GRE Subject Test: Biology : Understanding Hormone Functions

Study concepts, example questions & explanations for GRE Subject Test: Biology

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Example Questions

Example Question #81 : Endocrine System

The interaction between blood pressure and kidney function in humans requires coordination by the renin-angiotensin-aldosterone system (RAAS). This system involves the dynamic interplay of the kidneys, lungs, and blood vessels to carefully regulate sodium and water balance.

A normal human kidney has cells adjacent to the glomerulus called juxtaglomerular cells. These cells sense sodium content in urine of the distal convoluted tubule, releasing renin in response to a low level. Renin is an enzyme that converts angiotensinogen to angiotensin I (AI). AI is converted to angiotensin II (AII) by angiotensin converting enzyme (ACE) in the lung.

AII stimulates aldosterone secretion in the zona glomerulosa of the adrenal gland. Aldosterone then acts to upregulate the sodium-potassium pump on the basolateral side of distal tubule epithelial cells to increase sodium reabsorption from the urine, as well as increasing potassium excretion.

Renin is most likely to drive the formation of angiotensin I from angiotensinogen by doing which of the following?

I. Increasing the concentration of angiotensinogen

II. Lowering the activation energy of the reaction from angiotensinogen to angiotensin I

III. Stabilizing the angiotensin I molecule to lower the energy of the products

Possible Answers:

I,II, and III

III only

II and III

I only

II only

Correct answer:

II only

Explanation:

Renin, as the passage establishes, is an enzyme. Enzymes always work by leaving the thermodynamic energies of the products and reactants the same, but lower activation energy of the reaction. Angiotensinogen is released by the liver, and converted by renin to angiotensin I. Renin does not directly act on the liver to stimulate angiotensinogen release.

Example Question #2 : Endocrine System

What is the name of the hormone responsible for raising blood calcium levels?

Possible Answers:

Calcitonin

Parathyroid hormone

Thyroxine

Glucagon

Correct answer:

Parathyroid hormone

Explanation:

Blood calcium levels are controlled primarily by two hormones: parathyroid hormone and calcitonin. Calcitonin is synthesized by the thyroid gland and decreases blood calcium levels. Parathyroid hormone acts as an antagonist to calcitonin and raises blood calcium levels.

Thyroxine, or T4, is a thyroid hormone involved in increasing basal metabolic rate. Glucagon stimulates the liver to release glucose into the blood, and raise blood glucose levels.

Example Question #3 : Endocrine System

What is the purpose of antidiuretic hormone in the body?

Possible Answers:

Increases blood calcium levels

Lowers the blood pressure

Concentrates the urine

Raises the basal metabolic rate

Correct answer:

Concentrates the urine

Explanation:

Antidiuretic hormone is released by the posterior pituitary gland, and acts on the kidneys in order to concentrate the urine. Alcohol can inhibit ADH, which can result in excessive urine production and potential dehydration.

Example Question #4 : Endocrine System

Which of the following hormones will increase cortisol secretion in a normal individual?

Possible Answers:

Aldosterone

Thyroid stimulating hormone

Luteinizing hormone

Adrenocorticotropic hormone

Correct answer:

Adrenocorticotropic hormone

Explanation:

Cortisol is secreted by the adrenal gland. We need to identify the hormone responsible for stimulating the adrenal gland and prompting it to release cortisol. This job is accomplished by adrenocorticotropic hormone (or ACTH). While aldosterone is secreted by the adrenal gland, it does not impact the release of cortisol to any significant degree.

Example Question #1 : Understanding Hormone Functions

Which of the following features would you expect to see in an individual with a deficient posterior pituitary gland?

Possible Answers:

Low testosterone levels

Reduced basal metabolic rate

Dehydration

Low blood calcium levels

Correct answer:

Dehydration

Explanation:

The two main hormones of interest that are secreted by the posterior pituitary gland are antidiuretic hormone (ADH) and oxytocin. Antidiuretic hormone plays a key role in retaining water at the level of the kidney. In patients with no ADH, fluid retention is severely diminished. Symptoms of this include frequent urination, hyperosmolality, and dehydration.

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