Endocrine System Flashcards

The MCAT requires an in-depth understanding of hormones, from the difference between peptides and steroids to their effects on other organ systems. Use these cards to master endocrine organs, specific hormones, and the complex interactions involved.

1
Q

Describe the major function of the endocrine system.

A

The endocrine system controls cellular, tissue, and organ processes through the release of chemical signals.

These processes mainly relate to growth, metabolism, homeostasis, and reproduction.

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2
Q

What is the function of an endocrine gland?

A

Endocrine glands release chemical messengers called hormones into the bloodstream. These hormones can then affect the functioning of target organs.

In general, a gland is an organ or other structure that secretes products within or outside the body.

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3
Q

Define:

hormone

A

A hormone is a molecule that is released into the bloodstream by an endocrine gland. Hormones act as chemical messengers and bind to receptors on their target organs.

Two large classes of hormones are peptides and steroids.

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4
Q

What features characterize a peptide hormone?

A

Peptide hormones are polar molecules composed of amino acids.

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5
Q

What features characterize a steroid hormone?

A

Steroid hormones are nonpolar molecules derived from cholesterol.

Most steroid hormones are named using the suffixes “-ol,” -one,” or “-en.”

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6
Q

Some hormones are classified as neither steroids nor peptides. From which amino acid are most of these hormones derived?

A

Tyrosine

Tyrosine derivatives include the thyroid hormones T3 and T4. The catecholamines, namely epinephrine and norepinephrine, are also part of this category.

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7
Q

With regard to solubility, do tyrosine derivatives resemble peptide or steroid hormones?

A

Some tyrosine-based hormones resemble peptides, while others resemble steroids.

Like peptides, epinephrine and norepinephrine are water-soluble. However, the thyroid hormones are lipid-soluble, like steroids.

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8
Q

How do steroid and peptide hormones differ in their location of synthesis within the cell?

A

Peptides are synthesized in the rough ER, while steroids are modified from cholesterol in the smooth ER.

ER stands for “endoplasmic reticulum,” a membrane-bound organelle.

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9
Q

How do steroid and peptide hormones differ in their method of travel within the blood?

A

Peptides can travel freely in the bloodstream, while steroids generally must be bound to carrier proteins.

Like most differences between the hormone types, this can be explained by solubility characteristics. Peptides are hydrophilic (water-soluble), while steroids are hydrophobic.

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10
Q

Name the four-ringed biological molecule that acts as the precursor for all steroid hormones.

A

Cholesterol

This molecule’s rings and hydrocarbon tail make it hydrophobic, or insoluble in water.

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11
Q

How do steroid hormones interact with their target cells?

A

Steroids diffuse through the cell membrane, travel to the nucleus, and alter transcription of certain DNA sequences.

As hydrophobic molecules, steroids can easily pass through the phospholipid bilayer. However, they must be bound to a specific receptor when in the cytoplasm.

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12
Q

How do peptide hormones interact with their target cells?

A

Peptides bind to specific receptors on the cell membrane, promoting an intracellular signaling cascade.

As hydrophilic molecules, peptides cannot cross the phospholipid bilayer and never actually enter the target cell.

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13
Q

Since peptides cannot cross the cell membrane, they rely on signaling molecules inside the target cell to effect a change. What term describes this kind of pathway?

A

This pathway is a second messenger system.

The first messenger is the hormone itself; the second is an intracellular ion or molecule, like Ca2+ or cAMP. These systems commonly involve G protein-coupled receptors, or GPCRs.

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14
Q

Ghrelin is a hormone that acts on brain cells to stimulate hunger. It is hydrophilic and interacts with target cells by binding to membrane receptors. Which type of hormone does ghrelin exemplify?

A

Ghrelin is an example of a peptide hormone.

Unlike steroids, peptides are hydrophilic, or water-soluble. They also bind to membrane receptors instead of diffusing into the cell.

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15
Q

The anterior pituitary secretes several hormones that stimulate other endocrine organs instead of non-endocrine target cells. What term describes such hormones?

A

Tropic hormones

One example is TSH, or thyroid-stimulating hormone. Instead of directly altering a cellular process on its own, it stimulates the thyroid to produce its own hormones.

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16
Q

What is the difference between negative and positive feedback?

A

In negative feedback, formation of the product of a certain process decreases the rate of that process. In positive feedback, product formation increases the rate of the process that produces it.

On the MCAT, negative feedback is occasionally referred to as “feedback inhibition.”

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17
Q

Homeostasis is primarily maintained through which type of feedback mechanism?

A

Negative feedback maintains homeostasis.

Homeostasis relates to an organism’s need to maintain fairly stable conditions within its body and cells. Since negative feedback acts to prevent product concentrations from becoming too high, it helps preserve this stability.

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18
Q

When plasma calcium levels are high, the release of parathyroid hormone is inhibited. What type of feedback does this action exemplify?

A

The inhibition of PTH by calcium is an example of negative feedback.

Parathyroid hormone (PTH) functions to increase plasma levels of calcium ion. When plenty of calcium is already present, PTH activity decreases; this prevents Ca2+ levels from becoming too high.

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19
Q

In the circulatory system, the presence of several clotting factors indirectly stimulates their own production. What type of feedback does this action exemplify?

A

Blood clotting is an example of positive feedback.

One example is thrombin, an enzyme. Thrombin activates platelets and other factors, which leads to additional thrombin production. This allows the clotting process to occur quickly.

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20
Q

What type of feedback loop is seen during labor contractions?

A

Positive feedback is involved in labor.

When a pregnant female begins labor contractions, the process must be continued until birth. Oxytocin acts to stimulate these contractions, which feed back to stimulate more oxytocin release.

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21
Q

What is a portal system, and how does it relate to endocrine function?

A

A portal system is a circulatory structure in which one capillary bed drains into another. The hypophyseal portal system allows hormones to be transported from the hypothalamus to the pituitary gland.

A similar example is the hepatic portal system. However, its main function is digestive, not endocrine.

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22
Q

What endocrine function does the hypothalamus serve?

A

The hypothalamus secretes chemicals that control the release of hormones from the anterior pituitary. It also produces the two posterior pituitary hormones, ADH and oxytocin.

The hypothalamus is connected to the pituitary via the hypophyseal portal system.

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23
Q

Both the anterior and posterior pituitary secrete important hormones. How do these hormones differ in their location of synthesis?

A

Hormones that are secreted from the anterior pituitary are also synthesized there. In contrast, posterior pituitary hormones are synthesized in the hypothalamus.

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24
Q

Which hormones are secreted by the anterior pituitary?

A

The main hormones secreted by the anterior pituitary are follicle-stimulating hormone (FSH), luteinizing hormone (LH), adrenocorticotropic hormone (ACTH), growth hormone (GH), prolactin, and thyroid-stimulating hormone (TSH).

(A useful mnemonic device is FLAT PEG)

25
Q

Which hormones are secreted by the posterior pituitary?

A

The posterior pituitary secretes antidiuretic hormone (ADH) and oxytocin.

Note that these hormones are synthesized in the hypothalamus. Only after synthesis are they transported to the pituitary for release into the blood.

26
Q

What endocrine function does the thyroid gland serve?

A

The thyroid gland releases thyroid hormones (namely T3 and T4), which control metabolism. It also secretes calcitonin.

The endocrine activity of the thyroid is determined by thyroid-stimulating hormone (TSH), which is secreted from the anterior pituitary.

27
Q

Which hormone is produced by the parathyroid glands, and what role does it serve?

A

The parathyroid glands produce parathyroid hormone (PTH). This hormone increases plasma calcium levels by stimulating the breakdown of bone.

Many MCAT questions deal with the difference between PTH and calcitonin, which have opposite functions.

28
Q

What endocrine function does the pancreas serve?

A

The pancreas secretes insulin and glucagon, two hormones that have opposite effects on plasma glucose levels.

A third hormone released by the pancreas is somatostatin, but the MCAT mentions it much less frequently.

29
Q

What is the difference between endocrine and exocrine activity?

A

Endocrine organs release hormones into the blood, while exocrine structures secrete enzymes or other substances through ducts.

The pancreas is a notable example of an organ with both endocrine and exocrine roles.

30
Q

Which enzymes are secreted as part of the exocrine function of the pancreas?

A

Exocrine products of the pancreas include pancreatic lipase, pancreatic amylase, and trypsinogen, as well as other digestive enzymes.

On the other hand, the pancreas’ endocrine products are insulin, glucagon, and somatostatin.

31
Q

Which hormone is produced by the pineal gland, and what role does it serve?

A

The pineal gland produces melatonin, which helps regulate circadian rhythms.

32
Q

Name the two major parts of the adrenal gland.

A

The two main parts are the cortex, or outer region, and the medulla, or inner region.

33
Q

What are the main hormones secreted by the adrenal cortex?

A

The adrenal cortex secretes aldosterone and cortisol.

More broadly, the cortex produces glucocorticoids (such as cortisol and cortisone) and mineralocorticoids (such as aldosterone). It also synthesizes some sex hormones.

34
Q

What are the main hormones secreted by the adrenal medulla?

A

The adrenal medulla secretes epinephrine and norepinephrine, both catecholamines.

Notably, these products can function as either hormones or neurotransmitters, depending on the location of release.

35
Q

Which type of hormone does the adrenal cortex produce?

A

The products of the adrenal cortex are steroid hormones.

For the MCAT, this can be remembered by recalling their broad classification: corticosteroids.

36
Q

A certain individual gets the majority of her sodium intake from uniodized sea salt. Which endocrine gland might this affect?

A

A lowered consumption of iodine might affect the thyroid gland.

Iodine is required for thyroid hormone synthesis. Most table salt is iodized to protect against goiter, a condition in which the thyroid gland becomes enlarged to compensate for an iodine deficiency.

37
Q

The body contains several organs that are not classically considered endocrine glands, but do secrete hormones. Which such organ serves a major circulatory function?

A

The heart

While the main function of the heart is to pump blood, it does secrete one hormone, atrial natriuretic peptide. ANP promotes water and sodium excretion when blood pressure is high.

38
Q

The body contains several organs that are not classically considered endocrine glands, but do secrete hormones. Which such organ is only present temporarily?

A

The placenta

Present only in pregnant females, this organ provides contact with a blood supply without activating the maternal immune system. It secretes hCG, estrogen, and progesterone.

39
Q

What function is served by antidiuretic hormone (ADH)?

A

ADH stimulates the kidneys to increase water reabsorption. Specifically, it increases the number of functional aquaporins in the collecting duct of the nephron.

This function prevents blood pressure from becoming too low.

40
Q

What function is served by aldosterone?

A

Aldosterone stimulates the kidneys to increase sodium reabsorption; water follows and is passively reabsorbed as well. Specifically, aldosterone acts mainly on the distal convoluted tubule.

This function prevents blood pressure from becoming too low.

41
Q

A patient exhibits lowered production of a certain kidney enzyme, leading to chronic low blood pressure. In which enzyme is the patient likely deficient?

A

The patient is probably deficient in renin, an enzyme vital to the release of aldosterone. Specifically, renin activates angiotensinogen, the first step that promotes aldosterone secretion.

While other deficiencies (in ADH, for example) could cause low blood pressure, renin is the only example that is released from the kidney itself.

42
Q

ACE inhibitors are a class of medication commonly used to treat high blood pressure. How would benazepril, an ACE inhibitor, affect a patient’s aldosterone levels?

A

This drug would decrease aldosterone levels.

Angiotensin-converting enzyme (ACE) is part of the pathway that activates aldosterone when blood pressure is low. A blood pressure medication would aim to block this pathway, preventing the resulting pressure increase.

43
Q

A lab report mentions that a certain sample shows increased vasopressin activity. What does this mean about the sample’s levels of ADH?

A

ADH levels would also be increased.

Vasopressin is simply an alternative term for antidiuretic hormone, or ADH.

44
Q

What function is served by insulin?

A

Insulin removes glucose from the blood and facilitates its storage in the tissues as glycogen. It is released when plasma glucose levels are high, such as after a meal.

Insulin is secreted by pancreatic beta cells.

45
Q

What function is served by glucagon?

A

Glucagon facilitates the conversion of stored glycogen to glucose. This process increases plasma glucose levels.

Glucagon is secreted by pancreatic alpha cells.

46
Q

Regulation of which ion involves both the thyroid and parathyroid glands?

A

Plasma concentrations of calcium ion (Ca2+) are controlled by both of these glands.

The parathyroid glands secrete parathyroid hormone (PTH), which increases plasma calcium levels. Calcitonin, a product of the thyroid, has the opposite effect.

47
Q

What effect would excess production of parathyroid hormone have on plasma calcium levels?

A

Plasma calcium levels would increase.

PTH is released from the parathyroid glands when plasma calcium is low. Among other functions, it stimulates osteoclasts to break down bone and release calcium into the extracellular fluid.

48
Q

What effect would excess production of calcitonin have on plasma calcium levels?

A

Plasma calcium levels would decrease.

Calcitonin is released from the thyroid when plasma calcium levels are high. It stimulates osteoblasts to increase bone formation, taking calcium out of the blood in the process.

49
Q

When a bone sample from a certain patient was analyzed, unusually high osteoclast activity was observed. In which hormone might this patient be deficient?

A

The patient might be deficient in calcitonin.

Abnormally high osteoclast activity means that excess bone is being broken down. This can result from high levels of parathyroid hormone (PTH) or low levels of calcitonin.

50
Q

Briefly describe the role of follicle-stimulating hormone (FSH) in females.

A

In keeping with its name, FSH promotes the development of mature follicles. Its levels are highest before ovulation and low during pregnancy.

Both FSH and LH are peptide hormones secreted from the anterior pituitary.

51
Q

Briefly describe the role of follicle-stimulating hormone (FSH) in males.

A

FSH facilitates spermatogenesis by stimulating Sertoli cells in the testes.

Both FSH and LH are peptide hormones secreted from the anterior pituitary.

52
Q

Briefly describe the role of luteinizing hormone (LH) in females.

A

LH promotes ovulation with a peak in concentration known as the LH surge. It also facilitates the development of the corpus luteum.

Both FSH and LH are peptide hormones secreted from the anterior pituitary.

53
Q

Briefly describe the role of luteinizing hormone (LH) in males.

A

LH increases the production of testosterone by stimulating Leydig cells in the testes.

Both FSH and LH are peptide hormones secreted from the anterior pituitary.

54
Q

What function is served by erythropoietin (EPO)?

A

EPO is secreted by the kidney and increases the rate of red blood cell formation.

Red blood cells are called erythrocytes, so their formation is termed erythropoiesis.

55
Q

What function is served by melatonin?

A

Melatonin is secreted by the pineal gland and is involved in the regulation of circadian rhythms.

Specifically, melatonin levels increase at night and promote sleep.

56
Q

A student reads that a certain hormone functions to increase bone resorption. Which hormone is likely being described?

A

Parathyroid hormone (PTH)

It is important to know alternative ways that the MCAT can phrase common terms. “Bone resorption” simply describes the breakdown of bone by osteoclasts, which is promoted by PTH.

57
Q

A healthy 25-year-old man moves to Boulder, CO, where the elevation is approximately 5000 feet above sea level. In three weeks, which hormone is likely to have an increased concentration in this patient?

A

Erythropoietin (EPO) will likely be increased.

EPO, a kidney hormone, increases the rate of red blood cell formation. Its production is increased whenever oxygen becomes scarce, such as at high altitudes.

58
Q

A 14-year-old boy suffers from Type I diabetes. Administration of which pancreatic hormone would exacerbate (worsen) his condition?

A

Glucagon would make this boy’s condition worse.

Type I diabetes involves a lack of insulin, a hormone that reduces plasma glucose levels. Thus, this boy would likely have high blood sugar. Glucagon, the hormone that acts antagonistically to insulin, would raise his blood glucose levels further.