Endocrinology Practice Questions

Q: Which of the following forms of thyroid hormone is most readily found in the circulation?

Thyroxine (T4).. ***Thyroxine (T4)*** - **Thyroxine (T4)** is the primary thyroid hormone secreted by the thyroid gland and is the most abundant form found in the circulation. - Approximately **80%** of the thyroid hormone released is T4, which then undergoes peripheral deiodination to form the more active T3. *TSH* - **TSH (Thyroid-Stimulating Hormone)** is a pituitary hormone that *regulates* thyroid function, not a thyroid hormone produced by the thyroid gland itself. - TSH levels are used to assess thyroid gland activity, but it is not the most abundant thyroid hormone in circulation. *Thyroglobulin* - **Thyroglobulin** is a large glycoprotein produced by thyroid follicular cells that serves as the precursor and storage protein for thyroid hormones *within* the thyroid gland. - While it contains T3 and T4 residues, most thyroglobulin is not released into circulation under normal physiological conditions; elevated levels can indicate thyroid damage or cancer. *Tri-iodothyronine (T3)* - **Tri-iodothyronine (T3)** is the biologically *active* form of thyroid hormone, but it is primarily derived from the peripheral conversion of T4. - Although T3 is more potent than T4, it is present in much lower concentrations in the circulation compared to T4.

Q: DEXA scan of lumbar vertebra and femoral neck are assessed for bone mineral density in menopausal women because of all except

Lumbar vertebra is 80% compact bone.. ***Lumbar vertebra is 80% compact bone.*** - This statement is incorrect. The vertebral bodies of the lumbar spine are predominantly composed of **trabecular (spongy) bone**, accounting for approximately 75% of their mass, not compact bone. - **Compact bone** is dense and found mainly in the shafts of long bones and the outer layer of all bones, while **trabecular bone** is porous and found in the ends of long bones and inside vertebrae. *Trabecular bone has faster re-modelling rate.* - This is a correct statement and a reason why these sites are chosen for DEXA scans. **Trabecular bone** undergoes faster bone turnover compared to cortical bone, making it more sensitive to metabolic changes and bone loss. - Due to its higher metabolic activity, changes in bone density at these sites can be detected earlier in conditions like **osteoporosis**. *Early rapid bone loss can be determined by evaluation of this site with trabecular bone.* - This is a correct statement. Since the lumbar vertebrae and femoral neck contain a significant amount of **trabecular bone**, which has a higher remodeling rate, these sites are ideal for detecting **early and rapid bone loss**, especially in postmenopausal women. - The rapid turnover of trabecular bone means that changes in bone density due to estrogen deficiency or other causes will manifest here sooner than in predominantly cortical bone sites. *Lumbar vertebrae contain primarily trabecular bone.* - This is a correct statement and a reason for choosing this site. The **lumbar vertebral bodies are rich in trabecular bone**, which makes them highly susceptible to bone loss in conditions like osteoporosis. - The high proportion of **trabecular bone** in these areas allows for sensitive detection of density changes using a DEXA scan.

Q: Hypothalamus controls the hormone secretion of:

Anterior hypophysis. ***Anterior hypophysis*** - The hypothalamus controls the **anterior hypophysis** (adenohypophysis) through releasing and inhibiting hormones transported via the **hypothalamic-hypophyseal portal system**. - These hormones stimulate or inhibit the secretion of **tropic hormones** like TSH, ACTH, FSH, LH, GH, and Prolactin from the anterior pituitary. *Posterior hypophysis* - The hypothalamus produces **ADH** and **oxytocin**, which are then stored and released by the posterior hypophysis, but it does not control its *secretion* in the same direct endocrine feedback loop as the anterior pituitary. - The posterior hypophysis (neurohypophysis) is essentially an extension of the hypothalamus, serving primarily as a **storage and release site** for neurohormones produced in the hypothalamic nuclei. *Kidney* - The kidney's hormonal functions, such as producing **erythropoietin** and **renin**, are regulated by factors like blood oxygen levels, blood pressure, and circulating hormones like aldosterone, not directly by the hypothalamus. - While the hypothalamus can influence kidney function indirectly through **ADH secretion** (affecting water reabsorption), it does not control the kidney's own endogenous hormone production. *Pineal gland* - The pineal gland primarily secretes **melatonin**, which is regulated by the **light-dark cycle** detected by the retina and transmitted via the suprachiasmatic nucleus, not directly by hypothalamic releasing hormones. - The hypothalamus influences the pineal gland indirectly through neural pathways, but it primarily *receives* information about circadian rhythms from the pineal gland rather than directly controlling its hormone secretion.

Q: 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?

Prolactin. ***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.

Q: Which of the following hormones is controlled by feedback control?

Corticosteroids. ***Corticosteroids*** - **Corticosteroids** (particularly cortisol) are the classic example of **negative feedback control** via the **hypothalamic-pituitary-adrenal (HPA) axis**. - **Mechanism:** Hypothalamus releases CRH → Anterior pituitary releases ACTH → Adrenal cortex secretes cortisol → **High cortisol levels inhibit CRH and ACTH release** (negative feedback). - This is one of the most fundamental examples of endocrine feedback regulation taught in physiology. *ADH* - While **ADH** secretion is regulated by osmolality and blood volume changes, this represents a **homeostatic response** to physiological stimuli rather than the classic hormonal feedback loop. - ADH responds directly to osmoreceptors and baroreceptors, not through a multi-tiered hormonal axis with feedback inhibition. *Insulin* - **Insulin** secretion responds to **blood glucose levels** as a direct stimulus-response mechanism. - While it demonstrates homeostatic regulation, it does not involve the classic **hypothalamic-pituitary-target gland feedback axis** that characterizes endocrine feedback control. *Prolactin* - **Prolactin** is primarily under **tonic inhibition by dopamine** from the hypothalamus. - Its regulation involves more complex mechanisms including positive feedback during lactation, but it doesn't follow the classic negative feedback pattern of the HPA, HPT, or HPG axes.

Q: Which hormone is under inhibitory control -

Prolactin. ***Correct: Prolactin*** - Prolactin secretion is primarily regulated by **dopamine** from the hypothalamus, which acts as a tonic inhibitory factor. - Absence of this dopamine inhibition, such as via **dopamine antagonists** or conditions affecting the hypothalamus, leads to increased prolactin release. *Incorrect: FSH* - **Follicle-stimulating hormone (FSH)** is primarily under **stimulatory control** by **gonadotropin-releasing hormone (GnRH)** from the hypothalamus. - Its secretion is also modulated by **feedback from gonadal steroids** (**estrogen** and **testosterone**) and **inhibin**, but the primary HPA axis control is stimulatory. *Incorrect: GH* - **Growth hormone (GH)** secretion is mainly regulated by two hypothalamic hormones: **growth hormone-releasing hormone (GHRH)** (stimulatory) and **somatostatin** (inhibitory). - While somatostatin provides an inhibitory component, the *overall* control involves both stimulatory and inhibitory inputs, and its baseline secretion is not solely defined by tonic inhibition. *Incorrect: LH* - **Luteinizing hormone (LH)**, like FSH, is primarily stimulated by **gonadotropin-releasing hormone (GnRH)** from the hypothalamus. - Its release is critically involved in **ovulation** and **testosterone production**, and its regulation is predominantly through positive and negative feedback from gonadal steroids, not tonic inhibition.

Q: Which hormone does not increase in burns -

LH. ***LH*** - In severe burn injury, the **hypothalamic-pituitary-gonadal (HPG) axis** is typically suppressed, leading to decreased levels of gonadotropins like **Luteinizing Hormone (LH)** and Follicle-Stimulating Hormone (FSH). - This suppression is part of the overall stress response and can contribute to **gonadal dysfunction** in burn patients. *Glucagon* - **Glucagon** levels typically *increase* significantly after a burn injury due to the intense **stress response** and the need for increased glucose availability. - This hormone promotes **gluconeogenesis** and **glycogenolysis** to combat the hypermetabolic state induced by burns. *Epinephrine* - **Epinephrine** (adrenaline) is a key **catecholamine** released in large quantities following severe burns as part of the fight-or-flight response. - Its increase contributes to **tachycardia**, **vasoconstriction**, and the general **hypermetabolic state**. *Cortisol* - **Cortisol**, a primary stress hormone, is consistently *elevated* after burn injury. - It plays a crucial role in the **metabolic adaptations** to stress, including increasing **gluconeogenesis** and modulating the immune response.

Q: Receptors for thyroid hormones are present:

Inside the cells. ***Inside the cells*** - Thyroid hormones are **lipophilic** and can easily pass through the cell membrane to bind with receptors located in the **cytoplasm or nucleus**. - These intracellular receptors then act as **transcription factors**, regulating gene expression. *On the cell membrane* - Receptors on the cell membrane are typically for **hydrophilic hormones** (e.g., peptide hormones) that cannot freely cross the lipid bilayer. - While there are some non-genomic effects mediated by cell surface receptors, the primary action of thyroid hormones is via intracellular receptors. *In association with G-proteins* - **G-protein coupled receptors** are cell membrane receptors that transduce signals through effector enzymes or ion channels, often for peptide or catecholamine hormones. - Thyroid hormones do not primarily signal through G-protein coupled receptors for their genomic effects. *Across the cell membrane* - This option refers to transmembrane proteins that span the entire cell membrane, which are characteristic of many cell surface receptors. - **Thyroid hormone receptors** are not transmembrane proteins but are found within the cell, often in the nucleus.

Q: Oxytocin causes all EXCEPT:

Milk production. ***Milk production*** - **Oxytocin** is primarily involved in the **milk ejection reflex** (let-down), but prolactin is the hormone responsible for **milk synthesis** or production. - While oxytocin facilitates the release of milk already produced, it does not stimulate the **mammary glands** to produce more milk. *Milk ejection* - Oxytocin causes contraction of the **myoepithelial cells** surrounding the alveoli in the mammary glands, leading to the **ejection of milk** into the ducts. - This reflex is crucial for **breastfeeding** and is often stimulated by the suckling of an infant. *Induction of labour* - **Oxytocin** stimulates rhythmic contractions of the **uterine smooth muscle**, making it a key hormone for initiating and progressing **labor**. - It is often administered exogenously to **induce** or augment labor due to its **uterotonic effects**. *Stimulates myoepithelial cells* - Oxytocin directly acts on the **myoepithelial cells** within the breast to cause their contraction. - This contraction generates pressure that forces milk from the **alveoli** into the **lactiferous ducts**, leading to milk ejection.

Q: Iodine is transported to the thyroid gland by what?

Active transport. ***Active transport*** - Iodine uptake by the thyroid gland, specifically by the **follicular cells**, is an **energy-dependent process** mediated by the sodium-iodide symporter (NIS). - This mechanism allows the thyroid to **concentrate iodide** against its electrochemical gradient, which is crucial for thyroid hormone synthesis. *Diffusion* - **Does not allow accumulation** of a substance against its concentration gradient, which is necessary for iodine uptake by the thyroid. - Would result in an equal distribution of iodine across the membrane, not the high intracellular concentrations observed in thyroid cells. *Passive transport* - Encompasses several mechanisms (like diffusion or facilitated diffusion) that **do not require metabolic energy**. - This broad category is incorrect because iodide transport into the thyroid gland specifically requires energy. *Pinocytosis* - A form of **endocytosis** where cells internalize liquids and small particles by engulfing them in vesicles. - While cells can internalize substances this way, it is not the primary or most efficient mechanism for transporting small ions like iodide into thyroid follicular cells.

Question 1

Which of the following forms of thyroid hormone is most readily found in the circulation?

Accepted Answer

Thyroxine (T4).

Answer

TSH.

Answer

Thyroglobulin.

Answer

Tri-iodothyronine (T3).

Question 2

DEXA scan of lumbar vertebra and femoral neck are assessed for bone mineral density in menopausal women because of all except

Accepted Answer

Lumbar vertebra is 80% compact bone.

Answer

Trabecular bone has faster re-modelling rate.

Answer

Early rapid bone loss can be determined by evaluation of this site with trabecular bone.

Answer

Lumbar vertebrae contain primarily trabecular bone.

Question 3

Hypothalamus controls the hormone secretion of:

Accepted Answer

Anterior hypophysis

Answer

Posterior hypophysis

Answer

Kidney

Answer

Pineal gland

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?

Accepted Answer

Prolactin

Answer

FSH

Answer

TSH

Answer

ACTH

Question 5

Which of the following hormones is controlled by feedback control?

Accepted Answer

Corticosteroids

Answer

Insulin

Answer

Prolactin

Answer

ADH

Question 6

Which hormone is under inhibitory control -

Accepted Answer

Prolactin

Answer

FSH

Answer

GH

Answer

LH

Question 7

Which hormone does not increase in burns -

Accepted Answer

LH

Answer

Glucagon

Answer

Epinephrine

Answer

Cortisol

Question 8

Receptors for thyroid hormones are present:

Accepted Answer

Inside the cells

Answer

On the cell membrane

Answer

In association with G-proteins

Answer

Across the cell membrane

Question 9

Oxytocin causes all EXCEPT:

Accepted Answer

Milk production

Answer

Milk ejection

Answer

Induction of labour

Answer

Stimulates myoepithelial cells

Question 10

Iodine is transported to the thyroid gland by what?

Accepted Answer

Active transport

Answer

Diffusion

Answer

Passive transport

Answer

Pinocytosis

Endocrinology — MCQs

Endocrinology — MCQs

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