WEEK 12. 1st, 2nd and 3rd Week of Development

What happens in the 13th day of the development?

- Bleeding occurs at the implantation site as a result of increased blood flow into the lacunar spaces. - Secondary yolk sac or definitive yolk sac is formed. - The extraembryonic coelom expands to form the chorionic cavity. - The extraembryonic mesoderm then lines the cytotrophoblast and is called the chorionic plate. - The extraembryonic mesoderm only traverses the chorionic cavity in the connecting stalk (connecting the embryo with the trophoblast). - With development of blood vessels, the stalk becomes the umbilical cord.

When and how is the exocoelomic or Heuser's membrane formed?

- around the 9th day. - cells from the hypoblast spread around the blastocoele.

The bilaminar germ disc: 1. consists of epiblast and mesoblast 2. is derived from the outer cells of the morula 3. forms the embryo proper 4. synthesizes human chorionic gonadotropin, HCG

3. forms the embryo proper

The amniotic cavity appears as a slit-like space near the embryonic polar trophoblast and within the: 1. extraembryonic mesoderm 2. exocoelomic membrane 3. inner cell mass 4. connecting body stalk 5. cytotrophoblast

3. inner cell mass

At fertilization, the main results are:

1. Restoration of the diploid number of chromosomes. 2. Determination of the sex of the new individual. 3. Initiation of cleavage.

Blastomeres are

formed by a compact ball of cells held together by tight junctions hence, this process is called compaction.

The exocoelomic membrane comes from what?

hypoblast

Migratory paths of neural crest cells are in which region? And what does it gives rise to?

in the head region; it gives rise to the head, visceral, cranial and neck. They also form 1 to 6 pharyngeal arches.

Near the time of implantation, the epiblast and hypoblast becomes a layer of epiblast cells where they are placed.....

layer of epiblast cells dorsally and layer of hypoblast cells ventrally.

In adults, the notochord exists as what?

nucleus pulposus of the intervertebral discs.

When does the lateral edges of the neural plate becomes elevated?

on the 19th day.

When does the somite shows/occurs?

on the 20th day.

Intermediate mesoderm, temporarily connects

paraxial mesoderm with the lateral plate.

Neural crest cells are sometimes referred to as ............

the 4th germ layer.

What does the inner cell mass of the morula gives rise to?

to the tissues of the embryo proper.

The secondary yolk sac comes from where?

endoderm

The amnioblasts come from where?

epiblast

At the early blastocyst stage, embryoblast differentiate into

epiblast and hypoblast cells.

Neural cells will undergo an _______ to ____ transition.

epithelial-to-mesenchymal transition

What happens after compaction of the morula?

Formation of Blastocyst happens where the morula will enter the uterine cavity and forms a single cavity called blastocele. At this time, the embryo is a blastocyst. Cells of the inner cell mass, now called the embryoblast, are at one pole, and those of the outer cell mass, or trophoblast, flatten and form the epithelial wall of the blastocyst.

What is the 3rd week of development called as?

Gastrulation where three germ layers are established such as endoderm, mesoderm and ectoderm.

The results of fertilization include the determination of chromosomal sex and initiation of cleavage. A. True B. False

True

When is neurulation considered complete?

Upon the closing of the caudal neuropore on the 28th day (25-somite stage).

The definitive yolk sac of the embryo appears by what day? 1. 13th 2. 26th 3. 72nd 4. 94th 5. 2nd

1. 13th

The intracellular cavities in the lateral plate mesoderm divides into two layers:

1. A layer continuous with mesoderm covering the amnion, known as the somatic or parietal mesoderm layer. 2. A layer continuous with mesoderm covering the yolk sac, known as the splanchnic or visceral mesoderm layer.

Each somites differentiates into......, .......... and ........ and what do they develop into?

1. Sclerotome (the tendon cartilage and bone component). 2. Myotome (providing the segmental muscle component) and, 3. Dermatome, which forms the dermis of the back.

What happens in the 11th and 12th day of the development?

1. The blastocyst is completely embedded in the endometrial stroma. 2. Syncytiotrophoblast penetrate deeper into the stroma and erode the endothelial lining of the maternal capillaries, which are congested and dilated, known as sinusoids. 3. The uteroplacental circulation is established. 4. Cytotrophoblast also differentiates. On its inner surface, cells delaminate to form a fine, loose tissue, the extraembryonic mesoderm, which fills the space between external trophoblast and amnion and internal yolk sac.

The second week of development is known as the week of 2's:

1. The trophoblast differentiates into two layers: the cytotrophoblast and syncytiotrophoblast. 2. The embryoblast forms two layers: the epiblast and hypoblast. 3. The extraembryonic mesoderm splits into two layers: the somatic and splanchnic layers. 4. Two cavities form: the amniotic and yolk sac cavities.

The fifth day of human development is characterized by embryonic cells of the: 1. inner cell mass 2. embryonic hypoblast 3. epiblast 4. primitive streak 5. amnion

1. inner cell mass

Implantation will not take place unless the zona _________ is lost. 1. pellucida 2. limitans 3. orbicularis 4. corona 5. oophorus

1. pellucida

Which layer is acellular, does not expand mitotically, and produces human chorionic gonadotropin (hCG) which stimulates progesterone production by the corpus luteum? 1. syncytiotrophoblast 2. cytotrophoblast 3. epiblast 4. endoderm 5. ectoderm 6. mesoderm

1. syncytiotrophoblast

Both the neurenteric canal and the notochordal plate are present in the conceptus at the same time. 1. true 2. False

1. true

What are the stages of embryogenesis?

1.Fertilization 2.Cleavage - Compaction, Differentiation. 3.Gastrulation 4.Organogenesis 5.Metamorphosis 6.Gametogenesis

The allantois or allantoenteric diverticulum appears around the _____ day of development.

16th day

What two layers does the trophoblast differentiate into once attached to the uterine lining? 1. Zona pellucida / corona radiata 2. Cytotrophoblast / syncytiotrophoblast 3. Endoderm / ectoderm 4. Ectoderm/ mesoderm 5. Blastocyst / embryoblast

2. Cytotrophoblast / syncytiotrophoblast

Extraembryonic somatic mesoderm is inclose association with what? 1.Syncytiotrophoblast. 2.Cytotrophoblast and amnion. 3.Yolk sac. 4.Syncytiotrophoblast and Cytotrophoblast.

2. Cytotrophoblast and amnion.

At the 32-cell stage of division, the embryo is known as a morula that contains inner cell mass and outer cell mass. What do the inner and outer cell masses eventually become? 1. Placenta / embryo and fetus 2. Embryo and fetus / placenta 3. Chorionic membrane / amniotic membrane 4. Amniotic membrane / chorionic membrane

2. Embryo and fetus / placenta

During development, the notochordal process: 1. Arises from involuting endodermal cells. 2. Extends from the prochordal plate to the primitive node. 3. Is involved in the induction of the primitive gut. 4. Becomes the appendicular skeleton.

2. Extends from the prochordal plate to the primitive node.

The _______ is/are part(s) of the 4-day blastocyst: 1. syncytiotrophoblast 2. blastocyst cavity 3. notochord 4. somitomeres

2. blastocyst cavity

The cloacal membrane consists of: 1. embryonic endoderm, mesoderm and ectoderm 2. endoderm of the roof of the yolk sac and embryonic ectoderm 3. a spherical area of endoderm fused to embryonic mesoderm 4. the prochordal plate and the overlying embryonic endoderm 5. none of the above

2. endoderm of the roof of the yolk sac and embryonic ectoderm

From what does the extraembryonic somatic mesoderm arise? 1. cytotropblast 2. hypoblast

2. hypoblast

Which of the following events are directly related to implantation? 1. interaction between uterine endometrium and hypoblast 2. release of proteolytic enzymes 3. loss of the decidua 4. acrosome reaction 5. capacitation

2. release of proteolytic enzymes

When does the anterior neuropore close?

25th day (18-to 20-somite stage)

At the caudal end of the primitive streak, ectoderm and endoderm fuse as the: 1. Notochordal canal. 2. Coelom. 3. Cloacal membrane. 4. Neural groove. 5. Notochord.

3. Cloacal membrane.

Intraembryonic mesoderm differentiates into: 1. Yolk sac. 2. Neural tube. 3. Intermediate mesoderm. 4. Primordial germ cells. 5. Somites 6. Lateral plate mesoderm

3. Intermediate mesoderm.

The amniotic cavity develops: 1. on the 10th day 2. within the inner cell mass 3. between inner cell mass and trophoblast 4. in the extraembryonic mesoderm 5. between two layers of cytotrophoblast

3. between inner cell mass and trophoblast

The seven-day blastocyst: 1. has a single layer of trophoblast at the embryonic pole 2. has an amniotic cavity 3. is attached to the endometrial epithelium 4. is surrounded by a degenerating zona pellucida 5. is called the hypoblast

3. is attached to the endometrial epithelium

The yolk sac in the human embryo: 1. does not contribute to the embryonic gut 2. is devoid of hemopoietic activity, or blood cell formation 3. is the site of primordial germ cell production 4. stores nutrients throughout pregnancy

3. is the site of primordial germ cell production

The blastocoele becomes the: 1. amniotic cavity 2. extraembryonic coelom 3. primary yolk sac 4. chorionic cavity 5. secondary cavity

3. primary yolk sac

Which layer invades into the maternal endometrium and forms the lacunar network for placental-maternal exchange? 1. blastocyst 2. cytotrophoblast 3. syncytiotrophoblast 4. endoderm 5. ectoderm 6. mesoderm

3. syncytiotrophoblast

Extraembryonic somatic mesoderm is in close association with: 1. syncytiotrophoblast 2. cytotrophoblast & amnion 3. yolk sac 4. syncytio- & cytotrophoblast

3. yolk sac

In the third week of human embryonic development: 1. The amnion appears. 2. A bilaminar embryonic disc is formed. 3. The body stalk moves ventrally and joins with the yolk sac stalk to form the umbilical cord. 4. The neural plate is induced by the notochordal process and associated mesoderm. 5. The uteroplacental circulation is established.

4. The neural plate is induced by the notochordal process and associated mesoderm.

During the second week, the embryonic disc is composed of: 1. ectoderm 2. ectoderm and mesoderm 3. endoderm 4. epiblast and hypoblast 5. ectoderm, mesoderm and endoderm

4. epiblast and hypoblast

Cytotrophoblast cells become: 1. secondary yolk sac 2. amnioblasts 3. exocoelomic membrane 4. syncytiotrophoblast

4. syncytiotrophoblast

Major events beginning in the second week of development include: 1. notochord differentiation 2. somite formation 3. angiogenesis 4. yolk sac development

4. yolk sac development

How many somites are formed by the end of the 5th week of development?

42 to 44 pairs of somites are present.

The first week of human development is characterized by formation of the: 1. inner cell mass 2. hypoblast 3. trophoblast 4. blastocyst 5. all of the above

5. all of the above

During the morula stage: 1. tight junctions appear between peripheral cells, isolating the inner cells from uterine fluid 2. the location of the cells dictates their fate 3. the outer cells pump fluid, creating a fluid- filled blastocoele 4. attachment to the uterine epithelium has not yet occurred 5. all of the above are correct

5. all of the above are correct

The part of the 13-day embryoblast from which the embryo proper is formed: 1. lies between the amniotic cavity and yolk sac 2. also contributes to the roof of the yolk sac 3. is composed of two primary germ layers 4. is attached to the amnion 5. all of the above are correct

5. all of the above are correct

Which statement about the 14-day blastocyst is NOT true? 1. villi are absent 2. extraembryonic coelom surrounds the yolk sac 3. primitive uteroplacental circulation is established 4. extraembryonic mesoderm is split into two layers 5. none of the above

5. none of the above

The ___________ gives rise to the extraembryonic mesoderm. 1. ectoderm 2. hypoblast 3. blastocyst 4.trophoblast 5. syncytiotrophoblast 6. cytotrophoblast 7. blastocoele 8. inner cell mass 9. notochord 10. prochordal plate 11. primary yolk sac 12. amniotic cavity 13. intraembryonic coelom 14. secondary yolk sac

6. cytotrophoblast

Morula

A solid ball of at least 16-cells that makes up an embryo; in humans, this stage occurs within four days of fertilization.

During the second week of development, the trophoblast differentiates into: A. syncytiotrophoblast B. ectoderm C. intraembryonic mesoderm D. yolk sac (secondary)

A. syncytiotrophoblast

Both the neurenteric canal and the notochordal plate are present in the conceptus at the same time: A.True B.False

A.True.

The completion of interstitial implantation, so that the conceptus is entirely within the endometrium occurs: A)On about the 20 day. B)By about day 11. C)By the end of the first week. D)By erosion of the myometrial lining. E) As a result of endometrial proliferation.

B)By about day 11.

The first two intraembryonic germ layers to differentiate are the: A. syncytio - & cytotrophoblast B. epiblast & hypoblast C. ectoderm & endoderm D. ectoderm & mesoderm

B. epiblast & hypoblast

At fertilization: A. the haploid number of chromosomes is restored B. the chromosomal sex is determined C. cleavage is inhibited D. the inner cell mass becomes recognizable E. the ovum becomes the blastocyst

B. the chromosomal sex is determined

Much of intraembryonic coelom forms within paraxial mesoderm: A.True B.False

B.False

The second week of development is the

Bilaminar germ disc

Which day of development the blastocyst is completely embedded in the endometrial stroma?

By the 11th and 12th day of development.

The early stages of cleavage are characterized by: A. formation of a hollow ball of cells B. increase in the size of the cells in the zygote C. increase in the number of cells in the zygote D. none of the above

C. increase in the number of cells in the zygote

The amniotic cavity develops: A. on the tenth day B. within the outer cell mass C. within the inner cell mass near the cytotrophoblast D. in extraembryonic mesoderm E. none of the above

C. within the inner cell mass near the cytotrophoblast

What forms the Exocoelomic membrane (Heuser's membrane)?

Cells from the hypoblast forms the Exocoelomic membrane.

What do you mean by the Extraembryonic splanchnopleuric mesoderm?

Covering the yolk sac is called the extraembryonic splanchnopleuric mesoderm

The lining of the _____________ forms the lining of the embryonic gut. A. primary yolk sac B. amniotic cavity C. notochord D. extraembryonic mesoderm E. secondary yolk sac

E. secondary yolk sac

Mesoderm cells are derived from _______ & ____________.

Epiblast and extraembryonic tissues.

Which are the two layers of the bilaminar disc?

Epiblast and hypoblast

Which membrane together with the hypoblast forms the lining of the exocoelomic cavity or primitive yolk sac?

Exocoelomic membrane (Heuser's membrane)

What does the outer cell mass of the morula forms?

It forms the trophoblast, which later contributes to the placenta.

What does the ectodermal germ layer gives rise to?

It gives rise to organs and structures that maintain contact with the outside world. Such as: - The (central nervous system, peripheral nervous) system; - The sensory epithelium of the ear, nose, and eye; - The epidermis, including the hair and nails. - Glands such as (Subcutaneous, mammary, pituitary). - The Enamel of the teeth.

What is the most distinctive feature in the presence of the pharyngeal arches?

It is the development of the head and neck.

What is the first step of gastrulation (Day 16)?

It is the formation of the primitive streak on the surface of the epiblast.

Blood cells and blood vessels arise from _____ .

Mesoderm

What are the pharyngeal arches?

Pharyngeal Arches are 6 curved cylindrical mesenchymal thickening on each side of primitive pharynx.

Cleavage process of development

Right after fertilization as the zygote has reaches a two-cell stage, it divides mitotically, increasing the number of cells hence, then form blastomeres.

What do you mean by the Extraembryonic somatopleuric mesoderm?

The extraembryonic mesoderm lining the cytotrophoblast and amnion is called the extraembryonic somatopleuric mesoderm

Extraembryonic SPLANCHNIC mesoderm is in close association with what?

Yolk sac

Blastomeres are surrounded with what?

Zone pellucida which then disappears at the end of the fourth day.

Which layer of the bilaminar embryonic disc forms part of the lining of the amniotic cavity? a. epiblast b. hypoblast c. blastocyst d. trophoblast e. syncytiotrophoblast f. cytotrophoblast g. blastocoele h. inner cell mass i. notochord j. prochordal plate k. primary yolk sac l. amnioblast m. intraembryonic coelom n. secondary yolk sac

a. epiblast

Crest cells from the trunk region leave the neuroectoderm or neural tube before or after closure of the neural region?

after the closure of the neural folds.

The blastocele becomes the: a. Extraembryonic coelom. b. Primary yolk sac. c. Chorionic cavity. d. Secondary cavity. e. Amniotic cavity.

b. Primary yolk sac.

Cleavage divisions are always: a. meiotic b. mitotic c. amniotic d. anucleotic e. by binary fission

b. mitotic

Crest cells from the cranial region leave the neuroectoderm or neural tube before or after closure of the neural region?

before the closure of the neural folds.

When does the definitive yolk sac form?

by the end of the 2nd week

At which of the following stages of development is division of embryonic material likely to result in normal monozygotic twinning? a. 2-cell stage b. morula c. blastocyst d. implanting embryo e. all of the above

e. all of the above

During implantation, the blastocyst: a. implants in the endometrium b. usually attaches to endometrial epithelium at its embryonic pole c. usually implants in the posterior wall of the body of the uterus d. causes change in the endometrial tissues e. all of the above are correct

e. all of the above are correct

With the light microscope, the zona pellucida appears as a translucent membrane surrounding the: a. primary oocyte b. zygote c. morula d. very early blastocyst e. all of the above are correct

e. all of the above are correct

The two—cell stage is reached approximately _____ hours after fertilization; the four—cell stage is reached at approximately ___ hours; the 12—to 16—cell stage is reached at approximately _____ days; and the late morula stage is reached at approximately ______ days.

two-cell stage = 30 hrs; four-cell stage = 40 hrs; 12-16 cell stage = 3 days; late morula stage = 4 days.

Intermediate mesoderm differentiates into:

urogenital structures

How does the blastocoele become the primary yolk sac?

when the blastocoele is surrounded by the exocoelomic membrane.