Lecture Oct-27-11 Chapter 18

8/3/2019 Lecture Oct-27-11 Chapter 18

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Ch-18 The Endocrine System

Bio 2870 A & P1

Introduction to Anatomy and Physiology

Chapter 18

The Endocrine System


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Homeostasis and Intercellular Communication

Direct Communication Exchange of ions and molecules between adjacent cells across gap

junctions

Occurs between two cells of same type

Highly specialized and relatively rare

Paracrine Communication

Uses chemical signals to transfer information from cell to cell withinsingle tissue

Most common form of intercellular communication

Endocrine Communication

Endocrine cells release chemicals (hormones) into bloodstream

Alters metabolic activities of many tissues and organs simultaneously


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The Endocrine System

Regulates long-term processes Growth

Development

Reproduction

Uses chemical messengers to relay information and instructions

between cells

Target Cells Are specific cells that possess receptors needed to bind and read

hormonal messages

Hormones Stimulate synthesis of enzymes or structural proteins Increase or decrease rate of synthesis

Turn existing enzyme or membrane channel on or off


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Introduction to the Endocrine System

Figure 181 Organs and Tissues of the Endocrine System.


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Introduction to the Endocrine System

Figure 181 Organs and Tissues of the Endocrine System.


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Ch-18 The Endocrine System Hormones

Figure 18

2 A Structural Classification of Hormones


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Circulate freely or bound to transport proteins

1) Free Hormones Remain functional for less than 1 hour

Diffuse out of bloodstream:

bind to receptors on target cells

Are broken down and absorbed:

by cells of liver or kidney

Are broken down by enzymes:

in plasma or interstitial fluids

2) Transport Proteins bound hormones

Thyroid and Steroid Hormones

Remain in circulation much longer

Enter bloodstream

More than 99% become attached to special transport proteins

Bloodstream contains substantial reserve of bound hormones

Secretion and Distribution of Hormones


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Mechanisms of Hormone Action

Hormone Receptor Is a protein molecule to which a particular molecule binds

strongly

Responds to several different hormones

Different tissues have different combinations of receptors

Presence or absence of specific receptor determines hormonalsensitivity

Hormones and Plasma Membrane Receptors Catecholamines and peptide hormones

Are not lipid soluble

Unable to penetrate plasma membrane

Bind to receptor proteins at outer surface of plasmamembrane (extracellular receptors)


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Hormones and Plasma Membrane Receptors

Bind to receptors in plasma membrane

Cannot have direct effect on activities inside target cell

Use intracellular intermediary to exert effects

First messenger:

leads to second messenger may act as enzyme activator, inhibitor, or cofactor

results in change in rates of metabolic reactions

Important Second Messengers Cyclic-AMP (cAMP) : Derivative of ATP

Cyclic-GMP (cGMP) : Derivative of GTP

Calcium ions :


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The Process ofAmplification

Is the binding of a small number of hormone molecules tomembrane receptors

Leads to thousands of second messengers in cell

Magnifies effect of hormone on target cell

Down-regulation

Presence of a hormone triggers decrease in number of hormonereceptors

When levels of particular hormone are high, cells become less sensitive

Up-regulation

Absence of a hormone triggers increase in number of hormonereceptors

When levels of particular hormone are low, cells become more sensitive


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Figure 183 G Proteins and Hormone Activity

1) G Protein Enzyme complex coupled to

membrane receptor

Involved in link between firstmessenger and second

messenger Binds GTP

Activated when hormone bindsto receptor at membrane surfaceand changes concentration ofsecond messenger cyclic-AMP

(cAMP) within cell:

increased cAMP levelaccelerates metabolicactivity within cell

Hormones and Plasma Membrane Receptors


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Figure 18

3 G Proteins and Hormone Activity

2) G Proteins and Calcium Ions Activated G proteins trigger

opening of calcium ion channels inmembrane

release of calcium ions from

intracellular stores G protein activates enzyme

phospholipase C (PLC)

Enzyme triggers receptor cascade:

production ofdiacylglycerol

(DAG) and inositoltriphosphate (IP3) frommembrane phospholipids


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Figure 184a Effects of Intracellular Hormone Binding

Hormones andIntracellular Receptors

Alter rate of DNAtranscription in nucleus

Change patterns of

protein synthesis Directly affect metabolic

activity and structure oftarget cell

Includes steroids and

thyroid hormones


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Figure 184b Effects of Intracellular Hormone Binding

Hormones andIntracellular Receptors

Alter rate of DNAtranscription in nucleus

Change patterns of

protein synthesis Directly affect metabolic

activity and structure oftarget cell

Includes steroids and

thyroid hormones

O


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Endocrine Reflexes

Endocrine Reflexes Functional counterparts of neural reflexes

In most cases, controlled by negative feedback mechanisms

Stimulus triggers production of hormone whose effects reduceintensity of the stimulus

Endocrine reflexes can be triggered by

1) Humoral stimuli

Changes in composition of extracellular fluid

2) Hormonal stimuli

Arrival or removal of specific hormone

3) Neural stimuli

Arrival of neurotransmitters at neuroglandular junctions

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Endocrine Reflexes

Simple Endocrine Reflex

Involves only one hormone

Controls hormone secretion by the heart, pancreas, parathyroidgland, and digestive tract

Complex Endocrine Reflex Involves

One or more intermediary steps

Two or more hormones The hypothalamus

Neuroendocrine Reflexes

Pathways include both neural and endocrine components

Complex Commands Issued by changing

Amount of hormone secreted

Pattern of hormone release:

hypothalamic and pituitary hormones released in sudden bursts

frequency changes response of target cells

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Endocrine Reflexes

Figure 18

5 Three Mechanisms of Hypothalamic Control

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Pituitary Gland

Figure 186a The Anatomy and Orientation of the Pituitary Gland.

Also called hypophysis

Lies within sella turcica

Diaphragma sellae

A dural sheet that locks

pituitary in position Isolates it from cranial

cavity

Hangs inferior tohypothalamus

Connected byinfundibulum

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Pituitary Gland

Median Eminence

Swelling near attachment ofinfundibulum

Where hypothalamic neuronsrelease regulatory factors

Into interstitial fluids

Through fenestratedcapillaries

Releases nine important peptide

hormones Hormones bind to membrane

receptors

Use cAMP as secondmessenger

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Pituitary Gland

Figure 187 The Hypophyseal Portal System and the Blood Supply to the Pituitary Gland.

Portal Vessels Blood vessels link two

capillary networks

Entire complex is portal

system Ensures that regulatory

factors reach intendedtarget cells beforeentering generalcirculation

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Pituitary Gland

Anterior lobe (also called adenohypophysis) Hormones turn on endocrine glands or support other organs

Can be subdivided into three regions:

1. Pars distalis

2. Pars intermedia

3. Pars tuberalis

Posterior lobe (also called neurohypophysis) Contains unmyelinated axons of hypothalamic neurons

Supraoptic and paraventricular nuclei manufacture Antidiuretic hormone (ADH)

Oxytocin (OXT)

Oct-27-2011Ch 8 Th E d i S


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Pituitary Gland

Figure 188a Feedback Control of Endocrine Secretion

Releasing hormones (RH)

Stimulate synthesis andsecretion of one or morehormones at anterior lobe

Inhibiting hormones (IH)

Prevent synthesis andsecretion of hormonesfrom the anterior lobe

Rate of secretion is controlledby negative feedback

Two Classes of Hypothalamic Regulatory Hormones

Oct-27-2011Ch 8 Th E d i S t


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Pituitary Gland

Figure 188b Feedback Control of Endocrine Secretion.



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Pituitary Gland

Figure 18

9 Pituitary Hormones and Their Targets.



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Pituitary Gland

Oct-27-2011Ch 18 The Endocrine System


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Pituitary Gland



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The Thyroid Gland

Figure 1810a The Thyroid Gland.

Lies anterior to thyroid cartilage of larynx

Consists of two lobes connected by narrowisthmus



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The Thyroid Gland

Figure 1810b-c The Thyroid Gland.

Thyroid follicles

Hollow spheres lined by cuboidal epithelium

Cells surround follicle cavity that contains viscous colloid

Surrounded by network of capillaries that

deliver nutrients and regulatory hormones

accept secretory products and metabolic wastes

Oct-27-2011Ch-18 The Endocrine System


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The Thyroid Gland

Thyroglobulin (Globular Protein) Synthesized by follicle cells

Secreted into colloid of thyroid follicles

Molecules contain the amino acid tyrosine

Thyroxine (T4

) Also called tetraiodothyronine

Contains four iodide ions

Triiodothyronine (T3) Contains three iodide ions

C (Clear) Cells of the Thyroid Gland

Produce calcitonin (CT)

Helps regulate concentrations of Ca2+ in body fluids



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The Thyroid Follicles

Figure 1811a Synthesis, Storage,and Secretion of Hormones

Figure 1811b The Regulation ofThyroid Secretion.



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Ch 18 The Endocrine System

The Thyroid Gland

Thyroid-Stimulating Hormone (TSH)

Absence causes thyroid follicles to become inactive Neither synthesis nor secretion occurs

Binds to membrane receptors

Activates key enzymes in thyroid hormone production

Thyroid Hormones

Enter target cells by transport system

Affect most cells in body

Bind to receptors in

Cytoplasm Surfaces of mitochondria

Nucleus

In children, essential to normal development of

Skeletal, muscular, and nervous systems



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The Thyroid Gland

Calorigenic Effect

Cell consumes more energy resulting in increased heat generation Is responsible for strong, immediate, and short-lived increase in rate of

cellular metabolism



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Parathyroid Glands

Figure 1812 The Parathyroid Glands.

Embedded in posterior surface of thyroid gland

Parathyroid hormone (PTH) Produced by chief cells In response to low concentrations of Ca2+



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C 8 e doc e Syste

Parathyroid Glands

Four Effects of PTH1) It stimulates osteoclasts

Accelerates mineral turnover and releases Ca2+ from bone

2) It inhibits osteoblasts

Reduces rate of calcium deposition in bone

3) It enhances reabsorption of Ca2+ at kidneys, reducingurinary loss

4) It stimulates formation and secretion ofcalcitriol at

kidneys Effects complement or enhance PTH

Enhances Ca2+, PO43- absorption by digestive tract



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y

6-8 THE SKELETON AS A CALCIUM RESERVE

I. HORMONES & CALCIUM

BALANCEC. VITAMIN D

i. FUNCTIONS:

i. Calcium Resorption In TheIntestines

ii. Increases Osteoclastsiii. Maintains Proper Function Of

PTH



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Calcium Homeostasis

The Skeleton as a Calcium Reserve

Bones store calcium and other minerals

Calcium is the most abundant mineral in the body

Calcium ions are vital to: membranes

neurons

muscle cells, especially heart cells

Homeostasis is maintained Bycalcitonin and parathyroid hormone

Which control storage, absorption, and excretion



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6-8 Calcium Homeostasis

Calcitonin and parathyroid hormone control and affect

Bones :Where calcium is stored

Digestive tract :Where calcium is absorbed

Kidneys :Where calcium is excreted

Parathyroid Hormone (PTH)

Produced by parathyroid glands inneck

Increases calcium ion levels by

Stimulating osteoclasts Increasing intestinal absorption of

calcium

Decreasing calcium excretion atkidneys

Calcitonin

Secreted by C cells (parafollicularcells) in thyroid

Decreases calcium ion levels by

Inhibiting osteoclast activity Increasing calcium excretion at

kidneys



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I. HORMONES & CALCIUM BALANCE

A. Parathyroid Hormone (PTH)

B. Calcitonin



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I. HORMONES & CALCIUM BALANCE

A. Parathyroid Hormone (PTH)

B. Calcitonin



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Parathyroid Glands

Figure 1813 The Homeostatic Regulation of Calcium Ion Concentrations.



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Parathyroid Glands



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Suprarenal (Adrenal) Glands

Lie along superior border of each

kidney Subdivided into

Superficial suprarenal cortex

Stores lipids, especially cholesterol and fatty

acids

Manufactures steroid hormones:

adrenocortical steroids (corticosteroids)

Inner suprarenal medulla

Secretory activities controlled by sympatheticdivision of ANS

Produces epinephrine (adrenaline) and

norepinephrine

Metabolic changes persist for several minutes



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Suprarenal Glands

Figure 1814a The Suprarenal Gland.


l l d


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Suprarenal Glands

Suprarenal Cortex

Subdivided into three regions:1. Zona glomerulosa

2. Zona fasciculata

3. Zona reticularis

1) Zona Glomerulosa

Outer region of suprarenal cortex

Produces mineralocorticoids

For example, aldosterone:

stimulates conservation of sodium ions and elimination ofpotassium ions

increases sensitivity of salt receptors in taste buds

Secretion responds to:

drop in blood Na+, blood volume, or blood pressure

rise in blood K

+

concentration


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Suprarenal Glands

2) Zona Fasciculata Produces glucocorticoids

For example, cortisol (hydrocortisone) with corticosterone

Liver converts cortisol to cortisone

Secretion regulated by negative feedback

Has inhibitory effect on production of

Corticotropin-releasing hormone (CRH) in hypothalamus

ACTH in adenohypophysis

Accelerates glucose synthesis and glycogen formation

Shows anti-inflammatory effects

Inhibits activities of white blood cells and other components ofimmune system

3) Zona Reticularis Network of endocrine cells

Forms narrow band bordering each suprarenal medulla

Produces androgens under stimulation by ACTH



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Suprarenal Glands

Figure 1814b-c The Suprarenal Gland.

Contains two types of secretory cells

One produces epinephrine(adrenaline)

75 to 80% of medullary secretions

The other producesnorepinephrine (noradrenaline)

20 to 25% of medullary secretions

Suprarenal Medulla



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Suprarenal Glands



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Pineal Gland

Lies in posterior portion of roof ofthird ventricle

Contains pinealocytes

Synthesize hormonemelatonin

Functions of Melatonin

Inhibiting reproductivefunctions

Protecting against damage byfree radicals

Setting circadian rhythms

Figure 145 The Diencephalon and Brain Stem.



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Pancreas

Figure 1815 The Endocrine Pancreas

Lies between

Inferior border of stomach

And proximal portion of small intestine

Contains exocrine and endocrine cells



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Pancreas

Figure 1815 The Endocrine Pancreas

Endocrine Pancreas Consists of cells that form

clusters known as pancreaticislets, or islets of Langerhans

1) Alpha cells produce

glucagon2) Beta cells produce insulin

3) Delta cells produce peptidehormone identical to GH-IH

4) F cells secrete pancreaticpolypeptide (PP)


P


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Pancreas

Figure 18

16 The Regulation of Blood Glucose Concentrations

Blood Glucose Levels

1) When levels rise

Beta cells secreteinsulin, stimulatingtransport of glucoseacross plasmamembranes

2) When levels decline

Alpha cells releaseglucagon, stimulating

glucose release by liver



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Pancreas

Insulin

Is a peptide hormone released by beta cells

Affects target cells

Accelerates glucose uptake

Accelerates glucose utilization and enhances ATP production

Stimulates glycogen formation

Stimulates amino acid absorption and protein synthesis Stimulates triglyceride formation in adipose tissue

Glucagon

Released by alpha cells

Mobilizes energy reserves

Affects target cells

Stimulates breakdown of glycogen in skeletal muscle and liver cells

Stimulates breakdown of triglycerides in adipose tissue

Stimulates production of glucose in liver



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Pancreas



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Endocrine Tissues of Other Systems

Many organs of other body systems have secondaryendocrine functions

1) Intestines (digestive system)

Produce hormones important to coordination of digestive

activities2) Kidneys (urinary system) :

Produce the hormones calcitriol and erythropoietin

Produce the enzyme renin

3) Heart (cardiovascular system)4) Thymus (lymphoid system and immunity)

5) Adipose Tissue Secretions

6) Gonads (reproductive system)



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Endocrine Functions of the Kidneys

Figure 1817b : Overview of theRenin-angiotensin System

Figure 1817a : The Productionof Calcitriol


E d i Ti f O h S


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3) Heart

Produces natriuretic peptides (ANPand BNP) When blood volume becomes excessive

Action opposes angiotensin II

Resulting in reduction in blood volume and blood pressure

4) Thymus Produces thymosins (blend of thymic hormones)

That help develop and maintain normal immune defenses

5) Adipose Tissue Secretions

Leptin

Feedback control for appetite

Controls normal levels of GnRH, gonadotropin synthesis

Resistin

Reduces insulin sensitivity



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6A) Testes (Gonads) Produce androgens in interstitial cells

Testosterone is the most important male hormone

Secrete inhibin in nurse (sustentacular) cells

Support differentiation and physical maturation of sperm

6B) Ovaries (Gonads)

Produce estrogens

Principle estrogen is estradiol

After ovulation, follicle cells Reorganize into corpus luteum

Release estrogens and progestins, especiallyprogesterone



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Hormone Interactions

Antagonistic (opposing) effects

Synergistic (additive) effects

Permissive effects: one hormone is necessary foranother to produce effect

Integrative effects: hormones produce different and

complementary results

Hormones Important to Growth

GH

Thyroid hormones

Insulin PTH

Calcitriol

Reproductive hormones



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Growth Hormone (GH)

In children

Supports muscular and skeletal development

In adults

Maintains normal blood glucose concentrations

Mobilizes lipid reserves

Thyroid Hormones

If absent during fetal development or for first year

Nervous system fails to develop normally

Mental retardation results

If T4 concentrations decline before puberty

Normal skeletal development will not continue


H I t ti


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Insulin

Allows passage of glucose and amino acids across plasmamembranes

Parathyroid Hormone (PTH) and Calcitriol

Promote absorption of calcium salts for deposition in bone

Inadequate levels causes weak and flexible bones

Reproductive Hormones

Androgens in males, estrogens in females

Stimulate cell growth and differentiation in target tissues Produce gender-related differences in

Skeletal proportions

Secondary sex characteristics



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Diabetes Insipidus Inadequate release of ADH from neurohypophysis

Water conservation at kidneys is impaired and

excessive amounts of water is lost in the urine

(Polyuria)

In severe cases, fluid loss can lead to dehydration and

electrolyte imbalance and prove fatal.

The condition can be treated by administration ofdesmopressin, a synthetic form of ADH




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Diabetes Mellitus

Characterized by glucose levels that are high enough to impair

resorption capabilities of kidneys

Glucose is secreted in urine (glycosuria) and associated with excessiveurine production (polyuria)

DM can be caused due to genetic abnormalities1) Inadequate synthesis of Insulin

2) Production of abnormal insulin3) Production of defective receptor proteins4) May also result from injuries, pathological conditions, immune

disorders or hormonal imbalance

Obesity accelerates the onset of DM

Two types:Type 1: individual do no produce insulin and require insulininjections to surviveType 2: individuals produce insulin, but their body is not able toutilize the same


HormoneInteractions


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Diabetes Mellitus

Due to inadequate glucose levels stabilization, DM leads to a spectrumof chronic medical problems

Tissue face chronic energy crisis and lead to break down of lipids andeven proteins.

Conditions is made worse with co-existing hypertension and highcholesterol

Targeting any of these three can alleviate the related health issues

1) Diabetic retinopathy2) Increased incidence of cataracts3) Diabetic nephropathy4) Diabetic neuropathy5) Degenerative blockage of cardiac circulation6) Blood flow to distal limbs is disrupted. e.g. feet

may develop tissue death, ulceration, infection orloss of toes.




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Figure 18

18 The General Adaptation Syndrome.

General Adaptation Syndrome (GAS) Also called stress response

How body responds to stress-causing factors

Is divided into three phases:

1. Alarm phase

2. Resistance phase

3. Exhaustion phase




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Figure 1818 The General Adaptation Syndrome.


i


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Hormone Changes

Can alter intellectual capabilities, memory, learning,and emotional states

Affect behavior when endocrine glands are over-

secreting or under-secreting

Aging

Causes few functional changes

Decline in concentration of

Growth hormone

Reproductive hormones

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Lecture Oct-27-11 Chapter 18