Embryology and Development Practice Questions

Q: Rohr's stria found in the placenta are due to:

Deposition of fibrin. **Explanation:** **Rohr’s stria** refers to a layer of **fibrinoid deposition** found at the bottom of the intervillous space, specifically on the maternal side of the placenta [2]. It is located within the **decidua basalis**, just superficial to the basal plate. 1. **Why Option A is Correct:** During placental development, fibrinoid material (a mixture of fibrin, placental proteins, and degenerating cells) accumulates at the feto-maternal interface [2]. There are two major fibrinoid layers: * **Rohr’s Stria:** Located in the intervillous space, covering the basal plate [2]. * **Nitabuch’s Layer:** A deeper layer of fibrinoid degeneration between the trophoblast and the decidua. It is clinically significant as it prevents overly deep penetration of the placenta into the myometrium. 2. **Why Other Options are Incorrect:** * **Option B (Blood vessels):** While the placenta is highly vascular, Rohr’s stria is an acellular, proteinaceous deposit, not a vascular structure [2]. * **Option C (Langhan’s cells):** Also known as cytotrophoblasts, these are the inner layer of the trophoblast. Their accumulation does not form these specific striae [1]. * **Option D (Hofbauer cells):** These are specialized macrophages found in the stroma of the chorionic villi [1]. They serve an immunological function and are not involved in fibrinoid layer formation. **High-Yield Clinical Pearls for NEET-PG:** * **Nitabuch’s Layer:** Absence of this layer is associated with **Placenta Accreta**, where the placenta adheres directly to the myometrium. * **Location Tip:** Remember **"R"** for Rohr’s is more **"R"**elated to the intervillous space (superficial), while Nitabuch’s is deeper. * **Composition:** Both layers consist of **Fibrinoid** (Type X collagen, laminin, and fibronectin).

Q: What is the approximate number of primordial follicles in an ovary at birth?

2 million. ### Explanation The correct answer is **A. 2 million**. Oogenesis is a finite process that begins during fetal life and involves a significant reduction in the germ cell population through atresia before birth [1]. **1. Why Option A is Correct:** During fetal development, oogonia undergo mitosis to reach a peak population of approximately **6–7 million** by the 5th month of gestation [1]. Following this peak, a massive process of programmed cell death (atresia) begins. By the time a female infant is born, the number of primordial follicles has decreased to approximately **2 million** in both ovaries combined [1]. **2. Why Other Options are Incorrect:** * **Option B (6 million):** This represents the peak number of oogonia present at the **20th week (5th month)** of intrauterine life, not at birth. * **Option C (5 million):** This is an intermediate number during the decline from the 5th-month peak but does not represent the standard clinical value for the birth population. * **Option D (10 million):** This exceeds the maximum number of germ cells ever recorded during human oogenesis. **3. High-Yield Facts for NEET-PG:** * **At Puberty:** The number of follicles further depletes to approximately **300,000 to 400,000** [1]. * **Reproductive Life:** Only about **400–500** follicles will actually ovulate during a woman's lifetime [1]. * **Meiotic Arrest:** Primordial follicles are arrested in the **Diplotene stage of Prophase I** (also known as the Dictyate stage) until puberty [1]. * **Clinical Correlation:** The rapid decline in follicle count (atresia) is a natural process; however, an accelerated loss before age 40 leads to **Premature Ovarian Insufficiency (POI)**.

Q: Which of the following structures remain from the embryological first pharyngeal arch?

Sphenomandibular ligament. The first pharyngeal arch (Mandibular arch) is a high-yield topic in NEET-PG neuroanatomy and embryology. It is associated with **Meckel’s cartilage**, which serves as the framework for the development of the mandible and several key middle ear and ligamentous structures. ### **Why Option A is Correct** The **Sphenomandibular ligament** is a direct derivative of the perichondrium of Meckel’s cartilage (the dorsal part of the first arch). As the mandible develops, the middle portion of Meckel’s cartilage regresses, leaving behind a fibrous band that connects the spine of the sphenoid to the lingula of the mandible. Other first-arch derivatives include the **Malleus**, **Incus**, and the **Anterior ligament of the malleus**. ### **Why Other Options are Incorrect** * **B & D (Stylohyoid/Styloid ligament):** These are derivatives of the **Second pharyngeal arch (Reichert’s cartilage)**. The second arch also gives rise to the Stapes, Styloid process, and the Lesser cornu of the hyoid bone. * **C (Stylomandibular ligament):** This is not a pharyngeal arch derivative. It is a specialized thickening of the **deep cervical fascia** (specifically the parotid fascia) and is not derived from branchial cartilage. ### **NEET-PG High-Yield Pearls** * **Nerve of the 1st Arch:** Mandibular nerve (V3). * **Muscles of the 1st Arch:** Muscles of mastication, Mylohyoid, Anterior belly of digastric, Tensor tympani, and Tensor veli palatini. * **Mnemonic for 1st Arch Ligaments:** "S.A.M." — **S**phenomandibular and **A**nterior ligament of **M**alleus. * **Clinical Correlation:** Treacher Collins Syndrome results from the failure of first arch neural crest cells to migrate properly, leading to mandibular hypoplasia.

Q: Hypoblast forms what structure?

Prochordal plate. ### Explanation The **hypoblast** (primitive endoderm) is the ventral layer of the bilaminar germ disc [1]. At the beginning of the third week of development, the hypoblastic cells in the cephalic (cranial) region become columnar and firmly adhere to the overlying epiblast. This localized thickening is known as the **Prochordal Plate** (or Prechordal Plate). **Why the correct answer is right:** * **Prochordal Plate:** It is the first sign of the cranio-caudal axis and marks the future site of the mouth (buccopharyngeal membrane). It also serves as an important signaling center for organizing the forebrain. **Analysis of Incorrect Options:** * **A. Notochord:** This is derived from **epiblast** cells that invaginate through the primitive node (mesodermal origin). * **B. Apical ligament of atlas:** This is a remnant of the **notochord**, which, as stated above, is derived from the epiblast/mesoderm, not the hypoblast. * **C. Endoderm:** While the hypoblast was historically thought to form the definitive endoderm, we now know that the **definitive endoderm** is formed by epiblast cells that migrate through the primitive streak and displace the hypoblast [1]. The hypoblast primarily contributes to the extraembryonic mesoderm and the yolk sac lining. **High-Yield Facts for NEET-PG:** * **Fate of Hypoblast:** It forms the **Heuser’s membrane** (lining the primary yolk sac) and the **prochordal plate** [1]. * **The "Rule of 2s" (2nd Week):** Trophoblast differentiates into 2 layers (Syncytio & Cytotrophoblast); Embryoblast into 2 layers (Epiblast & Hypoblast); 2 cavities form (Amniotic & Yolk sac) [1]. * **Clinical Pearl:** The prochordal plate is essential for head development; defects in this area can lead to severe holoprosencephaly or facial midline defects.

Q: Meckel's cartilage develops from which branchial arch?

I branchial arch. **Explanation:** The pharyngeal (branchial) arches are fundamental embryonic structures that give rise to specific skeletal, muscular, and neural components of the head and neck. **1. Why Option A is Correct:** **Meckel’s cartilage** is the cartilaginous bar of the **first branchial arch** (Mandibular arch). While most of the mandible develops via intramembranous ossification around Meckel’s cartilage, the cartilage itself serves as a template. Its dorsal end ossifies to form two middle ear ossicles: the **Malleus** and the **Incus**. The perichondrium of its middle portion forms the **Sphenomandibular ligament** and the anterior ligament of the malleus. **2. Why Other Options are Incorrect:** * **Option B (II Arch):** Also known as the Hyoid arch, its cartilage is **Reichert’s cartilage**. It gives rise to the Stapes, Styloid process, Stylohyoid ligament, and the Lesser cornu (and upper body) of the hyoid bone. * **Option C (III Arch):** This arch forms the **Greater cornu** and the lower part of the body of the hyoid bone. * **Option D (IV Arch):** Along with the VI arch, it contributes to the **laryngeal cartilages** (Thyroid, Cricoid, Arytenoid, Corniculate, and Cuneiform), excluding the epiglottis. **NEET-PG High-Yield Pearls:** * **Nerve of I Arch:** Mandibular nerve ($V_3$). * **Nerve of II Arch:** Facial nerve (VII). * **Muscles of I Arch:** Muscles of mastication, Mylohyoid, Anterior belly of digastric, Tensor tympani, and Tensor veli palatini. * **Clinical Correlation:** Defective development of the first arch leads to **Treacher Collins Syndrome** (mandibulofacial dysostosis) or **Pierre Robin Sequence**.

Q: A harelip is due to the non-fusion of which structures during embryonic development?

Medial nasal process with maxillary process. ### Explanation **Concept Overview:** The development of the face occurs between the 4th and 8th weeks of gestation through the fusion of five facial primordia: the single frontonasal process, two maxillary processes, and two mandibular processes. **Why Option C is Correct:** A **harelip (cleft lip)** occurs due to the failure of fusion between the **medial nasal process** (a derivative of the frontonasal process) and the **maxillary process** [1]. * The medial nasal processes fuse in the midline to form the **intermaxillary segment**, which gives rise to the philtrum of the upper lip, the premaxilla (carrying the four incisors), and the primary palate. * The maxillary processes grow medially to fuse with the intermaxillary segment [1]. Failure of this fusion on one or both sides results in a unilateral or bilateral cleft lip [1]. **Analysis of Incorrect Options:** * **Option A:** Fusion of the medial nasal processes with each other forms the bridge of the nose and the philtrum. Failure here leads to a rare **median cleft lip**. * **Option B:** Failure of fusion between the lateral nasal process and the maxillary process results in an **oblique facial cleft**, exposing the nasolacrimal duct. * **Option D:** The palatal processes (palatine shelves) are internal extensions of the maxillary processes. Their failure to fuse with each other or the primary palate results in a **cleft palate**, not a cleft lip [1]. **High-Yield Clinical Pearls for NEET-PG:** * **Unilateral Cleft Lip:** Most common congenital facial abnormality [1]. * **Cleft Palate:** Failure of fusion of **lateral palatine shelves** with each other or with the **primary palate** (median palatine process). * **Macrostomia:** Failure of fusion between the maxillary and mandibular processes. * **Rule of 10s for Surgery:** Cleft lip repair (Cheiloplasty) is usually done at 10 weeks of age, 10 lbs weight, and 10 g/dL hemoglobin.

Q: After how many days of ovulation does embryo implantation occur?

7-9 days. **Explanation:** The correct answer is **B. 7-9 days**. **Medical Concept:** Following ovulation, fertilization typically occurs in the ampulla of the fallopian tube within 12–24 hours. The zygote then undergoes cleavage as it travels toward the uterus. It reaches the uterine cavity as a **morula** on day 3–4 and transforms into a **blastocyst** by day 5. Implantation begins when the blastocyst apposes and adheres to the endometrium (decidua), which occurs during the "implantation window." This process typically starts **6–7 days after fertilization** (which closely follows ovulation) and is completed by day 9–10. Therefore, the 7–9 day range is the most accurate clinical window for active implantation. **Analysis of Incorrect Options:** * **A. 3-5 days:** At this stage, the conceptus is still a morula or an early blastocyst either traveling through the fallopian tube or just entering the uterine cavity; it has not yet begun the process of implantation. * **C. 10-12 days:** By this time, implantation is usually complete, and the blastocyst is fully embedded within the endometrium. * **D. 13-15 days:** This corresponds to the time of the missed period and the beginning of the production of detectable levels of hCG in maternal urine. **NEET-PG High-Yield Pearls:** * **Implantation Window:** Occurs during the mid-luteal phase (Days 20–24 of a 28-day cycle). * **Site of Implantation:** Most commonly the upper posterior wall of the uterine body. * **hCG Detection:** Human Chorionic Gonadotropin (hCG) can be detected in maternal serum as early as **8–9 days after ovulation** (immediately following implantation). * **Trophoblast:** It is the outer layer of the blastocyst that differentiates into the cytotrophoblast and syncytiotrophoblast to facilitate invasion.

Q: The sinus venosus receives blood from all except:

Subcardinal vein. In the middle of the 4th week of development, the **sinus venosus** (the venous end of the heart tube) consists of a central body and two lateral extensions called **sinus horns**. Each sinus horn receives blood from three major paired veins: 1. **Vitelline Veins:** Carry oxygen-poor blood from the yolk sac. 2. **Umbilical Veins:** Carry oxygenated blood from the placenta [1]. 3. **Common Cardinal Veins:** Formed by the union of the anterior and posterior cardinal veins; they drain the body of the embryo proper. **Why Option D is Correct:** The **Subcardinal veins** are part of a complex system (along with supracardinal and sacrocardinal veins) that develops later to form the **Inferior Vena Cava (IVC)**. They do not drain directly into the sinus venosus; instead, they drain into the posterior cardinal veins. Therefore, they are not primary tributaries of the sinus horns. **Why Other Options are Incorrect:** * **A & B:** The vitelline and umbilical veins are the primary extracardiac vessels entering the sinus venosus during early development [1]. * **C:** The common cardinal vein is the primary systemic vessel entering the sinus venosus before the definitive venae cavae are formed. **High-Yield Facts for NEET-PG:** * **Fate of Sinus Venosus:** The right horn is incorporated into the right atrium to form the **smooth part (Sinus Venarum)**. The left horn regresses to form the **Coronary Sinus** and the **Oblique vein of the left atrium (of Marshall)**. * **Sinoatrial Orifice:** Guarded by right and left venous valves. The right valve forms the **Crista Terminalis**, the valve of the IVC (Eustachian), and the valve of the coronary sinus (Thebesian) [1]. * **Vitelline Vein Fate:** The right vitelline vein forms the terminal portion of the IVC and the portal vein.

Question 1

The gut tube develops from which germ layer?

Accepted Answer

Endoderm

Answer

Ectoderm

Answer

Mesoderm

Answer

Neuroectoderm

Question 2

Rohr's stria found in the placenta are due to:

Accepted Answer

Deposition of fibrin

Answer

Blood vessels

Answer

Langhan's cells accumulation

Answer

Hofbauer cells accumulation

Question 3

What is the approximate number of primordial follicles in an ovary at birth?

Accepted Answer

2 million

Answer

6 million

Answer

5 million

Answer

10 million

Question 4

Which of the following structures remain from the embryological first pharyngeal arch?

Accepted Answer

Sphenomandibular ligament

Answer

Stylohyoid ligament

Answer

Stylomandibular ligament

Answer

Styloid ligament

Question 5

Hypoblast forms what structure?

Accepted Answer

Prochordal plate

Answer

Notochord

Answer

Apical ligament of atlas

Answer

Endoderm

Question 6

Meckel's cartilage develops from which branchial arch?

Accepted Answer

I branchial arch

Answer

II branchial arch

Answer

III branchial arch

Answer

IV branchial arch

Question 7

A harelip is due to the non-fusion of which structures during embryonic development?

Accepted Answer

Medial nasal process with maxillary process

Answer

Medial nasal process with lateral nasal process

Answer

Lateral nasal process with maxillary process

Answer

Lateral nasal process with palatal process

Question 8

After how many days of ovulation does embryo implantation occur?

Accepted Answer

7-9 days

Answer

3-5 days

Answer

10-12 days

Answer

13-15 days

Question 9

The sinus venosus receives blood from all except:

Accepted Answer

Subcardinal vein

Answer

Vitelline vein

Answer

Umbilical vein

Answer

Common cardinal vein

Question 10

Midline caecum results from which of the following abnormalities?

Accepted Answer

Mixed rotation

Answer

Malrotation

Answer

Reverse rotation

Answer

Non-rotation

Embryology and Development — MCQs

Embryology and Development — MCQs

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