Cardiac Physiology Flashcards
What are the three layers of the heart?
- The myocardium-thick muscle layer
- Endocardium-flat cells that line the inner layer of the heart (continuous with endothelium of blood vessels)
- Epicardium-outer later of the heart, also called the visceral pericardium (layer on surface like the peel of an apple)
The heart is surrounded by pericardial fluid that is enclosed by the fibrous pericardium
The parietal pericardium lines the fibrous pericardium
What is the function of the pericardial fluid?
It is a lubricant so the heart can beat within the sac with no friction
The epicardium aka visceral pericardium and the parietal pericardium are membranes that secrete this fluid
What is the function of the 2 pumps in the heart?
The right side of the heart pumps blood to the lungs in the pulmonary circulation or circuit (from right atrium, right ventricle, pulmonary artery, lungs, pulmonary veins)
The left side pumps blood to the rest of the body in the systemic circulation or circuit (left atrium, left ventricle, to aorta, to diff muscles and organs, venae cavae back to right atrium, right ventricle)
Describe the flow of blood through the heart
- Deoxygenated blood enters the right atrium from the superior and inferior vena cava.
- The deoxygenated blood travels through the tricuspid valve (right atrioventricular valve) and enters the right ventricle. (The ventricle contracts)
- The deoxygenated blood then travels through the semilunar valve then into the pulmonary arteries where it goes to the lungs to exchange CO2 for O2. The blood is now oxygenated.
- The oxygenated blood returns to the heart via the pulmonary veins (normally 4) and enters the left atrium.
- The oxygenated blood then travels through the bicuspid valve (left AV) into the left ventricle. (Ventricle contracts)
- The blood then travels through the aortic semilunar valve into the aorta to all the body except the lungs and alveoli of lungs.
NOTE: The coronary arteries that supply the heart muscle branch off the aorta (just past semilunar valve). Blood returns to heart chamber via coronary sinus which drains into right atrium.
What causes myocardial infarction?
Myocardial infarction is death of cardiac cells.
This is due to the coronary arteries, which supply the heart muscle with nutrients and oxygen, becoming blocked.
The heart muscle is too thick to get nutrients through diffusion from blood inside the hearts chambers. It must rely on vessels.
What direction do the valves of the heart and veins flow?
They allow only 1 way flow of blood.
Valves close and prevent backward flow (unidirectional flow of blood)
How it works?
- when pressure is greater behind the valve it opens
- when pressure is greater in front of the valve it closes *doesn’t open in opposite direction because it’s one way
What is the purpose of the chordate tendineae?
Fibrous cords attached to the valve edges of cuspid (AV) valves
They restrain the valve edges (keeps the valve edges from going up into the atria when ventricles contract)
Right atrioventricular (AV) valve
3 cusps (tricuspid)
Valve leading from right atrium to the right ventricle
Left atrioventricular valve
2 cusps (bicuspid/mitral)
Located between left atrium and left ventricle
Aortic or pulmonary valve
Also known as the semilunar valve
The pulmonary valve is located in the right ventricle leading to the pulmonary arteries
The aortic valve is located in the left ventricle leading to the aortic artery
What are gap junctions?
Small connecting “tunnels” between cells
Allows the action potential to go from cell to cell-current (positive charge) flows into the next cell- causes an action potential in the next cell
*current carried by ions in the body
If action potential occurs in any part of the muscle, it passes throughout the muscle and the muscle contracts as a unit
Acts as functional syncytium = merging (connected) cells that act together (electrically and mechanically)
What are the two functional syncytia in the heart?
1 in the atria; 1 in the ventricles
They are separated by the heart’s fibrous skeleton which provide attachment for heart valves and for the hearts muscle fibers
*fibrous skeleton doesn’t conduct impulses
The 2 syncytia are separated except in one point (AV node)
How can the heart beat on its own?
Pacemaker potentials cause action potentials
Needs action potentials to cause contraction but does not require neural stimulation to contract
The action potential originates in the heart itself
Why does the inherent rate differ from the normal (or resting) rate?
The inherent rate equals 100 bpm with nothing affecting heart rate except the heart itself
The normal rate equals 70 bpm. This is because the parasympathetic nervous system is dominant at rest- acts as a brake on the heart.
How is heart rate changed?
By changing the slope of the pacemaker potential
Parasympathetic impulses decrease the slope of the pacemaker potential (flatter) . Takes longer to reach threshold-decreases heart rate
Sympathetic impulses increase slope of pacemaker potential (steeper). Quicker to reach threshold-increases heart rate.
How is the slope changed?
- nerves (ANS)
- hormone epineferen
What part of the heart sets the inherent rate and why?
The pacemaker or sinoatrial node (SA node)
The SA node is chosen because it gets to threshold the quickest/first
What happens if the SA node is damaged?
The normal pacemaker activity is 70 bpm (heart rate set by SA node, the fastest autorhythmic tissue).
If the SA node is damaged (nonfunctional), the AV node can take over and heart rate will decrease to 50 bpm.
If the AV node is nonfunctional the link to the ventricle will be lost (causes complete heart block) The purkinje fibers can take over but heart rate would be 30-40 bpm. (Person would be unconscious)
What is an ectopic focus?
pacemaker is taken over by ectopic focus. The whole heart will be driven more rapidly by an abnormal pacemaker
Why is the refractory period of cardiac muscle (of the membrane) long?
- Prevents prolonged or tetanic contraction (tetanus) in the heart.
- The heart needs a long enough refractory period to guarantee relaxation so blood can fill into heart.
- a second contraction can be stimulated before the first is over, which means you can get summation, and if the stimulation is rapid enough, you get tetanus
What causes the plateau in cardiac action potential?
Depolarization first occurs due to opening of voltage gated Na+ channels
Then Na+ channels close
The plateau then occurs because K+ permeability decreases and Ca++ membrane permeability increases
Ca++ brings in positive charges from ECF and keeps membrane depolarized at plateau level (balances)
Depolarization then occurs when Ca++ and K+ change back to permeabilities before action potential.
Then K+ permeability increases positive change moves out which causes repolarization
How do Ca++ levels in the cytosol affect the strength of contraction of the heart?
Ca++ enters cell from ECF during action potential (during plateau) this can induce Ca++ release from SR.
A small amount of the Ca++ that entered the cell can directly activate contractile machinery (Ca++ binds to troponin)
The majority of the Ca++ that binds to troponin comes from SR
AN INCREASE OF CA++ IN CYTOSOL OF THE CRLL CAN INCREASE STRENGTH OF CONTRACTION
epinephrine and norepinephrine can increase strength of cardiac contraction by increasing Ca++ in cytosol
What does the drug digitalis do?
Used to treat heart failure (heart fails as a pump) so digitalis increases the amount of Ca++ in the cytosol
What occurs if all Ca++ channels on the heart muscle cells were blocked?
The heart would not be able to contract
SA node
Sinoatrial node
Pacemaker of a normal heart
Near the superior vena cava
Mass of specialized cardiac muscle cells
Autorhythmic (100 bpm or 70)
Action potential generated from its pacemaker potential spreads from regular cell to cell through gap junctions.
Atria contract together
