Biology - Hormones And The Endocrine System

Front 1

What is a hormone?

Back 1

Chemical signals in the endocrine system

Front 2

What is a target cell?

Back 2

Chemical communication requires both a cell (or group of cells) that produces and releases the hormone and a cell (or group of cells) with an appropriate receptor that receives the hormone.

The interaction between the hormone and the receptor activates mechanisms within the target cell that lead ultimately to anatomical, physiological, or behavioral changes.

Front 3

What are endocrine glands?

Back 3

Most hormones in humans are produced by endocrine glands, which are aggregations of cells that secrete hormones into the extracellular fluid, from which they enter the blood. After entering the blood, the hormones may be transported throughout the body.

The major human endocrine glands are shown in Figure 41.5.

Some hormones in humans are secreted by endocrine cells that are not part of discrete endocrine glands.

The endocrine system contains both lipid-soluble and water-soluble hormones, which differ in how they bind to receptors in or on the target cells.

Front 4

How do lipid-soluble and water-soluble hormones differ?

Back 4

They differ in how they bind to receptors in or on the target cells.

Lipid-soluble hormones include the steroid hormones. They pass readily through the lipid-rich plasma membrane that surrounds the target cell, and bind to receptors in the cytoplasm or nucleus of the cell.
Their chemical structure allows them to dissolve in lipids.

Water-soluble hormones do not pass readily through the lipid-rich plasma membrane that surrounds the target cell. Their mechanism of action is very different from lipid-soluble. Instead, they bind with receptors on the surface of the target cell.

Front 5

As discussed in lecture, what sequence of biochemical steps occurs when a lipid-soluble hormone, such as cortisol, arrives at a target cell (i.e., what is the mechanism of action of a lipid-soluble hormone)?

Back 5

They pass readily through the lipid-rich plasma membrane that surrounds the target cell, and bind to receptors in the cytoplasm or nucleus of the cell.

In most cases, lipid-soluble hormones stimulate the synthesis of new kinds of proteins by altering gene expression in the target cell.

The synthesis of new kinds of proteins leads ultimately to anatomical, physiological, or behavioral changes.

Because they synthesize new kinds of proteins, rather than modify proteins, their actions are slower and last longer than those of water-based proteins.

Front 6

Where is the following lipid-soluble hormone produced, and what are its primary effects on the human body: cortisol?

Back 6

Cortisol is produced by the adrenal glands, specifically the adrenal cortex. (The adrenal glands are located above the kidney.)

It is important in regulating the body’s response to (longer-term) stress.

It causes a decrease in the metabolism of glucose in most cells, except the brain and muscles, and an increase in the metabolism of proteins and fats.

It also blocks immune system reactions.

They’re not sure why it does these things, but the think it allows most of the energy to be channeled to the brain and muscles.

Front 7

Where is the following lipid-soluble hormone produced, and what are its primary effects on the human body: androgen?

Back 7

Androgens are produced by the testes of males.

They stimulate the development and maintenance of male sexual characteristics and behavior.

They also stimulate sperm production.

Front 8

Where is the following lipid-soluble hormone produced, and what are its primary effects on the human body: estrogen and progesterone?

Back 8

Estrogen and progesterone are produced by the ovaries of females.

They stimulate the development and maintenance of female sexual characteristics and behavior.

Front 9

As discussed in lecture, what sequence of biochemical steps occurs when a water-soluble hormone, such as epinephrine, arrives at a target cell (i.e., what is the mechanism of action of a water-soluble hormone)?

Back 9

Water-soluble hormones do not pass readily through the lipid-rich plasma membrane that surrounds the target cell. Their mechanism of action is very different from lipid-soluble.

Instead, they bind with receptors on the surface of the target cell.
The receptors (glycoprotein complexes) have a binding domain that projects beyond the outside of the plasma membrane and a catalytic domain that projects into the cytoplasm of the cell. This process is analogous to the olfactory system.

Directly or indirectly, most receptors initiate cellular responses by activating protein kinases, which catalyze the transfer of phosphate groups from ATP to specific proteins.

Phosphorylation of specific proteins causes them to become activated or de-activated, thereby leading ultimately to anatomical, physiological, or behavioral changes.

Front 10

What function do protein kinases serve?

Back 10

They catalyze the transfer of phosphate groups from ATP to specific proteins.

Front 11

Where is the following water-soluble hormone produced, and what are its primary effects on the human body: epinephrine?

Back 11

Epinephrine is produced by the adrenal glands, specifically the adrenal medulla.

It is important in regulating the body’s immediate response to stress (the so-called “fight or flight” reactions).

It causes increases in heart rate, breathing rate, blood pressure, and blood sugar concentration.

It also diverts blood flow to active skeletal muscles (to run or to fight). Complementary to cortisol.

Front 12

Where is the following water-soluble hormone produced, and what are its primary effects on the human body: insulin?

Back 12

Insulin is produced b the pancreas gland. (The pancreas gland is located just below the stomach.)

It stimulates the uptake and metabolism of glucose, and increases the conversion of glucose to glycogen and fat.

Front 13

Where is the following water-soluble hormone produced, and what are its primary effects on the human body: luteinizing hormone and follicle-stimulating hormone?

Back 13

Lutenizing hormone and follicle-stimulating hormone are produced by the anterior pituitary gland. (The pituitary gland is located in a depression at the bottom of the skull just over the back of the roof of the mouth.)

Lutenizing hormone stimulates the production and release of androgens by the testes.

Lutenizing hormone and follicle-stimulating hormone stimulate the production and release of estrogens and progesterone by the ovaries.

Lutenizing hormone and follicle-stimulating hormone are also known as gonadotropins.

Front 14

What is the hypothalamus?

Back 14

The hypothalamus is part of the brain (specifically the diencephalon), and is thus part of the nervous system.

It also functions as a key endocrine gland.

Front 15

How is the hypothalamus connected to the anterior pituitary gland?

Back 15

The hypothalamus is connected to the anterior pituitary gland by a specialized set of portal blood vessels.

Front 16

What are neurohormones?

Back 16

Neurohormones synthesized in neurons in the hypothalamus are secreted near capillaries that give rise to the portal blood vessels.

The neurohormones are then transported in the blood vessels to the anterior pituitary gland, where they regulate secretion of the so-called tropic hormones.

Front 17

What are tropic hormones?

Back 17

Tropic hormones produced by the anterior pituitary gland are hormones that control the activities of other endocrine glands.

Front 18

Where are gonadotropin-releasing hormones produced and what are their respective functions?

Back 18

As one example, gonadotropin-releasing hormone is a neurohormone produced by the hypothalamus.

Gonadotropin-releasing hormone stimulates the production and release of the two tropic hormones, luteinizing hormone and follicle-stimulating hormone, by the anterior pituitary gland.

In turn, luteinizing hormone stimulates the production and release of androgens by the testes (in males), and luteinizing hormone and follicle-stimulating hormone stimulate the production and release of estrogens and progesterone by the ovaries (in females).

Front 19

Where are corticotropin-releasing hormones produced and what are their respective functions?

Back 19

Corticotropin-releasing hormone is a neurohormone produced by the hypothalamus.

Corticotropin-releasing hormone stimulates the production and release of the tropic hormone, corticotropin, by the anterior pituitary gland.

In turn, corticotropin stimulates the production and release of cortisol by the adrenal cortex.

Front 20

How might negative feedback loops regulate the “chain of command” from the hypothalamus to the anterior pituitary gland to other endocrine glands?

Back 20

Multiple negative feedback loops may regulate the “chain of command” from the hypothalamus to the anterior pituitary gland to other endocrine glands, as illustrated in Figure 41.9.

For example, when sufficient cortisol reaches the anterior pituitary gland in the circulating blood, it inhibits the further release of corticotropin.

In addition, sufficient cortisol reaching the hypothalamus inhibits the further release of corticotropin-releasing hormone.

In some cases, a tropic hormone also exerts negative feedback control on the hypothalamus, inhibiting the production of the corresponding releasing hormone.