Homeostasis of gas concentrations & blood pressure

Regulation of breathing Gas concentrations

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

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 http://www.georgiahealth.edu/itss/edtoolbox/7370/pulmonary/neuralcontrol/engage.swf

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

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

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

Regulation of heart rate & blood pressure

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

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

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

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

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

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

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