Microscopic Anatomy of Endocrine Glands — MCQs
The function of which of the following is increased by an elevated parathyroid hormone concentration:
Insulin secretion is induced by following EXCEPT:
What is the average daily volume of pancreatic secretion in humans?
A patient with a known brain tumor learns that his pituitary stalk has been affected. Secretion of which of the following hormones is increased after the sectioning of the pituitary stalk?
A 20-year-old male presents with weight loss, heat intolerance, bilateral exophthalmos, a lid lag, sweating, and tachycardia. These symptoms are due to an increased production and secretion of a hormone that is derived from which one of the following?
Increased aldosterone and ADH secretion following major trauma results in all the following except?
Acidophilic cells of anterior pituitary secrete?
What structures are derived from the neural crest?
All are derived from ectoderm except for which of the following?
Which of the following cell types is neuroectodermal in origin?
Microscopic Anatomy of Endocrine Glands Indian Medical PG Practice Questions and MCQs
Question 1: The function of which of the following is increased by an elevated parathyroid hormone concentration:
- A. Action of osteoblasts only
- B. Osteoclasts (Correct Answer)
- C. Phosphate reabsorptive pathways in the renal tubules
- D. Hepatic formation of 25-hydroxycholecalciferol
Explanation: ***Osteoclasts*** - **Parathyroid hormone (PTH)** primarily acts to increase serum calcium levels by stimulating **osteoclasts**, leading to bone resorption and release of calcium and phosphate into the bloodstream. - While PTH does not directly act on osteoclasts, it binds to receptors on osteoblasts, which then release factors that activate osteoclasts. *Action of osteoblasts only* - PTH indirectly affects **osteoblasts** by binding to their receptors, but this action primarily leads to **RANKL expression**, which then stimulates osteoclast activity, not a direct increase in osteoblastic bone formation. - Chronic elevation of PTH, as seen in primary hyperparathyroidism, can paradoxically lead to a net loss of bone mass due to increased osteoclastic activity. *Phosphate reabsorptive pathways in the renal tubules* - PTH actually **decreases reabsorption of phosphate** in the renal tubules, leading to phosphaturia. This helps to prevent calcium-phosphate precipitation by lowering serum phosphate levels while raising calcium. - This is a key mechanism by which PTH increases serum calcium—by both mobilizing it from bone and reducing its renal excretion, while simultaneously promoting renal phosphate excretion. *Hepatic formation of 25-hydroxycholecalciferol* - The **liver** is responsible for the hydroxylation of vitamin D3 (cholecalciferol) to **25-hydroxycholecalciferol (calcidiol)**, a process that is not directly regulated by PTH. - PTH primarily stimulates the **kidneys** to convert 25-hydroxycholecalciferol to its active form, **1,25-dihydroxyvitamin D (calcitriol)**, which then enhances intestinal calcium absorption.
Question 2: Insulin secretion is induced by following EXCEPT:
- A. Somatostatin (Correct Answer)
- B. Estrogens
- C. Growth hormone
- D. Placental lactogen
Explanation: ***Somatostatin*** - **Somatostatin** directly inhibits insulin secretion from pancreatic beta cells, acting as a paracrine regulator to modulate islet hormone release. - It binds to **somatostatin receptors (SSTRs)** on beta cells, leading to a reduction in cAMP and inhibition of voltage-gated calcium channels, thereby decreasing insulin exocytosis. *Estrogens* - **Estrogens** generally enhance insulin secretion and improve insulin sensitivity, especially during pregnancy or in response to high glucose levels. - They can increase **beta-cell mass** and survival, contributing to better glycemic control. *Growth hormone* - **Growth hormone (GH)** can indirectly induce insulin secretion by promoting insulin resistance, which necessitates increased insulin production to maintain normal glucose levels. - Chronically elevated GH, as seen in **acromegaly**, often leads to hyperinsulinemia and can even cause diabetes. *Placental lactogen* - **Human placental lactogen (hPL)** is a hormone produced during pregnancy that primarily increases maternal insulin resistance to ensure adequate glucose supply to the fetus. - This increased resistance compensatorily stimulates **maternal beta cells** to secrete more insulin, leading to hyperinsulinemia.
Question 3: What is the average daily volume of pancreatic secretion in humans?
- A. 5.0 L
- B. 10 L
- C. 1.5 L (Correct Answer)
- D. 2.5 L
Explanation: ***1.5 L*** - The **pancreas** produces approximately **1.5 liters (1200-1500 mL) of pancreatic juice** daily in humans. - This secretion is rich in **digestive enzymes** (amylase, lipase, proteases) and **bicarbonate** for neutralization of gastric acid in the duodenum. - This is the standard value cited in **major physiology textbooks** (Ganong, Guyton & Hall). *2.5 L* - **2.5 liters** overestimates the typical daily pancreatic secretion volume. - This value may represent **combined secretions** from multiple sources or confuse pancreatic output with total upper GI secretions. - Normal pancreatic secretion ranges from **1-2 liters**, making 2.5 L above the physiological range. *5.0 L* - **5.0 liters** represents an abnormally high volume for daily pancreatic secretion alone. - This volume is closer to the **total daily secretions** from stomach, pancreas, and bile combined. - Not consistent with **normal pancreatic physiology**. *10 L* - **10 liters** is grossly excessive for pancreatic secretion and represents approximately the **total volume of all gastrointestinal secretions** (saliva, gastric, pancreatic, bile, intestinal) combined daily. - This is **not physiologically realistic** for pancreatic output alone.
Question 4: A patient with a known brain tumor learns that his pituitary stalk has been affected. Secretion of which of the following hormones is increased after the sectioning of the pituitary stalk?
- A. FSH
- B. Prolactin (Correct Answer)
- C. TSH
- D. ACTH
Explanation: ***Prolactin*** - Prolactin is **unique** among anterior pituitary hormones as it is under **tonic inhibitory control** by dopamine from the hypothalamus. - Sectioning of the pituitary stalk disrupts dopamine delivery via the hypothalamic-hypophyseal portal system. - This leads to a **loss of tonic inhibition**, causing an **increase in prolactin secretion** from the anterior pituitary. - This phenomenon is known as the **"stalk effect"** or **hyperprolactinemia due to stalk section**. *FSH* - **Follicle-stimulating hormone (FSH)** secretion is regulated by **gonadotropin-releasing hormone (GnRH)** from the hypothalamus, which is **stimulatory**. - Stalk section interrupts GnRH delivery via the portal system, leading to a **decrease** in FSH secretion. *TSH* - **Thyroid-stimulating hormone (TSH)** secretion is positively regulated by **thyrotropin-releasing hormone (TRH)** from the hypothalamus. - Interruption of the pituitary stalk reduces TRH delivery, causing a **decrease** in TSH secretion. *ACTH* - **Adrenocorticotropic hormone (ACTH)** secretion is positively regulated by **corticotropin-releasing hormone (CRH)** from the hypothalamus. - Damage to the pituitary stalk diminishes CRH stimulation, resulting in a **decrease** in ACTH secretion.
Question 5: A 20-year-old male presents with weight loss, heat intolerance, bilateral exophthalmos, a lid lag, sweating, and tachycardia. These symptoms are due to an increased production and secretion of a hormone that is derived from which one of the following?
- A. Tryptophan
- B. Dopamine
- C. Cholesterol
- D. Tyrosine (Correct Answer)
Explanation: ***Tyrosine*** - The symptoms described (weight loss, heat intolerance, exophthalmos, lid lag, sweating, tachycardia) are characteristic of **hyperthyroidism**, specifically **Graves' disease**. - Thyroid hormones (**T3 and T4**) are synthesized from the amino acid **tyrosine** through iodination of tyrosine residues on thyroglobulin in the thyroid gland. - This makes tyrosine the direct precursor for thyroid hormone synthesis. *Tryptophan* - **Tryptophan** is a precursor for the synthesis of **serotonin** and **melatonin**, neurotransmitters involved in mood regulation and sleep-wake cycles, not thyroid function. - Deficiency or altered metabolism of tryptophan is associated with conditions like **depression** or **carcinoid syndrome**, which have different clinical presentations. *Dopamine* - **Dopamine** is a catecholamine neurotransmitter, not a precursor for thyroid hormones. - While dopamine is synthesized from tyrosine (via the pathway: tyrosine → L-DOPA → dopamine), this is a completely separate biochemical pathway from thyroid hormone synthesis. - Symptoms of altered dopamine levels are associated with conditions like **Parkinson's disease** (dopamine deficiency) or **schizophrenia** (dopamine dysregulation), which do not match this patient's hyperthyroid presentation. *Cholesterol* - **Cholesterol** is the precursor for **steroid hormones** (glucocorticoids, mineralocorticoids, androgens, estrogens) and vitamin D, but not thyroid hormones. - Conditions related to altered cholesterol-derived hormone metabolism include various **endocrine disorders** involving adrenal or gonadal dysfunction, which present with different clinical features.
Question 6: Increased aldosterone and ADH secretion following major trauma results in all the following except?
- A. Increased osmolarity of urine
- B. Increased water excretion (Correct Answer)
- C. Increased K+ excretion in urine
- D. Decreased Na+ excretion in urine
Explanation: ***Increased water excretion*** - **ADH (antidiuretic hormone)** increases water reabsorption in the collecting ducts, leading to a *decrease* in water excretion, not an increase. - Increased aldosterone and ADH would promote fluid retention to maintain blood volume following trauma, thus reducing water loss via urine. *Decreased Na+ excretion in urine* - **Aldosterone** acts on the renal tubules to increase **sodium reabsorption** and potassium excretion. - This response is crucial in **conserving sodium** and thereby maintaining extracellular fluid volume after trauma. *Increased K+ excretion in urine* - **Aldosterone** directly stimulates **potassium secretion** into the urine in the principal cells of the collecting ducts. - This is a normal physiological consequence of increased aldosterone levels. *Increased osmolarity of urine* - **ADH** increases the permeability of the collecting ducts to water, leading to **more water reabsorption** back into the bloodstream. - This removal of water from the urine concentrates the solutes, resulting in a **more concentrated (higher osmolarity)** urine.
Question 7: Acidophilic cells of anterior pituitary secrete?
- A. ACTH
- B. GH (Correct Answer)
- C. TSH
- D. ADH
Explanation: ***GH*** - **Growth Hormone (GH)** is secreted by **somatotrophs**, which are a type of acidophilic cell in the anterior pituitary. - These cells stain readily with **acidic dyes** due to their abundant secretory granules. *ACTH* - **Adrenocorticotropic hormone (ACTH)** is secreted by **corticotrophs**, which are **basophilic cells** in the anterior pituitary. - Corticotrophs stain with basic dyes due to different intracellular granule content. *TSH* - **Thyroid-stimulating hormone (TSH)** is secreted by **thyrotrophs**, which are a type of **basophilic cell** in the anterior pituitary. - Basophilic cells are characterized by their affinity for basic dyes. *ADH* - **Antidiuretic hormone (ADH)**, also known as vasopressin, is produced by the **hypothalamus** and released from the **posterior pituitary**, not the anterior pituitary. - It is not secreted by acidophilic cells.
Question 8: What structures are derived from the neural crest?
- A. Melanocytes
- B. Dental papillae
- C. Adrenal medulla
- D. All of the options (Correct Answer)
Explanation: ***All of the options*** - The **neural crest** is a multipotent, migratory cell population that contributes to the formation of many diverse tissues and organs during vertebrate development. - Neural crest cells give rise to a wide array of derivatives, including components of the nervous system, pigment cells, skeletal and connective tissues of the head and face, and endocrine glands [1]. *Melanocytes* - **Melanocytes**, the pigment-producing cells found in the skin, hair, eyes, and other tissues, are derived from the **neural crest** [2]. - These cells migrate extensively during development from the neural crest to their final destinations throughout the body. - Neural crest-derived melanocytes produce melanin, which provides pigmentation and protection against UV radiation [2]. *Dental papillae* - The **dental papilla** is crucial for tooth development and is formed from **ectomesenchymal cells** that are derived from the cranial neural crest. - These cells differentiate into the odontoblasts that produce dentin and also contribute to the pulp of the tooth. *Adrenal medulla* - The cells of the **adrenal medulla**, which produce catecholamines like epinephrine and norepinephrine, are specialized **postganglionic sympathetic neurons** derived from the neural crest. - They develop from neuroectodermal cells that migrate to the developing adrenal gland.
Question 9: All are derived from ectoderm except for which of the following?
- A. Hair follicles
- B. Nails
- C. Lens of the eye
- D. Adrenal cortex (Correct Answer)
Explanation: ***Adrenal cortex*** - The adrenal cortex is derived from the **intermediate mesoderm**, specifically from the cells lining the posterior abdominal wall. The cells migrate to develop into the adrenal cortex. - It produces various steroid hormones, including **aldosterone**, **cortisol**, and **androgens**, which regulate diverse bodily functions. *Lens of the eye* - The lens of the eye is derived from the **surface ectoderm**. It forms from an invagination of the surface ectoderm called the lens placode. - Its primary function is to **focus light** onto the retina. *Hair follicles* - Hair follicles develop from the **surface ectoderm** [1]; they are invaginations of the epidermis that extend into the dermis. - They produce hair, which provides **insulation** and **protection** [1]. *Nails* - Nails are also derivatives of the **surface ectoderm**, forming thickened plates on the dorsal surface of the distal phalanges. - They provide **protection** to the fingertips and aid in grasping objects.
Question 10: Which of the following cell types is neuroectodermal in origin?
- A. Smooth muscle cells (Correct Answer)
- B. Skeletal muscle cells
- C. Endothelial cells
- D. Cardiac muscle cells
Explanation: ***Smooth muscle cells*** - This is the **correct answer** based on a **specific exception**: smooth muscle cells of the **iris dilator and sphincter muscles** and the **ciliary muscle** in the eye are derived from **neuroectoderm** (specifically from the **optic cup**, an outgrowth of the neural tube). - **Important note:** The vast majority of smooth muscle in the body is of **mesodermal origin** (e.g., in blood vessels, GI tract, respiratory tract). This question tests knowledge of this **notable embryological exception**. - In the context of the given options, this is the only cell type with any neuroectodermal component. *Skeletal muscle cells* - Skeletal muscle cells are entirely derived from the **paraxial mesoderm**, specifically from **somites** (myotome portion). - They form the voluntary muscles of the body and are **never** of neuroectodermal origin. *Endothelial cells* - Endothelial cells lining blood vessels and lymphatic vessels are derived from the **mesoderm** (specifically from **angioblasts**). - They are part of the cardiovascular system and are **entirely mesodermal** in origin. *Cardiac muscle cells* - Cardiac muscle cells are derived from the **splanchnic mesoderm** (lateral plate mesoderm). - The heart musculature is **entirely mesodermal** with no neuroectodermal contribution. **Clinical Pearl:** Classic neuroectodermal derivatives include neurons, glial cells (astrocytes, oligodendrocytes), ependymal cells, and neural crest derivatives (Schwann cells, melanocytes, chromaffin cells). The smooth muscle of the iris represents an important exception to the general rule that smooth muscle is mesodermal.
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