Fertilization

Question 1

How long is the female reproductive cycle?

Answer 1

about 28 days

Question 2

Days 1-14 of female reproductive cycle

Answer 2

FSH –> Estrogen –> Proliferative

Question 3

Days 15 - 28 of female reproductive cycle

Answer 3

LH –> Progesterone –> Secretory
- increase in vascular supply to endometrium

Question 4

What disrupts the female reproductive cycle?

Answer 4

• pregnancy = causes hormones to keep going, endo stays, increase progesterone

Question 5

What causes women to feel sick when pregnant?

Answer 5

progesterone

Question 6

Gametogenesis

Answer 6

• meiosis (splitting in half)
• sperm/oocyte become haploid

Question 7

What happens on Day 14?

Answer 7

• ovulation
• increasing progesterone

Question 8

What happens on Days 15-16?

Answer 8

• fertiliization
• happens in ampulla of tube
• sperm penetrates zona pellucida

Question 9

What does the zona pellucida do?

Answer 9

allows only 1 sperm to fertilize egg

Question 10

Once fertilization occurs, what does the ovum become?

Answer 10

• a zygote
• restores # of chromosomes to diploid (now 23 pairs)

Question 11

Basic embryology after fertilization

Answer 11

• fertilization = unicellular embryo
• repeated mitotic divisions occur (cleavage)
• shape of blastomeres change & interact differently
• networks of blood vessels suck the sperm into the egg

Question 12

What is the result of repeated mitotic divisions (cleavage)?

Answer 12

• rapid increase in # of cells (blastomeres): 2, 4, 8, 16, 32
• occurs w/in fallopian tubes

Question 13

What happens when the blastomeres change shape?

Answer 13

• 16 blastomeres = morula
• usually time for it to enter the uterus

Question 14

Process of fertilization

Answer 14

• 2-cell stage
• 4-cell stage
• 8-cell stage
• Morula
• Early blastocyst
• Later blastocyst
• Rearrangement of cells creates and inner cell mass called Blastocyst

Question 15

2-cell stage

Answer 15

polar body, zon pellucida, blastomere

Question 16

4-cell stage

Answer 16

4 blastomeres

Question 17

8-cell stage

Answer 17

has zona pellucida

Question 18

Morula

Answer 18

has zona pellucida

Question 19

Early blastocyst

Answer 19

• inner cell mass
• degenerating zona pellucida
• blastocyst cavity
• trophoblast

Question 20

Later blastocyst

Answer 20

• inner cell mass
• blastocyst cavity
• trophoblast

Question 21

Creation of blastocyst

Answer 21

• fluid filled space separates the outer layer (trophoblast) & central blastomeres (inner cell mass)
• zona pellucida is shed
• trophoblasts attach to endo, proliferate into 2 layers

Question 22

2 layers of trophoblasts

Answer 22

• cytotrophoblasts (inner)
• syncytiotrophoblasts (outer)

Question 23

Structures of a blastocyst

Answer 23

• polar body
• inner cell mass
• blastocyst cavity
• trophoblast
• remnant of zona pellucida

Question 24

Does a pregnancy stay in the blastocyst cavity?

Answer 24

No, it surrounds itself w/ endometrium

Question 25

How do syncytiotrophoblasts work?

Answer 25

implant into the endometrium by 'burrowing'

Question 26

How do trophoblasts contribute to pregnancy?

Answer 26

- become the membranes surrounding the pregnancy (Chorion) - inner cell mass becomes the embryo (baby)

Question 27

Embryology Timeline (Days)

Answer 27

- Day 15: fertilization - Day 16: mitosis-cleavage, morula - Days 19-21: blastocyst, zona pellucida shed - Days 21-28: human chorionic gonadotrophin released, implantation

Question 28

What percentage of pregnancies fail?

Answer 28

75% (most don't know they are pregnant)

Question 29

Hormones levels during fertilization/morula/blastocyst stage

Answer 29

- LH & FSH declining - progesterone increasing

Question 30

Hormone levels during implantation stage

Answer 30

- trophoblasts produce hCG - progesterone continues increasing - blastocyst must 'burrow' into endometrium

Question 31

Are menstrual & gestational the same? Why or why not?

Answer 31

- yes - duration of pregnancy based on menstrual cycle & the physiology of the components of gestation

Question 32

What is the embryological age?

Answer 32

the age since fertilization only (some books say ovulation)

Question 33

What is the gestational age?

Answer 33

- pregnancy is clinically evaluated in terms of 'weeks' - 40 weeks or 10 lunar months (28 day cycles) is considered term

Question 34

Summary of fertilization

Answer 34

- physiological extension of the female reproductive cycle - zygote formation & early embryology - pregnancy detection