Lecture 13

Question 1

What are the key features of the placenta? What does it do and what are its main roles?

Answer 1

Placenta is developed during pregnancy. Takes over production of steroid/peptide hormones needed for fetal development and uterine support. Metabolizes hormones from the mother to protect the fetus. Major role in coordinating the pituitary-adrenocortical axis. Acts as a go-between to transport nutrients between the woman and fetus. Autocrine/paracrine functions allow for growth and differentiation of the placenta.

Question 2

What are the time scales of sperm cells moving through the female reproductive system during ovulation?

Answer 2

Sperm cells take 1-3 minutes after ejaculation to pass through vaginal wall into cervix. Take 10-20 minutes to reach uterus. Take 30-60 minutes to reach upper ends of fallopian tube to interact with egg.

Question 3

How are the egg cells moved from the ovaries to the uterus?

Answer 3

Egg is released from ovaries. Fallopian tube captures and wafts egg towards the uterus for potential implantation.

Question 4

What is the zone of pellucida?

Answer 4

The zone of pellucida is a glycoprotein wall found around oocytes. It must be penetrated by sperm to allow sperm to release its nuclear material and enable the oocyte to undergo divisions to develop into a blastocyst.

Question 5

How long does it take for the oocyte to begin growing?

Answer 5

It takes a few days for the fertilized egg to start growing, dividing, and replicating as it slowly travels along the fallopian tube.

Question 6

What does the egg cell become when it reaches the uterus?

Answer 6

The egg cell should have developed into a morula (16-cell stage), almost at the blastocyst stage.

Question 7

What does the fertilized egg cell become to be implanted into the uterus?

Answer 7

It becomes a blastocyst (16 cells or more).

Question 8

What do blastocysts do?

Answer 8

Cells surrounding the blastocyst produce hCG, which induces changes in the uterine lining to support implantation. Blastocyst also induces changes in the uterine lining to make it more receptive to implantation.

Question 9

What are the 2 key gonadotropins in the menstrual cycle?

Answer 9

LH (Luteinizing Hormone), FSH (Follicle-Stimulating Hormone).

Question 10

What happens to the levels of progesterone between day 14 and day 28 of the menstrual cycle?

Answer 10

Progesterone increases as the corpus luteum (CL) develops. The CL takes over progesterone production for 14 days to prepare the uterus for implantation. If there is no implantation, CL regresses to corpus albicans and progesterone levels drop.

Question 11

What is the key difference between a menstrual cycle with unsuccessful implantation of a blastocyst and successful implantation?

Answer 11

In successful implantation, hCG is produced instead of shedding the uterine lining.

Question 12

What does hCG do?

Answer 12

hCG stabilizes the corpus luteum, preventing it from regressing. This ensures continuous progesterone production to maintain the uterine lining for implantation. hCG maintains the corpus luteum and prevents shedding of the uterine lining.

Question 13

Where are oestrogen receptors found?

Answer 13

Oestrogen receptors are found throughout the body, including the brain, where they regulate food intake.

Question 14

How many key forms of oestrogen are there? Why?

Answer 14

Four. Different tissues produce different forms of oestrogen, leading to variations in the types produced.

Question 15

What is the key form of oestrogen produced in the ovaries?

Answer 15

The main form of oestrogen produced by developing follicles in the ovaries is oestradiol.

Question 16

What can happen to the form of oestrogen produced as pregnancy progresses?

Answer 16

As pregnancy progresses, the form of oestrogen may shift from oestradiol to estrone, affecting receptor activation and downstream effects.

Question 17

What is the structure of the oestrogen receptor?

Answer 17

Two isoforms: alpha and beta. The receptor has variable amino-terminal domains (A/B), a central DNA-binding domain (C), a hinge region (D), and a ligand-binding domain (E). The receptor can form dimers even without a ligand, but ligand binding causes conformational changes.

Question 18

What are some of the symptoms of knocking out the alpha form of the oestrogen receptor? What role does this show the alpha form having?

Answer 18

Symptoms include obesity, poor mammary development, small uterus, and anovulation. The alpha form is involved in energy balance, breast and uterine maturation, and ovulation.

Question 19

What are some of the symptoms of knocking out the beta form of the oestrogen receptor?

Answer 19

Symptoms include lean body composition, incomplete mammary gland differentiation during lactation, poor cell-cell interactions, poor placental differentiation, uterine hypersensitivity, and reduced ovulation.

Question 20

What is luteinisation?

Answer 20

Luteinisation is the process by which a ruptured follicle develops into the corpus luteum, which becomes a progesterone-secreting organ.

Question 21

What are the physiological actions of progesterone in the ovaries?

Answer 21

Progesterone plays a role in ovulation and luteinisation.

Question 22

Where can progesterone receptors be found?

Answer 22

Progesterone receptors are found in the ovaries, uterus/endometrium, brain/CNS, and bones.

Question 23

What are the physiological actions of progesterone in the uterus/endometrium?

Answer 23

Progesterone promotes proliferation, differentiation, implantation, and myometrium quiescence, which prevents contractions during pregnancy.

Question 24

What are the physiological actions of progesterone in the brain/CNS?

Answer 24

Progesterone affects the HPA axis and sexual behavior.

Question 25

What are the physiological actions of progesterone in the bone?

Answer 25

Progesterone increases bone formation by stimulating osteoblastic growth.

Question 26

What is a key function of progesterone?

Answer 26

Progesterone drives breast tissue development.

Question 27

What happens to your breast tissue during pregnancy?

Answer 27

Progesterone induces side branching of ducts and alveolar cell development for milk production, which occurs more intensively during lactation.

Question 28

What happens to your breast tissue after lactation?

Answer 28

After lactation ends, breast tissue involutes and returns to the mature "young adulthood" state.

Question 29

How do we know that progesterone is involved in the development of mammary glands?

Answer 29

Knockout of progesterone receptors leads to a lack of side branching and alveolar cells, proving progesterone's involvement in mammary gland development.

Question 30

How many isoforms of the progesterone receptor are there?

Answer 30

Two isoforms: alpha and beta.

Question 31

What happens when the alpha isoform of the progesterone receptor is knocked out?

Answer 31

Knockout results in severely impaired ovulation, impaired implantation, decidualisation, and infertility.

Question 32

What happens when the beta isoform of the progesterone receptor is knocked out?

Answer 32

Knockout results in reduced mammary ductal morphogenesis and reduced mammary gland development.

Question 33

What is the classical pathway for progesterone action?

Answer 33

The classical pathway involves progesterone acting as a nuclear transcription factor.

Question 34

What is the non-classical pathway for progesterone action?

Answer 34

In the non-classical pathway, progesterone acts via membrane-bound receptors, triggering intracellular signaling cascades (e.g., cAMP and MAPK pathways).

Question 35

Ultimately, what happens after the 2 routes of progesterone action?

Answer 35

Both pathways affect transcriptional changes.

Question 36

What is decidualisation?

Answer 36

Decidualisation is the process by which cells lining the uterus change to create favorable conditions for implantation.

Question 37

What does decidualisation do?

Answer 37

It helps make the uterus more receptive to genetically stable embryos, promotes nutrient-rich conditions, and suppresses uterine natural killer cells to prevent rejection.

Question 38

What is prolactin?

Answer 38

Prolactin is a marker for decidualisation and is produced after cells in the uterus begin to support implantation.

Question 39

What occurs during decidualisation and how does this help select for optimum embryos?

Answer 39

Haemostasis, immunomodulation, and oxidative stress defenses occur to create a favorable environment for embryo development and prevent rejection of genetically unstable embryos.

Question 40

What does decidualisation require and how do we know this?

Answer 40

Decidualisation requires the activation of two convergent pathways (via progesterone receptors and cAMP). When both pathways are activated, prolactin secretion significantly increases.

Question 41

What drives the shift from the regression of the corpus luteum in the menstrual cycle to the maintenance of the corpus luteum during pregnancy?

Answer 41

hCG, produced by trophoblasts during implantation, maintains the corpus luteum, supporting continued progesterone and estrogen production during pregnancy.

Question 42

What is hCG?

Answer 42

hCG is human chorionic gonadotropin, produced by trophoblasts to support pregnancy.

Question 43

Where are trophoblasts found?

Answer 43

Trophoblasts are found around the blastocyst and help with implantation and hCG secretion.

Question 44

What happens to the hCG levels during pregnancy?

Answer 44

hCG levels surge after implantation (around 4 weeks), peak between weeks 8-12, and then stabilize at lower levels after week 16.

Question 45

What happens to the source of hCG during pregnancy? What is the purpose of this?

Answer 45

Initially, hCG is secreted by trophoblasts. As trophoblast secretion decreases, the placenta takes over hCG production, which ensures the continuation of hormone production necessary to sustain pregnancy.

Question 46

What takes over from trophoblasts in hCG production?

Answer 46

The placenta takes over hCG production as trophoblast secretion decreases.

Question 47

How is the blood supply in a fetus different in the amniotic fluid to when it is born?

Answer 47

Fetal blood is oxygenated by the mother, bypassing the lungs and partially bypassing the liver. The ductus venosus allows blood to bypass the liver.

Question 48

How does fetal blood bypass the respiratory circulation and why?

Answer 48

Blood passes through the foramen ovale from the right atrium to the left atrium, bypassing the right ventricle and lungs. This allows oxygenated blood to be delivered to the body.

Question 49

What is the structure of the blood system in the placenta and how does this allow contact between the mother and fetus?

Answer 49

Maternal blood enters via arterial flow into pools surrounded by chorionic villi. The villi contain fetal capillaries, allowing nutrient and gas exchange between maternal and fetal blood.

Question 50

Which hormone is secreted from the mother and is key in fetal development?

Answer 50

Cortisol is key in fetal development.

Question 51

What effect does cortisol have on the developing fetus?

Answer 51

Cortisol helps develop the fetal adrenal glands and impacts the pituitary and HPA axis development, which is crucial for the growth and function of secretory organs.

Question 52

What can pass through the wall of the amniotic sac and what does this allow?

Answer 52

Prostaglandins can pass through the amniotic sac wall, allowing local effects on uterine contractions and influencing the myometrium during labor.