Download Endocrine System

Endocrine System
The endocrine system includes all of the hormone­producing glands
in 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 System
The glands of the endocrine system produce hormones in response to changes in the body's internal environment. Each hormone will have
very specific effects.
When an endocrine gland is stimulated, it releases hormones directly into
the blood stream. The hormone then circulates until it comes in contact
with 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 target
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Endocrine System
These 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 System
There 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 System
Three important facts to remember about hormone action:
1)
Only very small quantities of hormone are required to
produce a reaction in the target organs
2)
Hormones circulating through the bloodstream come
into contact with almost all of the body's organs, but only produce a response in the target organ bearing
their specific receptors
3)
A single hormone can set off a chain reaction, causing
not just one but a whole series of responses...this makes
hormones 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 Feedback
Hormones 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 Feedback
In 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
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Gland 2
Negative Feedback
In a negative feedback situation, the interacting hormones have opposing physiological properties. These are referred to as antagonistic hormones.
Hormone 1 levels
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Hormone 1 levels
Two Types of Hormones
Hormones 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 Hormones
Steroid hormones are manufactured from cholesterol.
CH3
CH3
CH
CH3
CH2
CH2
CH2
CH
CH2
CH3
CH3
HO
Cholesterol molecule is composed of four rings of carbon, with four distinct
side 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 Hormones
A steroid hormone retains the ring structure of cholesterol, but alters the side chains.
CH3
CH
CH3
OH
CH3
O
CH3
CH3
CH3
O
O
progesterone
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testosterone
Steroid Hormones
A steroid hormone retains the ring structure of cholesterol, but alters the side chains.
OH
OH
CH
C O
CH3
O
O
OH
CH C
HO
CH3
CH3
O
O
cortisol
aldosterone
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Steroid Hormones
Steroid 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 Hormones
Mechanism of a steroid hormone action
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Non­Steroid Hormones
Non­steroid 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 Hormones
How 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
Adrenaline OH
HO
CH CH2 NH CH3
Insulin
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Non­Steroid Hormones
Mechanism of a non­steroid hormone action
in
active
enzyme
in
active
enzyme
ATP
in
active
enzyme
in
active
enzyme
Final hormone
effect
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Homework
Read 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 hormones
thyroid 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 Gland
At 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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Hypothalamus
The 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 Gland
The 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 Gland
The 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 Gland
The 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 the
thyroid gland
Adrenocorticotropin (ACTH)
Stimulates production and release of hormones from the
cortex (outer layer) of the adrenal glands
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Hormones of the Anterior Pituitary Gland
Prolactin (PRL)
Stimulates development of mammary gland tissue and
milk production after a female gives birth
Human Growth Hormone (HGH)
Also referred to as somatotropin . Increases absorption of
calcium, 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 Gland
Gonadotropins:
Follicle Stimulating Hormone (FSH)
In females, stimulates the development of egg cells in the ovaries
In males, controls development of sperm cells in the testes
Leutinizing Hormone (LH)
Causes the release of egg cells from the ovaries in females
In both males and females, it controls the production of
sex hormones
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Pituitary Gland
The major hormones of the posterior pituitary gland include:
Antidiuretic Hormone (ADH)
Also called vasopressin. Regulates sodium levels in the
bloodstream; stimulates vasoconstriction (constriction
of severed arteries to reduce blood loss); controls
reabsorption of water by the kidneys
Oxytocin
Stimulates contraction of uterine muscles during
childbirth, and the release of milk following childbirth;
may also promote bonding between a mother and baby
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Questions #2 & 4, pg 426
2.
(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 426
4.
Compare the way steroid and non­steroid hormones affect
cellular activity.
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Steroid Hormones
Mechanism of a steroid hormone action
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Non­Steroid Hormones
Mechanism of a non­steroid hormone action
in
active
enzyme
in
active
enzyme
ATP
in
active
enzyme
in
active
enzyme
Final hormone
effect
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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 action
of 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
Thyroxine
Calcitonin
Parathyroid
Parathyroid hormone (PTH)
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Thyroid
Thyroxine
•
•
•
Calcitonin
•
•
•
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non­steroid hormone
increases base metabolic rate, especially in the skeletal muscle, heart, liver, and kidneys
necessary for normal mental and physical development
increases rate of calcium deposit in bone cells
increases calcium excretion in the kidneys
result: decreased calcium levels in the blood
Parathyroid
Parathyroid 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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Skin
Vitamin D
•
•
•
•
•
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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
The Pancreas
Insulin
Glucagon
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The Pancreas
Insulin
•
•
•
•
•
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 Pancreas
Glucagon
•
•
steroid hormone
triggers the liver to convert glycogen to glucose, and
release glucose into the blood
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The Pineal Gland
Melatonin
•
•
follows a cyclic pattern of rising and falling
(Circadian rhythm)
Induces feeling of sleepiness
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The Thymus Gland
Thymosin
•
•
normally present only until puberty
stimulates maturation of lymph cells into T­cells
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Chapter Review Questions
2)
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 Questions
3)
Why is caffeine banned for Olympic athletes? What hormones would you expect to be banned?
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Chapter Review Questions
4)
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 Questions
5)
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 Questions
6)
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 Questions
7)
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 Questions
8)
Explain and give an example of a negative feedback loop in the
human body.
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Chapter Review Questions
10) Explain the difference between a steroid and non­steroid hormone,
in terms of their chemical structure and how they alter the chemistry
of a cell.
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What type of Hormone?
in
active
enzyme
in
active
enzyme
ATP
in
active
enzyme
in
active
enzyme
Final hormone
effect
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What type of Hormone?
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Homework
Read 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 Cortex
The major hormones produced by the adrenal cortex include:
Cortisol
Aldosterone
Androgens
Estrogens
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Cortisol
Cortisol
•
Usually follows a 24­hour cycle (called a circadian rhythm)
•
Triggers conversion of proteinsto glycogen, providing
ready supplies of glucose that can be dumped into the blood
from 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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Cortisol
Cortisol
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 risk
of 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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Aldosterone
Aldosterone
•
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 absorption
of water into the blood
•
End result, increased blood pressure
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Aldosterone
Aldosterone
Under normal circumstances, levels of aldosterone are controlled
by 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 syndrome
or Addison's disease.
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Sex Hormones
Androgens
•
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, and
the hormone plays a major role in normal development of male
sexual characteristics;
in females, the adrenal cortex accounts for about half of the
testosterone produced
•
promotes muscle and skeletal development
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Sex Hormones
Estrogens
•
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 Medulla
The major hormones produced by the adrenal cortex include:
•
Adrenaline (epinephrine)
•
Noradrenaline (norepinephrine)
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Adrenaline
The adrenal medulla produces the body's short­term response to stress, or immediate danger. This is also called the:
"fight or flight response"
•
•
•
•
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
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Adrenaline
The 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 down
absorption of food from the digestive system
•
These hormones break down quickly, so the effect passes rapidly
once the stressful situation is removed (think of recovering
from being scared)
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Anaphylactic Shock
Allergies 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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