Week 5 - Cardiac structure and Function Flashcards
Brief outline of the journey of blood in the heart.
Right atrium receives blood from super and inferior vena cava.
Travels to right ventricles via tricuspid valve.
Goes into pulmonary circulation via the pulmonary artery and returns to the left atrium via the pulmonary vein.
Then into left ventricle through the mitral valve and ejected through aorta into systemic circulation.
What are the 3 structures of the heart wall?
1) Epicardium
2) Myocardium
3) Endocardium
Describe the characteristics and function of the 3 structures that make up the heart wall.
Epicardium
- Characteristics: serous membrane including blood capillaries, lymph capillaries and nerve fibers
- Function: serves as a lubricative outer cover.
Myocardium:
- Characteristics: cardiac muscle tissue separated by connective tissues and includes blood capillaries, lymph capillaries and nerve fibers
- Function: provides muscular contractions that eject blood from the heart chambers.
Endocardium
- Characteristics: endothelial tissue and a thick subendothelial layer of elastic and collagenous fibers
- Function: serves as protective inner lining of the chambers and valves.
The heart receives blood supply (oxygen and nutrients) via what arteries?
coronary arteries - it has a high demand for oxygen and nutrients
Myocardial infarction (MI) and influence of exercise.
Blockage in coronary blood flow which results in cell damage.
Exercise training protects against heart damage during an MI.
Structural differences between heart muscle and skeletal muscle.
1) Nuclei
2) Neural control
3) Calcium store
4) Shape of muscle fibers
5) Regeneration potential
6) Energy production
1) Nuclei: heart muscle has single, whereas skeletal has multiple
2) Neural control: heart is involuntary and skeletal voluntary
3) Calcium store: heart sources are SR and extracellular calcium, skeletal is SR
4) Shape of muscle fibers: heart has shorter muscle fibers and have branching, skeletal is elongated - no branching.
5) Regeneration potential: heart has none (no satellite cells) whereas skeletal has some possibilities via satellite cells.
6) Energy production: heart is aerobic (primary) whereas skeletal muscle is aerobic and anaerobic
The contraction of the heart depends on the electrical stimulation of…
a) Epicardium
b) Myocardium
c) Endocardium
Myocardium
Cardiac automaticity
when the heart can generate its own action potentials
What are the two types of cells in the heart?
Nodal cells (e.g. SA node, AV node - makes up 1%) and muscular cells (actin, myosin)
What is the intrinsic regulation of the heart controlled by?
SA node - pacemaker and initiates depolarization by generating AP.
Atrioventricular node (AV node)
Passes depolarization to ventricles and has a brief delay to allow for ventricular filling.
What are the two mechanistic reasons for AV node having a brief delay for ventricular filling?
1) There are less gap junctions at the AV node so conduction moves slower through.
2) Diameter of the cells are smaller in the AV node so slows conduction.
Bundles branches / Bundle of His
branch that connects the atria to left and right ventricle - travels down the septum
Purkinje fibers
spread wave of depolarization throughout the ventricles
Describe the 4 steps of the conduction system of the heart.
1) Action potentials originate in the sinoatrial (SA) node and travel across the wall of the atrium from the SA node to the atrioventricular (AV) node.
2) There is a slight pause in the AV node to allow for ventricular filling. APs then pass through the AV node and along the AV bundle, which extends from the AV node, through the fibrous skeleton, into the interventricular septum.
3) The Atrioventricular (AV) bundle divides into right and left bundle branches, and APs descend to the apex of each ventricle along the bundle branches.
4) APs are carried by the Purkinje fibers from the bundle branches to the ventricular walls.
Bundle branches become depolarized, the ventricles contract, the ventricular pressure increases, and blood exits the ventricles.