Homeostasis
Homeostasis: The maintenance of a constant internal environment
Helps to maintain optimal conditions for enzyme action and all cell functions.
Many diseases involve a disturbance of homeostasis.
Two main systems are involved in homeostasis:
o Endocrine System
o Nervous System
Factors maintained within narrow limits by homeostasis include:
o Blood Pressure
o Blood Glucose level
o pH of body fluids
o Body Temperature
o Water and Electrolyte concentration
How does a Homeostatic System work?
A homeostatic system is made up of 5 components.
Stimulus
o Any physical, chemical or environmental factor/change which brings about a change in the internal
environment.
o Causes the body to bring about a response.
o E.g. drop/rise in temperature, glucose levels
Receptor
o Sensory organs that detect the change in the environment, i.e. stimulus
o Sends signals to the control centre.
Control centre / Coordinator
o Receives and processes the electrical signal
o Identifies the change (i.e. too high or low) through comparing it to a set point.
o Sends out commands to the effectors for further action if needed
o E.g. Brain, Spinal cord, Pancreas
Effector
o Initiates a response through either movement or hormone secretion
o Muscles or glands
Response
o What is done to correct the change
Feedback Systems
Negative feedback system – restores homeostasis
o Allows the maintenance of a set point and prevents overshoot by counteracting changes
o Once the normal is achieved, signals are sent to the brain and the brain stops sending out commands
to initiate the response.
o E.g. thermoregulation; blood glucose control
Positive feedback system – do not result in homeostasis
o Amplifies the initiated change, often resulting in an unstable condition and extreme state.
E.g. childbirth
, Thermoregulation
Optimum body temp. (set point) = 37.5°C
o This is the optimum temperature for enzyme action
Thermoreceptors in the skin detect any change in temperature (stimulus).
The hypothalamus in the brain holds the thermoregulatory centre (coordinator).
Effectors:
o Hair on skin
o Muscles
o Blood Vessels
Extremely low temperatures can cause hypothermia, and sometimes death.
Response when too cold:
o Hairs on our body stand up – “goosebumps”
Erector muscles attached to hair follicles contract to make hairs stand up.
An insulation layer is formed to keep heat in the body.
o Muscle Contraction – “shivering”
Involuntary process
More respiration occurs to release heat energy
o Vasoconstriction
Blood vessels lose heat through the surface of the skin.
Blood vessels are narrowed so less blood flows through them, therefore less heat radiates
through the skin.
Extremely warm temperatures can cause dehydration and heat stroke.
Response when too hot:
o Hairs on our body lay flat
This means that heat can escape.
o Sweating
Heat energy is used when sweat evaporates from the surface of our skin, so we cool down.
o Vasodilation
Blood vessels dilate so there is more blood flow close to the skin, therefore more heat
radiates into the environment.
Controlling Blood Glucose
Glucose is stored in the muscles and liver as glycogen and in fat cells (by conversion into fatty acids).
Receptors on the pancreas sense when blood sugar levels are too low high and
release hormones in response.
Alpha cells in the pancreas release glucagon when blood glucose is low.
o Promotes the breakdown of glycogen and fats into glucose.
Beta cells in the pancreas release
insulin when blood glucose is high.
o Promotes the uptake of
glucose into muscle cells,
the liver and fat cells.
Alpha and beta cells are collectively
known as the Islets of Langerhans.
Homeostasis: The maintenance of a constant internal environment
Helps to maintain optimal conditions for enzyme action and all cell functions.
Many diseases involve a disturbance of homeostasis.
Two main systems are involved in homeostasis:
o Endocrine System
o Nervous System
Factors maintained within narrow limits by homeostasis include:
o Blood Pressure
o Blood Glucose level
o pH of body fluids
o Body Temperature
o Water and Electrolyte concentration
How does a Homeostatic System work?
A homeostatic system is made up of 5 components.
Stimulus
o Any physical, chemical or environmental factor/change which brings about a change in the internal
environment.
o Causes the body to bring about a response.
o E.g. drop/rise in temperature, glucose levels
Receptor
o Sensory organs that detect the change in the environment, i.e. stimulus
o Sends signals to the control centre.
Control centre / Coordinator
o Receives and processes the electrical signal
o Identifies the change (i.e. too high or low) through comparing it to a set point.
o Sends out commands to the effectors for further action if needed
o E.g. Brain, Spinal cord, Pancreas
Effector
o Initiates a response through either movement or hormone secretion
o Muscles or glands
Response
o What is done to correct the change
Feedback Systems
Negative feedback system – restores homeostasis
o Allows the maintenance of a set point and prevents overshoot by counteracting changes
o Once the normal is achieved, signals are sent to the brain and the brain stops sending out commands
to initiate the response.
o E.g. thermoregulation; blood glucose control
Positive feedback system – do not result in homeostasis
o Amplifies the initiated change, often resulting in an unstable condition and extreme state.
E.g. childbirth
, Thermoregulation
Optimum body temp. (set point) = 37.5°C
o This is the optimum temperature for enzyme action
Thermoreceptors in the skin detect any change in temperature (stimulus).
The hypothalamus in the brain holds the thermoregulatory centre (coordinator).
Effectors:
o Hair on skin
o Muscles
o Blood Vessels
Extremely low temperatures can cause hypothermia, and sometimes death.
Response when too cold:
o Hairs on our body stand up – “goosebumps”
Erector muscles attached to hair follicles contract to make hairs stand up.
An insulation layer is formed to keep heat in the body.
o Muscle Contraction – “shivering”
Involuntary process
More respiration occurs to release heat energy
o Vasoconstriction
Blood vessels lose heat through the surface of the skin.
Blood vessels are narrowed so less blood flows through them, therefore less heat radiates
through the skin.
Extremely warm temperatures can cause dehydration and heat stroke.
Response when too hot:
o Hairs on our body lay flat
This means that heat can escape.
o Sweating
Heat energy is used when sweat evaporates from the surface of our skin, so we cool down.
o Vasodilation
Blood vessels dilate so there is more blood flow close to the skin, therefore more heat
radiates into the environment.
Controlling Blood Glucose
Glucose is stored in the muscles and liver as glycogen and in fat cells (by conversion into fatty acids).
Receptors on the pancreas sense when blood sugar levels are too low high and
release hormones in response.
Alpha cells in the pancreas release glucagon when blood glucose is low.
o Promotes the breakdown of glycogen and fats into glucose.
Beta cells in the pancreas release
insulin when blood glucose is high.
o Promotes the uptake of
glucose into muscle cells,
the liver and fat cells.
Alpha and beta cells are collectively
known as the Islets of Langerhans.
