HOMEOSTASIS
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Refers to the body’s ability to maintain a constant internal environment.
This is important because it allows your body to function well in spite of the
ever changing external environment.
Substances need to be maintained inside the body:
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Water
Glucose
Carbon Dioxide and Oxygen
Mineral Salt
All cellular activities are controlled by different feedback mechanisms that regulate
body temperature, body fluids, gas concentration, blood pressure, and glucose
Any changes in the external environment may affect the body’s internal
environment, which will cause the body to continually adjust.
Brief definition of the stimulus response feedback model:
1. Stimulus - A structure that produces the change
2. Receptor - A structure that detects the change
3. Control Center - A structure that determines the appropriate response to the
stimulus
4. Effector - Can be organs, glands, or tissues that are instructed to adjust the amount
of output that produces a desired effect
5. Response - The outcome of the adjustment that should remove the initial stimulus.
NEGATIVE FEEDBACK MECHANISM
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Allows the internal condition of the body to go back to its normal or ideal
state by inhibiting or removing the stimulus.
As the concentration of products or substances inside the body increases, the
rate of process decreases.
Example of Negative Feedback Mechanism:
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When your body absorbs a lot of glucose from the food you eat. As
the glucose level in your blood increases, the receptors in your body
will signal the brain to command the pancreas to secrete insulin into
the blood.
Once the insulin is secreted, the blood sugar level effectively
decreases.
When the sugar level in your blood finally reaches homeostasis, the
pancreas will then stop will then stop secreting insulin.
POSITIVE FEEDBACK MECHANISM
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The increase in the concentration or products or substances also results in an
increase in the rate of process.
Allow the output to enhance the original stimulus.
Example of Positive Feedback Mechanism:
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This can be observed during childbirth.
As the mother labors, oxytocin is released inside her body.
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Oxytocin, a hormone, causes muscle contractions to speed up and intensify.
An increase in muscle contractions allows more oxytocin to be released until
the baby is born.
The birth of the baby ends the continuous release of oxytocin, and thus the
positive feedback mechanism halt.
Regulation of Temperature
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Your body needs to maintain a relatively constant internal temperature for
metabolic processes to proceed efficiently.
If the internal temperature of your body changes, your body will find ways to
maintain its temperature.
High Temperature
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Makes the blood warmer than the hypothalamic set point.
The heat-loss center in the hypothalamus is activated, which will signal the
sweat glands to secrete sweat.
The sweat in your body is vaporized by your body heat to lower internal body
temperature.
The hypothalamus also signals the blood vessels in the skin to become
dilated.
This allows the capillaries to become flushed with warm blood, permitting the
heat to radiate from the surface of the skin.
Once your body temperature decreases or when or when you cool down, the
heat-loss center in the hypothalamus shuts off.
This heat-loss mechanism protects the body from excessively high
temperature.
Low Temperature
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When the environment or your blood temperature falls, the heat-promoting
center in the hypothalamus is activated.
This allows your skeletal muscles to start shivering and for the diameter of
your blood vessels to become small.
Shivering occurs to help your muscles generate heat, and blood vessels
constriction allows your blood to be diverted from your skin to the deeper
body tissues to minimize overall heat loss from the skin surface.
When the body temperature finally increases or when you feel warmer, the
hypothalamus is triggered to shut down the heat-promoting center.
REGULATION OF BODY FLUIDS
 Water needs to be regulated inside your body.
 It is continually released from your body through sweat and urine.
1) Stimulus – an increase in osmotic pressure (water concentration in plasma
decreases)
2) Receptor – Osmoreceptors in hypothalamus
3) Modulator – hypothalamus
 Sends message for release of ADH from posterior lobe of the pituitary.
 Nerve impulses will come from the drinking cener of the
hypothalamus.
4) Effector
 Makes kidney tubules become more permeable to water
 Stimulates drinking behavior.
5) Response
Increased in reabsorption of water into plasma causes a decrease in osmotic
pressure water intake causes a decrease in osmotic pressure.
REGULATION OF GAS CONCENTRATION
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Carbon Dioxide and Oxygen are two important gases that must have a
normal concentration inside the body.
The respiratory system helps in maintaining the concentration of these two
gases.
The respiratory system also maintains the pH level inside your body.
Oxygen enters the body as an essential component for the process of
respiration, and carbon dioxide is produced as its by-product.
When oxygen supply is insufficient, cells cannot produce energy.
On the other hand, carbon dioxide should also be at constant concentration
inside the cell; if the carbon dioxide level is not carefully managed, it would
accumulate at problematic levels.
The pH level is also maintained by the respiratory system because it is
directly influenced by the concentration of carbon dioxide.
The parts of the respiratory system, along with the help of the circulatory
system, aid in the intake of oxygen and the release of carbon dioxide out of
the body.
REGULATION OF BLOOD PRESSURE
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The circulatory system is a very important body system because it does not
only control the temperature, body fluids, and gases – it regulates blood
pressure.
Blood pressure is the pressure exerted by the blood against the walls of the
blood vessels.
As the blood travels farther from the heart, these blood vessels branch off and
gradually decrease in size.
If the blood pressure rises too high, it could damage the blood vessels.
However, if the blood pressure is too low, the organs in your body would not
receive adequate oxygen and nutrients.
If there are stimuli that can cause the increase or decrease of blood pressure,
the nervous system helps in regulating it.
Blood pressure is closely monitored by baroreceptors that send messages to
the cardio-regulatory center of your medulla oblongata.
As baroreceptors detect changes in the blood pressure, they transmit the
information to the brain.
The brain responds by initiating mechanisms that bring the blood pressure
back to normal.
If there is high blood pressure, baroreceptors will send signals that cause
vasodilation, or the expanding of the walls of the blood pressure.
Vasodilation allows the peripheral resistance of the blood to decrease, which
actually causes a decrease in blood pressure.
A low blood pressure causes a decrease in the signals sent to the cardioregulatory center of your medulla oblongata.
Therefore, the sinoatrial node (SA node), which is responsible for creating
nerve impulses, would fire more frequently to increase the heart rate.
When the heart is stimulated to increase its pumping force, the blood
pressure increases.
REGULATION OF GLUCOSE CONCENTRATION
GLUCOSE - An important sugar in our body. Many functions in the body are based on the
energy sourced from glucose. Glucose should be regulated as too much or too less of it might
result in brain damage and loss of consciousness.
Important Hormones in regulating blood glucose levels in the body:
Insulin
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Allows glucose level to decrease.
If there is an increase in the blood glucose level, the islets of Langerhans secrete
insulin into the blood.
A hormone that facilitates glucose transport into the cells.
The presence of it in the bloodstream makes the glucose level in the bloodstream
decreases.
Once the blood glucose level returns to normal, the release in insulin by the
pancreas is inhibited.
Glucagon
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Allows glucose level to increase.
If the blood glucose level decreases, the pancreas detects this change and secretes
glucagon.
A hormone produced by the pancreas that raises the blood glucose level by
stimulating the breakdown of glycogen into glucose and by allowing glucose
production from amino acids and fatty acids.
The liver also breaks down the stored glycogen to be secreted as blood glucose.
When the blood glucose level returns to normal, the secretion of glucagon is
inhibited.