MCAT Biology : Endocrine System

Study concepts, example questions & explanations for MCAT Biology

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Example Questions

Example Question #18 : Hormone Mechanisms And Effects

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,II, and III

II only

II and III

III only

I only

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 #19 : Hormone Mechanisms And Effects

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 is involved in follicle maturation

It immediately precedes degeneration of the corpus luteum

It stimulates release of human chorionic gonadotropin

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.

Example Question #21 : Hormone Mechanisms And Effects

What two hormones have opposite effects?

Possible Answers:

Calcitonin and parathyroid hormone

Insulin and epinephrine

Estrogen and progesterone

Cortisol and cortisone

Angiotensin I and angiotensin II

Correct answer:

Calcitonin and parathyroid hormone

Explanation:

Calcitonin decreases blood calcium levels, while parathyroid hormone increases blood calcium levels.

Example Question #81 : Endocrine System

All of the following hormones exhibit periods of spiked concentration in the mestrual cycle EXCEPT __________.

Possible Answers:

LH

estrogen

prolactin

FSH

progesterone

Correct answer:

prolactin

Explanation:

FSH, LH, estrogen, and progesterone all increase around ovulation to make an environment in the uterus that will be healthy if fertilization occurs. Prolactin promotes milk production at the end of pregnancy and while a mother is breast feeding a child.

Example Question #82 : Endocrine System

Antidiuretic hormone (ADH) is released from the posterior pituitary in response to increased plasma osmolarity. It acts on the kidney nephrons to increase water permeability in the distal convoluted tubule and collecting duct. This allows for greater water reabsorption from the filtrate, and results in higher body fluid volume.

Which of the following would NOT be reasonably associated with increased levels of ADH?

Possible Answers:

Increased solute concentration in the urine.

High levels of atrial naturitic hormone.

Decreased volume of urine.

Increased arterial pressure.

Correct answer:

High levels of atrial naturitic hormone.

Explanation:

Release of ADH would not be associated with release of atrial naturitic hormone. ADH increases blood pressure, while atrial naturitic hormone decreases blood pressure.

Example Question #83 : Endocrine System

Recall that parathyroid hormone (PTH) is a peptide hormone secreted by the parathyroid glands that serves to increase serum calcium.

Which of the following is not a mechanism by which PTH increases serum calcium?

Possible Answers:

Increased osteoclast absorption of calcium from bone

Increased absorption of vitamin D from skin

Increased calcium reabsorption by kidneys

Increased calcium uptake from gut

Correct answer:

Increased absorption of vitamin D from skin

Explanation:

Parathyroid hormone (PTH) does not enhance absorption of vitamin D through the skin.

It does, however, act independently on the bones, kidneys, and gut, to increase blood calcium. Interestingly, cancer cells in various types of cancers (breast and lung) can secrete parathyroid hormone-related protein (PTHrP), which acts similarly to PTH and can cause hypercalcemia (high serum calcium) in cancer patients.

Example Question #84 : Endocrine System

If an individual with type I diabetes injects themselves with too much insulin, which of the following would be a possible result?

Possible Answers:

Hypocalcemia

Hypercalcemia

Increased urine glucose levels

Hypoglycemia

Hyperglycemia

Correct answer:

Hypoglycemia

Explanation:

Insulin functions to decrease blood glucose levels, causing cells to take up glucose from the blood. If someone takes too much insulin it would result in hypoglycemia, or decreased blood glucose levels. Insulin has no effect on calcium levels. Glucose is rarely found in the urine and can be a sign of extremely high blood glucose levels, or hyperglycemia.

Example Question #85 : Endocrine System

What happens to the levels of FSH and LH in a human female, once her ovaries have begun to atrophy during menopause?

Possible Answers:

Levels of FSH and LH both increase

Levels of FSH and LH both decrease

 

FSH levels decrease, while LH levels increase

FSH levels increase, while LH levels decrease

Correct answer:

Levels of FSH and LH both increase

Explanation:

This question requires knowledge of the negative feedback loop between the anterior pituitary hormones (FSH and LH) and the sex hormones (estrogen and progesterone). Prior to menopause, FSH and LH production is inhibited by estrogen production in the ovaries. When ovarian estrogen production decreases, during menopause, FSH and LH levels increase uninhibited.

Example Question #86 : Endocrine System

A patient goes to his doctor for a normal check-up, and the doctor sees that he ihas very high levels of Na+ and Cl- in his blood.  He runs some tests, and determines that:

Possible Answers:

The patient has high blood pressure caused by underproduction of aldosterone.

The patient has high blood pressure caused by no production of aldosterone.

The patient has low blood pressure caused by overproduction of aldosterone.

The patient has low blood pressure caused by underproduction of aldosterone.

The patient has high blood pressure caused by overproduction of aldosterone.

Correct answer:

The patient has high blood pressure caused by overproduction of aldosterone.

Explanation:

Aldosterone functions to make the collecting duct and distal convoluted tubule in the kidneys to make them more permeable to Na+, Cl–, K+, and H+. When Na+ and Cl– are reabsorbed, water follows them into the blood, thus increasing total blood volume and raising blood pressure.

Example Question #87 : Endocrine System

An increase in aldosterone will __________.

Possible Answers:

decrease blood volume

decrease blood osmolarity

decrease sodium reabsoprtion

increase water secretion

increase antidiuretic hormone (ADH) release

Correct answer:

increase antidiuretic hormone (ADH) release

Explanation:

An increase in aldosterone will cause an increase in sodium reabsoption, an increase in blood osmolarity, an increase in antidiuretic hormone (ADH) release, an increase in water reabsoption, and an increase in blood volume.

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