Early Embryology

Question 1

Totipotent

Answer 1

Can form any cell type in the body plus extraembryonic (placental) cells

Blastomeres are totipotent before compaction

Question 2

Pluripotent

Answer 2

Can form all cell types in the body

Blastomeres are pluripotent after compaction

Question 3

Multipotent

Answer 3

Can form other cell types, but are limited in their ability to differentiate

Question 4

Zygote

Answer 4

Sperm + Egg

Question 5

Fertilization Age

Answer 5

Day 1 is the time of fertilization; term equals 38 weeks

Question 6

Gestational Age

Answer 6

Day 1 is the day of the last menstrual cycle; term equals 40 weeks (is more reliable in a clinical setting)

Question 7

Main events of week 1-2 of development (pre-embryonic period)

Answer 7

• Cell division (cleavage)
• Compaction (days 3-4)
• Blastocyte formation (days 4.5-5)
• Implantation (days 5-7)

(See outline for more info)

Question 8

Notochord

Answer 8

• Plays role in induction of the nervous system and vertebral bodies
• Group of migrating cells form a condensed, midline mass of mesoderm to form the notochord
• Producsed Sonic HedgeHog (SHH) hormone

Question 9

Neurulation

Answer 9

• Occurs at the end of week 3

- Formation of neural plate –> neural folds –> neural tube

Question 10

What does the neural tube form?

Answer 10

The brain and spinal cord

Question 11

HOX genes

Answer 11

Encode transcription factors which specify anterior-posterior axis

Question 12

Sonic Hedgehog (SHH) hormone

Answer 12

• Creates concentration gradient over cells and controls the expression of different transcription factors depending on the cells location in the SHH gradient
• SHH secreted from notochord and floor plate helps specify distinct neuronal subtypes in the neural tube
• Important in patterning and digit (finger/toe) specification

Question 13

Teratogen

Answer 13

Agent that produces birth defects:

• Infectious agents
• Drugs/chemicals
• Heavy metals
• Ionizing radiation
• Maternal health