MCAT Biology : Hormone Mechanisms and Effects

Study concepts, example questions & explanations for MCAT Biology

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Example Questions

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Example Question #63 : Endocrine System

All of the following are expected to increase after a meal has been consumed except __________.

Possible Answers:

insulin

GLUT-4 receptors

cholecystokinin

glucagon

secretin

Correct answer:

glucagon

Explanation:

When an a meal is consumed, the digestive system is stimulated. This causes the release of secretin and cholecystokinin, hormones that are involved in digestion. Once glucose is in the bloodstream, it interacts with beta cells and causes the release of insulin. Insulin enters the bloodstream and stimulates widespread expression of the GLUT-4 receptor. Glucagon, on the other hand, counters the effects of insulin in a negative feedback loop and would not be expected to increase after a meal is consumed.

Example Question #64 : Endocrine System

A lack of which of the following hormones could cause high plasma calcium levels?

Possible Answers:

Calcitriol

Parathyroid hormone

Glucagon

Aldosterone

Calcitonin

Correct answer:

Calcitonin

Explanation:

If the lack of a certain hormone can cause high calcium levels, that means the hormone acts to lower plasma calcium when it is present. Only one of the choices, calcitonin, decreases blood calcium. Parathyroid hormone (PTH) and calcitriol increase plasma calcium levels. Aldosterone and glucagon are unrelated to calcium regulation—aldosterone regulates kidney activity to increase blood pressure and glucagon increases blood sugar levels.

Example Question #65 : Endocrine System

John goes to the doctor and is told that his anterior pituitary is not functioning. Which of the following hormones is likely at lower levels than normal?

Possible Answers:

Parathyroid hormone

Melatonin

Glucagon

Thyroid-stimulating hormone (TSH)

Atrial natriuretic hormone

Correct answer:

Thyroid-stimulating hormone (TSH)

Explanation:

Of all the choices, the only one released by the anterior pituitary is TSH (thyroid-stimulating hormone). Glucagon is released from the pancreas, parathyroid hormone is released from the parathyroid glands, melatonin comes from the pineal gland, and atrial natriuretic hormone is a heart hormone.

Example Question #66 : Endocrine System

Which hormone is most responsible for decreased levels of blood calcium?

Possible Answers:

Parathyroid hormone (PTH)

Glucagon

Insulin

Calcitonin

Correct answer:

Calcitonin

Explanation:

Calcitonin lowers plasma calcium, while parathyroid hormone (PTH) increases it. Insulin and glucagon are responsible for blood glucose, not calcium.

Example Question #1 : Hormone Mechanisms And Effects

After ingesting a meal heavy in polysaccharides, an individual has their blood drawn. Levels of which hormone would you expect to be higher than normal?

Possible Answers:

Gastrin

Insulin

Glucagon

Oxytocin

Correct answer:

Insulin

Explanation:

The polysaccharides from the meal will be digested down into glucose by various enzymes in the digestive track. That glucose will be absorbed in the small intestine and travel into the bloodstream. This increase in blood glucose will cause a release of insulin to allow for tissue to take up the glucose and use it for energy. In this individual's blood, we would expect insulin to be higher than normal.

Conversely, when little blood glucose is present, glucagon is released to break down glycogen and fat into glucose that is needed for energy. Gastrin, while also involved in digestion, is closely linked to the release of hydrochloric acid, which activates pepsin to digest proteins. Gastrin is not linked to the digestion of carbohydrates and polysaccharides.

Oxytocin is not involved in digestion.

Example Question #68 : Endocrine System

The endocrine system regulates many aspects of human physiology through the release of hormones, which are chemical messengers that act on target organs and are generally transported via the bloodstream. The following are statements about one of these hormones, aldosterone. Which statement is incorrect?

Possible Answers:

Aldosterone is released by the anterior pituitary

Though their mechanisms of regulation are different, both aldosterone and antidiuretic hormone (ADH) act to increase blood volume

Administration of an angiotensin-converting enzyme (ACE) inhibitor will decrease aldosterone secretion

Aldosterone is a steroid hormone

Correct answer:

Aldosterone is released by the anterior pituitary

Explanation:

Aldosterone is a mineralcorticoid, meaning that it is released by the adrenal cortex, not the anterior pituitary.

Mineralcorticoids are also steroids, and are able to cross the cell membrane due to their lipophilic nature. Both aldosterone and antidiuretic hormone (ADH) increase blood volume by acting on different regions of the nephrons in the kidney. Finally, angiotensin-converting enzyme (ACE) inhibitors do decrease the secretion of aldosterone, since aldosterone is activated by the renin-angiotensin system and the inhibitors block a vital conversion step in this chain.

Example Question #2 : Hormone Mechanisms And Effects

Which steroid hormone, produced in the ovaries, is responsible for preparing and maintaining the uterus for pregnancy?

Possible Answers:

Estrogen

Luteinizing hormone

Follicle-stimulating hormone

Progesterone

Correct answer:

Progesterone

Explanation:

Progesterone is responsible for maintaining the uterine environment during pregnancy. In contrast, estrogen is responsible for the development of female secondary sex characteristics, and luteinizing hormone and follicle-stimulating hormone help stimulate follicle growth, ovulation, and estrogen production.

Example Question #70 : Endocrine System

Which steroid hormone, produced in the ovaries, is responsible for the growth of female sex organs and is responsible for causing a surge in luteinizing hormone through positive feedback?

Possible Answers:

Testosterone

Androstenedione

Progesterone

Estrogen

Correct answer:

Estrogen

Explanation:

Estrogen is produced by the combination of luteinizing hormone and follicle-stimulating hormone in the ovaries. Estrogen is responsible for causing the luteinizing hormone surge through positive feedback (one of the only examples of positive feedback in endocrine biology) and the growth of the female sex organs.

Progesterone is responsible for preparing and maintaining the uterus for pregnancy.

Example Question #3 : Hormone Mechanisms And Effects

Which hormone is responsible for increasing episodes of mitosis, increasing cell size, and increasing the rate of protein synthesis?

Possible Answers:

Adrenocorticotropic hormone

Prolactin

Growth hormone

Thyroid-stimulating hormone

Correct answer:

Growth hormone

Explanation:

Growth hormone is secreted by the anterior pituitary and is responsible for increased metabolism and cell growth. Growth hormone increases glucose and free fatty acid levels in the blood, increasing substrates for metabolism for other cells in the body.

Example Question #4 : Hormone Mechanisms And Effects

Which anterior pituitary hormone plays a role in stimulating spermatogenesis in males?

Possible Answers:

Follicle-stimulating hormone

Testosterone

Adrenocorticotropic hormone

Estradiol

Correct answer:

Follicle-stimulating hormone

Explanation:

Under normal conditions, spermatogenesis is somewhat inhibited. Follicle-stimulating hormone, luteinizing hormone, and testosterone can act to overcome this inhibition and promote sperm development. Testosterone, however, is produced in the testes, not the anterior pituitary.

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