Lecture 11 - Body Plan III

Question 1

Initial signaling for endoderm formation occurs during ___.
Depends on…
Gradient?
Gut?

Answer 1

Gastrulation.

Nodal expression during gastrulation

Ant/Post gradient: ^levels of nodal anteriorly and lower posteriorly. Also post is FGF-4

Post: Cdk-2
Ant: Hex, Sox-2, Foxa-2
Refined differentiation of gut depends on Hox genes

Question 2

Both the oropharyngeal membrane and cloaca plate are form by __ and __ with no intervening __.

Perforations are the result of…

Stomodeum becomes the…
Proctodeum becomes the…

Answer 2

Endoderm and ectoderm; mesoderm

Instability created by lack of mesoderm

Oral cavity
Anal region

Question 3

Fourth Week Embryo

Answer 3

4mm long

Rudiments for most major organs are now present (save for kidneys and limbs)

Prominent pharyngeal arches

Wolffian ridge

Question 4

Wolffian Ridge

Answer 4

IDk

Question 5

48-hour chick embryo

Answer 5

Pharyngeal Arches: Mandibular, hyoid
Pharyngeal slits 1-3

Overall J shape

Yolk sac is empty (give rise to primordial germ cells)

circulatory arcs are present, basic but bidirectional

Question 6

In a 10 mm Pig embryo…

Answer 6

Maxillary process, mandibular arch, stomodeum

U-shaped nervous system

Pharynx/glottis

Question 7

4-week human embryo

Answer 7

Similar to 48- hr chick
Overall J shape

Yolk sac is empty (give rise to primordial germ cells)

circulatory arcs are present, basic but bidirectional

Question 8

Amnion

Answer 8

Inner cell mass, epiblast derivative

Extraembryonic tissue

Question 9

Yolk Sac

Answer 9

Inner cell mass, hypoblast derivative

Extraembryonic tissue

Question 10

Chorion

Answer 10

Part of fetal maternal interface

Extraembryonic tissue

Question 11

Allantois

Answer 11

Inner cell mass, interfaces with placenta via umbilical cord

Extraembryonic

Question 12

Placenta

Answer 12

Trophoblast derivative (implantation)

Fetal-maternal interface (“embryonic stock”)

Question 13

Chorion

Answer 13

Trophoblast derivative

Fetal-maternal interface (“embryonic stock”)

Question 14

Amnion

Answer 14

• Buffer against mechanical injury
• accommodates growth
• allows normal movements
• protects fetus from adhesions

Question 15

Hydramnios

Answer 15

Relate to esophageal atresia and anencephaly????

Question 16

Oligohydramnios

Answer 16

Relate to renal agenesis ???

Question 17

Formation of amniotic fluid

Answer 17

Phase I:

• first 20 weeks of pregnancy
• free diffusion of electrolytes through fetal ectoderm
• secretion by amniotic membrane

Phase II:

• contributions from fetal urine
• filtration from vessels associated with chorion laevae
• possible other sources

Question 18

Yolk sac ___ in size and exists ___ the amniotic cavity. Eventually degrading.

Answer 18

Decreases

Outside

Question 19

Yolk Sac Functions

Answer 19

May Concentrate:

• folic acid
• vitamins A, B, E

Site of origin of primordial germ cells

Location of blood islands (origin of initial blood cells)

Meckel’s diverticulum?

Question 20

Extraembryonic hematopoiesis

Answer 20

Formation of blood cells outside of embryo

Related to blood islands of yolk sac

Question 21

Meckel’s diverticulum

Answer 21

Blind sac/pouch

Leftover/rudimentary yolk

Question 22

Allantois

Answer 22

Umbilical vessels develop in mesoderm of allantois

Proximal part=urachus

• associated with urinary bladder
• becomes median umbilical ligament

Question 23

Placental Development

Answer 23

Previllous embryo
Primary Villous Stage
Secondary V Stage
Tertiary V Stage
Final Development

Question 24

Previllous Embryo

Answer 24

No villi have formed on trophoblast

Question 25

Primary Villous Stage

Answer 25

Solid, cytotrophoblastic, ectodermal primary villi appear

Question 26

Secondary Villous Stage

Answer 26

Mesodermal cores appear within the primary villi

Question 27

Tertiary Villous Stage

Answer 27

Characterized by the appearance of blood vessels within the mesenchymal core of the secondary villi

Question 28

Final Development

Answer 28

Cytotrophoblastic columns Cytotrophoblastic shells -formed by expansion of the cytotrophoblastic columns over th maternal decidual cells Anchoring villi -villi that are anchored to the cytotrophoblastic shell (as opposed to floating villi)

Question 29

Blood Flow Pathway (Maternal)

Answer 29

- Maternal blood enters inter Villous spaces (trophoblastic lacunae) from spiral arteries - exchange of materials (resp gases, nutrients, waste products) between maternal blood in lacunae and fetal blood in capillaries in the villi - maternal blood returns to maternal veins in the decidua basalis

Question 30

Blood Flow Pathway (Fetal)

Answer 30

- Fetal Blood is entirely enclosed within vessels - travels to capillary beds within placental villi via umbilical arteries (usually 2) - returns from cap beds within placental villi via umbilical vein (1)

Question 31

What is the purpose of villi in the placenta of a developing embryo?

Answer 31

Greatly increases surface area allowing for greater gas exchange and absorption of the placenta