The circulatory systemThe circulatory system consists of two major sub-circuits, the systemiccirculation and the pulmonary circulation. 2
The circulatory system The Heart: Four chambered double pump. Blood vessels: Carry Blood from the heart to the vital organs and back. Arteries carry blood away from the heart and branch to form the arterioles. They all carry oxygenated blood except the pulmonary arteries. Veins return blood to the heart and start as venules. They all carry deoxygenated blood except the pulmonary veins. Blood capillaries are found as a network Between arteries and veins. 3
Human and animal heartsWhich one is a human heart? 4
Exterior structure of the heart • Inflow ports consisted of the superior and inferior vena cava and pulmonary veins. • Outflow ports mainly the aorta, and pulmonary arteries. 5
Structure of the heart (interior view) • Atria (right atrium and left atrium) • Ventricles (right ventricle and left ventricle) Right and left heart sides are normally completely separate. Right atrium and left ventricles open in the corresponding ventricles by a valve. 6
Atrioventricular valves The atria are connected to the ventricles by atrioventricular valves. Tricuspid valve on the right side. Bicuspid valve (mitral valve) on the lefty side The valves are passively operated by the difference in blood pressure between the heart champers. The papillary muscles are connected to the valves by tendons called Chordae tendinae which help to keep them in place. There are other valves, called semilunar valves at the entrance of the aorta and the pulmonary artery. They are one way valves!. 7
Blood vesselsArteries have muscular walls and smaller lumen.Veins have thinner walls and bigger lumen.Blood capillaries are single layer of endothelial cells.Arteries are high pressure vessels while veins have lower pressure and bloodflow is helped by valves to go back to the heart.
Histology of the blood vessels Both arteries and veins are Artery Vein composed of three coats (layers), tunica externa Tunica (tunica adventitia), tunica interna media and tunica interna Valve (intima). Elastin Tunica media Tunica interna consists of three parts. Elastic tissue Tunica fibers, the basement externa membrane and the inner endothelium. Serosa The blood capillary is single cell thick which is endothelium. Capillary 10
Cardiac cycleCardiac cycle is a repeated pattern of contraction and relaxation. The phase ofcontraction is systole and relaxation is diastole.Average heart rate (beat per minutes) is ~ 75 B/min cardiac cycle lastsabout 0.8 sec. 0.5 sec 0.3 sec diastole systole Even before contraction of atria, the ventricles are filled with blood by up to 80%, the remaining 20% enter the ventricles after contraction of atria. 11
States of heart during cardiac cycle When the ventricles fill up with blood this is called end diastolic volume (EDV). The ventricle contract during systole to eject two third of the amount it contains (stroke volume (SV)). Stroke volume (SV): volume of blood ejected during one cardiac cycle. The one third left is the end-systolic volume (ESV). 12
-Right Atrium = RAHeart and Circulation -Left Atrium = LA -Right Ventricle = RV -Left Ventricle = LV1- Venous blood containing CO2 returns from body tissues to RA Tricuspid valve2- From RA RV Pulmonary artery3- From RV Lungs Pulmonary vein4- From Lungs LA5- From LA Bicuspid valve LV Aorta6- From LV Body
Pressure changes during cardiac Cycle-Ventricles are filled with blood (e.g. 120 ml) and ventricular muscle contracts without-change in length this is called isovolumic contraction: Isovolumetric No change Increase in contraction in volume intraventricular pressure Intraventricular pressure > Aortic pressure Ejection Ejection Volume and pressure decrease Isovolumic relaxationThe pressure produced by the left ventricleduring systole is about 120 mmHg and duringdiastole is about 80 mmHg. The blood pressureis represented by systole/diastole = 120/80.
Heart Sounds- The valves between atria and ventricles are called atrio-ventricular (AV) valves-and the valves between right ventricles and pulmonary artery + left ventricle and-aorta are called semilunar valves.- Closing of the AV valves and semilunarvalves produces sounds that can be heardby stethoscope. These sounds are calledheart sounds. They sound like “lub-dub”.- First sound (“lub”) is produced by closureof AV valves. Second heat sound (“dub”) isproduced by closure of semilunar valves lub dub