Endocardium
Inner epithelial lining of the heart, in contact with “chamber blood”
Epicardium
Outer serous membrane in contact with the myocardium and continuous with the inner layer of the pericardium (superficial to myocardium)
Pericardium
Continuation of the epicardium as an invagination of serous membrane, creating a thin space of enveloping serous fluid around the heart.
The outer aspect of the pericardium serves as an attachment point to surrounding structures in the thoracic cavity.
[aids against friction]
Myocardial tissue
Cardiac Muscle: voluntary or involuntary?
Cardiac muscle that is found only in the heart
Cardiac muscle is INVOLUNTARY – all muscle is excitable, contracts, and returns to resting membrane. Cardiac muscle contraction is INVOLUNTARY.
What lines closed cavities and produces serous fluid that AIDS in reducing friction upon organ movement?
Serous membranes (epithelial tissue)
Cardiac Myocyte
Similar to skeletal muscle in what ways? (4)
Is a cell type that makes up the myocardium
Similar to skeletal muscle:
- membrane and cytoplasm are referred to as sarcolemma and sarcoplasm, and it’s sarcoplasmic reticulum is a storage site for Ca
- it as T tubules that carry an action potential transversely across each cell
- actin and myosin are the contractile proteins of the cell (thus, striated)
- mitochondria and myoglobin are abundant to meet energy demands
Cardiac Myocyte
Differs from skeletal muscle how?
- anatomically cardiac myocytes contain only one nucleus, and are interwoven and interconnected with adjacent myocytes to allow for a rapid spread of action potentials resulting in a unified contraction
Physiologically, how are cardiac myocytes unique?
They do not require innervation to initiate an action potential, though innervation may override this self-regulation
What are the 2 variants of heart muscle cells?
Where does the difference lie?
Pacemaker Cells & Contractile Cells
Difference lies in their resting membrane potential and length of action potential
Pacemaker Cells
Make up the nodes, bundles, and fibers
[smaller threshold to overcome e.g. -60 to -50]
Contractile Cells
Make up the atria and ventricles
[larger threshold to overcome e.g. -80 to -50]
What element plays a much bigger role in cardiac muscle than in skeletal muscle?
Calcium
- rapid influx of Ca ions causes depolarization initiating action potential
- slower continual influx of Ca (different pump) produces a prolonged action potential in the contractile cells of the atria and ventricles
- Ca triggers Ca release from Sarco Reticulum
What are the chambers and valves lined with?
What do the conduction units carry?
- endocardium
- carry action potentials within the myocardium
Passageways of Note:
- Superior/Inferior Vena Cava
- Right Atrium
- Tricuspid Valve
- Right Ventricle
- Pulmonary Valve
- Pulmonary Arteries
- Pulmonary Veins
- Left Atrium
- Mitral Valve
- Left Ventricle
- Aortic Valve
- Aorta
Blood moves through the organ because of?
The circulation of blood as it relates to the heart can be divided into:
- pressure differences and the pump action of muscle tissue
- Pulmonary Circulation
- Systemic Circulation
- Coronary Circulation
Pulmonary Circulation
Heart –> Lungs –> Heart
RV to LA
Systemic Circulation
LV –> tissues –> RA
Aorta to Vena Cava
Coronary Circulation
To and from myocardium
Aorta?
Conduction Units of note (4)
Sinoatrial node: natural, inborn pacemaker (Ac starts)
Atrioventricular node: slows down Ac
Atrioventricular Bundle
Purkinje fibers
Auscultation of the heart
What does it provide?
Under normal conditions, what is the rhythm maintained by?
What is the term for the sequence of events from the beginning of one heartbeat to the next?
(Palpation of the pulse)
- provides a window into the rhythm of the heartbeat
- maintained by the heart’s own conduction system
- sequence termed: CARDIAC CYCLE (begins with SA node with a spontaneous action potential)
Since myocytes do not require nerve innervation to contract, what allows for this automaticity?
What happens after depolarization?
- constant motion of Na+, K+, and Ca++ in and out of the cell
- after depolarization, the speed of the return back to resting potential differs among heart cells and thus creates a hierarchy of control over the rate of contractions
- –SA node at top of hierarchy; “the pacemaker”, depolarizing 60-100x per min
What is the propagation of the action potential of each cardiac cycle?
What is the result?
SA node –> through both atria –> AV node –> AV bundle –> left and right bundle branches continue through the ventricles via the Purkinje fibers from the apex to the base of the heart
- result is bilateral atrial contraction followed by bilateral ventricular contraction
What are the heart sounds of a normal cardiac cycle?
LUB: atrioventricular valves closing – [TV and MV snapping shut simultaneously]
[allows atriums to fill and “get their stretch on”]
Dub: aortic and pulmonary valves closing
[ventricles filling when these are open]
Frank Starling Mechanism
- as venous return increases, so does the stretch of the atrial chambers’ this results in an increased force and rate of contraction
[venous return determines cardiac output]
