GRE Subject Test: Biology : Endocrine System

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

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Example Questions

Example Question #1 : 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:

III only

II only

II and III

I only

I,II, and III

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 #1 : Understanding Hormone Functions

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

Possible Answers:

Glucagon

Thyroxine

Parathyroid hormone

Calcitonin

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 #1 : Understanding Hormone Functions

What is the purpose of antidiuretic hormone in the body?

Possible Answers:

Lowers the blood pressure

Increases blood calcium levels

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 #3 : Understanding Hormone Functions

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

Possible Answers:

Thyroid stimulating hormone

Luteinizing hormone

Aldosterone

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 #4 : 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 blood calcium levels

Reduced basal metabolic rate

Low testosterone levels

Dehydration

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.

Example Question #1 : Understanding Glands And Target Organs

Which gland releases hormones that help regulate blood glucose levels?

Possible Answers:

Anterior pituitary gland

Adrenal cortex

Pancreas

Parathyroid gland

Correct answer:

Pancreas

Explanation:

The two major hormones that control blood sugar levels are glucagon and insulin. Glucagon helps raise blood glucose levels, while insulin decreases blood sugar levels. Both of these hormones are created and secreted by the pancreas.

The parathyroid gland secretes parathyroid hormone, which stimulates the synthesis of bone matrix to lower blood calcium levels. The adrenal cortex releases glucocorticoids, such as aldosterone, cortisone, and cortisol. The anterior pituitary gland secretes a number of hormones, including adrenocorticotropic hormone, thyroid-stimulating hormone, and growth hormone.

Example Question #1 : Understanding Glands And Target Organs

Which gland releases oxytocin and antidiuretic hormone?

Possible Answers:

Anterior pituitary gland

Thyroid gland

Adrenal cortex

Posterior pituitary gland

Correct answer:

Posterior pituitary gland

Explanation:

The pituitary gland has two separate sections: the anterior and posterior lobes. The anterior pituitary gland releases, among other hormones, growth hormone, prolactin, and thyroid-stimulating hormone. The posterior pituitary gland only releases two hormones: oxytocin and antidiuretic hormone. These hormones are synthesized in the hypothalamus and transferred to the posterior pituitary for release.

The thyroid gland releases the thyroid hormones T3 and T4, as well as calcitonin. The adrenal cortex secretes glucocorticoids, such as aldosterone, cortisone, and cortisol.

Example Question #71 : Animal Biology

Adrenocorticotropic hormone will enter the blood stream, and act on which structure in the body?

Possible Answers:

Liver

Kidney

Adrenal gland

Pituitary gland

Correct answer:

Adrenal gland

Explanation:

Adrenocorticotropic hormone (ACTH) is secreted by the anterior pituitary gland. It then travels and stimulates the adrenal gland cortex to release its hormones.

Example Question #1 : Understanding Glands And Target Organs

Which endocrine gland releases aldosterone?

Possible Answers:

Adrenal gland

Pancreas

Thyroid gland

Posterior pituitary gland

Correct answer:

Adrenal gland

Explanation:

Aldosterone is secreted by the adrenal gland, specifically the adrenal cortex.

Example Question #1 : Endocrine System

A person with low blood calcium will have increased activity in which gland?

Possible Answers:

Thyroid gland

Pancreas

Pituitary gland

Parathyroid glands

Correct answer:

Parathyroid glands

Explanation:

Blood calcium levels are controlled primarily by the thyroid and parathyroid glands. The parathyroid glands secrete parathyroid hormone (or PTH), which raises blood calcium levels, while the thyroid gland decreases blood calcium levels via the hormone calcitonin. Since the person currently has low blood calcium, the goal is to raise the blood calcium to normal levels. As a result, we can expect to see increased activity in the parathyroid glands.

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