Embryology (Gray's Anatomy Review & Lippincott & BRS)

Angelman's Syndrome vs. Prader-Willi Syndrome

(micro)Deletion occurs on the maternal chromosome 15 in Angelman's Syndrome (more prone to laughter) Deletion occurs on the paternal chromosome 15 in Prader-Willi Syndrome (more prone to obesity)

Which of the following events is involved in cleavage of the zygote during week 1 of development? (A) A series of meiotic divisions forming blastomeres (B) Production of highly differentiated blastomeres (C) An increased cytoplasmic content of blastomeres (D) An increase in size of blastomeres (E) A decrease in size of blastomeres

E. Cleavage is a series of mitotic divisions whereby the large amount of zygote cytoplasm is successively partitioned among the newly formed blastomeres. Although the number of blastomeres increases during cleavage, the size of individual blastomeres decreases until they resemble adult cells in size.

Between which two layers is the extraembryonic mesoderm located? (A) Epiblast and hypoblast (B) Syncytiotrophoblast and cytotrophoblast (C) Syncytiotrophoblast and endometrium (D) Exocoelomic membrane and syncytiotrophoblast (E) Exocoelomic membrane and cytotrophoblast

E. The extraembryonic mesoderm is derived from the epiblast and is located between the exocoelomic membrane and the cytotrophoblast. The overall effect is to completely separate the embryoblast from the trophoblast with the extraembryonic mesoderm serving as a conduit (connection) between them.

Ectoderm

1) Epidermis 2) Nervous System 3) Retina See touch think outside (Ecto-outside)

Why is the cytotrophoblast important?

Absorb nutritive fluid from lacunar networks in the synctitotrophob. then to the embryo

In which phase does oogenesis stop in female infants?

After repeated mitotic divisions oogonia stops in prophase of meiosis I to form primary oocytes.

Where does fertilization occur and when does it end?

Fertilization occurs in the ampulla of the fallopian tube and is completed within 24 hours of ovulation. After the egg is released, it moves into the fallopian tube. It stays there for about 24 hours, waiting for a single sperm to fertilize it.

Secondary c.v.

Forms when mesenchyme/mesoderms grows into the primary villi, covering chorionic sac--> capillaries and blood cells

T/F? Paternal genes regulate most of the development of trophoblasts. KEEP IMAGE IN MIND-->

True

What are decidual cells?

Uterine connective tissue cells that degenerate adjacent to the syncytiotrophoblast (outer) and sync. engulfs them to provide embryonic nutrition. The decidua is the modified mucosal lining of the uterus known as the endometrium that forms in preparation for pregnancy.

What is the embryonic disc? Where does it lie?

-A bilaminar combination of Epiblast (primitive ectoderm) & Hypoblast (primitive endoderm) -It lies between the umbilical vesicle and amniotic cavity

What are the usual cause of birth defects?

-Birth defects (10%) -Spontaneous abortions (50%)

Tertiary c.v./Definitive placental villi

-Capillaries fuse to form networks that become the embryonic heart - Cytotrophob. proliferate into synctitotropho forming cytotrophoblastic shell -Branch villi

What is the importance of the branch villi/terminal/free villi?

-Main exchange of material between mother and embryo

What is molar pregnancy?

-Produce high HCG -Benign/malignant tumor (choriocarcinoma) -Trophoblasts abnormally create hydatidiform mole -Cells of molar pregnancy are diploid but their entire genome is paternal -Arise from fertilization of an oocyte lacking a nucleus--> duplication of male chromosome to ensure 2n

What are stem/anchoring chorionic villi?

-Villi that attach to the maternal tissue (decidua basalis) through the cytotrophoblastic shell -Gives rise to branch chorionic villi (terminal/free villi)

What are the stages of the cleavage of a zygote?

1) 2-cell stage 2) 4-cell stage 3) 8-cell stage 4) Morula 5) Early blastocyst 6) Later blastocyst

What are some signs of an ectopic pregnancy?

1) Abdominal pain and tenderness 2) Bleeding 3) Irritation of the pelvic peritoneum

What happens during the 8th day of implantation?

1) Above embryoblast trophoblast differentiates into cytotrophoblast (inner) and syncytiotrophoblast (outer) 2) More cells of the embryoblast becomes hypoblast and epiblast (adjacent to amniotic cavity)

Primary chorionic villi

1) Appear at end of 2nd week 2) Has core of cytotrophoblast

What are barrier methods of birth controls?

1) Condom 2) Diaphragm 3) Cervical cap 4) Sponge

When IVF is given to this group you have best results versus congenital malformations:

1) Congenital problems--> Elderly women 2) Higher success--> Younger women

What are some of the changes that occurs in the endometrial tissue in preparation for a growing embryo?

1) Decidual reaction secondary to cAMP & progesterone signaling 2)Cells swollen due to accumulation of glycogen and lipids

Describe the early and later blastocyst stage.

1) Embryoblast (inner cell mass) 2) Degenerating zona pellucida 3) Blastocystic cavity 4) Trophoblast

What happens during the 10th day of implantation?

1) Epiblast forms the amnion 2) Hypoblast forms the roof of the exocoelomic cavity and is continuous with the cells migrating from the hypoblast (exocoelomic membrane) and lines the internal surface of the cytotrophoblast 3) Primary umbilical vesicle formation (from the exocoelomic membrane) 4) Lacunae forms within synct.trophoblasts (filled with maternal blood from ruptured capillaries and cellular debris) 5) Embryotroph (nourishing fluid) forms and pass into the embryonic disc

What happens during the 13-14th day of implantation?

1) Extraembryonic coelom splits mesoderm into 2 -somatic mesoderm=lines trophoblast + cover amnion -splanchnic mesoderm= surrounds yolk sac 2) Somatic mesoderm--> chorion (forms wall of gestational sac within which the embryo and its amniotic and yolk sac are suspended) 3) Prechordal plate forms (thickening of the hypoblast that shows future site of mouth and head)

KNOW THIS:

1) Fertilization normally occurs in the ampullary region of the uterine tube 2) Low AFP levels rules out Down Syndrome 3) Week 1 of embryonic development is characterized by the events of fertilization through implantation. Fertilization occurs in the ampullary part of the uterine tube. The zygote moves through the uterine tube, dividing into the morula (16-cell) stage by the time it enters the uterine cavity. Finally, it forms the blastocyst and begins implantation in the uterine mucosa by day 7. 4) Week 2 of embryonic development features development of the bilaminar germ disc, which includes the completion of implantation of the embryo into the uterine mucosa and full development of the blastocyst. Remember to think of "twos" for week 2 of development. The blastocyst is composed of two main parts: the inner cell mass (embryoblast) and outer cell mass (trophoblast). The inner cell mass forms the embryo proper and differentiates into two parts that form a bilaminar disc: the epiblast and the hypoblast. The outer cell mass contributes to the formation of the placenta and differentiates into two parts: an inner cytotrophoblast and outer syncytiotrophoblast. 4) Week 3 of embryonic development is characterized by the formation of the trilaminar germ disc. The featured event within this week of development is gastrulation, which results in formation of all three embryonic germ layers: ectoderm, mesoderm, and endoderm. Thus, we should remember "threes" for week 3. Weeks 3 to 8 are denoted as the embryonic period of development, which is the period of organogenesis during which the three germ layers form all tissues and organs. By the end of the 2nd month, the main organ systems are formed and the major external body features are established. Because organ primordia are very sensitive to teratogenic agents, weeks 3 to 8 of development are regarded as the sensitive period. If exposed to teratogens, gross structural organ defects can manifest during the period of organogenesis. Week 5 represents approximately the middle of the embryonic period of development, with organogenesis well underway. By the completion of week 5 of development, the embryo has developed significantly beyond the stages of neurulation and somite formation.

What happens during the 13-14th day of implantation?

1) Formation of primary chorionic villi (extension of cytotrophoblast into syn.tropho.) induced by the extraembryonic somatic mesoderm 2) Extraembryonic coelomic spaces appear within the mesoderm--> Extraembryo. Coelom 3) Primary yolk sac--> Secondary yolk sac

What are the steps of IVF?

1) Hormonal stimulation using gonadotropins of mature oocytes 2) Mature follicles made 3) Oocyte on petri dish with sperm (IVF) 4) Cleavage of oocyte until 4-8 cell stage is reached 5) Take 1/2 cleaving embryos and place them in uterine cavity

What happens during the 12th day of implantation?

1) Lacunae within the sync.trophoblast fuse to form intervillous space (vessels for mom and embryo) 2) Increased growth of trophoblast in comparison to the embryonic disc growth forms extraembryonic mesoderm 3) Extraembryonic coelom forms around the amnion and umbilical vesicle 4) Primary and secondary umbilical vesicle forms 5) Large part of primary umbilical vesicle falls off and the umbilical vesicle has a role in transfer of nutritive materials to embryonic disc

What are two main ways to inhibit implantation?

1) Large doses of estrogen (morning after pills) 2) Intrauterine device (slow release progesterone, copper IUD, ievono. IUD)

What is sacrococcygeal teratoma?

1) Made from remnants of the primitive streak 2) Large tumor formed 3) Tumor has all 3 germ layers

What are the three stages of a primordial follicle?

1) Preantral/primary 2) Antral/Vesicular 3) Mature vesicular/Graafian follicle PAM Primordial follicle

Describe the development of the chorionic villi:

1) Primary chorionic villi 2) Secondary c.v. 3) Tertiary c.v.

Describe how the embryonic disc looks during week three:

1) Primitive streak + notochord development 2) Differentiation of 3 germ layers (Endo, Meso, Ecto) 3) Ultrasonography possible here 4) Start of organogenesis

Describe the 2-cell stage.

1) Second polar body 2) Zona pellucida 3) Blastomere

What are the stages of sperm development starting with the spermatogonia?

1) Spermatogonia 2) Primary spermatocyte 3) Spermatid 4) Spermatozoa

Can a zygote be tested for a genetic disorder before being implanted? How is this possible?

1) The sex of the embryo is detectable from a blastomere taken from a 6-8 cell zygote and analyzed by DNA amplification of sequences from the Y chromosome. 2) IVFs are being used to detect female embryos in cases in which a male embryo would be at risk for a serious X-linked disorder

Why is ectopic pregnancy a major threat?

1) Uterine tube rupture 2) Hemorrhage 3) Death of the embryo 4) Maternal death likely

Where can an ectopic pregnancy occur?

1) Uterine tubes 2) Abdominal cavity (attaches to peritoneal lining of the rectouterine cavity/ Pouch of Douglas) & (Into the omentum or peritoneal lining of intestines)--> MOSTLY 3) Ovaries

What are sterilization forms of birth controls?

1) Vasectomy (involves surgically cutting or blocking the vas deferens, the tubes that carry sperm from the testicles to the penis) 2) Tubal ligation

During which week does the heart beat and the villi supply the embryo with nutrients and oxygen?

4th week

What happens during the 7th day of implantation?

A layer called the hypoblast (primary endoderm) appears as a separation from the embryoblast

During week 2 of development, the embryoblast receives its nutrients via (A) diffusion (B) osmosis (C) reverse osmosis (D) fetal capillaries (E) yolk sac nourishment

A. During week 2 of development, the embryoblast receives its nutrients from endometrial blood vessels, endometrial glands, and decidual cells via diffusion. Diffusion of nutrients does not pose a problem given the small size of the blastocyst during week 2. *Although the beginnings of a uteroplacental circulation are established during week 2, no blood vessels have yet formed in the extraembryonic mesoderm to carry nutrients directly to the embryoblast (this occurs in week 3).*

In the production of male gametes, which of the following cells remains dormant for 12 years? (A) Primordial germ cell (B) Primary spermatocyte (C) Secondary spermatocyte (D) Spermatid (E) Sperm

A. Primordial germ cells migrate from the wall of the yolk sac during week 4 of embryonic life and enter the gonad of a genetic male, where they remain dormant until puberty (about age 12) when hormonal changes in the young man stimulate the production of sperm

In the process of meiosis, DNA replication of each chromosome occurs thereby forming a structure consisting of two sister chromatids attached to a single centromere. What is this structure? (A) A duplicated chromosome (B) Two chromosomes (C) A synapsed chromosome (D) A crossover chromosome (E) A homologous pair

A. The structure formed is a duplicated chromosome. DNA replication occurs so that the amount of DNA is doubled (2 x 2N = 4N). However, the chromatids remain attached to the centromere forming a duplicated chromosome.

What process must occur within endometrial cells to facilitate implantation?

Apoptosis

In the production of female gametes, which of the following cells can remain dormant for 12 to 40 years? (A) Primordial germ cell (B) Primary oocyte (C) Secondary oocyte (D) First polar body (E) Second polar body

B. Primary oocytes are formed by month 5 of fetal life and remain dormant until puberty, when hormonal changes in the young woman stimulate the ovarian and menstrual cycles. From 5 to 15, oocytes then begin maturation with each ovarian cycle throughout the woman's reproductive life.

Where does the blastocyst normally implant? (A) Functional layer of the cervix (B) Functional layer of the endometrium (C) Basal layer of the endometrium (D) Myometrium (E) Perimetrium

B. The blastocyst implants in the functional layer of the uterine endometrium. The uterus is composed of the perimetrium, myometrium, and endometrium. Two layers are identified within the endometrium: (1) the functional layer, which is sloughed off at menstruation, and (2) the basal layer, which is retained at menstruation and serves as the source of regeneration of the functional layer. During the progestational phase of the menstrual cycle, the functional layer undergoes dramatic changes; uterine glands enlarge and vascularity increases in preparation for blastocyst implantation.

Which of the following components plays the most active role in invading the endometrium during blastocyst implantation? (A) Epiblast (B) Syncytiotrophoblast (C) Hypoblast (D) Extraembryonic somatic mesoderm (E) Extraembryonic visceral mesoderm

B. The syncytiotrophoblast plays the most active role in invading the endometrium of the mother's uterus. During the invasion, endometrial blood vessels and endometrial glands are eroded, and a lacunar network is formed.

Which of the following structures must degenerate for blastocyst implantation to occur? (A) Endometrium in progestational phase (B) Zona pellucida (C) Syncytiotrophoblast (D) Cytotrophoblast (E) Functional layer of the endometrium

B. The zona pellucida must degenerate for implantation to occur. Early cleavage states of the blastula are surrounded by a zona pellucida, which prevents implantation in the uterine tube.

When does the period of the morula being and ends?

BEGINS: -12-32 cell stage END: -When blastocyst forms

When is the blastocyst implanted in the endometrium?

By the end of week 1

When does a secondary oocyte complete its second meiotic division to become a mature ovum? (A) At ovulation (B) Before ovulation (C) At fertilization (D) At puberty (E) Before birth

C. At ovulation, a secondary oocyte begins meiosis II, but this division is arrested at metaphase. The secondary oocyte remains arrested in metaphase until a sperm penetrates it at fertilization. Therefore, the term "mature ovum" is somewhat of a misnomer, because it is a secondary oocyte that is fertilized and, once fertilized, the new diploid cell is known as a zygote. If fertilization does not occur, the secondary oocyte degenerates.

A 16-year-old girl presents on May 10 in obvious emotional distress. On questioning, she relates that on May 1 she experienced sexual intercourse for the first time, without any means of birth control. Most of her anxiety stems from her fear of pregnancy. What should the physician do to alleviate her fear? (A) Prescribe diazepam and wait to see if she misses her next menstrual period (B) Use ultrasonography to document pregnancy (C) Order a laboratory assay for serum hCG (D) Order a laboratory assay for serum progesterone (E) Prescribe diethylstilbestrol ("morningafter pill")

C. Human chorionic gonadotropin (hCG) can be assayed in maternal serum at day 8 of development and in urine at day 10. If this teenager is pregnant, the blastocyst would be in week 2 of development (day 10). Laboratory assay of hCG in either the serum or urine can be completed; however, serum hCG might be more reliable. It is important to note that if she is pregnant, she will not miss a menstrual period until May 15 at which time the embryo will be entering week 3 of development.

A young woman enters puberty with approximately 40,000 primary oocytes in her ovary. About how many of these primary oocytes will be ovulated over the entire reproductive life of the woman? (A) 40,000 (B) 35,000 (C) 480 (D) 48 (E) 12

C. Over her reproductive life, a woman ovulates approximately 480 oocytes. A woman ovulates 12 primary oocytes per year provided that she is not using oral contraceptives, does not become pregnant, or does not have any anovulatory cycles. Assuming a 40-year reproductive period, 40 x 12 = 480.

Individual blastomeres were isolated from a blastula at the 4-cell stage. Each blastomere was cultured in vitro to the blastocyst stage and individually implanted into four pseudopregnant foster mothers. Which of the following would you expect to observe 9 months later? (A) Birth of one baby (B) Birth of four genetically different babies (C) Birth of four genetically identical babies (D) Birth of four grotesquely deformed babies (E) No births

C. This scenario would result in four genetically identical children. Blastomeres at the 4-cell to 8-cell stage are totipotent, that is, capable of forming an entire embryo. Since blastomeres arise by mitosis of the same cell (zygote), they are genetically identical. This phenomenon is important in explaining monozygotic (identical) twins. About 30% of monozygotic twins arise by early separation of blastomeres. The remaining 70% originate at the end of week 1 of development by a splitting of the inner cell mass.

How much DNA does a primary spermatocyte contain? (A) 1N (B) 2N (C) 4N (D) 6N (E) 8N

C. Type B spermatogonia give rise to primary spermatocytes by undergoing DNA replication, thereby doubling the amount of DNA (2 x 2N = 4N) within the cell.

Mesoderm

CVD Blood Bone marrow etc.

KNOW THIS:

Cardiac muscle is derived from the visceral layer of lateral plate mesoderm (splanchnic mesoderm) that surrounds the primitive paired endothelial heart tubes

When does cleavage of the zygote occur and end?

Cleavage begins at the 12-16 cell stage and ends when the blastocyst forms. *Cleavage and morula formation occurs as the zygote passes through the uterine tube*

Describe the 8-cell stage.

Contains pellucida

A 42-year-old woman presents with complaints of severe headaches, blurred vision, slurred speech, and loss of muscle coordination. Her last pregnancy 5 years ago resulted in a hydatidiform mole. Laboratory results show a high hCG level. Which of the following conditions is a probable diagnosis? (A) Vasa previa (B) Placenta previa (C) Succenturiate placenta (D) Choriocarcinoma (E) Membranous placenta

D. After a hydatidiform mole, it is very important to ensure that all the invasive trophoblastic tissue is removed. High levels of hCG are a good indicator of retained trophoblastic tissue because such tissue produces this hormone. In this case, the trophoblastic tissue has developed into a malignant choriocarcinoma and metastasized to the brain, causing her symptoms of headache, blurred vision, and so on.

During meiosis, pairing of homologous chromosomes occurs, which permits large segments of DNA to be exchanged. What is this process called? (A) Synapsis (B) Nondisjunction (C) Alignment (D) Crossing over (E) Disjunction

D. Synapsis (pairing of homologous chromosomes) is a unique event that occurs only during meiosis I in the production of gametes. Synapsis is necessary so that crossing over, in which large segments of DNA are exchanged, can occur.

Which of the following are components of the definitive chorion? (A) Extraembryonic somatic mesoderm and epiblast (B) Extraembryonic somatic mesoderm and cytotrophoblast (C) Extraembryonic somatic mesoderm and syncytiotrophoblast (D) Extraembryonic somatic mesoderm, cytotrophoblast, and syncytiotrophoblast (E) Extraembryonic visceral mesoderm, cytotrophoblast, and syncytiotrophoblast

D. The definitive chorion consists of three components: extraembryonic somatic mesoderm, cytotrophoblast, and syncytiotrophoblast. The chorion defines the chorionic cavity in which the embryoblast is suspended and is vital in the formation of the placenta.

KNOW THIS:

During early fetal life, oogonia undergo mitotic divisions to populate the developing ovary. All the oogonia subsequently give rise to primary oocytes by month 5 of fetal life; at birth no oogonia are present in the ovary. At birth, a female has her entire supply of primary oocytes to carry her through reproductive life.

When are primordial germs cells derived from epiblast?

During the second week *Which move to the wall of yolk sac*

For each or the following statements or words concerning a 14-day-old blastocyst, select the most appropriate structure in the diagram (right). -Future site of the mouth -Forms definitive structures found in the adult -Chorion -Chorionic cavity -Primary chorionic villi -Connecting stalk

E. The prochordal plate indicates the site of the future mouth. At this early stage of development, the orientation of the embryo in the cranial versus caudal direction is established. The prochordal plate is a thickening of hypoblast cells that are firmly attached to the epiblast cells. C. The bilaminar embryonic disk develops definitive adult structures after gastrulation occurs, in contrast to the trophoblast, which is involved in placental formation. D. The chorion consists of three layers; namely, extraembryonic somatic mesoderm, cytotrophoblast, and syncytiotrophoblast. The chorion is vital in the formation of the placenta. G. The chorion forms the walls of the chorionic cavity in which the conceptus is suspended by the connecting stalk. Note that the inner lining of the chorionic cavity is extraembryonic mesoderm. A. The cytotrophoblast is mitotically active so that local mounds of cells (primary chorionic villi) form that bulge into the surrounding syncytiotrophoblast. As development continues, primary chorionic villi form secondary chorionic villi, and finally tertiary chorionic villi as part of placental formation. B. The extraembryonic mesoderm can be thought of as initially forming in a continuous layer and then splitting as isolated cavities begin to appear everywhere except dorsally near the amniotic cavity and epiblast. When the isolated cavities coalesce, the extraembryonic coelom (or chorion cavity) and connecting stalk are formed.

What happens to the blastocyst if the corpus luteum does not produce enough progesterone and estrogen?

Early implantation of the blastocyst may fail to occur in this case *This tend to happen in patients whose last menstrual period is delayed and whose last menstrual flow is abundant. *This scenario indicates early spontaneous abortion which may be the background for chromosomal abnormalities*

During which week of embryological development does the oxygen and nutrient transfer from the maternal blood in the intervillous space to the embryo's blood?

End of 3rd week

What are primordial germ cells derived from?

Epiblast

Endoderm

Epithelial linings

What is the name of the fluid filled cavity that surrounds the amnion and yolk sac except where they are attached to the chorion by the connecting stalk?

Extraembryo. Coelom

KNOW THIS:

Hypoblast cells migrate outward to line the inner surface of the cytotrophoblast. Together, they demarcate the exocoelomic cavity (primitive yolk sac). With further development, the primitive yolk sac is reduced in size. Its remnant becomes the secondary yolk sac (definitive yolk sac), which will give rise to the gut tube. At day 9-10 of embryonic development, cells from the hypoblast begin to migrate to the embryonic pole, forming a layer of cells just beneath the cytotrophoblast, called Heuser's Membrane. It surrounds the exocoelomic cavity (primitive yolk sac), i.e. it lines the inner surface of the cytotrophoblast. At this point, the exocoelomic cavity replaces the blastocyst cavity. The cytotrophoblast is mitotically active. It contributes to the wall of the primitive yolk sac, forms the primary chorionic villi that extend into the syncytiotrophoblast, and provides cells that migrate into the syncytiotrophoblast and allow it to expand.

Where does implantation take place?

In the endometrium, superiorly in the body, in the posterior wall of the uterus

When does implantation begin and end?

It begins at the end of the first week and is completed by the end of the second week

When does the zona pellucida disappear?

It disappears by the late blastocyst stage (5 days). Once it disappears you can have increase in size of embryo.

How is the secondary yolk sac formed?

It is formed by the extraembryonic endodermal cells that migrate inside the primary yolk sac from the hypoblast of the embryonic disc

Where is the embryoblast found?

It is found in the blastocystic cavity

Why is the yolk sac important?

It plays a role in selective transfer of nutrition to the embryonic disc

Which structure is derived from the same embryonic primordium as the kidney? (A) Gonad (B) Epidermis (C) Pineal gland (D) Liver (E) Adrenal medulla

The answer is A: Gonad. -Both the kidneys and the gonads are derived from the intermediate mesoderm. This longitudinal dorsal ridge of mesoderm forms the urogenital ridge, which is involved with the formation of the future kidneys and gonads. -The liver is derived from the lateral plate mesoderm (specifically the splanchnic mesoderm), not the intermediate mesoderm. -The lateral plate mesoderm is a thin plate of mesoderm in which large spaces (intraembryonic coelom) form. These spaces coalesce and divide the lateral plate mesoderm into the intraembryonic somatic mesoderm and the intraembryonic splanchnic (visceral) mesoderm.

A young couple hoping for a pregnancy buys an overthe-counter pregnancy kit. What substance will this test most likely detect? (A) Early pregnancy factor (EPF) (B) Human chorionic gonadotropin (C) Progesterone (D) Estrogen (E) Luteinizing hormone (LH)

The answer is B: Human chorionic gonadotropin. Early pregnancy detection kits most likely detect the level of human chorionic gonadotropin (hCG) in the female. hCG is a glycoprotein hormone produced by the syncytiotrophoblast to prevent the disintegration of the corpus luteum of the ovary. While hCG is a reliable marker of pregnancy, it cannot be detected until after implantation (6 to 12 days after fertilization), which results in false negatives if the test is performed during the very early stages of pregnancy.

The notochord forms the initial axial skeletal element of the body and induces the formation of the neural plate. Which of the following structures is the sole postnatal remnant of the embryonic notochord? (A) Spinal cord (B) Nucleus pulposus (C) Rib cage (D) Anulus fibrosus (E) Spinal meninges

The answer is B: Nucleus pulposus. The only remnant of the notochord is the central core portion of each of the intervertebral discs, the nucleus pulposus. This hydrostatic structure is the component of the disc that herniates out of its normal position in cases of herniated ("slipped") discs.

A married woman who is having diffi culty getting pregnant undergoes an endometrial function test (EFT), which determines that the endometrium of her uterus is not capable of implantation. Which of the following substances would likely increase the chances for implantation of the fertilized oocyte (or preimplantation embryo) into the uterine mucosa? (A) Follicle-stimulating hormone (B) Testosterone (C) Progesterone (D) Estrogen (E) Luteinizing hormone

The answer is C: Progesterone. Progesterone is a steroid hormone produced by the ovaries, brain, and placenta of pregnant females. In the menstrual cycle, progesterone production remains low until after ovulation. The corpus luteum (the remnant of the collapsed ovarian follicle after ovulation) produces progesterone, which halts endometrial proliferation and builds the endometrial lining of the uterus in preparation for implantation of the fertilized oocyte (zygote). Therefore, progesterone supplementation would increase the chances for implantation of the fertilized oocyte into the uterine mucosa of this patient. Because increased serum levels of progesterone and estrogen suppress its release, FSH levels remain low during the buildup of the endometrial lining of the uterus, which is crucial for implantation. Also, the production of FSH peaks approximately 3 days after menstruation because serum levels of progesterone and estrogen are low. Therefore, FSH supplementation would decrease the chances for implantation of the fertilized oocyte into the uterine mucosa.

A 28-year-old woman who does not know that she is pregnant undergoes a chemotherapy treatment at the end of her 1st week of pregnancy. Chemotherapy is associated with slowing the rate of mitosis in exposed cells, which is good in cancer treatment. However, this treatment may also have a negative influence on the implantation and growth of an embryo. In which of the following layers would a lowered rate of cell division be most likely to hinder implantation of the blastocyst? (A) Amnioblast (B) Epiblast (C) Hypoblast (D) Cytotrophoblast (E) Syncytiotrophoblast

The answer is D: Cytotrophoblast. The trophoblast forms the fetal part of the placenta, so it is concerned with implantation. The cytotrophoblast is the mitotically active inner part of the trophoblast, and it forms the primary chorionic villi that extend into the syncytiotrophoblast. The cytotrophoblast also provides the cells that migrate into the syncytiotrophoblast and allow it to expand. Thus, chemotherapy may directly affect mitotic activity in the cytotrophoblast, causing stunted growth of both it and the syncytiotrophoblast and possibly hindering implantation. Choice A (Amnioblast) is incorrect. Amnioblasts are the epiblast cells that line the amniotic cavity adjacent to the cytotrophoblast. They are mitotically active in the growth of the amniotic membrane; however, they are not involved in implantation. Choice B (Epiblast) is incorrect. The epiblast is the dorsal cell layer of the bilaminar germ disc. It contributes to the formation of the embryo proper. While certainly mitotically active, it is not involved in implantation. Choice C (Hypoblast) is incorrect. The hypoblast is the ventral cell layer of the bilaminar germ disc. It also contributes to the formation of the embryo proper. Choice E (Syncytiotrophoblast) is incorrect. The syncytiotrophoblast is the outer, multinucleated part of the trophoblast that is mitotically inactive. The syncytiotrophoblast erodes the maternal endometrium and contributes to the formation of the primitive uteroplacental circulation. However, its growth depends on incorporation of new cells from the active cytotrophoblast. Thus, chemotherapy in this case would not affect cell division within the syncytiotrophoblast.

A married couple having diffi culty with conception keeps a daily diary of the female's basal body temperature (BBT) throughout the month. On Friday, the woman noted a slight elevation in her BBT of approximately one-half to one degree Fahrenheit (one-quarter to one-half degree Celsius), which may indicate that she is ovulating. If her ovum, depicted on the right side in the given figure, is expelled into the peritoneal cavity from the ovary (ovulation), the secondary oocyte resides at what specific stage of meiosis? (A) Prophase of meiosis I (B) Prophase of meiosis II (C) Metaphase of meiosis I (D) Metaphase of meiosis II (E) Meiosis is completed at the time of ovulation

The answer is D: Metaphase of meiosis II. The secondary is arrested in metaphase of meiosis II about 3 hours before ovulation, and it will remain in this meiotic stage until fertilization occurs. Oogonia are formed in month 5 of a woman's fetal life. Of these 7 million oogonia, 5 million degenerate or become atretic before birth, leaving 2 million oogonia to differentiate into primary oocytes before birth. No oogonia are present at birth. *The primary oocytes are dormant in prophase of meiosis I until puberty because they are surrounded by follicular cells, which secrete oocyte maturation inhibitor (OMI) that causes the arrest of meiosis I.*

In a 15-day embryo, the epiblast is capable of forming which of the following germ layers? (A) Ectoderm only (B) Ectoderm and mesoderm only (C) Ectoderm and endoderm only (D) Mesoderm and endoderm only (E) Ectoderm, mesoderm, and endoderm

The answer is E: Ectoderm, mesoderm, and endoderm. The epiblast is capable of forming all three germ layers (ectoderm, mesoderm, and endoderm) during gastrulation. Epiblast cells migrate to the primitive streak and invaginate into a space between the epiblast and the hypoblast

A 4-month-old male infant presents with a "growing sore" located posterior to his left ear. This sore is diagnosed as a postauricular hemangioma, as seen in the given photo with the auricle pulled anterior. The cells forming the hemangioma are derived from which of the following cell layers? (A) Endoderm (B) Neural crest (C) Neuroectoderm (D) Ectoderm (E) Mesoderm

The answer is E: Mesoderm. The mesoderm forms during gastrulation when invaginating epiblast cells form an additional germ layer between the endoderm and the ectoderm. The mesoderm has many notable derivatives, including muscle, connective tissue, bone, cartilage, blood cells, dermis of the skin, and organs, such as the kidney, spleen, and gonads.

What marks the beginning of the primordial uteroplacental circulation?

The communication of eroded uterine vessels with the lacunae

When does the increase in the size of the embryo occur?

The increase in the size of the embryo occurs when the zona pellucida degenerates.

KNOW THIS:

The prochordal plate is a circular, midline thickening of hypoblast cells that are firmly attached to the overlying epiblast cells. The plate eventually develops into a membrane called the oropharyngeal membrane at the site of the future mouth. It is interesting to note that at this early stage of development the cranial versus caudal region of the embryo is established by the prochordal plate. And since the prochordal plate is located in the midline, bilateral symmetry is also established.

What happens during the 6th day of implantation?

The trophoblast becomes attached to the endometrial epithelium at the embryonic pole of the blastocyst

Why do teratomas form?

They form if a germ cell has left its normal migratory path. They form into bone, hair, and muscle.

What is the role of the syncytiotrophoblast (outer) in enabling the blastocyst to burrow deep into the endometrium?

They invade endometrial connective tissue that supports uterine capillaries and glands and they produce proteolytic enzymes that erode maternal tissue enabling the blastocyst to burrow *Uterine connective tissue cells around the implantation site then becomes loaded with lipids and glycogen*

How do hormonal method forms of birth control work?

They prevent ovulation by preventing the release of FSH and LH from the pituitary glands changing the uterine lining, thickening the cervical mucus to prevent sperm entry into the uterus. Male pill contains synthethic androgens that prevents both FSH and LH secretions, prevents sperm production or decreasing its number to a level of infertility

What happens to primordial germ cells in males?

They remain dormant until puberty

What is the function of syncytiotrophoblast?

This is the tissue zone that invades and erodes maternal tissues. It roots into the endometrium to form lacunae filled with maternal blood and glandular secretions. This lacunar network forms the primitive uteroplacental circulation. Eroded endometrial blood vessels and glands leak into the lacunar network of the syncytiotrophoblast as part of the early uteroplacental circulation.

T/F? Growth of the bilaminar embryonic disc is slower compared to the growth of the trophoblast.

True

KNOW THIS:

Week 4 is characterized by most of neurulation, much of somite differentiation, the appearance of the pharyngeal (branchial) apparatus, and the appearance of the upper limb bud. Neurulation (the process of formation of the neural tube) begins late in week 3 with formation of the neural groove and neural folds. However, most of the process, including formation and completion of the neural tube, occurs during week 4. Differentiation of the trophoblast (the outer cell mass of the blastocyst) into cytotrophoblast and syncytiotrophoblast areas occurs early in week 2. These layers form the fetal component of the placenta and thus are critical to full implantation. At the same time, the embryoblast (the inner cell mass of the blastocyst) differentiates into the bilaminar germ disc, consisting of the epiblast and hypoblast.