Endocrine System (a review) The endocrine system consists of glands which secrete hormones into the bloodstream. Each hormone has an effect on one or more target tissues. In this way the endocrine system regulates the metabolism and development of most body cells and body systems. To be more specific, the Endocrine system has sex hormones that can activate sebaceous glands, development of mammary glands, alter dermal blood flow and release lipids from adipocytes and MSH can stimulate melanocytes on our skin. Our bone growth is regulated by several hormones, and the endocrine system helps with the mobilization of calcitonin and calcium. In the muscular system hormones adjust muscle metabolism, energy production, and growth. In the nervous system hormones affect neural metabolism, regulate fluid/electrolyte balance and help with reproductive hormones that influence CNS development and behaviors. In the Cardiovascular system we need hormones that regulate the production of RBC's, elevate and lower blood pressure. Hormones also have anti-inflammatory affects as well as stimulates the lymphatic system. In summary, the endocrine system has a regulatory effect on basically every other body system.

Here is a great (kinda boring) video on the different glands in the body as well as what each gland does. Have fun: http://www.youtube.com/watch?v=IVUG74D1BzQ

Endocrine Glands and Hormones
Hormones are regulatory molecules secreted into the blood by endocrine glands. Chemical categories of hormones include steroids, amines, polypeptides, and glycoproteins. Interactions between the various hormones produce effects that may by synergistic.

• Endocrine Glands – lack the ducts that are present in exocrine glands. The endocrine glands secrete their products, which are biologically active molecules called hormones, into the blood. The blood carries the hormones to target cells that contain specific receptor proteins for the hormones, and which therefore can respond in a specific fashion to them.

Chemical classification of Hormones
Hormones secreted by different endocrine glands vary widely in chemical structure. All hormones, however, can be divided into a few chemical classes.
In terms of their actions in target cells, hormone molecules can be divided into those that are polar, and therefore water-soluble, and those that are nonpolar, and thus insoluble in water. Since the nonpolar hormones are soluble in lipids, they are often referred to as lipophilic hormones. Unlike the polar hormones, which cannot pass through plasma membranes, lipophilic hormones can gain entry into their target cells. These lipophilic hormones include the steroid hormones and thyroid hormones.

• Amines – These are hormones derived from the amino acids tyrosine and tryptophan. They include the hormones secreted by the adrenal medulla, thyroid, and pineal glands. Some are polar (most) and some are nonpolar.
  
• Polypeptides and Proteins – Polypeptide hormones generally contain less than 100 amino acids; an example is antidiuretic hormone. These are always polar (a chain of amino acids)
• Glycoproteins – These molecules consist of a long polypeptide bound to one or more carbohydrate groups. Examples are follicle-stimulating hormone and luteinizing hormone.
  • Amines, Polypeptides and Glycoproteins will utilize a secondary messenger system. a secondary messenger system is a method of cellular signalling where the signalling molecule does not enter the cell, but rather utilizes a cascade of events that transduces the signal into a cellular change
• Steroids – These are lipids derived from cholesterol. They include the hormones testosterone, estradiol, progesterone, and cortisol. (non polar, they pass through the cell membrane and meet up with a receptor in the nucleus or just outside in the cytoplasm)

Hormone: A substance, usually a peptide or steroid, produced by one tissue and conveyed by the bloodstream to another to effect physiological activity, such as growth or metabolism.A chemical produced in one part of the body and released into the blood to trigger or regulate particular functions of the body. For example, insulin is a hormone made in the pancreas that tells other cells when to use glucose for energy.

Endocrine glands: Glands that produce and secrete hormones into the blood or lymph systems, including the thyroid, parathyroid, hypothalamus, pineal, pituitary, adrenal, islets of Langerhans in the pancreas, and the gonads (testes and ovaries). The effects of these hormones may affect one organ or tissue, or the entire body.

Exocrine Glands: Glands which secrete substances through ducts to surrounding surfaces. Includes sweat, salivary and tear glands, as well as the mucous glands in the digestive, respiratory, and genitourinary systems. These glands are greatly affected in CF. Their ducts may be obstructed by mucus.

Mechanisms of Hormone Action

I. Steroid and thyroid hormones enter their target cells and bind to receptor proteins.

• Thyroid hormones attach to chromatin-bound receptors located in the nucleus.

• Steroid hormones bind to cytoplasmic receptor proteins and translocate to the nucleus.

• Attachment of the hormone receptor protein complex to the cromatin activates genes and thereby stimulates RNA and protein synthesis.

II. Polar hormones bind to receptor proteins on the outer surface of the target cell membrane, indirectly activating a specific enzyme in the cell membrane.

• In the case of some hormones, activation of adrenylate cyclase occurs, resulting in the intracellular production of cyclic AMP.

• Cyclic AMP activates a cytoplasmic enzyme called protein kinase. Protein kinase phosphorylates specific enzyme protein and thereby changes the metabolism of the target cell for those hormones that use cAMP as a second messenger.

• In the case of other hormone actions, the enzyme phospholipase C is activated in the cell membrane, causing the release of inositol triphosphate into the cell.

• Inositol triphosphate stimulates the release of Ca++ from the endoplasmic reticulum of the target cell.

• Ca++ binds to regulatory proteins, such as calmodulin, that can influence the metabolism of the target cell.

PITUITARY GLAND

I The pituitary gland secretes eight hormones.

A The anterior pituitary secretes growth hormone, thyroid-stimulating hormone, adrenocorticotripic hormone, folicle-stimulating hormone, lutienizing hormone and prolactin.

B The posterior pituitary releases antidiuretic hormone and oxytocin, both of which are produced in the hypothalamus and transported to the posterior pituitary by the hypothalomo-hypophyseal tract.

II The release of posterior pituitary hormones is controlled by reflexes.

III Secretions of the anterior pituitary are controlled by hypothalamic hormones that stimulate or inhibit these secretions.

A These hormones are carried to the anterior pituitary by the hypothalamo-hypophyseal portal system.

IV Secretions of the anterior pituitary are also regulated by the feedback exerted by target gland hormones.

V Higher brain centers, acting through the hypothalamus, can influence pituitary secretions.

*Pituitary Gland: roughly size of a pea. Anterior and posterior secrete different hormones. Pituitary is under control of the hypothalamus. It is called the master gland because it influences so many other glands. Hypothalamus should be called the master gland because it controls the Pituitary Gland.

Hormones of the Posterior Pituitary Gland:

Antidiuretic Hormone (AKA. ADH or Vasopressin)
Functions:

• Increases water reabsorption by the kidney tubules (water returns to the blood)
• Decreases sweating
• Causes vasoconstriction (in large amounts)

Regulation of Secretion:

• Decreased water content in the body (alcohol inhibits secretion)

Oxytocin
Functions:

• Promotes contraction of myometrium of uterus (labor)
• Promotes release of of milk from mammary glands

Regulation of secretion:

• Nerve impulses from hypothalamus, the result of stretching of cervix or stimulation of nipple
• Secretion from placenta at end of gestation--- the stimulus is unknown

Hormones of the Anterior Pituitary Gland:

Growth Hormone (GH)
Functions:

• Increases rate of mitosis
• Increases amino acid transport in to cells
• Increases rate of protein synthesis
• Increases use of fats for energy

Regulation of Secretion:

• GHRH (hypothalamus) stimulates secretion
• GHIH---somatostatin (hypothalamus) inhibits secretion

Thyroid-Stimulating Hormone
Functions:

• Increases secretion of thyroxine and T3 by thyroid gland

Regulation of Secretion:

• TRH (hypothalamus)

Adrenocorticotropic Hormone (ACTH)
Functions:

• Increases secretion of cortisol by the adrenal cortex

Regulation of Secretion:

• CRH (Hypothalamus)

Prolactin
Functions:

• Stimulates milk production by the mammary glands

Regulation of secretions:

• PRH (hypothalamus) stimulates secretion
• PIH (hypothalamus) inhibits secretion

Follicle-Stimulating Hormone (FSH)
Functions in Women:

• Initiates growth of ova in ovarian follicles
• Increases secretion of estrogen by follicle cells

Functions in Men:

• Initiates sperm production in the testes

Regulation of Secretion:

• GnRH (hypothalamus) stimulates secretion
• Inhibin (ovaries or testes) inhibits secretion

Luteinizing Hormone (LH) (ICSH)
Functions in Women:

• Causes ovulation
• Causes the ruptured ovarian follicle to become the corpus luteum
• Increases secretion of progesterone by the corpus luteum

Functions in Men:

• Increases secretion of testosterone by the interstitial cells of the testes

Regulation of Secretion:

• GnRH (hypothalamus)

AUTOCRINE & PARACRINE REGULATION
1.Autocrine regulators are produced and act within the same tissue of an organ, whereas paracrine regulators are produced within one tissue and regulate a different tissue of the same organ.Both types are local regulators-they do not travel in the blood.

2.Prostaglandins are special twenty-carbon-long fatty acids produced by many different organs.They usually have regulatory functions within the organ in which they are produced.

Diseases of the Thyroid

Thyroid-stimulating hormone (TSH) from the anterior pituitary stimulates the thyroid to secrete thyroxine; however, it also exerts a trophic (growth stimulating) effect on the thyroid. This effect is evident in people who develop an iodine-deficiency goiter, an abnormal growth of the thyroid gland. With the lack of adequate iodine in the diet it interferes with the negative feedback control of TSH secretion, resulting in the formation of an endemic goiter.

Graves disease is a thyroid disorder characterized by goiter, exophthalmos, "orange-peel" skin, and hyperthyroidism (has excessive thyroxine secretion).

Because of its stimulation of protein synthesis, children need thyroxine for body growth and, most importantly, for th proper development of the central nervous system. The need for thyroxine is particularly great when the brain is undergoing its greatest rate of development – from the end of the first trimester of prenatal life to 6 months after birth. Hypothyroidism during this time may result in cretinism. Unlike people with dwarfism, who have inadequate secretion of growth hormone from the anterior pituitary, people with cretinism suffer severe mental retardation.

How Your Thyroid Works "A delicate Feedback Mechanism"

Your thyroid gland is a small gland, normally weighing less than one ounce, located in the front of the neck. It is made up of two halves, called lobes, that lie along the windpipe (trachea) and are joined together by a narrow band of thyroid tissue, known as the isthmus.

The thyroid is situated just below your "Adams apple" or larynx. During development (inside the womb) the thyroid gland originates in the back of the tongue, but it normally migrates to the front of the neck before birth. Sometimes it fails to migrate properly and is located high in the neck or even in the back of the tongue (lingual thyroid) This is very rare. At other times it may migrate too far and ends up in the chest (this is also rare).




The function of the thyroid gland is to take iodine, found in many foods, and convert it into thyroid hormones: thyroxine (T4) and triiodothyronine (T3). Thyroid cells are the only cells in the body which can absorb iodine. These cells combine iodine and the amino acid tyrosine to make T3 and T4. T3 and T4 are then released into the blood stream and are transported throughout the body where they control metabolism (conversion of oxygen and calories to energy). Every cell in the body depends upon thyroid hormones for regulation of their metabolism. The normal thyroid gland produces about 80% T4 and about 20% T3, however, T3 possesses about four times the hormone "strength" as T4.



The thyroid gland is under the control of the pituitary gland, a small gland the size of a peanut at the base of the brain (shown here in orange). When the level of thyroid hormones (T3 & T4) drops too low, the pituitary gland produces Thyroid Stimulating Hormone (TSH) which stimulates the thyroid gland to produce more hormones. Under the influence of TSH, the thyroid will manufacture and secrete T3 and T4 thereby raising their blood levels. The pituitary senses this and responds by decreasing its TSH production. One can imagine the thyroid gland as a furnace and the pituitary gland as the thermostat. Thyroid hormones are like heat. When the heat gets back to the thermostat, it turns the thermostat off. As the room cools (the thyroid hormone levels drop), the thermostat turns back on (TSH increases) and the furnace produces more heat (thyroid hormones).


The pituitary gland itself is regulated by another gland, known as the hypothalamus (shown in our picture in light blue). The hypothalamus is part of the brain and produces TSH Releasing Hormone (TRH) which tells the pituitary gland to stimulate the thyroid gland (release TSH). One might imagine the hypothalamus as the person who regulates the thermostat since it tells the pituitary gland at what level the thyroid should be set.

Pancreas and Other Endocrine Glands

Beta cells in the islets secrete insulin, and alpha cells secrete glucagon.

1. Insulin lowers blood glucose and stimulates the production of glycogen, fat, and protein.
2. Glucagon raises blood glucose by stimulating the breakdown of liver glycogen. It also promotes lipolysis and the formation of keytone bodies.
3. The secretion of insulin is stimulated by a rise in blood glucose following meals. The secretion of glucagon is stimulated by a fall in blood glucose during periods of fasting.

The pineal gland, located on the roof of the third ventricle of the brain, secretes melatonin.

1. Melatonin secretion is regulated by the suprachiasmatic nucleus of the hypothalamus, which is is the major center for the control of circadian rhythms.
2. Melatonin secretion is highest at night, and this hormone has a sleep-promoting effect. In many species, it also has an antigonadotropic effect and may play a role in timing the onset of puberty in humans although this is as yet unproven.

The thymus is the site of T cell lymphocyte production and secretes a number of hormones that may help to regulate the immune system.

The gastrointestinal tract secretes a number of hormones that help to regulate digestive functions.

The gonads secrete sex steroid hormones.

1. Leydig cells in the interstitial tissue of the testes secrete testosterone and other androgens.
2. Granulosa cells of the ovarian follicles secrete estrogen.
3. The corpus luteum of the ovaries secretes progesterone, as well as estrogen.

The placenta secretes estrogen, progesterone, and a variety of polypeptide and protein hormones that have actions similar to some anterior pituitary hormones.

In the News

• Did you know that almost all the research on stress has been conducted with men and that recent studies have found that women respond to stress in fundamentally different ways than men? Rather than simply "fight or flight," a woman's stress response may be to "tend and befriend." Read more about it here.

Question Review
1. What year was the first hormone discovered?
a. 1910
b. 1898
c. 1849
d. 1902
e. 1906

2. When you are dehydrated, your body will produce more ________ to conserve ____________.
a. ADH, water
b. TSH, iodine
c. oxytocin, water
d. water, MSH
e. none of the above

3.Steroid hormones are secreted by ___________.
a. the adrenal cortex
b. the gonads
c. the thyroid
d. both a and b
e. both b and c

4. Which is not apart of the endocrine system?
a. thyroid
b. pancreas
c. pituitary
d. brain

5. Why does insulin need to be given as a shot?
a. so the proteins can get into the blood stream
b. cause the insulin get though the body faster
c. because if taken as a pill the body will digest the insulin before it makes it to the blood stream.
d. both a and c

6. A_________hormone binds to a receptor within the target cell.
a. nonsteroid
b. cAMP
c. steroid
d. adenylate cyclase

7. The hormone properly called _______is also commonly known as adrenaline.
a. epinephrine
b. aldosterone
c. phospholipase c
d. oxytocin

8. All hormones can be divided into four chemical classes, they are.
a. Leptin, Aldosterone, Glucagon, Epinephrine
b. Amines, Polypeptides and proteins, Glycoproteins and Steroids
c. Melatonin, Oxytocin, Somatomedins and Glucocorticois
d. None of the above

9. What disease results from hyposecretion of GH ( in a child )?
a. dwarfism
b. cretinism
c. graves' disease
d. goiter
e. all of the above

10. Which is not produced in the anterior lobe of the Pituitary Gland?
a. growth hormone
b. prolactin
c. luteinizing hormone
d. Oxytocin
e. none of the above

11. Which disease causes fatigue, weight gain, hair loss and dry skin?
a. hyperkalemia
b. pancreatitis
c. cushings syndrome
d. hypothyroidism
e. all of the above

12. This gland is often called the master gland.
a. thymus
b. pituitary
c. thyroid
d. parathyroid
e. none of the above

13. Which of the following are considered Endocrine glands?
a. Pineal
b. Pituitary
c. islets of Langerhans
d. none of the above
e. all of the above

14. How many hormones does the pituitary gland secrete?
a. 8
b. 5
c. 10
d. 3
e. 9