What percentage of gastric secretion is attributed to the cephalic phase?
Which hormone primarily inhibits gastric acid secretion in response to acidic chyme?
Prostaglandins (PGs) in semen are secreted by?
Wolff–Chaikoff effect is due to?
Growth hormone level is highest during
Insensible water loss per day is ?
Which of the following factors increases the rate of particle diffusion across the cell membrane?
Peripheral and central chemoreceptors may both contribute to the increased ventilation that occurs as a result of which of the following?
Transpulmonary pressure is the difference between:
Which of the following components are included in microcirculation?
NEET-PG 2012 - Physiology NEET-PG Practice Questions and MCQs
Question 61: What percentage of gastric secretion is attributed to the cephalic phase?
- A. 20% (Correct Answer)
- B. 70%
- C. 10%
- D. 100%
Explanation: ***20%*** - The **cephalic phase** of gastric secretion is initiated by the sight, smell, taste, or even thought of food and accounts for approximately **20-30%** of total gastric acid secretion. - This phase is mediated by the **vagus nerve**, stimulating parietal cells (via acetylcholine) and G cells (via gastrin-releasing peptide) to release acid and gastrin, respectively. *70 %* - **70%** represents the approximate contribution of the **gastric phase** to total gastric secretion, which is the largest phase. - This phase is activated by the presence of food in the stomach, distension, and the presence of amino acids and peptides. *10%* - **10%** is a value that is too low for the cephalic phase; it typically accounts for a more significant portion of initial acid secretion. - This percentage is sometimes associated with the intestinal phase, which produces a smaller amount of acid secretion after chyme enters the duodenum. *100%* - **100%** is incorrect because gastric secretion is a complex process involving multiple phases (cephalic, gastric, intestinal), each contributing a portion of the total secretion. - Each phase has distinct stimuli and regulatory mechanisms, ensuring a coordinated digestive response.
Question 62: Which hormone primarily inhibits gastric acid secretion in response to acidic chyme?
- A. Secretin
- B. Somatostatin (Correct Answer)
- C. Insulin
- D. Gastrin
Explanation: ***Somatostatin*** - **Somatostatin** is the **primary hormone** that inhibits gastric acid secretion in response to acidic chyme. - Released by D cells in the stomach and duodenum when pH drops below 3.0. - **Direct inhibitory effects:** Inhibits parietal cells directly, suppresses gastrin release from G cells, and blocks histamine release from ECL cells. - Acts as the main **negative feedback mechanism** to prevent excessive gastric acidification. *Secretin* - **Secretin** is released by S cells in the duodenum in response to acidic chyme (pH < 4.5). - Its **primary function** is to stimulate pancreatic bicarbonate secretion to neutralize duodenal acid. - While it does have a **secondary effect** of inhibiting gastric acid secretion, this is not its primary role. *Gastrin* - **Gastrin** is a hormone that **stimulates** gastric acid secretion, not inhibits it. - Released by G cells in the gastric antrum in response to peptides, amino acids, and gastric distension. - Promotes acid secretion by stimulating parietal cells and ECL cells (which release histamine). *Insulin* - **Insulin** is a pancreatic hormone primarily involved in **glucose metabolism** and cellular glucose uptake. - It has **no significant role** in the regulation of gastric acid secretion.
Question 63: Prostaglandins (PGs) in semen are secreted by?
- A. Prostate
- B. Seminal vesicle (Correct Answer)
- C. Sperms
- D. Testes
Explanation: ***Seminal vesicle*** - The **seminal vesicles** are the primary source of **prostaglandins (PGs)** in semen, contributing significantly to the seminal fluid volume. - These PGs play a crucial role in promoting **sperm motility** and facilitating fertilization. *Prostate* - The **prostate gland** primarily secretes **citrate**, **acid phosphatase**, and **prostate-specific antigen (PSA)**, which contribute to sperm activation and semen liquefaction. - It does not significantly contribute to the prostaglandin content of semen. *Sperms* - **Spermatozoa** themselves primarily contribute genetic material and are not a significant source of prostaglandin synthesis in semen. - Their main function is fertilization, not the production of accessory gland secretions. *Testes* - The **testes** are responsible for **spermatogenesis** (sperm production) and the synthesis of **androgens** like testosterone. - They do not secrete prostaglandins into the seminal fluid.
Question 64: Wolff–Chaikoff effect is due to?
- A. Decreased iodination of MIT
- B. Excess iodine intake (Correct Answer)
- C. Suppression of TSH secretion
- D. Decreased conversion of T4 to T3
Explanation: ***Excess iodine intake*** - The **Wolff-Chaikoff effect** is a phenomenon where a high intake of iodine acutely **inhibits thyroid hormone synthesis** and release. - This effect protects the body from excessive thyroid hormone production during periods of very high iodine availability. *Decreased iodination of MIT* - While the Wolff-Chaikoff effect does inhibit **iodination**, the direct cause is the excessive iodine itself, which triggers an autoregulatory shutdown. - Decreased iodination is a *consequence* of the high iodine leading to inhibition of thyroid peroxidase activity, but not the primary cause of the effect. *Suppression of TSH secretion* - **TSH (Thyroid Stimulating Hormone)** secretion is primarily regulated by negative feedback from thyroid hormones (T3 and T4) and TRH from the hypothalamus. - The Wolff-Chaikoff effect directly involves the thyroid gland's response to iodine and is not primarily mediated by TSH suppression. *Decreased conversion of T4 to T3* - The **conversion of T4 to T3** primarily occurs in peripheral tissues, mediated by deiodinase enzymes. - The Wolff-Chaikoff effect focuses on the inhibition of **iodine organification** and hormone release within the thyroid gland itself, not peripheral conversion.
Question 65: Growth hormone level is highest during
- A. Sleep (Correct Answer)
- B. Hypoglycemia
- C. Fasting
- D. Exercise
Explanation: ***Sleep*** - Growth hormone (GH) secretion is **pulsatile**, with the largest and most consistent pulses occurring during **slow-wave sleep** (deep sleep). - This nocturnal surge contributes significantly to the overall daily GH output and is crucial for growth and metabolic regulation. *Hypoglycemia* - While **hypoglycemia** is a potent stimulus for GH release, it is an acute stress response rather than a state where GH levels are consistently highest. - The body's primary response to hypoglycemia is to raise blood glucose, and while GH helps, it is not the peak physiological secretion time. *Fasting* - **Prolonged fasting** can increase GH secretion as a mechanism to mobilize fat stores and conserve glucose. - However, the peak levels due to fasting are generally less pronounced than the dramatic surge observed during deep sleep. *Exercise* - **Vigorous exercise** can acutely stimulate GH release, particularly with sustained effort. - This increase is typically transient and not as high or consistently cyclical as the secretion during nocturnal sleep.
Question 66: Insensible water loss per day is ?
- A. 100 ml
- B. 1000 ml (Correct Answer)
- C. 700 ml
- D. 300 ml
Explanation: ***1000 ml*** - **Insensible water loss** occurs through the skin (evaporation) and respiratory tract (exhalation) without conscious perception. - The typical daily insensible water loss in an adult is approximately **800-1000 ml/day**. - **Breakdown**: Skin evaporation (~400-500 ml) + Respiratory tract (~300-400 ml) = **~900-1000 ml total**. - **1000 ml** is the standard value cited in major physiology textbooks (Guyton & Hall, Ganong) and is the most commonly accepted answer for NEET PG examinations. *100 ml* - This value is significantly **lower** than the actual insensible water loss, which occurs continuously throughout the day. - Such a low volume would imply negligible evaporation and respiratory loss, which is not physiologically accurate. *300 ml* - While greater than 100 ml, 300 ml is still **far below** the typical range for daily insensible water loss. - This amount represents only about one-third of the actual insensible losses from the skin and respiratory system combined. *700 ml* - Although this value is sometimes mentioned in literature, it is at the **lower end** of the physiological range. - The more widely accepted standard value for insensible water loss in a healthy adult under normal conditions is **900-1000 ml/day**. - 700 ml would underestimate the normal daily insensible losses.
Question 67: Which of the following factors increases the rate of particle diffusion across the cell membrane?
- A. Decreasing the lipid solubility of the substance
- B. Increasing the size of the opening in the cell membrane
- C. Maintaining a concentration gradient across the membrane (Correct Answer)
- D. Increasing the size of the particle
Explanation: ***Maintaining a concentration gradient across the membrane*** - **Diffusion** is the net movement of particles from an area of higher concentration to an area of lower concentration, driven by the **concentration gradient**. - A steeper gradient means a larger difference in concentration, leading to a faster rate of net diffusion until equilibrium is reached. - According to **Fick's Law**, the rate of diffusion is directly proportional to the concentration gradient across the membrane. *Decreasing the lipid solubility of the substance* - The cell membrane is primarily composed of a **lipid bilayer**, meaning that substances with **higher lipid solubility** can more easily pass through it via simple diffusion. - Decreasing lipid solubility would **hinder** the substance's ability to cross the membrane, thus slowing down or preventing diffusion. *Increasing the size of the opening in the cell membrane* - While increasing channel or pore diameter can increase diffusion rate for **channel-mediated transport**, this option is less comprehensive than maintaining a concentration gradient. - The concentration gradient is the **primary driving force** for diffusion across all types of membrane transport (simple diffusion through lipid bilayer, channel-mediated, and carrier-mediated). - Channel size is relevant only for specific facilitated diffusion pathways, not for general particle diffusion. *Increasing the size of the particle* - **Smaller particles** generally diffuse faster than larger particles because they have higher diffusion coefficients and can more easily navigate through the membrane. - According to the **Stokes-Einstein equation**, diffusion rate is inversely proportional to particle size. - Increasing particle size would therefore **decrease** the rate of diffusion.
Question 68: 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 69: 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 70: 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.