Endocrine SystemThe endocrine system includes all of the hormone­producing glandsin the body.

What is meant by a hormone?

Hormones are chemical messengers.

In some ways the endocrine system serves a similar function to the nervous system: it communicates with various parts of the body, and controls their actions.

Unlike the nervous system, which uses electrical impulses (action potential) to communicate, the endocrine system uses chemicals...the hormones.

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Endocrine SystemThe glands of the endocrine system produce hormones in response to changes in the body's internal environment. Each hormone will havevery specific effects.

When an endocrine gland is stimulated, it releases hormones directly intothe blood stream. The hormone then circulates until it comes in contactwith specialized receptor sites on a target organ.

Each hormone fits only its own receptor sites, similar to the lock­and­key model of enzyme action. When the receptor site is triggered, the targetorgan will undergo a reaction.

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Endocrine SystemThese reactions could do anything from:

changing heart rate or blood pressure;

to beginning or shutting down an immune response;

to controlling the growth and development of the body,;

to regulating cycles of the reproductive system;

to changing a person's emotional state.

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Endocrine SystemThere are several endocrine glands located throughout the body.

Other glands, called exocrine glands, are different in that they do not empty into the bloodstream, but rather release their secretions through narrow tubes, or ducts.

The pancreas is a gland that serves a dual role...it produces insulin, the hormone responsible for controlling blood sugar levels; it also produces digestive enzymes which are released into the small intestine through the pancreatic duct and aid in the breakdown of fats, proteins, and carbohydrates.

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Endocrine SystemThree important facts to remember about hormone action:

1) Only very small quantities of hormone are required toproduce a reaction in the target organs

2) Hormones circulating through the bloodstream comeinto contact with almost all of the body's organs, but only produce a response in the target organ bearingtheir specific receptors

3) A single hormone can set off a chain reaction, causingnot just one but a whole series of responses...this makeshormones very powerful tools in maintaining homeostasis

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Homework

Read Section 13.1, pages 420­426

Take notes on these sections, following the guidelines given in class (for details, see the Bio 621 website)

Be prepared to review questions on this section during class tomorrow.

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Positive and Negative FeedbackHormones are not secreted by the endocrine glands at a constant rate. Instead, the glands adjust their production according to the needs of the body.

Endocrine glands may be stimulated by nerve impulses, or by chemical means. In some cases, the glands may monitor conditions in the body, and react to changing body chemistry, such as blood sugar levels. In other cases, the gland itself is triggered by hormones produced by a separate endocrine gland.

The interaction between two endocrine glands can take the form of a positive or a negative feedback loop.

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Positive FeedbackIn a positive feedback situation, an increase in production of one hormone causes an increase in production of a second hormone; increased levels of the second hormone cause a further increase in the first. The result is an amplification of the original hormone action.

Gland 1 Gland 2

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Negative FeedbackIn a negative feedback situation, the interacting hormones have opposing physiological properties. These are referred to as antagonistic hormones.

Hormone 1 levels Hormone 1 levels

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Two Types of HormonesHormones fall into one of two general categories:

1) Steroid hormones

2) Non­steroid, or protein­type hormones

Each category has a specific structure, and uses a different method to produce its effect.

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Steroid HormonesSteroid hormones are manufactured from cholesterol.

HO

CH3

CH3CHCH3 CH2 CH2 CH

CH2 CH2

CH3

CH3

Cholesterol molecule is composed of four rings of carbon, with four distinctside chains attached.

Cholesterol is manufactured mainly in the liver, and released into the bloodstream. Most steroid hormones are produced in the adrenal gland and in the gonads (testes and ovaries).

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Steroid HormonesA steroid hormone retains the ring structure of cholesterol, but alters the side chains.

O

CH3

CH3CH

CH3

O

progesterone testosteroneO

CH3

CH3OHCH3

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Steroid HormonesA steroid hormone retains the ring structure of cholesterol, but alters the side chains.

O

CH3

CH3

OH

OH

OH

C O

cortisolO

CH3

CH

OH

OHC O

OCH

aldosterone

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Steroid HormonesSteroid hormones operate using a mechanism called the one­messenger model.

Because they are small, lipid­soluble molecules, they are able to pass through the membrane. These hormones are able to enter most of the cells in the body, but produce their effects only on their target cells.

All cells contain receptor proteins, but they are different for the cells that make up different organs. A hormone will only have an effect when it enters a cell containing the correct receptor.

The receptor protein joins with a steroid hormone in a lock­and­key fashion, reacting with it and forming an active factor. This active factor then enters the nucleus, and triggers a response in the cell's DNA, causing a change in the rate of a chemical reaction within the cell...this change is the hormone effect. (Note that a change in the rate of a reaction may be to start or stop a reaction completely.)

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Steroid HormonesMechanism of a steroid hormone action

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Non­Steroid HormonesNon­steroid hormones operate using a mechanism called the two­messenger model.

Protein type hormones may actually be amino acids, peptides (linked chains of amino acids) or complete proteins. They can usually not cross a cell membrane. Instead, they bind with a receptor on the surface of a target cell.

The combination of non­steroid hormone and receptor activates enzymes in the cell membrane, which produce a compound that acts as a second messenger. Some common second messengers include cAMP (cyclic adensosine monophosphate, derived from ATP), calcium, or other enzymes from within the cell.

The second messenger can then trigger a series of chemical reactions within the cell. One important note is that while many different types of cells may use the same second messenger, the actual chain of reactions it triggers may be completely different in each cell type.

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Non­Steroid HormonesHow does caffeine act as a stimulant?

Caffeine inhibits the breakdown of cAMP, amplifying its effects,such increasing blood sugar, increasing heart and respiration rate,etc.

How does nicotine act as a stimulant?

Nicotine stimulates production of adrenaline, adrenocorticotropin(ACTH), cortisol, and antidiuretic hormone (ADH)

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Non­Steroid Hormones

HO

HOHO

CH CH2 NH CH3Adrenaline

Insulin

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Non­Steroid HormonesMechanism of a non­steroid hormone action

ATP

activeenzymein

activeenzymein

activeenzymein

activeenzymein

Final hormoneeffect

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HomeworkRead Pages 427­431 in Sectin 13.2

Describe the role of the pituitary gland in the body, including:*The difference between the posterior and anterior pituitary

*The origin and actions of the pituitary hormonesthyroid stimulating hormone (TSH)adrenocorticotropin (ACTH)prolactin (PRL)human growth hormone (HGH)follicle stimulating hormone (FSH)leutinizing hormone (LH)antidiuretic hormone (ADH)oxytocin

*Complete Questions #2 and 4 on page 426

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The Hypothalamus and Pituitary GlandAt this point, you should have a good general idea of how the endocrine system uses hormones to maintain homeostasis by controlling reactions in the body's systems.

The endocrine system is controlled largely by the hypothalamus. Remember from Chapter 12 that the hypothalamus is located near the middle of the brain, and is connected to the pituitary gland.

The hypothalamus monitors information entering the brain, and controls the autonomic nervous system.

By controlling the pituitary, the hypothalamus exerts control over the the other endocrine glands, as well as over many other ograns in the body.

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HypothalamusThe hypothalamus constantly monitors conditions within the body, and responds to those changing conditions.

It may be stimulated either by nerve signals coming from various locations, or by increasing or decreasing hormone levels in the blood.

The hypothalamus is directly linked to the pituitary gland, which is also called the "master gland", because the hormones it produces in turn control the hormone production of other endocrine glands.

These hormones which are specialized to regulate hormone production in other glands are called tropic hormones .

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Pituitary GlandThe anterior pituitary is located in front of the posterior pituitary (obviously!)

It is formed during embryonic development from cells near the roof of the mouth.

The posterior pituitary is composed of nerve tissue.

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Pituitary GlandThe hypothalamus uses two methods to control the pituitary.

The anterior pituitary is controlled through the use of hormones secreted by the hypothalamus, called releasing factors . These releasing factors travel through a short network of blood vessels from the hypothalamus to the anterior pituitary gland, and trigger a response.

The posterior pituitary gland is connected to the hypothalamus by a set of nerve fibers. These nerve fibers produce hormones and transfer them to the posterior pituitary gland, where they are temporarily stored and released as needed.

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Hormones of the Anterior Pituitary GlandThe major hormones of the anterior pituitary gland include:

thyroid stimulating hormone (TSH)

adrenocorticotropin (ACTH)

prolactin (PRL)

human growth hormone (HGH)

follicle stimulating hormone (FSH)

leutinizing hormone (LH)

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Hormones of the Anterior Pituitary Gland

Thyroid Stimulating Hormone (TSH)

Stimulates the production and release of thyroxin by thethyroid gland

Adrenocorticotropin (ACTH)

Stimulates production and release of hormones from thecortex (outer layer) of the adrenal glands

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Hormones of the Anterior Pituitary Gland

Prolactin (PRL)

Stimulates development of mammary gland tissue andmilk production after a female gives birth

Human Growth Hormone (HGH)

Also referred to as somatotropin . Increases absorption ofcalcium, which results in growth of bone and cartilage tissue;also stimulates protein synthesis and lipid metabolism

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Hormones of the Anterior Pituitary GlandGonadotropins:

Follicle Stimulating Hormone (FSH)

In females, stimulates the development of egg cells in the ovariesIn males, controls development of sperm cells in the testes

Leutinizing Hormone (LH)

Causes the release of egg cells from the ovaries in femalesIn both males and females, it controls the production ofsex hormones

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Pituitary GlandThe major hormones of the posterior pituitary gland include:

Antidiuretic Hormone (ADH)

Also called vasopressin . Regulates sodium levels in thebloodstream; stimulates vasoconstriction (constrictionof severed arteries to reduce blood loss); controlsreabsorption of water by the kidneys

Oxytocin

Stimulates contraction of uterine muscles duringchildbirth, and the release of milk following childbirth;may also promote bonding between a mother and baby

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Questions #2 & 4, pg 4262. (a) How is an exocrine gland different from an

endocrine gland?

(b) Identify two organs that act as both endocrine and exocrine glands.

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Questions #2 & 4, pg 4264. Compare the way steroid and non­steroid hormones affect

cellular activity.

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Steroid HormonesMechanism of a steroid hormone action

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Non­Steroid HormonesMechanism of a non­steroid hormone action

ATP

activeenzymein

activeenzymein

activeenzymein

activeenzymein

Final hormoneeffect

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Homework

Read pages 431­436, beginning with the subsection titled"The Thyroid and Parathyroid "and ending at (and including) the subsection titled"The Pancreas "

Take notes on these sections, including the specific actionof the major hormones.

Complete Question #1 and 3 on page 440

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Homework

• Read the remainder of Section 13.2 (pages 435­440)

• Complete the list of endocrine hormones and their functions, similar to what we began during class on Friday

• Complete Questions #2­8 and 10 on page 447

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Thyroid and Parathyroid Glands

Thyroid

Parathyroid hormone (PTH)

Parathyroid

ThyroxineCalcitonin

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ThyroidThyroxine

• non­steroid hormone• increases base metabolic rate, especially in the

skeletal muscle, heart, liver, and kidneys• necessary for normal mental and physical

development

Calcitonin• increases rate of calcium deposit in bone cells• increases calcium excretion in the kidneys• result: decreased calcium levels in the blood

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ParathyroidParathyroid Hormone (PTH)

• causes bone tissue to release calcium into the blood

Promotes Vitamin D synthesis, which:• increases calcium re­absorption by the kidneys• increases calcium absorption by small intestine• result: increased calcium levels in the blood

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SkinVitamin D

• steroid hormone, synthesized starting in the skin• requires exposure to UV rays to begin process• helps regulate blood calcium and phosphate levels• increases release of calcium into blood from bone• increases reabsorption of calcium in kidney

and absorption of calcium in duodenum

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The Pancreas

Insulin

Glucagon

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The PancreasInsulin

• steroid hormone• triggers the liver to absorb glucose from the blood,

and store it as glycogen• increase fat tissue absorption of glucose, fatty acids,

and amino acids• stimulates protein synthesis and tissue growth• suppresses glocose metabolism in liver and muscle cells

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The PancreasGlucagon

• steroid hormone• triggers the liver to convert glycogen to glucose, and

release glucose into the blood

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The Pineal GlandMelatonin

• follows a cyclic pattern of rising and falling(Circadian rhythm)

• Induces feeling of sleepiness

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The Thymus GlandThymosin

• normally present only until puberty• stimulates maturation of lymph cells into T­cells

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Chapter Review Questions2) Name the gland and hormones associated with each disease,

and the symptoms

a) Acromegaly

b) SAD

c) Diabetes

d) Hypothyroidism

e) Goiter

f) Gigantism

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Chapter Review Questions3) Why is caffeine banned for Olympic athletes?

What hormones would you expect to be banned?

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Chapter Review Questions4) Explain how hormones regulate the level of calcium in the blood.

The thyroid gland secretes calcitonin in responce to high blood calcium levels. This promotes uptake of calcium into bone tissue, and excretion of calcium by the kidney. This decreases the levels of calcium in the blood.

As calcium levels fall, the parathyroid is stimulated to produce parathyroid hormone (PTH). This causes the bone tissue to release calcium into the blood, and at the same time increases synthesis of Vitamin D. This causes the kidney to reabsorb more calcium and the small intestine to absorb increased amounts of calcium. This raises the overall level of calcium in the blood.

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Chapter Review Questions5) Why is goiter much less common in most parts of the world now?

Goiter is caused by low levels of iodine in the blood, which results in growth of thyroid tissue. This is becuase iodine is needed by the thyroid to produce thyroxine (four iodine atoms per thyroxine molecule).

Since iodine is now added to table salt, iodine deficiencies are uncommon in most parts of the world.

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Chapter Review Questions6) How do levels of HGH change as we age? What is the affect?

HGH levels tend to decrease as we get older. This typically results in decreased muscle mass, and possibly lower bone density, as well as wrinkles and weight gain from lower levels of lipid metabolism.

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Chapter Review Questions7) Give some examples of hormone levels changing in response to:

a) the nervous sytsem

b) other hormones

c) changes in body chemistry

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Chapter Review Questions8) Explain and give an example of a negative feedback loop in the

human body.

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Chapter Review Questions10) Explain the difference between a steroid and non­steroid hormone,

in terms of their chemical structure and how they alter the chemistryof a cell.

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What type of Hormone?

ATP

activeenzymein

activeenzymein

activeenzymein

activeenzymein

Final hormoneeffect

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What type of Hormone?

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HomeworkRead Section 13.3 (pages 441­446) and take notes on the section.

Bring questions to class tomorrow for discussion.

Project due dates?

Class day to work on projects?

Test date?

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The Adrenal Glands

The Adrenal glands are located at the top of the kidneys.

The major function of the adrenal glands is controlling the body's response to stress.

The adrenal glands are controlled by nerve impulses and tropic hormones from the hypothalamus.

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The Adrenal Glands

The adrenal glands are covered by a capsule of connective tissue and fat.The glands themselves contain two layers, the outer cortex and the inner medulla. These areas function independently.The medulla controls the body's reaction to short­term stress, while the cortex is responsible for reacting to long­term stress.

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The Adrenal CortexThe major hormones produced by the adrenal cortex include:

Cortisol

Aldosterone

Androgens

Estrogens

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CortisolCortisol

• Usually follows a 24­hour cycle (called a circadian rhythm)

• Triggers conversion of proteinsto glycogen, providingready supplies of glucose that can be dumped into the bloodfrom the liver; also, the breakdown of lipids in fat cells

• Anti­inflammatory effects (decreases fluid buildup)

• Suppresses production of T­cells and antibodies(immune response)

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CortisolCortisol

Under normal circumstances, levels of cortisol rise during the early morning, just before waking up. This simply has the effect of increasing wakefulness and energy during the day.

However, during periods of prolonged stress, this can cause a number of negative effects, including:

• depressing the immune response, increasing the riskof infection and onset of cancer

• redistribution of energy stored in muscle protein to fat tissue, creating greater risk of Type 2 diabetes, high blood pressure, and heart disease

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AldosteroneAldosterone

• Maintains normal mineral balance in the blood

• Increases reabsorption of sodium by the kidneys and colon, while also increasing excretion of potassium from the kidneys

• This triggers production of ADH, which increases absorptionof water into the blood

• End result, increased blood pressure

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AldosteroneAldosterone

Under normal circumstances, levels of aldosterone are controlledby changes in blood pressure.

• As blood pressure rises, aldosterone production drops

• As blood pressure falls, aldosterone production increases

Hypersecretion (overproduction) or hyposecretion (underproduction)of aldosterone can lead to disorders such as Cushing's syndromeor Addison's disease.

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Sex HormonesAndrogens

• found in both males and females, with higher levels in males

• only a small amount of this hormone is secreted by the adrenal cortex: in males, most is produced in the testes, andthe hormone plays a major role in normal development of malesexual characteristics;in females, the adrenal cortex accounts for about half of thetestosterone produced

• promotes muscle and skeletal development

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Sex HormonesEstrogens

• found in both males and females, with higher levels in females

• only a small amount of this hormone is secreted by the adrenal cortex (until after menopause in females)

• promotes development of female sexual characteristics

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The Adrenal MedullaThe major hormones produced by the adrenal cortex include:

• Adrenaline (epinephrine)

• Noradrenaline (norepinephrine)

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AdrenalineThe adrenal medulla produces the body's short­term response to stress, or immediate danger. This is also called the:

• Secretion is controlled by nerve impulses from the hypothalamus• Adrenaline and noradrenaline act as neurotransmitters for the

sympathetic nervous system• They are chemically similar, and produce similar effeects• They are secreted by the medulla in about an 85/15 ratio

"fight or flight response"

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AdrenalineThe effects of adrenaline and noradrenaline include:

• Increase heart rate, breathing rate, and blood pressure

• Dilation of blood vessels in the heart and respiratory system;while constricting blood bessels to other areas

• Increase of release of glucose from the liver, while slowing downabsorption of food from the digestive system

• These hormones break down quickly, so the effect passes rapidlyonce the stressful situation is removed (think of recoveringfrom being scared)

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Anaphylactic ShockAllergies are an overreaction by the immune system to a normally harmless substance, such as peanut oil or other foods, latex (for example, found in the gloves used in lab), bee stings, pollen, dust, smoke, penicillin or other medications, etc.

Any of these chemicals are recognized by cells of the immune system because of "markers" on their surface. These are called antigens. During an allergic reaction, these antigens cause the release of histamine into the blood.

Histamine is an inflammatory chemical, causing dilation of capillaries, fluid buildup, swelling, pain, and the attraction of macrophages. Normally, this reaction is controlled and mild.

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Anaphylactic Shock

In people with severe allergies, the reaction is severe. The leak of fluid from blood is enough to lower blood pressure and oxygen levels in the bloodstream; swelling may be enough to shut off airways. In very severe cases, it can lead to death in a matter of minutes.

Fortunately, administration of adrenaline through an injection (epi­pen) can quickly counteract these effects. By constricting small blood vessels and increasing heart rate, adrenaline will lower the amount of fluid leaking from the bloodstream; this quickly raises blood pressure and reduces swelling in the affected areas.

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Homework

Read Section 13.3 (pages 441­446)

Now that we have covered the major glands of the endocrine system, create a complete chart, listing all of the glands discussed, the hormones associated with each gland, and the specific effects of each hormone.

Bring questions to class tomorrow for discussion.

Project due dates?

Class day to work on projects?

Test date?

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