies accept milk proteins?

Answer 25

1. Low acidity - so proteins are not denatured
2. More permeable intestinal epithelium - so milk proteins can gain entry
   AIDS and drugs can be transported though breast milk, alcohol conc in maternal plasma ≃ breast milk

(this is in first 6 - 12 months)

Question 26

What happens during each nursing period to sustain lactation?

Answer 26

During each nursing period large secretary bursts of prolactin occur - these cease several days after mother stops nursing infant