Chapter 18

Copyright © John Wiley & Sons, Inc. All rights reserved.

CHAPTER 18The Endocrine System


INTRODUCTION The nervous and endocrine systems

coordinate all of the body systems

The nervous system does so through the

action of neurons, and the

neurotransmitters they secrete

The endocrine

system uses

hormones produced

by endocrine structures

to produce their

effects


Hormones are simply mediator

molecules that have effects on cells in the

local environment, or in a distant part of the

body

Some hormones, called autocrine

hormones are local hormones that are

secreted, and bind to the same cell.

TYPES OF HORMONES


TYPES OF HORMONES Hormones as mediator molecules …

Paracrine hormones are local hormones

that are secreted into interstitial fluid and

act on nearby cells


Hormones as mediator molecules …

Endocrine hormones are secreted into

interstitial fluid and then absorbed into the

bloodstream to be carried systemically

to any cell that

displays the

appropriate type

of receptor

TYPES OF HORMONES


SOLUBILITY OF HORMONES Hormones can be divided into two broad

chemical classes. This chemical

classification is useful because the two

classes exert their effects differently

Lipid soluble hormones bind to receptors

in the cytoplasm or nucleus of the cell

Water soluble hormones bind to

receptors on the surface of the cell


SOLUBILITY OF HORMONES Lipid soluble hormones consist of steroid

hormones, thyroid hormones, and the gas

nitric oxide

Steroid hormones are derived from

cholesterol

Thyroid hormones (T3 and T4) are

synthesized by attaching iodine to the

amino acid tyrosine

The gas nitric oxide (NO) is both a hormone

and a neurotransmitter. Its synthesis is

catalyzed by the enzyme nitric oxide

synthase


SOLUBILITY OF HORMONES Lipid soluble hormones require a carrier

protein for transport in the watery

environment of the blood


1 Lipid-solublehormonediffuses into cell

Blood capillary

Target cell

Transportprotein

Free hormone


Blood capillary

Activatedreceptor-hormonecomplex altersgene expression

NucleusReceptor

mRNA

DNA

Cytosol

Target cell

Transportprotein

Free hormone

2


Blood capillary


NucleusReceptor

mRNANewly formedmRNA directssynthesis ofspecific proteinson ribosomes

DNA

Cytosol

Target cell

Transportprotein

Free hormone

Ribosome

2

3


Blood capillary


NucleusReceptor

mRNANewly formedmRNA directssynthesis ofspecific proteinson ribosomes

DNA

Cytosol

Target cell

New proteins altercell's activity

Transportprotein

Free hormone

Ribosome

Newprotein

2

3

4

Lipid-SolubleHormone Action


SOLUBILITY OF HORMONES Water soluble hormones include peptide

and protein hormones (and others with an

amine group), and a group of local hormones

derived from the arachidonic acid on our cell

membranes called eicosanoids

Peptide hormones and protein hormones are

amino acid polymers

The two major types of eicosanoids are

prostaglandins and leukotrienes – both play

a role in mediating the inflammatory

response


SOLUBILITY OF HORMONES Water soluble hormones are easy to

transport in the watery blood. The plasma

membrane of target cells, however, is

impermeable to them

Water soluble hormones exert their effects

by binding to receptors exposed to the

interstitial fluid on the surface of target

cells

• the hormone binding to its receptor acts

as the first messenger in a cascade of

signal transduction


The first messenger (the hormone) then

causes production of a second messenger

inside the cell, where specific hormone-

stimulated responses take place

One common second messenger is

cyclic AMP (cAMP). Neuro-

transmitters, neuropeptides, and

several sensory transduction

mechanisms (vision) also act via

second-messenger systems

SOLUBILITY OF HORMONES


Water-solublehormone

Receptor

G protein

Blood capillary

Binding of hormone (first messenger)to its receptor activates G protein,which activates adenylate cyclase

Adenylate cyclase

Target cell

1


Receptor

G protein

cAMP

Second messenger

Activated adenylatecyclase convertsATP to cAMP

Blood capillary


Adenylate cyclase

Target cell

ATP

1

2


Receptor

cAMP serves as asecond messengerto activate proteinkinases

G protein

Protein kinases

cAMP

Second messenger


Blood capillary


Adenylate cyclase

Target cell

ATP

1

2

3 Activatedproteinkinases


Receptor


G protein

Protein kinases

cAMP

Activatedproteinkinases

Second messenger


Activated proteinkinasesphosphorylatecellular proteins

Blood capillary


Adenylate cyclase

Target cell

ATP

1

2

4

3

Protein— P

ADP

Protein

ATP


Receptor


G protein

Protein kinases

cAMP


Protein—

Second messenger



Millions of phosphorylatedproteins cause reactions thatproduce physiological responses

Blood capillary


Adenylate cyclase

Target cell

P

ADP

Protein

ATP

ATP

1

2

4

3

5


Receptor


G protein

Protein kinases

cAMP


Protein—

Second messenger

Phosphodiesteraseinactivates cAMP



Millions of phosphorylatedproteins cause reactions thatproduce physiological responses

Blood capillary


Adenylate cyclase

Target cell

P

ADP

Protein

ATP

ATP

1

2

6

4

3

5

Water-Soluble Hormone Action


EFFECTS OF HORMONES Prostaglandins (PGs) and leukotrienes are

eicosanoid hormones with local control. They

are synthesized from membrane lipids and

have widespread effects

PG’s mediate pain, platelet aggregation,

fever, and inflammation. They regulate

smooth muscle contraction, gastric acid

secretion, and airway size

• aspirin is a drug that works by inhibiting an

enzyme necessary for synthesis of certain

PGs: the ones that facilitate pain and the

inflammatory response


EFFECTS OF HORMONES Endocrine hormones control a variety of

physiological processes. Among other

things, they:

Balance the composition and volume of

body fluids

Regulate metabolism and energy

production

Direct the rate and timing of growth and

development

Exert emergency control during physical

and mental stress (trauma, starvation,

hemorrhage)

Oversee reproductive mechanisms


EFFECTS OF HORMONES(Interactions Animation)

o Introduction to endocrine hormones: Regulation, secretion and concentration

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ENDOCRINE SYSTEM GLANDS Glands that secrete endocrine hormones into

the bloodstream are called endocrine

glands

They are one of two major types of glands

in the body, the other being exocrine

glands (which

secrete their products into ducts )

In this chapter we will focus our

study on the endocrine glands

and the widespread effects of

endocrine hormones


CONTROL OF HORMONES When stimulated, an endocrine gland will

release its hormone in frequent bursts,

increasing the concentration of the hormone

in the blood

Hormone secretion is regulated by signals

from the nervous system, chemical

changes in the blood, and other

hormones

• Most hormonal regulatory systems work

via negative feedback, but a few

operate via positive feedback


CONTROL OF HORMONES This example shows how PTH and calcitonin

have negative feedback influence on one

another


CONTROL OF HORMONES In a positive feedback

system the hormone

output reinforces and

encourages the stimulus.

For example, during

childbirth, the hormone

oxytocin stimulates

contractions of the uterus,

and uterine contractions in

turn stimulate more

oxytocin release, a positive

feedback effect


CONTROL OF HORMONES(Interactions Animation)

o Hormones Summary


http://www.wiley.com/college/tortora/0470084715/animations/over_hormones/screen0.swf


THE ENDOCRINE SYSTEM The endocrine system consists of the

pituitary, thyroid, parathyroid, adrenal

and pineal glands

Some of the most important glands of the

endocrine system are not exclusively

endocrine glands: The hypothalamus,

thymus, pancreas, ovaries, and testes

are paramount;

the kidneys, stomach, liver,

small intestine, skin, heart,

and placenta also contribute


THE ENDOCRINE SYSTEM


THE HYPOTHALAMUS The hypothalamus is the major link

between the nervous and endocrine systems

It receives input from several regions in the

brain including the

thalamus, the

RAS, and

the limbic

system


THE PITUITARY GLAND The hypothalamus mainly controls the

pituitary gland, which is also called the

hypophysis

The pituitary hangs down from the

hypothalamus

on a stalk called the infundibulum

The gland is divided into an anterior

adenohypophysis and a posterior

neurohypophysis - the anterior pituitary

accounts

for about 75% of the total

weight of the gland


THE ADENOHYPOPHYSIS The anterior pituitary (adenohypophysis) is

anatomically and functionally connected

to the hypothalamus by blood vessels that

form a portal system called the

hypophyseal portal system

In a portal system, blood flows from one

capillary network into a portal vein, and

then into a second capillary network before

returning to the heart

• The name of the portal system indicates

the location of the second capillary

network


Specialized neurosecretory cells in the

hypothalamus secrete releasing hormones

into the hypophyseal portal system

that supplies blood to the

anterior pituitary

gland

THE ADENOHYPOPHYSIS


THE ADENOHYPOPHYSIS The second capillary system of the

hypophyseal portal system delivers the

hypothalamic releasing hormones to the

anterior pituitary

5 types of anterior pituitary cells secrete

seven hormones


ANTERIOR PITUITARY HORMONES

Hypothalamus Hormone

Hormone released from Adenohypoph

ysis

Major Function/ Target

Growth hormone releasing hormone (GHRH)

Human Growth Hormone (hGH)

Also called somatostatin, stimulates secretion of insulin-like growth factors (IGFs) that promote growth

Thyrotropin releasing hormone (TRH)

Thyroid Stimulating Hormone (TSH)

Stimulates synthesis and secretion of thyroid hormones by the thyroid gland

Prolactin releasing hormone (PRH)

Prolactin (PRL)

Stimulates breast growth, and development of the mammary glands



Hypothalamus Hormone

Hormone released

from Adenohypop

hysis


Gonadotropic releasing hormone (GnRH)

Follicle Stimulating hormone (FSH)

Ovaries initiate development of oocytes; testes initiate development of spermatozoa

Gonadotropic releasing hormone (GnRH)

Luteinizing hormone (LH)

Ovaries stimulate ovulation; testes stimulate testosterone production



Hypothalamus

Hormone

Hormone released from Adenohypoph

ysis


Corticotropin releasing hormone (CRH)

Adrenocorticotropic Hormone (ACTH)

Stimulates release of mineralocorticoid, glucocorticoid, and androgen hormones from the adrenal cortex

Corticotropin releasing hormone (CRH)

Melanocyte Stimulating hormone (MSH)

Stimulate the production and release of melanin by melanocytes in skin and hair. MSH signals to the brain have effects on appetite and sexual arousal


ANTERIOR PITUITARY HORMONES(Interactions Animation)

hGH Stimulating Glyc

ogenolysis

hGH Growth and Dev

elopment


http://www.wiley.com/college/jenkins/0470227583/animations/index_17_03_01.html






Cortisol

ACTH and Cortisol






TRH and TSH





Tropic hormones are hormones produced

and secreted by the anterior pituitary that

target other endocrine glands

All hormones in the previous lists target

other endocrine glands (are trophic

hormones) except hGH, Prolactin, and

MSH, which directly target the end organs


THE NEUROHYPOPHYSIS The posterior pituitary (neurohypophysis)

is embryologically derived from and

anatomically connected to the hypothalamus

– it releases, but does not synthesize any

hormones

When stimulated, neurosecretory

cells in the hypothalamus

release oxytocin and

ADH from their axon

terminals located in

the posterior pituitary


THE NEUROHYPOPHYSIS Oxytocin targets smooth muscle in the

uterus and breasts. In the uterus, oxytocin

stimulates uterine contractions, and in

response to the sucking from an infant,

oxytocin stimulates “milk letdown” in the

breasts

ADH targets the collecting ducts in the

kidney and sweat glands in the skin to

minimize water loss. It also directly causes

arterioles to constrict thereby increasing

blood pressure


THE NEUROHYPOPHYSIS

This graphic

demonstrates the

regulation of ADH

secretion


POSTERIOR PITUITARY HORMONES

Antidiuretic Hormone Animation




PITUITARY GLAND DISORDERS Acromegaly occurs as a result of excess HGH

during adulthood. This disease is marked by

enlargement and elongation of the bones of

the face, jaw, cheeks, and hands (the long

bones of

the extremities are

unaffected because the

growth plates have

already closed)


PITUITARY GLAND DISORDERS Diabetes Insipidus (DI) is very different from

the disease called sugar diabetes (diabetes

mellitus)

DI is caused by the insufficient release of

ADH from the neurohypophysis. Without

ADH acting on the collecting ducts in the

kidneys, the normal urine output of 1–1.5

liters per day increases to over 2.5 liters

per day and dehydration and

hypernatremia results


THE THYROID GLAND The butterfly-shaped thyroid gland is

located inferior to the larynx and anterior to

the trachea. It has two laterally placed lobes

separated by a bridge-like isthmus


THE THYROID GLAND Most of the thyroid gland is composed of

spherical groups of follicular cells called

thyroid follicles

The follicles store

a 100-day supply

of its two hormones

in an inactive

gel-like substance

called TGB (for

thyroglobulin)


Thyroid-stimulating hormone (TSH) is

released by the anterior pituitary gland in

response to TRH secreted into the portal

system

The hypothalamus

responds to higher

circulating levels of

T3 and T4 via negative

feedback to inhibit

TRH secretion

THYROID HORMONES


Low blood levels of T3

and T3 or low metabolicrate stimulate release of

HypothalamusTRH

Actions of Thyroid Hormones:

Increase basal metabolic rate

Stimulate synthesis of Na+/K+ ATPase

Increase body temperature (calorigenic effect)

Stimulate protein synthesis

Increase the use of glucose and fatty acids for ATP production

Stimulate lipolysis

Enhance some actions of catecholamines

Regulate development and growth of nervous tissue and bones

1

Anteriorpituitary

TRH, carriedby hypophysealportal veins toanterior pituitary,stimulatesrelease of TSHby thyrotrophs



Hypothalamus

TSH

TRH







Stimulate lipolysis



1

2

Anteriorpituitary


TSH released intoblood stimulatesthyroid follicular cells

Thyroidfollicle



Hypothalamus

Anteriorpituitary

TSH

TRH







Stimulate lipolysis



1

2

3

T3 and T4

released intoblood byfollicular cells



Thyroidfollicle



Hypothalamus

Anteriorpituitary

TSH

TRH







Stimulate lipolysis



1

2

3

4 T3 and T4

released intoblood byfollicular cells

ElevatedT3inhibitsrelease ofTRH andTSH(negativefeedback)



Thyroidfollicle



Hypothalamus

Anteriorpituitary

TSH

TRH







Stimulate lipolysis



1

2

3

5

4

Thyroid HormoneRegulation


A goiter is an enlargement of the thyroid

gland and may be associated with

hyperthyroidism, hypothyroidism, or

euthyroidism

In many third-word countries

dietary iodine intake is inadequate;

the resultant low level of thyroid

hormone in the blood stimulates

secretion of TSH, which causes

thyroid gland enlargement

THYROID HORMONES


THE PARATHYROID GLANDS The parathyroid glands are small, round

masses of tissue attached to the posterior

surface of the lateral lobes of the thyroid

gland

There are usually two

parathyroid glands

attached to each

lobe of the thyroid,

one superior and one inferior


PARATHYROID HORMONES Calcitonin (Thyrocalcitonin) is made by the

parafollicular (C-cells) of the thyroid gland

and

when secreted lowers the blood calcium

level

An increase in blood calcium will stimulate

the C-cells of the thyroid to secrete calcitonin

Increased calcitonin will cause a negative

feedback inhibition of parathyroid hormone

(PTH) which

causes a decrease in blood calcium and an

increase in blood phosphate levels


PARATHYROID HORMONES(Interactions Animation)

Calcitonin




Parathyroid hormone (PTH) is made by the

more numerous chief (principal) cells of the

gland

PTH increases absorption

of Ca2+ from the GI tract

and stimulates osteoclastic

activity so that Ca2+ is

released from bone into

the blood

PARATHYROID HORMONES


PARATHYROID HORMONES(Interactions Animation)

Parathyroid Hormone




1 High level of Ca2+ in bloodstimulates thyroid glandparafollicular cells to release more CT.


CALCITONIN inhibitsosteoclasts, thus decreasingblood Ca2+ level.

2


Low level of Ca2+ in bloodstimulates parathyroid gland chief cells to release more PTH.


3

2




PARATHYROID HORMONE (PTH)promotes release of Ca2+ frombone extracellular matrix intoblood and slows loss of Ca2+ in urine, thus increasing bloodCa2+ level.

3

4 2

1

PTH also stimulatesthe kidneys to releaseCALCITRIOL.

High level of Ca2+ in bloodstimulates thyroid glandparafollicular cells to release more CT.




3

4 25

1

CALCITRIOL stimulatesincreased absorption ofCa2+ from foods, whichincreases blood Ca2+ level.

PTH also stimulatesthe kidneys to releaseCALCITRIOL.

High level of Ca2+ in bloodstimulates thyroid glandparafollicular cells to release more CT.




3

4 25

6

Calcium Regulation


THE ADRENAL GLANDS There are two adrenal glands, one superior

to each kidney (also called the suprarenal

glands). During embryonic development,

the adrenal glands differentiate into two

structurally and functionally distinct regions

• the adrenal cortex

• the adrenal medulla Catecholamines like norepinephrine

Steroid hormones like cortisol


THE ADRENAL GLANDS


THE ADRENAL CORTEX The adrenal cortex is peripherally located

and makes up 80-90% of the total weight of

the gland

The cortex is subdivided into three zones,

each of which secretes a different group of

steroid hormones, all formed

from the cholesterol

molecule


Just deep to the CT capsule, the cells of the

zona glomerulosa synthesize

mineralocorticoid hormones

The middle zone, or zona fasciculata,

secrete mainly glucocorticoid hormones,

primarily cortisol

The inner zona reticularis

is the site of synthesis

of weak androgens

(masculinizing hormones)

ADRENOCORTICAL HORMONES


Mineralocorticoids regulate the

concentrations of Na+ and K+ in the blood

(affects blood volume/pressure)

Aldosterone is the major hormone in this

group

Glucocorticoids influence glucose

metabolism and the ability to resists the

effects of stress

Cortisol is the major hormone in this group

Weak androgens (masculinizing sex

hormones) have little effect in men, but play

an important role in promoting libido in

women

ADRENOCORTICAL HORMONES


The most important effects of aldosterone is

seen in the renin-angiotensin-aldosterone

system (RAAS)

The RAAS is stimulated by a decrease in

blood volume and/or blood pressure – as in

cases of dehydration or hemorrhage. Low

BP stimulates juxtaglomerular cells

in the kidney to

secrete the

enzyme renin

RAAS


RAAS Renin converts the plasma protein

angiotensinogen (produced in the liver) into

angiotensin I. As angiotensin I circulates to the

lungs, an enzyme called angiotensin converting

enzyme (ACE) converts angiotensin I to

angiotensin II

Angiotensin II stimulates the adrenal cortex to

secrete aldosterone (salt and H20 resorption

indirectly increases BP), and it is a

potent vasoconstrictor (which

directly increases BP)


RAAS


GLUCOCORTICOIDS Glucocorticoids (mainly cortisol) regulate

metabolism by promoting the breakdown of

proteins and fats to form glucose

(gluconeogenesis). Increased blood sugar

levels assist the body to cope with stress Their inflammatory effects result from

inhibiting white blood cells. Unfortunately

they also retard tissue repair and slow

wound healing • glucocorticoids are very useful in the

treatment of chronic inflammatory

disorders such as Lupus, though long

term side-effects are severe


GLUCOCORTICOIDS High levels of circulating cortisol, as

seen with corticosteroid drugs (prednisone),

or tumors (adrenal cortex, pituitary gland) is

called Cushing’s syndrome

Manifestations include hyper-

glycemia, poor wound healing,

osteoporosis, dermatitis, fat

redistribution (spindly arms and

legs, moon face, buffalo hump at

the neck), and truncal obesity


GLUCOCORTICOIDS In adults, hyposecretion of

glucocorticoids and aldosterone, usually as

a result of an autoimmune disorder, is called

Addison’s disease

The physiologic effects include

hypoglycemia, Na+ loss, low BP,

dehydration, and muscle weakness

• only after his death did the world

learn that President Kennedy

suffered from Addison’s disease


THE ADRENAL MEDULLA The inner region of the adrenal gland, the

adrenal medulla, is a modified sympathetic

ganglion that develops from the same

embryonic tissue as all other sympathetic

ganglia of the ANS and is innervated by

sympathetic preganglionic neurons

The catecholamines epinephrine (80%),

and norepinephrine (20%), are secreted

at the adrenal medulla and serve to

prolong the sympathetic response


ADRENAL MEDULLA HORMONES(Interactions Animation)

Epinephrine/Norepinephrine




THE PANCREAS The pancreas is both an endocrine and an

exocrine gland. It is located posterior and

inferior to the stomach. We will discuss its

endocrine functions here and its exocrine

functions

in detail in chapter 24


Most of the exocrine cells of the pancreas

are arranged in clusters called acini and

produce digestive enzymes which flow

through ducts into the GI tract

Distributed among the acini are clusters of

endocrine tissue

called pancreatic

islets (islets of

Langerhans)

THE PANCREAS


Each pancreatic islet contains four types of

hormone-secreting cells: alpha (A), beta (B),

delta (D), and F cells

Alpha cells secrete glucagon which

increases blood glucose levels by acting

on hepatocytes to

convert glycogen

to glucose

Beta cells secrete

insulin

PANCREATIC HORMONES


PANCREATIC HORMONES Insulin is an anabolic hormone - it decreases

blood glucose levels by acting on

hepatocytes to convert glucose

to glycogen and then facilitating

diffusion of glucose into the cells

Insulin and glucagon are counter-

regulatory hormones in that

their actions act to balance one

another in terms of blood glucose


Somatostatin acts in a paracrine manner to

inhibit both insulin and glucagon release

from neighboring beta and alpha cells. It

also inhibits the secretion

of hGH

The interactions of the

four pancreatic hormones

are complex and not

completely understood

PANCREATIC HORMONES


Low blood glucose(hypoglycemia)stimulates alphacells to secrete

1

GLUCAGON

Glucagon acts onhepatocytes(liver cells) to:

• convert glycogen into glucose (glycogenolysis)• form glucose from lactic acid and certain amino acids (gluconeogenesis)


GLUCAGON

1

2 Glucagon acts onhepatocytes(liver cells) to:


Glucose releasedby hepatocytesraises blood glucoselevel to normal


GLUCAGON

1

2

3




If blood glucosecontinues to rise,hyperglycemia inhibitsrelease of glucagon


GLUCAGON

1

2

3

4






High blood glucose(hyperglycemia)stimulates beta cellsto secrete

GLUCAGON

1 5

2

3

4

INSULIN

Insulin acts on variousbody cells to:

• accelerate facilitated diffusion of glucose into cells• speed conversion of glucose into glycogen (glycogenesis)• increase uptake of amino acids and increase protein synthesis• speed synthesis of fatty acids (lipogenesis)• slow glycogenolysis• slow gluconeogenesis







INSULINGLUCAGON

1 5

2

3

4

6 Insulin acts on variousbody cells to:


Blood glucose level falls







INSULINGLUCAGON

1 5

2

3

4

6

7

Insulin acts on variousbody cells to:


If blood glucose continuesto fall, hypoglycemiainhibits release ofinsulin

Blood glucose level falls







INSULINGLUCAGON

1 5

2

3

4

6

7

8

Glucose/InsulinRegulation


PANCREATIC HORMONES(Interactions Animation)

Insulin




GONADAL HORMONES The ovaries are paired oval bodies located

in the female pelvic cavity. They produce

several steroid hormones including two

estrogens (estradiol and estrone),

progesterone, relaxin, and inhibin

Estrogens, along with FSH and

LH from the anterior pituitary,

regulate the menstrual cycle,

maintain pregnancy, and prepare

the mammary glands for lactation


GONADAL HORMONES Ovarian hormones also promote

enlargement of the breasts and widening of

the hips at puberty, and help maintain these

female secondary sex characteristics

Progesterone prepares the uterus lining for

implantation of a fertilized ovum


OVARIAN HORMONES(Interactions Animation)

Hormonal Regulation of Female Reproductive System





GONADAL HORMONES The male gonads, the testes, are oval

glands that lie in the scrotum. The main

hormone produced and secreted by the

testes is testosterone, an androgen (male

sex hormone)

Testosterone is needed for

production of sperm and

maintenance of male

secondary sex characteristics


TESTICULAR HORMONES(Interactions Animation)

Hormonal Regulation of Male Reproductive Function





THE PINEAL GLAND The pineal gland is a small

endocrine gland

attached to the roof of the

third ventricle – it is part of

the epithalamus

The pineal gland secretes the hormone

melatonin, which contributes to

maintaining the biological clock (seasonal

and daily cycles)

• more melatonin is secreted in darkness;

the pineal gland is very developed in

nocturnal animals


THE THYMUS GLAND The thymus gland secretes thymosin, which

promotes the proliferation and maturation of

T cells

T cells are a type of white blood cell

(lymphocyte) that destroys microorganisms

and foreign substances

through direct

cellular contact


GENERAL ADAPTATION SYNDROME

The general adaptation syndrome (GAS)

or stress response refers to the

consequences of failure to respond

appropriately to emotional or physical

threats, whether actual or imagined

Interestingly, stressful situations can be

events normally considered to be “good”,

as well as bad

• for instance, a marriage can be as

stressful as a divorce, a birth as stressful

as a death, etc.



It is impossible to remove all of the stress from

our everyday lives, and some levels of stress

actually help us perform well and be productive.

Regardless, the body’s homeostatic mechanisms

attempt to counteract stress, and maintain a

constant internal environment whenever

possible

If stress is extreme, unusual, or long lasting,

the normal mechanisms may not be enough,

and they may elicit a series of changes called

the stress response or GAS



There are three stages to a prolonged

stress response: alarm reaction, resistance

reaction, and exhaustion

The alarm reaction is the short-lived

fight-or-flight response initiated by the

hypothalamus and mediated by the

sympathetic division of the ANS

• it brings huge amounts of glucose and

oxygen to the brain, the lungs, and

skeletal muscles

• the RAAS is also activated to maintain

blood volume and BP


THE ALARM REACTION(Interactions Animation)

The Alarm Reaction





The three stages to the GAS continued…

The resistance reaction is initiated in

large part by hypothalamic releasing

hormones and is a longer-lasting response.

The release of high levels of cortisol and

thyroid hormones assures that the tissues

of the body can sustain necessary

metabolic needs



The alarm reaction leads to a resistance response.



The three stages to the GAS continued… Exhaustion occurs when the body’s

reserves become so depleted that they

cannot sustain the resistance stage

• Prolonged exposure to high levels of

cortisol and other hormones causes

wasting of muscle, suppression of the

immune system, ulceration of the GI tract,

and failure of pancreatic beta cells…

disease often ensues


THE GAS(Interactions Animation)

General Adaptation Syndrome


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Chapter 18

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