Perfusion and Heart Rate Homeostasis PDF

PERFUSION AND HEART RATE HOMEOSTASIS Perfusion describes the main goal of the arteriole system to provide adequate blood flow through capillary beds to ensure adequate oxygenation for normal cell /tissue/organ function. What is the importance of Oxygen? “Our body’s batteries” ATP is our body bat...

PERFUSION AND HEART RATE HOMEOSTASIS Perfusion describes the main goal of the arteriole system to provide adequate blood flow through capillary beds to ensure adequate oxygenation for normal cell /tissue/organ function. What is the importance of Oxygen? “Our body’s batteries” ATP is our body battery and drives all our cellular and enzyme function, Without oxygen we cannot make enough ATP batteries for our cells to function Hypoxaemia/Hypoxia led to ineffective perfusion Hypoxia is a broad term used for a condition where oxygen demand exceeds oxygen supply. As a result of hypoxia, ATP levels drop, cellular functions cannot be maintained, and–if the insult lasts long enough–cells die Outcome :cell tissue damage, organ failure, cell death THE CARDIOVASCULAR SYSTEM The circulatory system and ability to ensure blood pressure and blood flow are adequate to deliver oxygen to all cells, tissues and organs. Functions of the CVS The cardiovascular system acts as a dynamic transport system: Deliveries substances ( 02, nutrition, hormones) to cells all over the body Removes Co2 and metabolic end products from tissues and delivers it to the appropriate organ for break down (liver, lung or kidney) Temperature homeostasis-> A key function of the cardiovascular system is to exchange heat between the internal body tissues, organs and the skin to maintain internal temperature within normal range. Blood circulation approx. 5.5 L/min. Therefore, blood circulates around the body approx. every minute. HEART RATE HOMEOSTASIS Heart rate is also known as pulse rateIt is the number of times a person’s heart beats per minute (bpm). Resting heart rate (RHR) -> BETWEEN 50 AND 90 BEATS PER MINUTE (BMP) varies during the day and decreases during the night. Heart rate varies with many influences Day and night Body Position/ Level Of Activity Air Temperature Emotional State (Positive Or Negative) Stress/Pain Age Heart Condition Medication. Children The Heart rate/pulse of children is higher than adults It falls gradually with age with children Foetal heart rate-> Approx. 110-160bpm ADULTS Resting non-athlete adult – 60-90BPM Parasympathetic Keeps within normal resting level (Dominant during normal heart rate/rest/sleep) Sympathetic Increases heart rate HR ( Dominant during exercise/activity) THE HEARTBEAT The heartbeat causes a wave or ‘pulse’ that is transmitted throughout all arteries in the body. You can feel a pulse in any artery lying close to the skin surface. The entire heart contracts in series first the atria then the ventricles However it is considered a single contraction of the heart (0.8sec) 2 Types of cardiac muscle cells achieve a heartbeat Conducting cells Contractile cells Myocardial cells are the contractile cells The heart’s myocardial cells are interconnected by gap junctions which make up the myocardium. Gap junctions permit conduction of electrical current An electrical current/impulse that originates in a group of myocardial cells (the nodal cells) can spread to all cells in the heart. THE HEARTBEAT IS CONTROLLED BY 2 SYSTEMS: THE CONDUCTION SYSTEM CARDIAC CENTRE AND AUTONOMIC NERVOUS SYSTEM THE CONDUCTION SYSTEM The system includes Sinoatrial node (PACEMAKER) Atrioventricular node Interconnecting pathways that connect SA and AV nodes and distribute stimulus through myocardium. The AV node is connected to the AV bundle (bundle of HIS)that burrows through the septum and connects with purkinje fibres that are found within the walls of the myocardium. A system of specialized ‘Inbuilt’ cells in the heart. Initiates and distributes electrical impulses in ONE direction ONLY from SA node to the Purkinje fibers (cardiac cycle)’ 1. The Sinoatrial (SA) node (PACEMAKER) A tiny cell mass in the posterior wall of the right atrium. Connected to AV node by internodal pathway The SA node generates 90 action potentials per minute. – The electrical activity spread very rapidly to adjacent myocardial cells in both the right and left atria 2. The Atrioventricular (AV) node Situated between the atria and ventricles in the floor of right atrium. Receives impulse from SA node (Step 2) and delays impulse (Step 3) 3. Atrioventricular bundle (Bundle of His) (3) The Bundle branches are situated in the septum and receive input from AV node. The electrical activity is taken in two pathways through the left and right bundle branches (no 4). This conducts to the (5) Purkinje fibres in the right and left ventricle wall (myocardium). 5. Purkinje fibres(ventricular contraction) Purkinje fibres bore into the ventricle walls The rapid conduction rate means that ventricle contraction begins just 0.1 to 0.2 secs after atrial contraction. CARDIAC CENTRE The Cardiac Centre is one of the vital centres in the medulla oblongata within the brain stem. It co-ordinates the autonomic nerve supply of the heart. If any injury or disorder were to affect the cardiac centre the heart would stop beating immediately CARDIAC CYCLE Cardiac cycle: repetitive pumping process that begins with onset of contraction and ends with beginning of next contraction The cardiac cycle is marked by a succession of pressure and blood volume changes within the heart. 2 phases: Systole = contraction of heart muscle (ventricular contraction) Diastole = relaxation of heart muscle (ventricular relaxation) Principles Blood moves through the circulatory system from areas of higher to lower pressure. Contraction of the heart produces pressure. When the right and left atria contract (simultaneously) they pump out the same volume of blood per beat as does the right and left ventricles during their contraction P H A S E S O F T H E C A R D I A C C YC L E 1.Heart relaxed: passive ventricular filling. 2.Atrial contraction 3.Ventricular contraction-isovolumetric 4.Ventricular systole: period of ejection. 5.Ventricular diastole: period of isovolumetric relaxation. From the perspective of the ventricles  1. Before a cardiac cycle begins, all chambers are relaxed As the blood moves into the atria, much of it flows into the ventricles for two reasons: (a) The AV valves are open and (b) atrial pressure is slightly greater than ventricular pressure. This time period when blood is passively moving into the ventricles is called passive ventricular filling 2. The SA node fires which stimulates atrial contraction. Atrial contraction begins the cardiac cycle. As the atria contract, they ‘top up’ the ventricles by pumping blood into them. The semi lunar valve remains closed, so ventricles fill. 3. The Purkinje fibers stimulate ventricular systole (contraction). As the ventricles contract, ventricular pressures increase and causes 2 important value changes : AV valves forced closed. Semilunar valves remain closed at this point as well. As Ventricular contraction continues, and ventricular pressures rises. This brief interval is called the period of isovolumetric (iso, same) contraction because the volume of blood in the ventricles does not change, even though the ventricles are contracting. 4. Ventricular contraction continues, and ventricular pressure builds until it overcomes the pressures in the pulmonary trunk and aorta. As a result, the semilunar valves are pushed open, and blood flows from the ventricles into those arteries. 5. The ventricles relax (diastole) Ventricular pressures decrease below the pressures in the pulmonary trunk and aorta. Blood begins to flow back toward the ventricles, causing the semilunar valves to close. With closure of the semilunar valves, all the heart valves are closed, and no blood flows into the relaxing ventricles during the period of isovolumetric relaxation. C L I N I C A L A P P L I C AT I O N : H E A R T S O U N D S U S I N G A S T E R E O S C O P E/ ECG Heart sounds-> LUB-BUB First heart sound lubb it is the beginning of the ventriculatìr systole Second heart sound dupp its the beginning of the ventricular diastole, lasts longer. ELECTROCARDIOGRAM (E.C.G.)-> it is a non-invasive procedure that involves placing electrodes on the skin and recording the impulses detected. It simply provides a ‘picture’ of the electrical activity of the heart. P wave: depolarisation of the atria QRS wave: depolarisation of ventricles T wave: Repolarisation of atria Heart abnormalities can be quickly detected on an ECG tracing.