Embryology

Question 1

embryology

Answer 1

study of the origin and development of a single individual

Question 2

prenatal periods

Answer 2

embryonic period - first 8 weeks

fetal period - 9 weeks to birth

Question 3

early embryonic sequence: days 0-6

Answer 3

day 0: conception with zygote formation
day 1: two blastomere cells
day 2: four cells
day 3: morula (16-32 cells)
day 4: early blastocyst, enters into uterine cavity
day 5: late blastocyst
day 6: blastocyst reaches uterine wall and zona pellucida dissolves

Question 4

early embryonic sequence: days 7-16

Answer 4

day 7: implantation begins
day 9: embryonic laminar disc (epiblast and hypoblast)
day 11: implantation complete with amniotic cavity, yolk sac, and uterine sinusoids
day 15: first missed menses/positive pregnancy test
day 16: trilaminar embryo with endoderm, mesoderm, and ectoderm

Question 5

week 1 post fertilization

Answer 5

pre-implantation embryo moves through oviduct to arrive at the surface of the uterus endometrium as a blastocyst with inner cell mass

Question 6

week 2 post fertilization

Answer 6

implantation occurs and 2-layered embryonic disc (epiblast and hypoblast) forms from inner cell mass

Question 7

week 3 post fertilization

Answer 7

3 layered embryo (ectoderm, mesoderm, endoderm) develop from epiblast layer

Question 8

primitive streak

Answer 8

forms on the dorsal face of the developing embryo, toward the caudal or posterior end
marks the start of gastrulation (formation of 3 germ layers)

Question 9

ectoderm

Answer 9

brain, spinal cord, skin epidermis

Question 10

mesoderm

Answer 10

bones, muscle, connective tissue, epithelium lining inside of blood vessels (endothelium), epithelial lining of ventral body cavity (mesothelium), kidneys, gonads

Question 11

endoderm

Answer 11

forms inner epithelial lining of the gut tube and its derivatives (respiratory tubes, digestive organs, and urinary bladder) and secretory cells of some glands

Question 12

embryonic period

Answer 12

first 8 weeks post-fertilization

fertilization -> 1-week conceptus -> 3-week embryo (3 mm) -> 5-week embryo (10 mm) -> 8-week embryo (22 mm)

Question 13

potency

Answer 13

specifies a cell’s potential to differentiate into different cell types
totipotent, pluripotent, multipotent, and unipotent

Question 14

totipotency

Answer 14

zygote (1 day old), morula (3 days old)

cells can differentiate and produce all the cells in an organism, including all the extra-embryonic placental tissues

Question 15

pluripotency

Answer 15

inner cell mass of blastocyst (5-7 days old) and the epiblast layer in 2nd week
cells can differentiate into all embryonic cells of the three cell masses (endo/ecto/mesoderm)

Question 16

multipotency

Answer 16

cells which can differentiate into 2 or more cell types, but are not able to differentiate into all embryonic cell types

Question 17

unipotency

Answer 17

terminally differentiated to form only one cell type

e.g. a neuron

Question 18

stem cells in tissues

Answer 18

many tissues in both children and adults contain populations of stem cells that renew themselves continually and divide to produce new cells as needed