Organ Systems I: Heart (Part 1)
The pumping action of the heart gives strength and direction to circulation. Cardiomyopathy can lower strength, valve issues can compromise direction.
Heart location: in the middle mediastinum, posterior to sternum, slightly to the left and between the 2nd and 6th ribs. The right half is forward, and apex points down and left.
LAYERS
PERICARDIUM is a bursa surrounding the heart, in two layers:
1) Fibrous pericardium, thick CT level adhered to sternum, diaphragm and parietal pleura (lung bursa)
2) serous or "true" pericardium, slippery layer reduces friction between heart and adjacent structures, forms pericardial cavity full of lubricant. "Fist in a balloon" model. Two layers of the serous layer:
a) parietal -- outer layer adhered to inner surface of fibrous percardium
b) visceral serous pericardium = epicardium, moves a lot, "invests" heart, CT adhered to exterior surface
Myocardium = cardiac muscle, three kinds:
1) bulbospiral muscle - wrings out blood
2) pectinate muscle = thin atrial cardiac muscle fibers
3) trabeculae carnae = thick ventricular cardiac fibers on inner surface
Endocardium = CT lining inner surface
SIDES
right to lungs
left to body
tri before you bi
THE PATH OF BLOOD
--superior and inferior vena cava bring deoxygenated blood from body
--right atrium (site of fossa ovalis, pectinate muscles, auricle, drainage of coronary sinus)
--tricuspid valve aka right AV valve, 3 cusps (closing activated by early ventricular contraction (papillary muscles & chordae tendinae prevent eversion)
--right ventricle
--pulmonary semilunar valve (cusps are cups that catch blood during diastole and close the valve when full)
--pulmonary trunk
--pulmonary arteries (left and right)
--lungs
--pulmonary veins
--left atrium (little pectinate muscle, has vestigial auricle)
--mitral valve aka mitral aka left AV valve (prolapse is common here) (closing = lubb sound, semilunars are open)
--left ventricle
--semilunar valve (closing = dupp sound)
--aorta
SYSTOLE = expulsion of blood from heart
--AV valves are closed when ventricular contraction increases blood pressure and cusps are pushed together
--semilunar valves are pushed open by blood ejection
DIASTOLE = filling of the heart
--AV valves are open as blood flows into heart
--semilunar valves prevent backflow from lungs or body
HEART SOUNDS
--lubb = closure of AV valves
--dupp = closure of semilunar valves
CORONARY ARTERIES
--left CA branches into anterior descending (interventricular) and circumflex arteries. Circumflex anastomoses with right coronary artery.
--right CA branches into marginal and posterior descending (interventricular)
--coronary blood perfusion occurs during diastole (filling) as semilunar valves close and backflow from the aorta pushes into coronary arteries (low pressure)
CORONARY VEINS
--great cardiac vein parallels anterior descending artery
--middle cardiac vein parallels posterior descending artery
--small cardiac vein parallels marginal artery
--coronary sinus drains into right atrium
CORONARY BYPASS
--involves inserting a shunt form the aorta to the affected coronary artery beyond the point of occlusion (due to atherosclerosis, etc)
--shunt vessel usually stolen from saphenous leg vein (for small ones) or internal thoracic arteries such as anterior descending (mammary)
CT ANGIOGRAPHY
--xrays read density of tissue
--conventional xrays are usually adjusted ("windowed") to detect bones and pass thru other tissues, but can be adjusted to read grayscales
--a CT (computed tomography) is a series of xrays used to mathematically recontruct the inner densities of an organ into a 3D image
--images can be windowed to focus on any density of tissue
--contrast agents such as iodine can be used to highlihgt vessels