The Heart: Pulmonary and Systemic Circulations PDF

# Pulmonary and Systemic Circulations in Relation to the Heart - The circulatory system is responsible for transporting materials throughout the human body throughout life. - Systemic circulation: transports oxygenated blood to the body and deoxygenated blood back to the heart. - Pulmonary circula...

# Pulmonary and Systemic Circulations in Relation to the Heart - The circulatory system is responsible for transporting materials throughout the human body throughout life. - Systemic circulation: transports oxygenated blood to the body and deoxygenated blood back to the heart. - Pulmonary circulation: transports deoxygenated blood to the lungs and oxygenated blood back to the heart. - Capillary networks are located in the lungs, upper and lower body. ### KEY - **O2-rich blood** - **O2-poor blood** # Blood Flow Through the Heart - **Superior vena cava:** returns blood from head and upper limbs. - **Right pulmonary veins:** return blood from right lung. - **Pulmonary semilunar valve:** located between right ventricle and pulmonary artery (opens during ventricular contraction). - **Right atrium:** receives deoxygenated blood from superior and inferior vena cava. - **Right atrioventricular valve:** allows blood to flow from the right atrium to the right ventricle (opens during atrial contraction). - **Right ventricle:** pumps deoxygenated blood to the pulmonary artery. - **Inferior vena cava:** returns blood from trunk and legs. - **Aorta:** largest artery in the body, carries oxygenated blood from the left ventricle. - **Right and left pulmonary arteries:** carry deoxygenated blood to the lungs. - **Left pulmonary veins:** return oxygenated blood from the left lung. - **Left atrium:** receives oxygenated blood from the pulmonary veins. - **Aortic semilunar valve:** located between the left ventricle and aorta (opens during ventricular contraction). - **Left atrioventricular valve:** allows blood to flow from the left atrium to the left ventricle (opens during atrial contraction). - **Left ventricle:** pumps oxygenated blood to the aorta. - **Septum:** separates the right and left sides of the heart. # Cardiac Muscle Fibers - Cardiac muscle fibers are branched and interconnected by intercalated discs. - Intercalated discs contain desmosomes and gap junctions. - Desmosomes hold muscle fibers together. - Gap junctions allow ions to flow from one cell to another, creating a functional syncytium. # Specialized Conduction System Of The Heart - This system controls the heart rate and ensures coordinated contraction of the atria and ventricles. - The **sinoatrial (SA) node** is the heart's pacemaker. - The **internodal pathway** conducts impulses from the SA node to the AV node. - The **atrioventricular (AV) node** delays impulses slightly, allowing the atria to contract before the ventricles. - The **bundle of His** conducts impulses from the AV node to the ventricles. - The **right and left branches of the bundle of His** conduct impulses to the right and left ventricles. - **Purkinje fibers** spread impulses throughout the ventricles, causing ventricular contraction. # Pacemaker Cells - Generate electrical impulses that cause the heart to beat. - They have unique ion channels that create a slow depolarization called the pacemaker potential. - The pacemaker potential triggers an action potential, which causes the heart to contract. # Cardiac Muscle Cells - They have a different action potential than pacemaker cells. - The rapid rising phase is due to the opening of fast sodium channels. - The plateau phase is due to the opening of slow calcium channels. - The falling phase is due to the opening of potassium channels. # Excitation-Contraction Coupling In Cardiac Contractile Cells - This process connects the electrical activity of cardiac muscle to its mechanical contraction. - An action potential travels down T tubules. - Ca2+ enters the cytoplasm through L-type calcium channels, triggering the release of even more Ca2+ from the sarcoplasmic reticulum through ryanodine receptors. - The increased cytosolic Ca2+ binds to troponin. - This shift moves tropomyosin away from the myosin-binding sites on actin. - Cross-bridge cycling occurs, causing filament sliding and muscle contraction.