What is the primary change in fetal circulation that occurs at birth?
Testes are not palpable in
Osteoclasts have all of the following functions except -
Gamma waves of REM sleep are associated with?
Which type of pain is characterized by unknown etiology?
Which of the following is not true about sleep -
Most recently identified taste sensation is?
Vibration sense is detected by ?
Stress induced hyperglycemia is mediated through which hormone:
NEET-PG 2015 - Physiology NEET-PG Practice Questions and MCQs
Question 111: What is the primary change in fetal circulation that occurs at birth?
- A. Closure of the ductus venosus
- B. Increased activity of the right ventricle
- C. Closure of the foramen ovale (Correct Answer)
- D. Closure of the patent ductus arteriosus
Explanation: ***Closure of the foramen ovale*** - The **foramen ovale** undergoes functional closure within minutes of birth, making it the **primary immediate circulatory change** - At birth, the first breath causes **dramatic decrease in pulmonary vascular resistance** and **increased pulmonary blood flow**, which raises **left atrial pressure** - Simultaneously, umbilical cord clamping **increases systemic vascular resistance** and **decreases right atrial pressure** (loss of placental return) - This **pressure gradient reversal** (left atrial pressure > right atrial pressure) causes the **septum primum** to be pushed against the **septum secundum**, achieving functional closure - This immediately separates the systemic and pulmonary circulations, which is the **most critical primary change** in transitioning from fetal to neonatal circulation *Closure of the patent ductus arteriosus* - The **ductus arteriosus** undergoes **functional closure over 10-15 hours** after birth, followed by **anatomical closure over 2-3 weeks** - Closure occurs due to increased arterial oxygen tension and decreased prostaglandin E2 levels, causing smooth muscle constriction - While important, this is a **secondary change** that occurs more gradually compared to the immediate foramen ovale closure *Closure of the ductus venosus* - The **ductus venosus** closes functionally within 3-7 days as umbilical venous flow ceases - This redirects portal blood through the liver but does not directly impact the critical pulmonary-systemic circulation separation *Increased activity of the right ventricle* - After birth, the **left ventricle** becomes dominant as it pumps against higher systemic vascular resistance - The right ventricle actually experiences **decreased afterload** due to falling pulmonary vascular resistance - This is a consequence of, not the primary change in, the circulatory transition
Question 112: Testes are not palpable in
- A. SRY deletion (Correct Answer)
- B. DAX 1 deletion
- C. WNT- 4 gene mutation
- D. RSPO-1 gene mutation
Explanation: ***SRY deletion*** - **SRY (Sex-determining Region Y) gene** is the master regulator of male sex determination on the Y chromosome; its deletion in 46,XY individuals results in **Swyer syndrome** (pure gonadal dysgenesis). - Without functional SRY, **testes fail to develop entirely**, and the gonads remain as non-functional **streak gonads** rather than differentiating into either testes or ovaries. - Result: **No palpable testes** because testicular tissue never forms; individuals develop female external genitalia despite XY karyotype. *DAX1 deletion* - DAX1 (NR0B1) normally **antagonizes testicular development** and supports adrenal/gonadal development. - **Deletion of DAX1** would actually **reduce anti-testis effects**, allowing testicular development to proceed more readily if SRY is present. - DAX1 **duplications** (not deletions) can impair male development; deletions cause **adrenal hypoplasia congenita** but do not prevent testicular formation. *WNT-4 gene mutation* - **WNT4** promotes **ovarian development** and opposes male differentiation pathways in normal female development. - **Loss-of-function mutations** in WNT4 do not prevent testicular development in 46,XY individuals where SRY is present and functional. - WNT4 overexpression (not loss-of-function mutation) could theoretically interfere with male development, but standard WNT4 mutations do not cause absent testes. *RSPO-1 gene mutation* - **RSPO1** (R-spondin 1) enhances **Wnt/β-catenin signaling** and supports ovarian differentiation; primarily relevant in 46,XX sex development. - Loss-of-function mutations in RSPO1 lead to **46,XX testicular/ovotesticular DSD**, where testicular tissue develops inappropriately in XX individuals. - In 46,XY individuals with functional SRY, RSPO1 mutations would **not prevent testicular development**, so testes would be palpable.
Question 113: Osteoclasts have all of the following functions except -
- A. Receptor for parathormone (Correct Answer)
- B. Ruffled border
- C. Bone resorption
- D. RANK ligand production
Explanation: ***Receptor for parathormone*** - **Osteoclasts** do not directly have receptors for **parathormone (PTH)**; instead, **osteoblasts** have PTH receptors. - When PTH binds to osteoblasts, they release factors (like **RANKL**) that stimulate osteoclast activity, thus indirectly regulating bone resorption. *Bone resorption* - **Osteoclasts** are specialized cells primarily responsible for **resorbing bone matrix**, a critical process in bone remodeling. - They secrete **acids and enzymes** to break down the mineral and organic components of bone. *Ruffled border* - The **ruffled border** is a characteristic morphological feature of active osteoclasts, representing a highly folded plasma membrane. - This specialized structure increases the surface area for the secretion of **protons and lysosomal enzymes** into the bone-resorbing compartment. *RANK ligand production* - **Osteoclasts** do not produce **RANK ligand (RANKL)**; rather, they have **RANK receptors** that bind to RANKL produced by **osteoblasts and stromal cells**. - The binding of RANKL to RANK is essential for the **differentiation, activation, and survival** of osteoclasts.
Question 114: Gamma waves of REM sleep are associated with?
- A. Dream consciousness and memory consolidation
- B. Deep subconscious processing
- C. Non-REM sleep
- D. Subconscious processing (Correct Answer)
Explanation: ***Subconscious processing*** - **Gamma waves (30-100 Hz)** during **REM sleep** represent high-frequency neural oscillations associated with **complex cognitive processing** occurring below the level of conscious awareness. - These waves reflect **integration of neural activity** across different brain regions, facilitating information processing and neural plasticity during sleep. - The term encompasses the underlying **neural mechanisms** that support dream generation and memory consolidation processes. *Dream consciousness and memory consolidation* - While **gamma waves** do correlate with dreaming and memory processes during **REM sleep**, these represent the **experiential and functional outcomes** rather than the primary neurophysiological association. - Dream consciousness is a **manifestation** of the underlying subconscious processing, not the direct association with gamma wave activity itself. *Deep subconscious processing* - The term "deep subconscious" is **non-specific** and lacks precise neurophysiological definition in the context of gamma wave activity. - While directionally correct, this option uses imprecise terminology compared to the more accurate "subconscious processing." *Non-REM sleep* - **Gamma waves** are characteristic of **waking states** and **REM sleep**, not non-REM sleep stages. - **Non-REM sleep** (stages N1, N2, N3) is dominated by **slower wave activity** including theta waves (stage N1), sleep spindles and K-complexes (stage N2), and delta waves (stage N3/deep sleep).
Question 115: Which type of pain is characterized by unknown etiology?
- A. Nociceptive pain
- B. Neuropathic pain
- C. Idiopathic pain (Correct Answer)
- D. Inflammatory pain
Explanation: ***Idiopathic pain*** - This term refers to pain where the **underlying cause** or pathology cannot be identified, despite thorough investigation. - It signifies that the **etiology is unknown**, fitting the description in the question directly. *Nociceptive pain* - This type of pain arises from the activation of **nociceptors** due to actual or threatened tissue damage. - Its etiology is typically clear, involving an injury, inflammation, or mechanical stress. *Neuropathic pain* - This pain results from damage or disease affecting the **somatosensory nervous system**. - The etiology is known to be nerve damage or dysfunction, not an unknown origin. *Inflammatory pain* - This pain is driven by the inflammatory process, involving the release of **pro-inflammatory mediators** at the site of tissue injury or infection. - The cause is directly linked to inflammation, making its etiology known.
Question 116: Which of the following is not true about sleep -
- A. Dreams come in REM sleep
- B. REM sleep comes earlier than NREM sleep (Correct Answer)
- C. REM sleep is also called paradoxical sleep
- D. Sleep walking comes in NREM sleep
Explanation: ***REM sleep comes earlier than NREM sleep*** - This statement is **incorrect** because the sleep cycle typically begins with **NREM (non-rapid eye movement) sleep**, specifically NREM stage 1, before progressing to NREM stages 2 and 3, and then finally entering REM sleep. - NREM sleep accounts for about **75% of total sleep time** and occurs prior to REM sleep in a typical nocturnal sleep episode. *Dreams come in REM sleep* - This statement is **true** as **vivid, memorable dreams** are most commonly associated with **REM sleep**. - During REM sleep, brain activity significantly increases, mimicking the awake state, which facilitates complex dream formation. *REM sleep is also called paradoxical sleep* - This statement is **true** because **REM sleep** is characterized by **high brain activity** (similar to wakefulness) and rapid eye movements, yet the body experiences **muscle atonia**, leading to a state of profound relaxation. - This paradoxical combination of an active brain and a paralyzed body gives it the name **paradoxical sleep**. *Sleep walking comes in NREM sleep* - This statement is **true** as **sleepwalking (somnambulism)** typically occurs during **slow-wave sleep**, which is **NREM stage 3 (deep sleep)**. - During this stage, arousal thresholds are very high, and complex motor behaviors can occur while the individual remains in a sleep state.
Question 117: Most recently identified taste sensation is?
- A. Sour
- B. Bitter
- C. Umami (Correct Answer)
- D. Sweet
Explanation: ***Umami*** - **Umami** is the most recently identified **fifth basic taste**, often described as a savory or meaty taste. - Its discovery and recognition as a distinct taste sensation occurred in the **early 20th century** by Kikunae Ikeda, who isolated glutamate from kombu. *Sour* - The sensation of **sourness** is one of the traditionally recognized basic tastes, identified much earlier than umami. - It is typically associated with **acids**, such as those found in lemons or vinegar. *Bitter* - **Bitterness** is another long-standing basic taste that serves an important protective function, often signaling potential toxins. - It is one of the earliest tastes understood and recognized, with receptors for a wide range of bitter compounds. *Sweet* - **Sweetness** is a fundamental and ancient taste, universally recognized as pleasurable and indicating energy-rich foods. - The perception of sweet taste, primarily from sugars, has been understood for centuries.
Question 118: Vibration sense is detected by ?
- A. Superficial receptors
- B. Free nerve endings
- C. Nociceptors
- D. Deep receptors (Correct Answer)
Explanation: ***Deep receptors*** - **Vibration sense** is primarily mediated by **Pacinian corpuscles** and **Meissner's corpuscles**, which are considered deep receptors. - **Pacinian corpuscles** are located in the **deep dermis** and **subcutaneous tissue** and are highly sensitive to **high-frequency vibration** (200-300 Hz). - **Meissner's corpuscles** in dermal papillae detect **lower frequency vibration** and are rapidly adapting mechanoreceptors. *Superficial receptors* - **Superficial receptors** like **Merkel cells** primarily detect **sustained touch** and **pressure**, providing information about texture. - While they contribute to tactile sensation, they are **slowly adapting** and not specialized for rapidly oscillating stimuli like vibration. *Free nerve endings* - **Free nerve endings** are unmyelinated or lightly myelinated nerve terminals that detect **pain**, **temperature**, and **crude touch**. - They are not specialized mechanoreceptors and lack the structural organization needed to transduce vibratory stimuli. *Nociceptors* - **Nociceptors** are specialized sensory receptors that detect **noxious (harmful) stimuli** and mediate the sensation of **pain**. - They respond to extreme temperatures, intense mechanical stress, or chemical irritants, not to non-painful vibration.
Question 119: Stress induced hyperglycemia is mediated through which hormone:
- A. Cortisol (Correct Answer)
- B. Epinephrine
- C. Insulin
- D. Growth hormone
Explanation: ***Cortisol*** - **Cortisol** is the **primary mediator** of stress-induced hyperglycemia among the counter-regulatory hormones - It promotes **gluconeogenesis** (formation of new glucose from amino acids and glycerol) in the liver - Stimulates **protein catabolism** in muscles, providing substrates for gluconeogenesis - Induces **insulin resistance** in peripheral tissues, reducing glucose uptake - Released as part of the **HPA axis response** to stress, with sustained elevation during prolonged stress - This is the **correct answer** for stress-induced hyperglycemia mediation *Epinephrine* - **Epinephrine** (adrenaline) is a potent hyperglycemic hormone but acts as an **acute, immediate response** to stress - Rapidly increases blood glucose through **glycogenolysis** (breakdown of glycogen) in liver and muscles - Stimulates **gluconeogenesis** and inhibits insulin secretion - Effects are **rapid but short-lived**, making it more of an emergency response rather than the sustained mediator - Works synergistically with cortisol but is not the primary sustained mediator *Growth hormone* - **Growth hormone** does contribute to hyperglycemia through **anti-insulin effects** and promoting lipolysis - Its hyperglycemic effects are **slower and less pronounced** compared to cortisol and epinephrine - Plays a role in **chronic stress** but is not the primary acute mediator - More important for **long-term metabolic adaptation** rather than immediate stress response *Insulin* - **Insulin** is a **glucose-lowering hormone** that facilitates glucose uptake into cells - During stress, insulin secretion is **suppressed** and tissues become **insulin-resistant** due to counter-regulatory hormones - It does **not mediate** stress-induced hyperglycemia; rather, its action is **opposed** by stress hormones - Decreased insulin action contributes to hyperglycemia but insulin itself is not the mediator