Fertilisation & Embrology

Question 1

Define embryo

Answer 1

From implantation until 8 weeks gestation

Question 2

The placenta is fully formed at week

Answer 2

week 10

Question 3

The fetus is fully formed at how many weeks?

Answer 3

29 weeks

Question 4

Define fetus

Answer 4

From 8-40 weeks gestation

Question 5

Meconium forms in the fetal gut from weeks

Answer 5

13-16 weeks

Question 6

The fetus begins to swallow amniotic fluid and pass urine from weeks

Answer 6

8-12 weeks

Question 7

What is ECTOPIC PREGNANCIES?

Answer 7

is when the fertilised ovum implants itself outside of the uterus e.g: the fallopian tube. This is more likely in pelvic infections / STD and it damages the cilia → if the zygote is not removed it can cause pain in the shoulder and cilia may burst so women may lose part of the fallopian tubes.

Question 8

Fertilisation

Answer 8

Each month in the menstrual cycle, females produce 1 egg per ovary. The egg develops on day 14 → ovulation and its when women can get pregnant.
Sperm travels in the fallopian tube and is where fertilisation occurs (specifically in the ampulla) → fertilization can only occur if the male has a high sperm count.

Fertilisation is more likely to happen when intercourse takes place more than 48 hours before or 24 hours after ovulation

uring the onset of fertilisation, the DNA in the nucleus of the spermatozoa is released which triggers the final meiotic division by the female chromosomes.
Two sets of female chromosome is created which then only one joins with the male chromosome → CREATING 46 CHROMOSOMES AND IS NOW CALLED A ZYGOTE.

The zygote moves along the fallopian tube for 3-5 days and meiotic cell division takes place.
The zygote is still contained in the zona pellucida while its dividing to prevent adhering to the mucosa of the uterine tubes and being recognised and rejected by the maternal immune system
Eventually ZYGOTE → MORULA (undifferentiated cells).
MORULA → BLASTOCYST
CELLS SPECIALISATION BEGINS.

Question 9

What can be mistaken as menstruation?

Answer 9

Implantation bleed can occur from the vagina

Question 10

How does chronic villi aid implantation?

Answer 10

Small finger-like projections (chorionic villi) develop around the entire blastocyst that aids implantation.
Some chorionic villi will continue to develop into the mature placenta while the remainder will from the chorionic membrane which lines the uterus.

Question 11

When is fertilisation completed?

Answer 11

Fertilisation is completed around the 11th day.

Question 12

What is decidua ?

Answer 12

Endometrium is known as DECIDUA
Influence of the high levels of hormones, decidua thickens and nourishes the blastocyst during the pregnancy.
The area in which the blastocyst implants heals and covers over.
The portion beneath the embedded blastocyst becomes the decidua basalis
Decidua capsularis is the portion that covers the blastocyst.

Question 13

How are miscarriages caused?

Answer 13

Clotting disorders can create miscarriage as the blastocyst can’t attach to the
if women are diagnosed with clotting disorders they are given aspirin.
Or a miscarriage can just be that the embryo has a genetic disorder

The blastocyst implants itself near the fundus anterior

Question 14

What happens once the embryo is embedded?

Answer 14

Once blastocyst has become embedded → EMBRYO (developing mass of cells from implantation until 8 weeks gestation).

Question 15

Explain the rapid development of embryo?

Answer 15

Formation of two enclosed cavities:
The amniotic sac: is filled with fluid that will eventually surround the embryo.

Yolk sac: provides nourishment for the trophoblast.

The embryo develops between these two sacs called the embryo disc and three layers develop in this region:

Ectoderm: the layer closest to the amniotic sac and will form the skin and the CNS of the embryo.

Mesoderm: the central layer in which bones, muscles, heart, blood vessels and internal organs including the kidneys will form.

Endoderm: the layer closest to the yolk sac with form the digestive and respiratory system as well as the glands and mucous membranes.

Question 16

In terms of the embryo what happens between day 13 - 21?

Answer 16

Day 13: Chorionic villi begin to secrete human chorionic gonadotrophin (hCG) and stimulates the corpus luteum to continue producing the hormones necessary. → this is done until the placenta is mature enough to take over.

Day 15: Cells specialisation begins

Days 18-21: The nervous system begins to fold in position and the heart starts to twitch.

Question 17

In terms of the embyo what happens between week 3 - week 12

Answer 17

Week 3: Heart begins to pump blood and the brain divides.
Week 5: Umbilical cord is formed.
Facial features such as the eyes start to develop.
Week 8: Hands and feet are now well formed
By the end of the week all the body system and organs are formed. EMBRYO → FETUS
Week 10: The placenta is fully formed.
Week 12:
FIRST SCAN

Question 18

fetal development?

Answer 18

Extends from the 8th week of gestation until birth.

Weeks 8-12:
Teeth form in gums and fingernails can be seen.
Intestines become established in the abdominal cavity and the fetus begins to swallow amniotic fluid.
Fetus is able to pass urine.
External genitalia differentiates

Week 13-16:
Facial features migrate to the correct position and the face is identifiable as human.
Muscle and bones develop
Meconium begins to form.

Week 17-24:
Fetal heartbeat can be heard
Mother begins to feel movement
Lungs are well formed

Week 29:
The fetus is fully formed and the organs are able to function to some extent. For the remainder of the pregnancy, organs mature and the fetus continues to lay down fat and muscle.