Download There are two types of glands: Endocrine Glands Hormones

THE HUMAN ENDOCRINE SYSTEM
Introduction to The Human Endocrine System
The purpose of the Endocrine
Biology 12
A. Allen
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system is to aid in maintaining
homeostasis.
The endocrine system produces
hormones. Hormones are chemical
regulators produced by cells in one
part of the body that effects cells in
another part of the body.
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Endocrine Glands
There are two types of glands:
Exocrine glands – secrete their products onto body surfaces or into
body cavities like the digestive tube. E.g. Mucus glands, sweat glands,
oil glands, salivary glands
Endocrine glands – ductless glands which secrete hormones directly
into the bloodstream. Hormones travel via the blood to target organs
and tissues where they have some effect on the target
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...Hormones
Hormones
Function of Hormones
Hormones exert their effects on specific locations in the
body called target tissues (this could be a whole organ or
just a few cells). Their effects are long term, controlling
functions such as growth, metabolism, maturity and the
balance of chemicals in the body.
The ability of a cell to respond to a hormone depends on
whether or not the cell has the correct receptor for that
hormone.
Without the receptor, there will be no effect!
TARGET CELLS - specific cells with receptor sites that
bind with hormones
Hormones are produced and
secreted into the blood stream
by the endocrine glands. The
circulatory system carries
hormones to other parts of the
body via the blood.
Hormones are chemical
messengers responsible for
co-ordinating certain body
functions. In general they are
stimulatory.
The word hormone comes
from the Greek hormon,
meaning “to excite or set into
motion”.
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hormonal communication
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...Hormones
(Wait!...what’s Metabolism?)
The Mode of Action of Hormones
Hormones act at the molecular level by causing
changes in cell metabolism, for example:
The sum of the chemical reactions occurring within a
cell or a whole organism; includes the energy-releasing
breakdown of molecules (catabolism) and the
synthesis of new molecules (anabolism).
protein synthesis
enzyme activity
permeability of cell membranes
DNA translation
there are two basic ways in which hormones do this,
based on the type of hormone:
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Steroid hormones and quiz
...Hormones
Steroid Hormones
The hormone diffuses
directly into the cell.
Here it fuses with a
receptor molecule.
This receptor molecule is
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only present in the target
cells for that particular
hormone.
The hormone/receptor
combination effects the
translation of DNA in the
nucleus.
...Hormones
Epinephrine-a protein hormone
Protein Hormones:
The hormone binds to a receptor
molecule located on the surface
of the cells of the target tissue.
This causes the production of a
secondary messenger molecule
within the cell, e.g.. cyclic AMP.
The secondary messenger
molecule causes a change in cell
metabolism, e.g.. activates an
enzyme.
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Examples of Hormones
Protein Hormones
Negative Feedback
Feedback that reduces the output of a system.
Steroid Hormones
Release of hormones is controlled by negative feedback
loops
•Insulin
•Growth hormone
•Thyroid Stimulating
Hormone
•Sex hormones
•Glucocorticoids
•mineralocorticoids
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The response solves the problem caused by the stimulus
This maintains normality and resets the normal condition
In a negative feedback system some factor (stimulus)
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such as blood pressure, changes. The change is detected
by a sensor. The sensor sends a message to an integrating
center which in turn stimulates an effector. The effector
will do something to alter the factor that changed.
In the example to the right blood pressure has increased.
Receptors in the carotid arteries detect the change in
blood pressure and send a message to the brain. The brain
will cause the heart to beat slower and thus decrease the
blood pressure. Decreasing heart rate has a negative effect
on blood pressure.
Negative feedback: An simple example
Positive Feedback
When thermostat senses house is cooling down, it tells
On the other hand…
furnace to turn on and send warm air into house. When
thermostat senses house is warm enough, it tells furnace to
turn off (same for cooling down)
This is negative feedback! (The temperature returns to
normal)
Imagine that when thermostat senses house getting cool, it
sends message to open the windows to let more cool air in.
This is positive feedback! (the problem gets worse)
An example of Positive Feedback
The Pituitary Gland: The Master Gland
An outgrowth from the base of the fore-brain and in direct
nervous contact with it.
This gland secretes a range of hormones;
Some of these hormones have a direct effect on their target organs...
while others have an indirect effect by causing other glands to secrete
further hormones.
• It is for this reason that the
pituitary gland is often called
the master gland, as it
regulates the secretions of a
number of other endocrine
glands.
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... The Pituitary Gland
Structure
The POSTERIOR Pituitary
The pituitary
The posterior lobe of the
gland consists of
two lobes, the
anterior and the
posterior lobes.
Each releases
specific
hormones under
the direction of
the
hypothalamus.
pituitary stores and releases
hormones which have been
produced by the hypothalamus.
The hormones travel by way of
specialized nerve cells from the
hypothalamus to the pituitary.
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The Hormones of the POSTERIOR Pituitary
The ANTERIOR Pituitary
• The anterior lobe of the pituitary, unlike the posterior
Antidiuretic Hormone (ADH)
regulates water balance in the
body by increasing water
absorption by the kidneys
lobe, produces its own hormones.
• Like the posterior lobe, the anterior lobe is richly
supplied with nerves from the hypothalamus.
• The hypothalamus regulates the release of hormones
Hormonal Communication …ADH
from the anterior pituitary. Hormones are secreted from
the nerve ends of the cells of the hypothalamus and
transported in the blood to the pituitary gland. Most of
these hormones activate specific cells in the pituitary,
causing the release of pituitary hormones, which are then
carried by the blood to target tissues.
Oxytocin:
stimulates uterine contractions during
birth
also stimulates milk production
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...The Hormones of the ANTERIOR Pituitary
The Hormones of the ANTERIOR Pituitary
• Somatotropin (STH) or Growth Hormone (GH)
has a direct effect on the growth of tissues
is produced in greater quantities during childhood
• Thyroid Stimulating Hormone (TSH)
has an indirect effect on metabolic rate, by affecting the thyroid
gland
stimulates the thyroid gland, causing it to produce the hormone
thyroxin
• Adrenocorticotropic Hormone (ACTH)
stimulates the adrenal cortex to produce a range of hormones
responsible for stress relief
• Gonadotropic Hormones:
Follicle Stimulating Hormone (FSH)
Females: stimulates the development and
production of ova, causes the release of estrogens
• Males: stimulates the production of sperm cells
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Lutinizing Hormone (LH)
•
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Females: causes the development of the corpus luteum. (A structure that
develops in the ovary and secretes progesterone )
Males: (called interstitial cell stimulating hormone - ICSH) stimulates the
production of testosterone from the interstitial cells of the testes
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...The Hormones of the ANTERIOR Pituitary
• Prolactin
stimulates milk production after birth
• Melanocyte Stimulating Hormone
(MSH)
stimulates melanin (a brown pigment)
production in the skin
responsible for changing the skin colour of
certain reptiles and amphibians
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Abnormalities Associated with the
Pituitary
Abnormalities Related to the Secretion of Growth
Hormone:
Dwarfism
Caused by under secretion of GH during childhood
resulting in reduced over all growth.
Under secretion in adults has been linked to early
senility.
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Acromegaly
Gigantism
[ak-ruh-meg-uh-lee]
caused by over secretion
caused by over secretion of
of GH during childhood.
GH during adulthood,
leading to excessive growth
of facial bones and those of
the hands and feet.
Andre the Giant 7’ 4” 500 lbs
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HORMONES THAT AFFECT
BLOOD SUGAR
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The Pancreas
…The Pancreas
The pancreas has both endocrine (regulation of blood sugar)
and exocrine functions (Digestive enzyme production)
• Patches of
specialized cells
produce two
hormones, insulin
and glucagon, that
are secreted into the
blood stream.
• These patches of
cells are referred to
as the islets of
Langerhans
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The islets have two types of secretory cells:
alpha cells secrete glucagon
beta cells which secrete insulin
These two hormones are responsible for the control of
glucose metabolism by controlling the breakdown and
synthesis of glycogen, the carbohydrate store in the body.
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Glucagon
Insulin
Released into the bloodstream in response to increasing
blood glucose concentration, for example after a meal. It
has two effects:
1. It increases the permeability of the cells of the liver and
muscles to glucose so that glucose is readily absorbed by these
cells.
2. It promotes the conversion of glucose to glycogen in these
cells.
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Has an antagonistic (in opposition) effect to insulin, it
promotes the break down of glycogen to glucose and its
release into the blood stream, therefore increasing the
blood glucose level in the blood.
It is released when the blood glucose level falls during
periods of exercise or fasting between meals.
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Symptoms of Diabetes
Diabetes Mellitus
1.
When the beta cells of the pancreas deteriorate and
2.
fail to produce adequate amounts of insulin and the
blood sugar level rises above normal.
This is known as hyperglycemia.
3.
4.
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Glucose in the urine (glycosuria) caused by excretion
of glucose by the kidneys as the blood glucose level
rises above renal threshold (160mg/100mL of blood)
Production of large volumes of urine (diuresis) in
order to excrete the glucose results in dehydration and
excessive thirst. (This symptom is usually the first
noticed by new diabetics)
Low energy levels due to the unavailability of glucose
for cellular respiration. Despite the abundance of
glucose in the blood, little moves into the cells and so
the cells are starved of energy. This may cause
unconsciousness.
The smell of propanone (acetone) on the breath.
Propanoneis a by product of fat metabolism
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Type I (Juvenile)
Treatment of diabetes
10% of diabetics have type I.
Occurs usually before 20 years of age
Autoimmune disorder
is caused by the early degeneration of the beta cells in the
pancreas.
Daily injections of insulin are necessary to replace the
missing insulin, for this reason this type of diabetes is also
known as insulin dependent.
Injections are administered by the patient
subcutaneously, since insulin is a protein hormone and
would be digested if given orally.
There are two forms of diabetes mellitus
Type I (juvenile or early-onset diabetes)
Type II (adult or late-onset diabetes)
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Visceral Fat and Type 2 Diabetes
Type II (adult)
Around 90% of diabetics develop the condition as adults.
Resistin
It is due to reduced insulin output by the beta cells of the
hormone released by fat tissue causes tissues, especially the liver to be less
sensitive to the action of insulin.
pancreas or ineffective use of the insulin the body does
produce (the receptors on cells in the body that normally
respond to the action of insulin fail to be stimulated by it).
Controlled with diet, exercise & Sulfonamide drugs prescribed to stimulate the beta cells to produce a little more
insulin.
Not necessary to give insulin and so this condition is also
known as non insulin dependent diabetes.
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type 2 diabetes
Obesity has been shown to increase serum resistin.
Patients who have undergone gastric bypass have shown improvement in their
diabetes.
Adiponectin
a hormone released by fat tissue enhances insulin sensitivity and glucose
uptake. Decreases in obese persons and increases after weight loss.
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The Adrenal Glands
Secretions from the Adrenal Cortex
These are located just above each kidney
Adrenal Cortex produces
Ad (to) + renes (kidneys)
They consist of two layers, an outer cortex and an inner
1.
medulla.
Each layer secretes specific hormones.
2.
3.
Glucocorticoids - hormones that predominantly affects
the metabolism of carbohydrates.
Mineralocorticoids - a group of steroid hormones, such
as aldosterone, that are secreted by the adrenal cortex and
regulate the balance of water and electrolytes
Sex hormones -…
The Adrenal Cortex is responsible for long-term stress response
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…Secretions from the Adrenal Cortex
…Secretions from the Adrenal Cortex
Glucocorticoids
Cortisol (a steroid hormone)
Increases amino acids in blood liver
converts these to glucose blood sugar is
raised more energy for cells to recover
from stress. Excess amino acids used to make
proteins to repair damaged cells.
Mineralocorticoids
the most important being
aldosterone. This hormone
stimulates the absorption of
sodium ions by the kidneys
to maintain salt and water
balance in the blood.
Cortisone also reduces the allergic and
inflammatory responses caused in damaged
tissues, by inhibiting the immune system.
(Cortisone is a drug given in many instances to
reduce inflammation or allergic response)
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Secretions from the Adrenal Medulla
Control of the secretions from the Adrenal Cortex
Secretions from the adrenal cortex are stimulated by
The Adrenal Medulla produces two hormones: epinephrine
ACTH from the anterior pituitary.
The control of these secretions demonstrates the feedback
mechanism:
and norepinephrine (protein-hormones). They are secreted
in times of stress.
Unlike the adrenal cortex, which is under hormonal control,
the release of hormones from the adrenal medulla is
controlled by the nervous system. These hormones have
several effects on the body…
The Adrenal MEDULLA is responsible for short-term stress response
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Fight or Flight:
Effects of Epinephrine and Norepinephrine on Body
80% epinephrine, 20% norepinephrine released.
Increased blood sugar levels by converting glycogen to glucose (for greater
energy reserve available to tissues)
Action of Epinephrine on a Liver Cell
Increase heart rate
Some blood vessels dilate (norepinephrine)
Some blood vessels constrict-liver/kidneys (epinephrine)
breathing rate increases
Cell metabolism increases
pupils dilate
blood is diverted from non-essential tasks, such as digestion, to the muscles
for activity
anal and bladder sphincters relax.
face becomes pale (blood diverted from here)
hair stands on end, sweating increases
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The role of epinephrine in fight or flight
The Thyroid Gland:
Produces three hormones;
HORMONES THAT AFFECT
METABOLISM
Thyroxine: (T4) which controls the basic metabolic rate and also
influences growth rate by controlling the growth and differentiation
of cells.
Triiodothyroxine: (T3), which appears to have the same functions
as thyroxine. mcgraw-hill T3 & T4 animation
– Calcitonin: Lowers calcium level
of the blood by…
– Inhibiting calcium
absorption by intestines.
– prevent calcium release
from bone cells (inhibition
of osteoclast activity).
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Stop & Think
Solution to ‘Stop & Think’
Thyroxine regulates metabolic rate.
Higher levels of thyroxine:
faster oxidization of sugars other nutrients.
approximately 60% of the glucose oxidized in the body is released as heat
(which explains why these individuals usually feel warm).
The remaining 40% is transferred to ATP, the storage form for cell energy.
This added energy reserve is often consumed during activity. Therefore, these
individuals tend not to gain weight.
Be an endocrinologist: Some people are able to eat
whatever they want and not put on weight while others
must carefully watch their food intake to avoid gaining
weight.
Can you suggest a reason for these differences in terms
of variations in endocrine function?
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Lower levels of thyroxine:
slower oxidization of nutrients excess blood sugar is eventually converted
into liver and muscle glycogen however, once the glycogen stores are
filled, excess sugar is converted into fat.
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Thyroid Disorders
Control of Thyroxine Production
Thyroid absorbs iodine from blood.
Iodine is assimilated into thyroglobulin.
This provides an example of negative feedback
When stimulated, thyroglobulin becomes
thyroxine.
Goiter-caused by lack of iodine in diet
the precursor to thyroxine
(thyroglobulin) builds up in the thyroid
gland. Thyroxine can’t be produced TSH (from pituitary) builds up thyroid continues to develop goiter
Iodine is added to table salt, i.e.. iodized
salt, to overcome the problem of dietary
deficiency of iodine. Other sources of
iodine; fish, dairy, plant in iodine-rich
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soil
control of the endocrine system:
Key:
TRH: Thyroid releasing hormone
TSH:Thyroid stimilating hormone
T4: Thyroxine
T3: Triiodothyronine
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Hyperthyroidism
Hypothyroidism
Over secretion of thyroxine:
Symptoms:
In adults this condition causes over activity, decreased
body weight, increased heart rate and blood pressure,
which can lead to heart failure - called thyrotoxicosis
(poisoning from hyperthyroidism ).
Under secretion of thyroxine:
In infants: results in retarded mental and physical development called
cretinism. This can be easily treated by early administration of thyroid
extract.
In adults: causes sluggishness and over-weight. This condition is called
myxoedema.
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The Parathyroid Glands
Parathyroid Disorders
These are located as two pairs of small glands on either
Over secretion of Parathormone
Hyperparathyroidism results in excess PTH
which triggers…
side of the thyroid gland
They secrete parathormone (PTH) which increases
plasma calcium concentrations (opposite effect to
calcitonin)
Parathormone stimulates the breakdown of calcium in the
bones and causes it to be released into the blood.
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release of too much calcium into the bloodstream.
too much calcium may be absorbed from food. The levels
of calcium may increase in the urine, causing kidney
stones.
the bones soften due to excess calcium released from the
bone.
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…Parathyroid Disorders
Under secretion of parathormone
Hypoparathyroidism causes muscle cramps due to
lack of calcium for muscle contraction, it is all
absorbed into bone.
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