t. innermost lumenal General Circulatory system heart and blood vessels walls have 3 layers (inside to outside) 1-Tunica interna: aka tunica intima layer--lumenal layer epithelium--endothelium simple squamous epithelium squamous cells + underlying CT + SMFs 1 2-Tunica media: middle layer (media ='middle') muscle fibers (smooth or cardiac). 3-Tunica externa: aka tunica adventitia outermost layer dense irregular CT. Smaller blood vessels no t. externa and/or t. media interna is usually present 2
3 = pump force pushes the blood through the CV system Mammalian heart right and left ventricles (RV, LV) right and left atria (RA, LA) auricle; lower, outer part of atrium auricle = 'ear' looks like a dog's ear. Pressure pushes blood into the atria 70% of the blood flows into the ventricles before atrial contraction Atrial contraction sends remaining blood into the ventricles. 4
stroke regulated total Ventricles contract, ejecting blood into the elastic arteries. Animal heart is myogenic muscle tissue generates contraction no exogenous stimulation rate (bpm) and volume (volume pumped per beat) by nervous and endocrine systems With adequate 0 2 and chemical energy heart will beat absence of all neural or hormonal stimuli. 5 Wall structure Tunica interna: endocardium. Small hearts (example: mouse) endocardium ;simple tissue: endothelium. Medium to large hearts subendothelial layer of loose CT. May contain elastic and collagen fibers sometimes smooth muscle fibers. Rat's heart ; subendothelial layer not visible. 6
7 Tunica media: myocardium. entirely cardiac muscle tissue; larger blood vessels and some adipose tissue. Tunica externa: epicardium. simple squamous epithelium + dense interwoven CT. Rat's heart ; dense C.T. may be too thin. Adipocytes 8
Cardiac 9 Special structures: Valves Two sets of one-way valves; prevent blood back-flow tricuspid and bicuspid valves (R and L AV) between atria and ventricles R and L semilunar valves between ventricles and aortic or pulmonary trunks Composed of two or three flaps of thick endocardium (dense CT). No myocardium or epicardium 10
tendinous papillary Chordae tendonae and papillary muscles Tension-cords prevent inversion of the tricuspid and bicuspid valves In ventricle s lumen cord; muscle. Ventricles contract, cords prevent valve inversion Papillary muscle contracts because the length of cords shortens during ventricular contraction. 11 The tunica media of all four chambers of the heart are continuous from the RA to the LA from the interatrial septum to the interventricular septum. Membrane impulse begins at sinoatrial (SA) node 'pacemaker' SA node lies near the opening to superior vena cava from SA node the membrane impulse spreads to the LA. 12
Medium to large hearts, Purkinje fibers cardiac muscle fibers; unusually high diameter rapidly transmits electrical signals through the atrial cardiac muscle tissue. Only weakly contractile; for high speed conduction more abundant in the ventricles 13
Impulse reaches the inter-atrial septum and the auricle 0.1 sec later. Atrial cardiac muscle tissue contracts instantly Bottom of the inter-atrial septum; impulse reaches the atrioventricular node (AV node) mass cardiac muscle fibers of unusually low diameter. speed of conduction slows Takes another 0.1 sec to pass through the AV node Delay provides time for ventricular filling. 15 Atrial tunica media thinner than that of the ventricles less force needed to pump blood into the ventricles. impulse leaves the AV node enters the inter-ventricular septum then the bundle of His > Bundle branches speed increases 16
Purkinje fibers extends down the interventricular septum and extend into ventricular wall smaller branches into the ventricular myocardium Membrane impulse reaches the upper ventricular walls only 0.1 after reaching the bundle of His. ventricles contracts together 17 The outer wall of the RV is much thinner than that of the LV. Less force is required to pump blood into the pulmonary trunk than into the aortic trunk. Thickness of the inter-ventricular septum = outer wall of the LV. LV lumen much more apparent in sections of the heart than lumen of the RV. 18
19 20
The heart sounds; closure of the two sets of valves. First sound ('lubb') does not occur when the atria contract, but rather when the ventricles contract closure of the tricuspid and bicuspid valves Second sound ('dupp') occurs when the ventricles relax closure of the semilunar valves 21 The depolarization and repolarization of the cardiac muscle tissue can be detected with electrodes placed on the skin Electrical patterns detected represent the EKG electrocardiogram 22
P wave is due to atrial depolarization QRScomplex ventricular depolarization T wave ventricular repolarization. no wave due to atrial repolarization included in the QRS 23