MCAT Biology : Hormone Mechanisms and Effects

Study concepts, example questions & explanations for MCAT Biology

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Example Questions

Example Question #11 : Hormone Mechanisms And Effects

Which hormone is required for milk secretion in women?

Possible Answers:

Oxytocin

Prolactin

Luteinizing hormone

Estrogen

Correct answer:

Oxytocin

Explanation:

Oxytocin is responsible for milk secretion in women. Notice that prolactin is responsible for milk production, but oxytocin is responsible for milk secretion. Oxytocin is released from the posterior pituitary and is responsible for contractions during pregnancy and milk secretion.

Example Question #11 : Hormone Mechanisms And Effects

Mineralocorticoids, including aldosterone, are able to maintain blood pressure during times of stress. Which of the following is not an effect of aldosterone?

Possible Answers:

Decreased blood potassium levels

Decreased urine sodium content

Decreased blood sodium levels

Increased blood pressure

Correct answer:

Decreased blood sodium levels

Explanation:

The mineralocorticoid aldosterone is stimulated by the renin-angiotensin system of the kidney when blood volume falls. Aldosterone acts at the distal convoluted tubule of the kidney to increase sodium reabsorption, thus raising sodium levels in the blood and lowering sodium levels in the urine. Aldosterone also increases potassium excretion, thus causing low levels of potassium in the blood. The overall retention of sodium draws water from the filtrate into the blood, causing increased blood pressure by increasing blood volume.

Example Question #11 : Hormone Mechanisms And Effects

Cortisol, a glucocorticoid, is able to help maintain the body's metabolic state during times of stress. Which of the following is not a function of cortisol?

Possible Answers:

Increase sex hormone levels

Increase blood free fatty acids

Increase blood glucose

Increase protein metabolism

Correct answer:

Increase sex hormone levels

Explanation:

Cortisol secretion, stimulated from the adrenal cortex by adrenocorticotropic hormone from the anterior pituitary, is responsible for protecting against hypoglycemia and hypotension. Cortisol increases blood glucose, increases blood free fatty acids by stimulating lipolysis, and increases breakdown of muscle proteins. The net result is more substrate to undergo glycolysis and the citric acid cycle during periods of poor nutrition and starvation.

Cortisol does not elevate sex hormone levels. Evolutionarily, it is disadvantageous to produce offspring during times of stress or poor nutrition.

Example Question #681 : Systems Biology And Tissue Types

What hormone is directly responsible for increasing the amount of water reabsorbed in the kidney collecting ducts?

Possible Answers:

Aldosterone

Renin

Adrenocorticotropic hormone

Vasopressin

Correct answer:

Vasopressin

Explanation:

Vasopressin (antidiuretic hormone) is responsible for placing aquaporin channels on the collecting ducts of the kidney to allow for increased water reabsorption. This increased water reabsorption allows for blood pressure to be maintained. Interestingly, coffee and alcohol are vasopressin blockers, causing a large increase in urine volume when ingested.

Aldosterone, in contrast, causes a retention of sodium ions, which indirectly draws water out of the filtrate to concentrate the urine. Aldosterone does not affect permeability of the collecting duct to water. Renin indirectly leads to increases in both vasopressin and aldosterone, but has no direct effect on the collecting duct by itself.

Example Question #14 : Hormone Mechanisms And Effects

Which hormone is responsible for stimulating milk production in women?

Possible Answers:

Estrogen

Oxytocin

Prolactin

Luteinizing hormone

Correct answer:

Prolactin

Explanation:

Prolactin is responsible for stimulating milk production in women. While other hormones need a stimulus to trigger secretion, prolactin is tonically secreted, but its action is stopped by the neurotransmitter dopamine. During the period of nursing, the stimulus of the baby suckling inhibits dopamine, allowing for the release of prolactin and the production of milk.

Example Question #15 : Hormone Mechanisms And Effects

Which hormone is responsible for stimulating the production of T4 and T3 from the thyroid gland?

Possible Answers:

Parathyroid hormone

Thyroid-stimulating hormone

Growth hormone

Thyrotropin-releasing hormone

Correct answer:

Thyroid-stimulating hormone

Explanation:

Thyroid-stimulating hormone is produced by the anterior pituitary, and is responsible for stimulating T4 (tetraiodothyronine) and T3 (triiodothyronine) release from follicular cells in the thyroid gland. Too much thyroid-stimulating hormone can cause large lumps in the neck due to thyroid gland inflammation, called goiters. Goiters commonly result from an iodine deficiency, as the structures of both T4 and T3 require a central iodine atom.

Thyrotropin-releasing hormone is responsible for stimulating release of thyroid-stimulating hormone. Parathyroid hormone is important for regulating blood calcium, while growth hormone is involved in mitotic stimulation and nutrient balances.

Example Question #11 : Hormone Mechanisms And Effects

Which hormone is responsible for stimulating estrogen synthesis in the female ovaries?

Possible Answers:

Follicle-stimulating hormone

Prolactin

Oxytocin

Progesterone

Correct answer:

Follicle-stimulating hormone

Explanation:

Follicle-stimulating hormone is responsible for stimulating estrogen synthesis in the female ovaries.

Luteinizing hormone acts on Theca cells to stimulate androstenedione production (the precursor to estrogen), then follicle-stimulating hormone acts on granulosa cells to stimulate estrogen production. Both luteinizing hormone and follicle-stimulating hormone are required for estrogen production, but follicle-stimulating hormone is ultimately required for estrogen synthesis and secretion.

Example Question #12 : Hormone Mechanisms And Effects

A camper becomes lost and does not drink water for 48 hours. At the end of this time, which significant changes in hormone production would be expected in the camper?

Possible Answers:

Decreased aldosterone

Decreased glucocorticoids

Increased antidiuretic hormone (ADH)

Increased insulin

Correct answer:

Increased antidiuretic hormone (ADH)

Explanation:

The function of antidiuretic hormone, or vasopressin, is to reabsorb water in the kidney tubules, thereby retaining water in the body. After dehydration, the camper's antidiuretic hormone levels would be high in order to preserve the water in his or her body.

Glucocorticoids, such as cortisol, have various functions; they reduce inflammation and prepare the body for long-term stress. Dehydration signals the body to prepare for long-term stress, increasing glucocorticoid levels.

Aldosterone increases sodium retention, drawing water out of filtrate and acting to counter dehydration. We would expect aldosterone to be elevated.

Insulin lowers blood glucose, but the camper would need to use glucose as energy causing this hormone to be decreased.

Example Question #1 : Understanding Hormone Functions

The interaction between blood pressure and kidney function in humans requires coordination by the renin-angiotensin-aldosterone system (RAAS). This system involves the dynamic interplay of the kidneys, lungs, and blood vessels to carefully regulate sodium and water balance.

A normal human kidney has cells adjacent to the glomerulus called juxtaglomerular cells. These cells sense sodium content in urine of the distal convoluted tubule, releasing renin in response to a low level. Renin is an enzyme that converts angiotensinogen to angiotensin I (AI). AI is converted to angiotensin II (AII) by angiotensin converting enzyme (ACE) in the lung.

AII stimulates aldosterone secretion in the zona glomerulosa of the adrenal gland. Aldosterone then acts to upregulate the sodium-potassium pump on the basolateral side of distal tubule epithelial cells to increase sodium reabsorption from the urine, as well as increasing potassium excretion.

Renin is most likely to drive the formation of angiotensin I from angiotensinogen by doing which of the following?

I. Increasing the concentration of angiotensinogen

II. Lowering the activation energy of the reaction from angiotensinogen to angiotensin I

III. Stabilizing the angiotensin I molecule to lower the energy of the products

Possible Answers:

I only

II and III

III only

II only

I,II, and III

Correct answer:

II only

Explanation:

Renin, as the passage establishes, is an enzyme. Enzymes always work by leaving the thermodynamic energies of the products and reactants the same, but lower activation energy of the reaction. Angiotensinogen is released by the liver, and converted by renin to angiotensin I. Renin does not directly act on the liver to stimulate angiotensinogen release.

Example Question #691 : Biology

What is the significance of the LH surge in the menstrual cycle?

Possible Answers:

It is involved in proliferation of the endometrial lining

It immediately precedes ovulation

It stimulates release of human chorionic gonadotropin

It is involved in follicle maturation

It immediately precedes degeneration of the corpus luteum

Correct answer:

It immediately precedes ovulation

Explanation:

The LH surge, a spike in levels of luteinizing hormone, immediately precedes the luteal phase of the menstrual cycle, which begins with ovulation and ends with degeneration of the corpus luteum.

Estradiol, an estrogen, is secreted by theca cells and promotes growth of the endometrium to prepare for implantation.

Follicle-stimulating hormone is important for follicle maturation.

Degeneration of the corpus luteum into corpus albicans occurs in the absence of implantation. This degeneration process typically occurs 14 days after ovulation.

Human chorionic gonadotropin is only released during pregnancy and is responsible for maintaining the corpus luteum.

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