Embryology and Development Practice Questions

Q: Which of the following statements is NOT true regarding paramedian pits?

They are found on the upper lip.. **Explanation:** **Paramedian Pits** (also known as congenital lip pits) are rare developmental malformations. The correct answer is **Option B** because these pits are characteristically found on the **lower lip**, not the upper lip. 1. **Why Option B is correct (The Concept):** Paramedian pits occur due to the failure of the embryonic **lateral labial sulci** to obliterate during the development of the mandibular process. Since the mandibular process forms the lower lip, these pits are anatomically restricted to the lower lip. Finding pits on the upper lip is extremely rare and usually associated with different syndromic patterns (like commissural pits). 2. **Why other options are incorrect:** * **Option A & C:** These are true anatomical descriptions. Paramedian pits are typically bilateral, symmetric indentations located on either side of the midline on the vermilion border of the lower lip. * **Option D:** This is a true clinical association. Paramedian lip pits are a hallmark feature of **Van der Woude Syndrome**, which is the most common form of syndromic orofacial clefting. **High-Yield Clinical Pearls for NEET-PG:** * **Van der Woude Syndrome:** Autosomal Dominant inheritance; caused by a mutation in the **IRF6 gene**. It is characterized by the triad of paramedian lower lip pits, cleft lip, and/or cleft palate. * **Kabuki Syndrome:** Another condition where lower lip pits may be seen, alongside skeletal abnormalities and intellectual disability. * **Embryology:** Remember that the lower lip forms from the fusion of the two **mandibular prominences**, while the upper lip forms from the fusion of the **medial nasal prominences** and the **maxillary prominences**.

Q: The diaphragm is formed of all the following except?

Paraxial mesoderm. The diaphragm is a complex musculotendinous partition that develops from four distinct embryonic sources during the 4th to 12th weeks of gestation. ### **Why Paraxial Mesoderm is the Correct Answer** The diaphragm is primarily derived from **lateral plate mesoderm** and **somites** (specifically cervical somites C3-C5), not paraxial mesoderm. While paraxial mesoderm gives rise to the axial skeleton and skeletal muscles of the trunk, the specific muscular components of the diaphragm migrate from the cervical somites into the other three primordia. ### **Analysis of Other Options (The Four Sources)** 1. **Septum Transversum (Option A):** This is the primordium of the **central tendon** of the diaphragm [1]. It initially lies opposite the cervical somites, explaining the phrenic nerve's origin (C3, 4, 5). 2. **Pleuroperitoneal Membranes (Option C):** These close the communication between the pleural and peritoneal cavities. Failure of these membranes to fuse is the most common cause of **Congenital Diaphragmatic Hernia (Bochdalek).** 3. **Dorsal Mesentery of Oesophagus (Option D):** This forms the **crura** of the diaphragm. 4. **Body Wall (Lateral Plate Mesoderm):** Though not listed as a primary option, the peripheral muscular part of the diaphragm is derived from the internal layer of the lateral body walls. ### **High-Yield Clinical Pearls for NEET-PG** * **Mnemonic for Sources:** "**S**everal **P**arts **B**uild **D**iaphragm" (**S**eptum transversum, **P**leuroperitoneal membrane, **B**ody wall, **D**orsal mesentery). * **Nerve Supply:** "C3, 4, 5 keep the diaphragm alive." The phrenic nerve provides both motor and sensory supply to the central part. * **Bochdalek Hernia:** Most common (85-90%), occurs posterolaterally, usually on the **left side** due to the earlier closure of the right pleuroperitoneal canal and the presence of the liver. * **Morgagni Hernia:** Occurs anteriorly through the space of Larrey.

Q: Ossification of long bones begins at what age?

7th week of gestation. The development of the human skeleton occurs through two types of ossification: intramembranous and endochondral [1]. Most long bones develop via **endochondral ossification**, where a hyaline cartilage model is gradually replaced by bone [1]. **Why Option B is Correct:** Primary centers of ossification for most long bones (such as the femur and humerus) typically appear during the **7th to 8th week of intrauterine life (IUL)**. Specifically, the clavicle is the first bone to begin ossifying (around the 5th–6th week), followed closely by the femur and other long bones by the 7th week. This marks the transition from the embryonic period to the fetal period. [1] **Analysis of Incorrect Options:** * **Option A (3rd week):** This is the period of gastrulation (formation of the three germ layers). Bone formation has not yet begun; the mesoderm is just beginning to differentiate into somites. * **Option C (5th week):** During this stage, limb buds are just forming, and mesenchymal condensation begins to create the initial "scaffold." Only the clavicle (a membrane bone) starts ossifying late in this period. [1] * **Option D (9th week):** By this time, ossification is already well underway in the primary centers of the diaphysis of most long bones. **High-Yield Clinical Pearls for NEET-PG:** * **First bone to ossify:** Clavicle (5th–6th week IUL) via intramembranous ossification. [1] * **First long bone to ossify:** Femur. * **Primary Center:** Usually appears before birth (diaphysis). * **Secondary Center:** Usually appears after birth (epiphysis), with the exception of the **distal end of the femur** and **proximal end of the tibia**, which appear just before birth (used as a medico-legal indicator of fetal maturity).

Q: What is the name of the congenital anomaly this child is suffering from?

Anencephaly. ***Anencephaly*** - Results from **failure of anterior neural tube closure** during the 3rd-4th week of embryonic development, leading to absence of the **cranial vault** and **cerebral hemispheres**. - Characterized by **exposed neural tissue** (cerebrovasculosa) and **prominent eyes** due to lack of overlying skull and brain tissue. *Encephalocele* - A **neural tube defect** where brain tissue herniates through a **skull defect**, typically in the **occipital region**. - The **cranial vault remains intact** except for the localized defect, unlike the complete absence seen in anencephaly. *Hydranencephaly* - A condition where **cerebral hemispheres are replaced by fluid-filled sacs**, but the **skull and scalp remain normal**. - The **cranial vault is present and intact**, distinguishing it from anencephaly where the vault is completely absent. *Diastematomyelia* - A **spinal cord malformation** where the cord is split by a **bony or fibrous septum**, affecting the **vertebral column**. - This is a **spinal neural tube defect**, not a cranial anomaly, and does not involve the brain or skull.

Q: During development, the parts of the ear develop at different intervals. All of the following structures are of adult size at birth, EXCEPT?

Maxillary antrum. **Explanation:** In human development, the auditory apparatus is unique because several of its components reach adult dimensions before or at the time of birth. This is a high-yield concept in embryology and ENT anatomy. **1. Why Maxillary Antrum is the Correct Answer:** The **Maxillary Antrum (Maxillary Sinus)** is the only option listed that is **not** adult-sized at birth. At birth, it is merely a small, fluid-filled slit (measuring approximately 7 x 4 x 4 mm). It undergoes biphasic growth (at ages 0–3 and 7–12) and only reaches its full adult volume after the eruption of all permanent teeth, around age 15–18. **2. Analysis of Incorrect Options:** * **Ear Ossicles (Malleus, Incus, Stapes):** These are the first bones to fully ossify in the body (by the 4th–5th month of fetal life) and are of **full adult size at birth**. * **Oval Window:** Along with the internal ear structures (like the cochlea and vestibule), the oval window reaches adult dimensions during the fetal period to accommodate the already adult-sized stapes footplate. * **Middle Ear Cavity (Tympanic Cavity):** The cavity itself, along with the tympanic membrane, is essentially of adult size at birth, although the surrounding mastoid air cells have not yet pneumatized. **Clinical Pearls for NEET-PG:** * **Mastoid Antrum:** Like the middle ear, the mastoid antrum is of **adult size at birth**, but the **mastoid process** is absent (it develops at age 2 due to the pull of the Sternocleidomastoid muscle). * **Internal Ear:** The bony labyrinth reaches adult size by the 20th week of gestation. * **Ethmoid Sinus:** Present at birth (like the maxillary sinus) but not adult-sized. * **Frontal and Sphenoid Sinuses:** These are typically **absent at birth** and start developing postnatally.

Q: Oogonia reach their maximum number at which of the following stages of human development?

Five months of fetal life. ### Explanation **Correct Option: A. Five months of fetal life** The development of female gametes follows a unique "peak and decline" pattern. Primordial germ cells migrate to the gonadal ridge and undergo rapid mitotic division to become **oogonia**. This mitotic activity reaches its peak during the **5th month of intrauterine life**, at which point the total number of oogonia is estimated to be approximately **7 million** [1]. After this peak, no new oogonia are formed. Instead, a process of programmed cell death (atresia) begins. By the time of birth, many oogonia have either degenerated or entered the first meiotic division to become primary oocytes, reducing the count to about 600,000 to 2 million [1]. **Why other options are incorrect:** * **B, C, and D:** These options represent postnatal stages. Unlike males, who produce sperm continuously from puberty onwards, females are born with a finite number of oocytes. By **puberty**, the number has already depleted significantly to approximately **300,000 to 400,000** due to continuous atresia. Therefore, the count at puberty or adulthood is significantly lower than the mid-fetal peak. --- ### High-Yield Clinical Pearls for NEET-PG: * **The "7-2-4" Rule:** Remember the numbers: **7 million** at 5 months gestation (peak), **2 million** at birth, and **400,000** at puberty [1]. * **Meiotic Arrest:** Primary oocytes begin Meiosis I during fetal life but are arrested in the **Diplotene stage of Prophase I** (dictyotene stage) until puberty [1], [2]. * **Completion of Meiosis:** Meiosis I is completed just before ovulation (forming the secondary oocyte and first polar body) [2]. Meiosis II is only completed if **fertilization** occurs. * **Atresia:** Over 99% of the original germ cell population is lost through atresia; only about 400–500 oocytes are actually ovulated during a woman's reproductive lifespan [1].

Question 1

Which of the following is NOT a true statement regarding the derivatives of the aortic arches?

Accepted Answer

The 5th aortic arch is absent in approximately 5% of embryos.

Answer

The pulmonary artery develops from the 6th aortic arch.

Answer

The maxillary artery derives from the 1st aortic arch.

Answer

Not all six aortic arches are present simultaneously during embryonic development.

Question 2

Which of the following statements is NOT true regarding paramedian pits?

Accepted Answer

They are found on the upper lip.

Answer

They are found on the lower lip.

Answer

They are located on either side of the midline.

Answer

They are associated with cleft lip and palate.

Question 3

The Glossopharyngeal nerve supplies the posterior 1/3 of the tongue because it develops from which embryological structure?

Accepted Answer

Hypobranchial eminence

Answer

Hyoid arch

Answer

Tuberculum impar

Answer

Mandibular arch

Question 4

The diaphragm is formed of all the following except?

Accepted Answer

Paraxial mesoderm

Answer

Septum transversum

Answer

Pleuroperitoneal membranes

Answer

Dorsal mesentery of oesophagus

Question 5

Ossification of long bones begins at what age?

Accepted Answer

7th week of gestation

Answer

3rd week of gestation

Answer

5th week of gestation

Answer

9th week of gestation

Question 6

What is the name of the congenital anomaly this child is suffering from?

Accepted Answer

Anencephaly

Answer

Encephalocele

Answer

Hydranencephaly

Answer

Diastematomyelia

Question 7

The visceral efferent column of the neural tube arises from which embryonic structure?

Accepted Answer

Basal plate

Answer

Alar plate

Answer

Roof plate

Answer

Floor plate

Question 8

During the first 3-4 months of gestation, erythrocytes are formed by which structure?

Accepted Answer

Bone marrow

Answer

Yolk sac

Answer

Liver

Answer

Spleen

Question 9

During development, the parts of the ear develop at different intervals. All of the following structures are of adult size at birth, EXCEPT?

Accepted Answer

Maxillary antrum

Answer

Oval window

Answer

Ear Ossicles

Answer

Middle ear cavity

Question 10

Oogonia reach their maximum number at which of the following stages of human development?

Accepted Answer

Five months of fetal life

Answer

Puberty (12 to 14 years of age)

Answer

Adolescence (16 to 20 years of age)

Answer

Early adulthood (21 to 26 years of age)

Embryology and Development — MCQs

Embryology and Development — MCQs

On this page

Practice by Chapter

Want unlimited practice?