Physiological organization of CVS PDF

Physiological organization of CVS Prof. Mohammed Bendary  Learning Objectives By the end of this lecture, the student should be able to:  circulatory system contributes to homeostasis To maintain homeostasis, essential materials such as O2 and nutrients mus...

Physiological organization of CVS Prof. Mohammed Bendary  Learning Objectives By the end of this lecture, the student should be able to:  circulatory system contributes to homeostasis To maintain homeostasis, essential materials such as O2 and nutrients must continually be picked up from the external environment and delivered to the cells, and waste products must continually be removed. Homeostasis also depends on the transfer of hormones, important regulatory chemical messengers, from their site of production to their site of action. The circulatory system, which contributes to homeostasis by serving as the body’s transport system.  Components of the circulatory system 1. The heart is the pump that imparts pressure to the blood to establish the pressure gradient needed for blood to flow to the tissues. Like all liquids, blood flows down a pressure gradient from an area of higher pressure to an area of lower pressure. 2. The blood vessels are the passageways through which blood is directed and distributed from the heart to all parts of the body and subsequently returned to the heart. The smallest of the blood vessels are designed for rapid exchange of materials between the surrounding tissues and the blood within the vessels 3. Blood is the transport medium within which materials being transported long distances in the body, such as O2, CO2, nutrients, wastes, electrolytes, and hormones, are dissolved or suspended  Cardiovascular system (CVS) Heart BVs 1. Arteries & arterioles 2. Capillaries 3. Venules & veins  The heart Site The heart lies inside the chest cavity between the lungs (2/3 of the heart lies to the left but 1/3 lies to the right of the median plane) Size The size of the heart is roughly equals a closed man’s fist Shape The heart looks like an inverted cone with a base above and an apex is below at the 5th intercostal space at mid- clavicular line (MCL) Weight In an adult male, heart is about 300 gram (0.5 % of the body weight). Pericardial covering of the heart (pericardium) 1-Outer fibrous pericardium: 2-Inner serous pericardium: a-Parietal pericardium b-Visceral pericardium The wall of the heart 1. Epicardium (outer layer) 2. Myocardium (middle layer) 3. Endocardium (inner layer) Chambers of the heart 2 superior chambers called 2 atria Blood reservoir – right atrium (RA) – left atrium (LA). 2 inferior chambers called 2 ventricles -right ventricle (RV) Central pump -left ventricles (LV) Valves of the heart There are 4 valves. Found at entry & exit of each ventricle. On the fibrous tissue ring separating the atria from the ventricles. The valves allow blood flow in only one direction. 1-Atrio-ventricular (A-V) valves Tricuspid valve (T) separates RA from RV. Mitral valve (M) separates LA from LV. 2-Semilunar valves Pulmonary valve separate RV from pulmonary artery Aortic valve separate LV from aorta Muscle fibers of the heart 1-Ordinary fibers (contractile 99%) – Each cardiac muscle cell is relatively short, thick that are branched forming a branching network – Between the muscle fibers there are intercalated disc (ID) and gap junctions Desmosomes: a type of adhering junction that mechanically holds cells together. Gap junctions: are areas of low electrical resistance that allow action potentials to spread from one cardiac cell to adjacent cells. 2-Nodal fibers (non contractile) – Sinoatrial node (SAN) – Atrioventricular node (AVN) 3-Conducting fibers (non contractile) – AV bundle (Bundle of His) – Left bundle branch and right bundle branch. – Purkinje fibers  Conducting system of the heart 1-Sinoatrial node (SA) node The isolated SAN discharge rate is (100 +/- electrical impulse/ min). 2- Atrioventricular node (AV) (40-60/min) has the slowest conduction velocity (0.05 m/s) (why?) AVN delay 3-AV bundle (Bundle of His) 4- Left bundle branch (LBB) and right bundle branch (RBB). 5-Purkinje fibers Have the fastest conduction velocity (4 m/s) (why) The heart is a functional syncytium Since the AP can spread between adjacent cardiac cells, why the atria and the ventricles do not contract at the same time? No gap junctions join the atrial and ventricular contractile cells. The atria and the ventricles are separated by the electrically nonconductive fibrous skeleton that surrounds and supports the valves. So how the electrical impulses are transmitted from the atria to the ventricles??  Types of blood vessels 1. Arteries = Elastic vessels (prevent marked pressure variation) 2. Arterioles = Resistance vessels (offers the main resistance to blood flow in the circulation) 3. Capillaries = Exchange vessels 4. Veins = Capacitance vessels (reservoir) Vessels wall comparison  Types of capillaries Continuous, because these capillaries have no perforations and allow only small molecules to pass through. They are present in muscle, skin, fat, and nerve tissue. Fenestrated, due to small pores in the capillaries that allow small molecules to pass through. They are located in the intestines, kidneys, and endocrine glands. Sinusoidal or discontinuous, a type of capillary with large open pores—large enough to allow a blood cell through. They are present in bone marrow, lymph nodes, and the spleen, and are, in essence, the "leakiest" of the capillaries. "‫"وكل شئ عنده بمقدار‬ Lesser and greater circulation  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 pulmonary circulation consists of a closed loop of vessels carrying blood between the heart and the lungs. The systemic circulation is a circuit of vessels carrying blood between the heart and all body systems (except for the air sacs of the lungs, which are supplied by the pulmonary circulation). Systemic & Pulmonary circulations Blood distribution in CVS Respiration and Skeletal muscle contraction aids VR Clinical point