Cardiovascular system Flashcards
(38 cards)
What is the correct order of circulation from the heart to the lungs?
Right atrium,
tricuspid valve,
right ventricle,
pulmonary valve,
pulmonary trunk,
lungs
Cardiovascular system
- Consists of the heart and blood vessels
- Facilitates the movement of blood, enabling the exchange of water, gases, wastes and nutrients
Consists of systemic circuit and pulmonary circuit
Systemic circuit
- Provides blood to the tissues around the body
Pulmonary circuit
- Provides blood to the lungs to be re-oxygenated
Different blood vessels
Afferent
- vessels that return blood to the heart (veins and venules)
Efferent
- vessels that take blood away from the heart (arteries and arterioles)
Capillaries
- enable the exchange of substances between blood and tissue
Heart anatomy
The heart is made up of four chambers; right atrium, right ventricle, left atrium, left ventricle
Heart valves
- Tricuspid valve: separates the right atrium and right ventricle
- Pulmonary valve: separates the right ventricle and the pulmonary artery
- Mitral valve: separates the left atrium and left ventricle
- Aortic valve: separates the left ventricle and aorta
Layers of the heart
Pericardium
- double walled, fluid-filled sac of connective tissue surrounding the heart
- Contains pericardial fluid
Epicardium
- Outermost layer of the heart wall, the visceral membrane of the pericardium
Myocardium
- Middle layer of the heart wall, containing cardiac muscle tissue. Responsible for the pumping action of the heart
Endocardium
- Inner lining of the heart wall, consists of simple squamous epithelium and some loose connective tissue
Cardiac muscle
Cardiac muscle cells, also known as cardiomyocytes, are contractile cells that are branched, and contain a single nucleus per cell.
Cardiac muscle cells are joined by intercalated discs, which allow:
1. Ion and small molecule movement
2. Electrical signals to travel between cells
3. Strong connection between cardiac muscle cells, to resist mechanical stress
Automaticity
- Specialised cardiac muscle cells, called pacemaker cells, can spontaneously generate an electrical impulse, or depolarise.
Effect of the nervous system
- The nervous system can alter the pace and strength of contraction, in response to various situations, like stress or exercise
Conducting system
- responsible for distributing electrical impulses through the heart
- controls the contraction of the heart
- Starts with an action potential in the sinoatrial (SA) node.
Pacemaker cells
- Cells of the SA node, with unstable resting potential
- Able to spontaneously generate cardiac action potentials due to a slow influx of sodium ions.
- The signal generated by pacemaker cells in the SA node travels by the internodal pathways to the atrioventricular (AV) node, takes about 50ms. The signal pauses here for 100ms, allowing the atria to contract before the ventricles begin to contract.
- The signal then continues through the AV bundle, bundle branches, and purkinje fibres, contracting the ventricles.
Electrocardiogram (ECG)
An ECG is a measure of electrical activity that occurs in the heart.
P wave:
Represents depolarisation of the SA node, and the impulse spreading to the through the atria, so the atria contract
QRS complex:
Represents ventricular depolarisation. The signal travels across the AV node, to the AV bundle, then to purkinje fibres.
T wave:
Represents ventricular repolarisation, the recovery of ventricles following contraction.
Examples of diagnosis from ECG
Variations of PR interval= damage to conducting pathways or AV node
Variations to the QT interval= caused by electrolyte disturbances, medication, conduction problems, coronary ischemia or myocardial damage.
Electrical signal pathway
Step 1 shows atrial depolarisation which as stated earlier coincides with the P wave. The electrical signals move across the atria.
Step 2 shows the completion of atrial depolarisation, which coincides with the PR segment, or gap between the P wave and QRS complex.
Step 3 shows the beginning of ventricular depolarisation, which coincides with the QRS complex. At this point the electrical signal is moving through the AV bundle, and bundle branches, and up through the Purkinje fibres.
Step 4 shows the completion of ventricular depolarisation, which coincides with the ST segment.
Step 5 shows the beginning of ventricular repolarisation, or recovery. This coincides with the T wave.
Finally ventricular repolarisation is complete with Step 6.
Cardiac cycle
Systole = contraction = blood pushed out
Diastole = relaxation = blood moves in
Atrial systole
- Atria contract, forcing blood from the atria into the ventricles, through the atrioventricular (AV) valves
- Starts in the peak of the P wave
Atrial diastole
- Contraction stops and the cardiac muscle of the atria relax.
Ventricular systole
- Occurs simultaneously with atrial diastole
- Cardiac muscle in the ventricles contract, increasing pressure.
- This increased pressure closes the AV valves
- Once pressure is high enough the pulmonary and aortic valves open and eject blood from the heart to the lungs and body
- Starts with the peak of the QRS complex
Ventricular diastole
- Ventricles relax, while the atria are also still relaxed
- All heart valves are closed and ventricular pressure drops
- Once ventricular pressure is lower than atrial pressure the ventricles begin to fill passively
Heart sounds
S1 – ‘lub’ sound
- Created by the AV valves, mitral and tricuspid, snapping closed
S2 – ‘dub’ sound
- Created by the semilunar valves, pulmonary and aortic, snapping closed.
S3 sound
- Usually faint and inaudible
- Created by blood flowing into ventricles
- Can be heard during congestive heart failure, and if there is an enlarged left ventricular chamber
S4 sound
- Usually faint and inaudible
- Sound of atrial contraction
Cardiodynamic terms
End-diastolic volume (EDV)
- Volume of blood in the ventricles at the end of atrial systole (130 mL)
End-systolic volume (ESV)
- Residual volume left in the ventricles at the end of ventricular systole (50 mL)
Stroke volume (SV)
- EDV-ESV
- Volume of blood ejected from the heart during each cardiac cycle (70-80 mL)
Ejection fraction
- SV/EDV (%)
Cardiac output
- Heart rate (beats/min) x SV (mL/beat)
- Volume of blood ejected from the heart per minute (mL/min)
Factors controlling cardiac output
- Regulated by the autonomic nervous system, circulating hormones, and local factors such as venous return, and stretch receptors
- Sympathetic stimulation increases heart rate and stroke volume
- Parasympathetic stimulation decreases heart rate and cardiac output
- An increase in venous return increases cardiac output
