Embryology and Development Practice Questions

Q: What is the embryological basis for the uterine anomaly shown in the images?

Non-fusion of paramesonephric ducts. ***Non-fusion of paramesonephric ducts*** - The image shows a **uterus didelphys**, which is a complete duplication of the uterus and cervix. This anomaly occurs due to a complete failure of the two **paramesonephric (Müllerian) ducts** to fuse medially during embryogenesis. - The **paramesonephric ducts** are the embryological precursors to the fallopian tubes, uterus, cervix, and the upper one-third of the vagina. Their proper fusion is essential for forming a single uterine cavity. *Non-fusion of mesonephric duct* - The **mesonephric (Wolffian) ducts** are precursors to male internal genitalia (e.g., epididymis, ductus deferens, seminal vesicles) and largely regress in females. - Remnants of the mesonephric duct in females may form **Gartner's cysts**, but they do not contribute to the formation of the uterus. *Failure of fusion of metanephric duct* - The **metanephric duct**, or **ureteric bud**, is involved in the development of the urinary system, specifically the ureters, renal pelves, calyces, and collecting ducts of the kidneys. - This structure is entirely unrelated to the embryological development of the female reproductive tract. *Complete agenesis of Müllerian structures* - Complete agenesis of the **Müllerian structures** results in the congenital absence of the uterus, fallopian tubes, and upper vagina, a condition known as **Mayer-Rokitansky-Küster-Hauser (MRKH) syndrome**. - The image clearly depicts the presence of uterine horns and a cervix, which contradicts a diagnosis of agenesis (complete absence).

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 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: 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: 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.

Q: Which is wrong about the image given below?

Dorsal mesentery degenerates. ***Dorsal mesentery degenerates*** - The **dorsal mesentery** persists and develops into various mesenteries supporting the abdominal organs (e.g., mesentery proper, transverse mesocolon, sigmoid mesocolon). It does not degenerate. - The **ventral mesentery degenerates** in areas due to the rotation of the gut and fusion processes, but the dorsal mesentery generally remains. *Foregut meets the stomodeum at bucco-pharyngeal membrane which ruptures at 4 weeks* - The **buccopharyngeal membrane separates the foregut from the stomodeum** (primitive mouth). - This membrane normally **ruptures around the 4th week** of development to establish communication between the oral cavity and the foregut. *Hindgut meets the proctodeum which ruptures at 8th week* - The **hindgut meets the proctodeum** (primitive anal pit) at the **cloacal membrane**. - This **cloacal membrane ruptures around the 7th or 8th week** of development, forming the anal opening. *Lining epithelium of gut is endodermal* - The **endoderm is the primary germ layer** that forms the lining epithelium of the entire gastrointestinal tract. - This includes the epithelium of the esophagus, stomach, intestines, and associated glands.

Q: The condition shown below is due to ?

Patent vitello-intestinal duct. ***Patent vitello-intestinal duct*** - The image shows a **patent vitello-intestinal duct** (also called patent omphalomesenteric duct or patent vitelline duct), which is a persistent connection between the **ileum** and the **umbilicus**. - This represents failure of the vitelline duct to obliterate during the 5th-9th week of embryonic development. - Clinically presents as **umbilical fistula** with discharge of intestinal contents, **umbilical polyp**, or **umbilical sinus**. - The persistent duct connects the intestine to the umbilicus, which is visible in the image. *Patent urachus* - A patent urachus is a persistent connection between the **bladder** and the **umbilicus**, resulting from failure of obliteration of the allantois. - Presents with **urine leakage** from the umbilicus, not intestinal contents. - This is a urological anomaly, not associated with intestinal connection to the umbilicus. *Patent allantois* - The allantois is an embryonic structure that normally becomes the **urachus** connecting bladder to umbilicus. - Patent allantois is essentially the same as **patent urachus**. - Would present with urinary discharge, not the intestinal connection shown in the image. *Midgut loop hernia* - Midgut loop herniation is a **normal physiological process** occurring at 6-10 weeks of gestation where midgut herniates into the umbilical cord and then returns. - Failure of this to reduce leads to **omphalocele** (herniation of abdominal contents covered by peritoneum and amnion). - This is different from a patent vitello-intestinal duct, which is a **tubular connection** between ileum and umbilicus, not a herniation of abdominal organs.

Question 1

What is the embryological basis for the uterine anomaly shown in the images?

Accepted Answer

Non-fusion of paramesonephric ducts

Answer

Failure of fusion of metanephric duct

Answer

Non-fusion of mesonephric duct

Answer

Complete agenesis of Müllerian structures

Question 2

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

Accepted Answer

Blastocyst

Answer

Gastrula

Answer

Morula

Answer

Ova

Question 3

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 4

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 5

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 6

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 7

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

Question 8

Which is correct sequence about the blood supply of the primitive gut?

Accepted Answer

Foregut= Celiac trunk, Midgut= Superior mesenteric artery, Hindgut= inferior mesenteric artery

Answer

Foregut= Superior mesenteric artery, Midgut= Celiac trunk, Hindgut= inferior mesenteric artery

Answer

Foregut= Celiac trunk, Midgut= Superior mesenteric artery, Hindgut= ileocolic artery

Answer

Foregut= Celiac trunk, Midgut= Inferior mesenteric artery, Hindgut= inferior mesenteric artery

Question 9

Which is wrong about the image given below?

Accepted Answer

Dorsal mesentery degenerates

Answer

Foregut meets the stomodeum at bucco-pharyngeal membrane which ruptures at 4 weeks

Answer

Hindgut meets the proctodeum which ruptures at 8th week

Answer

Lining epithelium of gut is endodermal

Question 10

The condition shown below is due to ?

Accepted Answer

Patent vitello-intestinal duct

Answer

Patent urachus

Answer

Patent allantois

Answer

Midgut loop hernia

Embryology and Development — MCQs

Embryology and Development — MCQs

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