Layers of arteries
(Outermost to innermost)
- tunica externa: tough layer of connective tissue
- tunica media: muscle layer (smooth muscle) and elastic fibres made of protein elastin
- tunica intima: endothelium layer forming the lining of the artery
Structure of capillaries (walls)
- walls of capillaries consist of a single layer of epithelial cells created by a filter like protein gel (lamina) with pores
- walls of capillaries allow it to be semi-permeable
- basement membrane is semi-permeable to many substances
- one cell thick, allows for diffusion
- low pressure, blood travels slowly so there is more opportunity for exchange
Veins structure
- large lumen, low bp
- walls are thinner and less elastic compared to arteries
- contain valves which move blood through during low bp
- contain skeletal muscles which squeeze vein and pushes blood in one direction
William Harvey determined that:
- blood flow is unidirectional (valves prevent backflow)
- blood is recycled as flow rate of blood is too high to be consumed
Pulmonary circulation means:
To/from the lungs
Systemic circulation means:
To/from the body (other than the heart)
Parts of the heart
- atrium: receives blood from body/lungs
- ventricle: receives blood from the atrium, pumps it out of the heart through arteries
- AV (atrioventricular) valve: btwn atria and ventricles
- semi-lunar valve: btwn ventricles and atria
- pulmonary artery: carries unoxygenated blood from the heart to the lungs
- pulmonary vein: carries oxygenated blood from the lungs back to the heart
- coronary arteries: arteries which wrap around the heart to supply oxygenated blood to the heart muscle
- vena cava (superior and inferior) carries blood from the body to the heart
SA node
- located near the right atrium
- known as the pacemaker
- initiates the heartbeat
- made of a group of specialized muscle cells
- myogenic: initiates own contractions w/o neurons
Steps of a cardiac cycle
- SA node initiates a heartbeat, sends a signal
- this results in atria systole
- blood travels through the AV valve to the ventricles
- SA node signal sent to the AV node
- AV node sends a signal delayed by 0.1s through the bundle of his to the purkinje fibres
- ventricles undergo systole, AV valves snap shut, blood leaves the ventricles, enter atrium or leaves the heart
- semilunar valves close
- ventricles relax, AV valves open and blood fills the ventricles
- all four chambers are in diastole
- when atria filled and ventricles are 70% filled, cycle is complete
What controls heart rate?
Heart rate is controlled by
- the automatic nervous system: 2 nerves originating from the cardiovascular centre in the medulla —> send signals to the SA node
- cardiovascular centre in the medulla receives input from the receptors, monitor BP, blood pH [CO2] and [O2]
- adrenaline: when in bloodstream causes rapid inc. in heart rate in prep. for physical activity or flight-or-fight response: adrenaline produced by adrenal glands, controlled by the brain
