MCAT Biology : Hormone Mechanisms and Effects

Study concepts, example questions & explanations for MCAT Biology

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Example Questions

Example Question #93 : Endocrine System

Persons with diabetes mellitus have abnormally elevated blood glucose levels. In an attempt to rid the body of excess glucose, the kidneys filter the glucose into the urine for excretion. The amount of glucose in the urine overwhelms the kidneys, which are unable to reabsorb the glucose during concentration of the urine in the nephrons. What would be the blood volume status of a patient with uncontrolled diabetes mellitus?

Possible Answers:

Low blood volume

Normal blood volume

No conclusion can be drawn

High blood volume

Correct answer:

Low blood volume

Explanation:

Water moves to regions where solute concentrations are high. Because the kidney is unable to reabsorb the filtrate glucose, the urine has a high osmolarity and will draw water into the collecting duct to balance solute concentrations. The water that was part of the filtered blood volume is usually reabsorbed, but instead will be excreted. This excess loss of water will lead to decreased blood volume.

Example Question #691 : Systems Biology And Tissue Types

What process is increased through the action of insulin when glucose levels in the blood are high?

Possible Answers:

Beta-oxidation

Gluconeogenesis

Glycogenolysis

Glycogenesis

Correct answer:

Glycogenesis

Explanation:

When blood glucose levels are high, the body seeks to store this additional glucose as glycogen and fat. Glycogen is stored in a process called glycogenesis, which is mainly performed in the liver. Fat can also be produced by running glycolysis and using the acetyl-CoA products to create long-chain fatty acids. Glycogenesis is stimulated by insulin action.

In contrast, when glucose is low glycogenolysis, beta-oxidation, and gluconeogenesis all occur in order to restore glucose levels. Glycogenolysis is the break down of glycogen to produce glucose. Beta-oxidation is used to produce ketone bodies as alternative energy. Gluconeogenesis is the process of making glucose from non-carbohydrates.

Example Question #692 : Systems Biology And Tissue Types

Thyroid hormones T3 and T4 are responsible for which of the following actions?

Possible Answers:

Increased sodium excretion

Increased basal metabolic rate

Increased cortisol secretion

Decreased basal metabolic rate

Correct answer:

Increased basal metabolic rate

Explanation:

The thyroid hormones, T3 (triiodothyronine) and T4 (tetraiodothyronine), are synthesized and released from the thyroid gland after stimulation by thyroid-stimulating hormone (TSH) from the anterior pituitary. These two hormones serve to increase the basal metabolic rate in humans.

Cortisol secretion is stimulated by adrenocorticotropic hormone (ACTH) from the anterior pituitary, while sodium excretion is increased by atrial natriuretic hormone from the cardiomyocytes.

Example Question #96 : Endocrine System

Calcitonin, secreted from the thyroid gland, is responsible for which of the following actions?

Possible Answers:

Decrease blood phosphate

Increase blood calcium

Decrease blood calcium

Increase blood phosphate

Correct answer:

Decrease blood calcium

Explanation:

Calcitonin generally antagonizes the effect of parathyroid hormone (PTH). When the c-cells of the thyroid sense a high calcium level, they will secrete calcitonin. Calcitonin then serves to inhibit osteoclasts and stimulate osteoblasts, promoting osteogenesis and sequestration of blood calcium into the bone matrix.

In contrast, parathyroid hormone stimulated osteoclasts and inhibits osteoblasts, causing degeneration of the bone matrix and increase in blood calcium levels.

Example Question #97 : Endocrine System

Which hormone is secreted by the developing placenta and stimulates the corpus luteum to grow and release estrogen and progesterone?

Possible Answers:

Follicle-stimulating hormone

Human chorionic gonadotropin

Luteinizing hormone

Testosterone

Correct answer:

Human chorionic gonadotropin

Explanation:

Human chorionic gonadotropin is a water-soluble hormone that is secreted from the placenta, and stimulates the corpus luteum to grow and release estrogen and progesterone. It is vital for the maintenance of the uterine environment for the fetus to grow and develop.

Luteinizing hormone and follicle-stimulating hormone regulate ovulation and the menstrual cycle, while testosterone is responsible for development of male secondary sex characteristics.

Example Question #98 : Endocrine System

Which steroid hormone, produced in the male testes, is responsible for the development of secondary sexual characteristics in males?

Possible Answers:

Testosterone

Cortisol

Adrenocorticotropic hormone

Estrogen

Correct answer:

Testosterone

Explanation:

Testosterone is produced by the Leydig cells of the testes after stimulation by luteinizing hormone. Testosterone is responsible for the development of male secondary sexual characteristics such as deeper voices, increased muscle mass, testicular development, and pubic hair. 

Adrenocorticotropic hormone promotes release of cortisol in response to prolonged stressors, and estrogen is responsible for the development of sexondary sex characteristics in females.

Example Question #99 : Endocrine System

A scientist created a new drug that was found to have very similar chemical properties to testosterone. What is the most likely mechanism of action of this drug?

Possible Answers:

The drug binds to extracellular receptors on the surface of organs

The drug is most likely ineffective

The drug binds to the plasma membrane or to receptors in the cytosol

The drug binds to a receptor on the cell membrane and triggers secondary messengers

The drug passes through the plasma membrane and elicits effects inside the cell

Correct answer:

The drug passes through the plasma membrane and elicits effects inside the cell

Explanation:

There are three main classes of hormones: peptide hormones, steroid hormones, and tyrosine-derivatives. Peptide hormones act by binding to plasma membrane receptors. They are large and polar, preventing them from crossing the plasma membrane. Steroid hormones and tyrosine-derivatives, on the other hand, are lipid soluble and are able to cross through the plasma membrane and bind to receptors in the cytosol.

We know from the base of the question that this drug has similar chemical properties to testosterone. Testosterone is a steroid hormone; thus, our drug likely acts in a similar manner to steroid hormones by crossing the membrane and entering the cell to elicit its effects.

Example Question #701 : Systems Biology And Tissue Types

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

Diabetes is indicated by increased fasting blood glucose levels, while glucose intolerance is defined by elevated blood glucose levels following a glucose challenge. Assuming proper experimental design, which groups can be diagnosed with diabetes?

Elevated levels are accepted as being above 120mg/dL.

Possible Answers:

Groups B and C

None of the groups

Groups A and D

Group C

Correct answer:

None of the groups

Explanation:

None of the groups have a pre-injection blood glucose level greater than 120mg/dL, indicating that none of the groups have diabetes.

Groups B and C, however, have elevated final blood glucose levels after the glucose challenge, indicating that these groups have glucose intolerance.

Example Question #31 : 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

Why is it important that the mice were fasted?

Possible Answers:

The mice should not be fasted

To ensure that initial insulin levels are low

To control for altered blood glucose levels due to uncontrolled meal consumption

To ensure that the full dose of glucose will enter the blood stream

To ensure the mice are hungry enough to consume glucose

Correct answer:

To control for altered blood glucose levels due to uncontrolled meal consumption

Explanation:

The mice need to be fasted to control for consuming meals at irregular times. For example, if one mouse ate shortly before the test, it would have higher blood glucose levels than a mouse that did not, which would complicate the results. Fasting ensures that the mice have a controlled base blood glucose level before the injection.

Because the mice are injected with glucose, the mice do not need to orally consume the glucose for the test. While low blood glucose after a fast will also lower insulin levels, the insulin levels are never measured in the experiment and would not be a good explanation for fasting the mice.

Example Question #102 : 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

Insulin production can be altered due to reduced numbers of beta cells or due to less efficient beta cells. Which of the following methods cannot be used to distinguish between these two defects?

Possible Answers:

Calculating the rate of beta cell death

Any of these methods could be used

Measuring the amount of insulin in the pancreas

Calculating the total mass of beta cells

Measuring insulin secretion in response to glucose from equal-sized cell samples

Correct answer:

Measuring the amount of insulin in the pancreas

Explanation:

The total amount of pancreatic insulin is affected by the number of beta cells and the amount of insulin produced by each beta cell; therefore, an increase or reduction of pancreatic insulin cannot be used to distinguish the two possibilities. Insulin levels in the pancreas could be reduced due to lower cell numbers or due to less production from a large number of cells. There is no way to differentiate these two causes.

Measuring the mass of beta cells, and to an extent calculating the amount of beta cell death, can determine if there are fewer beta cells in the pancreas. Additionally, using an equal number of beta cells and measuring insulin secretion can determine if beta cell function is impaired.

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