MCAT Biology : Endocrine System

Study concepts, example questions & explanations for MCAT Biology

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Example Questions

Example Question #781 : Mcat Biological Sciences

Grave's Disease is an autoimmune disorder that causes antibodies to bind onto thyroid-stimulating hormone (TSH) receptors on the thyroid. This causes the thyroid to constantly release T3 and T4. What effect would this have on TSH levels?

Possible Answers:

TSH levels would decrease, and then increase

TSH levels would increase, and then decrease

TSH levels would be decreased

TSH levels would be increased

TSH levels would not be affected

Correct answer:

TSH levels would be decreased

Explanation:

Thyroid-stimulating hormone (TSH) levels would be decreased.

The thyroid hormones T3 and T4 act in a negative feedback loop to regulate thyroid activity. Release of TSH increases thyroid activity, while release of the thyroid hormones decreases thyroid activity by suppressing further release of TSH. Since the thyroid is overstimulated in Grave's Disease, excess T3 and T4 are being produced. These hormones will act on the feedback loop to suppress TSH release, lowering TSH levels in individuals with this disease. Since the antibodies bind to the TSH receptors, there are increased levels of T3 and T4 in the body, which negatively inhibit the production of TSH because the body is already flooded with the products of TSH action.

Example Question #1 : Endocrine Regulatory Mechanisms

Insulin is a peptide hormone responsible for lowering blood glucose levels. In some forms of diabetes mellitus, insulin is lacking. Why do diabetics inject insulin into their bodies rather than consuming an insulin pill?

Possible Answers:

Injecting insulin delivers it directly to the brain, while consuming a pill would require it to travel through the gastrointestinal tract first

There is no advantage to injecting insulin versus consuming an insulin pill; insulin is injected simply because that is how it is manufactured

Injecting insulin directly into the bloodstream is much safer than consuming an insulin pill

Injecting insulin allows for it to be dispensed in a slow-release fashion, while consuming an insulin pill releases the hormone rapidly

Injecting insulin delivers it directly into the bloodstream, while consuming a pill would require it to travel through the gastrointestinal tract before being utilized

Correct answer:

Injecting insulin delivers it directly into the bloodstream, while consuming a pill would require it to travel through the gastrointestinal tract before being utilized

Explanation:

Injecting insulin into the body delivers it directly into the bloodstream, while consuming an insulin pill would require it to pass through the gastrointestinal tract. In the gut, the pill would be degraded first and then absorbed into the bloodstream. This entire process would result in a small amount of insulin circulating in the blood, and therefore be much less effective than an insulin injection. Additionally, injecting insulin directly allows more rapid administration of a more consistent dose. 

Example Question #782 : Mcat Biological Sciences

Which hormones act as antagonists to bone growth?

Possible Answers:

Adrenalines and cortisols

Vasopressin and erythropoietin

Gonadotropins and luteins

Epinephrines and norepinephrines

Androgens and estrogens

Correct answer:

Androgens and estrogens

Explanation:

Androgens and estrogens, the sex hormones, feedback to inhibit somatotropins, the growth hormones. In humans, the sex hormones are produced in puberty, disabling the growth plates and halting growth.

Example Question #143 : Endocrine System

The pancreas is one of the few organs with both exocrine and endocrine functions. Exocrine glands can release a variety of substances via ducts, while endocrine glands release hormones directly into the bloodstream without the use of ducts. Which of these choices is a pancreatic exocrine secretion?

Possible Answers:

Insulin

Aldosterone

Somatostatin

Glucagon

Trypsinogen

Correct answer:

Trypsinogen

Explanation:

There are several pancreatic exocrine secretions, most of which are released into the duodenum of the small intestine. Trypsinogen, which is later cleaved into its active form of trypsin, is one of these. Insulin, glucagon, and somatostatin are endocrine secretions. Aldosterone is not released by the pancreas at all, but is instead secreted by the adrenal cortex.

Example Question #144 : Endocrine System

Which of these hormones is released by the posterior pituitary?

Possible Answers:

Thyroid-stimulating hormone

Oxytocin

Luteinizing hormone

Prolactin

Growth hormone

Correct answer:

Oxytocin

Explanation:

The posterior pituitary only releases two hormones: oxytocin and ADH (antidiuretic hormone). The rest of the hormones are released by the anterior pituitary.

Example Question #2 : Other Hormone Physiology

A gland that secretes both peptide and steroid hormones suddenly starts to malfunction. After analysis it is determined that the gland has dysfunctional free floating ribosomes and smooth endoplasmic reticulum. The rest of the cell machinery is working fine. Which of the following can you conclude about the gland?

Possible Answers:

The gland cannot synthesize and secrete both types of hormones

The gland can synthesize and secrete the steroid hormones but not the peptide hormones

The gland can still synthesize and secrete both types of hormones

The gland can synthesize and secrete the peptide hormones but not the steroid hormones

Correct answer:

The gland can synthesize and secrete the peptide hormones but not the steroid hormones

Explanation:

To answer this question you need to know the organelles within a cell that are involved in secreting peptide and steroid hormones. Peptide hormones are polar molecules made up of proteins. Since they are proteins, peptide hormones are synthesized on ribosomes. There are two kinds of ribosomes: free floating ribosomes and ribosomes on rough endoplasmic reticulum (RER). The free floating ribosomes exist in the cytoplasm and, therefore, create cytoplasmic proteins (proteins that are retained inside the cell’s cytoplasm). Ribosomes on RER, on the other hand, are involved in synthesizing proteins that will be exported out of the cell through exocytosis. Since they are secreted out into the blood, hormones are synthesized on RER ribosomes. The question doesn’t mention anything about the RER ribosomes; therefore, peptide synthesis should be normal.

Steroid hormones are nonpolar molecules that are synthesized in the smooth endoplasmic reticulum. Recall that smooth endoplasmic reticulum plays a major role in synthesis of lipids (particularly cholesterol), a major component of steroid hormones. Therefore, a dysfunctional smooth endoplasmic reticulum will halt steroid hormone production.

Example Question #783 : Mcat Biological Sciences

Which of the following hormones most likely affects gene expression in its target cell?

Possible Answers:

Cortisol

Glucagon

FSH

TSH

Correct answer:

Cortisol

Explanation:

Gene expression involves DNA replication, transcription, and translation. Regulation of these processes occur in the nucleus via regulation of essential factors. These factors are regulated by hormones that bind to receptors on the nuclear membrane (which is located inside the cell). Recall that only nonpolar molecules can traverse the nonpolar interior of the plasma membrane; therefore, only nonpolar hormones can enter the cell and bind to receptors on the nuclear membrane. Hormones are classified as peptide or steroid hormones. Peptide hormones  are polar because they contain several protein subunits whereas steroid hormones are nonpolar because they are mostly made up of cholesterol and other types of steroids. Of the given hormones, only cortisol is classified as a steroid hormone; therefore, cortisol most likely has its receptor on the nuclear membrane and functions to regulate gene expression. 

Note that most steroid hormones only bind to receptors on the nuclear membrane and initiate a response to regulate processes involved in gene expression, particularly transcription. This is why many steroid hormones are considered transcription factors. 

Example Question #784 : Mcat Biological Sciences

A researcher is analyzing the effects of a specific hormone. He observes that the hormone causes a signaling cascade in the cell that involves a second messenger molecule called cAMP. What can the researcher conclude about this hormone?

Possible Answers:

It is a peptide hormone and it binds to a receptor on the nuclear membrane

It is a steroid hormone and it binds to a receptor on the nuclear membrane

It is a peptide hormone and it binds to a receptor on the plasma membrane

It is a steroid hormone and it binds to a receptor on the plasma membrane

Correct answer:

It is a peptide hormone and it binds to a receptor on the plasma membrane

Explanation:

cAMP, or cyclic adenosine monophosphate, is a key signaling molecule found within cells. Upon activation, cAMP initiates many pathways within a cell that have various functions. Activation of cAMP typically involves an extracellular molecule that binds to and activates a membrane bound receptor. Since it activates cAMP, the hormone mentioned in this question must bind to a receptor on the plasma membrane. Recall that peptide hormones are polar molecules that cannot enter the cell; therefore, peptide hormones bind to receptors on the plasma membrane and activate subsequent pathways such as cAMP. 

Steroid hormones are nonpolar and can traverse through the nonpolar core of phospholipid bilayer (plasma membrane) and bind to receptors on the nucleus or in cytoplasm.

Example Question #785 : Mcat Biological Sciences

Consider two glands: gland A and gland B. Gland A releases insulin whereas gland B releases digestive zymogens. What can you conclude about these two glands? 

Possible Answers:

Both glands could be found in the pancreas

Gland A is an exocrine gland whereas gland B is an endocrine gland

Neither gland is controlled by the hypothalamus

Gland A and gland B release their respective substances into the bloodstream

Correct answer:

Both glands could be found in the pancreas

Explanation:

Recall that pancreas is an organ that has both endocrine and exocrine functions. The endocrine cells are found in specialized regions of pancreas called Islets of Langerhans and function to secrete insulin and glucagon. Insulin, a hormone involved in the uptake of glucose from blood, is synthesized and secreted in the beta cells whereas glucagon, a hormone involved in the release of glucose into blood, is synthesized and secreted in the alpha cells of Islets of Langerhans.

The exocrine portion of pancreas is involved in the release of several digestive zymogens into the small intestine. The pancreas connects directly to the duodenum of the small intestine and releases digestive zymogens such as tryspinogen, chymotrypsinogen, and pancreatic amylase. Remember that zymogens are inactive forms of enzymes; upon entering the small intestine these zymogens are cleaved by proteases and converted to their active forms.

Example Question #6 : Other Hormone Physiology

Which of the following is true regarding a peptide hormone and a steroid hormone?

I. Peptide hormones are polar and steroid hormones are nonpolar

II. Peptide hormones can travel freely through blood, but steroid hormones cannot

III. The components that make up peptide hormones are created during translation

Possible Answers:

I only

I, II, and III

II only

I and III

Correct answer:

I, II, and III

Explanation:

There are two main types of hormones: peptide hormones and steroid hormones. Peptide hormones, as the name suggests, are made up of protein subunits (polypeptide chains); therefore, peptide hormones are made from monomeric amino acids. Recall that amino acids contain polar groups such as carboxylic acids and amines. This means that peptide hormones are polar molecules. Steroid hormones are made up of steroid molecules. Recall that steroids are lipid molecules; therefore, steroid hormones are nonpolar. Statement I is true.

Hormones are part of the endocrine system and act on cells that are far away from the glands that released them. Glands release hormones into the bloodstream, which allows them to travel throughout the body (via blood) to the target cell. Since peptide hormones are polar, they can dissolve in the fluid of the blood (water); however, steroid hormones require an amphipathic (both polar and nonpolar regions) protein transporter that can dissolve in the blood. The steroid hormones attach to the nonpolar region of the protein whereas the polar region dissolves in the blood. Peptide hormones can travel freely through the blood, but stroid hormones cannot. Statement II is true.

Peptide hormones are polypeptide chains (proteins) that are made up of amino acids. Recall that translation is the cellular process that synthesizes polypeptide chains by joining amino acids; therefore, peptide hormones are created during translation. Statement III is true.

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