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 #71 : Hormones

The long-term use of corticosteroids may cause all of the following side-effects except for which of the following?

Possible Answers:

Immunodepression

Altered fat metabolism

Elevated blood glucose levels

Glycogenesis

Correct answer:

Glycogenesis

Explanation:

All of the following are examples of the effects that elevated blood cortisol levels have on the body's metabolism. Cortisol is glucocorticoid that is released in response to stress. One main function of cortisol is also to elevate blood glucose levels after long periods of fasting. Glycogenesis is incompatible with this effector response, and thus is the correct answer.

Example Question #72 : Hormones

Carbonic anhydrase is a very important enzyme that is utilized by the body. The enzyme catalyzes the following reaction:

A class of drugs that inhibits this enzyme is carbonic anhydrase inhibitors (eg. acetazolamide, brinzolamide, dorzolamide). These drugs are commonly prescribed in patients with glaucoma, hypertension, heart failure, high altitude sickness and for the treatment of basic drugs overdose.   

In patients with hypertension, carbonic anhydrase inhibitors will prevent the reabsorption of sodium chloride  in the proximal tubule of the kidney. When sodium is reabsorbed back into the blood, the molecule creates an electrical force. This electrical force then pulls water along with it into the blood. As more water enters the blood, the blood volume increase. By preventing the reabsorption of sodium, water reabsorption is reduced and the blood pressure decreases. 

When mountain climbing, the atmospheric pressure is lowered as the altitude increases. As a result of less oxygen into the lungs, ventilation increases. From the equation above, hyperventilation will result in more  being expired. Based on Le Chatelier’s principle, the reaction will shift to the left. Since there is more bicarbonate than protons in the body, the blood will become more basic (respiratory alkalosis). To prevent such life threatening result, one would take a carbonic anhydrase inhibitor to prevent the reaction from shifting to the left.  

Carbonic anhydrase inhibitors are useful in patients with a drug overdose that is acidic. The lumen of the collecting tubule is nonpolar. Due to the lumen's characteristic, molecules that are also nonpolar and uncharged are able to cross the membrane and re-enter the circulatory system. Since carbonic anhydrase inhibitors alkalize the urine, acidic molecules stay in a charged state.

Although carbonic anhydrase inhibitors prevent the reabsorption of water, dehydration rarely occurs. Which of following hormones play an important role in water regulation?

Possible Answers:

Norepinephrine

Epinephrine

Antidiuretic hormone

Hydratonin

Acetylcholine

Correct answer:

Antidiuretic hormone

Explanation:

When the body is dehydrated, the posterior pituitary will secrete antidiuretic hormone (ADH). ADH binds to the collecting tubules to allow for water to be reabsorbed.  

Example Question #81 : Hormones

The brain is a very delicate structure with little room to move around. Surrounding the brain and the spinal cord are three protective layers in addition to the skull and the vertebral column. Directly surrounding the brain and spinal cord is the pia mater. Following the pia mater is the arachnoid mater. Between the pia mater and the arachnoid mater is the sub-arachnoid space where the cerebrospinal fluid circulates. Finally, the protective layer is the dura mater is loosely attached to the arachnoid mater but is strongly associated with the skull bone.

Depending on the type of injury, a certain type of vein and/or artery are more susceptible to injury. For example, the meningeal artery and vein run through the foramen spinosum and travel between the two layers making up the dura mater. As the artery and the vein are traveling in between the dura mater, there is a vulnerable region at the temple. A strike to the temple region could rupture these vessels and result in a epidural hematoma. 

Traveling from the cerebral cortex to the venous dural sinus (located at certain regions between the two layers of the dura mater) is the cerebral vein. When an injury results in the dura mater shifting away from the arachnoid mater, the cerebral vein could rupture and lead to a subdural hematoma.

During a hematoma, the intracranial pressure could increase and push on certain regions of the brain. The compression of a certain region could either excite or inhibit the area. If patient A has a goiter secondary to hyperthyroidism, which region could be compressed?  

Possible Answers:

Anterior pituitary 

Adrenal medulla

Posterior pituitary 

Adrenal cortex

Cerebral aqueduct 

Correct answer:

Anterior pituitary 

Explanation:

The anterior pituitary releases thyroid-stimulating hormone (TSH) which binds to receptors on the thyroid gland and promote the synthesis of the thyroid hormones T3 and T4. Excess stimulation of the thyroid gland due to high level of TSH will cause the thyroid to enlarge and result in an observed goiter.  

Example Question #82 : Hormones

The brain is a very delicate structure with little room to move around. Surrounding the brain and the spinal cord are three protective layers in addition to the skull and the vertebral column. Directly surrounding the brain and spinal cord is the pia mater. Following the pia mater is the arachnoid mater. Between the pia mater and the arachnoid mater is the sub-arachnoid space where the cerebrospinal fluid circulates. Finally, the protective layer is the dura mater is loosely attached to the arachnoid mater but is strongly associated with the skull bone.

Depending on the type of injury, a certain type of vein and/or artery are more susceptible to injury. For example, the meningeal artery and vein run through the foramen spinosum and travel between the two layers making up the dura mater. As the artery and the vein are traveling in between the dura mater, there is a vulnerable region at the temple. A strike to the temple region could rupture these vessels and result in a epidural hematoma. 

Traveling from the cerebral cortex to the venous dural sinus (located at certain regions between the two layers of the dura mater) is the cerebral vein. When an injury results in the dura mater shifting away from the arachnoid mater, the cerebral vein could rupture and lead to a subdural hematoma.

During a hematoma, the intracrainal pressure could increase and push on certain regions of the brain. The compression of a certain region could either excite or inhibit the area. If a forty-year-old patient is showing signs of diabetes with excess bone growth, which region could be compressed and what hormone will be shown in excess from a blood test?

Possible Answers:

Anterior pituitary; growth hormone

Posterior pituitary; growth hormone

Posterior pituitary; luteinizing hormone 

Anterior pituitary; testosterone 

Anterior pituitary; luteinizing hormone

Correct answer:

Anterior pituitary; growth hormone

Explanation:

Post-puberty bone growth and diabetes-like hyperglycemia are symptoms associated with excess in growth hormone (GH). GH is released by the anterior pituitary and promotes bone growth pre-puberty but acromegaly in post-puberty. In addition, GH increases blood glucose level and therefore mimics diabetes. 

Example Question #83 : Hormones

The cellular membrane is a very important structure. The lipid bilayer is both hydrophilic and hydrophobic. The hydrophilic layer faces the extracellular fluid and the cytosol of the cell. The hydrophobic portion of the lipid bilayer stays in between the hydrophobic regions like a sandwich. This bilayer separation allows for communication, protection, and homeostasis. 

One of the most utilized signaling transduction pathways is the G protein-coupled receptor pathway. The hydrophobic and hydrophilic properties of the cellular membrane allows for the peptide and other hydrophilic hormones to bind to the receptor on the cellular surface but to not enter the cell. This regulation allows for activation despite the hormone’s short half-life. On the other hand, hydrophobic hormones must have longer half-lives to allow for these ligands to cross the lipid bilayer, travel through the cell’s cytosol and eventually reach the nucleus. 

Cholesterol allows the lipid bilayer to maintain its fluidity despite the fluctuation in the body’s temperature due to events such as increasing metabolism. Cholesterol binds to the hydrophobic tails of the lipid bilayer. When the temperature is low, the cholesterol molecules prevent the hydrophobic tails from compacting and solidifying. When the temperature is high, the hydrophobic tails will be excited and will move excessively. This excess movement will bring instability to the bilayer. Cholesterol will prevent excessive movement.

Epinephrine binds to its receptor on the surface of the cell. Molecule A also binds to the same receptor at the active site, thereby inactivating the receptor. What type of regulation is this? 

 
Possible Answers:

Cooperation 

Non-competitive inhibition 

None of the above 

Competitive inhibition 

Negative feedback

Correct answer:

Competitive inhibition 

Explanation:

Molecule A is competing with epinephrine for the binding site. However when bound, molecule A blocks the receptor rather than activating it. Competitive inhibitors can be overcome by increasing the concentration of substrate so it outcompetes the inhibitor for the enzyme active site.

Example Question #111 : Endocrine System

If a person has low blood glucose levels, which of the following is false?

Possible Answers:

Glucagon levels will be higher than normal in the body

Insulin release will be inhibited

Gluconeogenesis will be inhibited in the liver

Cortisol levels will be higher than normal in the body

Glycogenolysis will be stimulated in the liver

Correct answer:

Gluconeogenesis will be inhibited in the liver

Explanation:

Cortisol and glucagon are both elevated when a person is experiencing low blood glucose levels. Glucagon is responsible for elevating blood glucose levels by stimulating glycogenolysis in the liver, and cortisol increases blood glucose levels by stimulating gluconeogenesis in the liver.

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