The circulatory system Flashcards
What are the different types of blood vessels?
Large arteries, small arteries, arterioles, capillaries, venules, small veins, large veins
What is pulmonary circulation?
Circulation of blood between the heart and the lungs to oxygenate it
What is systemic circulation?
Circulation of blood between the heart and the rest of the body to transport oxygen and carbon dioxide to and from the respiring tissue
Where does gas exchange take place?
In the capillaries, at the alveoli and respiring tissue
How are capillaries suited for gas exchange?
They have a single layer of endothelial cells that allow gasses and nutrients to diffuse through
What is cardiac output?
The volume of blood pumped out of the ventricles on each contraction multiplied by the number of beats per minute (stroke volume x heart rate)
What are the stages of the cardiac cycle?
Atrial systole (contraction)
Ventricular systole (contraction)
Diastole (relaxation)
How is a pulse created?
Blood pumped into the aorta stretches the wall and creates a pressure wave or ‘shock wave’ which is very quickly transmitted through the walls of the arterial system
Where can a pulse be felt?
When arteries are close to the surface or pass over a bony part against which a finger can be pressed
What can you find out from the pulse?
Heart rate - bradycardia/tachycardia
Heart rhythm
Strength - stroke volume
What is arterial blood pressure measured in?
mmHg (millimetres of mercury)
Why does blood pressure not drop to zero in diastole?
Because of the elastic recoil of the arteries
What equipment measures blood pressure?
Sphygmomanometers
What factors can affect arterial BP?
Cardiac output and total peripheral resistance
What is total peripheral resistance?
The resistance of arterioles - arterioles fare the smallest arteries and create the most resistance
What factors can affect cardiac output?
If the heart contracts with less strength this will reduce stroke volume and therefore CO
If the blood volume is low and the heart fills less, this will reduce stroke volume and therefore CO
If heart rate drops this will cause a fall in CO
How do arterioles constrict and how does this affect BP?
Through contraction of smooth muscle cells in their walls - increases the resistance to the flow of blood making the pressure higher on their arterial side
How is blood pressure controlled in the short term?
Via the baroreceptor reflex - nerve endings that act as pressure sensors are present in the arterial wall in the aortic arch and the carotid sinus
How is blood pressure controlled in the long term?
Hormonal control - directed at controlling blood volume (acting at the kidney)
How is cardiac output controlled to meet demand?
The autonomic nervous system controls cardiac output - increased activity of the sympathetic nervous system increases release of noradrenaline and increases force of contraction by acting on ventricular myocytes
