feedback mechanisms. m aintaining e quilibrium living versus non-living living organisms have the...
TRANSCRIPT
FEEDBACKMECHANISM
S
MAINTAINING EQUILIBRIUM
Living versus non-living Living organisms have the ability to
sense and respond to changes in environment
The cells of living organisms function best in a constant, balanced internal environment
Organisms must maintain a “steady state” called homeostasis to survive
Cells, tissues, organs, and organ systems must work together to adjust to changing conditions
Cold temperatures: humans respond by shivering to increase body temperature by muscle movement
Hot temperatures: humans may respond by sweating to cool off
MAINTAINING EQUILIBRIUM
WHAT IS FEEDBACK?
Feedback is the process in which part of the output of a system is returned to its input in order to regulate its further output.
NEGATIVE FEEDBACK
Have you ever been scolded for not cleaning your room?
Cleaning your room is how you respond to being scolded.
A negative feedback system involves the detection of an undesirable condition and the response to make that condition ideal.
Negative Feedback
+
_
NEGATIVE FEEDBACK
Basic structure:
INPUT DETECTION RESPONSE OUTPUT SHUT OFF
NEGATIVE FEEDBACK
Negative feedback occurs when the output of a system acts to oppose changes to the input of the system
A thermostat is an example of a negative feedback system
A thermostat is a device for regulating the temperature of a system so that the system's temperature is maintained near a desired setpoint temperature.
Room temp is below the
setpoint
Room temp is above the
setpoint
Room temp increases
Room temp decreases
Set point
is reached
Set point
is reached
THERMOSTAT
NEGATIVE FEEDBACK IN BIOLOGY
Negative feedback also regulates many systems in organisms
The endocrine system is one example
This diagram shows a negative feedback loop for stress hormones
Areas of negative feedback are indicated with a minus sign, (-)
KEEPING THE BODY IN BALANCE!
ENDOCRINE SYSTEM
The endocrine system is composed of glands that produces chemical messengers called hormones
Hormones are produced in one part of the body and travel to target organs through the bloodstream
ENDOCRINE SYSTEM
The brain continuously sends signals to the endocrine glands to secrete and release hormones
The glands, in turn, send feedback to the nervous system
The hypothalamus in the brain is the master switch that sends signals to the pituitary gland which can release up to eight hormones into the bloodstream
The hormone travels to its target organ and usually results in the release of another hormone into the bloodstream
ENDOCRINE SYSTEM
The hypothalamus then detects the rising hormone levels from the target organ and decreases the release of hormones from the pituitary which results in a decrease in hormone release from the target organ
The process of maintaining normal body function through negative feedback mechanisms is called homeostasis
GLUCOSE AND INSULIN
Glucose intake occurs during digestion of food that is needed for energy expenditure to perform routine physical activities.
The pancreas is the key organ that regulates the glucose levels in body by secreting two hormones, insulin and glucagon.
The liver also helps to store the excess glucose in form of glycogen to be utilized later.
Pancreas
Liver
GLUCOSE AND INSULIN NEGATIVE FEEDBACK LOOP
Increases Glucose Levels
Eating cake
Stimulates β cells of pancreas to secrete insulin
Insulin stimulates the cells to take up
glucose from the blood
Lowers Blood Glucose levels
CYCLE 1(-)
Low Blood Glucose Levels Stimulated Alpha Cells in
Pancreas
Glucagon is released
Glucagon stimulates liver cells to release glucose into the blood
High blood glucose levels and Cycle 1 continues
CYCLE 2 (-)
GLUCOSE AND INSULIN NEGATIVE FEEDBACK LOOP
Two primary Hormones
The opposite actions of these two hormones helps to maintain normal blood sugar levels in the body hence maintain homeostasis of the body.
Insulin Glucagon
Lowers Blood Glucose Levels
Raises Blood Glucose Levels
TAKE A BREAK AND CHAT WITH YOUR NEIGHBOR!
Turn to the person behind or in front of you and discuss the following topics:
What is a feedback and an example of a negative AND positive system?
What is the endocrine system and why is it important?
Define homeostasis and how normal body function is maintained with feedback mechanisms.
KIDNEYS AND WATER REGULATION
The kidneys play a key role in maintaining water regulation.
KIDNEY AND WATER REGULATION
The nephron is the most important functional part of the kidney.
It filters nutrients like salts and amino acids in the Bowman’s capsule into ascending loop and filters the urine.
KIDNEY AND WATER REGULATION
Anti-Diuretic Hormone, ADH (also called vasopressin), is secreted by the pituitary gland and acts on the nephron to conserve water and regulate the tonicity of body fluids.
Anti- DiureticHormone
ADH acts on Nephron to reabsorb water and decrease blood osmolality (saltiness)
ADH REGULATED WATER CONSERVATION IN KIDNEYS
Excess water in the blood
Stimulates osmoreceptors in hypothalamus to send signals to
the pituitary gland
Pituitary glands secretes low levels of ADH
Less ADH makes the tubules less permeable and less water is reabsorbed
back into the bloodstream (urine is dilute).
Less water in the blood
ADH makes the tubules more permeable and more water is reabsorbed back into the
bloodstream (urine is concentrated).
Stimulates osmoreceptors in hypothalamus to send signals to
the pituitary gland
Pituitary glands secretes high levels of ADH
ADH REGULATED WATER CONSERVATION IN KIDNEYS
Osmoregulators send negative feedback to the hypothalamus about the concentration of water in the bloodstream.
The hypothalamus then stimulates the pituitary glands to secrete high or low concentrations of anti-diuretic hormone.
ADH then makes the tubules more or less permeable and hence, maintains water and electrolyte homeostasis.
TEMPERATURE REGULATION OF BODY
Animals that are capable of maintaining their body temperature within a given range are called homeotherms.
Temperature is regulated by negative feedback control.
Thermoreceptors located in hypothalamus detect temperature fluctuations in the body.
TEMPERATURE REGULATION OF THE BODY
Increased temperature causes vasodilatation (blood vessels near the surface of the skin dilate).
The large surface area allows heat to be lost from the blood and lowers the body temperature.
Sweating also helps lower the temperature.
Decreased temperature causes vasoconstriction (blood vessels constrict) and minimal heat loss occurs which helps maintain body temperature.
Hair on the body provides insulation and helps maintain body temperature.
POSITIVE FEEDBACK
A positive feedback loop occurs when the output of a system acts to enhance the changes to the input of the system.
One example of a biological positive feedback loop is the onset of contractions in childbirth. When a contraction occurs, the hormone
oxytocin is released into the body, which stimulates further contractions.
This results in contractions increasing in amplitude and frequency.
POSITIVE FEEDBACK
Another example is blood clotting. The loop is initiated when injured tissue
releases signal chemicals that activate platelets in the blood.
An activated platelet releases chemicals to activate more platelets, causing a rapid cascade and the formation of a blood clot.
Lactation involves positive feedback so that the more the baby suckles, the more milk is produced.
POSITIVE FEEDBACK
In most cases, once the purpose of the feedback loop is completed, counter-signals are released that suppress or break the loop. Childbirth contractions stop when the baby
is out of the mother's body. Chemicals break down the blood clot. Lactation stops when the baby no longer
nurses.
OTHER KINDS OF FEEDBACK
Feed-forward
Not technically feedback, but similar.
The system responds in anticipation of a change
Hunger is an example of feed-forward. If you typically eat lunch at noon, your body will begin to make digestive enzymes in anticipation.