Nokea
Thyroxine is a peptide hormone, but its mechanism is different from other peptide hormones. Which of the following statements is true concerning this difference?
- A. It causes positive feedback.
- B. It does not require a second messenger to effect a response.
- C. It is very specific in the cell type it targets.
- D. It is a stimulant of cellular metabolism and targets all cells.
Correct Answer: B
Rationale: The correct answer is B: Thyroxine does not require a second messenger to effect a response. Thyroxine is a non-peptide hormone derived from the amino acid tyrosine, not a peptide hormone. It acts directly on the cell by binding to nuclear receptors, which then bind to specific regions of DNA to regulate gene expression. This mechanism is different from peptide hormones, which typically require second messengers like cAMP or calcium to transmit their signal inside the cell. Therefore, choice B is correct. Choices A, C, and D are incorrect because thyroxine does not cause positive feedback, is not highly specific in cell targeting, and does not target all cells for cellular metabolism stimulation.
You may also like to solve these questions
The adrenal medulla:
- A. is an extension of the “feed-and-breed†division of the autonomic nervous system.
- B. secretes epinephrine and norepinephrine.
- C. secretes steroids.
- D. causes Cushing syndrome when it is overactive.
Correct Answer: B
Rationale: The correct answer is B because the adrenal medulla secretes epinephrine and norepinephrine, which are hormones involved in the body's response to stress or danger. These hormones help increase heart rate, blood pressure, and energy levels. Choices A, C, and D are incorrect because:
A: The adrenal medulla is actually part of the sympathetic division of the autonomic nervous system, which is responsible for the "fight-or-flight" response, not the "feed-and-breed" division.
C: Steroids are produced by the adrenal cortex, not the adrenal medulla.
D: Cushing syndrome is caused by overactivity of the adrenal cortex, not the adrenal medulla.
Chemical substances secreted by cells into the extracellular fluids that regulate the metabolic function of other cells in the body are called ________.
- A. enzymes
- B. antibodies
- C. proteins
- D. hormones
Correct Answer: D
Rationale: The correct answer is D: hormones. Hormones are chemical substances secreted by cells into extracellular fluids to regulate metabolic functions in other cells. They act as messengers, traveling through the bloodstream to target tissues. Enzymes (A) are catalysts that accelerate chemical reactions. Antibodies (B) are proteins produced by the immune system to neutralize pathogens. Proteins (C) are essential macromolecules for various cellular functions but do not specifically regulate metabolic functions in other cells like hormones do.
Which colour change is observed when water is added to anhydrous cobalt(II) chloride?
- A. blue to white
- B. blue to pink
- C. white to blue
- D. pink to blue
Correct Answer: B
Rationale: The correct answer is B: blue to pink. Anhydrous cobalt(II) chloride is blue, and when water is added, it forms a pink hexahydrate complex. This color change occurs because water molecules replace the chloride ions in the crystal lattice, resulting in the formation of the pink complex. Choice A (blue to white) is incorrect because the addition of water does not change the color to white. Choice C (white to blue) is incorrect as anhydrous cobalt(II) chloride is blue to begin with. Choice D (pink to blue) is incorrect as the addition of water causes the color change from blue to pink, not the other way around.
Bronzing:
- A. always accompanies hyperglycemia.
- B. is the most prominent symptom of Cushing syndrome.
- C. is characteristic of chronic adrenal cortical insufficiency (Addison’s disease).
- D. is a consequence of ADH insufficiency.
Correct Answer: C
Rationale: Rationale: Bronzing is a characteristic symptom of chronic adrenal cortical insufficiency (Addison's disease) due to increased production of melanin. In this condition, the adrenal glands do not produce enough steroid hormones, leading to skin hyperpigmentation. This differs from hyperglycemia (choice A), Cushing syndrome (choice B), and ADH insufficiency (choice D), which do not directly cause bronzing. Therefore, the correct choice is C.
Some medications for relief of cold/allergy symptoms contain pseudoephedrine, which acts as a decongestant. If a patient who is taking an MAO inhibitor takes pseudoephedrine, what is the likely outcome?
- A. Acute bronchospasm/asthma due to ACh release from the adrenal medulla
- B. Hypertensive crisis, possible stroke
- C. Heart rate and contractile force would drop significantly and quickly
- D. The cold symptoms would quickly get worse (increased secretions)
Correct Answer: B
Rationale: Step 1: MAO inhibitors prevent the breakdown of neurotransmitters like norepinephrine.
Step 2: Pseudoephedrine stimulates the release of norepinephrine.
Step 3: The combination can lead to excessive norepinephrine, causing hypertension and potential stroke.
Therefore, the likely outcome when a patient taking an MAO inhibitor also takes pseudoephedrine is a hypertensive crisis and possible stroke (Choice B).
Summary:
- Choice A (acute bronchospasm/asthma due to ACh release from the adrenal medulla) is incorrect because pseudoephedrine does not directly cause this response.
- Choice C (heart rate and contractile force would drop significantly and quickly) is incorrect as pseudoephedrine tends to increase heart rate and blood pressure.
- Choice D (the cold symptoms would quickly get worse - increased secretions) is incorrect as pseudoephedrine is a decongestant and would not worsen cold symptoms