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Chapter
18
The Endocrine
System
Pages 603-635
Copyright © 2009 Pearson Education, Inc.,
publishing as Pearson Benjamin Cummings
Endocrine System Introduction
Composed of glands and tissues that
secrete chemical regulators called
hormones
 Study of endocrine system is
endocrinology
 What do you call a doctor who
specializes in diseases of the endocrine
system?

Definitions
Hormones are chemicals regulators
 Most are secreted into the blood and
become circulating hormones
 They affect the functioning of other cells
 These “other cells” are called targets

Definitions
Hormones are specific for certain targets
because hormones bind to specific
receptors of target cells
 Targets range from specific tissues to
widespread tissues

Hormones Regulate
Growth
 Metabolism
 Fluid, electrolyte, and acid-base balance
 Reproduction
 Blood pressure
 and other processes such as heart rate,
digestion, etc.

Endocrine Glands and Tissues

Secrete hormones
Examples





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
Pituitary gland
(hypophysis)
Thyroid gland
Parathyroid glands
Adrenal glands
Pancreas
Gonads
Endocrine tissues
within other organs
Chemistry of hormones

Compounds that act as hormones are:

Amino Acid Derivatives



Thyroid hormones
Epinephrine, Norepinephrine and Dopamine
Peptide Hormones


Small polypeptides and small proteins
Glycoproteins
Chemistry of Hormones

Lipid Derivatives

Eicosanoids


Leukotrienes and prostaglandins
Steroids

Estrogen, testosterone and cortisol
Hormone Secretion
Stimulus (another hormone, changes in blood chemistry or nerve stimuli)
Endocrine Gland
----------------Hormone
Hormone secretion
Blood
Binds to Receptor-----------Target
cell
Actions
Regulation of Hormone Secretion

Hormone actions depend on cellular
receptors

Hormones that cannot enter the cell bind to
cell membrane receptors
Hormone acts as “first messenger”
 Hormone-receptor complex simulates formation
of “second messenger” – usually cyclic-AMP
 Second messenger produces hormones action
inside cell

Hormone Actions – Hormone Cannot Enter Cell
Hormone – 1st messenger
Membranes Receptor
ATP
c-AMP – 2nd messenger
Enzyme catalyzed
reactions
Actions
Most Hormones such as peptides and proteins work this way
Regulation of Hormone Secretion

Some Hormones can enter cell
Hormone binds to intracellular receptor
 Hormone-receptor complex enters nucleus
 DNA segments (genes) activated
 DNA codes for protein formation
 Protein produces hormone actions


Steroids and thyroid hormones work this
way
Hormone Actions – Hormone Enters Cell
Hormone Enters Cell
Intracellular
Receptor
DNA in
Nucleus
Protein
Actions
Regulation of Hormone Secretion

Hormone Concentration Affects Number of
Receptors

If hormone level high, receptor numbers decrease –
called down-regulation


If hormone levels low, receptor numbers increase –
called up-regulation


Cells become less sensitive to hormone
Cells become more sensitive to hormone
Up and down regulation help maintain
endocrine homeostasis
Control of Secretion

Negative feed back

Actions of Effector (Gland) decrease or inhibit
stimulus



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
Actions are usually hormone secretions
Most common control
Attempts to maintain normal levels of secretion
Thermostat analogy
Positive feed back


Actions of Effector increase or continue stimulus
What are two examples?
Negative Feedback
Pituitary Gland (Hypophysis)


Small gland connected to
hypothalamus
Two parts
 Anterior pituitary
(adenohypophysis)
 Posterior pituitary
(neurohypophysis)
 Infundibulum – a funnelshaped structure
connecting the pituitary to
the hypothalamus
hypothalamus
---------infundibulum
anterior
pituitary---------
-----posterior pituitary
Pituitary Gland (Hypophysis)

Posterior pituitary


Hormones produced by
hypothalamus and placed in
posterior pituitary for secretion
Secretes two hormones


Oxytocin (OT)
Antidiuretic hormone (ADH)
Pituitary Gland

Anterior pituitary largest part


Produces and secretes most
of the hormones
Under indirect control of
hypothalamus
 Hypothalamus secretes
releasing hormones (RH)
and inhibiting hormones
(IH)
 Reach anterior pituitary
through hypophyseal portal
circulation
Hormones of Anterior Pituitary

Human Growth Hormone (hGH)


Targets most cells especially skeletal and muscle
tissue
Actions
 ↑ rate of cell division for growth
 ↑ protein synthesis provides structure needed for
growth
 ↑ use of fat for energy, especially during prolonged
exercise
 ↑ rate of bone growth
Growth Hormone
Results in growth to adulthood and
maintenance of skeleton and muscles in
adults
 May work directly on tissues, but mostly
works indirectly by stimulating formation of
insulin-like growth factors (IGF’s) in liver
that then target muscle, skeletal and other
tissues

Growth Hormone Imbalances

Pituitary dwarfism
Caused by hyposecretion in children
 Results in small body

Giantism caused by hypersecretion in
infants and children resulting in height
of 7 to 8 feet
 Acromegaly caused by hypersecretion
in adults resulting in distorted features

Giantism
Acromegaly
Hormones of Anterior Pituitary

Thyroid stimulating hormone (TSH)
Targets thyroid gland
 Stimulates secretion of most thyroid
hormones


Adrenocorticotropic Hormone (ACTH)
Targets suprarenal (adrenal) cortex
 Stimulates secretion of most steroids from
suprarenal glands

Hormones of Anterior Pituitary

Prolactin (PRL)
Targets mammary glands
 Stimulates milk production in mammary
glands in concert with other hormones


Gonadotropins

Follicle Stimulating Hormone (FSH) and
Luteinizing Hormone (LH) target the ovaries
and testes (gonads) and control female and
male reproductive physiology
Hormones of the Posterior Pituitary

Oxytocin (OT)


Mostly targets smooth muscles of
reproductive system of both sexes
Actions in female



Labor (uterine) contractions
Release of milk from mammary glands (milk
letdown)
Actions in male

Contraction of smooth muscle in
reproductive tissue
Hormones of Posterior Pituitary

Antidiuretic Hormone (ADH)
(vasopressin)
Targets kidneys, sweat glands and
arterioles
 Actions

Causes kidneys and sweat glands to conserve
water
 Constricts arterioles


Do these actions affect blood pressure?
Summary of Pituitary Hormones
Question
Which of the following hormones causes birth?
1. prolactin
2. oxytocin
3. ADH
4. FSH
Thyroid Gland

Large butterflyshaped gland in
neck below voice
box (larynx)
 Has Two lobes
connected by an
isthmus
left lobe
right lobe
isthmus
Histology of Thyroid

Composed of many
follicles filled with jellylike (colloidal)
thyroglobulin protein
• Thyroid hormones
synthesized by follicle
cells and stored in
combination with
thyroglobulin
Thyroglobulin
Thyroid Follicles
Thyroid Hormones Formation

Thyroglobulin protein made by follicular cells
 Thyroid hormones formed by addition of iodine
to the thryroglobulin protein
 3 or 4 iodine atoms added to thyroglobulin


T3 (triiodothyronine) if 3 iodine atoms added
T4 (tetraiodothyronine or thyroxine) if 4 iodine atoms
added
Thyroid Hormone Formation
Synthesis and secretion stimulated by
anterior pituitary hormone TSH
(thyrotropin)
 When secreted, T3 and T4 combine with
blood proteins for transport to target cells
 Once in target cells, produce metabolic
effects to provide energy and stimulate
growth

Target Tissues and Actions of T3 & T4
 Targets
most tissues, but not all
 Actions
 ATP
production and use of ATP for
energy
 Normal growth
 Control
by negative feedback
Control of Thyroid Secretion
Question
Iodine is added to __________ to make T3
and T4.
1. thyroxine binding globulin
 2. thyroglobulin
 3. albumin
 4. gamma globulin

Imbalances of T3 & T4
 Thyroid
 Too
dwarfism (cretinism)
little from birth
 Severe form
Imbalances of T3 & T4

Hyperthyroidism



Too much T3 & T4
Grave’s disease most common form
Symptoms

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metabolic rate (MR)
tachycardia
body temperature (BT)
anxiety & irritability
goiter
Exophthalmia (exophthalmos)
heat intolerance
weight loss
Imbalances of T3 & T4

Hypothyroidism


Too little T3 & T4
Symptoms

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
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metabolic rate (MR)
bradycardia
body temperature (BT)
lethargy
goiter
weight gain
cold intolerance
swollen face (Myxedema)
Imbalances of T3 & T4
 Endemic
goiter and iodine
deficiency
Insufficient dietary iodine to make T3 & T4
 Endemic refers to
____________________
 Lack of negative feedback causes
overgrowth of thyroid
 Goiter results

Thyroid Disorders
Endemic Goiter
Exophthalmia
Parathyroid Glands

Thyroid and
parathyroid glands
contol blood calcium
 Four parathyroid
glands embedded in
back of thyroid gland
Control of Blood Calcium
 Calcitonin
(CT) from thyroid lowers
blood calcium by adding it to bones
 Parathyroid hormone from
parathyroid glands increases blood
calcium by removing it from bones
Calcium Homeostasis
Suprarenal (adrenal) Glands

Located on top of kidneys
 Hormones adjust metabolism
and affect


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
use of nutrients
ionic balance
energy consumption
Help maintain homeostasis
against stress
Suprarenal Layers

Capsule

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Cortex – outer layer

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Outer CT covering
Threes zones
Secretes steroids
Medulla – inner layer

Secretes catecholamines
Suprarenal Histology

Cortex


Secrete steroid hormones called corticoids
Three Zones

Glomerular (outer) zone

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Fascicular (middle) zone

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Cells in globular clusters
Secretes mineralocorticoids such as aldosterone
Cells form vertical elongated bundles
Secrete glucocorticoids such as cortisol
Reticular (inner) zone


Cells form irregular, net-like pattern
Secrete some sex steroids in both sexes
Suprarenal Layers

Capsule
 Cortical Zones


Glomerular zone

Fascicular zone

Reticular zone
Medulla
Corticoids
 Mineralocorticoids
from glomerular
zone
 Aldosterone
most important
 Regulates blood sodium, potassium
and acid – increases plasma sodium
and decreases plasma potassium
 Regulation affects fluid & electrolyte
homeostasis
Glucocorticoids from Fascicular Zone

Principal one is cortisol

Actions include:

Mobilizing Body’s Resources to Resist Stress
by
  Protein breakdown (catabolism) for
energy
  Formation of new glucose from amino
acids, lactic acid, and the glycerol part of fat
molecules-gluconeogenesis
Glucocorticoids from Fascicular Zone

Actions include:

Mobilizing Body’s Resources to Resist Stress
 Conversion of excess glucose to glycogen
(glycogenesis) for storage in liver-provides
energy reserve
 use of fat for energy assures glucose
availability for brain
 Maintaining bp by making blood vessels
sensitive to vasoconstriction
Glucocorticoids from Fascicular Zone

Actions include:

Reducing inflammation



Works with epinephrine (adrenaline) to reduce effects
of inflammation.
Various steroids including hydrocortisone, cortisone,
and synthetic steroids are used medically to reduce
inflammation
Excess cortisol causes fat deposition in
abdomen and face.
 Control is by negative feedback
Imbalances of Glucocorticoids

Addison’s disease

Insufficient glucocorticoids


Usually caused by own antibodies attacking
suprarenal cortex
Symptoms
Lack of energy
 Weight loss
 Inability to resist stress
 John F. Kennedy had it

Addison’s Disease – President Kennedy
Before Steroid Treatment
During Steroid Treatment
Imbalances of Glucocorticoids

Cushing’s Disease

Excessive glucocorticoid secretion


Muscle wasting


Usually caused by tumors in adrenals or
elsewhere
Spindly arms & legs
Fat redistribution
Large abdomen with stretch marks
 Rounded face
 Fatty hump between shoulders

Cushing’s Syndrome
Before
After
Question
Which of the following is one of the actions of
cortisol?
1. increased blood Calcium
2. blood glucose
3. gluconeogenesis
4.  use of fat for energy
5. 2&3
6. 3&4
Hormones of Suprarenal Medulla

Catecholamines - epinephrine (adrenaline)
and norepinephrine (noradrenaline)


Targets – most cells
React quickly to stress by:





heart rate and strength
blood flow to skeletal muscles, heart and brain
 dilation of airways (bronchodilation)
fuel for energy-release of glucose from glycogen
blood pressure
Suprarenal Medulla

Suprarenal medulla receives direct innervation
from sympathetic nervous system


Hormones are sympathomimetic



develop from same tissue as Autonomic neurons
effects mimic those of sympathetic NS
cause fight-flight behavior
Sympathetic stimulation increases hormone
secretion by suprarenal medulla
Question
Which hormone increases cell division, protein
synthesis and the use of fat for energy?
1. prolactin
2. hGH
3. TSH
4. ACTH
Pancreas
 Large
leaf-shaped
 Located in curve of small intestine and
behind stomach
 Both endocrine and exocrine
 Endocrine
part controls mostly blood
sugar
 Exocrine part secretes digestive enzymes
Anatomy of Pancreas


Five inches long
Consists of head, body
& tail
 Most of pancreas is
exocrine and secretes
digestive enzymes
 Endocrine cells produce
hormones that control
blood sugar and affect
metabolism and
digestion
Histology of Pancreas

Exocrine acinar cells
surround a small duct

Endocrine cells form
Pancreatic Islet (Islets of
Langerhans)

1 to 2 million Islets

Contain four types of cells
Cell Types in the Pancreatic Islets
Alpha cells (20%) produce glucagon
 Beta cells (70%) produce insulin
 Delta cells (5%) produce somatostatin
 F cells (5%) produce pancreatic
polypeptide
 Will stress glucagon and insulin
secretion

Actions of Insulin

Insulin lowers blood glucose by:
 uptake of glucose into cells
 synthesis of liver glycogen for storageglycogenesis


Insulin also protein & fat synthesis
Actions of Glucagon

Glucagon increases blood glucose by:
Synthesis of glucose from amino acids in
liver-gluconeogenesis
 breakdown of liver glycogen into glucoseglycogenolysis
 release of glucose from liver into blood

Regulation of Glucagon & Insulin Secretion
High blood glucose after meal stimulates
secretion of insulin and inhibition of
glucagon
 Low blood glucose when fasting
stimulates release of glucagon and
inhibition of insulin

Question
Which of the following happens after you eat?
1. More glucose released into blood from liver
2. More glucose moves into cells
3. gluconeogenesis
4.  breakdown (catabolism) of glycogen
Diabetes Mellitus
 Insulin
unavailable for uptake of
glucose into cells
 Blood glucose becomes elevated
– hyperglycemia
Diabetes Mellitus
 Two
Types:
 Type
I (IDDM) or juvenile DM
 Beta
cells destroyed by own immune
system
 Insulin levels low
 Insulin injections required
 Usually develops in people younger than 20
Diabetes Mellitus
 Type
II (NIDDM) or maturity onset DM
 Most
common type (90%)
 Insulin may still be secreted but cells may
be less sensitive to it
 Insulin injections may not be required
 Mostly in people over 35 who are obese
 May be controlled by diet
Three Signs (P’s) of DM
 Polyuria
 Polydypsia
 Polphagia
Complications of DM
Cardiovascular disease
 Loss of vision
 Kidney disease
 Diabetic Coma
 Most complications linked to high
glucose and acidosis
 Acidosis caused by excessive use of fat
for energy instead of glucose
