Endocrinology Practice Questions

Q: Melatonin is secreted by

Pineal gland. ***Pineal gland*** - The **pineal gland** is a small endocrine gland located in the brain that primarily produces **melatonin**. - Its main function is to regulate **sleep-wake cycles** (circadian rhythms), with melatonin secretion increasing in darkness. *Melanocytes* - **Melanocytes** are cells found in the skin and eyes that produce **melanin**, a pigment responsible for skin, hair, and eye color. - They are not involved in the production of melatonin. *Hypothalamus* - The **hypothalamus** is a crucial part of the brain that links the nervous system to the endocrine system via the pituitary gland. - It produces various **releasing and inhibiting hormones** that control other glands, but it does not secrete melatonin. *Adrenal cortex* - The **adrenal cortex** is the outer part of the adrenal gland, responsible for producing **steroid hormones** like glucocorticoids (e.g., cortisol) and mineralocorticoids (e.g., aldosterone). - It does not produce melatonin; melatonin production is distinctly associated with the pineal gland.

Q: All are true for oxytocin EXCEPT:

Secreted by anterior pituitary. ***Secreted by anterior pituitary*** - Oxytocin is synthesized in the **hypothalamus** (specifically the paraventricular and supraoptic nuclei) and then transported down axons to the **posterior pituitary gland**, where it is stored and released. - The **anterior pituitary** produces and secretes hormones like growth hormone, prolactin, TSH, ACTH, FSH, and LH, but not oxytocin or vasopressin. *Causes ejection of milk* - Oxytocin acts on **myoepithelial cells** surrounding the alveoli of the mammary glands, causing them to contract and eject milk during lactation. - This is known as the **milk ejection reflex** or "let-down" reflex, which is stimulated by suckling. *Polypeptide* - Oxytocin is a **peptide hormone** composed of nine amino acids, making it a small polypeptide. - Its specific amino acid sequence is **Cys-Tyr-Ile-Gln-Asn-Cys-Pro-Leu-Gly-NH2**, with a disulfide bond between the cysteine residues. *Secreted in both sexes* - While most recognized for its roles in childbirth and lactation in females, oxytocin is also produced and secreted in **males**. - In males, it is involved in various functions including **sperm transport**, sexual arousal, ejaculation, and social bonding behaviors.

Q: Which of the following causes hypocalcemia:

Calcitonin. ***Calcitonin*** - **Calcitonin** is a hormone secreted by the **parafollicular cells (C cells)** of the thyroid gland. - It **lowers serum calcium levels** by **inhibiting osteoclast activity** (preventing bone resorption) and **increasing renal calcium excretion**. - This is the only hormone among the options that causes hypocalcemia. *1,25-dihydroxycholecalciferol* - This is the **active form of vitamin D** (calcitriol), which **increases serum calcium levels**. - It promotes intestinal calcium absorption, enhances bone resorption, and increases renal calcium reabsorption. - Deficiency of this hormone leads to hypocalcemia, but the hormone itself raises calcium. *Parathormone* - **Parathyroid hormone (PTH)** is the primary regulator that **increases serum calcium levels**. - It stimulates **osteoclast activity** (releasing calcium from bone), increases renal calcium reabsorption, and promotes synthesis of 1,25-dihydroxycholecalciferol. - PTH acts opposite to calcitonin in calcium homeostasis. *Thyroid hormones* - **Thyroxine (T4) and triiodothyronine (T3)** primarily regulate metabolism and have **no direct role in calcium homeostasis**. - While severe thyroid dysfunction can indirectly affect bone turnover, thyroid hormones do not directly cause hypocalcemia.

Q: Neuroendocrine glands means:

Substance is released into the blood from the nerve. ***Substance is released into the blood from the nerve*** - Neuroendocrine glands are specialized neurons that synthesize and release **hormones** directly into the bloodstream, integrating the nervous and endocrine systems. - This **neurosecretion** allows neurons to exert widespread, long-lasting effects on target cells throughout the body. *Those acting at peripheral nervous system* - This describes the general function of peripheral nerves, which can be **motor**, **sensory**, or **autonomic**, but doesn't specifically define a neuroendocrine gland. - Neuroendocrine cells are typically found within the central and peripheral nervous systems but their defining characteristic is release into the **blood**, not just acting within the PNS. *Chemical acting at the synapse* - This describes a **neurotransmitter**, which is released from a neuron and acts locally on a postsynaptic neuron or effector cell across a synaptic cleft. - Unlike hormones, neurotransmitters exert their effects over very **short distances** and typically have a rapid, short-lived action. *Substance act on the cells that release it.* - This describes **autocrine signaling**, where a cell produces and secretes an extracellular mediator that binds to its own surface receptors. - While some neuroendocrine cells may exhibit autocrine regulation, their primary definition involves releasing substances into the **bloodstream** to act on distant targets, not solely on themselves.

Q: A patient with a pheochromocytoma is secreting large amounts of norepinephrine into the bloodstream. In a normal individual, this compound is usually released from the adrenal medulla in response to which of the following?

Acetylcholine. ***Acetylcholine*** - **Acetylcholine** is the primary neurotransmitter released by **preganglionic sympathetic fibers** that innervate the adrenal medulla. - Upon binding to **nicotinic receptors** on chromaffin cells, acetylcholine stimulates the release of catecholamines, including norepinephrine and epinephrine, into the bloodstream. *Normetanephrine* - **Normetanephrine** is a metabolite of **norepinephrine**, not a hormone that triggers its release. - It is formed by the action of **catechol-O-methyltransferase (COMT)** on norepinephrine. *Metanephrine* - **Metanephrine** is a metabolite of **epinephrine**, not a substance that stimulates catecholamine release from the adrenal medulla. - Like normetanephrine, it is also formed by the action of **COMT**. *Epinephrine* - **Epinephrine** (adrenaline) is a hormone primarily produced and released by the **adrenal medulla**, alongside norepinephrine. - While both are catecholamines, epinephrine does not trigger its own release or the release of norepinephrine in this context; instead, their release is stimulated by acetylcholine.

Q: Which of the following can cause an increase in growth hormone levels in blood?

Hypoglycemia. ***Hypoglycemia*** - **Hypoglycemia** is a potent stimulus for **growth hormone (GH) secretion**, as GH acts to raise blood glucose levels, serving as a counter-regulatory hormone. - The body perceives low blood glucose as a stressor, activating the **hypothalamic-pituitary-adrenal axis** and stimulating GH release to mobilize energy stores. *Cortisol* - **Cortisol** (a glucocorticoid) generally has an **inhibitory effect** on GH secretion at the hypothalamic and pituitary levels. - High levels of cortisol can lead to **suppression of GH pulsatility** and overall lower GH release. *Glucose* - An increase in **blood glucose** levels typically **suppresses growth hormone (GH) release**, as GH tends to increase blood glucose. - This negative feedback mechanism helps maintain **glucose homeostasis** within the body. *Methylprednisolone* - **Methylprednisolone** is a synthetic **glucocorticoid** that mimics the actions of cortisol. - Like cortisol, it suppresses GH secretion and can lead to **growth retardation** in children with chronic use.

Q: Steroid hormone that directly binds to intracellular cytoplasmic receptors

Glucocorticoids. ***Glucocorticoids*** - **Glucocorticoids** are **steroid hormones** that are **lipid-soluble** and can easily pass through the cell membrane to bind to **intracellular cytoplasmic receptors**. - This binding leads to the formation of a hormone-receptor complex that translocates to the nucleus to regulate **gene expression**. - This is the classic mechanism of action for steroid hormones. *Thyroxine* - **Thyroxine (T4)** is a **thyroid hormone**, **not a steroid hormone** - it is derived from tyrosine amino acids. - Although it does bind to intracellular receptors, it does not meet the criteria of being a steroid hormone as asked in the question. - Thyroxine primarily binds to nuclear receptors rather than cytoplasmic receptors. *Calcitonin* - **Calcitonin** is a **peptide hormone**, not a steroid hormone, that primarily binds to **cell surface receptors** on target cells like osteoclasts and renal tubule cells. - As a large, **water-soluble** molecule, it cannot directly cross the cell membrane to bind to intracellular receptors. *Vasopressin* - **Vasopressin**, also known as **antidiuretic hormone (ADH)**, is a **peptide hormone**, not a steroid hormone, that acts on **cell surface receptors** in the kidneys and blood vessels. - Its **hydrophilic** nature prevents it from penetrating the cell membrane to bind to intracellular receptors.

Q: All of the following hormones have cell surface receptors except:

Thyroxine. ***Thyroxine*** - **Thyroxine** (T4) is a **lipid-soluble thyroid hormone** that readily crosses the cell membrane to bind to **intracellular nuclear receptors** in the nucleus. - This binding leads to changes in gene expression, which then mediates its metabolic effects. - Unlike peptide hormones, thyroid hormones do not require cell surface receptors. *Insulin* - **Insulin** is a **peptide hormone** that binds to specific **cell surface receptors** (tyrosine kinase receptors) on target cells. - This binding initiates a signaling cascade that regulates glucose uptake and metabolism. *Adrenalin* - **Adrenalin** (epinephrine) is a **catecholamine hormone** that binds to **G protein-coupled receptors (GPCRs)** on the cell surface. - This binding triggers intracellular signaling pathways, leading to the "fight-or-flight" response. *Growth Hormone* - **Growth hormone** is a **protein hormone** that binds to **cell surface receptors** (cytokine receptors) on target cells. - This interaction activates the JAK-STAT signaling pathway, promoting growth and metabolism.

Q: The anterior pituitary is mainly composed of which of the following secretory cells?

Somatotrope. ***Somatotrope*** - **Somatotropes** are the most abundant cell type in the anterior pituitary, constituting about 50% of the gland's cells. - They produce and secrete **growth hormone (GH)**, which is crucial for growth, metabolism, and body composition. *Lactotrope* - **Lactotropes** produce **prolactin (PRL)**, which is involved in lactation. - They make up about 15-20% of the anterior pituitary cells, a significant but not the main proportion. *Corticotrope* - **Corticotropes** secrete **adrenocorticotropic hormone (ACTH)**, which stimulates the adrenal glands. - They constitute approximately 15-20% of the anterior pituitary cells, similar to lactotropes. *Thyrotrope* - **Thyrotropes** produce **thyroid-stimulating hormone (TSH)**, regulating thyroid function. - They are the least abundant cell type, making up only about 5% of the anterior pituitary cells.

Q: Which of the following actions of GH is mediated by IGF-1?

Antilipolysis. ***Antilipolysis*** * **Insulin-like growth factor 1 (IGF-1)**, stimulated by GH, plays a role in reducing **lipolysis** indirectly. * IGF-1 promotes **anabolic processes** and nutrient storage, which can lead to decreased fat breakdown. *Na+ retention* * **Na+ retention** is more directly influenced by hormones like **aldosterone** and **ADH**, not IGF-1. * While GH can exert some influence on fluid and electrolyte balance, this specific action is not primarily mediated by IGF-1. *decreases insulin* * IGF-1 and GH generally tend to **increase insulin sensitivity** in some tissues or antagonize insulin effects indirectly. * IGF-1's primary metabolic role is not to decrease insulin itself directly. *Lipolysis* * **Growth hormone (GH)** directly promotes **lipolysis**, breaking down fat for energy. * However, the question specifically asks for actions mediated by **IGF-1**, which has an opposite, antilipolytic effect.

Question 1

Melatonin is secreted by

Accepted Answer

Pineal gland

Answer

Melanocytes

Answer

Hypothalamus

Answer

Adrenal cortex

Question 2

All are true for oxytocin EXCEPT:

Accepted Answer

Secreted by anterior pituitary

Answer

Causes ejection of milk

Answer

Polypeptide

Answer

Secreted in both sexes

Question 3

Which of the following causes hypocalcemia:

Accepted Answer

Calcitonin

Answer

1, 25-dihydroxycholecalciferol

Answer

Parathormone

Answer

Thyroid hormones

Question 4

Neuroendocrine glands means:

Accepted Answer

Substance is released into the blood from the nerve

Answer

Those acting at peripheral nervous system

Answer

Chemical acting at the synapse

Answer

Substance acts on the cells that release it.

Question 5

A patient with a pheochromocytoma is secreting large amounts of norepinephrine into the bloodstream. In a normal individual, this compound is usually released from the adrenal medulla in response to which of the following?

Accepted Answer

Acetylcholine

Answer

Normetanephrine

Answer

Metanephrine

Answer

Epinephrine

Question 6

Which of the following can cause an increase in growth hormone levels in blood?

Accepted Answer

Hypoglycemia

Answer

Cortisol

Answer

Glucose

Answer

Methylprednisolone

Question 7

Steroid hormone that directly binds to intracellular cytoplasmic receptors

Accepted Answer

Glucocorticoids

Answer

Thyroxine

Answer

Calcitonin

Answer

Vasopressin

Question 8

All of the following hormones have cell surface receptors except:

Accepted Answer

Thyroxine

Answer

Insulin

Answer

Adrenalin

Answer

Growth Hormone

Question 9

The anterior pituitary is mainly composed of which of the following secretory cells?

Accepted Answer

Somatotrope

Answer

Lactotrope

Answer

Corticotrope

Answer

Thyrotrope

Question 10

Which of the following actions of GH is mediated by IGF-1?

Accepted Answer

Antilipolysis

Answer

Na+ retention

Answer

decreases insulin

Answer

Lipolysis

Endocrinology — MCQs

Endocrinology — MCQs

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