Cardiovascular System 1 PDF

Cardiovascular System 1 Dr/ Mai Adawi Lecturer of Physiology FOMSCU Introduction  The Cardiovascular system includes heart and blood vessels.  Heart is a muscular organ that pumps blood throughout the circulatory system. It is situated in between two lungs in the mediastinum....

Cardiovascular System 1 Dr/ Mai Adawi Lecturer of Physiology FOMSCU Introduction  The Cardiovascular system includes heart and blood vessels.  Heart is a muscular organ that pumps blood throughout the circulatory system. It is situated in between two lungs in the mediastinum. It is made up of four chambers, two atria and two ventricles.  The musculature of ventricles is thicker than that of atria. Force of contraction of heart depends upon the muscles. Vascular system  The heart is a dual pump  Although anatomically the heart is a single organ, the right and left sides of the heart function as two separate pumps.  The heart is divided into right and left halves and has four chambers, an upper and a lower chamber within each half  The upper chambers, the atria (singular, atrium), receive blood returning to the heart and transfer it to the lower chambers, the ventricles which pump blood from the heart.  The vessels that return blood from the tissues to the atria are veins, and those that carry blood away from the ventricles to the tissues are arteries.  The two halves of the heart are separated by the septum, a continuous muscular partition that prevents blood mixing from the two sides of the heart.  This separation is extremely important because the right side of the heart receives and pumps O2-poor blood, whereas the left side of the heart receives and pumps O2-rich blood. Anatomical Overview  The two ventricles are separated by a muscular wall, the interventricular septum.  Located between the atrium and ventricle in each half of the heart are the one-way atrioventricular (AV) valves, which permit blood to flow from atrium to ventricle but not backward from ventricle to atrium.  The right AV valve is called the tricuspid valve because it has three fibrous flaps, or cusps. The left AV valve has two flaps and is therefore called the bicuspid valve (Mitral valve). Anatomical Overview  The opening and closing of the AV valves are passive processes resulting from pressure differences across the valves.  When the blood pressure in an atrium is greater than in the corresponding ventricle, the valve is pushed open and blood flows from atrium to ventricle.  In contrast, when a contracting ventricle achieves an internal pressure greater than that in its connected atrium, the AV valve between them is forced closed. Therefore, blood does not normally move back into the atria but is forced into the pulmonary artery trunk from the right ventricle and into the aorta from the left ventricle. The wall of the heart  Heart is made up of three layers of tissues:  1. Outer epicardium: A thin, external layer, the epicardium, that covers the heart formed of the visceral pericardium  2. Middle myocardium: which is composed of cardiac muscle and constitutes the bulk of the heart wall (myo means “muscle”)  3. Inner endocardium: A thin, inner layer, the endothelium, a unique type of epithelial tissue that lines the entire circulatory system  It lines the inner surface of the heart. Then, continues as endothelium of the blood vessels.  The Myocardium  It is the middle layer of wall of the heart and it is formed by cardiac muscle fibers or cardiac myocytes.  Myocardium forms the bulk of the heart and it is responsible for pumping action of the heart.  Myocardium has three types of muscle fibers:  i. Muscle fibers which form contractile unit of heart  ii. Muscle fibers which form pacemaker  iii. Muscle fibers which form conductive system. Properties of the cardiac muscle  The cardiac muscle has the following properties:  1- Rhythmicity  2- Excitability  3- Conductivity  4- Contractility  1- Rhythmicity  Rhythmicity is the ability of a tissue to produce its own impulses regularly. It is also called autorhythmicity.  There is a specialized structure in the heart called pacemaker. It is the structure of heart from which the impulses for heartbeat are produced.  The pacemaker of the heart is sinoatrial node (SA node). It is situated in the right atrium.  Rhythmicity  Rhythmicity of Different Parts of Human Heart  1. SA node : 70 to 80/minute  2. AV node : 40 to 60/minute  3. Atrial muscle : 40 to 60/minute  4. Purkinje fibers : 35 to 40/minute  5. Ventricular muscle : 20 to 40/minute.  Once an action potential occurs in any cardiac muscle cell, it is propagated throughout the rest of the myocardium via gap junctions and the specialized conduction system.  The entire heart becomes excited, triggering the contractile cells to contract and the heart to beat normally at 70 to 80 beats per minute.  If for some reason the SA node damage, the next-fastest engine (AV node) takes the control Properties of the cardiac muscle  2- Excitability:  Excitability is defined as the ability of cardiac muscle to respond to a stimulus. The initial response to a stimulus is electrical activity in the form of action potential. It is followed by mechanical activity in the form of contraction.  3- Conductivity:  Human heart has a specialized conductive system, through which impulses from SA node are transmitted to all other parts of the heart.  4- contractility:  Contractility is ability of the heart to contract after receiving a stimulus (impulse).  Conductivity of the heart muscle The conductive system of the heart  Conductive system of the heart is formed by the modified cardiac muscle fibers. These fibers are the specialized cells, which conduct the impulses rapidly from SA node to the ventricles. Conductive tissues of the heart are also called the junctional tissues.  Components of Conductive System in Human Heart :  1. SA node  2. intermodal pathways  3. AV node  4. Bundle of His  5. Right and left bundle branches  6. Purkinje fibers. The conductive system of the heart The conductive system of the heart SA node Both atria AV node Bundle of Hiss Right and left bundle branches Purkinje fibres pharmacy physiology lab4 Whole ventricular wall  Divisions of the circulation  The Pulmonary circulation is otherwise called lesser circulation. Blood is pumped from right ventricle to lungs through pulmonary artery.  Exchange of gases occurs between blood and alveoli of the lungs at pulmonary capillaries. Oxygenated blood returns to left atrium through the pulmonary veins.  Thus, left side of the heart contains oxygenated or arterial blood and the right side of the heart contains deoxygenated or venous blood.  Thus the right side of the heart carries de- oxygenated blood.  The left side of the heart carries oxygenated blood.  The pulmonary veins carry oxygenated blood from the lung to the heart.  The pulmonary artery carries deoxygenated blood from the heart to the lungs.  The cardiac cycle  Cardiac cycle is defined as the sequence of events taking place in the heart during each beat.  Duration of each cardiac cycle is about 0.8 second.  Each heartbeat consists of two major periods called systole and diastole. During systole, heart contracts and pumps the blood through arteries. During diastole, heart relaxes and blood is filled in the heart. All these changes are repeated during every heartbeat, in a cyclic manner.  The duration of systole is 0.3 second  The duration of diastole 0.5 second  Stroke volume: is the amount of blood pumped out by each ventricle during each beat.  The normal value of SV is 70 mL (60 – 80).  Cardiac output (CO): is the amount of blood pumped from each ventricle per minute. CO = SV × Heart rate (HR) the normal co is about 5L Thank you