Endocrine System

Question 1

Describe the major function of the endocrine system.

Answer 1

It controls cellular, tissue, and organ processes through the release of chemical signals.

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

Question 2

What is the function of endocrine glands?

Answer 2

They 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.

Question 3

Define:

hormone

Answer 3

It 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.

Question 4

What features characterize peptide hormones?

Answer 4

They are polar molecules composed of amino acids.

Question 5

What features characterize steroid hormones?

Answer 5

They are nonpolar molecules derived from cholesterol.

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

Question 6

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

Answer 6

Tyrosine

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

Question 7

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

Answer 7

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.

Question 8

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

Answer 8

• Peptides are synthesized in the rough ER.
• Steroids are modified from cholesterol in the smooth ER.

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

Question 9

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

Answer 9

• Peptides can travel freely in the bloodstream.
• 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.

Question 10

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

Answer 10

Cholesterol

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

Question 11

How do steroid hormones interact with their target cells?

Answer 11

They 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.

Question 12

How do peptide hormones interact with their target cells?

Answer 12

They 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.

Question 13

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?

Answer 13

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.

Question 14

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?

Answer 14

peptide hormone

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

Question 15

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

Answer 15

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.

Question 16

What is the difference between negative and positive feedback?

Answer 16

• 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.

Question 17

Homeostasis is primarily maintained through which type of feedback mechanism?

Answer 17

negative feedback

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.

Question 18

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

Answer 18

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.

Question 19

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

Answer 19

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.

Question 20

What type of feedback loop is seen during labor contractions?

Answer 20

positive feedback

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.

Question 21

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

Answer 21

It 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.

Question 22

What endocrine function does the hypothalamus serve?

Answer 22

It 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.

Question 23

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

Answer 23

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

Question 24

Which hormones are secreted by the anterior pituitary?

Answer 24

• follicle-stimulating hormone (FSH)
• luteinizing hormone (LH)
• adrenocorticotropic hormone (ACTH)
• growth hormone (GH)
• prolactin
• thyroid-stimulating hormone (TSH)

(A useful mnemonic device is FLAT PEG)

Question 25

Which hormones are secreted by the posterior pituitary?

Answer 25

• antidiuretic hormone (ADH)
• oxytocin

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

Question 26

What endocrine function does the thyroid gland serve?

Answer 26

It 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.

Question 27

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

Answer 27

• Parathyroid hormone (PTH)
• This hormone increases plasma calcium levels by stimulating the breakdown of bone.

Question 28

What endocrine function does the pancreas serve?

Answer 28

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

A third hormone released by the pancreas is somatostatin.

Question 29

What is the difference between endocrine and exocrine activity?

Answer 29

• Endocrine organs release hormones into the blood.
• Exocrine structures secrete enzymes or other substances through ducts.

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

Question 30

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

Answer 30

• pancreatic lipase
• pancreatic amylase
• trypsinogen
• as well as other digestive enzymes

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

Question 31

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

Answer 31

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

Question 32

Name the two major parts of the adrenal gland.

Answer 32

1. cortex, or outer region
2. medulla, or inner region

Question 33

What are the main hormones secreted by the adrenal cortex?

Answer 33

• aldosterone
• cortisol

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

Question 34

What are the main hormones secreted by the adrenal medulla?

Answer 34

• epinephrine
• norepinephrine

Both are catecholamines.

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

Question 35

Which type of hormone does the adrenal cortex produce?

Answer 35

steroid hormones

Question 36

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

Answer 36

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.

Question 37

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

Answer 37

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.

Question 38

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

Answer 38

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.

Question 39

What function is served by antidiuretic hormone (ADH)?

Answer 39

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.

Question 40

What function is served by aldosterone?

Answer 40

It 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.

Question 41

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

Answer 41

renin

Renin is 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.

Question 42

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?

Answer 42

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.

Question 43

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

Answer 43

ADH levels would also be increased.

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

Question 44

What function is served by insulin?

Answer 44

It 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.

Question 45

What function is served by glucagon?

Answer 45

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

Glucagon is secreted by pancreatic alpha cells.

Question 46

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

Answer 46

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.

Question 47

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

Answer 47

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.

Question 48

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

Answer 48

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.

Question 49

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

Answer 49

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.

Question 50

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

Answer 50

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.

Question 51

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

Answer 51

FSH facilitates spermatogenesis by stimulating Sertoli cells in the testes.

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

Question 52

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

Answer 52

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.

Question 53

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

Answer 53

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.

Question 54

What function is served by erythropoietin (EPO)?

Answer 54

It 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.

Question 55

What function is served by melatonin?

Answer 55

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

Specifically, melatonin levels increase at night and promote sleep.

Question 56

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

Answer 56

Parathyroid hormone

(PTH)

“Bone resorption” simply describes the breakdown of bone by osteoclasts, which is promoted by PTH.

Question 57

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?

Answer 57

Erythropoietin

(EPO)

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.

Question 58

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

Answer 58

glucagon

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.