MCAT Biology Review
Chapter 5: The Endocrine System
1. Which of the following associations between a hormone and its category is INCORRECT?
2. Testosterone—cortical sex hormone
2. Which of the following hormones directly stimulates a target tissue that is NOT an endocrine organ?
3. Increased synthetic activity of the parathyroid glands would lead to:
1. an increase in renal calcium reabsorption.
2. a decrease in the rate of bone resorption.
3. a decrease in basal metabolic rate.
4. a decrease in blood glucose concentration.
4. Which of the following statements concerning growth hormone is NOT true?
1. Overproduction of growth hormone in adults results in acromegaly.
2. It promotes growth of bone and muscle.
3. It is produced by the hypothalamus but secreted by the pituitary.
4. A childhood deficiency in growth hormone results in dwarfism.
5. Iodine deficiency may result in:
6. A patient has a very high TSH level. Which of the following would NOT cause a high TSH level?
1. Autoimmune destruction of thyroid cells that produce T3 and T4.
2. A tumor in the hypothalamus that secretes high levels of TRH.
3. High levels of T4 from thyroid replacement medications.
4. Cancerous growth of parafollicular cells in the thyroid, destroying other cell types in the organ.
7. Which of the following hormones is NOT derived from cholesterol?
8. Which of the following is true regarding pancreatic somatostatin?
1. Its secretion is increased by low blood glucose.
2. It is always inhibitory.
3. It is regulated by cortisol levels.
4. It stimulates insulin and glucagon secretion.
9. Destruction of all β-cells in the pancreas would cause:
1. glucagon secretion to stop and a decrease in blood glucose concentration.
2. glucagon secretion to stop and an increase in blood glucose concentration.
3. insulin secretion to stop and an increase in blood glucose concentration.
4. insulin secretion to stop and a decrease in blood glucose concentration.
10.Which of the following is FALSE regarding aldosterone regulation?
1. Renin converts the plasma protein angiotensinogen to angiotensin I.
2. Angiotensin II stimulates the adrenal cortex to secrete aldosterone.
3. Angiotensin I is converted to angiotensin II by angiotensin-converting enzyme.
4. A decrease in blood oxygen concentrations stimulates renin production.
11.A scientist discovers a new hormone that is relatively large in size and triggers the conversion of ATP to cAMP. Which of the following best describes the type of hormone that was discovered?
1. Amino acid-derivative hormone
2. Peptide hormone
3. Steroid hormone
4. Tropic hormone
12.A patient presents with muscle weakness, slow movement, and calcium deposits in his tissues. A blood test reveals very low calcium levels in the blood. Administration of which the following would be an appropriate treatment for the blood test findings?
2. Parathyroid hormone
13.Oxytocin and antidiuretic hormone are:
1. peptide hormones produced and released by the pituitary.
2. steroid hormones produced and released by the pituitary.
3. peptide hormones produced by the hypothalamus and released by the pituitary.
4. steroid hormones produced by the hypothalamus and released by the pituitary.
14.Excessive levels of dopamine in the brain are associated with psychosis. Accordingly, many antipsychotic medications block dopamine receptors. Which of the following effects may be seen in an individual taking antipsychotics?
1. Increased secretion of growth hormone
2. Decreased secretion of growth hormone
3. Increased secretion of prolactin
4. Decreased secretion of prolactin
15.A genotypically female infant is born with ambiguous genitalia. Soon after birth, she suffers from hyponatremia, or low blood concentrations of sodium. Which endocrine organ is most likely to be affected?
4. Adrenal cortex
Answers and Explanations
Unlike the other hormones listed here, ADH is not secreted by the adrenal cortex and is therefore not a –corticoid. Rather, ADH is a peptide hormone produced by the hypothalamus and released by the posterior pituitary that promotes water reabsorption. The other associations are all correct.
A hormone that directly stimulates a non-endocrine target tissue is referred to as a direct hormone. Glancing at the answer choices, we notice that all of the hormones are secreted by the anterior pituitary gland. The direct hormones secreted by the anterior pituitary are prolactin, endorphins, and growth hormone (GH). All of the other answer choices are tropic hormones; the tropic hormones of the anterior pituitary include follicle-stimulating hormone (FSH), luteinizing hormone (LH), adrenocorticotropic hormone (ACTH), and thyroid-stimulating hormone (TSH).
The parathyroid glands secrete parathyroid hormone (PTH), a hormone that functions to increase blood calcium levels. An increase in synthetic activity of the parathyroid glands would lead to an increase in PTH and, therefore, an increase in blood calcium levels through three mechanisms: increased calcium reabsorption in the kidneys (decreased excretion), increased bone resorption, and increased absorption of calcium from the gut (via activation of vitamin D).
Growth hormone is a direct hormone secreted by the anterior pituitary. Among its many functions, GH promotes growth in bone and muscle, eliminating choice (B). An overproduction of growth hormone in children results in gigantism, whereas in adults it results in acromegaly (enlargement of the small bones in the extremities and of certain facial bones, such as the jaw), eliminating choice (A). On the other hand, a childhood deficiency of growth hormone results in dwarfism, eliminating choice (D). GH is synthesized and secreted in the anterior pituitary;choice (C) describes antidiuretic hormone and oxytocin, not GH.
Inflammation of the thyroid or iodine deficiency can cause hypothyroidism, in which the thyroid hormones are undersecreted or not secreted at all. Hypothyroidism in newborn infants causes cretinism, which is characterized by poor neurological and physical development (including mental retardation, short stature, and coarse facial features). While iodine deficiency can result in a swelling of the thyroid gland (called a goiter), which can also be seen in causes of hyperthyroidism, iodine deficiency does not cause hyperthyroidism, eliminating choice (D). Galactorrhea, choice (A), is associated with prolactin; gigantism, choice (C), is associated with growth hormone.
The hypothalamic–pituitary–thyroid axis includes the secretion of thyroid-releasing hormone (TRH) from the hypothalamus stimulating the secretion of thyroid-stimulating hormone (TSH) from the anterior pituitary, which stimulates the secretion of triiodothyronine (T3) and thyroxine (T4) from the thyroid. Overproduction of TRH would promote overproduction of TSH, eliminating choice (B). Destruction of the follicular cells that produce T3 and T4 would remove negative feedback, allowing TSH levels to rise, eliminating choices (A) and (D). High levels of T4 would cause too much negative feedback and lower TSH levels, making choice (C) the correct answer.
Steroid hormones are derived from cholesterol. Many of their names end with –one, –ol, or –oid, and they include the hormones of the adrenal cortex and gonads. Aldosterone is a mineralocorticoid from the adrenal cortex, while estrogen and progesterone are sex hormones from the ovaries, eliminating choices (A), (B), and (D). Oxytocin is a peptide hormone and is thus not derived from cholesterol. Peptide and amino acid-derivative hormones often end with –in or –ine.
Pancreatic somatostatin secretion is increased by high blood glucose or amino acid levels, leading to both decreased insulin and glucagon secretion, eliminating choices (A) and (D). Somatostatin is thus always an inhibitory hormone, confirming choice (B). The stimuli for somatostatin release include high blood glucose or amino acids, as mentioned above, as well as certain gastrointestinal hormones, as is discussed in Chapter 9 of MCAT Biology Review—but not cortisol, eliminating choice (C).
β-cells are responsible for insulin production. The function of insulin is to lower blood glucose levels by promoting the influx of glucose into cells and by stimulating anabolic processes, such as glycogenesis or fat and protein synthesis. Thus, destruction of the β-cells would result in a cessation of insulin production, which would lead to hyperglycemia, or high blood glucose concentrations.
The stimulus for renin production is low blood pressure, which causes the juxtaglomerular cells of the kidney to produce renin, an enzyme that converts the plasma protein angiotensinogen to angiotensin I. Angiotensin I is then converted to angiotensin II by an enzyme in the lungs; angiotensin II ultimately stimulates the adrenal cortex to secrete aldosterone. Aldosterone helps to restore blood volume by increasing sodium reabsorption in the kidney, leading to an increase in water reabsorption. This removes the initial stimulus for renin production. Thus,choices (A), (B), and (C) correctly describe the renin–angiotensin–aldosterone system, while choice (D) describes the stimulus for erythropoietin secretion.
The question stem indicates that the newly discovered hormone functions as a first messenger, stimulating the conversion of ATP to cAMP; cAMP functions as a second messenger, triggering a signaling cascade in the cell. Hormones that act via secondary messengers and are relatively large in size (short peptides or complex polypeptides) are peptide hormones. This hormone could be a tropic hormone, but it is also entirely possible for it to be a direct hormone; thus, choice (D) can be eliminated.
Regardless of the cause, the low levels of calcium in the blood require treatment. While other therapies are more frequently used to treat hypocalcemia (low blood calcium levels), such as calcium gluconate or calcium chloride, administration of parathyroid hormone would also raise blood calcium concentration. Calcitonin would be a poor choice in this case, as this hormone lowers blood calcium concentrations, eliminating choice (A). Aldosterone and thymosin play no role in calcium homeostasis, eliminating choices (C) and (D).
Both oxytocin and vasopressin (another name for antidiuretic hormone) end with the suffix –in; this should hint that they are peptide or amino acid-derivative hormones. These two hormones are both synthesized by the hypothalamus, but released by the posterior pituitary. Remember that the posterior pituitary does not actually synthesize any hormones itself; rather, it contains the axons of cells originating in the hypothalamus and is the site of release for these hormones.
Dopamine is used in a number of neurological systems; most relevant to the endocrine system is the fact that dopamine secretion prevents prolactin release. Thus, an individual taking medications that block dopamine receptors would lose this inhibition on prolactin release and have elevated prolactin levels.
The question stem states that an infant who is genotypically female is born with ambiguous genitalia, meaning that the genitalia do not appear to be specifically female or specifically male. In a genotypic female, this indicates that she was exposed to androgens during the fetal period. In addition, she is also losing sodium, causing hyponatremia. This indicates that she has two defects. First, she has excess androgens. Second, she is lacking in aldosterone, a hormone required for proper reuptake of sodium in the kidneys. Both of these hormones are synthesized in the adrenal cortex, making choice (D) the correct answer. Note that neither of these hormones is regulated by the hypothalamic–pituitary–adrenal axis, eliminating choices (A) and (B).