Embryo: Week 3, Embryonic, and Fetal Periods

why is the 3rd week called the week of 3's?

(1) 3 germ layers (ectoderm, mesoderm, endoderm)

(2) 3 cavities (amnion, yolk sac, chorion)

(3) 3 layered villi (syncytiotrophoblast, cytotrophoblast, extraembryonic mesoderm)

3 germ layers

ectoderm

mesoderm

endoderm

3 cavities

amnion

yolk sac

chorion

3 layers of villi

syncytiotrophoblast

cytotrophoblast

extraembryonic mesoderm

primitive streak

indentation into epiblast on dorsal side of embryo

primitive pit

Depression in primitive node

what do the following determine in the axes?

(1) epiblast cells

(2) hypoblast cells

(3) primitive streak

(4) primitive pit

(1) dorsal

(2) ventral

(3) caudal

(4) cranial

what happens to the hypoblast during gastrulation?

it disappears

all germ layers stem from the _____ in the embryoblast

epiblast

what is the fate of the first cells to "dive" into the primitive streak?

endoderm

what is the fate of the second cells to "dive" into the primitive streak?

mesoderm

what is the fate of the cells that don't "dive" into the primitive streak?

ectoderm

steps in notochord formation:

(1) primitive pit forms (with primitive streak)

(2) "tunnels" through embryo to prechordial plate (head)

what is the "tunneling" structure called during neurulation?

notochordal plate

what germ layer(s) does the notochord stem from?

(1) endoderm

(2) mesoderm

what does the notochord become / influence?

(1) CNS

(2) vertebral column

(3) midline

(4) NUCLEUS PULPOSUS

NOTOCHORD FINAL FATE =

NUCLEUS PULPOSUS

neurenteric canal

connection between amniotic cavity and yolk sac at primitive pit

**"tunnel" from notochord formation

neurenteric cysts

masses of endodermally derived tissue commonly associated with the spinal cord; derived from the neurenteric canal where ectoderm and endoderm are closely associated

things from the neurenteric cysts article:

- columnar or cuboidal epithelium w/ or w/o cilia + mucus gobules

- surgical resection

- spinal cord tumors

what is the characteristic epithelium shown in neurenteric cysts?

what type is shown in the image?

- columnar or cuboidal

- pseudostratified columnar

what does the image show?

neurenteric cyst

what do these images show?

neurenteric cyst

what are the stages of embryonic folding?

(1) longitudinal fold

(2) transverse fold

longitudinal fold

head and tail fold;

formation of primary curvature

transverse fold

lateral edges of ectoderm fuse with each other ventrally

what would failure of transverse fold closure result in?

ectopic chordis (heart on exterior)

what is the result of embryonic folding?

closing of embryo... flat layers to 3 dimensional embryo

ectopia chordis

failure to close transverse fold -- heart on outside of body

KNOW THIS ORIENTATION

what is the order of events in the 3rd week?

(1) gastrulation (forming trilaminar embryo)

(2) notochord formation (via primitive streak + pit)

(3) neurulation (formation of neural tube)

(4) longitudinal + transverse folding (closes off embryo)

situs inversus

reversed position of organs caused by a defect in body axis development

- defective cilia

**respiratory infections + infertility

dextrocardia

heart displaced to the right caused by defect in body axis development

caudal dysgenesis

Insufficient mesoderm during gastrulation

Issues with formation of lower limbs

Sirenomelia - aka Mermaid syndrome

sirenomelia

fusion of hind limbs caused by caused by not having enough mesoderm??

**mermaid syndrome

what would you expect to see in a pre-natal history if a fetus has sirenomelia? why?

oligohydraminos -- not able to urinate the swallowed amniotic fluid

examples of midline defects

(1) incisors fused

(2) cyclopsia

sacrococcygeal teratoma

mass derived from primitive streak -- ALL 3 GERM LAYERS

teratoma

tumor of all 3 germ layers

major thing that happens in:

(1) embryonic period

(2) fetal period

(1) organogenesis

(2) viable

malignant epithelial tumor

carcinoma (sarcomas?)

benign epithelial tumor

angioma, papilloma, adenoma

malignant CT tumor

sarcoma

benign CT tumor

fibroma, lipoma, osteoma, chondroma

malignant muscle tumor

sarcomyoma

benign muscle tumor

myoma

KNOW THE FATES OF 3 GERM LAYERS (BLACK SLIDE WITH BLUE, RED, and YELLOW TEXT)

KNOW THE FATES OF 3 GERM LAYERS (BLACK SLIDE WITH BLUE, RED, and YELLOW TEXT)

neurulation

(1) thickening of neuroectoderm (neural plate)

(2) invagination

(3) pinching off

neural crest cells

cells at tip of neural fold; migrate throughout embryo; come from surface ectoderm

when does cranial neuropore close?

caudal neuropore?

(1) day 24-25

(2) day 26-27

neural tube

end result of neurulation

what do neural crest cells form?

ganglia (parasympathetic, sensory, autonomic, dorsal root)

where do neural crest cells come from?

surface ectoderm

what does surface ectoderm give rise to? (other than neural crest cells)

(1) skin, hair, nails, cutaneous + mammary glands

(2) anterior pituitary

(3) enamel of teeth

(4) internal ear

(5) lens of the eye

mesodermal derivatives include:

(1) paraxial

(2) intermediate

(3) lateral

what is the fate of the paraxial mesoderm?

somites --> dermatomes, myotomes --> SKELETAL MUSCLE

what is the fate of the intermediate mesoderm?

urogenital systems

what is the fate of the lateral mesoderm?

**ORGANS

(1) somatic -- associated with ectoderm

(2) splanchnic -- associated with endoderm

what is the fate of the endoderm?

- form primitive gut tube with 2 membranes (buccopharyngeal and cloacal)

- visceral epithelium

- parenchyma (secretory part) of thyroid, parathyroid, liver, and pancreas

- STROMA (CT) of tonsils + thymus

stomodeum

primitive mouth

proctodeum

primitive anus

what is the vitelline duct + allantois?

(1) vitelline duct = connects to yolk sac

(2) allantois = connects to bladder

vitelline duct

the structure that connects the developing embryo to the secondary yolk sac

allantois

involved in early fluid exchange between the embryo and the yolk sac // connects to bladder

what are the structures at risk of congenital defects during the fetal period?

(1) brain

(2) eyes

(3) ears

(4) teeth

(5) palate

(6) external genitalia

name the important events for: weeks 9-12

(1) liver making RBC's

(2) external genitalia = male vs. female

name the important events for: weeks 13-16

(1) bone formation

(2) eyes move forward

name the important events for: weeks 17-20

(1) primary oocytes develop

(2) testes descend

name the important events for: weeks 21-25

(1) lungs produce surfactant

name the important events for: weeks 26-29

(1) lungs breath on own

(2) regulate temperature + breathing

(3) spleen --> bone marrow @ 28 weeks

name the important events for: weeks 30-34

NOTHING IMPORTANT

name the important events for: weeks 35-birth

(1) "finishing period" -- cardiovascular + respiratory

(2) fat accumulation

when are the following organs responsible for RBC formation?

(1) spleen

(2) bone marrow

(3) liver

(4) yolk sac

(1) 12-24 weeks

(2) 30+ weeks

(3) 12-30 weeks

(4) 0-12 weeks

when is amniocentesis performed?

when risk of congenital defects is higher than normal:

- mother is advanced age

- mother of down syndrome child

- chromosomal abnormalities

- X-linked carriers

** history of neural tube defects

- inborn errors of metabolism

what are the layers that must be penetrated by needle during amniocentesis?

(1) skin, fascia, etc.

(2) perimetrium

(3) myometrium

(4) endometrium

(5) syncytiotrophoblast

(6) cytotrophoblast

(7) extraembryonic mesoderm

(8) amnion

**STOP

alpha fetoprotein

protein produced by fetal liver; if hole in ectoderm / fetus, alpha fetoprotein will show up in amniotic fluid

what if alpha fetoprotein is found in a blood sample from a 23 year old male?

cancer