What lines the myocardium internally and externally?
Internally - endocardium
Externally - epicardium
What can be found within the epicardium?
Within the epicardium, coronary vesels and cardiac plexus permeate white fat that occupies the epicardium and acts as a shock absorber for the heart. This epicardial white fat is covered by the visceral layer of serous pericardium.
Describe the endothelium of endocardium.
Endocardial endothelium lines the cardiac chambers, covers the valvular cusps, chordae tendineae, and subendothelial connective tissue. It also has antithrombogenicity which inhibits blood coagulation thereby insuring regular flow through the heart.
What are valvular cusps made out of?
Valvular cusps are contain a core of dense connective tissue surrounded on both sides by endocardium.
How after invading the endocardium, can streptococcal bacterial infections in children and adolescents be life-threatening?
Streptococcal bacterial infection may lead to rheumatic heart disease which may cause inflammation of all three layers of the heart wall; however its most serious complication is an inflammatory effect on endocardium covering valves of the left side of the heart, which then become ulcerated, scarred, and deformed resulting in mitral insufficiency and aortic stenosis.
Where are myocytes derived from, what do they do, what allows them to do this?
Myocytes are derived from myoblasts of the crescent-shaped endocaridal tube.
They contract spontaneously thanks to gap junctions between adjacent cells that allow them to rhythmically contract the primitive myocardium.
In what orientation do myocytes wrap around the ventricular lumen during the bending of the primitive heart tube? Why?
Myocytes wrap around the ventricular lumen in a helical fashion making ventricular contraction analogous to wringing water from a wet towel, maximizing systolic output.
What is characteristic of cardiac muscle?
Intercalated disks my friend, intercalated disks.
Can myocytes regenerate after myocardial infarction?
No myocytes generally do not regenerate after injury since there are no satellite cells associated with them.
Why are myoctes stretched in patients with dilated cardiomyopathy?
Mutations occur in cytoskeletal proteins that disrupt intercalated disc morphology by dissociating junctions between myocytes and disrupting myofibrillar organization and contractile function.
What is the cardiac pacemaker?
Where are the perkinje fibers located and what do they form?
The cardiac pacemaker is the SA node becaue it contracts spontaneously at the fastest rate and therefore determines myocardial contractility.
The perkinje fibers are located in the ventricular endocardium and they form the left and right bundle branches of the conducting system.
What are the three layers of the aortic wall?
What do the inner and outer layers consist of?
The aortic wall consists of:
1) tunica intima - innermost, closest to the lumen, consists of endothelium and underlying connective tissue
2) tunica media - middle layer
3) tunica adventitia - outer layer, consists of dense connective tissue containing nutritive microvessels call the vasa vasorum.
What is the significance of the vasa vasorum?
The vasa vasorum supplies the outer media and adventitia since the wall thickness prohibits sifficient oxygen and nutrient diffusion from the lumen.
Which tissue abnormality characterizes Marfan syndrome?
Marfan syndrom is an inherited connective tissue disorder caused by molecular defects in the FBN1 gene that encodes the glycoproteins fibrillin-1. Abnormal elastic tissues in the body mark the disease. Mitral valve prolapse and weakening of the tunica media of the aorta resulting in rupture may occur. Loss of connective tissue support in heart valves creates a flappy valve that may contribute to heart failure.
What is an aortic aneurysm and why does Marfan syndrome increase its susceptibility?
An aneurysm is an abnormal localized dilation in the weakened wall of an artery. An aortic aneuryism occurs when the diameter of part of the aorta increases by 50% or more. Marfan syndrome weakens the connective tissue of the arterial walls increasing the susceptibility to aneurysms.
Why is the abdominal aorta susceptible to dilation and aneurysm formation?
The abdominal aorta lacks vasa vasorum, which may explain its susceptibility to dilation and aneurysm.
What makes up the thick tunica adventitia of the Superior Vena Cava?
The SVC contains bundles of type I collagen fibers and a dense vasa vasorum.
What structures are responsible for restricting overdistension in the SVC?
In the Tunica Adventitia - collagen I fibers
In the Tunica Media - tonic contraction of helical smooth muslce layers
What unique characterisitic does the IVC have and what is the function?
The IVC has bundles of longitudinal smooth muscle fibers within its tunica adventitia which are tonically contracted to assist blood flow against gravity into the right atrium.
Why are vasa vasorum more extensive in veins than in the arteries?
Vasa vasorum is more extensive in veins because veins carry deoxygenated blood so it needs another source of oxygen supply.