What triggers the cephalic phase of gastric secretion?
Which of the following statements about gastric secretion is true?
Ptyalin is secreted by?
What is the body's first physiological response to hypoglycemia?
What is the process by which water moves from the extracellular space to the intracellular space?
What is the fixed length of a myosin filament?
Haploid number of chromosomes is first seen in?
What is the Bohr effect in relation to hemoglobin's affinity for oxygen?
What is the consequence of tibial nerve injury/palsy?
Which of the following statements regarding the lower esophageal sphincter is TRUE?
NEET-PG 2012 - Physiology NEET-PG Practice Questions and MCQs
Question 61: What triggers the cephalic phase of gastric secretion?
- A. On food entering stomach
- B. On food entering intestine
- C. On seeing food (Correct Answer)
- D. On stress
Explanation: ***On seeing food*** - The **cephalic phase** of gastric secretion is initiated by sensory input such as the sight, smell, taste, or even the thought of food. - This phase is mediated by the **vagus nerve**, stimulating gastric acid and enzyme secretion in anticipation of food arrival. *On food entering stomach* - This describes the initiation of the **gastric phase** of digestion, where mechanical stretch and chemical presence of food in the stomach stimulate further secretions. - The gastric phase primarily involves local reflexes and hormonal mechanisms (like **gastrin** release), rather than purely sensory input from the head. *On food entering intestine* - This marks the beginning of the **intestinal phase** of digestion, which involves both stimulatory and inhibitory signals for gastric secretion. - The primary role of the intestinal phase is to regulate the rate at which chyme enters the small intestine and to coordinate bile and pancreatic enzyme release. *On stress* - While stress can impact digestive function, it typically affects the **autonomic nervous system** in a generalized way, often leading to inhibition of digestion or altered motility. - Stress does not specifically trigger the cephalic phase of gastric secretion, which is a physiological response linked to nutrient anticipation.
Question 62: Which of the following statements about gastric secretion is true?
- A. Inhibited by curare
- B. Stimulated by nor adrenaline
- C. Increased by stomach distention (Correct Answer)
- D. Stimulated by an increase in tonic activity
Explanation: ***Increased by stomach distention*** - **Stomach distention** activates local reflexes and the **vagovagal reflex**, leading to the release of **acetylcholine** and **gastrin**, which stimulate gastric acid secretion during the gastric phase. - This is a physiological response that prepares the stomach for digestion of incoming food. *Inhibited by curare* - **Curare** is a **nicotinic acetylcholine receptor antagonist** that primarily affects neuromuscular junctions, causing muscle paralysis. - It does not directly inhibit the primary mechanisms of gastric acid secretion, which are largely mediated by **muscarinic acetylcholine receptors**, histamine, and gastrin. *Stimulated by nor adrenaline* - **Noradrenaline** (norepinephrine) is a neurotransmitter of the **sympathetic nervous system**, which generally **inhibits** gastric motility and secretion. - Activation of alpha-2 adrenergic receptors can decrease gastric acid secretion. *Stimulated by an increase in tonic activity* - This statement is vague; "tonic activity" can refer to various physiological processes. If it refers to **sympathetic nervous system** tonic activity, it would **inhibit** gastric secretion. - If it implies increased vagal tone (parasympathetic activity), then secretion would be stimulated, but the phrasing is not precise enough to be unequivocally true for gastric secretion in general.
Question 63: Ptyalin is secreted by?
- A. Gastric gland
- B. Salivary gland (Correct Answer)
- C. Duodenal gland
- D. Pancreatic gland
Explanation: ***Salivary gland*** - **Ptyalin**, also known as **salivary amylase**, is an enzyme produced by the salivary glands. - Its primary role is to initiate the **digestion of carbohydrates** (starches) in the mouth. *Gastric gland* - Gastric glands primarily secrete **hydrochloric acid** and **pepsinogen**, involved in protein digestion. - They do not produce ptyalin or enzymes for carbohydrate digestion. *Duodenal gland* - Duodenal glands (Brunner's glands) secrete alkaline mucus to protect the duodenum from acidic chyme. - They are not involved in the production of carbohydrate-digesting enzymes like ptyalin. *Pancreatic gland* - The pancreas produces **pancreatic amylase**, which continues starch digestion in the small intestine. - While it secretes an amylase, it is distinct from salivary amylase (ptyalin) and released into the duodenum, not the mouth.
Question 64: What is the body's first physiological response to hypoglycemia?
- A. Decreased insulin (Correct Answer)
- B. Increased glucagon
- C. Increased cortisol
- D. Increased norepinephrine
Explanation: ***Decreased insulin*** - **Decreased insulin secretion** is the body's **first and earliest** physiological response to falling blood glucose levels, occurring at approximately **80-85 mg/dL**. - This represents the **primary defense mechanism** against hypoglycemia - by reducing insulin release from pancreatic beta cells, the body removes the most potent glucose-lowering stimulus. - This allows blood glucose to stabilize before it drops further, and occurs **before** any active counterregulatory hormones are released. - This is a critical **first-line defense** that prevents the need for more aggressive counterregulatory responses. *Increased glucagon* - **Glucagon** is the **second line of defense** against hypoglycemia, with secretion increasing at glucose levels around **65-70 mg/dL**. - While glucagon is the most important **active counterregulatory hormone** (stimulating glycogenolysis and gluconeogenesis), it is not the *first* response. - The temporal sequence is: insulin suppression occurs first, followed by glucagon release if glucose continues to fall. *Increased cortisol* - **Cortisol** is a late counterregulatory hormone, responding to more severe or prolonged hypoglycemia (glucose <65 mg/dL). - It promotes gluconeogenesis and reduces peripheral glucose utilization over hours, not minutes. - Along with growth hormone, cortisol provides sustained glucose elevation but is not an early response. *Increased norepinephrine* - **Norepinephrine** (and epinephrine) are part of the sympathetic/adrenomedullary response to hypoglycemia at approximately **65-70 mg/dL**. - These catecholamines provide important counterregulation but are activated after insulin suppression has already occurred. - They contribute to both glucose mobilization and the symptomatic (adrenergic) response to hypoglycemia.
Question 65: What is the process by which water moves from the extracellular space to the intracellular space?
- A. Osmosis (Correct Answer)
- B. Diffusion
- C. Filtration
- D. Active transport
Explanation: ***Osmosis*** - **Osmosis** is the movement of water across a **semipermeable membrane** from an area of higher water concentration (lower solute concentration) to an area of lower water concentration (higher solute concentration). - In the context of fluid shifts, if the **extracellular fluid** becomes hypotonic relative to the **intracellular fluid**, water will move into the cells to equalize the solute concentration. *Diffusion* - **Diffusion** refers to the net movement of particles from an area of higher concentration to an area of lower concentration, down their **concentration gradient**. - While water molecules can diffuse, **osmosis** specifically describes the net movement of water across a membrane due to **solute concentration differences**, which is the precise mechanism for water moving between fluid compartments. *Filtration* - **Filtration** is the process by which water and solutes move across a membrane due to a **pressure gradient**, typically a **hydrostatic pressure gradient**. - This process is crucial in the kidneys for forming filtrate, but it is not the primary mechanism for water movement between the intra- and extracellular spaces based on solute concentration. *Active transport* - **Active transport** involves the movement of molecules across a membrane against their **concentration gradient**, requiring **energy expenditure** (e.g., ATP). - Water movement between fluid compartments is generally a passive process, relying on **osmotic gradients** rather than direct energy input to pump water molecules.
Question 66: What is the fixed length of a myosin filament?
- A. 0.16 nm
- B. 1.6 micrometers (Correct Answer)
- C. 16 nm
- D. 1.6 mm
Explanation: ***1.6 micrometers*** - Myosin filaments, also known as **thick filaments**, are integral components of muscle contraction and have a characteristic fixed length. This length is precisely **1.6 micrometers** in mammalian skeletal muscle. - This consistent length is crucial for the **sliding filament model** of muscle contraction, ensuring proper overlap with actin filaments and efficient force generation. *0.16 nm* - This value is significantly too small; **nanometers (nm)** are typically used for atomic or molecular distances, not for entire protein filaments like myosin. - A myosin filament is composed of hundreds of myosin molecules, making its overall length much larger than a fraction of a nanometer. *16 nm* - While nanometers are used for molecular structures, 16 nm is still too small for a myosin filament. The entire filament is roughly **100 times larger** than this value. - This dimension might be more appropriate for the diameter of a single myosin molecule's head region, but not the entire filament's length. *1.6 mm* - This value is significantly too large; **millimeters (mm)** are visible to the naked eye and represent macroscopic objects. - Muscle filaments are microscopic structures, and a length of 1.6 mm would imply they are many times longer than an entire muscle cell.
Question 67: Haploid number of chromosomes is first seen in?
- A. Spermatogonia
- B. Primary spermatocytes
- C. Secondary spermatocyte (Correct Answer)
- D. Spermatids
Explanation: ***Secondary spermatocyte*** - A secondary spermatocyte is formed after **meiosis I**, where the homologous chromosomes are separated, resulting in a cell with a **haploid number of chromosomes (n)**, although each chromosome still consists of two sister chromatids. - This is the **first stage** where haploidy is achieved in spermatogenesis. - These cells are transient and quickly undergo meiosis II to form spermatids. *Spermatogonia* - Spermatogonia are **diploid (2n)** germline stem cells that undergo mitosis to produce more spermatogonia or differentiate into primary spermatocytes. - They contain the full complement of chromosomes found in somatic cells. *Primary spermatocytes* - Primary spermatocytes are also **diploid (2n)** cells that enter meiosis I. - Before meiosis I, DNA replication occurs, so each chromosome consists of two sister chromatids, but the cell still maintains a diploid chromosome number. *Spermatids* - Spermatids are formed after **meiosis II** from secondary spermatocytes and are also **haploid (n)**. - However, secondary spermatocytes become haploid **earlier** in the process, immediately following the reductional division of meiosis I.
Question 68: What is the Bohr effect in relation to hemoglobin's affinity for oxygen?
- A. Decrease in CO2 affinity of hemoglobin when the pH of blood falls
- B. Decrease in O2 affinity of hemoglobin when the pH of blood rises
- C. Decrease in O2 affinity of hemoglobin when the pH of blood falls (Correct Answer)
- D. Decrease in CO2 affinity of hemoglobin when the pH of blood rises
Explanation: ***Decrease in O2 affinity of hemoglobin when the pH of blood falls*** - The **Bohr effect** describes how **hemoglobin's affinity for oxygen decreases** in acidic environments (lower pH), leading to increased oxygen release to tissues. - This physiological response is crucial in active tissues, where increased metabolism produces more **carbon dioxide** and **lactic acid**, lowering the local pH. *Decrease in CO2 affinity of hemoglobin when the pH of blood falls* - This statement incorrectly relates the Bohr effect to **CO2 affinity** and its change with pH in this manner. - The Bohr effect primarily concerns oxygen affinity, not CO2 affinity; CO2 and H+ directly influence oxygen binding. *Decrease in O2 affinity of hemoglobin when the pH of blood rises* - An **increase in pH** (alkaline environment) would, in fact, **increase hemoglobin's affinity for oxygen**, promoting oxygen uptake in the lungs. - This describes the opposite of the Bohr effect, which is about oxygen release in acidic conditions. *Decrease in CO2 affinity of hemoglobin when the pH of blood rises* - While pH changes do affect CO2 transport, this statement does not accurately describe the Bohr effect. - The **Haldane effect** is more relevant to the relationship between oxygenation status and hemoglobin's CO2 affinity.
Question 69: What is the consequence of tibial nerve injury/palsy?
- A. Loss of plantar flexion (Correct Answer)
- B. Dorsiflexion of foot at ankle joint
- C. Loss of sensation of dorsum of foot
- D. Paralysis of muscles of anterior compartment of leg
Explanation: **Loss of plantar flexion** - The **tibial nerve** innervates the muscles of the **posterior compartment of the leg**, which are primarily responsible for **plantar flexion** of the foot. - Injury to this nerve directly impairs the function of muscles like the gastrocnemius, soleus, and tibialis posterior, leading to a significant loss of the ability to point the foot downwards. *Dorsiflexion of foot at ankle joint* - **Dorsiflexion** is primarily mediated by muscles in the **anterior compartment of the leg**, such as the tibialis anterior, which are innervated by the **deep fibular nerve**. - Tibial nerve injury would not directly affect these muscles or their function; rather, it leads to issues with the opposing action. *Loss of sensation of dorsum of foot* - Sensation to the **dorsum of the foot** is primarily supplied by the **superficial fibular nerve** (for most of the dorsum) and the **deep fibular nerve** (for the first web space). - While the tibial nerve provides sensation to the sole of the foot, it does not typically innervate the dorsum. *Paralysis of muscles of anterior compartment of leg* - The muscles of the **anterior compartment of the leg** (e.g., tibialis anterior, extensor digitorum longus, extensor hallucis longus) are innervated by the **deep fibular nerve**. - A tibial nerve injury would paralyze muscles in the posterior compartment, not the anterior compartment.
Question 70: Which of the following statements regarding the lower esophageal sphincter is TRUE?
- A. It relaxes in response to swallowing. (Correct Answer)
- B. It remains contracted during swallowing to prevent regurgitation.
- C. Its tone is primarily influenced by the myogenic properties of the smooth muscle.
- D. It contracts in response to gastric distension.
Explanation: ***It relaxes in response to swallowing.*** - The **lower esophageal sphincter (LES)** normally maintains high resting tone to prevent gastroesophageal reflux but **relaxes completely during swallowing** to allow passage of food into the stomach. - This relaxation (called **receptive relaxation**) is mediated by **vagal nerve stimulation** through release of nitric oxide (NO) and vasoactive intestinal peptide (VIP). - The relaxation occurs **before the peristaltic wave arrives**, allowing coordinated transit of the bolus. *It remains contracted during swallowing to prevent regurgitation.* - This is **incorrect** - the LES must **relax during swallowing** to allow food passage into the stomach. - Failure of LES relaxation during swallowing is the pathophysiology of **achalasia**, leading to dysphagia. - The LES only maintains contraction between swallows to prevent reflux. *Its tone is primarily influenced by the myogenic properties of the smooth muscle.* - While the LES contains smooth muscle with intrinsic myogenic properties, its tone is **predominantly regulated by neural and hormonal factors**. - **Neural control:** Vagal cholinergic pathways (increase tone), non-adrenergic non-cholinergic (NANC) pathways with NO and VIP (decrease tone). - **Hormonal factors:** Gastrin increases tone, while progesterone, CCK, and secretin decrease tone. *It contracts in response to gastric distension.* - This is **incorrect** - gastric distension actually triggers **transient LES relaxations (TLESRs)**, which are the primary mechanism of physiological reflux. - TLESRs are vagally mediated reflex responses that allow venting of gastric air. - Increased LES contraction in response to gastric distension would be counterproductive.