Single Circulation is a circulatory system in which the blood passes through the heart once, in its passage around the body. eg. Fish
Things to remember :-
The aorta takes oxygenated blood TO the body.
The vena cavae bring deoxygenated blood BACK to the heart.
The pulmonary artery takes deoxygenated blood TO the lungs.
The pulmonary vein brings oxygenated blood back to the heart.
The vagus nerve is used to slow down the heart. It sends its impulses to the SAN and to the AVN.
The sympathetic is used to speed up the heart. It sends its impulses to the walls of the heart. These two nerves work in opposite to each other.
These two nerves can be effected by many different things :-
Blood pressure - Baroreceptors/stretch receptors in the aorta and also in the walls of the carotoid artery are sensitive to any changes in pressure. When the blood pressure changes these receptors send messages to the medulla oblongta, which then reacts accordingly.
The concentration of carbon dioxode - If there is a low pH then there's an increase in CO2 levels, chemoreceptors in the brain, aorta and carotoid arteries detect these changes and then send messages to the medulla oblangta. N.B. The concentration of oxygen does NOT affect the heart rate, the carbon dioxide concentration does.