Nokea
Isoprenaline produces the following actions EXCEPT:
- A. Direct stimulation of beta adrenoceptors
- B. Relaxation of bronchial smooth muscles
- C. Decreased blood pressure
- D. Increased intestinal motility
Correct Answer: D
Rationale: Step-by-step rationale:
1. Isoprenaline is a beta-adrenergic agonist.
2. It directly stimulates beta adrenoceptors, leading to effects like increased heart rate.
3. Isoprenaline causes bronchodilation by relaxing bronchial smooth muscles.
4. It also causes vasodilation, leading to decreased blood pressure.
5. Isoprenaline does not have a direct effect on intestinal motility, making option D incorrect.
Summary:
Option D is incorrect as isoprenaline does not increase intestinal motility. Options A, B, and C are correct as isoprenaline directly stimulates beta adrenoceptors, relaxes bronchial smooth muscles, and decreases blood pressure, respectively.
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What stimulates the release of PTH from the parathyroid gland?
- A. TSH from the posterior pituitary gland
- B. high levels of calcium in the blood
- C. calcitonin from the anterior pituitary gland
- D. low levels of calcium in the blood
Correct Answer: D
Rationale: The correct answer is D: low levels of calcium in the blood. When calcium levels drop, the parathyroid gland releases parathyroid hormone (PTH) to increase calcium levels in the blood. This is a negative feedback mechanism to maintain calcium homeostasis. A: TSH from the posterior pituitary gland is incorrect because TSH is involved in regulating thyroid function, not PTH release. B: High levels of calcium in the blood would not stimulate PTH release as the body aims to lower, not raise, calcium levels. C: Calcitonin from the anterior pituitary gland is incorrect because calcitonin is released by the thyroid gland and works to lower blood calcium levels, opposing the action of PTH.
Aldosterone:
- A. is a mineralocorticoid secreted by the adrenal cortex.
- B. functions in the regulation of blood glucose levels.
- C. stimulates the kidney to excrete sodium and reabsorb potassium.
- D. All is applicable.
Correct Answer: A
Rationale: Step-by-step rationale for why choice A is correct:
1. Aldosterone is a mineralocorticoid hormone secreted by the adrenal cortex.
2. It plays a key role in regulating electrolyte balance, specifically sodium and potassium levels.
3. Aldosterone acts on the kidneys to increase sodium reabsorption and potassium excretion.
4. This hormone helps to maintain blood pressure and fluid balance in the body.
Summary of why other choices are incorrect:
- Choice B (functions in the regulation of blood glucose levels): Aldosterone does not play a significant role in blood glucose regulation.
- Choice C (stimulates the kidney to excrete sodium and reabsorb potassium): This statement is partially true, but aldosterone actually stimulates sodium reabsorption and potassium excretion.
- Choice D (All is applicable): While aldosterone has various functions, not all statements apply to its actions.
Which mechanism is primarily responsible for maintaining hormone levels within a narrow range?
- A. negative feedback mechanisms
- B. positive feedback mechanisms
- C. hormone-receptor complexes
- D. hormone-gene complexes
Correct Answer: A
Rationale: The correct answer is A: negative feedback mechanisms. Negative feedback mechanisms help maintain hormone levels within a narrow range by inhibiting further hormone production once a certain level is reached. When hormone levels rise, negative feedback signals the body to decrease hormone production, preventing excessive levels. Positive feedback mechanisms, on the other hand, amplify hormone production. Hormone-receptor complexes and hormone-gene complexes are not directly responsible for maintaining hormone levels within a narrow range but rather play roles in hormone signaling and gene expression, respectively.
Which sequence is part of the life cycle of a very large mass star?
- A. red giant → planetary nebula + neutron star
- B. red giant → planetary nebula + black hole
- C. red supergiant → supernova → neutron star
- D. red supergiant → supernova → black hole
Correct Answer: D
Rationale: The correct answer is D: red supergiant → supernova → black hole. This sequence is part of the life cycle of a very large mass star. Red supergiants are massive stars in the later stages of their evolution. When a red supergiant goes supernova, it explodes in a massive stellar explosion, leaving behind a remnant that can collapse into a black hole due to the immense gravitational forces. Choices A and B are incorrect because planetary nebulae form from the outer layers of lower mass stars, not very large mass stars. Choice C is incorrect as neutron stars are more likely to form from the remnants of less massive stars.
Adrenocorticotropic hormone (ACTH) stimulates the ___ to produce and release its hormones.
- A. anterior pituitary
- B. adrenal medulla
- C. kidneys
- D. adrenal cortex
Correct Answer: D
Rationale: The correct answer is D: adrenal cortex. ACTH stimulates the adrenal cortex to produce and release its hormones, including cortisol. The anterior pituitary produces ACTH, but it does not release hormones itself. The adrenal medulla is primarily stimulated by the sympathetic nervous system, not ACTH. The kidneys are not directly stimulated by ACTH to produce and release hormones. Therefore, the adrenal cortex is the correct choice as it directly responds to ACTH stimulation.