In the breast, lactiferous ducts are formed under the influence of which hormone?
LH surge is associated with?
Which hormone increases with age?
The primary oocyte remains arrested in which stage until ovulation?
Which of the following statements about thyroid hormone receptors is correct?
After injecting testosterone in a hypoandrogenic male, which of the following occurs ?
Which type of muscle fibers has fewer mitochondria?
Which of the following statements is true about red muscle fibers?
Integration center of tonic labyrinthine reflex is?
Which part of the brain is primarily responsible for the righting reflex?
NEET-PG 2013 - Physiology NEET-PG Practice Questions and MCQs
Question 41: In the breast, lactiferous ducts are formed under the influence of which hormone?
- A. Progesterone
- B. LH
- C. FSH
- D. Estrogen (Correct Answer)
Explanation: ***Estrogen*** - **Estrogen** plays a primary role in the development and branching of the **lactiferous ducts** in the breast. - It stimulates the proliferation of ductal epithelial cells, contributing to the growth of the duct system. *Progesterone* - **Progesterone** is primarily responsible for the development of the **lobuloalveolar system** and secretory differentiation within the breast. - While essential for lactation, its main function is not duct formation but rather the maturation of secretory units. *LH* - **Luteinizing hormone (LH)** is crucial for ovulation and the formation of the **corpus luteum** in the ovaries. - It has no direct role in the structural development of the lactiferous ducts in the breast. *FSH* - **Follicle-stimulating hormone (FSH)** is essential for the growth and maturation of **ovarian follicles**. - It does not directly influence the formation or development of lactiferous ducts in the breast.
Question 42: LH surge is associated with?
- A. Increased estrogen & decreased progesterone (Correct Answer)
- B. Increased estrogen & increased progesterone
- C. Decreased estrogen & increased progesterone
- D. Decreased estrogen & decreased progesterone
Explanation: ***Increased estrogen & decreased progesterone*** - The **LH surge** is triggered by a significant rise in **estrogen** levels from the dominant follicle, indicating ovarian readiness. - At the time of the LH surge, **progesterone** levels remain low; they only begin to rise significantly after ovulation, when the corpus luteum forms. *Increased estrogen & increased progesterone* - While **estrogen** levels are high, **progesterone** only significantly increases *after* ovulation, as the corpus luteum develops. - High estrogen *and* high progesterone together are typically seen in the **luteal phase**, not at the peak of the LH surge. *Decreased estrogen & increased progesterone* - A decrease in **estrogen** would suppress LH, not trigger a surge. - Increased **progesterone** would also inhibit LH release via negative feedback in the follicular phase if it were to occur pre-ovulation. *Decreased estrogen & decreased progesterone* - Both **decreased estrogen** and **decreased progesterone** would lead to low FSH/LH levels and would not promote an LH surge or ovulation. - This hormonal profile is more characteristic of the very early follicular phase or menopause.
Question 43: Which hormone increases with age?
- A. GH
- B. Prolactin
- C. Parathormone (Correct Answer)
- D. Insulin
Explanation: ***Parathormone*** - **Parathormone (PTH)** levels in the blood tend to increase with age, often due to a decline in renal function and reduced vitamin D synthesis, leading to compensatory hyperparathyroidism. - This age-related increase in PTH can contribute to **bone demineralization** and an increased risk of osteoporosis. *GH* - **Growth hormone (GH)** levels generally **decrease with age**, leading to a condition known as somatopause. - Reduced GH contributes to changes in body composition, such as increased adiposity and decreased lean muscle mass, as well as reduced bone density. *Prolactin* - **Prolactin** levels typically remain relatively stable or may slightly decrease with age in men, while in women they can fluctuate due to hormonal changes like menopause but do not show a consistent increase with age. - High prolactin levels are often associated with specific pathological conditions like **prolactinomas** rather than normal aging. *Insulin* - While **insulin resistance** often increases with age, leading to higher fasting insulin levels in some individuals, the overall picture of insulin secretion can be complex and is often influenced by factors such as diet, exercise, and genetics rather than solely age. - A *decline in pancreatic beta-cell function* with age can also lead to impaired insulin secretion in some elderly individuals, complicating the simple relationship between age and insulin levels.
Question 44: The primary oocyte remains arrested in which stage until ovulation?
- A. Diplotene stage (Correct Answer)
- B. Pachytene stage
- C. Metaphase
- D. Telophase
Explanation: ***Diplotene stage*** - The primary oocyte enters **meiosis I** during fetal development but arrests in the **prophase I substage of diplotene**. - This arrest is maintained until **puberty** and **ovulation**, when hormonal surges trigger the completion of meiosis I. *Pachytene stage* - The **pachytene stage** of prophase I is when **crossing over** (recombination) occurs between homologous chromosomes. - While an important step in meiosis, it precedes the **diplotene arrest** point. *Metaphase* - **Metaphase** is a stage where chromosomes align at the metaphase plate, either in meiosis I or meiosis II. - The primary oocyte's arrest occurs much earlier, during **prophase I**, not metaphase. *Telophase* - **Telophase** is the final stage of mitosis or meiosis where chromosomes decondense and nuclear envelopes reform. - The oocyte's initial arrest point is in **prophase I**, long before telophase.
Question 45: Which of the following statements about thyroid hormone receptors is correct?
- A. They directly bind to thyrotropin-releasing hormone (TRH)
- B. They directly bind to thyroid-stimulating hormone (TSH)
- C. They cause nuclear transcription after binding with T4
- D. They are intracellular receptors that mediate gene transcription after binding with T3 or T4, but their primary action is through T3. (Correct Answer)
Explanation: ***They are intracellular receptors that mediate gene transcription after binding with T3 or T4, but their primary action is through T3.*** - **Thyroid hormone receptors** are indeed **intracellular** and act as **ligand-activated transcription factors**, regulating gene expression. - While both **T3** and **T4** can bind, **T3 (triiodothyronine)** is the more potent and active form, binding with much higher affinity to the receptors to exert its primary metabolic effects. *They directly bind to thyrotropin-releasing hormone (TRH)* - **TRH (thyrotropin-releasing hormone)** is produced by the hypothalamus and acts on the **pituitary gland** to stimulate TSH release, not directly on thyroid hormone receptors. - Thyroid hormone receptors bind to thyroid hormones (**T3 and T4**), not to the hypothalamic releasing hormones like TRH. *They directly bind to thyroid-stimulating hormone (TSH)* - **TSH (thyroid-stimulating hormone)** is produced by the pituitary gland and primarily acts on receptors located on the **thyroid gland cells** to stimulate thyroid hormone synthesis and release. - Thyroid hormone receptors are distinct from TSH receptors and bind to the hormones themselves (**T3/T4**), not the stimulating hormone TSH. *Causes nuclear transcription after binding with T4* - While **T4 (thyroxine)** can bind to thyroid hormone receptors, it is primarily a **prohormone**. - T4 is largely converted to the more active **T3** within target cells, and **T3** is the main mediator of nuclear transcription through these receptors.
Question 46: After injecting testosterone in a hypoandrogenic male, which of the following occurs ?
- A. Decreased LH secretion
- B. Decreased FSH secretion (Correct Answer)
- C. Increased spermatogenesis
- D. None of the options
Explanation: ***Decreased FSH secretion*** - Exogenous testosterone administration leads to **negative feedback** on the hypothalamic-pituitary-gonadal axis, suppressing **GnRH** release, which in turn decreases both **LH** and **FSH** secretion. - FSH suppression is particularly clinically significant because it results in **inhibition of spermatogenesis**, which is a key consideration when using testosterone replacement therapy. - The decrease in FSH, combined with reduced **intratesticular testosterone** (due to LH suppression), impairs Sertoli cell function and sperm production. *Decreased LH secretion* - **This also occurs** with exogenous testosterone administration due to negative feedback on the hypothalamus and pituitary. - Testosterone primarily suppresses **LH** through direct negative feedback at the hypothalamic-pituitary level. - However, in the context of this question focusing on the consequences in a hypoandrogenic male receiving testosterone, the **FSH suppression** and its impact on spermatogenesis is the more clinically emphasized outcome. - **Note:** Both LH and FSH decrease; this question likely emphasizes FSH due to its role in fertility concerns with testosterone therapy. *Increased spermatogenesis* - This is **incorrect**. Exogenous testosterone actually **suppresses spermatogenesis** through multiple mechanisms: - Decreased **FSH** (essential for Sertoli cell function) - Decreased **intratesticular testosterone** concentration (despite high systemic levels) - The high local testosterone concentration within the seminiferous tubules (30-100x serum levels) cannot be achieved by systemic testosterone alone. *None of the options* - This is incorrect because exogenous testosterone administration clearly causes **suppression of gonadotropins** (both LH and FSH) through well-established negative feedback mechanisms.
Question 47: Which type of muscle fibers has fewer mitochondria?
- A. Type I fibers (Red fibers)
- B. Type IIb fibers (Fast-twitch fibers) (Correct Answer)
- C. Type IIa fibers
- D. Type IIx fibers (Intermediate fibers)
Explanation: ***Type IIb fibers (Fast-twitch fibers)*** - These fibers rely primarily on **anaerobic glycolysis** for ATP production, which is a less efficient process than aerobic respiration and therefore requires fewer mitochondria. - Their primary function is rapid, powerful contractions over short durations, leading to quick fatigue. *Type IIa fibers* - These fibers are **fast-twitch oxidative-glycolytic** fibers, meaning they have a moderate number of mitochondria to support both aerobic and anaerobic metabolism. - They are capable of generating strong contractions and are more fatigue-resistant than Type IIb fibers but less so than Type I fibers. *Type I fibers (Red fibers)* - Known as **slow-twitch oxidative fibers**, they have a high density of mitochondria to support continuous **aerobic respiration** for sustained, low-intensity contractions. - Their rich blood supply and high myoglobin content give them their characteristic red color and make them highly fatigue-resistant. *Type IIx fibers (Intermediate fibers)* - These fibers are very similar to Type IIb fibers in their metabolic profile, often considered an intermediate or even functionally equivalent type depending on the species. - They also primarily utilize **anaerobic glycolysis** and have a relatively low mitochondrial content, making them prone to fatigue.
Question 48: Which of the following statements is true about red muscle fibers?
- A. Contain fewer mitochondria than white muscle fibers
- B. Have less myoglobin than white muscle fibers
- C. Exhibit more oxidative capacity (Correct Answer)
- D. Utilize glycolytic metabolism
Explanation: ***Exhibit more oxidative capacity*** - **Red muscle fibers**, also known as **slow-twitch fibers**, are rich in **mitochondria** and enzymes for aerobic respiration, allowing for sustained contractions and high oxidative capacity. - Their high oxidative capacity is crucial for activities requiring **endurance**, such as long-distance running or maintaining posture through efficient **ATP production** via the **electron transport chain**. *Contain fewer mitochondria than white muscle fibers* - **Red muscle fibers** contain **more mitochondria** than white muscle fibers to support their greater reliance on **aerobic metabolism** for sustained energy production. - **Mitochondria** are the primary sites of **oxidative phosphorylation**, which is essential for the continuous ATP supply needed by these endurance specialized fibers. *Utilize glycolytic metabolism* - While red fibers can perform some glycolysis, their primary metabolic pathway is **oxidative phosphorylation**, utilizing **fatty acids** and **glucose** aerobically. - **Glycolytic metabolism** is more characteristic of **white muscle fibers (fast-twitch)**, which rely on anaerobic pathways for rapid, high-intensity contractions. *Have less myoglobin than white muscle fibers* - **Red muscle fibers** are characterized by a **high content of myoglobin**, which gives them their characteristic red color and high oxygen storage capacity. - **Myoglobin** is crucial for oxygen delivery to the mitochondria, supporting the sustained aerobic metabolism of these fibers, in contrast to white fibers which have less myoglobin.
Question 49: Integration center of tonic labyrinthine reflex is?
- A. Spinal cord
- B. Medulla (Correct Answer)
- C. Midbrain
- D. Cerebral cortex
Explanation: ***Medulla*** - The **tonic labyrinthine reflex** is a primitive reflex originating in the **vestibular system**, specifically the otolith organs, which respond to head position changes. - Its integration center lies in the **medulla oblongata**, a part of the brainstem responsible for essential involuntary functions. *Spinal cord* - The spinal cord integrates simpler reflexes like **stretch reflexes** and **withdrawal reflexes**. - It does not process the complex vestibular input required for the tonic labyrinthine reflex. *Midbrain* - The **midbrain** is involved in integrating reflexes related to visual and auditory stimuli, such as the **startle reflex** and **pupillary light reflex**. - It is superior to the primary integration center for the tonic labyrinthine reflex. *Cerebral cortex* - The **cerebral cortex** is responsible for higher cognitive functions, voluntary movements, and conscious sensation. - Reflexes like the tonic labyrinthine reflex are subcortical and operate without conscious control.
Question 50: Which part of the brain is primarily responsible for the righting reflex?
- A. Pons
- B. Spinal cord
- C. Cortex
- D. Midbrain (Correct Answer)
Explanation: ***Midbrain*** - The **midbrain** plays a crucial role in regulating posture and movement, including the **righting reflex**. - It integrates sensory information from the **vestibular system**, eyes, and proprioceptors to maintain upright posture. *Pons* - The pons is primarily involved in relaying signals between the **cerebrum** and **cerebellum** and regulating respiration and sleep. - While it contributes to motor control, it is not the primary center for the righting reflex. *Spinal cord* - The spinal cord mediates **reflex arcs** and transmits sensory and motor information, but it does not independently control complex postural reflexes like the righting reflex. - It contains the circuits for basic reflexes such as the **stretch reflex** and **withdrawal reflex**. *Cortex* - The cerebral cortex is responsible for **voluntary movements**, higher cognitive functions, and conscious perception. - While it can influence posture, the righting reflex is a subcortical, involuntary process.