MCAT Biology : Pancreas, Liver, and Kidney

Study concepts, example questions & explanations for MCAT Biology

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Example Questions

Example Question #16 : Glands

What is the site of synthesis of glucagon?

Possible Answers:

Islets of Langerhans

Alpha cells

Pancreas

Anywhere glucagon synthase is present

All of these are sites of glucagon synthesis

Correct answer:

All of these are sites of glucagon synthesis

Explanation:

Glucagon acts in a negative feedback loop with insulin to regulate blood sugar concentration. Both hormones are secreted from the Islets of Langerhans in the pancreas. Alpha cells in the pancreas have high levels of glucagon synthase, allowing them to synthesize the hormone.

Essentially, glucagon synthase is located in alpha cells, which are found in Islets of Langerhans within the pancreas; thus, all of these answers describe the site of glucagon synthesis.

Example Question #14 : Endocrine System

Which of the following structures acts as both an exocrine and an endocrine gland?

Possible Answers:

The gall bladder

The pancreas

The thyroid

The adrenal cortex

Correct answer:

The pancreas

Explanation:

There is a key difference between exocrine and endocrine glands. Exocrine glands release their product to the external environment, while endocrine glands release their product directly into bodily fluids. The answer is the structure that accomplishes both of these actions. The pancreas does both: it releases digestive enzymes into the small intestine (external environment), and releases hormones into the bloodstream (body fluid). Remember that the entire digestive tract is considered part of the outside environment and is lined by epithelium, rather than endothelium.

The adrenal cortex and thyroid perform only endocrine functions, while the gall bladder is only exocrine.

Example Question #1 : Pancreas, Liver, And Kidney

Insulin is secreted from what endocrine structure?

Possible Answers:

Beta cells of the pancreas

Acinar cells of the pancreas

Alpha cells of the pancreas

Adrenal cortex

Adrenal medulla

Correct answer:

Beta cells of the pancreas

Explanation:

Insulin is secreted from the beta cells of the pancreas. The alpha cells secrete glucagon, which acts in a negative feedback loop with insulin to regulate blood glucose levels.

The acinar cells of the pancreas secrete digestive enzymes, and serve the exocrine (rather than the endocrine) function of the pancreas. The adrenal medulla secretes epinephrine and norepinephrine, while the adrenal cortex releases aldosterone.

Example Question #16 : Endocrine System

Which hormone, released from delta cells in the pancreas, is responsible for inhibiting both insulin and glucagon release?

Possible Answers:

Amylin

Somatostatin

Ghrelin

Thyroxine

Correct answer:

Somatostatin

Explanation:

Somatostatin is synthesized in the delta cells in the islets of Langerhans in the pancreas, and serves to inhibit insulin and glucagon secretion from beta and alpha cells, respectively. Somatostatin serves a number of other purposes, including inhibition of growth hormone and inhibition of the release of pancreatic digestive enzyme release.

Amylin, along with insulin, is released from the beta cells of the pancreas and acts as a synergist to insulin. Ghrelin is released from epsilon cells of the pancreas and has an array of different functions, including inducing appetite. Thyroxine refers to the thyroid hormone T4, or tetraiiodothyronine, which plays a role in metabolism.

Example Question #2 : Pancreas, Liver, And Kidney

Which of the following does NOT perform endocrine function?

Possible Answers:

Pancreas

Thyroid

Testes

Liver

All of these are endocrine organs

Correct answer:

All of these are endocrine organs

Explanation:

Endocrine organs are capable of secreting hormones into the bloodstream. Each of the given answer options performs some sort of endocrine function.

The testes secrete testosterone, and are responsible for the development of most secondary sex characteristics in males.

The thyroid gland secretes calcitonin and thyroid hormones, responsible for elevating calcium levels and increasing metabolism, respectively.

The pancreas and liver are both endocrine AND exocrine organs. As an endocrine organ, the pancreas secretes the hormones insulin and glucagon. As an exocrine organ, it secretes several enzymes that are essential for digestion in the small intestine. The liver secretes insulin-like growth factors in response to stimulation by growth hormone. As an exocrine organ, it is also responsible for producing bile to aid in digestion.

Example Question #3 : Pancreas, Liver, And Kidney

Which of the following is not a function of the endocrine system?

Possible Answers:

Hypothalamic secretions to the anterior pituitary

Anterior pituitary secretions to the ovaries

Pancreatic secretions to the intestine

Thyroid secretions throughout the body

Correct answer:

Pancreatic secretions to the intestine

Explanation:

The endocrine system involves secretions by ductless glands into the bloodstream. The pancreas, pituitary gland, thyroid, and hypothalamus are all endocrine organs that secrete hormone signals to the body. The pancreas, however, also functions as an exocrine gland. When the pancreas secretes insulin and glucagon into the blood stream, it serves as an endocrine organ. When it secretes digestive enzymes through the pancreatic duct into the small intestine, it serves an exocrine function.

Example Question #22 : Glands

Consider two hormones: hormone A and hormone B. Both hormones act on the collecting ducts of the kidneys. Hormone A increases the permeability of water in the collecting ducts, whereas hormone B increases sodium reabsorption in the collecting ducts. What can you conclude about these two hormones?

Possible Answers:

Both hormone A and hormone B cannot dissolve in water

Only hormone A can dissolve in water

Both hormone A and hormone B can dissolve in water

Only hormone B can dissolve in water

Correct answer:

Only hormone A can dissolve in water

Explanation:

The question states that both hormone A and hormone B act on the collecting ducts of the kidneys. There are two major hormones that act on the collecting ducts: aldosterone and antidiuretic hormone (ADH). Aldosterone is a steroid hormone that functions to increase sodium and chlorine reabsorption from urine in the collecting ducts, whereas ADH is a peptide hormone that functions to increase water reabsorption from urine in the collecting ducts (by increasing the permeability to water). This means that hormone A is ADH and hormone B is aldosterone.

Recall thatsteroid hormones, such as aldosterone, are nonpolar molecules. On the other hand, peptide hormones are made up of protein subunits and consist of many polar groups; therefore, ADH is a polar molecule. Since water is a polar molecule, only ADH (hormone A) will dissolve in water.

Example Question #22 : Endocrine System

Which of the following is false regarding insulin and calcitonin?

I. Insulin functions to decrease glucose concentration in blood, whereas calcitonin functions to increase calcium concentration in blood

II. They are antagonistic hormones

III. Insulin and calcitonin can only act on cells near their respective glands

Possible Answers:

I only

I and III

I, II, and III

III only

Correct answer:

I, II, and III

Explanation:

Insulin is released into the blood from the pancreas and functions to decrease the glucose concentration in the blood. Elevated levels of blood glucose induces insulin release. Once released, insulin transports glucose back into the cells or facilitates the formation of glycogen. Glycogen consists of multiple glucose subunits and is stored in the liver for later use. Calcitonin, on the other hand, functions to decrease the calcium concentration in the blood. Osteoclasts are cells in bones that break down bones and release bone calcium into the blood. Calcitonin inhibits the activity of osteoclasts and decreases the calcium concentration in the blood. Statement I is false.

Antagonistic hormones are a pair of hormones that have the opposite effects. For example, insulin and glucagon are antagonistic hormones because insulin functions to decrease blood glucose levels, whereas glucagon functions to increase blood glucose levels. Similarly, calcitonin and parathyroid hormone (PTH) are antagonistic hormones because calcitonin functions to decrease blood calcium levels whereas PTH functions to increase blood calcium levels. Insulin and calcitonin are not antagonistic hormones because they do not have opposite effects. Statement II is false.

Recall that insulin and calcitonin are part of the endocrine system. Hormones in the endocrine system are characterized by their ability to travel through blood and act on cells that are far away from the glands that released them; therefore, insulin and calcitonin do not act on cells surrounding their respective glands alone. Statement III is false.

Example Question #4 : Pancreas, Liver, And Kidney

The beta cells of the islets of Langerhans secrete which of the following hormones?

Possible Answers:

Thyroxine

Glucagon

Cortisol

Calcitonin

Insulin

Correct answer:

Insulin

Explanation:

Insulin is secreted by the beta cells of the islets of Langerhans in the pancreas in response to high blood glucose levels. Alpha cells in the islets of Langerhans secrete glucagon, the antagonist of insulin, in response to low blood glucose levels.

The thyroid secretes thyroxine (also known as tetraiodothyronine or T4), which controls the body's metabolism. The thyroid also secretes calcitonin, which promotes bone formation. Cortisol is secreted by the adrenal cortex and works to regulate blood glucose levels and has an anti-inflammatory effect. Cortisol is a corticosteroid that is secreted in response to adrenocorticotropic hormone.

Example Question #5 : Pancreas, Liver, And Kidney

Which of the following might explain type I diabetes, also known as juvenile diabetes?

Possible Answers:

Antibodies directed against -cells in the islets of the pancreas

Consumption of a severely calorie-restricted diet during the first few years of life

Antibodies directed against - cells in the islets of the pancreas

Consumption of a high-caloric diet over a number of years

Correct answer:

Antibodies directed against -cells in the islets of the pancreas

Explanation:

Seeing as type I diabetes results from the destruction of the -cells in the pancreas, this is the only feasible answer. These cells are responsible for producing insulin.

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