Homeostasis

- Maintenance of a steady internal state where the body responds to external/internal changes.

- Dynamic Equilibrum.

- It involves high level of coordination and control.

- Changes are detected by a sensor (receptor).

- The receptor will send an electrical impulse to the brain which sends the message to an effector.

- The change will either be reversed or increased.

- Negative feedback systems are more common which work to restore equilibrum. E.g. if the concentration of something goes up the effector will work to bring it down.

- Communication in feedback system may be by hormones or nerve impulses. 

- During exercise conditions change rapidly and demands on the system are high. So the body has to respond quickly to supply muscles with glucose/oxygen and remove carbon dioxide.

- The negative feedback enables us to exercise effectively and efficiently.

- The medulla oblongata monitors our heart and breathing rate. Chemical and stretch receptors in the lining of blood vessels and chambers of the heart sned nerve impulses to the cardiovascular centre.

Two types of nerve carry impulses: sympathetic is excitatory (stimulates SAN at a faster rate) and parasympathetic is inhibitory (slow the heart rate).

Due to the muscles in the legs and arms squeezing more blood along the veins as they work, more blood flows to the atria causing the receptors to stretch; sending an impulse to the c.v.c. So the sympathetic then carries and impulse to the SAN causing the heart rate to increase. 

Baroreceptors found in sinuses of carotid arteries in the neck are important towards the end of exercise. The blood pressure increases so the receptors stretch and this causes message to be sent to the brain. The parasympathetic nerve carries an impulse to slow the heart beat and cause vasodilation; so lower bp.

When exercise begins blood vessels dilate in response to adrenaline release so the bp falls a little. The c.v.c sends signals along the sympathetic nerve to stimulate the heart and this increases bp.

- Surface temp. fluctuates regularly but internal is kept steady because of enzyme activity. We produce a lot more heat energy due to respiration in muscles when exercising.

If our temperature falls below the low critical temperature it is very important to bring it back up. So cold receptors in skin detect the decrease and communicare with the hypothalamus. The heat gain centre sends impulses to hair erector muscles to contract making hairs stand up. Muscles also 'shiver' (contract rapidly) to generate heat energy. Bloods vessels constrict to reduce heat loss from the skin- radiation is reduced and blood is diverted through the shunt vessels as these dilate.

If our temperature rises, warm receptors detect this change and communicate with the heat loss centre to send electrical impulses to the hair erector muslcs causing them to relax- lie flat. Sweat glands secrete more sweat which evaporates taking heat away. Vasodilation occurs so more blood can flow at the surface of skin, increasing radiation. 

- Oxygen needs changes rapidly from low levels at rest to high levels during strenuous exercise. 

- It is the CO2 levels in the blood that causes the ventilation rate to alter.

- Increased carbon dioxide concentration leads to the subsequent fall in pH. Chemoreceptors are sensitive to CO2 levels and pH of the blood (found in carotid bodies, carotid arteries and aortic bodies in the aortic arch). The receptors send impulses to the inspiratory centre (medulla oblongata). The centre then stimulates breathing muscles- rate is faster and deeper. 

- If levels fall the expiratory centre inhibits breathing muscles and breathing becomes slower and shallower. 

As inhale the stretch receptors fire off but as exhale they are silent.