L6 - The Heart as a Pump Flashcards
Layers of the heart (hint: 4)
- Pericardium
- Epicardium
- Myocardium
- Endocardium
Pericardium
A fluid filled membranous sac
Epicardium
- Fibrous inner lining of pericardium
- Contains blood capillaries, lymph capillaries, nerve fibres
- watery fluid between pericardium + epicardium - serves as lubricant as the heart moves within the sac.
Myocardium
- The walls of the heart which is composed of cardiac muscle cells
- Cardiac tissues separated by connective tissues
- Contains blood capillaries, lymph capillaries, nerve fibres
- Provides muscular contractions that eject blood from the heart chambers.
Endocardium
- Inner surface of the walls that is in contact with blood - composed of endothelial cells
- Endothelial tissue + thick sub-endothelial layer of elastic and collagenous fibres.
- Serves as protective inner lining of the chambers and valves.
Antrio-ventricular (AV) valves
- Prevent flow from ventricles back into the atrium
- Tricuspid valve - right AV valve
- Mitral valve - left AV valve
Pulmonary valve
Prevents the back flow of blood from pulmonary trunk into the right ventricle during ventricular relaxation
- aka “semilunar valves”
Aortic valve
Prevents the back flow of blood from aorta into the left ventricle during ventricular relaxation
- aka “semilunar valves”
What is cardiac ejection fraction (EF)?
- A measurement of how much blood the left ventricle pumps out with each contraction
- EF = SV / EDV
where, SV = Stroke volume (left ventricle contraction)
EDV = end-diastolic volume
- EF depends of volume, heart chamber dimensions, ventricular heart rate, valve function, preload and afterload
What is preload?
The force (pressure of the blood) that stretches the cardiac muscle (particularly ventricles) at the end of diastole (prior to contraction/ systole)
What is afterload?
The amount of resistance (pressure) the heart must overcome to open the aortic valve and push the blood volume out of the heart during systole (contraction)
What is the sinoatrial (SA) node (aka sinus node)?
- Located in the right atrium near the entrance of of superior vena cava
- Generates an electrical signal that causes the upper heart chambers (atria) to contract.
- The signal then passes through the AV (atrioventricular) node to the lower heart chambers (ventricles), causing them to contract/pump.
- The SA node is considered the pacemaker of the heart.
Control of heart rhythm - steps
- SA node (pacemaker) generates depolarisation - a wave of signals to contract
- Signals delayed at AV node (0.1s delay)
- Signals pass to heart apex via bundle of His between the atria and ventricles
- Signals rapidly spread throughout ventricles via Purkinje fibres - rapid conduction causes depolarisation of atrial myocardium and then contraction of the muscle to push blood out of ventricles
Cardiac myocytes (myocardial cells)
- Electrically excitable — NOT nerve cells
- Resting intracellular voltage = -90 mV (
- SA node is -40mV – slightly more positive due to more susceptible to stimulation from electrical pulse
- At resting state - K+ inside and Na+ outside of cell (Na+/K+ pump)
- Action potential (depolarisation) occurs when Na+ enters cell
What is inotropy?
- Influencing muscular contractility : increasing or decreasing the force of muscular contractions.
- Inotropes are drugs/any substance that alters the force or energy of muscular contractions
- They work by altering the movement of ions in the membrane (via Na+/K+ pump)
- Increase in muscular contraction by inotropic drug = increased cardiac output (CO)
