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Melatonin is secreted by which gland?
- A. Pineal gland
- B. Thyroid
- C. Thymus
- D. Adrenal
Correct Answer: A
Rationale: The correct answer is A: Pineal gland. Melatonin is a hormone that regulates sleep-wake cycles and is primarily secreted by the pineal gland located in the brain. The pineal gland responds to darkness by releasing melatonin, which helps to induce sleep. The other choices, B: Thyroid, C: Thymus, and D: Adrenal, do not secrete melatonin. The thyroid gland produces hormones that regulate metabolism, the thymus gland is involved in immune function, and the adrenal glands secrete hormones like cortisol and adrenaline. Therefore, the pineal gland is the correct answer for melatonin secretion.
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Which of the following inhibits the secretion of growth hormone by the anterior pituitary?
- A. Sleep
- B. Stress
- C. Puberty
- D. Somatomedins
Correct Answer: D
Rationale: The correct answer is D: Somatomedins. Somatomedins, also known as insulin-like growth factors (IGFs), inhibit the secretion of growth hormone by negative feedback on the anterior pituitary. When somatomedins are present in sufficient levels, they signal to the pituitary gland to decrease the secretion of growth hormone.
A: Sleep does not directly inhibit the secretion of growth hormone. In fact, growth hormone is predominantly secreted during sleep.
B: Stress can stimulate the secretion of growth hormone, rather than inhibit it.
C: Puberty is a stage of development where growth hormone secretion is typically increased, not inhibited.
The relatively constant internal environment of the body is maintained by _______.
- A. negative feedback.
- B. positive feedback.
- C. homeostasis.
- D. metabolism.
Correct Answer: C
Rationale: The correct answer is C: homeostasis. Homeostasis refers to the body's ability to maintain a stable internal environment despite external changes. It involves various physiological mechanisms to regulate temperature, pH, blood sugar levels, and more. Negative feedback (choice A) is a key component of homeostasis, where the body reverses a deviation from the set point to restore balance. Positive feedback (choice B) amplifies a response and does not contribute to maintaining stability. Metabolism (choice D) is the sum of all chemical processes in the body and is necessary for homeostasis but does not directly regulate the internal environment.
Complete the following sentence: Hormones are chemical messengers that…
- A. Remain at a constant concentration in the blood
- B. Are synthesised by plasma proteins
- C. Are only produced after puberty
- D. Alter the activity of target tissues
Correct Answer: D
Rationale: The correct answer is D because hormones alter the activity of target tissues to regulate various physiological processes in the body. Hormones act on specific receptors in target tissues to initiate a response. Option A is incorrect because hormone levels fluctuate to maintain homeostasis. Option B is incorrect because hormones are typically synthesized by endocrine glands, not plasma proteins. Option C is incorrect because hormones are produced throughout life, not just after puberty.
Which of the following drugs is a direct stimulant of β1 and β2 adrenoceptors:
- A. Noradrenaline
- B. Isoprenaline
- C. Salbutamol
- D. Amphetamine
Correct Answer: B
Rationale: The correct answer is B: Isoprenaline. Isoprenaline directly stimulates both β1 and β2 adrenoceptors. It is a non-selective β-adrenergic agonist, leading to increased heart rate (β1 stimulation) and bronchodilation (β2 stimulation).
Incorrect choices:
A: Noradrenaline mainly acts on α-adrenoceptors.
C: Salbutamol is a selective β2 agonist, not stimulating β1 receptors.
D: Amphetamine primarily acts on catecholamine release and reuptake inhibition, not direct β-adrenoceptor stimulation.
The “melting of flesh into urine,†an old-timey name, is most descriptive of untreated:
- A. diabetes mellitus.
- B. Addison’s disease.
- C. diabetes insipidus.
- D. Cushing syndrome.
Correct Answer: A
Rationale: The correct answer is A: diabetes mellitus. This term describes the breakdown of body tissues for energy due to lack of insulin, leading to the production of ketones in the urine. In diabetes mellitus, the body cannot use glucose properly, causing the breakdown of fats and proteins. Addison's disease (B) involves adrenal insufficiency, not tissue breakdown. Diabetes insipidus (C) is a disorder of water balance, not tissue breakdown. Cushing syndrome (D) is characterized by excess cortisol production, not tissue breakdown into urine.