Cardiovascular Flashcards
Mention the layers of the heart from inner to outer layer
Endocardium
Myocardium
Visceral layer of serous pericardium
Pericardial cavity
Parietal layer of serous pericardium
Fibrous pericardium
Endocardium
1) Endothelium -> simple squamous epithelial tissue with areolar connective tissue
2) Functions
o Prevents blood in heart from clotting -> releases PGI2 and NO which inhibits platelet activation and aggregation.
o Act as a barrier between blood and tissue.
o Makes tight junctions which controls movement between cells.
o Continues as endothelium in blood vessels
o Lines the outer layer of the valves in the heart
Myocardium
1) Cardiac muscle tissues:
a. Contractile Cardiac Muscle
b. Non-Contractile Cardiac Muscle
o SA node -> nodal, auto-rhythmic cells, that can generate AP and set sinus rhythm
o AV node
o Bundle of His
o Bundle branches (right and left)
o Purkinje fibers
2) Functions:
a. Non-Contractile cardiac muscle -> generates and conducts action potentials.
b. Contractile cardiac muscle -> contracts as a unit to pump blood through and out of the heart.
Visceral layer of serous pericardium
o Also called epicardium
o Mesothelium: simple squamous with loose areolar connective tissue
o Secretes pericardial serous fluid into the cavity to lubricate tissue layers.
Pericardial cavity
o Contains serous fluid - usually has no blood under normal physiologic conditions.
o Prevents friction from two serous layers rubbing against each other.
Parietal layer of the serous pericardium
o Continuous with the epicardium
o Mesothelium: simple squamous + loose areolar connective tissue
o Secretes pericardial serous fluid into the cavity to lubricate tissue layers.
Fibrous pericardium
Tissue -> dense fibrous irregular connective tissue
Function:
o Anchors heart to surrounding structures
o Prevents heart from overfilling with blood because it’s not a distensible or “stretchy” tissue
o Protects the heart because it is a tough tissue
From where does the RA receives blood?
Received deoxygenated blood from three vessels:
o Cranial Vena Cava -> brings blood from structures above the diaphragm (head and neck and forelimbs)
o Caudal Vena Cava -> brings blood from structures below the diaphragm (abdomen, liver, hindlimb)
o Coronary Sinus -> brings blood from coronary circulation
From where does the LA receives blood?
Receives oxygenated blood from 4 pulmonary veins
o Two left pulmonary veins from the left lung
o Two right pulmonary veins from the right lung
Auricles
1) Left Auricle or left atrial appendage -> increases space and volume of right atrium. Thrombi very commonly forms here in heart disease (especially cats)
2) Right auricle or right atrial appendage -> increases space and volume of right atrium. Thrombi formation happens but not as common.
Heart valves / chordae tendineae / papillary muscle structure
1) Valve structure -> they are four annulus rings of fibrous tissue, and leaflets tissue hang from these annulus rings.
2) Chordae tendineae
o Anchors the leaflets to papillary muscles
o Collagen cords of connective tissue
o Attached to the cusps of the valves
o Keeps valve tight to prevent them from ballooning back into the atrium and causing blood backflow
3) Papillary muscles
o Projections of the myocardium
o Anchors the chordae tendineae
o If ischemic, muscles weaken -> unable to contract -> valve flaps loosen -> valve regurgitation
Atrioventricular valves
Between atria and ventricles -> prevents backflow of blood from ventricles into atria.
1) Tricuspid Valve -> between RA and RV. Contains three leaflets
2) Bicuspid or Mitral Valve -> between LA and LV. Contains two leaflets
Semilunar valves
o Have three crescent shaped cusps
o Between ventricles and pulmonary trunk and aorta
o Pulmonary trunk splits into the left and right pulmonary arteries
o Aorta -> Ascending aorta -> aortic arch -> descending aorta
1) Pulmonary Semilunar valve -> between RV and Pulmonary trunk
2) Aortic Semilunar Valve -> between LV and Ascending Aorta.
o Two coronary arteries arise from the aorta just beyond the semilunar valves;
o During diastole, the increased aortic pressure above the valve’s forces blood into the coronary arteries and thence into the musculature of the heart.
T/F The atrial and ventricular types of muscle contract in much the same way as skeletal muscle, except that the duration of contraction is much longer
TRUE
4 pacemakers in the heart?
SA node
AV node
Bundle of His
Purkinje fibers
The body decides who is the pacemaker is whoever is faster:
The SA node is normally 70-80 bpm
AV node 40-60bpm
Bundle of His about 40bpm
Purkinje fibers 15bpm
Therefore normally, the SA node is the one who dictates the HR and purkinje fibers is as a last resource in case the other pacemakers do not work.
What is the purpose of the gap junctions within the intercalated discs?
o Cardiac muscle is striated, similar to skeletal muscle but with some differences
o Cardiac muscle is a syncytium -> the muscle fibers are separated by intercalated discs (cell membranes that separate individual cardiac muscle cells)
o At each intercalated disc, the cell membrane fuse with one another to form permeable “communicating” junctions called “gap junctions”
o Gap junctions allow rapid diffusion of ions -> action potential travels rapidly.
How many syncytium is the heart composed off?
Two: atrial (walls of the 2 atria) and ventricular (walls of the 2 ventricles) syncytium.
T/F - The action potential recorded in a ventricular muscle fiber averages about 105mV, which means that the intracellular potential rises from a very negative value, about −85mV, between beats to a slightly positive value, about +20mV during each beat
TRUE
For how long the membrane rests depolarized?
0.1-0.2sec or 100-200milisec
That creates a plateau, typical of ventricular muscle cell action potential
What are the consequences of the plateau in ventricular action potentials?
Causes ventricular contraction to last as much as 15 times more compared to skeletal muscle
What are the major differences between cardiac and skeletal muscle that account for the differences in action potential?
o Action potential of skeletal muscle is caused almost entirely by the sudden opening of fast Na channels. They are called fast because they remain open for only a few thousands of a second and then they close.
o In cardiac muscle, the action potential is due to the opening of TWO type of channels:
* Same fast Na channels as in skeletal muscle
* L-type Ca channels (also called calcium-Na channels)
o The L-type Ca channels differs from the fast sodium channels in that they are slower to open (that is why there is a brief depolarization when K starts going out as Ca channels are slow to open) and, even more important, remain open for several tenths of a second.
o During this time, a large quantity of both calcium and sodium ions flows through these channels to the interior of the cardiac muscle fiber, and this activity maintains a prolonged period of depolarization, causing the plateau in the action potential
o The second major difference -> immediately after the onset of the action potential, the permeability of the cardiac muscle membrane for potassium ions decreases about fivefold, an effect that does not occur in skeletal muscle.
o The decreased potassium permeability greatly decreases the outflux of positively charged potassium ions during the action potential plateau and thereby prevents early return of the action potential voltage to its resting level - again, helps maintain the plateau phase.
What happens when the L-type Ca channels close?
o They close at the end of 0.2 to 0.3 second
o The influx of calcium and sodium ions ceases -> the membrane permeability for potassium ions also increases rapidly.
o This rapid loss of potassium from the fiber immediately returns the membrane potential to its resting level, thus ending the action potential.
Summary of phases of ventricular action potential
o Phase 0 (depolarization), fast sodium channels open. When the cardiac cell is stimulated and depolarizes, the membrane potential becomes more positive. Voltage-gated Na channels (fast Na channels) open and permit Na to rapidly flow into the cell and depolarize it. The membrane potential reaches about +20 millivolts before the Na channels close.
o Phase 1 (initial repolarization), fast Na channels close. The Na channels close, the cell begins to repolarize, and K ions leave the cell through open K channels.
o Phase 2 (plateau), Ca channels open and fast K channels close. A brief initial repolarization occurs and the action potential then plateaus as a result of increased Ca permeability and decreased K permeability. The voltage-gated Ca channels open slowly during phases 1 and 0, and Ca enters the cell. Potassium channels then close, and the combination of decreased K efflux and increased Ca influx causes the action potential to plateau.
o Phase 3 (rapid repolarization), Ca channels close and slow K channels open. The closure of Ca channels and increased K permeability, permitting K to rapidly exit the cell, ends the plateau and returns the cell membrane potential to its resting level.
o Phase 4 (resting membrane potential) averages about −90 millivolts.
What does it means “excitation-contraction coupling”?
o Refers to the mechanism by which the action potential causes the myofibrils of muscle to contract.