Embryology and Development Practice Questions

Q: What stage of embryonic development is shown in the following image?

Blastocyst. ***Blastocyst*** - The image shows a structure with a distinct fluid-filled cavity (the **blastocoel**, labeled X), an inner cell mass (**embryoblast**), and an outer cell layer (**trophoblast**), which are the defining features of a blastocyst. - This stage occurs around day 5 post-fertilization and is responsible for implantation into the **endometrium** of the uterine wall, which is depicted superior to the blastocyst in the illustration. *Morula* - A morula is a solid, compacted ball of 16-32 cells (**blastomeres**) that precedes the blastocyst stage; it does not have the large internal cavity shown in the image. - The morula forms around day 3-4 after fertilization, and it is the entry of fluid into the morula that transforms it into a blastocyst. *Ova* - An ovum (plural: ova) is a single, unfertilized female gamete (egg cell). - The image shows a multicellular embryo that is the result of fertilization and several rounds of cell division, not a single cell. *Gastrula* - Gastrulation is the process that follows the blastocyst stage, where the embryo organizes into three primary germ layers: **ectoderm**, **mesoderm**, and **endoderm**. - The structure shown is a pre-implantation embryo and has not yet undergone gastrulation, which is characterized by the formation of the **primitive streak**.

Q: What is the most common type of ventricular septal defect?

Membranous defect. ***Membranous defect***- This type of defect, also known as **perimembranous VSD**, is the most common form, accounting for approximately 70-80% of all ventricular septal defects [1].- It is located just below the aortic valve, involving the **proximal third** of the septum and is defined by its relationship to the fibrous trigones [1].*Muscular defect*- **Muscular VSDs** (or trabecular VSDs) are less common than membranous defects and can be found anywhere within the thick muscular portion of the septum.- These defects often have a higher rate of **spontaneous closure**, especially the small, multiple defects referred to as 'Swiss cheese' VSDs.*Non-development of the perimembranous part of the septum*- While the failure of complete septation of the **membranous portion** is the underlying embryological cause, the specific anatomical diagnosis defining the common VSD type is the *membranous defect*. - This phrasing is descriptive of the etiology but **membranous defect** identifies the most common resulting structure.*Incomplete fusion of the septum*- This is a generic description of the mechanism leading to VSD development (failure of the septal components to fuse correctly), but it does not specify the **most common anatomical location**.- The most critical and common fusion failure involves the development of the **membranous septum**, which results in the named *membranous defect*.

Q: Which of the following represents the most severe form of neural tube defect where neural tissue is completely exposed without overlying skin, vertebral arches, or meninges?

Open Neural tube defect. ***Open Neural tube defect*** - The image displays a severe congenital anomaly where the neural tube has failed to close, leaving the neural tissue completely exposed. This specific presentation is consistent with **rachischisis**, the most severe form of spina bifida. - Characteristic features visible are the complete absence of overlying skin, vertebral arches, and meninges, exposing the flattened, malformed spinal cord (neural placode) along the entire spine. *Meningocele* - A **meningocele** is a less severe defect where a sac containing only meninges and cerebrospinal fluid protrudes through an opening in the spine; the spinal cord itself is not displaced. - This is incorrect as the image clearly shows exposed **neural tissue**, which is not a feature of a simple meningocele. *Spina bifida* - **Spina bifida** is a broad term for a range of defects involving incomplete closure of the spine. It includes mild forms like **spina bifida occulta** and severe forms like myelomeningocele, which are typically localized. - The defect in the image is far more extensive than a typical localized spina bifida, affecting a large portion or the entire spine, making it a severe type of open neural tube defect known as rachischisis. *Myelomeningocele* - In a **myelomeningocele**, both the meninges and the spinal cord protrude through the defect, typically forming a sac on the infant's back. - The image does not show a contained sac but rather a completely open, flattened neural plate, which is characteristic of **rachischisis**, a more severe condition than a typical myelomeningocele.

Q: A child with fused carpal bones comes to your clinic. What is the gene associated with Hand-Foot-Genital Syndrome?

HOXA13. ***HOXA13 (Correct Answer)*** - Mutations in the **HOXA13** gene, a member of the HOX family of transcription factors, are responsible for **Hand-Foot-Genital Syndrome (HFGS)** - HFGS is an autosomal dominant disorder characterized by skeletal defects, including **fused carpal and tarsal bones** (as presented in this case), short digits, and genitourinary anomalies - The carpal fusion is a classic diagnostic feature of HOXA13 mutations *Incorrect: BCL6* - **BCL6** (B-cell lymphoma 6) is a transcriptional repressor primarily known for its role in regulating B-cell maturation and germinal center formation - Mutations or translocations involving BCL6 are implicated in **diffuse large B-cell lymphoma** and follicular lymphoma, not congenital skeletal abnormalities *Incorrect: FGFR* - **FGFR** (Fibroblast Growth Factor Receptor) genes are associated with skeletal dysplasias involving abnormal endochondral ossification - Mutations in FGFR genes cause conditions like **Achondroplasia** (FGFR3) or **craniosynostoses** (FGFR2), rather than the specific carpal-tarsal fusion pattern seen in HOXA13 defects *Incorrect: COL11* - **COL11A1** and **COL11A2** genes encode collagen type XI and are associated with **Stickler syndrome** and various collagenopathies - These conditions affect connective tissue broadly, causing features like myopia, hearing loss, and joint hypermobility, rather than the isolated carpal fusions characteristic of Hand-Foot-Genital Syndrome

Q: Which of the following structures develop from the 6th pharyngeal arch artery on the left side?

Ductus arteriosus. ***Ductus arteriosus*** - The **ductus arteriosus** develops from the persistence of the distal portion of the **left 6th pharyngeal arch artery**. [2] - This structure is critical in fetal circulation, allowing blood to bypass the non-functional fetal lungs by shunting flow from the left pulmonary artery to the descending aorta. [1], [3] *Arch of Aorta* - The **arch of the aorta** mainly develops from the **aortic sac** and the distal part of the **left 4th pharyngeal arch artery**. - The 6th arch contributes only to the pulmonary system and the ductus shunt, not the primary aortic arch. *Carotid arteries* - Both the **common carotid arteries** and the **internal carotid arteries** are major derivatives of the **3rd pharyngeal arch arteries**. - The 3rd arch artery structure is completely separate from the 6th arch involvement in lung circulation development. *Subclavian artery* - The **left subclavian artery** arises largely from the **7th cervical intersegmental artery**, which is not part of the aortic arch system itself. - The **right subclavian artery** develops from the right 4th pharyngeal arch artery, the 7th intersegmental artery, and the right dorsal aorta.

Q: The condition seen in the image results from failure of fusion of:

Medial nasal prominence and maxillary prominence. ***Medial nasal prominence and maxillary prominence*** - The upper lip is formed embryologically by the fusion of the two **medial nasal prominences** (which form the central philtrum) and the two **maxillary prominences** (which form the lateral parts of the upper lip). - Failure of these prominences to fuse results in a **cleft lip** (cheiloschisis), as depicted in the image, which can be unilateral or bilateral. *Lateral nasal prominence and maxillary prominence* - The fusion of the **lateral nasal prominence** and the **maxillary prominence** forms the side of the face and the nasolacrimal duct. - Failure of these structures to fuse results in an **oblique facial cleft**, a rare condition extending from the upper lip to the eye. *Lateral nasal prominence and mandibular prominence* - These two prominences do not fuse during facial development. The **lateral nasal prominence** forms the alae (wings) of the nose. - The **mandibular prominence** forms the lower jaw and the lower lip, which is anatomically separate from the nasal structures. *Medial nasal prominence and mandibular prominence* - The **medial nasal prominence** contributes to the upper lip and nose, while the **mandibular prominence** forms the lower lip and jaw. - These structures are located superior and inferior to the developing mouth, respectively, and do not fuse with each other.

Q: If the division in the zygote occurs between 9-12 days after fertilization, which of the following twins is expected?

Monochorionic monoamniotic. ***Monochorionic monoamniotic*** - Division of the inner cell mass (ICM) occurring between **9 and 12 days** after fertilization results in a twin pregnancy where both fetuses share a single **chorion** and a single **amnion**.- This stage marks division after the amnion has formed (around day 8) but before complete differentiation, leading to high risks like **cord entanglement**. *Dichorionic diamniotic* - This pattern results from division occurring very early, typically within the first **3 days** (2-cell stage to morula stage).- Since separation happens before the differentiation of the trophoblast and inner cell mass, both the **chorion** and the **amnion** are separate. *Conjoint twins* - Conjoint twins (Siamese twins) occur when the separation is delayed beyond the **13th day** after fertilization.- The division is incomplete, as it occurs *after* the formation of the **embryonic disc**. *Monochorionic diamniotic* - This type of twinning arises from division occurring between **4 and 8 days** after fertilization, typically during the blastocyst stage.- It leads to the sharing of the **chorion** but the development of separate **amnions**.

Q: A patient presents cyst on the neck with anterior to the sternocleidomastoid at the junction of the upper and middle third of the muscle. This cyst is due to the persistence of which of the following embryological clefts?

2nd cleft. ***2nd cleft***- A cyst appearing anterior to the **sternocleidomastoid muscle (SCM)**, especially at the junction of the upper and middle third, is the classical presentation of a second branchial cleft cyst (BCC) [1].- Persistence of the **cervical sinus**, which is formed by the rapid growth of the second arch covering the 2nd, 3rd, and 4th clefts, results in the most common type of BCC (over 90%).*1st cleft*- First branchial cleft cysts are rare and typically manifest near the **external auditory canal**, the angle of the mandible, or within the parotid gland [1].- These defects are often associated with the structures of the first arch, such as the **facial nerve** or parotid gland parenchyma.*3rd cleft*- Cysts derived from the third cleft are uncommon and usually present lower in the neck, often close to or piercing the **thyrohyoid membrane**.- A third cleft fistula would course **posterior to the carotid arteries** and anterior to the vagus nerve before ending in the pyriform sinus.*4th cleft*- Remnants of the fourth cleft are extremely rare and typically involve a fistula that tracks inferiorly to the great vessels (e.g., the **aortic arch** on the left side).- Fourth arch defects are often associated with recurrent **thyroiditis** or infection originating from the pyriform sinus.

Q: During a clinical examination, a senior resident asks an intern to examine the umbilical cord. How many arteries and veins are normally present in a healthy umbilical cord?

1 vein and 2 arteries. ***1 vein and 2 arteries*** - The normal configuration of a healthy umbilical cord is three vessels: **two umbilical arteries** and **one umbilical vein**. - The **umbilical vein** transports oxygenated blood from the placenta to the fetus, whereas the **two umbilical arteries** carry deoxygenated blood and metabolic waste from the fetus back to the placenta. *1 artery and 2 veins* - This configuration is incorrect; normally, the right umbilical vein **atrophies** early in gestation, leaving only a single left umbilical vein. - A cord with two veins suggests a **developmental anomaly** and is not the standard finding. *1 artery and 1 vein* - This pattern is an anomaly known as a **Single Umbilical Artery (SUA)**, which is found in 0.5% to 1% of pregnancies. - SUA is clinically significant as it is associated with an increased risk of **congenital anomalies**, especially renal, cardiac, and chromosomal defects. *2 arteries and 2 veins* - This is an abnormal configuration; while two arteries are standard, the presence of two veins instead of one is due to the failure of the **right umbilical vein** to involute, which is typically a normal event. - The persistence of two veins is highly **atypical** and often requires specialized fetal surveillance.

Q: The image shows a congenital cardiac defect. Abnormal development of which branch of aortic arch leads to this defect?

Left 6th aortic arch. ***Left 6th aortic arch*** - The **Ductus Arteriosus**, which shunts blood from the pulmonary artery to the aorta in fetal life, is embryologically derived from the distal portion of the **Left 6th Aortic Arch**. - **Patent Ductus Arteriosus (PDA)** is the failure of this fetal connection to close after birth. *Right 4th aortic arch* - The **Right 4th Aortic Arch** contributes to the formation of the proximal segment of the **Right Subclavian Artery**. - Defects in the right 4th arch are typically associated with vascular ring anomalies, such as an aberrant right subclavian artery. *Right 6th aortic arch* - The **Right 6th Aortic Arch** forms the proximal segment of the **Right Pulmonary Artery**. - The distal part of the right 6th arch normally involutes and disappears completely, unlike the persistence seen on the left side (PDA). *Left 4th aortic arch* - The **Left 4th Aortic Arch** forms the segment of the **Arch of the Aorta** located between the left common carotid and the left subclavian arteries. - This arch is primarily involved in forming the main aortic arch structure.

Question 1

What stage of embryonic development is shown in the following image?

Accepted Answer

Blastocyst

Answer

Gastrula

Answer

Morula

Answer

Ova

Question 2

What is the most common type of ventricular septal defect?

Accepted Answer

Membranous defect

Answer

Incomplete fusion of the septum

Answer

Non-development of the perimembranous part of the septum

Answer

Muscular defect

Question 3

Which of the following represents the most severe form of neural tube defect where neural tissue is completely exposed without overlying skin, vertebral arches, or meninges?

Accepted Answer

Open Neural tube defect

Answer

Meningocele

Answer

Spina bifida

Answer

Myelomeningocele

Question 4

A child with fused carpal bones comes to your clinic. What is the gene associated with Hand-Foot-Genital Syndrome?

Accepted Answer

HOXA13

Answer

BCL6

Answer

FGFR

Answer

COL11

Question 5

Which of the following structures develop from the 6th pharyngeal arch artery on the left side?

Accepted Answer

Ductus arteriosus

Answer

Arch of Aorta

Answer

Subclavian artery

Answer

Carotid arteries

Question 6

The condition seen in the image results from failure of fusion of:

Accepted Answer

Medial nasal prominence and maxillary prominence

Answer

Lateral nasal prominence and mandibular prominence

Answer

Lateral nasal prominence and maxillary prominence

Answer

Medial nasal prominence and mandibular prominence

Question 7

If the division in the zygote occurs between 9-12 days after fertilization, which of the following twins is expected?

Accepted Answer

Monochorionic monoamniotic

Answer

Dichorionic diamniotic

Answer

Monochorionic diamniotic

Answer

Conjoint twins

Question 8

A patient presents cyst on the neck with anterior to the sternocleidomastoid at the junction of the upper and middle third of the muscle. This cyst is due to the persistence of which of the following embryological clefts?

Accepted Answer

2nd cleft

Answer

1st cleft

Answer

3rd cleft

Answer

4th cleft

Question 9

During a clinical examination, a senior resident asks an intern to examine the umbilical cord. How many arteries and veins are normally present in a healthy umbilical cord?

Accepted Answer

1 vein and 2 arteries

Answer

1 artery and 1 vein

Answer

2 arteries and 2 veins

Answer

1 artery and 2 veins

Question 10

The image shows a congenital cardiac defect. Abnormal development of which branch of aortic arch leads to this defect?

Accepted Answer

Left 6th aortic arch

Answer

Right 6th aortic arch

Answer

Left 4th aortic arch

Answer

Right 4th aortic arch

Embryology and Development — MCQs

Embryology and Development — MCQs

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