BIOL1410 Lecture #12 Cardiovascular System PDF

Lecture #12 The Cardiovascular System  The Circulatory System The circulatory system includes: The heart The blood vessels The blood The lymphatic system The circulatory system functions to: 1. Transport gases, hormones, lymph, nutrients...

Lecture #12 The Cardiovascular System  The Circulatory System The circulatory system includes: The heart The blood vessels The blood The lymphatic system The circulatory system functions to: 1. Transport gases, hormones, lymph, nutrients and waste 2. Protect against disease and fluid loss  The Chambers of the Heart There are four chambers in the heart: 1. The right atrium: Receives deoxygenated blood from the superior and the inferior vena cava as well as the coronary sinus 2. The left atrium: Connects to four pulmonary veins Receives oxygenated blood from the lungs 3. The right ventricle: Connects to the pulmonary trunkà 2 pulmonary arteries Sends deoxygenated blood to the lungs 4. The left ventricle: Connects to the aorta Sends oxygenated blood out to the rest of the body  The Left vs the Right Side of the Heart The left side of the heart carries oxygenated blood The right side of the heart carries deoxygenated blood Veins carry blood to the heart Arteries carry blood away from the heart Septa divide the chambers of the heart Interatrial septum: separates the atria Interventricular septum: separates the ventricles The interventricular septum is apparent from the outside of the heart as a shallow and often fat-covered groove called the interventricular sulcus  The Vessels of the Heart Vessels that enter and exit the heart include: The superior and the inferior vena cava Deliver blood into the right atrium of the heart The pulmonary veins Return blood that has been oxygenated in the lungs back to the heart Deliver the blood to the left atrium The pulmonary arteries Take deoxygenated blood from the right ventricle into the lungs to be oxygenated The aorta Takes oxygenated blood from the left ventricle and delivers it into systemic circulation  The Heart Wall The heart wall is composed of the: 1. Epicardium: makes up the visceral layer of the pericardium Made up of stratified squamous epithelium and connective tissue 2. Myocardium: this is cardiac muscle Arranged in spiral or circular bundles The portion of the heart that contracts Reinforced by connective tissue that is collectively referred to as the fibrous skeleton of the heart 3. Endocardium: endothelium that lines the inner surface of the heart and all of the blood vessels Composed of simple squamous epithelium and connective tissues  The Fibrous Skeleton of the Heart The fibrous skeleton of the heart is connective tissue fibers that surround the muscles of the heart and provide electrical insulation Prevents the stretching of the vessels and the valves of the heart which would eventually occur because of the continuous flow of pressurized blood through the heart There are also rings of connective tissue present between the atria and the ventricles Allow the openings of the heart to remain open at all times Valves provide the ability to close off certain portions of the heart inhibiting blood flow in certain directions The valves are specifically found at the atrioventricular groove between the atria and the ventricles  Cardiac Muscle Cardiac muscle cells are similar to skeletal muscle cells Also striated and composed of myofibrils Composed of thin and thick filaments that are arranged into sarcomeres Cardiac muscle cells differ from skeletal muscle cells because: Cardiac muscle cells are branched and uninucleate Adjacent cardiac muscle cells are bound to one another by the plasma membrane forming intercalated discs The disks are attached to one another via desmosomes and gap junctions Desmosomes prevent the adjacent cells from separating from one another during contraction Gap junctions allow the exchange of ions between adjacent cells Allows the heart to conduct electrical impulses and to have all of the cells contract in unison  The Conduction System Cardiac muscle cells that are specially modified to allow them to conduct an electrical impulse that spreads from cell to cell via gap junctions The modified cardiac muscle cells that form the conduction system do not contract The components of the conduction system include: 1. The sinoatrial nodeà located in the right atrium at the base of the superior vena cavaà the pacemaker 2. The atrioventricular node (AV node)à located at the base of the right atrium 3. The bundle of HISà electrically connects the atria to the ventriclesà referred to as the AV bundle 4. The bundle branches à connect the bundle of HIS to each of the ventricles 5. The Purkinje fibersà supply the signal through each of the ventricles  The Heart Valves There are two main groups of valves: 1. Atrioventricular valves 2. Semilunar valves 1. Atrioventricular valves: a. Bicuspid (mitral) valve Divides the left atrium and the left ventricle Contains two cuspsà bi b. Tricuspid valve: Divides the right atrium and the right ventricle Contains three cuspsà tri The chordeae tendinae: Attach the cusps of the valves to the cardiac muscleà papillary muscles Composed of collagen connective tissue Referred to as the ‘heart strings’  The Heart Valves 2. Semilunar valves: These contain three cusps each Chordae tendineae are not used to anchor these valves to the papillary muscles a. The aortic semilunar valves divide the left ventricle and the aorta b. The pulmonary semilunar valves divide the right ventricle and the pulmonary trunk  The Location of the Heart The heart is located within the mediastinum The coverings of the heart include the: 1. The pericardium is a double walled sac that surrounds the heartà 3 layers Layer 1 is the fibrous pericardiumà the outermost layer composed of dense irregular connective tissue Anchors the heart to surrounding tissue such as the diaphragm and large vessels such as the aorta Layer 2 is the serous pericardiumà consists of 2 layers The parietal layer is fused to the fibrous pericardium Together the fibrous pericardium and the parietal layer make up the pericardial sac The visceral layer is called the epicardium and it is fused to the surface of the heart Functions as a key portion of the heart wall The pericardial cavity is the area between the visceral layer and the parietal layerà fluid filled to provide lubrication  The Circulatory Route Adult circulation is different from fetal circulation 1. Adult circulation: a. Pulmonary circulation functions to deliver and return blood to and from the lungs for oxygenation Deoxygenated blood in the right atrium is moved into the right ventricle The right ventricle passes deoxygenated blood to the lungs via the pulmonary arteries Blood that has been oxygenated in the lungs is then returned to the left atrium via the pulmonary veins  The Circulatory Route 1. Adult circulation: b. Systemic circulation functions to deliver and return blood to and from the entire body The left atrium passes oxygenated blood to the left ventricle The left ventricle then passes the oxygenated blood to the aorta which sends the blood out to the body The oxygenated blood then arrives at the organsà oxygen is removed from the blood by cells which also load carbon dioxide waste into the blood Nutrients are also delivered to cells by the blood and waste from metabolism is added by the cells into the blood The dirty blood rich in carbon dioxide and metabolic waste is then returned to the right atrium via the superior vena cava (upper body) and the inferior vena cava (lower body)  The Circulatory Route 2. Fetal circulation: In a developing fetus the lungs and the liver are non-functional The non-function of these organs significantly caps their oxygen and nutrient requirementsà blood is therefore shunted/diverted away from these organs The placenta is the site of gas and nutrient/waste exchange between the mother and the fetus The oxygen and nutrients are provided to the fetus from the mother’s blood via the placenta Wastes and carbon dioxide produced by the fetus are delivered to the mother’s blood via the placenta  The Circulatory Route 2. Fetal circulation: Because the fetal lungs are non-functional the blood pressure on the right side of the fetal heart is higher than the pressure on the left side of the heart This is the opposite of the situation in adult circulation The fetal heart has an opening called the foramen ovale located between the right atrium and the left atrium that allows the exchange of blood between the two sites This opening closes shortly after birth once the lungs become functional and the pressure on the left side of the heart becomes higher than the right side of the heart  The Circulatory Route 2. Fetal circulation: In the fetus systemic and pulmonary circulation still take place but with modifications In order to shunt blood away from the liver the ductus venosus diverts blood entering fetal circulation from the umbilical vein to the inferior vena cava Once blood enters the fetal heart via the inferior vena cava it is diverted away from the lungs by the foramen ovaleà moves blood directly from the right atrium to the left atrium The ordinary route would be from the right atrium to the right ventricle and onto the lungs  The Circulatory Route 2. Fetal circulation: Blood that does pass from the right atrium into the right ventricle and onto the pulmonary trunk is diverted into the aorta via the ductus arteriosusà bypasses pulmonary circulation once more The fetal lung still requires adequate blood supply to support the growth and development of the fetal lung From the aorta the partially oxygenated (mixed) blood is returned to the placenta via the umbilical arteriesà enters into maternal circulation  Coronary Circulation Oxygenated blood must also be delivered to the myocardium in order to provide oxygen and nutrients to these cellsà coronary circulation From the left ventricle oxygenated blood that is delivered to the aorta will enter into coronary circulation via two aortic branches The right and left coronary arteries The left coronary artery supplies the left side of the heart with oxygenated blood The left coronary artery branches into the: Anterior interventricular arteryà supplies the interventricular septum and the anterior wall of both ventricles Circumflex arteryà supplies the left atrium and the posterior walls of the left ventricle  Coronary Circulation The right coronary artery supplies the right side of the heart and branches into the: Posterior interventricular arteryà supplies the posterior ventricular walls Right marginal arteryà supplies the myocardium Blood then flows from the coronary arteries into the arterioles Arterioles then transition into capillaries which supply the myocardium Capillaries then transition into venules Venules then transition into cardiac veins Cardiac veins then transition into the coronary sinus The coronary sinus drains deoxygenated blood into the right atriumà sent to the lungs  Blood Vessel Anatomy The lumen is the central area of the vessel that contains the blood The tunica intima is the innermost layer of the blood vessel In direct contact with blood that is flowing in the lumen Composed of simple squamous endothelium that is continuous with the endothelial lining of the heart The tunica media is circularly arranged smooth muscle and sheets of elastin The tunica externa is the outermost layer of the vessel Composed of loosely arranged collagen fibers Anchors the vessel to surrounding fibers Protects and reinforces the vessel  Blood Vessel Arrangement From the heart blood flows into arteries From the arteries blood flows into arterioles From the arterioles blood flows into capillaries From the capillaries blood flows into venules From the venules blood flow into veins From veins blood flows back to the heart  Blood Vessel Anatomy Arteries: Transport blood away from the heart Two types of arteries: 1. Elastic arteries: contain elastin mainly located in the tunica media but also in the other two layers Example: the largest arteriesà aorta 2. Muscular arteries: contain more smooth muscle than elastin and the smooth muscle is mainly concentrated in the tunica media Example: most of the arteries in the body including the coronary artery Arterioles: These are the smallest arteries Very muscular vessels that function to regulate the flow and pressure of blood  Blood Vessel Anatomy Capillaries: Only contain a tunica intimaà endothelium and basement membrane only In the capillaries nutrients, wastes and gases are exchanged with cells Capillaries then merge and become venules Venules: These are the smallest veins (analogous to arterioles) There are two typesà small and large Small venules are composed only of the tunica intima Large venules are composed of a very thin tunica intima and a tunica externa Veins: Function to return blood back to the heart Contain valves in order to prevent backflow Especially important in the legs where gravity opposes motion Have a very large lumen and a thin tunica intima Prone to collapse