Chapter 12: The Circulatory System Anatomy Bowl prep study guide by Kush Bhorania

Overview: Understand… Basic components of the circulatory system. Understand what it means to have a closed circuit of blood vessels. Understand anatomy of heart, blood supply to the heart muscle, cardiac cycle, conducting system of heart, structure & function of blood vessels. Understand circulation, blood pressure, and pulse.

Anatomy of Heart Left atrium  lies anterior to esophagus. Right atrium and right ventricle make up most of the anterior view in anatomical position. Apex  formed by the left ventricle. Covering sac is called pericardium and is fibrous. Three major walls: a) myocardium – thick cardiac muscle. b) endocardium – inner lining that is very smooth. For example, it lines the muscles that close the mitral valve. c) epicardium- layer making up the heart itself. Questions to think about: What are the implications of having a fibrous sac around the heart? Why is it important for endocardium to be a smooth layer? What would happen if it was not smooth layer?

Understand the role of the valves during cardiac cycle Blood is brought into the right atrium from superior vena cava and inferior vena cava. The blood is then directed into the right ventricle by tricuspid valve. Blood is then pumped into pulmonary trunk from which deoxygenated blood is carried to the right and left lungs via pulmonary artery. Oxygenated blood is returned to the heart (left atrium, specifically) via the pulmonary veins. Blood is then directed into the left ventricle by mitral valve . The left ventricle contracts and pushes blood through aortic valve into the aorta. Things to consider What is the significance of superior and inferior vena cava. Why is the blood directed as opposed to simply flowing through the valves of heart? Why is the aorta so massive? What would happen to left ventricle if mitral valve stopped working?

Systole vs Diastole ? Ventricular systole refers to contraction of ventricle, closure of Atrioventricular valves, and opening of aortic and pulmonic valves. Ventricular diastole refers to contraction of atrium, but ventricular relaxation, and opening of Atrioventricular valves but closure of aortic and pulmonic valves. Something to consider: Blood pressure against aorta is highest in this artery during which cycle systole or diastole? Why? Blood fills right and left coronary arteries during diastole. Can you see why?

Conducting System of Heart Understand that the SA node initiates the contraction of the heart and that the nervous system only regulates this contraction. SA node  AV node  AV bundle (bundle of His)  Purkinje fibers. SA node is located near superior vena cava. AV node is located near opening of coronary sinus. Understand that there is a delay in signal through the initial part of conduction system so that proper flow of blood is maintained.

Structure of arteries, veins, and capillaries Tunica adventitia is outermost layer. Tunica media of arteries and veins is different in thickness. Understand why. Why are the capillaries only one layer? So that maximum gas exchange is allowed. Things to consider: 1) Pressure gradient in arteries vs veins vs capillaries. 2) Where is blood volume the greatest? Why? 3) Which have valves?

Circulation overview: Pulmonary circulation Systemic circulation Hepatic circulation Fetal circulation Be sure to understand the difference in fetal circulation from adult circulation.

Pulmonary circulation Blood enters superior and inferior vena cava which is then received by right atrium. The opening of inferior vena cava into right atrium has a valve but the opening of superior vena cava does NOT have a valve. This is because the inferior vena cava must work against gravity whereas the blood in superior vena cava is moved by the help of gravity. Blood from right atrium is DIRECTED into right ventricle by opening of tricuspid or right atrioventricular valve. The pulmonic valve is closed at this time. Blood from right ventricle is then DIRECTED into pulmonary trunk via pulmonic valve that is open. At the same time, the tricuspid valve is closed. The closing of this valve is directed by muscles in right ventricle (called papillary muscles). Blood from pulmonary trunk moves through pulmonary arteries to lungs. Note that the blood in pulmonary artery is deoxygenated. The oxygenated blood is picked up by pulmonary veins and returned to left atrium.

Systemic Circulation (from previous slide)…blood in left atrium is oxygenated. This blood is directed into left ventricle by mitral or bicuspid valve. During this stage the aortic valve is closed and right ventricle is filling with blood (diastole). Blood from the left ventricle is then directed into aorta by aortic valve (open during ventricular systole). The mitral valve is close at this time so that left atrium may collect blood from pulmonary veins. The aorta has three parts: Ascending part, Arch, and Descending part. The ascending part delivers blood to the heart itself via the coronary arteries. The arch of aorta delivers blood to head, neck, and upper extremity. The descending part delivers blood to everything below the level of heart. Consider: How would the pressure in systemic circulation differ from pressure in pulmonary circulation? Is there any difference?

Hepatic Portal Circulation The veins carrying the blood from spleen, stomach, pancreas, gallbladder, and intestines do NOT pour directly into inferior vena cava. The blood first goes through the liver in order to maintain blood glucose level and to detoxify poisonous substances that may be present in blood.

Fetal Circulation Lungs in fetus are NOT functional until the baby takes its first breath outside the uterus. The primary source of nutrients to the fetus is from the placenta. However, there is NO mixing of blood between the fetus and mother. There is gas exchange via capillaries. Be sure to understand the role of shunts: ductus venosus, foramen ovale, and ductus arteriosus.