Download How Our Bodies Maintain Balance

The Endocrine system
How Our Bodies Maintain Balance
Homeostasis
The human body works best a temperature of
37oC, a 0.1% blood glucose level, and a blood
pH of 7.35.
The environment we are in does not always
provide these ideals conditions for life.
Homeostasis
Our external environment is constantly
changing as is our internal environment.
If you eat an extremely salty meal, your body
has to work extra hard to balance salt and
water levels in your blood.
Homeostasis
Homeostasis is the process by which a
constant internal environment is maintained
despite changes in the external environment.
The body maintains a constant balance using a
series of adjustments. This system of balance
requires constant monitoring and feedback
about body conditions.
Homeostasis
An increase in heart rate during exercise and
the release of glucose from the liver to
restore blood sugar levels are a couple
examples of how adjustments are made.
This concept of homeostasis is central to how
the endocrine system works.
Homeostasis
All homeostatic control systems have three
functional components:
1. Receptor
2. Coordinating Centre
3. Effector
Homeostasis
Special receptors located in organs of the
body signal a coordinating centre once an
organ starts operating outside its normal
limits.
The coordinating centre relays information to
the appropriate effector,which helps to
restore normal balance.
Homeostasis
Homeostasis
Example:
When CO2 levels increase during exercise,
chemical receptors near the brainstem are
stimulated. (1)
Nerve cells carry from the brain (2) carry
impulses to effector muscles (3) which
increase the depth and rate of breathing.
Homeostasis
Homeostasis is often referred to as dynamic
equilibrium
- Although change is occurring in the body,
homeostatic mechanisms maintain balance to
keep us alive
Homeostasis
Blood glucose is
maintained within
a narrow range and
movement outside
this range can
signal diseases
like diabetes.
Homeostasis
Body temperature
can fluctuate by
+2oC with exercise
and -2oC with
sleep. More
drastic changes
can be indicative
of sickness.
Homeostasis
Systolic blood
pressure is
usually around
120mmHg but can
move as high as
240mmHg in a very
fit athlete during
strenuous
exercise.
Homeostasis
Blood pH operates
within a very
narrow range and
changes of +/- 0.2
can lead to death.
Feedback Systems
The systems that our body uses to control
homeostasis are referred to as feedback
systems.
There are two types of feedback that our
bodies use:
1. Negative Feedback
2. Positive Feedback
Feedback Systems
Negative feedback systems make adjustments to
bring the body back within an acceptable
range.
These feedback systems stop a small change
from becoming too large.
Most homeostatic mechanisms in animals
operate using negative feedback.
Feedback Systems
The best way to visualize a negative feedback
system is by thinking of the thermostat in
your house.
You set an ideal temperature that you want
the house to be at. If the temperature drops,
the furnace turns on to heat it back up. When
you hit the ideal temperature, the furnace
turns off.
Feedback Systems
The receptor would be the thermometer.
The coordinating centre would be the
thermostat.
The effector would be the furnace.
They all work together in order to maintain a
balanced temperature in your house.
Feedback Systems
Feedback Systems
It is called NEGATIVE feedback because once
the ideal level has been reached, it ‘feeds
back’ saying STOP!
The vast majority of the feedback we will be
talking about for the rest of the year will
follow this negative feedback loop.
Feedback Systems
Positive feedback systems are less common in
the body.
Positive feedback systems are designed to
reinforce a change.
This form of feedback moves the controlled
variable away from a steady shape.
It is used to amplify a response.
Feedback Systems
The value of this feedback system is that it
allows a discrete physiological event to be
accomplished very quickly.
Once the event is accomplished, the feedback
loop stops and a negative one kicks in to
rebalance the system.
Best example of positive feedback is the
birthing process.
Hormones
Hormones are the chemical regulators produced
by cells in one part of the body that affect
cells in another part of the body.
They are used to speed up or slow down
certain bodily processes.
Only small amounts are needed to alter cell
metabolism.
Hormones
Chemicals produced by endocrine glands and
secreted directly into the blood are called
endocrine hormones.
The hormones use the bloodstream to travel to
all the different parts of the body to target
the different effectors.
Hormones
Some hormones are referred to as non-target
hormones. These hormones can affect many
cells or tissues in the body. (ex. insulin)
Other hormones target specific cells or
tissues. (ex. TSH)
Chemical Control Systems
The nervous system and the endocrine system
work together to control the organs and
tissues of our body to maintain homeostasis.
The nervous system allows the body to adjust
to changes quickly while the endocrine system
is designed to maintain control over a longer
period of time.
Chemical Control Systems
The division between the
nervous and endocrine
systems is most subtle in
the hypothalamus. This
structure regulates the
pituitary gland through
nerve stimulation as well
as by releasing hormones.
Chemical Control Systems
It is important to know that hormones do not
affect all cells.
Cells contain receptors on their membranes.
Each receptor is matched with a hormone.
Some cells contain only one type of receptor,
while others contain many.
Chemical Control Systems
Hormones can also be classified by their
chemical nature.
Most hormones are water soluble and are
proteins. These hormones act from outside a
cell by binding to receptor sites on the cell
membrane causing activation of enzymes in the
cell to carry out certain actions.
Chemical Control Systems
Other hormones are fat soluble and work
inside the cell by diffusing into cells and
binding to receptors inside the cytoplasm
which signals the cell to produce specific
proteins.
Regulating Hormones
Hormone production needs to be regulated.
Once a hormone produces the desired effect,
production of the hormone needs to slow down
or stop to maintain balance.
This is done using negative feedback systems.
The Pituitary Gland
The pituitary gland is often called the
master gland because it exercises control
over the other endocrine glands.
It is connected to the hypothalamus so is
directly linked to the nervous system.
The pituitary produces and stores hormones
while the hypothalamus stimulates the release
of said hormones.
The Pituitary Gland
The pituitary gland is made up of two lobes:
1. Posterior Lobe
2. Anterior Lobe
The posterior lobes does not make hormones.
Instead it stores and releases hormones that
have been made by the hypothalamus.
The hormone ADH (antidiuretic hormone) is
stored and released from here.
The Pituitary Gland
The anterior pituitary gland synthesizes
(makes) its own hormones.
The hypothalamus them sends releasing factors
to the anterior pituitary saying “release
your hormones!” or inhibiting factors saying
“stop it!”
Hormones produced include TSH, ACTH, and hGH
Hormones and Blood Sugar
Two members of the endocrine system affect
blood sugar in humans: specific cells in the
pancreas (islets of Langerhans) and the
adrenal glands.
The islets of Langerhans, discovered by
German scientist Paul Langerhans consist of
more than 200 000 tiny islets, each
containing thousands of cells, scattered
throughout the pancreas.
Hormones and Blood Sugar
These islets contain alpha cells and beta
cells.
The alpha cells release glucagon into the
bloodstream. Glucagon then travels to the
liver where it changes glycogen into glucose.
Glucose is released into the blood and blood
sugar levels go up.
Hormones and Blood Sugar
The beta cells produce insulin which is
released into the bloodstream and travel to
the liver. The liver converts glucose to
glycogen and body cells become more permeable
to glucose, using it up thereby lowering the
blood sugar levels.
Diabetes
Insulin and glucagon work together to
maintain blood sugar balance in the body.
When these hormones do not work properly,
diabetes can occur.
Diabetes is a disease where your body cannot
produce enough insulin or is unable to use
insulin properly. This leads to unbalanced
blood sugar levels.
Diabetes
Even though there is an abundance of glucose
in the blood, the body can’t use it
effectively and the body needs to metabolize
fat instead. This can lead to a build up of
acetone in the body.
There is so much glucose in the body as well
that the kidneys cannot reabsorb proper
amounts so glucose can be detected in the
urine.
Diabetes
Three types of diabetes:
1. Type 1: pancreas cannot produce insulin
2. Type 2: decreased insulin production
3. Gestational Diabetes: temporary condition
that occurs in 2-4% of pregnancies.
Diabetes
How is it treated?
1. Insulin injections
2. Medications
3. Islet cell transplants
No treatment used today is a cure and
symptoms of diabetes can still occur.
Adrenal Glands
The adrenal glands are
located above the kidneys.
Each gland is made up of
two glands encased in a
shell. The inner gland is
called the adrenal medulla
(middle) and the outer
gland is called the adrenal
cortex.
Adrenal Glands
The medulla is regulated by the nervous system
while the cortex is regulated by hormones.
The medulla produces two hormones:
- Epinephrine (adrenaline)
- Norepinephrine (noradrenaline)
These hormones are stimulated by the
sympathetic nervous system during times of
stress.
Adrenal Glands
Epinephrine and norepinephrine are released
during times of stress into the blood and cause
blood sugar levels to rise, increase heart
rate, increase breathing rate, and dilate blood
vessels to large tissues (muscles).
Adrenal Glands
The adrenal cortex produces three different
types of steroid hormones:
1. Glucocorticoids
a. Cortisol
2. Mineralcorticoids
a. Aldosterone
3. Sex hormones
Cortisol
Cortisol is released after a stressful
situation has occurred and increases the level
of amino acids in the blood. These amino acids
then change into glucose allowing blood sugar
to raise allowing for cell recovery.
This release of cortisol is stimulated by ACTH,
which again, comes from the anterior pituitary.
Cortisol
When cortisol levels reach a certain point, a
negative feedback system is initiated and ACTH
levels drop causing the cortisol levels to drop
and the body to enter a balanced state once
again.
Summary of Hormones that Regulate Blood Sugar
Quick Review
Page 484
#2, 3, 4
Hormones that Regulate Metabolism
Three glands affect metabolism:
1. Thyroid gland
2. Parathyroid gland
3. Anterior Pituitary gland
Thyroid Gland
The thyroid gland helps to
regulate body metabolism the rate at which glucose
is broken down.
Produces hormones
triiodothyronine (T3),
thyroxine (T4), and
calcitonin.
Thyroid Gland
The reason that some people can eat an insane
amount of food and not gain a pound while
others can just think about food and seem to
gain weight is all due to the thyroid gland.
People who secrete high levels of thyroid
hormones can break down glucose quicker and
therefore ‘burn off the calories’ quicker.
Thyroid Gland
Individuals with lower levels of thyroid
hormone do not break down nutrients as
quickly and because of this, excess sugar can
be stored as fat.
People who secrete low levels of thyroid
hormones often feel weak, cold, and have dry
skin and hair.
Thyroid Gland
Low secretions of
thyroid hormone is
referred to as
hypothyroidism
Thyroid Gland
High secretions of
thyroid hormone is
referred to as
hyperthyroidism.
The Endocrine system
How Our Bodies Maintain Balance
Thyroid Hormones
Thyroxine (T4) and triiodothyronine (T3) are
produced by the thyroid and are used to help
regulate body metabolism (breaking down of
glucose) and the growth and differentiation
of tissues.
Even though they seem to have the same
function, about 65% of secretions are T4
Thyroid Hormones
T3 and T4 are released from the thyroid when
it is stimulated by TSH which is released
from the pituitary gland.
Thyroid Hormones
The thyroid also produces a hormone called
calcitonin.
This hormone acts on bone cells to help lower
the calcium levels found in blood.
Control of thyroid hormones is accomplished
through negative feedback.
Thyroid Hormones
Thyroid Hormones
Another issue that can affect the thyroid is
iodine deficiency. When you do not have
enough iodine in your diet, you can develop a
goiter.
This is an enlargement of the thyroid gland.
Thyroid Hormones
This happens because of a drop in T4 levels
which causes more and more TSH to be released
stimulating the thyroid over and over.
This causes the thyroid to keep working
harder and harder to produce more hormone
making it get bigger.
Parathyroid Glands
These glands help to regulate the calcium
levels in the blood and lower the phosphate
levels.
Parathyroid Glands
Parathyroid glands respond directly to
chemical changes in their immediate
surroundings.
Low calcium levels in the blood stimulate the
release of parathyroid hormone (PTH) and
inhibits the release of calcitonin from the
thyroid.
Parathyroid Glands
PTH causes kidneys and intestines to absorb
calcium while promoting release of calcium
from bones.
The bone cells break down and release calcium
from phosphate ions. Calcium is reabsorbed
and returned to the blood while phosphate is
lost in urine.
Parathyroid Glands
In summary, as PTH levels increase,
absorption of calcium increases.
When calcium levels have risen to a point,
PTH is inhibited and release of calcitonin is
stimulated causing calcium levels to drop.
(negative feedback)
Growth Hormone
Human growth hormone is produced by the
anterior pituitary gland and stimulates the
elongation of the skeleton (growing!).
When there is too little hGH, dwarfism can
occur and when there is too much, gigantism
can occur.
Growth Hormone
As people age, hGH production decreases and
cellular repair and protein replacement are
compromised.
Growth hormone also increases the use of fat
stores and promotes protein synthesis
reducing the amount of fat in the body. This
could explain why body fat is lost during a
growth spurt.
Hormones Affecting Water and Ion Balance
The body adjusts for increased water intake
by increasing urine output and vice versa.
These adjustments are accomplished by
antidiuretic hormone (ADH) and aldosterone.
ADH and Water Balance
ADH is a hormone made in the hypothalamus and
released from the posterior pituitary gland.
It enters the bloodstream and targets the
kidneys.
Once it reaches the kidneys, it regulates the
amount of water being reabsorbed or secreted
in the urine.
**ADH ONLY regulates WATER!
ADH and Water Balance
The main function of ADH is to reduce urine
output.
There are sensory receptors in the
hypothalamus called osmoreceptors that detect
changes in osmotic pressure in body fluids.
ADH and Water Balance
When you lower water intake or increase water
loss (sweating), blood solutes become more
concentrated.
This increases osmotic pressure.
ADH is released to cause the kidney to
reabsorb more water.
ADH and Water Balance
As osmotic pressure drops with increased
water, ADH levels will drop.
Drinking alcohol or caffeine which are called
‘diuretics’ will inhibit the release of ADH
which is why you may feel like urinating a
lot after consuming either of them. Your body
cannot reabsorb the water and because of
this, you can feel very dehydrated the next
day (hung over).
Aldosterone, Blood Pressure, and Blood Volume
Aldosterone is a hormone released from the
adrenal cortex and is used to regulate water
balance and Na+ balance.
A structure called the juxtaglomerular
apparatus (JGA) near the glomerulus in the
nephron of the kidney contains blood pressure
receptors.
Aldosterone, Blood Pressure, and Blood Volume
These receptors detect changes in blood
pressure.
When blood pressure is low, a protein is
released into the blood that causes
constriction of blood vessels, increasing the
blood pressure. The protein then stimulates
the cortex to release aldosterone.
Aldosterone, Blood Pressure, and Blood Volume
Aldosterone then travels to the kidneys in
the bloodstream and causes Na+ reabsorption.
As Na+ enters the blood, blood volume and
blood pressure will begin to rise.
As this process occurs, water is reabsorbed
as well increasing osmotic pressure.
Review
Pages 501-502
#1-11, 13, 14, 19