Cardiovascular Anatomy Flashcards
Blood volume in the pulmonary circuit
9%
Blood volume in the systemic circuit
84%
Blood volume in the heart
7%
Describe the flow of blood through the body
Deoxygenated blood is pumped from the heart to the lungs via medium pressure pulmonary arteries
Blood is oxygenated
Oxygenated blood returns to the heart via medium pressure pulmonary veins
Heart pumps oxygenated blood to systemic tissues via high pressure systemic arteries
Oxygen is deposited into systemic tissues
Deoxygenated blood returns to the heart via low pressure systemic veins
Auricle
Ear like appendages on the side of each atrium increases capacity for holding blood
Atrium
Blood reservoir upstream of pump
Accumulates venous blood so that it can flow quickly into the atrium during filling phase
Ventricle
Blood reservoir downstream of pump
Accumulates blood from the atrium during filling phase so that it can increase in pressure and pump the blood out at a high enough pressure to overcome resistance in the arteries
Vena Cava
Inferior or superior
Drains deoxygenated blood from the systemic circuit back to the right atrium
Aorta
Largest artery in the body that receives blood being pumped from the left ventricle to the systemic circuit
Pulmonary artery
Artery in the pulmonary circulation that carries deoxygenated blood from the right ventricle to the lungs to be oxygenated
Pulmonary vein
Vein in the pulmonary circulation that carries oxygenated blood from the lungs to the left atrium to be pumped through the systemic circuit
Pulmonary trunk
A major vessel of the heart that originates from the right atrium and branches into the right and left pulmonary arteries
Anterior interventricular sulcus
A groove that separates the left and right ventricles on the anterior face of the heart
Slopes diagonally down to the right of the heart when viewed face on
Posteriot interventricular sulcus
A groove that separates the left and right ventricles on the posterior face of the heart
Goes directly down the middle of the heart when viewed face on
3 branches of the aortic arch
Brachiocephalic trunk
Left common carotid artery
Left subclavian artery
Brachiocephalic trunk
First branch of the aortic arch
Divides into the right common carotid artery and the right subclavian artery further down
Supplies blood to right arm, head and neck
Left common carotid artery
Supplies blood to head and neck
Left subclavian artery
Behind the left common carotid artery
Supplies blood to the left arm
Sagittal section
Separates left and right sides
Transverse section
Separates top and bottom
Frontal section
Coronal section
Separates front and back
Bicuspid valve
Mitral valve
Found between the left atrium and the left ventricle
Atrioventricular
2 cusps
Tricuspid valve
Found between the right atrium and the right ventricle
Atrioventricular
3 cusps
Atrioventricular valves
Mitral and tricuspid
Inlet valves
Constructed from fibrous connective tissue
Tethered by tendinous cords to stop blood from escaping during the filling phase
Semi-lunar valves
Pulmonary and aortic
Outlet valves
When blood pools in them it gives them strength to not allow the blood to move back into the ventricle where it came from
Pulmonary valve
Found between the right ventricle and the pulmonary artery
Aortic valve
Found between the left ventricle and the aorta
Relative thickness of the ventricle walls
Left ventricle : Right ventricle
3 : 1
Relative peak pressures of the ventricles
Left ventricle : Right ventricle
5 : 1
Peak pressure of the left ventricle
120 mmHg
Peak pressure of the right ventricle
27 mmHg
Describe the path of blood through the heart
Deoxygenated blood enters the right atrium through the inferior and superior vena cava
Dexoygenated blood pools in the right atrium until a pressure gradient is reached, when the tricuspid inlet valve opens to allow blood into the right ventricle
Deoxygenated blood pools in the right ventricle until a pressure gradient is reached, when the pulmonary outlet valve opens to allow blood to be pushed through the pulmonary arteries into the lungs
Oxygenated blood returns from the lungs via the pulmonary veins and enters the left atrium where it pools until a pressure gradient is reached
The mitral inlet valve opens allowing the blood to flow from the left atrium to the left ventricle
Oxygenated blood pools in the left ventricle until a pressure gradient is reached strong enough to open the aortic outlet valve and push the blood into the aorta to be distributed around the systemic circuit
The right border of the heart
Formed mainly by the right atrium
The inferior border of the heart
Formed mainly by the right ventricle
The left border of the heart
Formed mainly by the left ventricle
Orientation of the heart
Apex (bottom) points inferiorly, anteriorly and to the left
About 1/3 of the heart lies to the right of the midline of the body and about 2/3 to the left
Describe the pericardium
The pericardium is a double walled bag made up of the parietal and visceral pericardium with a pericardial space in between filled with serous fluid and encased in fibrous pericardium for protection
Pericardium layers are made of simple squamous epithelium
Describe the fibrous skeleton
Two complete fibrous rings surround the mitral and aortic valve
An incomplete fibrous ring surrounds the tricuspid valve
No fibrous ring surrounds the pulmonary valve
Fatty connective tissue is present in areas where the fibrous skeleton is incomplete
It has two functions: to support and maintain the structural integrity of the heart and to act as an electrical insulator
The pacemakers of the heart
The SA node and the AV node
The SA node
Sinoatrial node
Sits at the top of the right atrium
Conducts electrical impulse slowly at 0.5 m/s
Purpose is to induce atrial contraction
The AV node
Atrioventricular node
Sits in the middle of the two ventricles at the top in a gap in the fibrous skeleton
Conducts electrical impulse from the SA node at a very slow speed of 0.05 m/s to cause a delay of 100 msec between the SA and AV nodes
AV bundle
Atrioventricular bundle of His
Stalk of conduction fibres joining the AV node and connecting it to Purkinje fibres
Conducts electrical impulse from the AV node at a fast speed of 5 m/s
Results in systole and even ventricular contraction
Purkinje fibres
Electrical conduction fibres extending from the AV bundle of His to around the left and right ventricles to induce even contraction across the whole ventricle
Describe why the wall of the left ventricle is 3x thicker than the right
The left ventricle sustains 5x more pressure than the right ventricle because of the amount of resistance that needs to be overcome in the aorta to push blood out and the left ventricle has to pump blood all the way around the systemic circuit whereas the right ventricle just has to pump to the lungs
To strengthen the heart under this much pressure the wall is thicker and ensures more force of contraction
The 5 phases of the cardiac cycle
Ventricular filling Atrial contraction Isovolumetric contraction Ventricular ejection Isovolumetric ventricular relaxation
Ventricular filling
Pressure in the ventricle drops below the pressure in the atrium
Mitral valve opens, blood enters the ventricle down the pressure gradient
Ventricle fills to about 80% capacity during this phase
Atrial contraction
Left atrium contracts to complete ventricular filling
Small rise in atrial pressure
Isovolumetric contraction
No change in volume of blood in the ventricle
Systole
Ventricle begins to contract, lifting the blood back towards the atrium and closing the mitral valve
Ventricular pressure is still below aortic pressure so the aortic valve remains closed
Ventricular ejection
Systole continuation
Ventricular pressure has reached a peak where it is now higher than the pressure in the aorta, setting up a pressure gradient where blood can flow from high to low and allowing the aortic valve to open
Blood is ejected into the aorta so fast that pressure continues to rise in both the ventricle and aorta but both decrease after a certain point
Isovolumetric ventricular relaxation
No change in volume of blood in the ventricle
Relaxation - diastole
Ventricular pressure drops, reversing flow in the aorta due to the changed pressure gradient and causing the aortic valve to close, preventing blood from reentering the ventricle
The mitral valve also remains closed because the ventricular pressure is still higher than atrial pressure
Describe why the rise in pressure during atrial contraction is small
The atrial muscle layer is thin so can’t withstand too high a pressure
There are no valves between the left atrium and the pulmonary veins and so there is nothing to prevent backflow of blood into the pulmonary veins which might occur if the pressure gets too high
Describe why ventricular pressure continues to increase past isovolumetric contraction
The pressure is so high in the ventricle that the speed that is ejects blood into the aorta is faster than it can run-off into the distributing arteries
Because the ventricle is still contracting, it increases in pressure as the resistance of the aorta and other distributing arteries prevents free blood flow
When the rate of ejection falls below the rate of run-off, both aortic and ventricular pressure drops
Describe the heart sounds
The first heart sound (lub) is caused by the turbulence of blood trying to flow back into the atrium where the pressure is lower and hitting the now closed mitral valve flaps
The second heart sound (dub) is caused by the turbulence of blood trying to flow back into the ventricle from the aorta when ventricular pressure drops and hitting the now closed aortic valve
Describe why semilunar valves are not attached to chordae tendinae
Chordae tendinae are fibres attached to the mitral and tricuspid valves that hold the valves shut to prevent backflow from the ventricles to the atria
The cusps of the semi-lunar valves are designed to allow blood to pool. When blood tries to backflow from the atria back to the pulmonary circuit, it collects in these cusps like water in a pocket, strengthening the valve. Semi-lunar valves don’t need chordae tendinae to keep them shut as they are designed to do it naturally
Describe aortic pressure throughout the cardiac cycle (left)
During ventricular filling, aortic pressure starts at about 100 mmHg and slowly decreases
By the time isovolumetric relaxation is complete, the aortic pressure is at 80 mmHg
The aortic pressure has now dropped below the ventricular pressure but rises with it during ventricular ejection. It reaches just under 120 mmHg (the peak pressure of the left ventricle) and falls with it
When the pressure of the ventricle drops below the pressure of the aorta again (about 100 mmHg) isovolumetric relaxation starts
During isovolumetric relaxation the aortic pressure increases slightly (to about 105 mmHg)
Aortic pressure then slowly decreases again through ventricular filling, atrial contraction and isovolumetric contraction
Describe ventricular pressure throughout the cardiac cycle (left)
During ventricular filling, the pressure of the ventricle is lower than the left atrial pressure (less than 4 mmHg)
The ventricular pressure rises very slightly during atrial contraction but is still less than the atrial pressure
Ventricular pressure increases rapidly, overtaking the atrial pressure and starting isovolumetric contraction. It continues to rise rapidly during isovolumetric contraction until it surpasses the aortic pressure (around 80 mmHg) and continues to rise steeply until about halfway through the ventricular ejection phase until it reaches its peak of 120 mmHg
Ventricular pressure falls quickly after reaching its peak, falling below aortic pressure at the beginning of isovolumetric relaxation (about 100 mmHg) and falling below the atrial pressure at the end of isovolumetric relaxation (around 5 mmHg)
Describe atrial pressure throughout the cardiac cycle (left)
Atrial pressure in the ventricular filling stage is just above the ventricular pressure in order to keep the mitral valve open - around 4 mmHg
During atrial contraction, the pressure rises very slightly to about 5 mmHg and then drops again as isovolumetric contraction starts and the ventricular pressure rises
Atrial pressure is at its lowest during the start of ventricular ejection but begins to rise during this stage as blood returns from the lungs and begins to pool in the atria again
By the end of isovolumetric relaxation, atrial pressure is at its peak (around 5 mmHg) and surpasses the dropping ventricular pressure as ventricular filling starts again
Describe the valves that open and close during diastole and systole (left)
The mitral valve is open during ventricular filling and atrial contraction as the pressure of the atria is above the pressure of the ventricle allowing blood to flow down the pressure gradient to collect in the ventricle
The mitral valve closes at the start of isovolumetric contraction to increase the pressure in the ventricle and stays closed through ventricular ejection (to prevent backflow into the atrium) and isovolumetric relaxation (to prevent blood from entrering from the atrium prematurely)
The mitral valve opens again at the start of ventricular filling when the atrial pressure surpasses the ventricular pressure
The aortic valve is closed during ventricular filling because the ventricular pressure is lower than the aortic pressure. It doesn’t open until the end of isovolumetric contraction when the ventricular pressure surpasses the aortic pressure.
The aortic valve stays open throughout ventricular ejection to allow all the blood in the ventricle into the systemic circuit. It closes again at the start of isovolumetric relaxation when the ventricular pressure drops below aortic pressure to stop backflow of blood into the ventricle from the aorta.
Elastic artery
Very large arteries near the heart which have elastic walls
Expand during systole to store blood leaving the ventricle
During diastole, push the blood out of the arterial tree by elastic recoil
Smooth the pulsatile flow of blood leaving the ventricle
Many thin sheets of elastin in the middle tunic
Muscular artery
Distribute blood around the body at high pressure and lungs at medium pressure
Rate of blood flow is adjusted by vasoconstriction and vasodilation
Small change in radius has large effect on flow rate
Many layers of circular smooth muscle wrapped around the vessel in the middle tunic
Arteriole
Controls blood flow to capillary beds
Thicker muscular wall relative to their size than any other blood vessel
Greatest pressure drop and greatest flow resistance occurs here
Between one and three layers of circular smooth muscle wrapped around the vessel in the middle tunic
Capillary
Tiny, thin walled vessels that allow gas, nutrient and waste exchange between blood and surrounding tissue fluid
Slow blood flow
Leaky vessels allowing plasma to escape
Just wide enough to admit one red blood cell at a time
Single layer of endothelium with an external basement membrane. No smooth muscle, therefore no ability to vasoconstrict, no connective tissue
Venule
Low pressure vessels that drain capillary beds
Site of extravasation of leukocytes
Small venules have usual epithelium plus some connective tissue
Larger venules also have some smooth muscle
Vein
Thin walled, low pressure vessels that drain blood back to the atria
Thin, soft and compliant walls
Small change in venous blood pressure causes a large change in venous volume
Act as blood reservoirs
Less muscle and connective tissue than arteries but otherwise similar
Larger veins have valves which prevent backflow
Coronary artery
Arising from the aorta downstream of the aortic valve
Supply the myocardium
Small muscular arteries
Describe what the degree of constriction in arterioles throughout the body determines
Total peripheral resistance
Mean arterial blood pressure
Blood volume found in systemic veins and venules
64%
Blood volume found in systemic arteries and arterioles
13%
Anastomoses
Artery - artery junctions
Cardiac veins
Drain deoxgenated blood away from myocardium to the right atrium
Peak pressure in the right atrium
1 - 2 mmHg
Peak pressure in the left atrium
5 mmHg
Peak pressure in the pulmonary trunk
8 mmHg
Dilated cardiomyopathy
Cause often unable to be identified
Viral infection in many cases
Infected muscle fibres attacked by lymphocytes, killing some and leaving others damaged and slow to contract
Left ventricle most affected because of high pressure
Left ventricle dilates, chamber enlarges, wall thickness can also increase
Fibrous ring surrounding mitral valve stretches
Mitral valve flaps now too far apart to meet during systole causing mitral regurgitation
Mitral regurgitation
Leaky mitral valve allows backflow of blood from ventricle to atrium
3 causes of mitral regurgitation
Endocarditis
Rheumatic fever
Damaged tissue
Describe how mitral regurgitation can cause breathlessness
When the mitral valve doesn’t fully close, blood leaks back from the ventricle into the atrium
Blood can then backflow from the atrium into the pulmonary veins leading to the lungs
Blood in the lungs increases pulmonary pressure causing the blood to be pushed into interstitial tissue
Lungs become wet and damp and the surface area of alveoli decreases
Less gas exchange takes place so rate of breathing goes up to maintain oxygen levels
