The cardiovascular system Flashcards
What are the atria?
- The atria are the thin-walled upper chambers of the heart.
- The right atrium receives deoxygenated blood from the body via the vena cava
- The left atrium receives oxygenated blood from the lungs via the pulmonary veins
- Both atria contract to push blood into the ventricles
What are the ventricles?
- The ventricles are the thick-walled (especially the left ventricle) lower chambers of the heart.
- The right ventricle pumps deoxygenated blood to the lungs via the pulmonary artery
- The left ventricle pumps oxygenated blood to the body via the aorta
- The thick walls allow powerful contractions for blood ejection
What is the bicuspid valve?
The bicuspid valve contains two flaps and is found between the left atrium and the right ventricle. It prevents the backflow of blood from the left ventricle into the left atrium when the ventricle contracts.
What is the tricuspid valve?
The tricuspid valve contains three flaps and is found between the right atrium and the right ventricle. It prevents the backflow of blood into the right atrium when the right ventricle contracts.
What is the aortic semilunar valve?
The aortic semilunar valve is found at the base of the aorta. It prevents blood from flowing back into the left ventricle after it has been ejected into the aorta.
What is the pulmonary semilunar valve?
The pulmonary semilunar valve is found at the base of the pulmonary artery. It prevents blood from flowing back into the right ventricle after it has been pumped into the pulmonary artery.
What is the vena cava?
- The vena cava consists of two large veins that return deoxygenated blood from the body into the right atrium.
- The superior vena cava is located at the top of the right atrium and brings deoxygenated blood from the upper body down into the right atrium
- The inferior vena cava is located at the bottom of the right atrium and brings deoxygenated blood from the lower body up into the right atrium
What is the aorta?
The aorta is the largest artery in the body. It carried oxygenated blood from the left ventricle to the rest of the body.
What is the pulmonary artery?
The pulmonary artery is the artery that splits into the left and right branches going into each lung. It carries deoxygenated blood from the right ventricle to the lungs for gas exchange.
What are the pulmonary veins?
The pulmonary veins consist of four veins, two stemming from each lung. It returns oxygenated blood from the lungs to the left atrium.
What is the septum?
The septum is the muscular wall dividing the left and right sides of the heart. It prevents the mixing of oxygenated and deoxygenated blood between the two sides of the heart.
What is the myocardium?
The myocardium is the thick muscular layer of the heart wall. It is responsible for contracting to pump blood. The strength of the myocardium (especially in the left ventricle) supports the high-pressure circulation of blood around the body.
Diagram of the heart
What is the pathway of blood?
- Deoxygenated blood enters the right atrium via the superior and inferior vena cava
- Blood flowers through the tricuspid valve into the right ventricle
- The right ventricle contracts, pushing blood through the pulmonary semilunar valve into the pulmonary artery
- Blood travels to the lungs for oxygenation
- Oxygenated blood returns to the left atrium via the pulmonary veins
- Blood flows through the bicuspid (mitral) valve into the left ventricle
- The left ventricle contracts, sending blood through the aortic semilunar valve into the aorta
- Blood is then distributed to the rest of the body
What is the conduction system of the heart?
The conduction system is an intrinsic electrical system made of specialised myogenic tissue, meaning that the heart can generate its own impulses without nerve input. This ensures the coordination and timing of the heartbeat for efficient blood flow.
What is the sinoatrial node?
- The sinoatrial node (SA node) is located on the upper wall of the right atrium, near the opening of the superior vena cava. The function of the sinoatrial node is that it:
- It acts as the heart’s natural pacemaker
- It generated electrical impulses (known as the wave of excitation) around 60-100 times per minute at rest
- It initiates each heartbeat
What is the effect of the sinoatrial node?
- The effect of the sinoatrial node is that:
- The electrical impulse spreads rapidly across the atrial walls, causing the right and left atria to contract simultaneously
- This is the beginning of the atrial systole, pushing blood into the ventricles
What is the atrioventricular node?
- The atrioventricular node (AV node) is located in the lower part of the right atrium, near the atrioventricular septum. The function of the atrioventricular node is that it:
- Acts as a relay point for the electrical signal
- Delays the impulse for about 0.1 seconds
What is the importance of the atrioventricular delay?
- Allows time for the atria to fully contract and empty all blood into the ventricles before ventricular contraction begins
- Ensures efficient ventricular filling
What is the wave of excitation?
The wave of excitation refers to the spread of the electrical signal from the SA node through the atria, then through the AV node, bundle of HIS and purkinje fibres. It causes the sequential contraction of the heart chambers and ensures that the heart beats in a coordinated rhythm, maintaining stroke volume and cardiac output.
What is the bundle of HIS?
- The bundle of HIS is located in the interventricular septum and is a specialised conducting tissue fibre. The function of the bundle of HIS is that it:
- Carries the impulse from the AV node down the septum towards the apex (bottom point) of the heart
- Prepares the ventricles for contraction by transmitting the signal to the purkinje fibres
What are the purkinjie fibres?
- The purkyne tissue (purkinje fibres) branches out from the bundle of HIS into the ventricular walls. The function of the purkinje fibres is that it:
- Spreads the impulse rapidly through the ventricular myocardium
- Triggers ventricular systole (ventricular contraction) from the bottom of the heart, upwards. This ensures that blood if efficiently pushed up towards the aorta and the pulmonary artery
how do the 5 key parts of the conduction system work together?
- The goal of the conduction system is to make sure that the heart contracts in the right order, at the right time and with the right force, so blood is pumped efficiently to the lungs and body. Here is how the five key parts of the conduction system work together:
- The sinoatrial node is the ‘starter motor’ of the heart. It creates an electrical impulse that spreads through the atria, causing them to contract together. The atria contraction (atrial systole) pushes blood into the relaxed ventricles. It also sets the pace of the heartbeat which is around 60-100bpm at rest which results in the efficiency movement of blood from the atria to the ventricles.
- The wave of excitation is the electrical impulse that tells the heart muscle when to contract. It travels from the SA node across the atria, then to the AV node.
- The atrioventricular node acts as a ‘pause button.’ It delays the impulse for about 0.1 seconds which gives the atria time to empty all their blood into the ventricles before the ventricles contract which prevents blood from being trapped or lost in the heart.
- The bundle of HIS acts as a high-speed cable network running down the septum. it carries the impulse to the bottom (apex) of the heart and prepares the ventricles to contract from the bottom upwards.
- The purkinje fibres are branches throughout the ventricular walls. It makes the ventricles contract from the apex upwards and results in the right ventricle pumping blood into the pulmonary artery and the left ventricle pumping blood into the aorta.
what happens to sa node activity during exercise?
During exercise, the brain sends signals to release adrenaline which increases SA node activity. This makes the heart beast faster and stronger, pumping more oxygenated blood to the muscles.
what is included in the cardiac cycle and how long is it
The cardiac cycle is one complete heartbeat, lasting around 0.8 seconds at rest. It includes atrial systole, ventricular systole and diastole.
what is atrial systole
Atrial systole lasts about 0.1 seconds and is triggered by the SA node. It occurs when the atria contracts, pushing blood through the atrioventricular valves.
* Right atrium -> right ventricle through the tricuspid valve
* Left atrium -> left ventricle through the bicuspid / mitral vale
* The ventricles remain relaxed while they receive blood from the atriums
what is ventricular systole
Ventricular systole lasts about 0.3 seconds.
* After the AV node delay, the impulse travels through the bundle of HIS and purkinje fibres
* This allows the ventricles to contract from apex upwards as the pressures rises inside the ventricles and the atrioventricular valves shut
* The semilunar valves open allowing blood to flow from the right ventricle into the pulmonary artery and the left ventricle into the aorta
what is diastole
Diastole lasts about 0.4 seconds and occurs when both atria and ventricles relax
* The semilunar valves close which prevents the backflow of blood into the ventricles
* Blood flows passively from the vena cava to the right atrium and the pulmonary veins into the left atrium
* The atrioventricular valves then open and the cycle is able to begin again
relationship between the electrical event, structure, mechanical event and phase of the cardiac cycle
what is the effect of adrenaline on the heart during exercise
During exercise, the SA node is stimulated by adrenaline and nervous input to increase the firing rate which increases heart rate. This shortens the cardiac cycle and allows for more beats per minute which increases cardiac output. The efficient coordination ensures adequate oxygen delivery to working muscles
heart rate
Heart rate (HR) is the number of beats per minute. Measured in bpm
stoke volume
Stroke volume (SV) is the volume of blood ejected from the left ventricle per beat. Measured in mL
cardiac output
Cardiac output (Q) is the volume of blood ejected from the heart per minute. Measured in litres per minute (L/min). Cardiac output = Heart rate x stroke volume
what is the relationship between heart rate and exercise
Heart rate increases with exercise to deliver move oxygen and remove carbon dioxide. It is controlled by the autonomic nervous system (ANS). At rest, a person’s typical bpm is 60-80 but is lower in trained individuals. During exercise, your bpm can reach up to 220 – your age
what is the relationship between stroke volume and exercise
Stroke volume increases with intensity up to 60% max effort, then plateaus (levels off). It depends on venous return (more blood coming back = more pumped out), contractility of the heart and elasticity of the left ventricle. At rest, it is typically around 70mL but in trained athletes it can be up to 120mL. Stroke volume increases due to Starling’s law which says that the more blood in = longer stretch = more blood out.
what is the relationship between cardiac output and exercise
Cardiac output is around 5L at rest but during maximal exercise in elite athletes it can reach up to 20-40L/min.
untrained individual values
trained individual values
sterlings law of the heart
Starling’s law of the heart states that the greater the venous return to the heart, the greater the stretch of the ventricular walls, leading to a stronger contraction and a larger stroke volume
how does neural control regulate heart rate
- Neural control: Baroreceptors are located in the carotid arteries and aorta, and they detect blood pressure changes and sends information to the cardiac control centre (CCC)
Chemoreceptors are located in the carotid and aortic bodies, and they detect changes in carbon dioxide, pH and oxygen and they stimulate an increase in heart rate if carbon dioxide levels are high
Mechanoreceptors are located in the muscles and joints, and they detect movement and signal to the CCC to increase heart rate in anticipation of exercise.
All information is processes by the cardiac control centre (CCC) in the medulla oblongata of the brain
hormonal control regulating heart rate
Adrenaline and noradrenaline are released by adrenal glands. They stimulate heart rate, contractility and the speed of conduction through the heart. They are released before and during exercise as part of the fight or flight response
intrinsic control regulating heart rate
Myocardium stretch states that more stretch = stronger contraction (Starling’s law) and temperature increase is caused by warmer blood speeding up nerve signals which increase heart rate
cardiac control centre regulating heart rate
Integrates neural, hormonal and intrinsic information and sends signals to the SA node to adjust heart rate
automatic nervous system regulating heart rate
Consists of the sympathetic nervous system which increase heart rate and the force of contraction via adrenaline and the parasympathetic nervous system which decrease heart rate via and vagus nerve
table of heart rate, stroke volume and cardiac output, between rest and recovery
long term training adaptations
what is venous return
Venous return is the volume of blood returning to the heart via the veins. During exercise, this is essential to increase stroke volume and cardiac output. However, because blood in veins is under low pressure, the body uses six different mechanisms to help it return efficiently:
skeletal muscle pump helping venous return
When muscles contract (especially in the legs), they squeeze nearby veins which pushes blood towards the heart. One-way vales in the veins prevent backflow. During exercise, this mechanism is highly active due to frequent muscle contracts, and this boosts venous return and supports increased cardiac output.
valves helping venous return
Valves are found inside of medium-sized veins, especially in the limbs. They prevent the backflow of blood due to gravity and help maintain the unidirectional flow of blood back to the heart. This is especially important during standing or upright activities.
respiratory pump helping venous return
When you breath in (inspiration), pressure in the chest cavity decreases and pressure in the abdominal cavity increases. This creates a pressure gradient which draws blood towards the thorax (heart). Breathing deeper and faster during exercise enhances this effect.
gravity helping venous return
Helps return blood from the upper body to the heart with ease as minimal effort is needed for blood to fall downward to the heart due to gravity.
smooth muscle/venous tone helping venous return
Veins contain smooth muscle in their walls. This muscle can contract slightly (venomotor tone), reducing the diameter of the vein and pushing blood forward. This is controlled by the sympathetic nervous system, especially during exercise or stress.
cardiac suction helping venous return
During diastole when the heart relaxes, the atria can expand which creates a suction effect and draws blood into the atria from the veins. This helps pull blood in and supports venous return.
vascular shunt mechanism
The vascular shunt mechanism controls how blood is distributed around the body.
* At rest: Most blood (approx. 75-80%) goes to organs (digestive system, kidneys, brain). A smaller portion (approx. 15-20% goes to working muscles. Blood supply supports maintenance functions like digestion and waste removal.
* During exercise: The vascular shunt mechanism redirects blood to where it is needed most – the working muscles. Up to 85-90% of cardiac output may be sent to muscles. Blood flow to non-essential organs is reduced (e.g. less to the digestive system). This ensures maximum oxygen delivery and waste removal for muscles
* During recovery: Blood flow begins to shift back to resting levels. Gradual return of blood to organs as muscle demand falls. This helps with the removal of waste product (e.g. lactic acid) and body temperature regulation.
controls of vascular shunt mechanism
The vascular shunt mechanism is controlled by the automatic nervous system (ANS), using receptors and the vasomotor control centre in the medulla oblongata.
automatic nervous sytstem controlling vascular shunt
Controls involuntary actions like heart rate and blood vessel diameter. Consists of two branches: Sympathetic nervous system (SNS) which speeds up heart rate and vasoconstricts non-essential vessels during exercise and the parasympathetic nervous system (PNS) which slows heat rate and is more active at rest.
receptors controlling vascular shunt mechanism
Detect internal body changes and send signals to the brain. Chemoreceptors detect rising carbon dioxide levels, high acidity and low oxygen levels. Baroreceptors detect blood pressure changes. Proprioceptors detect movement in muscles and joints.
vasomotor control centre controlling vascular shutn mechanism
Located in the medulla oblongata (brain). Receives signals from receptors and sends impulses via the sympathetic nerves to control arterioles and precapillary sphincters.
arterioles controlling vascular shunt mechanism
Small arteries that control blood flow into capillary beds. Vasoconstriction is when arterioles to non-essential areas narrow, causing less blood flow to that area. Vasodilation is when arterioles to muscles widen, allowing more blood flow to that area.
pre-capillary sphincter controlling vascular shunt
Tiny rings of muscles at the entrance of capillaries. Constrict or relax to control whether capillaries open. Relaxed allows the capillaries to open and blood to flow in. Contracted allows the capillaries to close and no blood to enter.
vasodilation and vascular shunt
Happens from arterioles to muscles to increase oxygen supply and remove carbon dioxide.
vasocontriction and vascular shunt
Happens from arterioles to organs to prioritise blood for muscles
how does vascular shunt mechanism componetns work together
The vascular shunt mechanism is the body’s way of redirecting blood flow during different situations – especially from organs to working muscles during exercise and back to organs during rest and recovery. Here is how the system works with all of the components working together:
* Proprioceptors in muscles and joints detect movement, chemoreceptors sense increases carbon dioxide and acidity (lactic acid) and baroreceptors detect changes in blood pressure. All of these receptors send signals to the vasomotor control centre (VCC) located in the medulla oblongata of the brain.
* The VCC interprets the information and sends impulses via the sympathetic nervous system which controls arterioles and precapillary sphincters throughout the body.
* The arterioles to organs narrow through vasoconstriction and the precapillary sphincters contract leading to those capillaries tightening, closing off blood flow which means less blood goes to non-working areas.
* The arterioles supply working muscles widen through vasodilation and the precapillary sphincters relax, allowing more blood flow into capillary beds in the muscles. This results in more oxygen and nutrients reaching the muscles and waste products being removed faster.
* To support this fast-moving redirected blood flow, the body boosts venous return using skeletal muscle pumps, valves, respiratory pumps, cardiac suction and smooth muscles in veins which maintain venous return and keeps stroke volume and cardiac output high.
* With increased venous return, the heart can pump more blood per beat, leading to a higher stroke volume. Combined with a higher heart rate from sympathetic activation, cardiac output rises which increases blood supply to muscles during exercise.
