Notes on the heart

These are notes on the heart following the AQA spec.

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Heart consists of 4 chambers
o Right atrium (RA)
o Right ventricle (RV)
o Left atrium (LA)
o Left ventricle (LV)
Blood flow
o Right atrium receives blood from
Superior vena cava (SVC) - carries blood from upper body (head, arms)
Inferior vena cava (IVC) - carries blood from lower body (chest, abdomen, legs)
o Blood flows from right atrium, across tricuspid valve, into right ventricle
o 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
o Blood from pulmonary vein enters left atrium
o Blood flows from left atrium, across mitral valve, into left ventricle
o Left ventricle has a thick muscular wall / generates high pressures during contraction
o Blood from LV is ejected, across aortic valve, into aorta
Muscle of left ventricle is thicker than right ventricle
o Pressure in aorta is higher than pulmonary artery
o Left ventricle must generate more pressure to overcome pressure of aorta
o Therefore, thicker muscle required in left ventricle
Tricuspid and mitral valves are atrioventricular (AV) valves
o Have fibrous strands (cordae tendinae) that attach to papillary muscles
o Papillary muscles contract during ventricular contraction
o 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

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Diastole: period of relaxation by heart muscle
Atrial systole
o Both atria contract and move blood across AV valves into ventricles
o 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
o Contraction of ventricles increases pressure
o AV valves close as blood is forced against them 1st heart sound
o This prevents backflow into atria
o Instead, blood is ejected into…read more

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Fibres that branch out to distant ventricles are called Purkinje Fibers
o Cause contraction of ventricles
Pressure Changes
Isovolumetric contraction
o Ventricles start to contract
o Intraventricular pressure rises and causes AV valves to close
o Ventricles are no longer filled with blood and volume says the same
o Pressure is not high enough to open semilunar valves
Pressure in LV > aorta
o Semilunar valves open
o Ventricular volume decreases
o Blood is ejected into aorta
Pressure in LV < aorta
o Back pressure…read more

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Muscular arteries branch into smaller arterioles (smallest arteries)
o Arterioles regulate blood flow into tissue capillaries
Made up of 3 layers:
o Tunica intima (innermost layer)
Simple squamous epithelium
Surrounded by a connective tissue basement membrane with elastic fibres
o Tunica media (middle layer)
Smooth muscle and usually thickest layer
Changes vessel diameter to regulate blood flow and BP
o 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…read more

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Enters through the vena cava into the right atrium
It's then pumped through a valve into the right ventricle chamber
And then up through the pulmonary valve into the pulmonary artery towards the lungs
Oxygenated blood
Enters through the pulmonary veins into the left atrium
It's then pumped through a valve into the left ventricle
And then through the aortic valve and out of the aorta to the rest of the body
Atrial Systole
Sinoatrial node contracts and transmits electrical impulses throughout atria.…read more

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Ventricular Systole
Electrical impulse passes to ventricles via atrioventricular node, bundle of His and Purkinje fibres.
Fibres do not contract, but pass impulse to base of ventricles.
Ventricle contract shortly after atria, squeezing blood upwards into arteries
Atria and ventricles relax > atria filll with blood
Cardiac output: blood flow at a given time
Cardiac output = heart rate x stroke volume
At rest ­ approx. 5500
Exercise ­ approx.…read more


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