Chapter: Central Nervous System; Topic: Sensory Pathways; Subtopic: Thalamic Processing of Sensory Information
Keyword Definitions:
• Thalamus: Major relay center for sensory information before reaching the cerebral cortex.
• Proprioception: Sense of body position and movement.
• Pain and Temperature: Sensations transmitted via spinothalamic tract to thalamus.
• Tactile Sensation: Touch and pressure perception mediated by dorsal column system.
• Somatosensory Cortex: Region that interprets sensory signals from thalamus.
• Spinothalamic Tract: Pathway for pain, temperature, and crude touch sensations.
• Ventral Posterior Nucleus: Thalamic nucleus relaying somatic sensations to cortex.
Lead Question – 2014
Sensations which are appreciated in thalamus
a) Proprioception
b) Pain & temperature
c) Tactile sensations
d) Pressure
Explanation: Pain and temperature sensations are primarily appreciated in the thalamus, even without cortical input. The thalamus acts as a sensory gateway, receiving inputs via the spinothalamic tract. While tactile and proprioceptive sensations reach the cortex for full perception, crude pain and temperature are recognized at thalamic level. Answer: (b) Pain & temperature.
1. Which thalamic nucleus is primarily involved in the relay of somatic sensations?
a) Ventral anterior nucleus
b) Ventral posterior nucleus
c) Medial geniculate body
d) Pulvinar
Explanation: The ventral posterior nucleus (VPN) of the thalamus receives somatic sensory input from the spinothalamic and medial lemniscal tracts. It relays sensations like pain, temperature, and touch to the somatosensory cortex. VPN damage leads to contralateral sensory loss. Answer: (b) Ventral posterior nucleus.
2. Crude pain sensation can be perceived even without cerebral cortex because:
a) Medulla perceives pain
b) Thalamus has pain receptors
c) Thalamus can appreciate crude sensations
d) Brainstem acts independently
Explanation: Crude pain and temperature sensations are appreciated at the thalamic level. The thalamus, particularly the ventral posterior nucleus, receives spinothalamic input. Even if cortical areas are damaged, crude sensations persist due to thalamic processing. Answer: (c) Thalamus can appreciate crude sensations.
3. Fine touch and proprioception reach the thalamus through which pathway?
a) Spinothalamic tract
b) Corticospinal tract
c) Dorsal column–medial lemniscus pathway
d) Reticulospinal tract
Explanation: The dorsal column–medial lemniscus pathway transmits fine touch, vibration, and proprioception to the thalamus. Fibers ascend ipsilaterally in dorsal columns, decussate in medulla, and terminate in the ventral posterior nucleus of thalamus. Answer: (c) Dorsal column–medial lemniscus pathway.
4. A patient with right thalamic stroke experiences left-sided loss of pain and temperature sensation. The tract involved is:
a) Dorsal column
b) Corticospinal tract
c) Spinothalamic tract
d) Spinocerebellar tract
Explanation: The spinothalamic tract carries pain and temperature sensations from the contralateral side of the body to the thalamus. A right thalamic lesion causes left-sided sensory deficits. This tract decussates soon after entering the spinal cord. Answer: (c) Spinothalamic tract.
5. Which of the following sensations is lost in a lesion of the ventral posterior nucleus of the thalamus?
a) Motor control
b) Sensation from opposite side of body
c) Vision
d) Hearing
Explanation: The ventral posterior nucleus relays sensory input from the contralateral body via the spinothalamic and medial lemniscal systems. Lesions cause loss of pain, temperature, touch, and proprioception on the opposite side. Answer: (b) Sensation from opposite side of body.
6. A 52-year-old man presents with burning pain following a thalamic infarct. This condition is known as:
a) Thalamic syndrome
b) Brown-Séquard syndrome
c) Guillain–Barré syndrome
d) Horner’s syndrome
Explanation: Thalamic syndrome (Dejerine–Roussy syndrome) occurs after thalamic infarction. It manifests as contralateral burning pain, sensory loss, and hyperesthesia due to disrupted sensory relay from thalamus to cortex. Answer: (a) Thalamic syndrome.
7. Which sensory modality is least affected by thalamic lesions?
a) Crude touch
b) Pain
c) Vision
d) Smell
Explanation: Olfactory sensation bypasses the thalamus and directly reaches the cerebral cortex via the olfactory tract. Thus, smell remains unaffected in thalamic lesions, unlike other sensory modalities that relay through thalamic nuclei. Answer: (d) Smell.
8. A 40-year-old woman has loss of proprioception but intact pain and temperature. The likely site of lesion is:
a) Thalamus
b) Medial lemniscus
c) Spinothalamic tract
d) Dorsal column
Explanation: Loss of proprioception with preserved pain and temperature indicates a dorsal column lesion. The dorsal column–medial lemniscus pathway carries proprioceptive information, while the spinothalamic tract conveys pain and temperature. Answer: (d) Dorsal column.
9. Which thalamic nucleus is connected with pain perception?
a) Ventral posterior nucleus
b) Lateral geniculate body
c) Medial geniculate body
d) Pulvinar
Explanation: The ventral posterior nucleus processes pain and temperature inputs received from the spinothalamic tract. It relays these sensations to the primary somatosensory cortex for interpretation. Answer: (a) Ventral posterior nucleus.
10. A 60-year-old stroke patient reports increased sensitivity to mild touch on the opposite side. This exaggerated pain response is due to:
a) Thalamic hyperactivity
b) Brainstem ischemia
c) Spinal cord lesion
d) Peripheral neuropathy
Explanation: Post-thalamic stroke, neurons in the thalamus become hyperexcitable, leading to exaggerated pain or allodynia. This abnormal processing of sensory signals, termed thalamic pain syndrome, causes severe discomfort from even light stimuli. Answer: (a) Thalamic hyperactivity.
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Chapter: Nervous System; Topic: Reflexes; Subtopic: Spinal Segmental Reflexes and Clinical Correlations
Keyword Definitions:
• Reflex: An involuntary, rapid, and predictable motor response to a stimulus.
• Spinal Segment: A region of the spinal cord giving rise to a pair of spinal nerves.
• Knee Jerk: A monosynaptic reflex testing L2–L4 spinal segments.
• Calcaneal Reflex: Also called ankle jerk, testing S1–S2 integrity.
• Patellar Reflex: Stretch reflex involving quadriceps contraction.
• Deep Tendon Reflexes (DTRs): Test spinal cord and peripheral nerve integrity.
• Monosynaptic Reflex: Reflex arc involving one synapse between sensory and motor neurons.
• Polysynaptic Reflex: Reflex involving one or more interneurons.
• Motor Neuron: Nerve cell carrying impulses from CNS to muscles.
• Spinal Shock: Transient loss of reflex activity after spinal cord injury.
Lead Question – 2014
S1 S2 is checked by which reflex?
a) Knee jerk
b) Patellar reflex
c) Calcaneal reflex
d) None
Explanation: The calcaneal reflex (ankle jerk) tests the integrity of the S1–S2 spinal segments, primarily S1. When the Achilles tendon is tapped, it stimulates the gastrocnemius and soleus muscles to contract, causing plantar flexion. This reflex assesses the health of the tibial nerve and corresponding spinal roots. Answer: (c) Calcaneal reflex.
1. Which spinal segment is tested by the knee jerk reflex?
a) L2–L4
b) L4–S1
c) S1–S2
d) C5–C6
Explanation: The knee jerk or patellar reflex assesses the L2–L4 spinal segments. Tapping the patellar tendon stretches the quadriceps muscle, causing contraction and leg extension. It evaluates the integrity of the femoral nerve and associated spinal segments. Answer: (a) L2–L4.
2. The biceps jerk tests which spinal level?
a) C5–C6
b) C7–C8
c) L2–L3
d) S1–S2
Explanation: The biceps jerk evaluates the integrity of C5–C6 spinal segments through the musculocutaneous nerve. Tapping the biceps tendon causes muscle contraction and forearm flexion. Absence indicates possible C5–C6 root lesion. Answer: (a) C5–C6.
3. The triceps reflex primarily checks which spinal root?
a) C4
b) C5
c) C6
d) C7
Explanation: The triceps reflex tests the C7 spinal segment via the radial nerve. Tapping the triceps tendon elicits elbow extension. Weak or absent response suggests a lesion in the C7 root or radial nerve. Answer: (d) C7.
4. The ankle jerk reflex involves which efferent nerve?
a) Femoral
b) Obturator
c) Tibial
d) Sciatic
Explanation: The ankle jerk or calcaneal reflex involves the tibial nerve, a branch of the sciatic nerve. It carries motor impulses to gastrocnemius and soleus muscles for plantar flexion. Impaired reflex suggests tibial or S1 root dysfunction. Answer: (c) Tibial.
5. Loss of ankle jerk is commonly seen in which condition?
a) Upper motor neuron lesion
b) Peripheral neuropathy
c) Parkinson’s disease
d) Multiple sclerosis
Explanation: Loss or reduction of ankle jerk reflex occurs in peripheral neuropathy, especially in diabetes mellitus. Damage to peripheral nerves or S1 root impairs the reflex arc, leading to diminished plantar flexion response. Answer: (b) Peripheral neuropathy.
6. A 55-year-old diabetic patient presents with absent ankle jerk but normal knee jerk. The lesion is likely at:
a) L2–L4
b) S1–S2
c) C5–C6
d) L5–S1
Explanation: Absence of ankle jerk with preserved knee jerk indicates S1–S2 root involvement. The calcaneal reflex tests the S1 segment. Diabetic neuropathy often affects distal sensory and motor fibers first. Answer: (b) S1–S2.
7. A lesion at S1 spinal root leads to loss of which reflex?
a) Knee jerk
b) Biceps jerk
c) Ankle jerk
d) Supinator jerk
Explanation: The S1 spinal root supplies the gastrocnemius and soleus muscles responsible for the ankle jerk reflex. Damage to S1 abolishes this reflex, while knee jerk remains unaffected. Answer: (c) Ankle jerk.
8. A patient with herniated L5–S1 disc complains of reduced plantar flexion. Which reflex is affected?
a) Knee jerk
b) Ankle jerk
c) Biceps jerk
d) Triceps jerk
Explanation: Herniation at L5–S1 compresses the S1 nerve root, leading to weakness in plantar flexion and loss of ankle jerk reflex. This clinical sign helps localize the lesion to S1. Answer: (b) Ankle jerk.
9. Which of the following best describes a monosynaptic reflex?
a) Withdrawal reflex
b) Stretch reflex
c) Crossed extensor reflex
d) Pupillary light reflex
Explanation: The stretch reflex (like patellar reflex) is monosynaptic, involving direct communication between a sensory and a motor neuron without interneurons. It helps maintain muscle tone and posture. Answer: (b) Stretch reflex.
10. A 45-year-old patient with spinal shock after trauma shows loss of all reflexes below the injury. This loss is due to:
a) Irreversible spinal cord damage
b) Transient suppression of reflex arcs
c) Motor neuron hyperactivity
d) Autonomic overactivity
Explanation: In spinal shock, there is temporary loss of all reflexes below the injury due to sudden interruption of descending facilitatory pathways. Reflexes gradually return as spinal neurons regain excitability. Answer: (b) Transient suppression of reflex arcs.
Chapter: Central Nervous System; Topic: Olfactory Pathways; Subtopic: Cellular Components of Olfactory Bulb
Keyword Definitions:
• Mitral Cells: Principal neurons of the olfactory bulb that receive input from olfactory receptor neurons.
• Periglomerular Cells: Interneurons surrounding glomeruli that modulate synaptic transmission.
• Olfactory Bulb: Brain structure involved in processing smell information.
• Glomeruli: Spherical structures where olfactory nerve fibers synapse.
• Medulla: Part of brainstem controlling vital reflexes.
• Geniculate Body: Thalamic nuclei for auditory and visual processing.
• Primary Visual Cortex: Area in occipital lobe for visual perception.
Lead Question - 2014
Mitral and periglomerular cells are seen in?
a) Medulla
b) Olfactory bulb
c) Primary visual cortex
d) Geniculate body
Explanation: The olfactory bulb contains both mitral cells and periglomerular cells. Mitral cells serve as the main relay neurons transmitting olfactory signals to higher centers like the olfactory cortex. Periglomerular cells regulate these synapses within glomeruli. Together, they help refine odor detection and processing, making option (b) the correct answer.
1) The first relay station for olfactory impulses is?
a) Olfactory bulb
b) Olfactory tract
c) Olfactory cortex
d) Hypothalamus
Explanation: The olfactory bulb acts as the first relay station where olfactory receptor neurons synapse with mitral and tufted cells. These signals are then transmitted to the olfactory tract and higher centers. Thus, option (a) is correct.
2) Which type of neurons are found in the olfactory epithelium?
a) Bipolar neurons
b) Unipolar neurons
c) Multipolar neurons
d) Pseudounipolar neurons
Explanation: The sensory neurons of the olfactory epithelium are bipolar neurons. They have a dendrite that detects odorant molecules and an axon that transmits signals to the olfactory bulb. Hence, the correct answer is (a).
3) Olfactory tract fibers project mainly to?
a) Medulla
b) Thalamus
c) Temporal lobe
d) Occipital lobe
Explanation: The olfactory tract primarily projects to the temporal lobe, particularly the piriform cortex and amygdala, which are involved in smell perception and emotion. Option (c) is correct.
4) Which neurotransmitter is predominantly used by periglomerular cells?
a) Glutamate
b) Dopamine
c) Serotonin
d) GABA
Explanation: Periglomerular cells are inhibitory interneurons that mainly use GABA as their neurotransmitter to modulate mitral cell activity. This inhibitory control helps fine-tune olfactory signal processing. Thus, the answer is (d).
5) Mitral cells send axons through which structure?
a) Olfactory tract
b) Optic nerve
c) Internal capsule
d) Mammillothalamic tract
Explanation: The axons of mitral cells form the olfactory tract, which conveys processed olfactory information from the bulb to the olfactory cortex. Therefore, option (a) is correct.
6) A patient with anosmia likely has a lesion in which area?
a) Olfactory bulb
b) Medulla
c) Occipital cortex
d) Pons
Explanation: Loss of smell, or anosmia, often results from damage to the olfactory bulb or the olfactory tract. Such injury interrupts odor signal transmission, making option (a) correct.
7) Damage to which cells reduces odor discrimination ability?
a) Mitral cells
b) Purkinje cells
c) Pyramidal cells
d) Betz cells
Explanation: Mitral cells in the olfactory bulb play a crucial role in odor discrimination by transmitting refined signals to higher olfactory areas. Their damage leads to difficulty differentiating odors. Hence, (a) is correct.
8) Which structure directly receives olfactory input without thalamic relay?
a) Piriform cortex
b) Thalamus
c) Hypothalamus
d) Cerebellum
Explanation: Unlike other senses, smell bypasses the thalamus and directly reaches the piriform cortex for initial processing. This makes option (a) correct.
9) In olfactory pathways, lateral inhibition is mainly mediated by?
a) Periglomerular cells
b) Mitral cells
c) Tufted cells
d) Pyramidal cells
Explanation: Periglomerular cells provide lateral inhibition, enhancing contrast between activated and inactive glomeruli. This improves odor discrimination and clarity. The correct answer is (a).
10) A 45-year-old man loses his sense of smell after head trauma. Which structure is likely damaged?
a) Cribriform plate
b) Thalamus
c) Hypothalamus
d) Cerebellum
Explanation: Trauma can shear olfactory nerve fibers as they pass through the cribriform plate of the ethmoid bone, leading to anosmia. Therefore, (a) is correct.
Topic: Sensory Physiology; Subtopic: Sensory Perception and Laws
Keyword Definitions:
• Weber–Fechner Law: States that the perceived intensity of a stimulus increases as the logarithm of the actual stimulus intensity.
• Stimulus: Any detectable change in the environment that can evoke a response in a sensory receptor.
• Sensation: The subjective experience resulting from sensory receptor stimulation.
• Phantom Limb: Sensation perceived in a limb that has been amputated.
• Cortical Plasticity: The brain’s ability to reorganize neural connections based on experience or injury.
• Receptor Potential: Graded electrical change generated by a sensory receptor in response to a stimulus.
• Threshold Stimulus: The minimum intensity required to evoke a detectable sensation.
Lead Question - 2014
Weber Fechner law is related to?
a) Phantom limb
b) Force of contraction in heart
c) Intensity of stimulus and sensation felt
d) Cortical plasticity
Explanation: The Weber–Fechner law describes the relationship between the magnitude of a physical stimulus and the perceived intensity of that stimulus. It states that the perceived sensation grows as the logarithm of stimulus intensity, meaning larger increments are needed for higher intensity detection. Thus, option (c) is correct — it relates to intensity and perception.
1) Which of the following best represents Weber’s law?
a) ΔI / I = k
b) I = k log S
c) S = k log I
d) ΔI = k log S
Explanation: Weber’s law states that the just noticeable difference (ΔI) is a constant fraction (k) of the original intensity (I). This ratio remains constant for a given sensory modality. Thus, the correct expression is ΔI/I = k, making option (a) correct.
2) Which sensory modality follows the Weber–Fechner law most accurately?
a) Vision
b) Smell
c) Hearing
d) Pain
Explanation: The Weber–Fechner law applies best to hearing and vision, where changes in sound or brightness are perceived logarithmically. Among them, hearing demonstrates a strong correlation between intensity and perceived loudness. Therefore, the correct answer is (c) hearing.
3) A patient reports that doubling the intensity of sound does not double its perceived loudness. This best illustrates?
a) Weber–Fechner law
b) Bell–Magendie law
c) Boyle’s law
d) Ohm’s law
Explanation: The phenomenon where perceived intensity increases less rapidly than actual intensity is governed by the Weber–Fechner law. It reflects the logarithmic relationship between stimulus and perception. Thus, option (a) is correct.
4) According to Weber’s law, the constant (k) varies with?
a) Type of receptor
b) Type of sensation
c) Intensity of light
d) Environmental temperature
Explanation: The constant k in Weber’s law is specific to the type of sensation such as sound, light, or touch. Each sensory system has a unique sensitivity threshold. Therefore, option (b) is correct.
5) Fechner extended Weber’s law by proposing that?
a) Sensation is proportional to log stimulus intensity
b) Sensation is proportional to stimulus intensity squared
c) Sensation is independent of stimulus intensity
d) Sensation decreases with intensity
Explanation: Fechner’s extension stated that perceived sensation (S) = k log (I/I₀), where I is stimulus intensity. This describes a logarithmic increase in sensation with intensity. Hence, (a) is correct.
6) In clinical practice, Weber–Fechner law helps explain?
a) Adaptation to constant stimuli
b) Threshold of pain
c) Visual accommodation
d) Muscle fatigue
Explanation: Clinically, the Weber–Fechner law explains how patients adapt to constant sensory input—such as getting used to bright light or loud sound—through gradual desensitization. It is vital for understanding sensory adaptation. Therefore, (a) is correct.
7) Which of the following is an example of Weber–Fechner law in daily life?
a) Adjusting to room brightness
b) Feeling of hunger
c) Reflex arc activation
d) Salivary secretion to food
Explanation: The gradual adjustment of visual perception in varying light levels is an example of Weber–Fechner law. When entering a bright room from darkness, the eyes adapt logarithmically to light intensity. Hence, (a) is correct.
8) In audiology, the relationship between sound intensity and loudness follows?
a) Weber–Fechner law
b) Laplace’s law
c) Boyle’s law
d) Ohm’s law
Explanation: Sound perception does not increase linearly with physical intensity. The perceived loudness increases logarithmically with intensity, following the Weber–Fechner law. This explains the decibel scale in audiology. Hence, (a) is correct.
9) A 45-year-old man with neuropathy perceives weak touch as intense pain. This phenomenon violates which principle?
a) Weber–Fechner law
b) Bell’s law
c) Henry’s law
d) Dalton’s law
Explanation: The Weber–Fechner law assumes a proportional relationship between stimulus and perception. In neuropathy, damaged sensory pathways distort this proportionality, causing allodynia (pain from non-painful stimuli). Thus, option (a) is correct.
10) In psychophysics, the smallest detectable change in a stimulus is termed?
a) Just noticeable difference
b) Minimal perceptible unit
c) Perceptual threshold
d) Response magnitude
Explanation: The just noticeable difference (JND) is the minimum change in stimulus required to detect a difference. It’s the basis of Weber’s law (ΔI/I = k). Therefore, (a) is correct.
Topic: Inflammatory Mediators; Subtopic: Prostaglandins and Their Sources
Keyword Definitions:
• Prostaglandins: Lipid compounds derived from arachidonic acid via the cyclooxygenase (COX) pathway that act as local hormones mediating inflammation, fever, and pain.
• Arachidonic Acid: A polyunsaturated fatty acid released from membrane phospholipids by phospholipase A₂.
• COX Enzymes: Cyclooxygenase enzymes (COX-1 and COX-2) responsible for prostaglandin synthesis.
• Inflammatory Mediators: Substances such as prostaglandins, leukotrienes, and histamine involved in inflammation.
• Endothelium: The inner lining of blood vessels that releases vasodilators like prostacyclin (PGI₂).
• Macrophages: Immune cells that release cytokines and prostaglandins during inflammation.
• Neutrophils: White blood cells that release prostaglandins and leukotrienes during immune response.
Lead Question - 2014
Prostaglandins are produced by?
a) Neutrophils
b) Endothelium
c) Macrophages
d) All of the above
Explanation: Prostaglandins are synthesized by nearly all nucleated cells, including neutrophils, macrophages, and endothelial cells, from arachidonic acid via the COX pathway. They regulate vascular tone, platelet aggregation, and inflammation. During inflammation, macrophages and endothelial cells are major producers. Hence, the correct answer is (d) All of the above.
1) Which enzyme is responsible for prostaglandin synthesis?
a) Lipoxygenase
b) Cyclooxygenase
c) Monooxygenase
d) Peroxidase
Explanation: Prostaglandins are derived from arachidonic acid through the cyclooxygenase (COX) pathway. COX enzymes (COX-1 and COX-2) catalyze the conversion to prostaglandin H₂, a precursor for other prostanoids. Hence, the correct answer is (b) Cyclooxygenase.
2) Which of the following prostaglandins causes uterine contraction?
a) PGE₁
b) PGF₂α
c) PGI₂
d) TXA₂
Explanation: PGF₂α is known for inducing uterine and bronchial smooth muscle contraction, playing a role in labor. PGE₂ also contributes to cervical ripening. Thus, the correct answer is (b) PGF₂α.
3) A woman in labor is given a prostaglandin analog to induce contractions. Which type is most likely used?
a) PGI₂ analog
b) PGF₂α analog
c) PGE₃ analog
d) TXA₂ analog
Explanation: PGF₂α analogs like carboprost are used clinically to induce uterine contractions and manage postpartum hemorrhage. They mimic natural prostaglandins’ effects on smooth muscle contraction. Hence, (b) is correct.
4) Which prostaglandin inhibits platelet aggregation?
a) PGF₂α
b) PGI₂
c) TXA₂
d) PGE₂
Explanation: PGI₂ (prostacyclin) produced by vascular endothelium inhibits platelet aggregation and causes vasodilation, balancing TXA₂’s vasoconstrictive and pro-aggregatory effects. Hence, (b) is correct.
5) Which of the following is a major function of prostaglandins in inflammation?
a) Decrease vascular permeability
b) Promote vasodilation and pain
c) Inhibit leukocyte migration
d) Suppress immune response
Explanation: Prostaglandins (mainly PGE₂) cause vasodilation, pain sensitization, and fever by acting on the hypothalamus. These actions enhance the inflammatory response. Therefore, the correct answer is (b) Promote vasodilation and pain.
6) A patient with chronic arthritis is given NSAIDs. These drugs primarily act by inhibiting?
a) Phospholipase A₂
b) Cyclooxygenase
c) Lipoxygenase
d) Thromboxane synthase
Explanation: NSAIDs inhibit cyclooxygenase (COX-1 and COX-2), preventing prostaglandin synthesis. This relieves pain, inflammation, and fever. Therefore, the correct answer is (b) Cyclooxygenase.
7) In asthma, which prostaglandin contributes to bronchoconstriction?
a) PGI₂
b) PGE₂
c) PGF₂α
d) TXA₂
Explanation: PGF₂α and TXA₂ induce bronchoconstriction and increase airway resistance in asthma. Hence, the correct answer is (c) PGF₂α.
8) Which prostaglandin is involved in fever generation?
a) PGE₂
b) PGI₂
c) PGD₂
d) TXA₂
Explanation: PGE₂ is synthesized in response to pyrogens and acts on the hypothalamus to elevate body temperature. This is the basis for the antipyretic effect of NSAIDs. Hence, (a) is correct.
9) A 50-year-old hypertensive patient is given aspirin. Which adverse effect may occur due to prostaglandin inhibition?
a) Hypotension
b) Gastric ulcer
c) Hyperglycemia
d) Edema
Explanation: Prostaglandins protect the gastric mucosa by promoting mucus and bicarbonate secretion. Inhibition by aspirin increases risk of gastric ulceration. Hence, (b) is correct.
10) Which of the following drugs selectively inhibits COX-2 and spares gastric mucosa?
a) Aspirin
b) Ibuprofen
c) Celecoxib
d) Paracetamol
Explanation: Celecoxib is a selective COX-2 inhibitor that reduces inflammation while minimizing gastric mucosal damage associated with COX-1 inhibition. Hence, (c) is correct.
Topic: Autacoids and Inflammation Mediators; Subtopic: Prostaglandins and Their Biological Origin
Keyword Definitions:
• Prostaglandins: Lipid compounds derived from arachidonic acid through cyclooxygenase enzymes, involved in inflammation, pain, and fever.
• Autacoids: Locally acting bioactive substances like histamine, serotonin, and prostaglandins that regulate physiological and pathological processes.
• Seminal Fluid: Secretion from male reproductive glands that contains sperm and enzymes essential for fertility and discovered prostaglandins.
• Cyclooxygenase (COX): Enzyme responsible for converting arachidonic acid into prostaglandins and thromboxanes.
Lead Question – 2014
Prostaglandin was discovered from ?
a) Tear
b) Saliva
c) Seminal fluid
d) Blood
Explanation: Prostaglandins were first discovered in human seminal fluid by Ulf von Euler in 1935. They were named “prosta-glandins” because they were initially thought to originate from the prostate gland. Later, they were found to be produced in many tissues and involved in inflammation, pain, and smooth muscle regulation. Answer: c) Seminal fluid.
1) Prostaglandins are derived from which precursor?
a) Linoleic acid
b) Arachidonic acid
c) Palmitic acid
d) Stearic acid
Explanation: Prostaglandins are synthesized from arachidonic acid, a 20-carbon unsaturated fatty acid found in membrane phospholipids. Cyclooxygenase (COX) converts it into prostaglandin intermediates, regulating inflammation, temperature, and vasodilation. This pathway is inhibited by NSAIDs like aspirin, reducing pain and fever. Answer: b) Arachidonic acid.
2) Which enzyme converts arachidonic acid into prostaglandin H2?
a) Lipoxygenase
b) Cyclooxygenase
c) Peroxidase
d) Phospholipase A2
Explanation: Cyclooxygenase (COX) is the key enzyme converting arachidonic acid into prostaglandin H2, the common precursor for prostaglandins, prostacyclins, and thromboxanes. Two isoforms exist: COX-1 (constitutive) and COX-2 (inducible). Inhibiting COX reduces inflammation and pain. Answer: b) Cyclooxygenase.
3) Which prostaglandin causes uterine contraction?
a) PGD2
b) PGE1
c) PGF2α
d) PGI2
Explanation: Prostaglandin F2α (PGF2α) causes strong uterine contractions, important during labor induction and menstruation. It is used therapeutically for abortion and postpartum hemorrhage control. It acts via G-protein-coupled receptors on uterine smooth muscle. Answer: c) PGF2α.
4) Which of the following prostaglandins inhibits platelet aggregation?
a) PGI2
b) PGE2
c) PGF2α
d) TXA2
Explanation: Prostacyclin (PGI2), produced by vascular endothelium, inhibits platelet aggregation and causes vasodilation. It counteracts thromboxane A2 (TXA2), which promotes clotting. This balance maintains hemostasis and prevents thrombosis. Answer: a) PGI2.
5) Which drug inhibits prostaglandin synthesis by blocking COX enzyme?
a) Aspirin
b) Prednisolone
c) Hydrocortisone
d) Atropine
Explanation: Aspirin irreversibly inhibits cyclooxygenase (COX) enzymes, preventing prostaglandin and thromboxane formation. This reduces inflammation, pain, and fever. Its antiplatelet effect is due to irreversible inhibition of COX in platelets. Answer: a) Aspirin.
6) A 45-year-old woman with rheumatoid arthritis takes NSAIDs for pain relief. Which mediator is reduced?
a) Histamine
b) Prostaglandin
c) Bradykinin
d) Leukotriene
Explanation: NSAIDs inhibit COX, decreasing prostaglandin synthesis. Prostaglandins mediate inflammation, pain, and fever. Their reduction alleviates pain in arthritis but may cause gastric irritation due to loss of protective mucosal prostaglandins. Answer: b) Prostaglandin.
7) A patient develops gastric ulcers after long-term NSAID use. Which mechanism explains this?
a) Increased acid secretion
b) Decreased mucosal prostaglandins
c) Increased H2 receptor activity
d) Decreased bile salts
Explanation: NSAIDs inhibit COX-1, reducing gastric prostaglandins that protect mucosa by increasing mucus and bicarbonate secretion. This loss leads to ulceration. Proton pump inhibitors (PPIs) are given to prevent this complication. Answer: b) Decreased mucosal prostaglandins.
8) Which prostaglandin is involved in fever generation?
a) PGD2
b) PGE2
c) PGF2α
d) PGI2
Explanation: PGE2 acts on the hypothalamus to increase the body’s temperature set point during infection. Cytokines like IL-1 and TNF stimulate its synthesis. Antipyretics like paracetamol reduce fever by blocking PGE2 production. Answer: b) PGE2.
9) A patient with myocardial infarction is treated with low-dose aspirin. What is its mechanism?
a) Blocks platelet aggregation
b) Promotes vasoconstriction
c) Stimulates prostaglandin synthesis
d) Activates COX-2
Explanation: Low-dose aspirin selectively inhibits platelet COX-1, preventing thromboxane A2 (TXA2) synthesis, which normally promotes platelet aggregation. This reduces clot formation risk after myocardial infarction. Answer: a) Blocks platelet aggregation.
10) A patient with preterm labor is given indomethacin. What is the purpose?
a) Stimulate uterine contraction
b) Inhibit prostaglandin synthesis
c) Promote cervical dilation
d) Increase uterine tone
Explanation: Indomethacin, a COX inhibitor, suppresses prostaglandin synthesis, thereby inhibiting uterine contractions and delaying preterm labor. However, prolonged use can cause fetal complications like ductus arteriosus closure. Answer: b) Inhibit prostaglandin synthesis.
Chapter: Endocrine Physiology; Topic: Reproductive Hormones and Steroidogenesis; Subtopic: Aromatase Enzyme and Estrogen Synthesis
Keyword Definitions:
• Aromatase: A cytochrome P450 enzyme that converts androgens (testosterone, androstenedione) into estrogens (estradiol, estrone) in gonads and adipose tissue.
• Estrogen: Female sex hormone essential for reproductive development, bone health, and secondary sexual characteristics.
• Androgens: Male sex hormones, such as testosterone, which serve as substrates for estrogen synthesis via aromatase.
• Steroidogenesis: The process of hormone synthesis from cholesterol in the adrenal cortex and gonads.
Lead Question – 2014
Aromatase produces estrogen from -
a) Progesterone
b) Cortisol
c) Aldosterone
d) Androgen
Explanation: Aromatase catalyzes the conversion of androgens (testosterone and androstenedione) to estrogens (estradiol and estrone) in ovaries, testes, placenta, and adipose tissue. This reaction is vital in maintaining female reproductive physiology. Inhibition of aromatase is used in treating estrogen-dependent cancers like breast carcinoma. Answer: d) Androgen.
1) The conversion of testosterone to estradiol occurs mainly in -
a) Liver
b) Ovary and adipose tissue
c) Thyroid
d) Kidney
Explanation: Testosterone is converted to estradiol by aromatase enzyme, predominantly in the ovary, placenta, and adipose tissue. In men, this process occurs in adipose tissue and brain, influencing libido and bone health. Aromatase activity is essential for hormonal balance. Answer: b) Ovary and adipose tissue.
2) Which enzyme converts testosterone to dihydrotestosterone (DHT)?
a) Aromatase
b) 5-alpha reductase
c) 17-beta hydroxylase
d) 21-hydroxylase
Explanation: 5-alpha reductase converts testosterone to dihydrotestosterone (DHT), a potent androgen that influences male sexual differentiation, prostate growth, and hair pattern. Deficiency leads to ambiguous genitalia. Drugs like finasteride inhibit this enzyme to treat benign prostatic hyperplasia. Answer: b) 5-alpha reductase.
3) Which of the following inhibits aromatase activity?
a) Letrozole
b) Spironolactone
c) Tamoxifen
d) Flutamide
Explanation: Letrozole is a selective aromatase inhibitor used in postmenopausal women to treat estrogen receptor–positive breast cancer. It blocks estrogen synthesis by inhibiting the conversion of androgens to estrogens, thus reducing tumor growth. Answer: a) Letrozole.
4) A 40-year-old woman with breast cancer is given an aromatase inhibitor. What is the drug’s main action?
a) Block estrogen receptors
b) Decrease estrogen synthesis
c) Increase progesterone
d) Inhibit cortisol secretion
Explanation: Aromatase inhibitors like anastrozole and letrozole decrease estrogen synthesis by blocking aromatase enzyme. This suppresses estrogen-driven tumor proliferation, especially in hormone-sensitive cancers. Answer: b) Decrease estrogen synthesis.
5) Aromatase enzyme is found abundantly in which of the following?
a) Adrenal medulla
b) Liver
c) Granulosa cells of ovary
d) Thyroid gland
Explanation: Aromatase is highly expressed in granulosa cells of the ovarian follicle, where it converts androgens from theca cells into estrogens, a process stimulated by FSH. This cooperation between theca and granulosa cells forms the two-cell theory of estrogen synthesis. Answer: c) Granulosa cells of ovary.
6) A male patient presents with gynecomastia. Which enzyme’s excess activity could cause this?
a) Aromatase
b) 11-beta hydroxylase
c) 21-hydroxylase
d) 17-alpha hydroxylase
Explanation: Increased aromatase activity converts excess testosterone to estradiol, leading to gynecomastia in males. This can occur due to tumors or genetic mutations enhancing aromatase expression. Answer: a) Aromatase.
7) A patient with congenital adrenal hyperplasia due to 21-hydroxylase deficiency has excess androgen. Which effect is likely?
a) Precocious puberty
b) Hypogonadism
c) Feminization
d) Reduced cortisol
Explanation: 21-hydroxylase deficiency causes shunting of precursors toward androgen synthesis, leading to virilization and precocious puberty. Cortisol synthesis is impaired, leading to increased ACTH and adrenal hyperplasia. Answer: a) Precocious puberty.
8) Estrogen synthesis in granulosa cells is stimulated by -
a) LH
b) FSH
c) Prolactin
d) GH
Explanation: FSH stimulates aromatase activity in granulosa cells, enhancing conversion of androgens (from theca cells under LH control) into estrogens. This FSH–aromatase–estrogen pathway is essential for follicle maturation and ovulation. Answer: b) FSH.
9) Which hormone inhibits aromatase activity in males?
a) Cortisol
b) Prolactin
c) Testosterone
d) Inhibin B
Explanation: Testosterone exerts a negative feedback effect by downregulating aromatase activity, maintaining androgen–estrogen balance. Excess aromatase causes high estrogen and reduced fertility in men. Answer: c) Testosterone.
10) A postmenopausal woman develops osteoporosis. Which role does aromatase play in this condition?
a) Increased estrogen formation prevents bone loss
b) Decreased aromatase lowers estrogen, increasing bone resorption
c) It increases calcium excretion
d) It enhances osteoclast formation
Explanation: After menopause, decreased aromatase activity leads to reduced estrogen synthesis in adipose tissue, increasing bone resorption and causing osteoporosis. Estrogen replacement or aromatase modulators can help preserve bone mass. Answer: b) Decreased aromatase lowers estrogen, increasing bone resorption.
Chapter: Endocrine Physiology; Topic: Female Reproductive Hormones; Subtopic: Actions and Regulation of Progesterone
Keyword Definitions:
• Progesterone: A steroid hormone secreted mainly by the corpus luteum that prepares the endometrium for implantation and maintains pregnancy.
• LH (Luteinizing Hormone): A pituitary hormone that triggers ovulation and formation of the corpus luteum.
• Oxytocin: A posterior pituitary hormone responsible for uterine contraction during labor and milk ejection during lactation.
• Proliferative Phase: The estrogen-dominated phase of the menstrual cycle where the endometrium regenerates after menstruation.
Lead Question – 2014
Action of progesterone?
a) Increased sensitivity of uterus to oxytocin
b) Inhibits LH secretion
c) Decrease in body temperature
d) Causes proliferative changes in uterus
Explanation: Progesterone inhibits LH secretion by negative feedback on the hypothalamic–pituitary axis. It also maintains the secretory phase of the endometrium, decreases uterine excitability, and increases body temperature post-ovulation. It prepares the uterus for implantation and supports early pregnancy. Answer: b) Inhibits LH secretion.
1) Which of the following is a physiological action of progesterone?
a) Increases uterine contractility
b) Inhibits milk secretion
c) Increases basal body temperature
d) Causes follicular development
Explanation: Progesterone increases basal body temperature after ovulation by acting on the hypothalamic thermoregulatory center. This temperature rise is often used to identify ovulation in fertility tracking. It also reduces uterine contractility, preventing premature labor. Answer: c) Increases basal body temperature.
2) Which phase of the menstrual cycle is dominated by progesterone?
a) Menstrual phase
b) Proliferative phase
c) Secretory phase
d) Follicular phase
Explanation: The secretory phase follows ovulation and is dominated by progesterone secreted from the corpus luteum. It converts the endometrium into a glandular, nutrient-rich lining ready for implantation. If fertilization does not occur, progesterone levels fall, leading to menstruation. Answer: c) Secretory phase.
3) A 28-year-old woman presents with infertility. Her luteal phase progesterone level is low. Which process is impaired?
a) Follicular maturation
b) Ovulation
c) Endometrial receptivity
d) Menstrual bleeding
Explanation: Progesterone prepares the endometrium for implantation by promoting glandular secretion and vascularization. Low progesterone during the luteal phase leads to a non-receptive endometrium, causing infertility. Answer: c) Endometrial receptivity.
4) Which hormone maintains pregnancy during the first trimester?
a) Estrogen
b) Progesterone
c) LH
d) FSH
Explanation: During early pregnancy, progesterone from the corpus luteum (maintained by hCG) maintains the endometrium and prevents uterine contractions. Later, the placenta becomes the main source. Answer: b) Progesterone.
5) A woman in her third trimester shows decreased uterine contractility. Which hormone is responsible?
a) Progesterone
b) Estrogen
c) Oxytocin
d) Relaxin
Explanation: Progesterone reduces uterine smooth muscle excitability, preventing premature uterine contractions and maintaining pregnancy. Estrogen, on the other hand, promotes uterine growth and increases oxytocin sensitivity. Answer: a) Progesterone.
6) Which of the following is decreased by progesterone?
a) Uterine contractility
b) Basal body temperature
c) Endometrial gland secretion
d) Alveolar development in breast
Explanation: Progesterone decreases uterine contractility and increases basal temperature. It enhances glandular secretion and alveolar development in the mammary glands in preparation for lactation. Answer: a) Uterine contractility.
7) A 25-year-old woman is treated with a progesterone-only contraceptive pill. What is its main mechanism?
a) Prevents follicle rupture
b) Increases FSH secretion
c) Enhances ovulation
d) Stimulates estrogen production
Explanation: Progesterone-only pills inhibit ovulation by suppressing LH surge, thicken cervical mucus to prevent sperm entry, and thin the endometrium, making implantation unlikely. Answer: a) Prevents follicle rupture.
8) During pregnancy, which structure secretes progesterone after 12 weeks?
a) Corpus luteum
b) Placenta
c) Ovary
d) Adrenal gland
Explanation: Initially, progesterone is secreted by the corpus luteum, maintained by hCG. After about 12 weeks, the placenta takes over progesterone synthesis, ensuring continued uterine quiescence and endometrial maintenance. Answer: b) Placenta.
9) Which of the following changes is mediated by progesterone in the uterus?
a) Proliferation of endometrial glands
b) Secretory transformation of endometrium
c) Shedding of endometrium
d) Uterine contraction
Explanation: Progesterone induces the secretory transformation of the endometrium, converting it into a nutrient-rich, glandular tissue that supports implantation and early embryonic growth. Answer: b) Secretory transformation of endometrium.
10) A patient using progesterone analogs reports mild rise in body temperature. What is the cause?
a) Stimulation of hypothalamic thermoregulatory centers
b) Activation of thyroid hormones
c) Increased peripheral vasoconstriction
d) Reduced sweating
Explanation: Progesterone acts on the hypothalamic thermoregulatory center, increasing basal body temperature during the luteal phase. This thermogenic effect is utilized in fertility awareness methods to identify ovulation. Answer: a) Stimulation of hypothalamic thermoregulatory centers.
Chapter: Reproductive Physiology; Topic: Female Reproductive Hormones; Subtopic: Corpus Luteum and Its Regression
Keyword Definitions:
• Corpus luteum: A temporary endocrine gland formed after ovulation from the ruptured follicle that secretes progesterone.
• Ovulation: The release of a mature ovum from the ovary into the fallopian tube.
• Progesterone: A hormone responsible for maintaining endometrial receptivity for implantation.
• Regression: The process of degeneration or atrophy of the corpus luteum in the absence of pregnancy.
Lead Question - 2014
Corpus luteum starts regressing after how many days of ovulation?
a) 5 days
b) 10 days
c) 24 days
d) None
Explanation: The corpus luteum functions for approximately 14 days after ovulation, secreting progesterone to maintain the endometrium. In the absence of fertilization, it begins to regress around the 10th day post-ovulation, leading to menstruation. If pregnancy occurs, hCG maintains it. Thus, the correct answer is (b) 10 days.
1. Corpus luteum is mainly formed from which ovarian structure?
a) Graafian follicle
b) Primordial follicle
c) Theca externa
d) Zona pellucida
Explanation: After ovulation, the ruptured Graafian follicle transforms into the corpus luteum. The granulosa cells and theca interna cells undergo luteinization, producing progesterone. This hormone supports the endometrial lining for possible implantation. Therefore, the correct answer is (a) Graafian follicle.
2. Which hormone maintains the corpus luteum during early pregnancy?
a) LH
b) FSH
c) hCG
d) Estrogen
Explanation: During early pregnancy, human chorionic gonadotropin (hCG) secreted by trophoblast cells prevents luteal regression and maintains progesterone secretion. LH maintains the luteal phase in a normal cycle but not during pregnancy. Hence, the correct answer is (c) hCG.
3. Which of the following hormones decreases when the corpus luteum regresses?
a) FSH
b) Progesterone
c) Estrogen
d) GnRH
Explanation: When the corpus luteum regresses, progesterone and estrogen levels fall sharply. This hormonal drop triggers menstruation and FSH rise for the next cycle. Therefore, the correct answer is (b) Progesterone.
4. In a 28-day cycle, corpus luteum regresses around which day?
a) 7th day
b) 10th day
c) 24th day
d) 28th day
Explanation: In a typical 28-day cycle, ovulation occurs around day 14, and the corpus luteum regresses near day 24 if fertilization does not occur. Its regression leads to hormonal decline and onset of menstruation. Hence, the correct answer is (c) 24th day.
5. Clinical: A woman misses her period; hCG levels are positive. What happens to the corpus luteum?
a) It regresses
b) It enlarges and persists
c) It converts to follicle
d) It undergoes necrosis
Explanation: In early pregnancy, hCG from the trophoblast maintains the corpus luteum, which enlarges and continues secreting progesterone until placental hormone production takes over around 12 weeks. Thus, the correct answer is (b) It enlarges and persists.
6. Which enzyme is mainly responsible for luteolysis in the absence of pregnancy?
a) Aromatase
b) Prostaglandin F2α
c) 5α-reductase
d) Oxytocin
Explanation: Prostaglandin F2α (PGF2α), produced by the uterus, is a major luteolytic agent. It reduces progesterone secretion and promotes structural regression of the corpus luteum. Hence, the correct answer is (b) Prostaglandin F2α.
7. Clinical: In luteal phase defect, the most likely deficiency is of:
a) LH
b) FSH
c) Progesterone
d) Prolactin
Explanation: Luteal phase defect results from insufficient progesterone secretion by the corpus luteum, leading to poor endometrial receptivity and infertility. Treatment includes progesterone supplementation. The correct answer is (c) Progesterone.
8. Corpus luteum of pregnancy functions for approximately how long?
a) 2 weeks
b) 6 weeks
c) 12 weeks
d) 20 weeks
Explanation: The corpus luteum of pregnancy continues progesterone secretion until the placenta becomes the main source at about 12 weeks. After that, it regresses naturally. Thus, the correct answer is (c) 12 weeks.
9. Clinical: A woman with corpus luteum cyst will show elevated levels of which hormone?
a) LH
b) FSH
c) Progesterone
d) Prolactin
Explanation: Corpus luteum cysts arise due to persistence and enlargement of the corpus luteum with increased progesterone secretion. This can cause delayed menstruation or amenorrhea. Hence, the correct answer is (c) Progesterone.
10. The corpus albicans represents:
a) Degenerated corpus luteum
b) Ovulated follicle
c) Unruptured follicle
d) Graafian follicle
Explanation: When the corpus luteum regresses completely, it becomes a fibrous scar known as corpus albicans. This nonfunctional structure remains in the ovary as a remnant. Hence, the correct answer is (a) Degenerated corpus luteum.
Chapter: Reproductive Physiology; Topic: Oogenesis; Subtopic: Meiotic Divisions in Female Gametogenesis
Keyword Definitions:
• Oogenesis: The process of formation and maturation of the female gamete (ovum) from oogonia.
• Polar body: Small cells produced during meiosis in oogenesis that usually degenerate and do not form gametes.
• Meiosis: A special type of cell division that halves the chromosome number, essential for gamete formation.
• Fertilization: The fusion of the male and female gametes to form a zygote.
Lead Question - 2014
First polar body is formed after?
a) Mitosis
b) First meiosis
c) Second meiosis
d) Fertilization
Explanation: During oogenesis, the primary oocyte undergoes the first meiotic division just before ovulation, producing a secondary oocyte and the first polar body. This polar body receives minimal cytoplasm and eventually degenerates. Hence, the correct answer is (b) First meiosis. The second polar body forms only after fertilization, marking meiosis II completion.
1. Second polar body is formed after?
a) Meiosis I
b) Meiosis II
c) Ovulation
d) Fertilization
Explanation: The secondary oocyte completes its second meiotic division only after fertilization, producing the second polar body and the mature ovum nucleus. This ensures a haploid zygote after sperm fusion. Therefore, the correct answer is (b) Meiosis II.
2. In which stage of meiosis is the primary oocyte arrested until puberty?
a) Prophase I
b) Metaphase I
c) Anaphase II
d) Telophase II
Explanation: The primary oocyte remains arrested in the diplotene stage of prophase I until puberty. Hormonal surges during the menstrual cycle resume meiosis, leading to ovulation. Thus, the correct answer is (a) Prophase I.
3. Clinical: A 25-year-old woman’s oocyte shows arrest in metaphase II. When does it complete meiosis?
a) During ovulation
b) After fertilization
c) Before fertilization
d) During implantation
Explanation: The secondary oocyte remains arrested in metaphase II until a sperm penetrates the zona pellucida. Only after fertilization does it complete meiosis II, forming the ovum and second polar body. Hence, the correct answer is (b) After fertilization.
4. Total number of polar bodies formed from one oogonium is?
a) One
b) Two
c) Three
d) Four
Explanation: One oogonium yields one mature ovum and two or sometimes three polar bodies. These polar bodies are by-products of meiosis I and II and usually degenerate. Thus, the correct answer is (b) Two.
5. Which hormone triggers the completion of meiosis I in the oocyte?
a) FSH
b) LH
c) Progesterone
d) Estrogen
Explanation: The LH surge during the mid-cycle triggers the completion of meiosis I in the primary oocyte, forming the secondary oocyte and the first polar body. This process prepares the oocyte for ovulation. Therefore, the correct answer is (b) LH.
6. Clinical: A woman with anovulation is treated with clomiphene citrate. What process does it enhance?
a) Mitosis of oogonia
b) Completion of meiosis I
c) Formation of zygote
d) Follicle degeneration
Explanation: Clomiphene citrate enhances LH and FSH release by blocking estrogen receptors, leading to follicular maturation and completion of meiosis I. It induces ovulation in anovulatory cycles. Hence, the correct answer is (b) Completion of meiosis I.
7. The process of extrusion of the first polar body occurs during?
a) Follicular phase
b) Ovulatory phase
c) Luteal phase
d) Menstrual phase
Explanation: The extrusion of the first polar body occurs just before ovulation during the ovulatory phase, after meiosis I completion. This is driven by the LH surge. The correct answer is (b) Ovulatory phase.
8. Clinical: A secondary oocyte has 23 chromosomes. How many chromatids does it have?
a) 23
b) 46
c) 92
d) 69
Explanation: The secondary oocyte contains 23 chromosomes, each with two chromatids (duplicated DNA). Hence, the total chromatid count is 46. Upon completion of meiosis II after fertilization, chromatids separate to restore the haploid condition. Thus, the correct answer is (b) 46.
9. Which structure degenerates to form the corpus albicans if fertilization does not occur?
a) Primary oocyte
b) Secondary oocyte
c) Corpus luteum
d) Graafian follicle
Explanation: After ovulation, the ruptured Graafian follicle becomes the corpus luteum. If fertilization fails, the corpus luteum degenerates to form a fibrous tissue called corpus albicans. The correct answer is (c) Corpus luteum.
10. Clinical: A woman’s oocyte fails to extrude the first polar body. Which phase of meiosis is affected?
a) Prophase I
b) Metaphase I
c) Anaphase I
d) Telophase I
Explanation: The extrusion of the first polar body occurs at the end of telophase I. A defect here prevents normal segregation of chromosomes, leading to aneuploidy or infertility. Hence, the correct answer is (d) Telophase I.