development

Question 1

organs

Answer 1

formed from 2 or more basic tissues, arising from the three primary germ layers

Question 2

developmental proteins that play a significant role in cancer

Answer 2

Wnt, hedgehog, Notch

Question 3

totipotent stem cells

Answer 3

give rise to any cell type
- zygote and morula cells
- induced in laboratory

Question 4

pluripotent stem cells

Answer 4

give rise to numerous cell types
- embryonic stem cells (different body tissues)

Question 5

multipotent stem cells

Answer 5

Give rise to some cell types
- organ stem cells

Question 6

stem cell niche

Answer 6

environment regulates differentiation with physical contact or soluble factors

Question 7

zygote -> morula

Answer 7

first 4 days:
- cells get smaller w every division
- around 32 cells

Question 8

blastocyst formation

Answer 8

~ day 5
- zona pellucida degenerates
- cavity forms
- embryoblasts and trophoblasts

Question 9

embryoblast

Answer 9

first appear in blastocyst
- mound of cells inside trophoblast membrane

Question 10

trophoblast

Answer 10

first appear in blastocyst
- form outer layer of cells

Question 11

implantation

Answer 11

days 6-7:
- embryoblasts -> hypoblasts + epiblasts
- trophoblasts -> syncytiotrophoblasts + cytotrophoblasts

days 8-9:
- syncytiotrophoblasts push into + digest endometrium, surround blastocyst
- form trophoblastic lacunae

• amniotic cavity forms within epiblast
• epiblast -> amnioblasts at wall, epiblasts at hypoblast
• hypoblasts migrate to form heuser membrane inside cytotrophoblasts
  day 10:
• space between hypoblast + heuser’s membr -> primary yolk sac
• Heuser’s membr secretes ECM of ret fibers and loose CT between cytotrophoblasts
• extraembryonic mesoderm from epiblast covers Heuser’s membr and lines cytotrophoblasts
  day 12-13:
• ECM breaks down, filling with fluid and forms chorionic cavity

day 13:
formation of definitive yolk sac:
- Heuser’s membr + extraembryonic mesoderm elongates and pinches in
- definitive yok sac forms, primary yolk sac breaks off

Question 12

syncytiotrophoblasts

Answer 12

appear during implantation
- extraembryotic tissue
- push into endometrium and surround cytoblast, forming lacunae
- secrete hCG
- establish placenta

Question 13

cytiotrophoblasts

Answer 13

appear during implantation
- extraembryonic tissue
- surround epiblast + hypoblast + blastocyst cavity

Question 14

hypoblasts

Answer 14

appear during implantation
- first attached to epiblast
- migrate along cytotrophoblasts, forming Heuser’s membrane

Question 15

epiblasts

Answer 15

appear during implantation
- become embryo
- secrete fluid within which forms amniotic cavity

Question 16

trophoblastic lacunae

Answer 16

cavities within syncytiotrophoblasts
- maternal capillaries erode, filling lacunae with maternal blood

Question 17

human chorionic gonadotropin hCG

Answer 17

secreted by syncytiotrophoblasts (6th day)
- similar to LH:
- maintains high levels of P+E: maintains corpus luteum
- prevents menstruation

Question 18

extraembryonic membranes

Answer 18

amnion
yolk sac
placenta

Question 19

amnion

Answer 19

protects fetus
- forms within epiblast

Question 20

yolk sac

Answer 20

initial production of blood cells, microglia (phagocytes in brain), and germ cells
- forms within hypoblast

Question 21

placenta

Answer 21

gas and nutrient exchange through blood

Question 22

extraembryonic mesoderm

Answer 22

forms during implantation from epiblasts
- covers heuser’s membrane
- lines cytotrophoblasts
- lines chorionic cavity
- separates cytotrophoblasts from amnioblasts

Question 23

placental formation

Answer 23

extraembryonic mesoderm + cytotrophoblasts penetrate into syncytiotrophoblasts (chorionic villi) near lacunae
- extraembryonic mesoderm begins to form blood vessels
- blood exchanges through a 4 layer barrier (blood vessel endothelium, CT, cytotrophoblasts, syncytiotrophoblasts)
- maternal component: decidua basalis
- highly vascularized, secretes growth factors

Question 24

gastrulation

Answer 24

end of week 2 to wend of week 3
rearrangement of cells into the 3 primary germ layers
- occurs at interface between epiblast and hypoblast

days 14-15:
- primitive streak appears
- cells at primitive streak diff and express slug
- cells lose adhesion and migrate through primitive streak
- dive into groove, migrate under epiblast epithelium

first they replace the hypoblast to become endoderm
second it’s mesoderm (day 16)
- cells that migrate thru primitive node go along the midline to form the prechordal plate mesoderm and notochord

day 17: trilaminar embryo established
- 3 germ layers and notochord

day 17-18: mesoderm differentiation
- somites form (balls)

Question 25

epithelial-mesenchymal transformation

Answer 25

epiblast cells at primitive streak differentiate and begin to express slug
- slug: TF that causes a loss of adhesion between cells
- cells turn migratory

Question 26

somites

Answer 26

differentiation of mesoderm
- becomes muscle, vertebrae, limbs

Question 27

neurulation

Answer 27

begins at the end of week 3
formation of the nervous system

as early as day 18-23:
notochord induces formation of nervous system
- releases proteins that instruct the overlying ectoderm to become neuronal
- noggin, chordin, cerberus, follistatin
- neural plate buckles inward and pinches off => NEURAL TUBE
- larger at the brain

neural tube and somites lateral to it

Question 28

eventually…

Answer 28

epiblast and yolk sac rotate so that yolk sac is facing the wall

amniotic cavity fills chorionic cavity - no more chorionic cavity