Fertilization and development L4

Question 1

What are 4 things that happen to sperm during sexual reproduction?

Answer 1

• Several hundred million sperm released into vagina per ejaculation
• Many sperm destroyed by vaginal acidity
• Sperm then travel up vagina through cervix
  → into uterus→ into oviduct
• Only a few dozen to a few hundred sperm
  survive to reach egg

Question 2

Where does fertilization happen?

Answer 2

Usually occurs in single oviduct (fallopian tube)

Question 3

How does fertilization happen?

Answer 3

head of one sperm cell penetrates egg plasma membrane - triggers completion of meiosis II in egg - sperm nucleus (n=23) and egg nucleus (n=23) fuse - formation of zygote (2n=46)

Question 4

When does the zygote go through it’s first miotic division?

Answer 4

Within 30 h of fertilization as it travels down
oviduct
* From 2 cells - 4 cells - 8 cells, zygote remains relatively same size

Question 5

What is the morula?

Answer 5

(16 cells) reaches uterus 3-5 days after
fertilization

Question 6

How is the blastocyst formed?

Answer 6

Morula fills with uterine fluid and two different groups of cells form a sphere called a blastocyst

Question 7

What are the two groups of cells that form the blastocyst and what do they do?

Answer 7

• Inner blastocyst cells - become embryo
• Outer cells (aka trophoblast) - become chorion (eventually forms placenta)

Question 8

What does the chorion of the blastocyst secrete?

Answer 8

Human chorionic gonadotropic hormone (hCG)

Question 9

Why does hCG get secreted by the chorion?

Answer 9

To maintain corpus luteum - maintains levels of progesterone and estrogen to maintain
endometrium

• hCG used in pregnancy tests

Question 10

When and how does gastrulation occur?

Answer 10

• During second week, blastocyst forms 3
  primary germ layers (meso-, ecto-, endo-
  derm)
• Developing embryo now called gastrula

Question 11

What is morphogenesis and when does it occur?

Answer 11

Differentiation = cell specialization
- Starts during gastrulation

Question 12

What happens during weeks 3-8?

Answer 12

Neurulation: organs form from primary germ layers (but are not fully functional!)

Question 13

What happens to the ectoderm, mesoderm, and endoderm during weeks 3-8?

Answer 13

• ectoderm: nervous system, epidermis
• mesoderm: skeleton, muscles,reproductive structures, RBCs
• endoderm: lining of the digestive and respiratory systems (pancreas/liver, etc), endocrine glands

Question 14

What are three supportive structures?

Answer 14

• Amnion
• Chorion
• Allantois

Question 15

What does the amnion do?

Answer 15

Forms fluid filled sac (amniotic sac) -
insulation and protection against dehydration, impact, infection, temp. changes etc.

Question 16

What does the chorion do?

Answer 16

chorionic villi invade endometrium -
Allows for transfer of nutrients/waste between maternal blood and fetal blood; becomes placenta

Question 17

What is the allantois?

Answer 17

Initial source of nutrients in first 5 weeks - forms umbilical cord

Question 18

What are the stages of fetal development?

Answer 18

• Fertilization
• Cleavage process
• Morula
• Blastocyst
• Implantation
• Gastrulation
• Neurulation and organ formation