MCAT Biology : Hormone Mechanisms and Effects

Study concepts, example questions & explanations for MCAT Biology

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Example Questions

Example Question #101 : Endocrine System

Type II diabetes results from defective pancreatic beta cells and increased insulin resistance, indicating that peripheral tissues (such as skeletal muscle) do not properly respond to insulin.

Mouse models have been developed to model type II diabetes. In addition to global mutations, tissue-specific mutations can be used to delete genes of interest in precise regions of the body. A group of investigators is interested in characterizing the role of the gene Dia in the onset of diabetes.

Four groups of male mice are compared. Group A is a control group, group B has a global deletion of Dia, group C has a beta cell-specific Dia mutation, and group D has a skeletal muscle-specific Dia mutation.

In order to measure the ability of these mice to respond to a glucose challenge, the mice are fasted overnight. Following the fast, their blood glucose levels are measured (in mg/dL). The mice are then injected with two grams of glucose, and blood glucose levels are measured at 30, 60, 90, and 120 minutes post-injection.

 

0 min

30 min

60 min

90 min

120 min

Group A

80

150

120

90

80

Group B

90

220

180

160

140

Group C

100

260

190

150

135

Group D

75

145

110

90

75

Assuming proper experimental design, which groups have impaired glucose clearance?

Possible Answers:

Group B

Groups B and C

Group D

Group C

Groups A and D

Correct answer:

Groups B and C

Explanation:

Assuming proper experimental design, group A should be used as a baseline for "normal" glucose clearance rate. Any groups showing glucose levels higher than group A demonstrate impaired clearance.

Group A and group D show similar trends, with similar values for the initial and final blood glucose samples. This indicates that the injection was cleared from the blood completely over the 2-hour sample period.

Group B and C, however, show higher blood glucose levels after two hours than their initial levels, indicating that they were unable to completely clear the injected glucose from the blood during this period. Although, the glucose levels decrease after the injection, the glucose levels after two hours are still greatly elevated compared to fasting levels, suggesting a defect in glucose tolerance.

Example Question #42 : Hormone Mechanisms And Effects

Type II diabetes results from defective pancreatic beta cells and increased insulin resistance, indicating that peripheral tissues (such as skeletal muscle) do not properly respond to insulin.

Mouse models have been developed to model type II diabetes. In addition to global mutations, tissue-specific mutations can be used to delete genes of interest in precise regions of the body. A group of investigators is interested in characterizing the role of the gene Dia in the onset of diabetes.

Four groups of male mice are compared. Group A is a control group, group B has a global deletion of Dia, group C has a beta cell-specific Dia mutation, and group D has a skeletal muscle-specific Dia mutation.

In order to measure the ability of these mice to respond to a glucose challenge, the mice are fasted overnight. Following the fast, their blood glucose levels are measured (in mg/dL). The mice are then injected with two grams of glucose, and blood glucose levels are measured at 30, 60, 90, and 120 minutes post-injection.

 

0 min

30 min

60 min

90 min

120 min

Group A

80

150

120

90

80

Group B

90

220

180

160

140

Group C

100

260

190

150

135

Group D

75

145

110

90

75

What flaws exist in the experimental design?

Possible Answers:

Both males and females should have been included to get accurate results

Blood glucose levels should have been measured every 15 minutes

The mice should have been injected both before and after fasting

The amount of glucose injected should have been adjusted according to mouse weight

The mice should not have been fasted

Correct answer:

The amount of glucose injected should have been adjusted according to mouse weight

Explanation:

The investigators are measuring for a relationship between blood glucose level and genetic mutation. They must isolate the variation between samples to only the genetic mutation in order to get accurate results. Variation in weight will alter the blood volume and metabolism of glucose in the blood, resulting in an uncontrolled variable. The investigators needed to weigh the mice, and provide different injection amounts based on the different mouse weights. As the experiment currently stands, heavier mice will metabolize the glucose injection faster than lighter mice.

While it may be important to eventually analyze the Dia gene in females, they should not be included in the same study as males because males and females can have different rates of clearing blood glucose. The exclusion of females limits the data, but does not result in a design flaw. Similarly, sampling data every 15 minutes would give more data points (more information), but sampling every 30 minutes does not represent a design flaw. Finally, the mice need to be fasted to eliminate the possibility of a mouse eating shortly before the test, complicating the results. Injecting the mice before and after fasting would neither increase, nor decrease the validity of the results, and does not represent a design flaw.

Example Question #101 : Endocrine System

Gigantism is a rare condition that is the result of hypersecretion of growth hormone from the anterior pituitary during childhood. Symptoms of gigantism include abnormal height (several standard deviations above average) and abnormal growth of the face, hands, and feet. 

Functions of growth hormone are best decribed by which of the following?

Possible Answers:

Increased glyconeogenesis in the liver and increased muscle mass

Increased liver uptake of glucose and decreased lipolysis

Increased protein synthesis and decreased mineralization of bone

Increased calcium retention and stimulation of the immune system

Correct answer:

Increased calcium retention and stimulation of the immune system

Explanation:

Growth hormone (GH) causes increased calcium retention and stimulation of the immune system. It reduces liver uptake of glucose and increases lipolysis. Growth hormone also causes increased protein synthesis, muscle mass, bone mineralization, and gluconeogenesis. 

Example Question #44 : Hormone Mechanisms And Effects

Which anterior pituitary hormone is most responsible for facilitating sperm development in the testes?

Possible Answers:

Luteinizing hormone (LH)

Thyroid-stimulating hormone (TSH)

Adrenocorticotropic hormone (ACTH)

Follicle-stimulating hormone (FSH)

Correct answer:

Follicle-stimulating hormone (FSH)

Explanation:

The following answer choices are all examples of anterior pituitary hormones, however, follicle-stimulating hormone (FSH) is the hormone that acts on Sertoli cells in the testes to nourish sperm and facilitate spermatogenesis.

Luteinizing hormone (LH) acts on the testes, but works on Leydig cells in producing testosterone. Adrenocorticotropic hormone (ACTH) and thyroid-stimulating hormone (TSH) do not act on the testes.

Example Question #45 : Hormone Mechanisms And Effects

Which of the following hormones would show the highest levels when the parasympathetic nervous system is active?

Possible Answers:

Cortisol

Insulin

Epinephrine

Aldosterone

Correct answer:

Insulin

Explanation:

The parasympathetic nervous system is responsible for the "rest and digest" functions of the body. When digesting, the body will be storing nutrients, converting them to fat and glycogen in the liver and other tissues of the body. Insulin is responsible for the lowering of blood glucose levels and storing glucose as glycogen in the liver.

All the other hormone options would be seen when the body is active and under stress. Cortisol is triggered during long-term stress, while epinephrine is secreted in response to an immediate threat. Aldosterone is raised when water levels in the body are low, a sign of possible dehydration or drought.

Example Question #46 : Hormone Mechanisms And Effects

What hormone is secreted to control glucose levels when blood glucose is high?

Possible Answers:

Acetylcholine

Insulin

Glucagon

Oxytocin

Correct answer:

Insulin

Explanation:

When blood glucose is high, beta cells of the islets of Langerhans in the pancreas sense the high glucose and release insulin. Insulin binds to cells throughout the body and encourages production of additional glucose transporters on the cell surface in order to take up more glucose from the blood.

Glucagon, in contrast, is secreted when glucose levels are low and acts to prevent glucose uptake from the blood. It also stimulates gluconeogenesis and glycogenolysis.

Example Question #47 : Hormone Mechanisms And Effects

Which hormone is secreted to control blood glucose levels when blood glucose is low?

Possible Answers:

Glucagon

Insulin

Acetylcholine

Prolactin

Correct answer:

Glucagon

Explanation:

When blood glucose is low, alpha cells of the islets of Langerhans in the pancreas sense the low glucose and release glucagon. Glucagon acts to prevent glucose uptake from the blood and stimulates gluconeogenesis and glycogenolysis in the liver.

In contrast, insulin binds to cells throughout the body when glucose levels are high. Insulin encourages production of additional glucose transporters on the cell surface in order to take up more glucose from the blood.

Example Question #48 : Hormone Mechanisms And Effects

Decreased blood glucose levels would trigger release of all of the following hormones except __________.

Possible Answers:

cortisol

growth hormone

glucagon

insulin

Correct answer:

insulin

Explanation:

A decreased blood glucose level would cause growth hormone, glucagon, and cortisol release to protect from the effects of hypoglycemia. Growth hormone promotes cell replication, which indirectly stimulates other pathways to create free glucose. Glucagon increases glucose levels by stimulating gluconeogenesis in the liver and glycogen breakdown in the liver. Cortisol acts to increase free fatty acid levels and increases gluconeogenesis.

Insulin promotes glucose sequestration, further decreasing blood glucose.

Example Question #49 : Hormone Mechanisms And Effects

Which hormone decreases calcium levels in the blood?

Possible Answers:

Parathyroid hormone

Insulin

Calcitonin

Glucagon

Correct answer:

Calcitonin

Explanation:

Calcitonin, produced by the thyroid, decreases (or "tones down") the blood calcium level. Calcitonin decreases the amount of calcium in the blood by inhibiting the activity of osteoclasts, which break down bone and release calcium in the bloodstream. By inhibiting osteoclasts, calcitonin directly reduces the blood calcium level.

Parathyroid hormone, released by the parathyroid gland, increases the blood calcium level. Parathyroid hormone stimulates osteoclasts to break down bone and release calcium into the bloodstream. Insulin and glucagon are produced by the pancreas and are responsible for the regulation of blood glucose levels. Insulin lowers blood glucose and increases glycogen stores, while glucagon increases blood glucose by stimulating the conversion of glycogen to glucose in the liver. 

Example Question #50 : Hormone Mechanisms And Effects

What is the most likely hormonal response immediately following a significant blood loss?

Possible Answers:

Increased level of ADH

Increased level of ACTH

Increased level of calcitonin

Decreased level of insulin

Decreased level of ADH

Correct answer:

Increased level of ADH

Explanation:

Significant amount of blood loss results in a sudden and large drop in blood pressure due to the decreased fluid volume in the body. To compensate for this change, the body will attempt to increase fluid retention. This is directly accomplished by increasing the level of ADH (anti-diuretic hormone) that allows reabsorption of water in the kidneys. Therefore, increased ADH level is the best response.

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