Anatomy
3 questionsWhat is the outer layer of the blastocyst called?
All are derived from ectoderm except for which of the following?
Which of the following is not a boundary of Koch's triangle?
NEET-PG 2012 - Anatomy NEET-PG Practice Questions and MCQs
Question 91: What is the outer layer of the blastocyst called?
- A. Embryo proper
- B. Trophoblast (Correct Answer)
- C. Primitive streak
- D. Yolk sac
Explanation: ***Trophoblast*** - The **trophoblast** is the outer layer of cells of the blastocyst, which goes on to form the **placenta** and other extraembryonic tissues [1]. - It plays a crucial role in the **implantation** of the blastocyst into the uterine wall and in producing hormones [1]. *Primitive streak* - The **primitive streak** is a structure that forms during **gastrulation**, much later than the initial blastocyst stage. - It establishes the **anterior-posterior axis** and initiates the formation of the three germ layers. *Yolk sac* - The **yolk sac** is an extraembryonic membrane that forms within the blastocyst cavity, but it is not the outermost layer of the entire structure. - It is involved in early **nutrient transfer** and **blood cell formation** before the placenta is fully functional. *Embryo proper* - The **embryo proper**, derived from the **inner cell mass (ICM)**, is the part of the blastocyst that will develop into the actual embryo [2]. - It is located *inside* the trophoblast layer, not forming the outer boundary of the blastocyst [2].
Question 92: All are derived from ectoderm except for which of the following?
- A. Hair follicles
- B. Nails
- C. Lens of the eye
- D. Adrenal cortex (Correct Answer)
Explanation: ***Adrenal cortex*** - The adrenal cortex is derived from the **intermediate mesoderm**, specifically from the cells lining the posterior abdominal wall. The cells migrate to develop into the adrenal cortex. - It produces various steroid hormones, including **aldosterone**, **cortisol**, and **androgens**, which regulate diverse bodily functions. *Lens of the eye* - The lens of the eye is derived from the **surface ectoderm**. It forms from an invagination of the surface ectoderm called the lens placode. - Its primary function is to **focus light** onto the retina. *Hair follicles* - Hair follicles develop from the **surface ectoderm** [1]; they are invaginations of the epidermis that extend into the dermis. - They produce hair, which provides **insulation** and **protection** [1]. *Nails* - Nails are also derivatives of the **surface ectoderm**, forming thickened plates on the dorsal surface of the distal phalanges. - They provide **protection** to the fingertips and aid in grasping objects.
Question 93: Which of the following is not a boundary of Koch's triangle?
- A. Limbus fossa ovalis (Correct Answer)
- B. Tricuspid valve ring
- C. Coronary sinus
- D. Tendon of Todaro
Explanation: ***Limbus fossa ovalis*** - The **limbus fossa ovalis** is a prominent oval ridge on the **interatrial septum** that surrounds the fossa ovalis. - It is **not involved** in forming the boundaries of Koch's triangle, which is located in the **right atrium** near the AV node [1]. *Tricuspid valve ring* - The **tricuspid valve ring** (or annulus) forms one of the key anatomical boundaries of **Koch's triangle**, specifically its base [1]. - This **fibrous ring** anchors the tricuspid valve leaflets and marks the inferior aspect of the triangle [1]. *Coronary sinus* - The **coronary sinus ostium** (opening) forms another crucial boundary of **Koch's triangle** [1]. - It is located at the **inferior-posterior aspect** of the interatrial septum, opening into the right atrium [1]. *Tendon of todaro* - The **Tendon of Todaro** is a fibrous structure that forms the superior boundary of **Koch's triangle** [1]. - It extends from the **Eustachian valve** (of the inferior vena cava) towards the central fibrous body, playing a role in **AV nodal localization** [1].
Biochemistry
1 questionsEnzyme causing covalent bond cleavage without hydrolysis ?
NEET-PG 2012 - Biochemistry NEET-PG Practice Questions and MCQs
Question 91: Enzyme causing covalent bond cleavage without hydrolysis ?
- A. Lyase (Correct Answer)
- B. Ligase
- C. Hydrolase
- D. Transferase
Explanation: ***Lyase*** - **Lyases** are enzymes that catalyze the cleavage of **covalent bonds** (C-C, C-O, C-N, and others) by means other than hydrolysis or oxidation, often creating a new double bond or a ring structure. - They remove groups from substrates to form double bonds, or conversely, add groups to double bonds. - **Examples:** Aldolase (cleaves C-C bonds in glycolysis), carbonic anhydrase (reversible cleavage of C-O bond), fumarase (C-C bond cleavage in TCA cycle). *Ligase* - **Ligases** are enzymes that join two large molecules by forming a new chemical bond, usually accompanied by the **hydrolysis of ATP**. - They are involved in synthesis reactions, not the cleavage of bonds. *Hydrolase* - **Hydrolases** specifically catalyze the hydrolysis of a chemical bond, involving the **addition of water** across the bond. - They break down large molecules into smaller ones using water - this is the key difference from lyases. *Transferase* - **Transferases** catalyze the transfer of a **functional group** from one molecule (the donor) to another (the acceptor). - They do not cause covalent bond cleavage without hydrolysis but rather move existing groups between molecules.
Internal Medicine
2 questionsProgressive distal-to-proximal motor recovery following nerve regeneration is most characteristic of which type of nerve injury?
Which of the following complications is commonly associated with mitral valve prolapse?
NEET-PG 2012 - Internal Medicine NEET-PG Practice Questions and MCQs
Question 91: Progressive distal-to-proximal motor recovery following nerve regeneration is most characteristic of which type of nerve injury?
- A. Axonotmesis (Correct Answer)
- B. Neurotmesis
- C. Neuropraxia
- D. Nerve injury
Explanation: ***Axonotmesis*** - Involves damage to the **axon** and myelin sheath, while the surrounding **epineurium** remains intact. - This preservation of the connective tissue allows for guided **regeneration** of axons from distal to proximal, leading to a good prognosis for recovery [1]. *Neurotmesis* - Refers to the **complete transection** of the nerve, including the axon, myelin, and all connective tissue sheaths. - Recovery is often **incomplete** or requires surgical repair, as significant misdirection of regenerating axons is common. *Neuropraxia* - Characterized by a **temporary block** in nerve conduction, typically due to **demyelination**, with the axon remaining intact. - Recovery is usually **rapid** and complete, occurring within days to weeks, as no axonal regeneration is needed. *Nerve injury* - This is a **general term** that encompasses all types of nerve damage, from mild to severe. - It does not specify a particular mechanism or pattern of recovery, making it less precise than the more specific classifications.
Question 92: Which of the following complications is commonly associated with mitral valve prolapse?
- A. Ventricular arrhythmia
- B. Stroke
- C. Infective endocarditis (Correct Answer)
- D. Mitral stenosis
Explanation: Mitral valve prolapse (MVP) involves myxomatous degeneration of the mitral valve leaflets, which can create a rough surface predisposing to bacterial adhesion and subsequent infective endocarditis [1]. While the overall risk is low, patients with MVP and accompanying mitral regurgitation or thickened leaflets are at higher risk [1]. Patients with valvular heart disease are generally susceptible to bacterial endocarditis, often associated with procedures or dental hygiene [2]. Stroke - Although MVP can sometimes be associated with embolic events (e.g., from thrombi forming on the prolapsing valve), stroke is not considered a commonly associated complication. - The risk of stroke is generally higher in MVP patients with concomitant atrial fibrillation or other cardiovascular risk factors. Mitral stenosis - Mitral valve prolapse is characterized by the displacement of mitral valve leaflets into the left atrium during systole, which can lead to mitral regurgitation [3], not stenosis. - Mitral stenosis involves narrowing of the mitral valve orifice, usually due to rheumatic fever, which is a different pathophysiology [4]. Ventricular arrhythmia - While palpitations (often benign supraventricular ectopy) are common in MVP, clinically significant ventricular arrhythmias are less common. - Severe ventricular arrhythmias are more typically seen with significant underlying myocardial disease or severe mitral regurgitation causing left ventricular dysfunction.
Obstetrics and Gynecology
1 questionsBlastocyst makes contact with endometrium on ?
NEET-PG 2012 - Obstetrics and Gynecology NEET-PG Practice Questions and MCQs
Question 91: Blastocyst makes contact with endometrium on ?
- A. < 3 days
- B. 5 - 7 days (Correct Answer)
- C. 8 - 11 days
- D. 15-16 days
Explanation: ***5-7 days*** - The **blastocyst makes initial contact** (apposition) with the **endometrium** around **day 5-6 after fertilization**. - **Implantation**, which includes adhesion and invasion, typically begins around day 6 and is complete by day 10. - This timeframe allows the blastocyst to travel from the fallopian tube to the uterus and for the uterine lining to be optimally prepared. *< 3 days* - Within the first few days after fertilization, the zygote is still undergoing **cleavage** and development into a **morula**, then a young blastocyst, while traveling down the fallopian tube. - It has not yet reached the uterus or developed sufficiently to interact with the endometrium. *8-11 days* - By 8-11 days, the process of implantation is usually **well underway or completed**, with the blastocyst already invading the endometrial wall. - Initial contact and attachment occur prior to this period. *15-16 days* - This timeframe is well beyond the typical window for initial blastocyst contact and implantation. - By 15-16 days post-fertilization, the embryo would be undergoing **gastrulation** and early organogenesis, assuming successful implantation.
Physiology
3 questionsWhat is the duration of the second heart sound (S2)?
Gastric secretions are essential for absorption of -
Which of the following hormones does not mediate its action through cAMP?
NEET-PG 2012 - Physiology NEET-PG Practice Questions and MCQs
Question 91: What is the duration of the second heart sound (S2)?
- A. 0.15 sec
- B. 0.1 sec
- C. 0.12 sec
- D. 0.08 sec (Correct Answer)
Explanation: ***0.08 sec*** - The second heart sound (S2) is composed of two components: A2 (aortic valve closure) and P2 (pulmonic valve closure). The normal duration of S2, encompassing both components, is approximately **0.08 seconds**. - This short duration reflects the rapid closure of the aortic and pulmonic valves at the beginning of **diastole**. *0.15sec* - A duration of **0.15 seconds** for S2 is significantly longer than normal, which could indicate abnormal valve function or conditions causing delayed valve closure. - Such prolonged duration might be observed in conditions like **severe pulmonic stenosis** or **pulmonic hypertension**, which are not the typical duration of a healthy S2. *0.12 sec* - A duration of **0.12 seconds** is also longer than the typical normal range for S2. - While still shorter than 0.15 seconds, it could suggest subtle delays in valve closure or splitting that exceeds the usual physiological splitting. *0.1 sec* - A duration of **0.1 seconds** is slightly prolonged but generally falls within a range that might be considered borderline or indicative of minimal physiological variations. - However, in typical healthy individuals, the S2 duration is closer to 0.08 seconds, making 0.1 seconds less precise for the most common duration.
Question 92: Gastric secretions are essential for absorption of -
- A. Cobalamin (Correct Answer)
- B. Fat
- C. Thiamine
- D. Folic acid
Explanation: ***Cobalamin*** - **Intrinsic factor**, secreted by gastric parietal cells, is crucial for the absorption of **vitamin B12 (cobalamin)** in the terminal ileum [1]. - Without sufficient intrinsic factor, **pernicious anemia** can develop due to impaired B12 absorption [2]. *Fat* - Fat digestion primarily occurs in the **small intestine** with the help of **bile salts** and **pancreatic lipases**. - While gastric lipase begins some fat digestion, it's not essential for overall fat absorption. *Thiamine* - **Thiamine (vitamin B1)** is absorbed in the jejunum and ileum, primarily via **active transport** and passive diffusion. - Gastric secretions do not play a direct, essential role in its absorption. *Folic acid* - **Folic acid** is absorbed in the **duodenum and jejunum** as monoglutamates after being deconjugated from polyglutamate forms. - This process is not directly dependent on gastric secretions [2].
Question 93: Which of the following hormones does not mediate its action through cAMP?
- A. Glucagon
- B. Follicle stimulating hormone
- C. Estrogen (Correct Answer)
- D. Luteinizing hormone
Explanation: ***Estrogen*** - **Estrogen** is a **steroid hormone** that mediates its action by binding to intracellular receptors, forming a complex that directly influences gene transcription. - Steroid hormones, due to their **lipophilicity**, can cross the cell membrane and do not typically rely on cell surface receptors or second messengers like cAMP. *Glucagon* - **Glucagon** acts on a **G protein-coupled receptor (GPCR)**, specifically a Gs-coupled receptor, leading to the activation of adenylyl cyclase. - This activation increases the intracellular concentration of **cAMP**, which then activates protein kinase A to mediate its effects, primarily on glucose metabolism. *Follicle stimulating hormone* - **FSH** binds to a **GPCR** on target cells, activating the Gs protein pathway. - This activation stimulates **adenylyl cyclase** and increases intracellular **cAMP** levels, which are critical for its role in gamete development. *Luteinizing hormone* - **LH**, like FSH, binds to a cell surface **GPCR** that activates the Gs protein. - This leads to the stimulation of **adenylyl cyclase** and an increase in **cAMP**, mediating its effects on steroidogenesis and ovulation.