embryogenesis genes

Question 1

What are the 4 main genes of embryogenesis? What are their MAIN responsibilities?

Answer 1

Sonic hedgehog: important for CNS development and anterior-posterior patterning (ie. difference btw thumb and pinky)
Wnt-7: dorsal-ventral patterning
FGF: alows for limb lengthening
Homeoboxy genes: segmental organization in the craniocaudal direction

Question 2

sonic hedgehog mutations and location

Answer 2

(CNS devo and anterior-posterior patterns). mutations cause holoprosencephaly. found at the base of the limbs in the zone of polarizing activity

Question 3

wnt-7 location

Answer 3

(organization of dorsal-ventral axis). found at the apical ectodermal ridge (thickened ectorderm at the distal end of each limb). wnt expression is found on the dorsal side.

Question 4

FGF gene location, function

Answer 4

apical ectodermal ridge (thickened ectoderm at distal end of the limbs). stimulates mitosis of underlying mesoderm, providing for lengthening of the limbs

Question 5

homeobox mutations

Answer 5

appendages in wrong locations

involved in the segmental organization of the embryo in a craniocaudal direction

Question 6

first week after fertilization

Answer 6

day 0: fertilization
day 2: zygote (nuclei of sperm and egg fuse)
day 3: morula (solid ball of cells with inner cell mass and outer cell mass)
day 5: blastocyst (compaction and cavitation- there is an the inner cell mass is now the embryoblast; the outer cell mass is separated by a hollow area and is called the trophoblast)
day 7-10: implantation of the blastocyst. hCG secretion begins around this time.

Question 7

What events happen during weeks 2 and 3 after fertilization?

Answer 7

week 2: bilaminar disc of epiblast and hypoblast
week 3: trilaminar disc, gastrulation. we see the primitive streak, notochord, mesoderm and its orgainzation, and the neural plate beginning to form.

Question 8

What is gastrulation?

Answer 8

process of forming a trilaminar embryonic disc. establishes the ectoderm mesoderm, and endoderm. starts with epiblast invaginating to form the primitive streak. happens during week 3

Question 9

week 4

Answer 9

by beginning of week 4, the nerual tube has formed and closed
heart begins to beat and upper and lower limb buds form (4 wks = 4 limbs)

Question 10

week 6 landmarks

Answer 10

fetal heartbeat detectable by transvaginal ultrasound

Question 11

week 10 landmarks

Answer 11

genitalia have male/female characteristics

Question 12

what important events occur during the embryonic period? what constitutes the embryonic period?

Answer 12

weeks 3-8
we see neural tube formation by neuroectoderm. it closes by week 4.
organogenesis
extreme susceptibility to teratogens

Question 13

What are important structures derived from the surface ectoderm? clinical relevance?

Answer 13

adenohypophysis from rathke pouch. benight rathke pouch tumor with cholesterol crystals and calcifications is a craniopharyngioma
lots of sensory stuff: lens of eye, sensory ear organs, olfactory epithelium
(and the obvious stuff I can guess- anus below pectinate ine, parotid, sweat, mammary glands, oral cavity lining, epidermis)

Question 14

What are the important structures derived from the neuroectoderm?

Answer 14

CNS: brain, retina and optic nerve, spinal cord. includes the neurohypophysis, neurons, oligodendrocytes, astrocytes, ependymal cells, pineal gland)

Question 15

What are the clinically relevant mesodermal defects?

Answer 15

VACTERL:
vertebral defects, anal atresia, cardiac defects, tracheo-esophageal fistula, renal defects, limb defects (bone and muscle)

Question 16

What does the mesoderm do?

Answer 16

serous linings of body cavities, spleen, CV, lymphatics, blood, wall of gut, vagina, kidneys, adrenal cortex, dermis, testes, ovaries

Question 17

What does endoderm due?

Answer 17

gut tube epithelium (anal canal above the pectinate line), ureethra, lungs, liver, gallbladder, pancreas, eustachian tube, thymus, parathyroid, thyroid follicular cells

Question 18

neural crest derivatives

Answer 18

PNS, melanocytes, chromaffin cells of medulla, parafollicular C cells of the thyroid, pia and arachnoid, skull bones, odontoblasts, aorticopulmonary septum.

Question 19

aplasia vs. agenesis

Answer 19

agenesis: organ is absent because of absence of primoridial tissue
aplasia: organ is absent even though the primordial tissue was present.

Question 20

deformation vs disruption vs malformation

Answer 20

deformation: extrinsic developmental problem that occurs after the embryonic period
disruption: previously normal tissue breaks down (ex. amniotic band syndrome)
malformation: intrinsic disruption that occurs in the embryonic period