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Endocrine System
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Endocrine System
• What is the endocrine system?
The endocrine system is comprised of the hormone
producing glands and tissues of the body.
Functioning of the Endocrine System
The endocrine system functions along with the
nervous system to help the nervous system to
help maintain homeostasis.
Endocrine system functions slower than the
nervous system but gives a more sustained effect
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Mechanisms of Hormone Action
• Certain secretory cells release chemical agents
(hormones) for the purpose of mediating biologic
responses in distant Target Cells.
• Hormones sources
– Single amino acid (catecholamines)
– Chains amino acids (peptide hormones of
hypothalamus)
– Cholesterol (steroids)
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Mechanisms of Hormone Action
• Hormones control and integrate many body functions with this
system.
• The endocrine system carries out its functions based upon messages
received from the Hypothalamus
• The hypothalamus monitors the blood and sends hormones from glands
into the blood when needed
• Organs await the arrival of hormones
• In general, hormonal control regulates the metabolic functions of the
body, the types of effects that occur inside the cell and determined
the character of the cell itself.
• The endocrine system works with the nervous system to regulate:
metabolism, water and salt balance, blood pressure, response to
stress, and sexual reproduction.
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Endocrine System
• Endocrine System Hormones/Glands whose functions are
solely endocrine include:
• pituitary (hypophysis)
• pineal
• thyroid
• parathyroids
• adrenals
• pancreas
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Types of Glands
• Endocrine: ductless glands that secrete hormones
directly into blood stream
• Exocrine: glands that have ducts and secrete
substances such as sweat salvia tears milk or
digestive enzymes
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Endocrine Glands
Pituitary Gland
Hypothalamus
Adrenal Cortex
Adrenal medulla
Thyriod
Parathyroid
Pancreas
Thymus
Kidney
Pineal
Ovaries
Testes
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Hormones
• These are chemicals that circulate throughout the
blood and exert some measure of control over
most every organ and tissue in the body.
Types of Hormones
Hormones are either Steroidal or Non-steroidal
1. Steroid Hormones- hormones manufactured
from fatty substances called cholesterol.
2. These substances are fat soluble. Ex. Cortisol
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Steroid Hormones
• Steroid hormones are produced
by chemical modification
of cholesterol
•Major classes steroid hormones
•glucocorticoids (cortisol)
•mineralocorticoids (aldosterone)
•androgens (testosterone)
•estrogens (estradiol)
•Vitamin D metabolites
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How steroid Hormones work
• These hormones enter a cell and binds to a
protein receptor in the cell. This creates a
hormone receptor complex.
• The hormone receptor complex enters the
nucleus where it activates a specific gene in the
DNA
• Activated gene produces an enzyme(protein)
that initiates a chemical reaction within the cell.
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Non Steroid Hormones
• Hormones composed of proteins, peptides or amino
acids
• These hormones are not fat soluble. They are unable
to enter cells because the are not soluble in the
membrane.
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How a Non-Steriod Hormone Works
• A hormone called a first messenger binds to
receptors on surfaces of target cells. The binding
causes ATP to be changed into cyclic AMP(cAMP).
• Cyclic AMP(second messenger) causes chemical
reactions to occur within the cell.
• Ex. Adrenaline, ACTH, LH, FSH, ADH
• http://www.youtube.com/watch?v=SVHXnLgV1fc&safety_mode=true&persist_
safety_mode=1&safe=active
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Summary of Steroidal. VS Non Steroidal
Hormones
Hormone
Solubility in cell
membrane
Location of Receptors
End Result
Steroidal
Within the cell
Gene produces a
protien
Non-steriodal
Surface of cell
cAMP causes chain
reaction
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Types of Hormones
• Antagonistic Hormones
These are hormones that work against each other
or they have opposite effects on the body.
Ex. Insulin and Glucagon
Parathyroid hormone and Calcitonin
Tropic Hormones
These hormones regulate the hormone production
of many other glands.
Ex. Thyroid stimulating hormone, HGH
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Endocrine Hormone Disorders
• Problems with most endocrine glands are either
caused by Hyposecretion or Hypersecretion of a
hormone.
• Hyposecretion; under secretion of a hormone within
the body
• Hypersecretion; A over secretion of a hormone
within a body.
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Feedback Mechanisms and Operation of
Hormones
• Hormones regulate endocrine function on the basis of
feedback mechanisms. There are two types of feedback
mechanisms
• 1. Negative feedback loop:
• A loop that works to reverse or decrease changes in the
body. When concentration of a hormone rises to above
desired levels, a series of steps is taken within the
system to cause the concentration to fall. Conversely,
steps are taken to increase concentration when the level
is too low.
• Ex. Hypothalamus-Pituitary-thyroid feedback mechanism
operation
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Positive feedback Mechanism or loop
A loop that serves to increase the effect of an
action.
Ex. Oxytocin feedback loop
• Diagrams pg 424 figure 13.3
• Pg. 432 figure 13.13
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Feedback Loops
• The release of a hormone is often triggered by a
change in the concentration of some substance in
the body fluids.
• Each hormone has a corrective effect, eliminating
the stimulus, which then leads to a reduction in
hormone secretion.
• This process is called a negative feedback
homeostatic control system to keep hormones at
normal levels. (if levels increased it would be called
positive feedback)
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Hypothalamus and Pituitary
• Pituitary has direct
neural and blood
connection to the
hypothalamus
• Hypothalamus sends
releasing factors to
anterior pituitary
• Hypothalamus
stimulates posterior
pituitary via neural
pathway
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Hypothalamus
• Hypothalamus can synthesize and release hormones
from its axon terminals into the blood circulation.
• controls pituitary function and thus has an important,
indirect influence on the other glands of the endocrine
system.
• exerts direct control over both the anterior and
posterior portions of the pituitary gland.
• regulates pituitary activity through two pathways:
a neural pathway and a portal venous pathway.
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Hypothalamus
• Neural pathways extend
from the hypothalamus to
the posterior pituitary
lobe, where the hormones
are stored and secreted.
• Portal venous pathways
connect the hypothalamus
to the anterior pituitary
lobe, carry releasing and
inhibiting hormones
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Pituitary Gland
• Pituitary Gland is located at the base of the skull in an
indentation of the sphenoid bone, and is called the
Master Gland.
• Is joined to the hypothalamus by the pituitary stalk and
consists of the anterior pituitary and the posterior
pituitary.
• Nervous system sends messages to the hypothalamus
to exert control over the pituitary
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Anterior pituitary gland
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anterior lobe has direct control over the secretion of:
HGH- Somatotropin or human growth hormone
ACTH - adrenocorticotrophic hormone
TTH - thyrotrophic hormone
FSH - follicle stimulating hormone
LH - leutinizing hormone
PRL- prolactin
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Posterior pituitary
• Stores and secretes hormones made in the
hypothalamus and contains many nerve fibers.
• ADH (Antidiuretic Hormone/Vasopressin), which
controls the rate of water excretion into the urine
• Regulates Na+ & K+ reabsorption in the kidneys this
influences blood volume & blood pressure
• Oxytocin, which, among other functions, helps
deliver milk from the glands of the breast.
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Adrenal Glands
• Located on top of
the kidneys
• Adrenal Glands
have an outer
cortex and an inner
medulla.
• The adrenal cortex
and medulla are
major factors in the
body's response to
stress, and are
controlled by the
hypothalamus
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Adrenal Glands
• ACTH - Adrenocorticotrophic Hormone causes adrenal
cortex to release 3 types of hormones: Cortisol
(Glucocorticoids), Aldosterone (Mineral corticoids), and
sex hormones
• The outer cortex is responsible for the secretion of
mineralocorticoids (steroid hormones that regulate
fluid and mineral balance) ALDOSTERONE
• glucocorticoids (steroid hormones responsible for
controlling the metabolism of glucose) Cortisol
• androgens (sex hormones).
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Adrenal Glands
• Centrally located adrenal medulla is derived
from neural tissue and secretes Epinephrine and
Norepinephrine
• Epinephrine circulates and acts upon the
sympathetic nervous system
• Norepinephrine released from sympathetic
nerve endings and from adrenal medulla in
small amounts
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Adrenal Mineral Corticoids
• ADH - antidiuretic hormone
• Regulates Na+ & K+ reabsorption in the kidneys
• regulates water retention
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Adrenal Steroids
• Testosterone - masculinizing affects, increase lean
body mass
• Estrogens - estrodial, estrone, estriol - stimulate
breast development and female pattern fat
deposition
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Thyroid Gland
• Located in the throat
• Butterfly shaped
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Thyroid Gland
• Thyroid function is regulated by the
hypothalamus and pituitary, feedback
controls an intrinsic regulator mechanism
• Hormones produced are:
• thyroxine (T4) & triiodothyronine (T3), regulate the
metabolic rate of the body and oxygen consumption and
increase protein synthesis
• It is released from the thyroid gland when stimulated by
TSH from the pituitary. TSH---- Thyroid gland---- release
Thyroxin
• TSH and Thyroxin work on a negative feedback loop.
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• calcitonin, has a weak physiologic effect on calcium
and phosphorus balance in the body.
• It moves calcium from the blood and into the
bones. This lowers the amount of calcium in the
blood
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Thyroid Problems
• Thyroid gland enlargement may or may not be
associated with abnormal hormone secretion.
• An enlarged thyroid gland can be the result of:
• iodine deficiency (Goiter)
• inflammation, or
• benign or malignant tumors
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Hyperthyroidism
• Hyperthyroidism or Grave’s Disease
• This disease causes excess production of thyroid
hormones
• Weight loss and exopthalmic goiter
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Hypothyroidism
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Caused by a deficiency of thyroxin
Refereed to as Myxedema
Reduced metabolism
Weight gain
Decreased mental capacity
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Thyroid imbalance can cause cretinism,
metabolic disorders, and goiter( due to lack
of iodine)
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Parathyroid Glands
• There are 4 parathyroid glands located
on the surface of the thyroid.
• Parathyroid Glands produce PTH (
parathyroid hormone)
• PTH causes bones to release calcium
into the bloodstream
• Causes kidneys to reabsorb calcium
from the blood thus increasing
amount of calcium in the body
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Pancreas
• Located near the small intestine.
• Contains specialized endocrine cells called islets
of langerhans
• Islets of langerhans is made up of both alpha
and Beta cells.
• Secretes insulin, glucagon (regulate blood sugar)
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Diabetes Mellitus
• Syndrome when insulin levels are inadequate to keep
blood sugar within normal range. Due to:
• Inadequate amount of insulin (Insulin-Dependent
Diabetes Mellitus). Results from severe insulin
deficiency secondary to loss of beta cells.
Autoimmune process selectively destroys beta cells.
• Inadequate response to normal or high insulin levels
(Non-Insulin-Dependent Diabetes Mellitus). More
common that IDDM, 90% NIDDM, associated with
obesity.
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Type I (insulin-dependent) diabetes
– Autoimmune disease in which pancreatic beta cells
are destroyed and thus not enough insulin is
produced
– Often develops before age 15
– Patient requires insulin supplement, often by
injection
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Type II (non-insulin-dependent) diabetes
– Pancreatic cells function properly and there are
sufficient amounts of insulin produced
– Body cells fail to respond to insulin
– Accounts for 90% of diabetes cases in the United States
– Associated with obesity
– Often develops after age 40
– Manageable
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Function of Insulin
• Created by the Beta cells of the islets of langerhans
• Causes the conversion of glucose into glycogen that
is stored in the liver
• Causes excess glucose to be changed into fat
• Helps regulate blood sugar levels. Insulin and
glycogen
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Pancreas( Islets of Langerhans)
• Function of Glucagon(created by the alpha cells of the
islets of Langerhans)
• Causes the conversion of Glycogen (Liver) into Glucose
that is released into the blood as needed.
• Operation of insulin and Glucagon in sugar(glucose)
regulation.
• Insulin and glucagen are antagonistic hormones. They
work opposite each other to maintain proper blood
sugar levels in a negative feedback loop.
• They work by either increasing or decreasing the amount
of glucose (sugar) in the blood.
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Blood Sugar Control
• Insulin and glucagon are produced by small groups of
cells in the pancreas (islets of Langerhans).
• Beta cell make insulin (beta cells) and Alpha cells that
make glucagon
• Insulin is released when the blood sugar rises too
high. Insulin tells the cells to use sugar.
• Glucagon is produced when the blood sugar is falling
too low. Glucagon tells the liver to release sugar that
was stored there when the blood sugar was higher.
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Insulin
• Insulin promotes glucose entry into cells
• Insulin effects enzymes that rule rate of
metabolism of CARBOHYDRATE, FAT, PROTEIN, &
ION TRANSPORT
• Carbohydrate metabolism
– stimulates glucose utilization, storage & also INHIBITS
glucose formation
– Insulin acts on LIVER depending upon plasma glucose
level
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Glucagon
• Secreted in response to: decreased blood glucose
levels, increased amino acid levels, or stimulation by
growth hormone
• primary function is to increase the circulating blood
glucose level: converts stored glucose (primarily in
the liver) to circulating glucose.
• promotes glucose formation (from fat and protein
when the need for glucose is greater than the amount
that can be mobilized from the liver)
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Chronic Diabetic Complications
• Retinopathy = due to dilations of retinal vessels from
microaneurysms.
• atherosclerotic process that occludes coronary and
other arteries. Leading cause of death in diabetic
subjects is coronary heart disease.
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The gonads secrete sex hormones
• The gonads secrete sex hormones
– Secretion is controlled by the hypothalamus and the
pituitary
• The steroid hormones are found in both sexes but in
different proportions
– estrogens
– progestins
– androgens
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Gonads
• Ovaries- found in females
• Produces estrogen and progesterone
• Estrogen controls secondary sex characteristics in
females
• Prepares the uterus for pregnancy
• Progesterone maintains the uterus during
pregnancy
• Estrogen and progestins
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Testes
Found in males
Produces testosterone
Controls secondary sex characteristics in males
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Pineal Gland
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Pineal Gland
• Its principal hormone is melatonin.
• Synthesis and release of melatonin is stimulated
by darkness and inhibited by light.
• Levels of melatonin in the blood rises and falls on
a daily (circadian) cycle with peak levels occurring
in the wee hours of the morning.
• Ingesting even modest doses of melatonin raises
the melatonin level in the blood. These levels
appear: to promote going to sleep and thus help
insomnia. Considered to be the biological clock
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Thymus Gland
• Located between the lobes of the lungs in the upper
chest. Disappears after puberty
• Produces Thymosin
• Function of Thymosin:Causes the production and
maturation of lymphocytes into T-cells
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Growth Hormone Problems
• Gigantism
• Dwarfism
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GH - Growth Hormone
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Release of somatomedins from the liver
Uptake of amino acids by tissues
Synthesis of new proteins
Long bone growth
Blunts insulin’s affect on glucose uptake
Induces gluconeogenesis
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Gigantism
• Acromegaly/Gigantism is a very rare disease and
syndrome results from a chronic exposure to GH
(Growth Hormone) leading to the classic clinical
features that the diagnosis seems to be easy
• High exposure to GH produces gigantism in
youths prior to epiphyseal fusion and acromegaly
in adults.
• In adults, the syndrome is characterized by local
overgrowth of bone (skull, mandible).
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Dwarfism
• Dwarfism results from growth hormone
deficiency. A pituitary dwarf has too little growth
hormone. The achondroplastic dwarf has an
orthopedic reason for having short limbs and a short
spinal column.
• Cause of this is unknown, a tumor or cyst in the
pituitary area may cause dwarfism.
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