the endocrine system

what is the endocrine system

The endocrine system is a system of glands that release chemical messenger molecules into the blood stream. The messenger molecules are called hormones. Hormones act slowly compared with the rapid transmission of electrical impulses of the nervous system. Endocrine hormones must travel through the bloodstream to the cells they control, and this takes time. On the other hand, because endocrine hormones are released into the bloodstream, they travel to cells everywhere in the body. For a good visual introduction to the endocrine system, watch this short video: http MEDIA Click image to the left or use the URL below. URL:

endocrine system diseases

Diseases of the endocrine system are fairly common. An endocrine disease usually involves the secretion of too much or not enough hormone by an endocrine gland. This may happen because the gland develops an abnormal lump of cells called a tumor. For example, a tumor of the pituitary gland can cause secretion of too much growth hormone. If this occurs in a child, it may result in very rapid growth and unusual tallness by adulthood. This is called gigantism. Type 1 diabetes is another endocrine system disease. In this disease, the bodys own immune system attacks insulin- secreting cells of the pancreas. As a result, not enough insulin is secreted to maintain normal levels of glucose in the blood. Patients with type 1 diabetes must regularly check the level of glucose in their blood. When it gets too high, they must give themselves an injection of insulin to bring it under control. You can learn more about glucose, insulin, and type 1 diabetes by watching this video: . MEDIA Click image to the left or use the URL below. URL:

how endocrine hormones work

Endocrine hormones travel throughout the body in the blood. However, each endocrine hormone affects only certain cells, called target cells.

hormones and target cells

A target cell is the type of cell on which a given endocrine hormone has an effect. A target cell is affected by a given hormone because it has proteins on its surface to which the hormone can bind. When the hormone binds to target cell proteins, it causes changes inside the cell. For example, binding of the hormone might cause the release of enzymes inside the cell. The enzymes then influence cell processes.

pituitary gland

The pea-sized pituitary gland is just below the hypothalamus and attached directly to it. The pituitary receives hormones from the hypothalamus. It also secretes its own hormones. Most pituitary hormones control other endocrine glands. Thats why the pituitary gland is called the master gland of the endocrine system. Table Pituitary Hormone Adrenocorticotropic (ACTH) hormone Target Glands/Cells adrenal glands Thyroid-stimulating (TSH) Growth hormone (GH) hormone thyroid gland Follicle-stimulating (FSH) hormone body cells ovaries or testes Luteinizing hormone (LH) ovaries or testes Prolactin (PRL) mammary glands Effects(s) Stimulates the cortex (outer layer) of the adrenal glands to secrete their hormones Stimulates the thyroid gland to se- crete its hormones Stimulates body cells to make pro- teins and grow Stimulates the ovaries to develop mature eggs; stimulates the testes to produce sperm Stimulates the ovaries or testes to secrete sex hormones; stimulates the ovaries to release eggs Stimulates the mammary glands to produce milk

other endocrine glands

There are several other endocrine glands. Find them in Figure 20.17 as you read about them below. The thyroid gland is a relatively large gland in the neck. Hormones secreted by the thyroid gland include thyroxin. Thyroxin increases the rate of metabolism in cells throughout the body. The pancreas is a large gland located near the stomach. Hormones secreted by the pancreas include insulin. Insulin helps cells absorb glucose from the blood. It also stimulates the liver to take up and store excess glucose. The two adrenal glands are glands located just above the kidneys. Each adrenal gland has an outer layer (cortex) and inner layer (medulla) that secrete different hormones. The hormone adrenaline is secreted by the inner layer. It prepares the body to respond to emergencies. For example, it increases the amount of oxygen and glucose going to the muscles. The gonads are glands that secrete sex hormones. Male gonads are called testes. They secrete the male sex hormone testosterone. The female gonads are called ovaries. They secrete the female sex hormone estrogen. Sex hormones stimulate the changes of puberty. They also control the production of sperm or eggs by the gonads.

hypothalamus

The hypothalamus is actually part of the brain, but it also secretes hormones. Some of its hormones go directly to the pituitary gland in the endocrine system. These hypothalamus hormones tell the pituitary to either secrete or stop secreting its hormones. In this way, the hypothalamus provides a link between the nervous and endocrine systems. The hypothalamus also produces hormones that directly regulate body processes. For example, it produces antid- iuretic hormone. This hormone travels to the kidneys and stimulates them to conserve water by producing more concentrated urine.

glands of the endocrine system

An endocrine gland is a gland that secretes hormones into the bloodstream for transport around the body (instead of secreting hormones locally, like sweat glands in the skin). Major glands of the endocrine system are shown in Figure 20.17. The glands are the same in males and females except for the ovaries and testes.

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feedback loops

Endocrine hormones control many cell activities, so they are very important for homeostasis. But what controls the hormones? Most endocrine hormones are controlled by feedback loops. In a feedback loop, the hormone produced by a gland feeds back to control its own production by the gland. A feedback loop can be negative or positive. Most endocrine hormones are controlled by negative feedback loops. .Negative feedback occurs when rising levels of a hormone feed back to decrease secretion of the hormone or when falling levels of the hormone feed back to increase its secretion. You can see an example of a negative feedback loop in Figure 20.18. It shows how levels of thyroid hormones regulate the thyroid gland. This loop involves the hypothalamus and pituitary gland as well as the thyroid gland. Low levels of thyroid hormones in the blood cause the release of hormones by the hypothalamus and pituitary gland. These hormones stimulate the thyroid gland to secrete more hormones. The opposite happens with high levels of thyroid hormones in the blood. The hypothalamus and pituitary gland stop releasing hormones that stimulate the thyroid.

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instructional diagrams

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questions

All endocrine glands secrete hormones into

-->  a. the bloodstream.

b. local tissues.

c. the digestive system.

d. target cells.

__messenger molecule released by an endocrine gland

a. hypothalamus

b. gonad

c. insulin

-->  d. hormone

e. endocrine gland

f. prolactin

g. pituitary gland

__pancreatic hormone that helps cells absorb glucose from the blood

a. hypothalamus

b. gonad

-->  c. insulin

d. hormone

e. endocrine gland

f. prolactin

g. pituitary gland

The feedback loop that controls the production of thyroxin includes the

a. pituitary gland.

b. thyroid gland.

c. hypothalamus.

-->  d. all of the above

Which endocrine gland secretes luteinizing hormone?

-->  a. pituitary gland

b. ovary

c. testis

d. two of the above

__any gland that secretes hormones into the bloodstream

a. hypothalamus

b. gonad

c. insulin

d. hormone

-->  e. endocrine gland

f. prolactin

g. pituitary gland

__gland that secretes sex hormones

a. hypothalamus

-->  b. gonad

c. insulin

d. hormone

e. endocrine gland

f. prolactin

g. pituitary gland

The hormone called ACTH

a. acts on the thyroid gland.

-->  b. is secreted by pituitary gland.

c. stimulates the secretion of sex hormones.

d. causes cells to make proteins and grow.

__part of the brain that secretes hormones affecting the pituitary gland

-->  a. hypothalamus

b. gonad

c. insulin

d. hormone

e. endocrine gland

f. prolactin

g. pituitary gland

Which statement about gigantism is true?

-->  a. It is characterized by excessive growth during childhood.

b. It occurs when blood levels of thyroxin are too high.

c. It may be caused by a tumor in the thyroid gland.

d. all of the above

__pituitary hormone that stimulates the mammary glands to produce milk

a. hypothalamus

b. gonad

c. insulin

d. hormone

e. endocrine gland

-->  f. prolactin

g. pituitary gland

__master gland of the endocrine system

a. hypothalamus

b. gonad

c. insulin

d. hormone

e. endocrine gland

f. prolactin

-->  g. pituitary gland

Which structure provides a link between the nervous and endocrine systems?

a. pituitary gland

-->  b. hypothalamus

c. adrenal gland

d. thyroid gland

Most pituitary hormones control

-->  a. other endocrine glands.

b. the hypothalamus.

c. body cells.

d. the brain.

The pituitary hormone called follicle-stimulating hormone stimulates the

-->  a. testes to produce sperm.

b. hair follicles to grow hair.

c. ovaries to secrete estrogen.

d. two of the above

Which gland secretes growth hormone?

a. adrenal gland

b. thyroid gland

c. ovary

-->  d. pituitary gland

Follicle-stimulating hormone is secreted by the gonads.

a. true

-->  b. false

The thymus gland is part of the endocrine system.

-->  a. true

b. false

Endocrine hormones influence target cells by

a. acting as enzymes and speeding up chemical reactions in the cells.

b. absorbing glucose and actively transporting it into the cells.

-->  c. binding with proteins on the surface of the cells.

d. creating negative feedback loops with the cells.

The output of most endocrine hormones is controlled by positive feedback loops.

a. true

-->  b. false

Males and females have the same endocrine glands except for the

a. thyroid gland.

b. pituitary gland.

c. adrenal glands.

-->  d. gonads.

What happens when the level of thyroxin rises in the blood?

a. The pituitary gland releases thyroid-stimulating hormone.

b. The thyroid gland starts releasing more hormones.

-->  c. The level of TSH in the blood falls.

d. two of the above

Type 1 diabetes occurs when the immune system attacks cells of the adrenal glands.

a. true

-->  b. false

The hormone adrenaline prepares the body for emergencies.

-->  a. true

b. false

Endocrine hormones travel more slowly than nerve impulses.

-->  a. true

b. false

Endocrine hormones affect only nearby cells.

a. true

-->  b. false

The pineal gland is part of the endocrine system.

-->  a. true

b. false

All hormones released by the hypothalamus control the pituitary gland.

a. true

-->  b. false

The pituitary gland is located in the neck.

a. true

-->  b. false

Growth hormone stimulates cells to make proteins.

-->  a. true

b. false

Luteinizing hormone is secreted by the gonads.

a. true

-->  b. false

diagram questions

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