What did William Harvey discover
- that blood flow is unidirectional
- that blood is recycled
- that the heart pumps blood out via arteries and in via veins
- also hypothesised that capillaries connect arteries and veins, but couldn’t prove it (lack of technology)
human circulatory system
- the heart pumps blood around the body in two separate circulatory systems
systematic circulation - LV —> body —> RA
- delivers oxygenated blood to tissues and returns deoxygenated blood to the heart
- blood is at high pressure to reach all cells
pulmonary circulation
- RV —> lungs —> LA
- drivers deoxygenated blood to the lungs and returns oxygenated blood to the heart
- blood is at low pressure as to not damage the lungs
composition of arteries
tunica externa
- tough protective outer layer made of collagen fibres
tunica media
- thick middle layer made of muscle cells and elastic fibres
tunica intima
- smooth inner lining made of a single layer of endothelial cells
how do structure of arteries help maintain blood pressure
muscle cells:
- helps with propulsion of blood to maintain blood pressure
elastic fibres:
- artery wall stretches when pressure is at its highest and when it returns to normal there is elastic recoil which propels blood forward
capillaries
- blood flows through tissues in capillaries
- capillaries have permeable walls to allow for material exchange b/w cells in tissue and blood in capillaries
- blood flows slowly and at low pressure to allow maximum time for material exchange
structure:
- capillary walls have pores to allow for exchange of larger molecules
- capillaries have a diameter of 10 micrometers, which is similar to an RBC meaning that they come in contact with capillary walls and allows for maximum exchange of oxygen
- capillary walls are only 1 cell thick which reduces the distance over which diffusion occurs
Veins
- collect blood at low pressure and return it to the atria of the heart ( low pressure due to collection from capillaries)
- have similar tunica externa to arteries
- have much thinner tunica media
- have wide lumen to optimise blood flow
- have valves to prevent back flow of blood (from low pressure)
- when skeletal muscles contract the veins are squeezed which propels blood towards the heart
Identification of blood vessels as arteries, capillaries or veins
the cardiac cycle
- blood flows into the atria
- as atria fills with blood the atrioventricular valves open to allow blood flow into ventricles
- atria contracts
- this pushes more blood into the ventricles
- atria relaxes
- ventricles start to contract
- the atrioventricular valves close to prevent back flow of blood into atria
- as ventricles continue to contract semi lunar valves open
- blood goes out of the ventricles into the aorta and pulmonary artery
- ventricles relax
- semi lunar valves close to prevent back flow of blood into the ventricles
- blood fills the atria
diagram of heart
cardiac cycle diagram
what causes lub sound
- when the atrioventricular valves close
- heard at the beginning of ventricular contraction
what causes dub sound
- when the semilunar valves close
- occurs during end of ventricular contraction
when is there no heart sound
- when the atria are filling with blood and heart is relaxed
what is diastole and systole
diastole is relaxation of muscle
systole is contraction of muscle
What happens during atrial and ventricular diastole
- The pressure in the LA is just higher than in the LV which keeps the
AV valve open so blood can flow from
the LA to the LV - the pressure in the aorta is much higher than in the LV so the semi-lunar valve is shut to prevent back flow of blood from the aorta to LV
What happens during atrial systole
- the pressure in the LA increases slightly as the atrium walls contract which forces more blood into LV (AT open)
- pressure in LV is still lower than in the aorta so semilunar valve remains closed
what happens during early ventricular systole
- when the LV begins to contact the pressure in LV increase above pressure in LA which cause left AV to close to prevent back flow of blood into atrium
- pressure in LV is still lower than that in the aorta so left semilunar valve remains closed
what happens during late ventricular systole
- pressure in the LV is much higher than in LA so left AV valve remains closed
- pressure in the LV increases greatly as the ventricle contracts & when it rises above pressure if the aorta the left semilunar valve opens and blood flows into the aorta
what is the heartbeat initiated by and what does it do
- specialised muscle cells in the right atrium called the sinoatrial node
- the SAN sends out an electrical signal at regular intervals to control and coordinate the heart beat
- it acts as a pacemaker
what does myogenic mean
it means that it spontaneously contracts without nervous stimulation
how is the myogenic activity controlled and to what function
- the SAN sends out an electrical signal which spreads across the walls of the atria to ensure they contract first
- the AVN delays the electrical excitation before sending it to the bottom of the ventricles to ensure they contract from the bottom up and only after the atria have contracted
how can heart rate increase or decrease via nervous control
how can heart rate increase or decrease via hormonal control
what are coronary arteries and what is their role
- coronary arteries are major blood vessels that branch off the aorta and supply the heart muscle with blood and thus oxygen and nutrients
