MCAT Biology : Endocrine System

Study concepts, example questions & explanations for MCAT Biology

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Example Questions

Example Question #21 : Hormone Mechanisms And Effects

A patient has a condition where the adrenal cortex is unable to be stimulated by adrenocorticotropic hormone (ACTH). Based on this condition, which of the following is true?

Possible Answers:

The patient will have low blood pressure

Sodium levels will be elevated in the blood

Cortisol secretion will increase

Aldosterone secretion will increase

Correct answer:

The patient will have low blood pressure

Explanation:

Addison's disease is a disorder in which the adrenal cortex is unable to be stimulated by adrenocorticotropic hormone (ACTH). The adrenal cortex is responsible for the secretion of aldosterone and cortisol. Aldosterone is responsible for the increased reabsorption of sodium and increased excretion of potassium, leading to water retention. This process helps raise the blood pressure. Since aldosterone is not being adequately produced in a patient with Addison's disease, the patient's blood pressure will be lower than normal.

Example Question #22 : Hormone Mechanisms And Effects

Which of the following is not a function of estrogen?

Possible Answers:

Increases fat storage

Binds to a DNA hormone response element

Promotes postpartum lactation

Triggers the onset of ovulation

Correct answer:

Promotes postpartum lactation

Explanation:

Estrogen is a very versatile hormone that regulates several biological processes, including structural roles (such as increasing fat stores and developing female reproductive organs) and reproductive roles (such as promoting ovulation and preparing the uterine lining to support a fertilized egg). In order for estrogen to have such diverse effects, it enters the cell and binds to the estrogen receptor. The estrogen-receptor complex translocates to the nucleus and binds to hormone response elements (also call estrogen response elements) to activate target gene expression. Finally, although estrogen plays a role in the differentiation and formation of the milk duct system, following birth estrogen levels are dramatically reduced because high levels of estrogen inhibit lactation.

Example Question #31 : Hormone Mechanisms And Effects

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

High blood volume

No conclusion can be drawn

Normal 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 #32 : Hormone Mechanisms And Effects

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

Possible Answers:

Gluconeogenesis

Glycogenesis

Glycogenolysis

Beta-oxidation

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 #33 : Hormone Mechanisms And Effects

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

Possible Answers:

Decreased basal metabolic rate

Increased cortisol secretion

Increased sodium excretion

Increased 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 #34 : Hormone Mechanisms And Effects

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

Possible Answers:

Increase blood calcium

Decrease blood calcium

Increase blood phosphate

Decrease 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 #35 : Hormone Mechanisms And Effects

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

Testosterone

Luteinizing hormone

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 #36 : Hormone Mechanisms And Effects

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

Possible Answers:

Estrogen

Testosterone

Adrenocorticotropic hormone

Cortisol

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 #37 : Hormone Mechanisms And Effects

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 #92 : 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

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

Groups A and D

Group C

None of the groups

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.

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