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Describe the major function of the endocrine system.

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.


What is the function of an endocrine gland?

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

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



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.


What is the difference between negative and positive feedback?

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.

Negative feedback is occasionally referred to as "feedback inhibition."


Homeostasis is primarily maintained through which type of feedback mechanism?

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.


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

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. Remember, negative feedback occurs when high levels of a biological product act to decrease production of that product.


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

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.


What type of feedback loop is seen during labor contractions?

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.


What features characterize a peptide hormone?

Peptide hormones are polar molecules composed of amino acids.


What features characterize a steroid hormone?

Steroid hormones are nonpolar molecules derived from cholesterol.

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


How do peptide hormones interact with their target cells?

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

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


How do steroid hormones interact with their target cells?

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.


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

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.


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

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.


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


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


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

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.


Which type of hormone requires membrane receptors to act on a target cell?

Peptide hormones, as well as the catecholamines epinephrine and norepinephrine, require membrane receptors.

As polar molecules, these hormones cannot pass through the hydrophobic cell membrane.


Which endocrine gland, located adjacent to the hypothalamus, is known as the "master gland" of the endocrine system?

The pituitary gland is termed the "master gland" because it secretes several hormones that act on organs throughout the entire body.

The pituitary gland has two parts: the anterior (front) pituitary and the posterior (rear) pituitary.


Which hormones are secreted by the anterior pituitary?

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).


Which hormones are secreted by the posterior pituitary?

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.


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

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


What endocrine function does the hypothalamus serve?

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.


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

A portal system is a circulatory structure in which one capillary bed drains into another. The hypothalamus and pituitary gland are connected by such a system, which allows hormones to be easily transported from the hypothalamus to the pituitary.

Remember, the hormones of the posterior pituitary are made in the hypothalamus and simply "shipped" to the posterior pituitary for later release.


Which endocrine gland secretes ACTH, and on what target organ does this hormone act?

Adrenocorticotropic hormone (ACTH) is secreted by the anterior pituitary and acts on the adrenal cortex.

Specifically, it stimulates the cortex to secrete its own hormones, which include glucocorticoids and mineralcorticoids.


Which endocrine gland secretes prolactin, and what role does this hormone play in the human body?

Prolactin is secreted by the anterior pituitary. It stimulates the production of milk in females who are nursing infants.


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

In keeping with its name, FSH promotes the development of mature follicles (structures that contain egg cells). Its levels are highest before ovulation and low during pregnancy.

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


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

FSH facilitates spermatogenesis, or sperm production, by stimulating Sertoli cells in the testes.

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


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

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.


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

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.


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

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.