10.17.96 Heart/cardiovascular system. Handout given: the Cardiovascular System: Is It For You? Function: transport of fluid, gases, wastes, nutrients control center: muscular pump called heart. two kinds of circulatory system. open system, in invertebrates eg worms, insects - blood=hemolymph, directly bathes organ, no vessels. CLOSED SYSTEM: circulatory system of more complex organisms. includes pump (heart), vessels: arteries, veins, capillaries), blood (carrier), spleen, bone marrow - creators of blood (hematopoiesis), lymphatic system. heart: double pump. obstacles include: keeping oxygen poor and oxygen rich blood separate, and transporting the blood through all chambers, and coordinating the two pumps to be effective working together. blood comes in R atrium through cranial and caudal vena cava, goes out R ventricle through pulmonary artery to lungs, comes into L atrium through pulmonary vein, leaves L ventricle through the aorta and goes to body. there's a septum separating the R and L sides: interatrial (IA) septum, and interventricular (IV) septum. L AV valve is the mitral valve, a bicuspid valve. R AV valve is a tricuspid valve. the aortic and PA valves are semilunar valves. The AV valves have papillary muscles and chordae tendinae, the semilunars do not. These valves are ENTIRELY passive. open/close only due to pressures. when valve is relaxed, it is open, when it is contracted, it is closed. The chordae tendinae act to retract valve if it starts prolapsing into the atrium. prolapsed valves would be a problem because you would not have complete contraction since the A and V are not totally separated. MURMURS: leaky valves. due to prolapsed or stenotic valves. With stenosis, pressure (P) will rise, since opening too narrow for blood to go through. heartbeat coordination: two phases. contraction (systole) and relaxation (diastole). blood fills the ventricles during DIASOTOLE and is pumped out in SYSTOLE. blood volume on R and L side are EQUAL, but the pressures are not equal. R side circulation lower pressure, since lungs are nearby, vessels larger and thinner walled PACEMAKER initiates contracting in the heart. pacemaker cells are active all the time. there are two kinds - low end: neurogenic pacemaker, meaning heartbeat initiated by neuron; high end: myogenic pacemaker, meaning specialized muscle cells in the heart initiate the heartbeat. vertebrates=myogenic. the pacemaker with the HIGHEST inherent rhythm will initiate the heartbeat, but there are some extra cells. main pacemaker cells are located in the SINO ATRIAL NODE. it's in the endothelial lining of the RA. can't see it grossly. so depolarization starts in RA, goes to LA w/in milliseconds, then goes into Atrial septum to the AV node. The AV node is the only electrical connection between the atria and the ventricles. so far, the speed of impulse propagation was 0.8 m/s, when it hits AV node slows to 0.1 m/s. then it hits a bundle of fibers called AV bundle, which has R and L branches going down walls of ventricles in the interventricular septum. this bundle is also called the bundle of His, but that isn't a veterinary anatomical term. the bundle branches extend laterally as purkinje fibers but we aren't allowed to call them purkinje fibers. note that fibers actually pass through the lumen of R ventricle --> called trabecula septomarginalis, as a shortcut to initiate contraction on the lateral side of the R ventricle. so once impulse gets to AV bundle it starts going at 5 m/s! so, the slowing of the impulse at the AV bundle is there so that the atria can contract and empty into the ventricle. you don't want all 4 chambers contracting at once. the atria contract first, then the ventricles. sometimes you have irregularities in the heartbeats...ARRYTHMIAs. there are multiple pacemaking regions in the heart, and sinoatrial node is the fastest. but sometimes, you get AV BLOCK, when the impulse gets stuck at the node, and the atria contract, but the ventricles don't get the impluse, so then you get a ventricular pacemaker taking over, at a slower rate. you feel skipped beats if this happens, and the next contraction is a doozy....usually only happens for a beat or two. you can also get a longer term ASYNCHRONY - which, if it happens randomly and chaotically is called FIBRILLATION. then you need a defibrillator - give jolt of electricity to heart, overriding the other pacemakers and trying to get the SA node back in charge. CPR: taking over for the heart and respiratory muscles. externally applied forces acting in place of heart and respiratory muscles, pumping blood and moving air. MEMBRANES: heart is lying in mediastinum. just like lungs, heart has a fluid filled bag surrounding it. this is the PERICARDIUM. the outer surface is the PARIETAL pericardium and the inside is the VISCERAL pericardium. there is a fluid filled cavity in the center filled w/serous fluid called the pericardial cavity. together this is called the serous lining of the heart. then you have one extra outer part called the FIBROUS pericardium, which is on the very outer part. Fibrous layer, in some mammals, has an additional extension ventrally anchoring the heart to the sternum, and this is called the sternopericardial ligament. there is also a phrenopericardial ligament extending to the diaphragm. recall the lung sitting in the thorax in its own serous lining called the pleura (mediastinal/parietal and visceral). there is no actual space between the parietal/mediastinal pleura of the lung and the fibrous pericardium of the heart. they are inimately associated. the heart itself has three tissue layers...the outermost epicardium , the bulk of the muscle - myocardium, and the inner endocardium, which extends through circulatory system as endothelium. the epicardium and the visceral pericardium are also intimately associated...no space between them. "skeleton" of the heart = annular rings these are cartilaginous rings around the AV and semilunar valves. ventricular muscle actually has origin on these annular rings. in ruminants, you do get ossification of the cartilage, changing the trigone region into the OSSA CORDIS. vessels also have three layers. outer tunica adventitia, middle tunica media, inner tunica intima (contiguous with endocardium), just endothelial cells. media can be either elastic, if you're near the heart, or muscular, if you're further away. see handout. arteries function as a pressure reservoir, a conduit, they control blood distribution (through arterioles, which can be active in vasomotion via contraction of smooth muscle, therefore redirection blood flow away from a region), dampen oscillation caused by turbulence of flow as heart pumps. do the elastic arteries can expand and contract to keep flow smooth. veins- volume reservoir. about 60% of all blood stored in veins. can get blood back to heart via pressure gradient (arteriole pushing blood in), venous valves, and thoracic pressure (breathing) - when you take a breath, abd pressure increases as thoracic pressure decreases. skipping fetal circulation - still need to know. final thing: specializations. vasa vasorum: if your artery is huge, it may need it's own blood supply, may have vessels coming into tunica media to supply the muscle. portal system: transfers blood from one capillary bed to another capillary bed, eg hepatic portal system which takes venous blood from GI tract to liver. anastomoses- arterial (collateral circulation) or arteriovenous (allows blood to be shunted) counter current exchange: blood flows in adjacent vessels in opposite directions to maximize heat exchange. in bird leg, artery is totally surrounded by veins. veins covered w/skin. so heat of arterial blood isn't lost to skin, it is carried backin by venous blood. gazelle has warm arterial blood going up to brain, cool venous blood going back down, which cooled off in nose area. artery forms capillary bed over veins before going to brain, transferring heat to veins to return to body, so hot blood isn't taken to brain.