What is the primary hormone responsible for the secretion of milk?
Which of the following hormones is not stored in cells?
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 ?
In the breast, lactiferous ducts are formed under the influence of which hormone?
What does spermiogenesis refer to?
Ossicles of middle ear are responsible for which of the following ?
NEET-PG 2013 - Physiology NEET-PG Practice Questions and MCQs
Question 71: What is the primary hormone responsible for the secretion of milk?
- A. Oxytocin
- B. Prolactin (Correct Answer)
- C. Glucocorticoids
- D. Relaxin
Explanation: ***Prolactin*** - **Prolactin** is the primary hormone synthesized and secreted by the pituitary gland that is responsible for **milk production** (lactogenesis) in the mammary glands after childbirth. - Its levels rise significantly during pregnancy and remain elevated with regular suckling, which stimulates its release and maintains milk supply. *Oxytocin* - **Oxytocin** is primarily responsible for the **milk ejection reflex** (let-down reflex), causing the contraction of myoepithelial cells around the alveoli to release milk. - It does not stimulate the production of milk itself but rather its expulsion from the breast. *Glucocorticoids* - **Glucocorticoids** (like cortisol) play a role in mammary gland development and maturation, and can have permissive effects on prolactin's action. - However, they are not the primary hormone directly responsible for stimulating milk secretion. *Relaxin* - **Relaxin** is a hormone primarily involved in relaxing ligaments in the pelvis and softening the cervix during childbirth. - It has no direct primary role in the production or secretion of breast milk.
Question 72: Which of the following hormones is not stored in cells?
- A. Thyroxin
- B. Renin
- C. Insulin
- D. Cortisol (Correct Answer)
Explanation: ***Cortisol*** - Cortisol is a **steroid hormone** that is synthesized from **cholesterol** on demand and is **not stored** in secretory vesicles or elsewhere within cells. - Being **lipophilic**, it diffuses freely across cell membranes immediately after synthesis. - Its release is regulated by the **hypothalamic-pituitary-adrenal (HPA) axis**, with synthesis and immediate secretion occurring upon stimulation. *Insulin* - Insulin is a **peptide hormone** synthesized as **proinsulin** and then cleaved into active insulin. - It is **stored in secretory granules** within pancreatic beta cells, allowing for rapid release in response to elevated blood glucose. *Thyroxine* - Thyroxine (T4) is a **thyroid hormone** that is synthesized from tyrosine and iodine. - It is **stored extracellularly** within the thyroid gland's follicles as part of a large protein called **thyroglobulin**. - Unlike cortisol (which is never stored), thyroxine has a **substantial storage pool** that can last weeks, though the storage is extracellular rather than intracellular. *Renin* - Renin is an **enzyme** produced by the **juxtaglomerular cells** of the kidney. - It is **stored in secretory granules** within these cells and released in response to decreased renal perfusion pressure or sympathetic stimulation.
Question 73: 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 74: 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 75: 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 76: 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 77: 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 78: 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 79: What does spermiogenesis refer to?
- A. Formation of spermatozoa from spermatogonia
- B. Formation of spermatozoa from spermatids (Correct Answer)
- C. Formation of spermatids from spermatocytes
- D. Formation of secondary spermatocytes from primary spermatocytes
Explanation: ***Formation of spermatozoa from spermatids*** - **Spermiogenesis** is the final stage of spermatogenesis, involving the remarkable transformation of a round **spermatid** into a motile, mature **spermatozoon**. - This process includes crucial morphological changes such as the formation of the **acrosome**, condensation of the nucleus, development of the flagellum, and shedding of excess cytoplasm. *Formation of spermatozoa from spermatogonia* - This describes the entire process of **spermatogenesis**, which begins with **spermatogonia** and encompasses multiple stages including mitosis, meiosis, and spermiogenesis. - While it's the ultimate outcome, it doesn't specifically define the detailed transformation from spermatid to sperm. *Formation of spermatids from spermatocytes* - This stage refers to **meiosis II**, where **secondary spermatocytes** undergo division to produce **spermatids**. - Spermatids are precursors to spermatozoa and still require significant morphological changes to become mature sperm. *Formation of secondary spermatocytes from primary spermatocytes* - This describes **meiosis I**, where a **primary spermatocyte** divides to form two **secondary spermatocytes**. - This step reduces the chromosome number by half but doesn't involve the final morphological changes seen in spermiogenesis.
Question 80: Ossicles of middle ear are responsible for which of the following ?
- A. Amplification of sound intensity
- B. Reduction of sound intensity
- C. Protecting the inner ear
- D. Reduction of impedance for sound transmission (Correct Answer)
Explanation: ***Reduction of impedance for sound transmission*** - The ossicles (malleus, incus, and stapes) act as a **lever system** to match the impedance between the air-filled outer ear and the fluid-filled inner ear. - This impedance matching ensures that maximum sound energy is transferred to the cochlea, preventing significant **sound reflection**. *Amplification of sound intensity* - While the ossicles do slightly amplify the sound pressure, their primary role is not extensive amplification but rather **impedance matching**. - The amplification achieved is a byproduct of efficient energy transfer, rather than a direct goal of increasing sound intensity for its own sake. *Reduction of sound intensity* - This function is primarily attributed to the **acoustic reflex**, where the middle ear muscles contract to stiffen the ossicular chain in response to loud sounds. - The primary function of the ossicles themselves is to transmit sound efficiently, not to reduce intensity under normal conditions. *Protecting the inner ear* - While the **acoustic reflex** (involving middle ear muscles attached to the ossicles) offers some protection against very loud sounds by stiffening the ossicular chain, this is a separate, reflexive mechanism. - The intrinsic structure and primary mechanical function of the ossicles are centered on efficient sound transmission, not direct physical protection of the inner ear.