Embryogenesis + Germ Layers B&B

Question 1

when can beta-hCG be used to detect pregnancy?

Answer 1

beta-hCG is secreted from the blastocyst, which implants in the uterine wall around days 6-10

Question 2

what are the outer and inner cells of the blastocyst called?

Answer 2

outer cells = trophoblasts, secrete blastocoel (watery fluid)

inner cells = embryoblast, give rise to growing embryo

Question 3

when the inner cell mass (embryoblast) of the blastocyst undergoes gastrulation, it first is divided into a bilaminar disc made of ___ and ____, separated by a basement membrane

Answer 3

epiblast (becomes the embryo) and hypoblast (becomes yolk sac)

Question 4

what is the indication of the start of gastrulation of the growing embryo?

Answer 4

when the primitive steak forms via invagination of the epiblast (part of bilaminar disc of embryoblast/inner cell mass)

Question 5

what organ systems develop from the ectoderm vs mesoderm vs endoderm?

Answer 5

ectoderm forms nervous system + integumentary (hair, skin, nails)

mesoderm forms the layers under our skin - muscular, skeletal, circulatory, lungs (outside), kidneys

endoderm forms metabolism structures underneath - digestive system, liver, pancreas, lungs (inner layers)

Question 6

what are the steps leading to the development of the neural tube?

Answer 6

1. notochord arises in mesoderm
2. notochord induces overlying ectoderm to form neural plate
3. neural plate folds, forming the neural tube

neural tube becomes CNS (neural crest becomes PNS)

Question 7

what part of the nervous system is derived from the mesoderm?

Answer 7

microglia (phagocytes) develop from mesoderm

everything else from ectoderm - neural tube becomes CNS, neural crest becomes PNS

Question 8

the CNS develops from _____, while the PNS develops from _____

Answer 8

nervous system develops from ectoderm - CNS from neural tube, PNS from neural crest

EXCEPT Microglia (phagocytes), which develop from Mesoderm!

Question 9

_____ gives rise to most connective tissue in adults

Answer 9

mesenchyme - embryonic connective tissue derived from mesoderm, not found in adults except for mesenchymal stem cells

note mesenchymal tumor = sarcoma

Question 10

a sarcoma is a tumor of…

Answer 10

sarcoma = mesenchymal tumor (of mesoderm origin)

mesenchymal is embryonic tissue that gives rise to most adult connective tissue (bones, cartilage, lymphatics, circulatory)

Question 11

when does organogenesis occur?

Answer 11

first 8 weeks after fertilization - most vulnerable period to teratogens!

aka embryonic period

Question 12

when do the following occur in the embryonic period?
a. heart begins beating
b. limbs form
c. baby begins moving
d. specific genitalia can be identified

Answer 12

a. heart begins beating - week 4
b. limbs form - week 4
c. baby begins moving - week 8
d. specific genitalia can be identified - week 10