12.4 Embryo Development Flashcards
What are the three stages of prenatal development?
- Germinal
- Embyronic
- Foetal
How long is the germinal stage?
2 weeks (weeks 1-2)
How long is the embryonic stage?
6 weeks (weeks 3-8)
How long is the foetal stage?
32 weeks (weeks 9-38)
Describe the germinal stage of prenatal development
Primitive germ layers are formed (What is this?)
Describe the embryonic stage of prenatal development
Major organ systems come into existence (developing human is now called embryo)
Explain clinical vs developmental age
Clinical: Since LMP
Developmental: 14 days after LMP (since this is usually how long after period before fertilization)
What is the sperm nucleus called when it increases in size inside the ovum?
- Male pronucleus
What is the ovum nucleus called when it increases in size upon sperm entry?
Female pronucleus
What are the cells within the zygote called as their numbers increase?
Blastomeres
How many days after fertilization is a morula formed? How many blastomeres in a morula?
- ~3 days post-fertilization
- Morula seems to have 16 blastomeres, although sources largely conflict
Describe the two types/structures of cells in a blastocyst
- Outer layers of large, squamous trophoblasts
- Cluster of cells inside called inner cell mass
What will the inner cell mass eventually become?
The embryo
What will the trophoblasts eventually become?
Placenta and associated blood vessels
Which hormones prepare the endometrium to receive the blastocyst
- Oestrogen
- Progesterone
How long does implantation into the endometrium take, and when is it finished?
- Takes about 5 days
- Finished about 12 days after ovulation
How do blastocysts prevent menstruation?
Trophoblasts secrete hCG to sustain the luteum
How many days until a morula is formed?
~4
How many days until a blastocyst is formed?
~5 (1 day after morula)
Which layer of the inner cell mass is closer/farther from the endometrium during implantation?
Closer: Epiblast
Farther: Hypoblast
How is the mesoderm formed?
- Gastrulation
- Folding of epiblast fold down in, forming the mesoderm
Describe the development of the nervous system
- Mesoderm develops into notochord
- Factors secreted by notochord cause a groove to form in the plate, and the folds gradually become larger until they fuse into a neural tube
What structures develop from the neural tube?
- Brain
- Spinal cord
How many days after conception before heartbeat?
22
How long after conception do primordial germ cells develop?
3-4 weeks
Where do gametes come from?
Endoderm
What are factors that cause birth defects called?
Teratogens
List some environmental factors that can lead to birth defects
- Thalidomide
- Alcohol
- Maternal-foetal infections
Which systems does teratogen exposure most affect?
Systems that are developing quickly.
Is teratogen exposure more likely to cause loss of pregnancy defects in early or late pregnancy?
Early
Are teratogens only chemicals?
No. Changes in the maternal environment can also have bad effects, such as maternal fever.
How does size at birth influence adult disease?
The following are decreased in low birthweight babies:
- Cardiovascular and metabolic disease
- Neurologicla and mental disorders
Some cancers are increased in high birth weight (same for allergy.
List some tissues/cells that arise from the ectoderm
- Skin
- Nervous system
- Hair
List some tissues/cells that arise from the mesoderm
- Blood
- Muscle
- Bones
List some tissues/cells that arise from the endoderm
- Epithelial lining of organs
- Gametes
