23B: Development

Question 1

prenatal development

Answer 1

• embryonic development (0-8 weeks)

- fetal development (9 weeks-birth)

Question 2

What is gestation and what major changes occur during each trimester?

Answer 2

• gestation: time spent in uterus
• 1st trimester: major systems develop
• 2nd trimester: body shape and proportions change
• 3rd trimester: largest weight gain, fully functional

Question 3

postnatal development

Answer 3

after birth development until maturity

Question 4

Describe the process of fertilization

Answer 4

1. ovulation releases secondary oocyte
2. fertilization and oocyte activation upon fusion of sperm and oocyte membrane (becomes ovum); rise in Ca2+ ensures only one sperm fertilizes egg
3. male and female pronuclei form
4. spindle fibres appear and cleavage starts
5. male and female pronuclei fuse and cleavage of zygote begins
6. cytokinesis begins; 1st cleavage forms two blastomeres

Question 5

Describe cleavage

Answer 5

• cytoplasm of the zygote gets divided among progressively smaller blastomeres
• blastomeres -> early morula -> advanced morula -> blastocyst
• implantation of blastocyst to endometrium
• trophoblast develops
• amniotic cavity forms
• yolk sac forms

Question 6

Describe gastrulation

Answer 6

• embryonic disc and its germ layers form

- superficial cells of blastodisc move toward central line and form ectoderm, mesoderm and endoderm

Question 7

Describe the stages of labor

Answer 7

• dilation stage: cervix dilates and contractions occur every 10-30 min
• expulsion stage: cerves completes dilation (10 cm) and contractions occur every 2-3 min
• placental stage: uterine contracts help eject placenta (afterbirth)