MCAT Biology : Endocrine System

Study concepts, example questions & explanations for MCAT Biology

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Example Questions

Example Question #4 : Hormones

Type I diabetes is the result of an immune-mediated destruction of the beta cells in the islets of Langerhans in the pancreas. Which hormone would be expected to be elevated in type I diabetes?

Possible Answers:

Somatostatin

Insulin

Glucagon

Oxytocin

Correct answer:

Glucagon

Explanation:

The first key to understanding this question is remembering that beta cells in the pancreas are responsible for secreting insulin. If the beta cells are destroyed, then insulin levels are low. Insulin and glucagon act in opposite ways to keep the concentration of blood glucose in the normal range, providing a negative feedback loop. Insulin inhibits glucagon, and glucagon inhibits insulin. If insulin is low, then glucagon will not be inhibited and will be produced at higher levels than normal.

Example Question #41 : Endocrine System

Type II diabetes results from prolonged overstimulation of the pancreatic beta cells as a result of obesity and chronically elevated glucose levels. After the beta cells have been overactive for an extended period of time, they begin functioning poorly and the person is considered diabetic. In a type II diabetes, what are the expected levels of insulin and glucagon with respect to normal values?

Possible Answers:

Insulin levels will be elevated and glucagon levels will be low

Insulin levels will be low and glucagon levels will be elevated

Insulin levels will be low and glucagon levels will be low

Insulin levels will be elevated and glucagon levels will be elevated

Correct answer:

Insulin levels will be low and glucagon levels will be elevated

Explanation:

Type II diabetes results from an eventual lack of function of the pancreatic beta cells. The first step to this problem is remembering that the beta cells produce insulin. If the beta cells do not function, insulin levels will be decreased. The second step to this problem is remembering that insulin and glucagon have contrasting actions in the regulation of blood glucose levels. They act in a negative feedback loop: insulin inhibits glucagon release, and glucagon inhibits insulin release. If insulin levels are low, then glucagon will no longer be inhibited. As a result, we would observe low levels of insulin and elevated levels of glucagon.

Example Question #2 : Hormone Origins And Targets

Which of the following is NOT a direct effect of the anterior pituitary?

Possible Answers:

T4 production

Water retention

Milk production

Bone growth

Ovulation

Correct answer:

Water retention

Explanation:

Milk production is influenced by prolactin (produced in the anterior pituitary). Bone growth is influenced by growth hormone (produced in the anterior pituitary). Ovulation is controlled by luteinizing hormone and follicle-stimulating hormone (both produced in the anterior pituitary). T4, a thyroid hormone, is controlled by thyroid-stimulating hormone (produced in the anterior pituitary). Water retention, on the other hand, is controlled by antidiuretic hormone (produced in the hypothalamus and released by the posterior pituitary).

Example Question #9 : Hormones

Scientists use a process called Flourescent In-Situ Hybridization, or FISH, to study genetic disorders in humans. FISH is a technique that uses spectrographic analysis to determine the presence or absence, as well as the relative abundance, of genetic material in human cells. 

To use FISH, scientists apply fluorescently-labeled bits of DNA of a known color, called probes, to samples of test DNA. These probes anneal to the sample DNA, and scientists can read the colors that result using laboratory equipment. One common use of FISH is to determine the presence of extra DNA in conditions of aneuploidy, a state in which a human cell has an abnormal number of chromosomes. Chromosomes are collections of DNA, the totality of which makes up a cell’s genome. Another typical use is in the study of cancer cells, where scientists use FISH labels to ascertain if genes have moved inappropriately in a cell’s genome.

Using red fluorescent tags, scientists label probe DNA for a gene known to be expressed more heavily in cancer cells than normal cells. They then label a probe for an immediately adjacent DNA sequence with a green fluorescent tag. Both probes are then added to three dishes, shown below.  In dish 1 human bladder cells are incubated with the probes, in dish 2 human epithelial cells are incubated, and in dish 3 known non-cancerous cells are used. The relative luminescence observed in regions of interest in all dishes is shown below.

 

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Aneuploidy can also affect some fertilized zygotes after abnormalities in fertilization or gametogenesis. Aneuploid zygotes are typically spontaneously aborted before a pregnancy comes to term. A normal zygote binds to uterine endometrium while it is at its thickest, supported by progesterone secretion from which of the following?

Possible Answers:

Anterior pituitary

Posterior pituitary

Hypothalamus

Graafian follicle

Corpus luteum

Correct answer:

Corpus luteum

Explanation:

The corpus luteum forms after ovulation, when a pregnancy would be most expected. The corpus luteum secretes progesterone, which maintains the endometrium for potential implantation.

Example Question #41 : Endocrine System

Glucose levels in the blood are maintained through the competing actions of two main hormones: insulin and glucagon. Other hormones, such as somatostatin, and catecholamines, such as acetylcholine, also serve to modulate glucose levels in the blood. Which molecule is produced by the alpha cells of the islets of Langerhans in the pancreas?

Possible Answers:

Somatostatin

Acetylcholine

Insulin

Glucagon

Correct answer:

Glucagon

Explanation:

Alpha cells in the islets of Langerhans are responsible for producing and secreting glucagon in response to high blood glucose levels. Insulin antagonizes the alpha cells to prevent glucagon release. In diabetes, when the beta cells of the pancreas are not functional, extremely high levels of glucagon exist in the blood due to loss of the negative feedback loop.

Beta and delta cells in the islets of Langerhans produce insulin and somatostatin, respectively. Neurons release acetylcholine to modulate glucose control through indirect processes.

Example Question #42 : Endocrine System

Which of the following hormones is least directly regulated by the anterior pituitary?

Possible Answers:

Cortisone

Thyroxine

Progesterone

Epinephrine

Correct answer:

Epinephrine

Explanation:

Epinephrine is released from the adrenal medulla and regulated by the sympathetic system.

Cortisone, progesterone, and thyroxin are regulated by adrenocorticotropic hormone (ACTH), luteinizing hormone (LH), and thyroid-stimulating hormone (TSH), respectively. These regulatory hormones are all released from the anterior pituitary. ACTH acts on the adrenal cortex to stimulate glucocorticoid release, including cortisone. LH acts on the ovaries to mediate estrogen and progesterone release. TSH acts on the thyroid to mediate the release of T3 and T4. T4 is also known as thyroxine.

Example Question #43 : Endocrine System

Glucose levels in the blood are maintained through the competing actions of two main hormones: insulin and glucagon. Other hormones like somatostatin, and catecholamines, such as acetylcholine, also serve to modulate glucose levels in the blood. Which molecule is produced by the beta cells of the islets of Langerhans in the pancreas?

Possible Answers:

Glucagon

Somatostatin

Acetylcholine

Insulin

Correct answer:

Insulin

Explanation:

Beta cells in the islets of Langerhans are responsible for producing and secreting insulin in response to high blood glucose levels. In type I diabetes these cells are destroyed by an autoimmune process, while in type II diabetes they are replaced with scar tissue.

Alpha and delta cells in the islets of Langerhans produce glucagon and somatostatin, respectively. Neurons release acetylcholine to modulate glucose control through indirect processes.

Example Question #44 : Endocrine System

Which of these is NOT true of steroid hormones? 

Possible Answers:

They are derived from cholesterol.

Their receptors are usually located inside the cell.

They interfere at the level of transcription.

Their effects are long-lived.

They cannot cross the cell membrane.

Correct answer:

They cannot cross the cell membrane.

Explanation:

Because of their nonpolar nature, steroid hormones can easily cross the cell membrane. This enables the hormone to work with its receptor, commonly located inside the cell. Their effects are long-lived since they involve genetic alteration at the transcription level. This, however, also means that steroid hormones take longer than peptide hormones to produce a response. 

Example Question #44 : Endocrine System

Which of the following is NOT one of the tropic hormones released by the anterior pituitary?

Possible Answers:

Prolactin

LH

ACTH

TSH

FSH

Correct answer:

Prolactin

Explanation:

Prolactin is an example of a non-tropic hormone released by the anterior pituitary.

Example Question #45 : Endocrine System

A male gymnast is suspected for using anabolic steroids (i.e. testosterone) to enhance in his athletic performance. Which of the following would you expect to be decreased in his blood?

Possible Answers:

Gonadotropin-releasing hormone only

Luteinizing hormone only

Luteinizing hormone, follicle-stimulating hormone, and gonadotropin-releasing hormone

Luteinizing hormone and follicle-stimulating hormone

Gonadotropin-releasing hormone and luteinizing hormone

Correct answer:

Luteinizing hormone, follicle-stimulating hormone, and gonadotropin-releasing hormone

Explanation:

All three hormones—luteinizing hormone, follicle-stimulating hormone, and gonadotropin-releasing hormone—are part of the hypothalamic-pituitary-gonadal axis. One should be familiar with this axis and with the fact that testosterone exerts negative control at both the level of the hypothalamus and the anterior pituitary.

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