Lecture 3 Homeostasis Flashcards
Define Homeostasis
Homeostasis is the maintenence of a constant internal environment
Define Negative feedback control mechanism
This is when a deviation from a set point/norm value will result in effectors being activated to restore the set point value. (eg effectors being muscle or gland)
Give an example of a negative feedback control mechanism
Control of core body temperature via thermoregulation
Define positive feedback mechanism
An initial stimulus produces a response that exaggerates or enhances the change in the original conditions, rather than opposing it. I.e a deviation from the set point results in processes that enhance that deviation further from the norm
Give an example of a positive feedback mechanism
Childbirth
.What are the two different systems employed in homeostatic regulation
Autoregulation
Extrinsic regulation
Define autoregulation
This describes local level, cellular/tissue level response to environmental change. Eg a change in the oxygen concentration will triger chemicals that widen/dilate blood vessels.
List the three components of a homeostatic regulatory mechanism
- Receptor, detects environmental stimuli
- Control center, recieves and processes information
- Effector, a cell or organ which responds to commands from control centre
Define extrinsic regulation
This involves nervous/endocrine control. For example, during exercise, the nervous system issues commands to increase heart rate so blood circulates faster.
Why is homeostatic regulation important
Because it is important to prevent harmful changes in body tissue fluid composition.
Define set point
This is a value at which a controlled variable should be maintained.
Define negative feedback control
aims to maintain a controlled variable at its set point. Controlled variable is some aspect of the internal environment, like blood pressure or plasma
Describe briefly the process of thermoregulation
The set point core body temperature is 37 degrees.
If temperature rises above core temp, receptors fire to the control centre.
Control centre fires to 2 target effectors.
1) Muscle tissue lining the walls of the blood vessels
2) sweat glands.
Blood vessels dilate to increase the skin surface blood flow.
Skin acts as a radiator by loosing heat to environment via sweat. Sweat evaporates.
As the set point for temp is restored, blood flow to skin returns to normal levels.
Explain the two ways in which heat loss is achieved in the event of elevated core body temperature ( >37.2 degs)
Increased blood flow to skin surface via skin capillaries.
Increased sweating
The control of body temperature can also be thought of as a thermostat. Describe this process
Set point = normal room temp
Stimulus = room temperature rises (deviation from sp)
Receptor = thermometer (detects change and sends info to control centre)
Control centre = Thermostat, sends commands to the effector to switch on
Effector = AC. unit, which turns on. effector then acts to lower the temp, and restore the room temp to within normal range.
Give an example of an effector
muscle or gland
Give an example of a receptor
Sensory receptor cells.
Describe how blood pressure is regulated via homeostasis
Baroreceptors detect fall in blood pressure
baroreceptors fire impulses to the c.c via the Glossopharyngeal nerve in medulla oblogata.
Medulla fires to the heart and blood vessels via autonomic to increase cardiac output and vasoconstriction
Effectors = heart and blood vessels which increase blood pressure and vasoconstriction.
State the name of the nerve that baroreceptors fire impulses along to the medulla oblongata
Glossopharyngeal nerve
In control of blood pressure, the medulla oblongata fires impulses to the heart and blood vessels along which nerves
The autonomic nerves.
Explain positive feedback mechanisms
This is where initial stimulus causes a response which continually reinforces itself.
Give some examples of positive feedback mechanisms
Action potentials in nerves
Ovulation
Blood clotting.
Explain how the process of clotting is a positive feedback mechanism
Damage to blood vessel causes
activation of clotting factors
causes activation of thrombin
causes formation of a blood clot
Which type of response is the nervous system involved in
Rapid, short term effectst hat last seconds usually
Which type of responses/effects is the endocrine system involved in
Long term effects, (minutes to days)
examples include growth and metabolism
What are thyroid hormones involved in
Metabolism control
What are the features of nerves from the autonomic nervous system
CNS has a preganglionic neuron
Peripheral ganglion is called a post ganglionic neuron,
These both fire to a target cell.
