NEET-PG 2012

1213 Questions — Page 43 of 122

Anatomy

3 questions

Q421

In which region of the human spine is the number of vertebrae usually constant?

Q422

Which structure is not seen at the L3 level?

Q423

All the following are characteristics of the oculomotor nerve except:

NEET-PG 2012 - Anatomy NEET-PG Practice Questions and MCQs

Question 421: In which region of the human spine is the number of vertebrae usually constant?

A. Cervical (Correct Answer)
B. Thoracic
C. Lumbar
D. Sacral

Explanation: ***Cervical*** - The human cervical spine almost universally consists of **seven vertebrae (C1-C7)**, making it the most constant region in terms of vertebral number. - This consistent number is crucial for normal neck movement and protection of vital neurological structures. *Thoracic* - While typically having **12 vertebrae**, variations in the thoracic region can occur, with some individuals having 11 or 13 due to transitional vertebrae. - These variations are less common but indicate that the number is not as strictly constant as in the cervical spine. *Lumbar* - The lumbar spine commonly has **five vertebrae (L1-L5)**, but variations such as four or six lumbar vertebrae can be seen due to lumbarization or sacralization. - **Lumbarization** involves the first sacral segment detaching, while **sacralization** involves the fifth lumbar vertebra fusing with the sacrum. *Sacral* - The sacrum is formed by the fusion of **five sacral vertebrae (S1-S5)**, but the number of *individual identifiable* vertebrae before fusion, or in cases of incomplete fusion, can vary. - The sacral region itself is a fused structure, and while it originates from five segments, the concept of "number of vertebrae" can be ambiguous due to its characteristic fusion.

Question 422: Which structure is not seen at the L3 level?

A. Iliac vessels
B. Aorta
C. Coeliac trunk (Correct Answer)
D. IVC

Explanation: ***Coeliac trunk*** - The **coeliac trunk** typically arises from the abdominal **aorta** at the level of **T12-L1**, which is significantly higher than L3. - It then immediately branches into the **left gastric**, **splenic**, and **common hepatic arteries** to supply foregut structures. *Iliac vessels* - The **common iliac arteries** and veins typically bifurcate from the **aorta** and **IVC** around the L4-L5 level. - Their presence, or the start of their formation, can be observed near or just above **L3**, depending on individual anatomical variation and how "at the L3 level" is interpreted (e.g., within the L3 vertebral body's span). *Aorta* - The **abdominal aorta** descends along the posterior abdominal wall and is a prominent structure at the **L3 level**. - It typically bifurcates into the common iliac arteries at the level of **L4**, meaning it is still a large, undivided vessel at L3. *IVC* - The **inferior vena cava (IVC)** ascends through the abdomen and is a significant vascular structure at the **L3 level**. - It is formed by the union of the common iliac veins at the level of **L5** and continues superiorly.

Question 423: All the following are characteristics of the oculomotor nerve except:

A. Carries parasympathetic nerve fibres
B. Supplies inferior oblique muscle
C. Enters orbit through the inferior orbital fissure (Correct Answer)
D. Enters orbit through the superior orbital fissure

Explanation: ***Enters orbit through the inferior orbital fissure*** - The oculomotor nerve **does not** enter the orbit through the **inferior orbital fissure**; it enters via the **superior orbital fissure**. - The **inferior orbital fissure** transmits structures like the **maxillary nerve (V2)**, **zygomatic nerve**, and **inferior ophthalmic vein**. *Carries parasympathetic nerve fibres* - The oculomotor nerve contains **parasympathetic preganglionic fibers** that synapse in the **ciliary ganglion** [1]. - These fibers control **pupillary constriction** (via the **sphincter pupillae**) and **accommodation** (via the **ciliary muscle**) [1]. *Supplies inferior oblique muscle* - The **inferior oblique muscle** is one of the **extraocular muscles** innervated by the **oculomotor nerve (CN III)** [2]. - This muscle works to **elevate** and **externally rotate** the eye [2]. *Enters orbit through the superior orbital fissure* - The oculomotor nerve indeed passes through the **superior orbital fissure** to enter the orbit. - This fissure serves as the passage for several cranial nerves and vessels, including the **oculomotor (III)**, **trochlear (IV)**, **abducens (VI)**, and branches of the **ophthalmic nerve (V1)**.

Biochemistry

2 questions

Q421

What is the role of nonsense codons in protein synthesis?

Q422

Taurine is biosynthesized from which amino acid?

Physiology

5 questions

Q421

Which of the following components are included in microcirculation?

Q422

Transpulmonary pressure is the difference between:

Q423

Peripheral and central chemoreceptors may both contribute to the increased ventilation that occurs as a result of which of the following?

Q424

Mean arterial pressure is calculated as:

Q425

What is the definition of preload in the context of cardiac physiology?

NEET-PG 2012 - Physiology NEET-PG Practice Questions and MCQs

Question 421: Which of the following components are included in microcirculation?

A. Capillaries
B. Aorta
C. Arteries and veins
D. Capillaries, venules, and arterioles (Correct Answer)

Explanation: ***Capillaries, venules, and arterioles*** - **Microcirculation** is the portion of the **circulatory system** that includes the **smallest blood vessels**, specifically the **arterioles**, **capillaries**, and **venules**. - These vessels are crucial for the **delivery of oxygen** and **nutrients** to tissues and the removal of waste products. *Capillaries* - While **capillaries** are a vital part of **microcirculation** and the primary site of nutrient and waste exchange, they alone do not encompass the entire microcirculatory unit. - The microcirculation also includes the vessels that feed into and drain from the capillaries: the **arterioles** and **venules**. *Aorta* - The **aorta** is the **largest artery** in the body, part of the **macrocirculation**, which distributes blood from the heart to the systemic circulation. - It is not considered part of the **microcirculation** due to its large size and primary function as a high-pressure conduit rather than a site of exchange. *Arteries and veins* - **Arteries** and **veins** are primarily components of the **macrocirculation**, responsible for transporting blood to and from the systemic and pulmonary circuits. - While arterioles and venules (small arteries and veins) are part of the microcirculation, the broader terms "arteries" and "veins" typically refer to the larger vessels and do not exclusively define the microcirculatory network.

Question 422: Transpulmonary pressure is the difference between:

A. Pressure in alveoli and intrapleural pressure (Correct Answer)
B. The pressure in the bronchus and atmospheric pressure
C. The difference between atmospheric pressure and intrapleural pressure
D. The difference between atmospheric pressure and intraalveolar pressure

Explanation: ***Pressure in alveoli and intrapleural pressure*** - Transpulmonary pressure is the **pressure gradient** across the lung wall, which is essential for maintaining alveolar inflation. - It is calculated as the **alveolar pressure minus the intrapleural pressure**. *The pressure in the bronchus and atmospheric pressure* - This difference would represent the pressure driving airflow through the **bronchial tree**, not the pressure across the lung wall itself. - It's a measure relevant to **airway resistance**, not lung distension. *The difference between atmospheric pressure and intrapleural pressure* - This difference is related to the **intrathoracic pressure**, which influences venous return and cardiac function, but not directly the distension of the lungs. - It does not account for the **alveolar pressure**, which is the primary internal pressure expanding the lung. *The difference between atmospheric pressure and intraalveolar pressure* - This difference is the **driving pressure for airflow** into or out of the lungs. - It represents the pressure gradient that causes air to move between the **atmosphere and the alveoli** during inspiration and expiration.

Question 423: Peripheral and central chemoreceptors may both contribute to the increased ventilation that occurs as a result of which of the following?

A. A decrease in arterial oxygen content
B. A decrease in arterial blood pressure
C. An increase in arterial carbon dioxide tension (Correct Answer)
D. A decrease in arterial oxygen tension

Explanation: ***An increase in arterial carbon dioxide tension*** - An increase in **arterial PCO2** (hypercapnia) leads to a rapid decrease in the **pH of the cerebrospinal fluid (CSF)**, which strongly stimulates **central chemoreceptors** in the medulla. - While overwhelmingly driven by central chemoreceptors, a significant increase in **arterial PCO2** also causes a slight decrease in **arterial pH**, which can additionally stimulate **peripheral chemoreceptors** in the carotid and aortic bodies, leading to increased ventilation. *A decrease in arterial oxygen content* - A decrease in **arterial oxygen content** (e.g., due to anemia or carbon monoxide poisoning) without a significant drop in **arterial PO2** primarily affects oxygen delivery to tissues. - It does not directly stimulate peripheral chemoreceptors, which are sensitive to **PO2**, not content, nor does it affect central chemoreceptors directly to increase ventilation in this manner. *A decrease in arterial blood pressure* - A decrease in **arterial blood pressure** is sensed by **baroreceptors** and primarily triggers cardiovascular reflexes (e.g., increased heart rate and vasoconstriction) to restore blood pressure. - It does not directly stimulate peripheral or central chemoreceptors to significantly increase ventilation unless severe hypoperfusion leads to significant changes in arterial blood gases. *A decrease in arterial oxygen tension* - A decrease in **arterial oxygen tension (PO2)**, especially when it falls below approximately 60 mmHg, acts as a potent stimulus for **peripheral chemoreceptors**. - However, **central chemoreceptors** are primarily sensitive to **PCO2** and CSF pH, and a decrease in **arterial PO2** alone has little direct effect on their activity.

Question 424: Mean arterial pressure is calculated as:

A. (DBP+3SBP)/2
B. (SBP+3DBP)/2
C. (DBP+2SBP)/3
D. (SBP+2DBP)/3 (Correct Answer)

Explanation: ***(SBP+2DBP)/3*** - This formula accurately calculates **mean arterial pressure (MAP)**, emphasizing the longer duration of diastole compared to systole in the cardiac cycle. - The diastolic blood pressure (**DBP**) is weighted twice as much as the systolic blood pressure (**SBP**) to reflect this physiological difference. *(DBP+2SBP)/3* - This formula incorrectly weighs the diastolic pressure less and the systolic pressure more, which does not reflect the **physiological duration of the cardiac cycle**. - While it attempts to average pressures, it does not correctly represent the **mean perfusion pressure**. *(SBP+3DBP)/2* - This formula is inaccurate for calculating MAP as the **denominator should be 3**, not 2, to account for the three components being averaged (one SBP and two DBP). - It also disproportionately weights **DBP** too high relative to the standard physiological formula. *(DBP+3SBP)/2* - This formula is incorrect as it applies an **excessive weighting to SBP** and uses an incorrect denominator. - It would yield a significantly higher and inaccurate value for **mean arterial pressure**.

Question 425: What is the definition of preload in the context of cardiac physiology?

A. Volume of blood in the ventricles at the end of systole
B. Volume of blood in the ventricles at the end of diastole (Correct Answer)
C. Amount of blood pumped by the heart per beat
D. Resistance to blood flow in the arteries

Explanation: ***Volume of blood in the ventricles at the end of diastole*** - Preload represents the **initial stretching** of the cardiac myocytes prior to contraction, largely determined by the **volume of blood filling the ventricles** at the end of relaxation (diastole). - This **end-diastolic volume** directly correlates with the ventricular muscle fiber length at the start of systole, influencing the force of contraction according to the **Frank-Starling mechanism**. *Volume of blood in the ventricles at the end of systole* - This describes the **end-systolic volume**, which is the amount of blood remaining in the ventricle after it has contracted and ejected blood. - End-systolic volume is a determinant of the **ejection fraction** but does not define preload. *Amount of blood pumped by the heart per beat* - This refers to the **stroke volume**—the volume of blood ejected from the left ventricle with each heartbeat. - While preload influences stroke volume, stroke volume itself is not the definition of preload. *Resistance to blood flow in the arteries* - This describes **afterload**, which is the pressure or resistance the ventricle must overcome to eject blood during systole. - Afterload primarily affects the *force* needed for contraction, rather than the initial stretch or filling volume of the heart.