Superior vena cava (SVC) - carries blood from upper body (head, arms)
Inferior vena cava (IVC) - carries blood from lower body (chest, abdomen, legs)
Blood flows from right atrium, across tricuspid valve, into right ventricle
Blood leaves right ventricle and enters pulmonary artery
Backflow into RV prevented by semilunar pulmonic valve
Deoxygenated blood arrives at lungs via pulmonary artery
Oxygenated blood leaves lungs via pulmonary vein
Blood from pulmonary vein enters left atrium
Blood flows from left atrium, across mitral valve, into left ventricle
Left ventricle has a thick muscular wall / generates high pressures during contraction
Blood from LV is ejected, across aortic valve, into aorta
Muscle of left ventricle is thicker than right ventricle
Pressure in aorta is higher than pulmonary artery
Left ventricle must generate more pressure to overcome pressure of aorta
Therefore, thicker musclerequired in left ventricle
Tricuspid and mitral valves are atrioventricular (AV) valves
Have fibrous strands (cordae tendinae) that attach to papillary muscles
Papillary muscles contract during ventricular contraction
Generate tension on valve via cordae tendinae to prevent AV valves from flapping back into atria
Semilunar valves (pulmonic and aortic) do not have these attachments
Cardiac Cycle
Atria receive blood from veins and store it prior to each heart beat
Systole: period of contraction by heart muscle
Diastole: period of relaxation by heart muscle
Atrial systole
Both atria contract and move blood across AV valves into ventricles
This reduces volume of atria but increases pressure
Pressure of RA > RV - forces tricuspid valve to open
Pressure of LA > LV - forces mitral valve to open
Ventricular systole
Contraction of ventricles increases pressure
AV valves close as blood is forced against them → 1st heart sound
This prevents backflow into atria
Instead, blood is ejected into arteries through aortic and pulmonary valves
Ventricular diastole
End of cardiac cycle, all chambers relax
Aortic and pulmonary valves close → 2nd heart sound
This prevents backflow into ventricles
Atria fill up again to start next cycle
Volume increases while pressure decreases
Electrical Activity
Heart has unique ability to beat (contract) on its own
Assisted by nerves and hormones in blood but can function without them
Sinoatrial (SA) node
Located at the top right atrium
Also known as the "natural pacemaker" controlling heart rate
Increases with physical activity and decreases when relaxing
Sends impulses across the atria to the AV node
Cause contraction of atria
Atrioventricular (AV) node
Located between atrium and ventricle
Ventricles are isolated from atria
Impulse must pass through AV node to travel across ventricles
AV node is connected to the Bundle of His
Branches into a right bundle (to right ventricle) and left bundle (to left ventricle)
Fibres that branch out to distant ventricles are called Purkinje Fibers
Cause contraction of ventricles
Pressure Changes
Isovolumetric contraction
Ventricles start to contract
Intraventricular pressure rises and causes AV valves to close
Ventricles are no longer filled with blood and volume says the same
Pressure is not high enough to open semilunar valves
Pressure in LV > aorta
Semilunar valves open
Ventricular volume decreases
Blood is ejected into aorta
Pressure in LV < aorta
Back pressure causes blood to move back and semilunar valves to shut
Isovolumetric relaxation
AV and semilunar valves are closed
Lasts until pressure in atria > ventricles
Pressure atria > ventricles
Ventricles are filled
Atrial contraction/systole - final amount of blood is emptied into ventricles immediately prior to next phase of isovolumetric contraction of ventricles^
Blood vessels
Arteries
Pulmonary artery
Transports deoxygenated blood from right ventricle into lungs
Systemic arteries
Transport oxygenated blood from left ventricle to body tissues
Carry ≈10% of total blood volume
Blood is pumped from left ventricle into large elastic arteries
Elastic arteries become smaller muscular arteries
Muscular arteries branch into smaller arterioles (smallest arteries)
Arterioles regulate blood flow into tissue capillaries
Made up of 3 layers:
Tunica intima (innermost layer)
Simple squamous epithelium
Surrounded by a connective tissue basement membrane with elastic fibres
Tunica media (middle layer)
Smooth muscle and usually thickest layer
Changes vessel diameter to regulate blood flow and BP
Tunica adventitia (outermost layer)
Attaches vessel to surrounding tissue
Connective tissue with varying amounts of elastic and collagenous fibers
Compared to veins, arteries have a relatively small lumen
Veins
Pulmonary veins
Transport oxygenated blood from lungs to left atrium
Systemic veins
Transport deoxygenated blood towards the heart
Carry ≈70% of total blood volume
After blood has passed through the capillaries, it runs into venules (smallest veins)
Become progressively larger until they reach the right atrium
Medium and large veins have valvesthat prevent backflow of blood due togravity
Made up of same 3 layers as arteries
BUTless smooth muscle and connective tissue
Makes walls of veins thinner with less pressure → larger lumen
Hold more blood than arteries
Latest Comments
34590 wrote on Tue, 15 Jun 2010 09:45:
Love it. but will there be any australian unit 1-4 bioloy test?? it will be sooo good！~
hamda wrote on Mon, 14 Jun 2010 14:14:
please explain what are systole and diastole?
hamda wrote on Tue, 16 Mar 2010 12:50:
it is the best heart explanation but can you do a diagram without animation of the heart but label it throughly!!!
Simon wrote on Fri, 20 Mar 2009 23:55:
I am not sure whether I understand your question but I just assume you are wondering how the impulse is generated within the SA node.
The SA node in the right atrium depolarises spontaneously as all cardiac cells have an unstable resting potential. What happens is that slow calcium channels on the cell membrane allow calcium to enter the cell. This activates more calcium channels which are found on SR tubules - a structure found within the cardiac cell. The high levels of calcium causes the depolarisation of the cardiac cell and this generates the impulse which is spreading from the SA node.
Changed by admin on Fri, 20 Mar 2009 23:56
Unknown User wrote on Fri, 20 Mar 2009 09:12:
Where from the impulse come in the sino-atrial node ?
Latest Comments
34590 wrote on Tue, 15 Jun 2010 09:45:
Love it. but will there be any australian unit 1-4 bioloy test?? it will be sooo good！~
hamda wrote on Mon, 14 Jun 2010 14:14:
please explain what are systole and diastole?
hamda wrote on Tue, 16 Mar 2010 12:50:
it is the best heart explanation but can you do a diagram without animation of the heart but label it throughly!!!
Simon wrote on Fri, 20 Mar 2009 23:55:
I am not sure whether I understand your question but I just assume you are wondering how the impulse is generated within the SA node.
The SA node in the right atrium depolarises spontaneously as all cardiac cells have an unstable resting potential. What happens is that slow calcium channels on the cell membrane allow calcium to enter the cell. This activates more calcium channels which are found on SR tubules - a structure found within the cardiac cell. The high levels of calcium causes the depolarisation of the cardiac cell and this generates the impulse which is spreading from the SA node.
Changed by admin on Fri, 20 Mar 2009 23:56
Unknown User wrote on Fri, 20 Mar 2009 09:12:
Where from the impulse come in the sino-atrial node ?
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