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The Heart and blood vessels Clinical Science Team School of Nursing and Midwifery The Heart and blood vessels Learning outcomes: The learner should be able to.. 1. 2. 3. 4. 5. 6. 7. 8. State the function of the heart and blood vessels Label a diagram of the heart, indicating its gross anatomical features State the function of the right and left sides of the heart State the function of the valves within the heart Describe the blood flow through the heart Outline the hearts electrical conduction pathway Describe the pressure changes that occur in the ventricles during the cardiac cycle Outline the neural and hormonal control of the heart The circulatory system List the components of the circulatory system: 1. 2. 3. 4. What are its main functions? a) b) c) The circulatory system The circulatory system consists of the following components: The Heart The blood vessels The blood The lymphatic system Functions of the Circulatory System • The circulatory system has the following main functions: • Transportation • Regulation • Protection Functions of the Circulatory System • Transportation: 1. Respiratory: transports oxygen to the tissues and carbon dioxide back to the lungs 2. Nutritive: Absorbed digested products are transported to the liver and to tissues 3. Excretory: Waste products from metabolism are transported to the kidneys for excretion in urine Functions of the Circulatory System • Regulation: –Hormonal: Hormones are carried from the endocrine glands to their target tissues –Temperature: The blood can be diverted to warm or cool the body Functions of the Circulatory System • Protection: • Clotting: Blood contains clotting factors and platelets- when activated prevent blood loss through clot formation • Immune: Blood contains leucocytes (white blood cells), cytokines, and complement which protects against infective pathogens The Heart Describe the Heart What is its function? The Heart The Heart The Heart The Heart • Slightly larger than the size of a fist • Contains four chambers • Right side supplies the pulmonary circulation • Left side supplies the systemic circulation • Two sides are separated by a muscular wall called the septum • Atria and ventricles are separated by a dense layer of fibrous tissue- the fibrous skeleton The Heart wall Myocardial tissue The Heart: Valves • The Heart contains four valves • The Tricuspid valve opens from the R atrium into the R ventricle • The Pulmonary (semilunar) valve opens from the R ventricle into the pulmonary artery • The Mitral valve opens from the L atrium into the L ventricle • The Aortic (semilunar) valve opens from the L ventricle into the Aorta The Heart: Valves Function of the valves • Situated at the entrance and exit of the ventricles • Ensure that blood moves only in one direction…Forward • Blood flows though the valves as a result of pressure changes Roche The Cardiac Cycle • Refers to the repeated pattern of contraction and relaxation of the heart. –Phase of contraction is called systole, –Phase of relaxation is called diastole • The heart has a two step pumping action: the atria contract simultaneously, followed approx 0.1-0.2 seconds later by the ventricles. cycle 5. Ventricles contract, about two thirds of the volume they contain is ejected, leaving one third called the end systolic volume 1. Atria fill with blood 4. Atria contract Contributing approx 20% To end diastolic volume 2.AV valve opens when pressure in atria exceeds ventricle The Cardiac cycle 3. Blood flows from atria to ventricles through open AV valve. This contributes approx 80% of end diastolic volume The Hearts conduction pathway conduct Nerve supply to the heart • The heart is influenced by autonomic nerves originating in the cardiovascular centre in the medulla oblongata – Consisting of sympathetic and parasympathetic nerves with antagonistic effects – The vagus nerves (parasympathetic) supply the SA node, AV node and atrial muscle. Parasympathetic stimulation decreases HR and force of contraction – Sympathetic nerves supply the SA node, AV node and the myocardium of the atria and ventricles. Sympathetic stimulation increases HR and force of contraction Factors affecting Heart Rate • • • • • • • • Gender Autonomic nerve activity Age Circulating hormones e.g adrenaline, thyroxine Activity and exercise Temperature The baroreceptor reflex Emotional states Waugh and Grant (2006) Cardiac blood supply • The heart receives its blood supply via the coronary arteries. • These arteries supply a huge network of capillaries • Ensures that myocardial cells are close to their blood supply • Diffusion of gases between the myocardial cells and capillaries occurs very quickly Cardiac blood flow • Cardiac blood flow is different from blood flow in other organs. • Blood flows around coronary vessels during diastole. • Myoglobin in myocardial cells stores oxygen. • This ensures that the heart muscle has a constant supply. Summary • The heart is a four chambered pump, which is effectively two pumps working together • The heart contains valves which function to ensure no backflow of blood • The wall of the heart is made up of the following layers: epicardium, pericardium, myocardium, endocardium • The heart has ‘autorhythmicity’ it will beat without outside nervous input • The heart has a specialist conduction pathwayensuring a smooth coordinated contraction, • Cardiac muscle contains large numbers of mitochondria, and the heart has an excellent blood supply Blood vessels Learning outcomes: 1. Compare the structure of an artery and a vein 2. Explain how the structure of an artery and a vein relates to its function 3. Describe the structure of a capillary and explain the physiological significance of this structure Blood vessel structure • Walls of arteries and veins are composed of three coats or tunics: 1. Tunica externa (composed of connective tissue) 2. Tunica media (composed of primarily of smooth muscle) 3. Tunica intima or interna (composed of three distinct layers, a) endothelium, b) basement membrane, c) internal elastic lamina) Blood vessels “ a tubular network throughout the body that permits blood to flow from the heart to all living cells of the body and then back to the heart. Blood leaving the heart passes through vessels of progressively smaller diameters, referred to as arteries, arterioles, and capillaries. Capillaries are microscopic vessels that join the arterial flow to the venous flow. Blood returning to the heart passes through vessels of progressively larger diameters, called venules and veins” Fox (2004) p 390 Blood vessel structure Differences between arteries and veins Why do we have different types of blood vessel? • Large arteries e.g. aorta are elastic arteries • Smaller arteries and arterioles are resistance arteries • Capillaries can be continuous, fenestrated or discontinuous, exchange takes place in these vessels • Veins are the capacity vessels, approx 64% of blood is here Distribution of blood in the vascular system Blood flow through the vessels Blood flow through vessels is directly proportional to the difference in pressure between the ends of the tube Blood flow through the vessels • Is inversely proportional to the resistance in the vessels. • Resistance- determined by blood viscosity, vessel length & vessel radius. • Blood viscosity & vessel length rarely change, radius can be changed by vasoconstriction (reducing radius) or vasodilation (increasing radius) Blood flow through the vessels Blood flow through vessels • Normally laminar, with the blood components arranged in layers • The plasma forms the outer layer & slides smoothly along the endothelium • Blood cells form the ‘axial’ layer in the centre of the blood stream • This allows the blood to flow smoothly, layers slide over each other, axial part moves fastest. Blood flow through vessels • When we take a blood pressure the sounds we here are caused by turbulent flow of blood • Turbulent flow -caused by change in vessel diameter, increase in velocity, & low blood viscosity