Cardiovascular system: The Heart Flashcards
What are the functions of the cardiovascular system (blood and heart)?
> Rapid transport of oxygen and nutrients (nutrients being glucose, amino acids, and fatty acids).
> Removal of waste products such as carbon dioxide, urea and creatinine (produced from metabolism in the muscles).
> Transport of hormones through the blood to their target organs.
> Secretion of hormones from the heart (like ANP is being secreted from the atria of the heart when there is a high volume of blood that enters the heart).
> Temperature regulation (vasodilation and vasoconstriction of surface capillaries during thermoregulation).
Where is the heart located in the body?
The heart is located in the thorax center but most of the heart situated to the left of the body.
What is the pericardium? What is its function?
The pericardium is a sac containing fluid that surrounds the heart.
Its function is that it fixes the heart in place in the thorax cavity; it prevents it from moving. It can do this because the sac is attached to the diaphragm, the sternum and other structures.
Another function is that it prevents the heart from overfilling. This is because the outer layer of the sac (fibrous pericardium) is strong and inextensible. It creates limit to the size at which the heart can expand to (prevents bursting?).
Another function of the sac is that it provides lubrication (due to the fluid in the sac) that prevents the friction generated with each pump of the heart.
Another function is that it prevents the heart from infection from the rest of the body (as there is a barrier between the heart and the other organs).
Give a description of the layers in the pericardium.
The pericardium (pericardial sac) is made of two layers: the fibrous pericardium and the serous pericardium.
The serous pericardium can be further subdivided into two layers- the outer parietal layer and inner visceral layer.
The inner visceral layer is actually referring to the epicardium, which is the outer layer of the heart. The outer parietal layer is the layer of cells that lines the inner portion of pericardial sac; it is also made of a meshwork of collagen fibres that restrains the heart. There is a space between the inner visceral layer (epicardium) and outer parietal layer which is called the pericardium cavity; it is the pericardium cavity that is filled with a fluid.
Also note that the inner visceral layer and outer parietal layer are epithelial layers, both consisting of epithelial cells called mesothelium.
The serous pericardium is contained by the next layer: the fibrous pericardium. The fibrous pericardium is made of tough connective tissue that prevents over-expansion of the heart from over filling of the heart. It is made of collagen and elastin fibers.
State the different vessels of the heart and where it carries blood to.
Superior vena cava- Carries deoxygenated blood form upper portion of the body to the heart.
Inferior vena cava- Carries deoxygenated blood from the lower portion of the body to the heart.
Pulmonary artery- Carris deoxygenated blood from the heart to the lungs (after leaving the heart, this pulmonary artery subdivides into the left pulmonary artery (carries blood to left lung) and right pulmonary artery (carries blood to right lung)).
Pulmonary veins- Carries oxygenated blood from the lungs to the heart.
Aorta- Carries oxygenated blood all around the body.
Note that the pulmonary artery and aorta are the vessels that comes out of the ventricles (and are mostly situated in the middle at the top of the heart). Veins are situated near the side of the heart at the top and are connected to the atria.
What are the different layers of the heart?
The most outer layer of the heart is called the epicardium. The epicardium is a layer of exposed mesothelium cells. This epicardium layer can also be referred to as the inner visceral layer of the serous pericardium (pericardial sac).
The next inner layer is called the myocardium. The myocardium is the muscular walls of the heart. It contains cardiac muscle tissue, blood vessels and nerves.
The innermost layer is called the endocardium. The endocardium is a layer of simple squamous epithelium that lines internal spaces of the heart (like the chambers) and it covers the valves.
How is the left and right atria separated from each other? How is the left and right ventricles separated from each other?
The left and right atria is separated by a layer of muscle that lies in the middle called the interracial septum.
The ventricles are also separated via a wall of muscle called the interventricular septum.
What are the different valves in the heart?
Tricuspid valve (or right atrioventricular valve)- A valve between right atria and right ventricle.
Bicuspid valve (or left atrioventricular valve)- A valve between left atria and left ventricle.
Pulmonary semilunar valve- prevents backflow of blood between pulmonary artery and right ventricle.
Aortic semilunar valve- prevents backflow of blood between aorta and left ventricle.
What are the function of valves in the heart?
Valves function in ensuring there is no backflow of blood- it ensures blood flows in one direction.
A backflow of blood would prevent blood from sufficiently reaching areas of the body.
What are chordae tendineae?
Chordae tendineae are fibrous connective tissues that connects the atrioventricular valves to the papillary muscles on the floor of their respective ventricles.
The structure of the chordae tendineae prevents the valves from prolapsing or naturally bulging into the atria (if the valve structures did protrude into the atria, it would prevent blood flowing from the atria to the ventricles).
What is the difference between the pulmonary circuit and systemic circuit? What vessels are in each circuit?
The pulmonary circuit is the circuit in which blood is pumped from the heart to the lungs, which then comes back round to the heart again. The vessels involved in the pulmonary circuit includes the pulmonary artery and pulmonary vein.
The systemic circuit is the circuit in which blood is pumped from the heart to the rest of the body, eventually coming back round to the heart. The vessels involved in this circuit are the superior vena cava, inferior vena cava and aorta.
What side of the heart holds and pumps deoxygenated blood?
The right side of the heart holds and pumps deoxygenated blood.
Deoxygenated blood from the body enters the heart (through vena cava) via the right atria. The same deoxygenated blood travels through the right ventricle and is pumped to the lungs via the pulmonary artery.
What side of the heart pumps and holds oxygenated blood?
The left side of the heart holds and pumps oxygenated blood.
Oxygenated blood from the lungs enters the left atria via the pulmonary vein. The same oxygenated blood travels into the left ventricle and is pumped all around the body via the aorta.
What two types of cells in the heart function in specifically helping the heart beat?
Mechanical cells which contracts to force the blood to move through the chambers. These cells are also striated. These cardiac myocytes (heart muscle cells) can be joined together by intercalated disks which consist of gap junctions and desmosomes. 99% of these cells are contractile while 1% is autorhythmic.
Electrical cells that generate and conduct electrical signals, which causes the mechanical cells to contract.
Where are the electrical cells found in the heart?
Electrical cells are found in 4 main regions around the heart that is essential to the beating of the heart.
The first group of electrical cells is called the Sinoatrial node and is found at the top of the right atria. The SA node is responsible for initiating a stimulus via depolarization.
The second group of electrical cells are found near the junction between the right aria and right ventricles, and is called the atrioventricular node.
The third group of electrical cells is called the Bundle of His and is found in the inperiventricular septum.
The last group of electrical cells is situated all around the walls of the right and left ventricles. They are called Purkinje fibres.
Why are electrical cells in the AV node described as ‘autorhythmic’?
Cells in the AV node are described as autorhythmic because they can generate an action potential (i.e depolarize) without the need of an external stimulus.
So each single heartbeat is initiated by the depolarization of electrical cells in the SA node.
Describe the steps of generation and conduction of electrical impulses through the heart during a heartbeat.
An ACTION POTENTIAL is INITIATED in the SA node via the depolarization of cells in that region. This action potential causes the atria to contract.
The electrical impulses generated travels to the AV node via the internodal pathways; the internodal pathways are systems of conducting fibres that run through the walls of the atria. These electrical impulses also travels to the left atrium via the interatrial pathways.
The electrical cells at the AV node conducts the impulse once it arrives. It is important to know that the AV node acts as a DELAYING device, because it shoots its action potentials less rapidly than any other electrical region in the heart- this is known as AV NODAL DELAY. This is purposely done so the atria contracts before the ventricles contracts; it prevents them from contracting simultaneously because if they do, the blood will not sufficiently move between the chambers.
Even though the AV node fires action potentials less frequently, it does fire action potentials to the Bundle of His.
The Bundle of His is a CONDUCTING BUNDLE; it conducts the impulse from the AV node. This impulse travels through the Bundle of His for a short distance before it branches into the left and right bundle branches and reaches the apex of the heart.
These 2 bundles of nerve fibres extends throughout the myocardium walls of the ventricles up to the valves. These nerve fibre extensions are known as the Purkinje fibres. When the impulse spreads through the ventricles, ventricular contraction initiates.
What does each cycle (each heartbeat) start with?
Depolarization at the SA node; atrial contraction.
Link the transmission of electrical impulses to the contraction of different chambers in the heart.
The depolarization of electrical cells at the SA node leads to atrial contraction. The atrial contraction forces blood out of the atria into the ventricles. The atrio-ventricular valves are also forced open to allow blood to flow from atria to ventricles.
When the nerve impulses reaches the AV node, there is a short delay in nerve transmission to the Bundle of His. This delay ensures the atria has finished contracting to fill the ventricles properly with blood, and so that the ventricles and atria do not contract simultaneously.
The nerve transmission reaches the Bundle of His, then travels to the Purkinje fibres that lies in the ventricular walls. Depolarization of cells in the ventricles forces the ventricles to contract, which forces blood out of the ventricles into the arteries. It is important to know that with ventricular contraction, the atrio-ventricular valves are forced shut (to prevent backflow of blood) and semi-lunar valves are forced open (to allow blood to move from ventricles to arteries).
What are the 4 stages of the cardiac cycle?
NOTE: The terms ‘systole’ and ‘diastole’ is usually used in reference to the ventricles. Even though the atria both undergo systole and diastole, these two general terms are used to show ventricular activity to show the cardiac cycle (if we want to refer to the atria, we say atrial systole or atrial diastole).
Phase 1: Mid to late diastole.
Phase 2: Systole; isovolumetric contraction.
Phase 3: Systole; ventricular ejection.
Phase 4: Isovolumetric relaxation.
What occurs in Phase 1 of the cardiac cycle?
This stage is mid to late diastole.
In mid diastole, both the atria and ventricles are relaxed. Blood is able to enter the atria from the veins because the pressure in the veins are greater than the pressure in the atria. Blood is able to flow into the atria, through the AV valves and into the ventricles, all under the pressure of the normal flow of blood. The blood cannot go any further than the ventricles because the semi-lunar valves are shut (as the pressure in the ventricles is less than the pressure in the arteries).
Note that 70% of blood in the atria passively flows into the ventricles during mid diastole.
In late diastole, enough blood has entered the atria and the atria contracts to force the remaining 30% of blood into the ventricles.
After this step, the atria relaxes (atrial diastole).
What happens in Phase 2 of the cardiac cycle?
Phase 2 of the cardiac cycle is systole or isovolumetric contraction.
This phase is when the ventricles starts to contract. When the ventricles contract, there is a reduce in volume but the same amount of blood, which ultimately causes an increase in pressure in the ventricles. When the ventricular pressure exceeds atrial pressure, the AV valves closes.
It is also important to know that the semilunar valves are still shut; even though there was an increase in ventricular pressure, this pressure is yet to exceed the pressure in the arteries, causing the semi-lunar valves to remain shut.
So, if the semi-lunar valves REMAINS SHUT and the AV valves have JUST SHUT, the ventricles becomes a closed chamber with a fixed volume of blood. As it is now a closed chamber (unlike before), the pressure now increases rapidly in the ventricles to around 80 mm Hg.
What occurs in Phase 3 of the cardiac cycle?
Phase 3 is still systole of the ventricles, but is referred to as ventricular ejection.
In this phase, the pressure in the ventricles in still increasing from Phase 2. When the pressure of the ventricles actually exceeds 80 mmHg, that means it has exceeded aortic pressure. This forces the semi-lunar valves, allowing blood to be pumped out of the ventricles into the arteries.
This phase is the stage where the ventricles reaches its highest or peak pressure.
What happens in Phase 4 of the cardiac cycle?
Phase 4 of the cardiac cycle is known as isovolumetric relaxation (early diastole).
When blood is pumped out of the ventricles, there is a decrease in the ventricular pressure and an increase in aortic pressure. When the ventricular pressure falls below aortic pressure, the semi-lunar valves close. At this point, ventricular ejection and ventricular systole has ended, and now ventricular diastole begins.
The ventricles are in a short period of relaxation.
After the aortic valves have closed, the aortic pressure also falls slowly, approaching 80 mmHg, ready for the next cycle.
What is stroke volume?
The volume of blood pumped with each heartbeat.
What is the normal (healthy) figure for a stroke volume?
A normal stroke volume can fall in the range 50ml to 100 ml.
How do we calculate stroke volume (SV)?
Stroke volume= end diastolic volume - end systolic volume
End diastolic volume is the volume of blood in the ventricles at the end of ventricular diastole; remember diastole is when the ventricles are relaxed which allows it to be filled with blood (mid to late diastole).
End systolic volume is the volume of blood in the ventricles at the end of ventricular systole; this is where the ventricles contracts to force blood in the arteries.
Based on this, the end systolic volume should normally be lower than end diastolic volume.
How do we calculate ventricular ejection fraction (EF)?
Ventricular ejection fraction is a relative percentage of the blood pumped from the ventricles (as not all blood may be pumped from the ventricles at the end of diastole).
EF = (stroke volume / end of diastole volume) x 100%
What is the ventricular ejection factor if the end of diastole volume is 90mls and the end of systole volume is 20ml?
Calculate stroke volume:
SV = 90 - 20 = 70 ml
Calculate EF:
(70 / 90) x 100 = 77% EF
This means of all the blood that filled the ventricles during mid to late diastole, 77% of that blood was pumped out of the heart.
What is cardiac output? How do we calculate cardiac output?
Cardiac output (Q) is the volume of blood ejected by the heart in litres per minute.
Q = stroke volume x heart rate
What is the cardiac output if stroke volume is 70ml and heart rate is 60bpm?
Q = 70ml x 60bpm
Q = 4200 ml per minute
Q = 4.2 litres per minute
What is preload and afterload?
Preload and afterload refers to the filling and emptying of the left ventricle.
Specifically, preload is the force acting on the ventricular muscle before contraction- the force that is stretching the muscle (due to it being filled with blood) before contraction. So it is essentially the force needed to stretch the myocardial fibres from its resting length (which is never reached in a health heart) during diastole of the ventricles.
Afterload refers to the resistance that the left ventricle must overcame to circulate blood. Shortening of myocardial fibres is essentially pulling them closer inwards and making them more compact (which is the contraction of the fibres to force blood out of the ventricles). In general, if we are forcing something inwards to make it smaller (similar to shortening of the fibres), there will be a force of tension working against us. Hence, afterload is the force needed to overcome the tension in the myocardial fibres during the shortening of these fibres for sufficient contraction of the ventricles (from the resting length to the shortened length).
Note that the myocardial fibres is never just at its resting length.
What is stroke volume determined by?
Determined by the size of the left ventricle and the degree of myocardial fibre shortening (myocardial fibre shortening induces a contraction).
