Lecture 24Outline of Last Lecture I. The Bone MarrowII. Ancestral Circulatory Plan III. Human Circulatory PlanIV. The HeartOutline of Current LectureI. Borders and Surface Anatomy of the HeartII. Blood Flow Through the HeartIII. The Heart ValvesIV. Conducting System of the HeartV. Nerves to the HeartVI. Blood Supply to the HeartVII. Histology of the HeartVIII. Fetal CirculationCurrent LectureI. Borders and Surface Anatomy of the Hearta. Upper right point: at third rib (costal cartilage), at the sternumb. Upper left point: at second rib, about 1.5 cm from sternumc. Lower left point: in the fifth intercostals space, in the left mid-clavicular lined. Lower right point: at sixth rib, about 1.5cm from sternumII. Blood Flow Through the Hearta. Avg resting adult resting heart rate = 72 bpmi. Do not beat in sequenceii. Atria contract together and then ventricles contract together b. R. Atrium R. Ventricle  Pulmonary Trunk  Pulmonary Circuit  L. Atrium  L. Ventricle  Aorta  Systemic Circuit  S/I Vena CavaIII. The Heart Valvesa. Large valves help direct the flow of bloodi. Do not move activelyii. Cusps are pushed open passively by the blood flowing through them iii. Pushed shut when blood starts to go the wrong way b. 2 pairs of heart of valves- all in a single oblique plane between the atria and ventriclesi. 1 pair btwn the atria and respective ventricles= atrioventricular (AV valves)1. Pushed shut when ventricles begin to contract and prevent ventricular blood from moving back up into the atria2. R. AV Valve: 3 cusps (tricuspid)3. L. AV Valve: 2 cusps (mitral valve)ii. 1 pair at base of the aorta and pulmonary trunk1. Aortic and pulmonary valvesa. Both are tricuspid2. Forces shut after the ventricles stop contractingBIOL_315 1nd Editioniii. Attached around the margins of the cups of the AV valves on ventricular side are chordate tenineae and papillary muscles 1. Papillary muscles contract when ventricles contract to prevent the AV valves from closing so hard that they turn inside out IV. Conducting System of the Hearta. Conducting system: part of the heart musculature that initiates each heart beat and determines the basic rate at which the heart pumps i. Coordinates the heartbeatii. Carries electrical impulses that signal the heart musculature to contractb. Pacemaker of the heart – sinoatrial node i. Develops from the sinus venosus, the heart chamber where the heartbeat originates in the embryoii. the impulse then spreads throughout the cardiac muscle fibers of both atriac. fibrous skeleton of the heart= barrier of connective tissue that prevents the impulse from spreading too rapidly from atria to ventriclesd. starts in SA Node  muscle of atria  atrioventricular nodeatrioventricular bundle, right and left crura  purkinje fibers, to the muscle of the right and left ventriclesV. Nerves to the Hearta. Heart rate can change by nervous inputb. Autonomic origin- throughout heart but concentrated at SA and AV Nodesi. Parasympathetic Ex) vagusii. Sympathetic c. Also visceral sensory nervesd. All nerves enter the heart directly after emerging from a network of nerves called = cardiac plexus i. Just posterior/superior to the heart VI. Blood Supply to the Hearta. Heart tissue supplied by large arteries and veins= coronary arteries and cardiac veinsb. Situated in the grooves btwn the heart chambersc. 3 main cardiac veins: great, middle , and smalli. All drain into larger- coronary sinus  R. atrium VII. Histology of the Hearta. Heart wall has 3 layersi. Endocardium: endothelium and loose connective tissue (internal)ii. Myocardium: muscular layer, pumps the blood, thickest layeriii. Epicardium: serous membrane, external layerVIII. Fetal Circulationa. Placenta: pancake-shaped organ attached to the wall of the mothers uterus, substances are exchanged btwn the blood of the fetus and blood of its mother i. Fetal blood picks up O and nutrients and rids of wasteii. Developing lungs need very little blood, only enough for growthb. Differences from postnatal circulation:i. Fetus has vessels to the placenta1. Umbilical arteries2. Umbilical vein3. Ductus venosusii. Bypassing the lungs: the fetal heart and arterial trunks1. Foramen ovale2. Ductus arteriosus3. If either of these ducts fail to close  patent ductus arteriosus and patent foramen ovalea. Patent =