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Being lipid soluble, steroids can do all the following EXCEPT:
- A. catalyze cyclic AMP
- B. diffuse through the plasma membranes of target cells
- C. enter the nucleus
- D. activate genes to transcribe mRNA for protein synthesis
Correct Answer: A
Rationale: Step 1: Steroids are lipid-soluble molecules, allowing them to easily diffuse through the plasma membrane of target cells.
Step 2: Once inside the cell, steroids can enter the nucleus to bind to specific receptors and regulate gene expression.
Step 3: Steroids do not catalyze cyclic AMP; this function is typically associated with non-steroid hormones like adrenaline.
Step 4: Therefore, the correct answer is A because steroids do not catalyze cyclic AMP, unlike other hormones.
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Which glands are responsible for the regulation of calcium levels in the blood?
- A. Parathyroid and thyroid
- B. Adrenal medulla and pancreas
- C. Testes
- D. Parathyroid and thymus
Correct Answer: A
Rationale: The correct answer is A: Parathyroid and thyroid. The parathyroid glands produce parathyroid hormone (PTH), which regulates calcium levels in the blood by increasing calcium absorption from the intestines and releasing calcium from bones. The thyroid gland produces calcitonin, which helps lower blood calcium levels by promoting calcium deposition in bones. The other choices (B: Adrenal medulla and pancreas, C: Testes, D: Parathyroid and thymus) are incorrect because they do not play a direct role in regulating calcium levels in the blood.
The posterior pituitary stores and releases .
- A. prolactin and oxytocin
- B. oxytocin and antidiuretic hormone (ADH)
- C. ADH and growth hormone
- D. growth hormone and prolactin
Correct Answer: B
Rationale: The correct answer is B: oxytocin and antidiuretic hormone (ADH).
1. The posterior pituitary stores and releases oxytocin and ADH.
2. Oxytocin is responsible for uterine contractions and milk ejection.
3. ADH regulates water balance by controlling water reabsorption in the kidneys.
Therefore, B is the correct answer.
A, C, and D are incorrect because prolactin, growth hormone, and other hormones are not stored or released by the posterior pituitary.
Blood levels of which of the following substances is decreased in Graves disease?
- A. Triiodothyronine (T3)
- B. Thyroxine (T4)
- C. Diiodotyrosine (DIT)
- D. Thyroid-stimulating hormone (TSH)
Correct Answer: D
Rationale: In Graves disease, there is an overproduction of thyroid hormones due to autoimmune stimulation. Thyroid-stimulating hormone (TSH) is decreased because the excessive thyroid hormones suppress its production through negative feedback. A and B are incorrect because both T3 and T4 levels are elevated in Graves disease. C is incorrect as DIT is a precursor to thyroid hormones and its levels may not necessarily be decreased in Graves disease.
Atropine:
- A. Is a competitive neuromuscular blocker
- B. Induces bradycardia
- C. Stimulates GIT motility and secretion
- D. Produces mydriasis
Correct Answer: D
Rationale: Step 1: Atropine is an anticholinergic drug that blocks muscarinic receptors.
Step 2: Blocking muscarinic receptors in the eye leads to dilation of the pupil, known as mydriasis.
Step 3: Therefore, the correct answer is D, as atropine indeed produces mydriasis.
Summary: A is incorrect because atropine is not a neuromuscular blocker. B is incorrect as atropine actually induces tachycardia. C is incorrect as atropine inhibits GIT motility and secretion.
Peptide hormones function by binding to receptor proteins within the ________. Once the hormone binds to a receptor, it activates ______.
- A. cell: a second messenger
- B. cell: particular genes
- C. plasma membrane: a second messenger
- D. plasma membrane: particular genes
Correct Answer: C
Rationale: The correct answer is C because peptide hormones typically bind to receptor proteins on the plasma membrane. This is because peptide hormones are not able to pass through the cell membrane due to their size and polarity. Once the hormone binds to the receptor on the plasma membrane, it activates a second messenger system within the cell, leading to various cellular responses.
Choice A is incorrect because peptide hormones do not bind directly to intracellular components like second messengers inside the cell. Choice B is incorrect because peptide hormones do not directly activate particular genes within the cell. Choice D is incorrect because peptide hormones do not bind directly to genes on the plasma membrane.