1. Homeostasis of gas concentrations & blood pressure

2. Regulation of breathing
Gas concentrations

3. Keywords Medulla oblongata Respiratory centre CO2 pH (acidity) O2
Chemoreceptors
Aortic bodies
Carotid bodies
Central chemoreceptor

4. Regulation of gas concentrations
The nerve impulses that travel to the diaphragm and the intercostal muscles are controlled by a respiratory centre in the medulla oblongata of the brain

5. Gas concentrations
The main gas that the body uses to regulate breathing is the level of CO2 in the blood
With an increase in CO2 there is also an accompanying increase in H+ ions (increase in acidity)
A relatively small increase in the CO2 concentration is enough to cause an increase in the rate of breathing

6. Gas concentrations
There are a group of cells that are sensitive to changes in the pH and changes in the concentration of O2 and CO2 in the blood.
These are called chemoreceptors.
Specifically, there are the aortic and carotid bodies on the arteries close to the heart and the central chemoreceptors in the medulla oblongata

7. Negative feedback loop
Chemoreceptors
Aorta
Carotid artery
Medulla oblongata
High CO2 (= low pH or high H+) or low O2
Stimulus
Receptor
Respiratory centres in brain stem
Levels of CO2 & O2 return to normal
Feedback
Regulation-
Control centre
Reflexes involving somatic nerves
Response
Effector
Increased rate and depth of breathing
Respiratory muscles

8. Regulation of heart rate & blood pressure

9. Keywords Sinoatrial node (SA node) Atrioventericular node (AV node)
Medulla oblongata
Respiratory regulating centre
Stroke volume

10. Heart rate There are 2 bundles of specialised cells in the heart:
Sinoatrial node (SA node)
Atrioventericular node
(AV node)
They initiate nerve impulses to stimulate muscle contractions
This allows the heart to beat of its own accord, without input from the nervous system

11. Heart rate
The SA node sends out nerve impulses that spread through the atria
The impulses reach the AV node. Contraction of the atria begins
The AV node sends out impulses that spread through the ventricles
Contraction of the atria has finished and contraction of the ventricles begins

12. Cardiac output
The cardiac output is the total amount of blood being pumped by the heart over a particular period of time – e.g. the minute volume is the amount of blood pumped by the heart over one minute
The cardiac output is affected by the stroke volume (the volume of blood pumped by each ventricle during a cardiac cycle) and the heart rate (the number of heart beats over a particular period of time).
Cardiac output = Stroke volume x Heart rate

13. Control of heart rate & blood pressure
The SA node is regulated by the ANS
The cardiovascular regulating centre in the medulla oblongata sends out messages to either increase the rate and strength of the contractions or decrease the rate and strength of contractions

14. Blood pressure Pressoreceptors respond to changes in blood pressure
The cardiovascular regulating centre in the medulla oblongata then responds by changing the cardiac output and changing blood vessel dilation

15. Negative feedback loop
Pressoreceptors
in heart
Change in blood pressure
Stimulus
Receptor
Cardiac centre in
medulla oblongata
Blood pressure is stabilised
Negative feedback
Regulation -control centre
Response
Effector
Sympathetic NS speeds heart up
Parasympathetic NS slows heart down
SA node