The Cardiovascular System Lecture PDF

The Cardiovascular System The Heart Human Anatomy and Physiology ASC_4_498 Alison Alvarez  Tuesday, 26 October 2021 Blood vessels Structure and functi...

The Cardiovascular System The Heart Human Anatomy and Physiology ASC_4_498 Alison Alvarez  Tuesday, 26 October 2021 Blood vessels Structure and function of the heart Cardiac Cycle Electrical Activity of the Heart Congenital heart defects and Cardiovascular disease  Overview of the Cardiovascular System  Generalized structure of arteries, veins, and capillaries. Tunica intima Endothelium Subendothelial layer Internal elastic membrane Tunica media (smooth muscle and Valve elastic fibers) External elastic membrane Tunica externa (collagen fibers) Vasa vasorum Lumen Lumen Artery Capillary network Vein Basement membrane Endothelial cells Capillary © 2013 Pearson Education, Inc.  Venous system Arterial system Large veins Heart (capacitance vessels) Elastic Large arteries lymphatic (conducting vessels arteries) Blood vessels Lymph node Muscular arteries Lymphatic (distributing system arteries) Small veins (capacitance vessels) Arteriovenous anastomosis Lymphatic capillaries Sinusoid Arterioles (resistance vessels) Terminal arteriole Postcapillary venule Metarteriole Thoroughfare Capillaries Precapillary channel (exchange sphincter © 2013 Pearson Education, Inc. vessels)  Arteries Arteries carry blood away from the heart from the ventricles under high pressure. They have a narrow lumen with thick walls. The walls contain: – Collagen which maintains shape and support – Elastic fibres which allow arteries to stretch and recoil – Smooth muscle which contract causing the lumen to narrow. The inner lining is called the smooth endothelium which reduces friction between the blood and the vessel walls The are more elastic arteries closer to the heart which then become more muscular as they move away from the heart.  Arteries ELASTIC ARTERIES Large thick-walled arteries with elastin in all three tunics Aorta and its major branches Large lumen offers low resistance MUSCULAR ARTERIES Distal to elastic arteries – Deliver blood to body organs Thick tunica media with more smooth muscle ARTERIOLES Smallest arteries Lead to capillary beds Control flow into capillary beds via vasodilation and vasoconstriction  Capillaries Microscopic blood vessels Walls of thin tunica intima – In smallest one cell forms entire circumference Pericytes help stabilize their walls and control permeability Diameter allows only single RBC to pass at a time In all tissues except for cartilage, epithelia, cornea and lens of eye Provide direct access to almost every cell Functions – Exchange of gases, nutrients, wastes, hormones, etc., between blood and interstitial fluid Three structural types 1. Continuous capillaries 2. Fenestrated capillaries 3. Sinusoid capillaries (sinusoids)  Capillaries Continuous capillary. Least permeable, and most common (e.g., skin, muscle). Fenestrated capillary. Large fenestrations (pores) increase permeability. Occurs in areas of active absorption or filtration (e.g., kidney, small intestine). Sinusoid capillary. Most permeable. Occurs in special locations (e.g., liver, bone marrow, spleen).  Capillary Beds Interwoven networks of capillaries between arterioles and venules  Veins Veins carry blood towards the heart They carry large volumes of blood under low pressure. They have a wide lumen with thinner walls. They contain valves to stop backflow Muscle contraction can help flatten veins, drawing blood upwards back to the heart.  Veins VENULES Formed when capillary beds unite – Very porous – endothelium and a few pericytes Larger venules have one or two layers of smooth muscle cells VEINS – Large-diameter lumens offer little resistance – Venous valves prevent backflow of blood – Venous sinuses: flattened veins with extremely thin walls The micrograph shows some mammalian blood vessels in cross section. Which shows an artery? E F Which shows a vein? vessel X How do you know? magnification x 12  Location of the Heart The heart is made up of cardiac muscle. It is the size of your fist and is situated in the thoracic cavity. It is surrounded by a fibrous membrane called the pericardium. This is a bag made from inelastic connective tissue. Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings Heart Structure Extra: pericardial fluid is secreted in between the pericardium and heart. This helps movement. The function of the pericardium is the prevent overexpansion of the heart. Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings  The Surface Anatomy of the Heart Auricle—Outer portion of atrium Coronary sulcus—Deep groove that marks boundary of atria and ventricles Anterior interventricular sulcus Posterior interventricular sulcus Mark boundary between left and right ventricles Sulci contain major cardiac blood vessels Filled with protective fat The Surface Anatomy of the Heart  The Heart Wall and Cardiac Muscle Tissue Epicardium (visceral pericardium) Outermost layer Serous membrane Myocardium Middle layer Thick muscle layer Endocardium Inner lining of pumping chambers Continuous with endothelium  The Heart Wall and Cardiac Muscle Tissue  The Heart Wall and Cardiac Muscle Tissue Cardiac Muscle Cells Shorter than skeletal muscle fibers Have single nucleus Have striations (sarcomere organization) Depend on aerobic metabolism Connected by intercalated discs Desmosomes transmit tension Gap junctions transmit action potential The Sectional Anatomy of the Heart The Valves of the Heart The Coronary Circulation Figure 12-7(a)  The Heartbeat Heartbeat Needs two Types of Cardiac Cells Contractile cells Provide the pumping action Cells of the conducting system Generate and spread the action potential Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings Internal Features of the Heart External Features of the Heart The wall of the left ventricle is thicker and the right ventricle Why is this??? Blood pumped from the left ventricle must be moved all the way around the body The right only to the lungs  The cardiac cycle The cardiac cycle is made up of a number of stages which involve the atria and ventricles relaxing and contracting. Systole = contraction Diastole = relaxation This is controlled by detecting pressure difference across the chambers. The cardiac cycle 1. Atrial diastole Atria muscles relaxes and blood fills the atria from the pulmonary vein and vena cava. This increases pressure inside the atria. The pressure is low in the ventricles so this pressure difference causes the atrioventricular valves to open. 2. Ventricular diastole/Atrial systole Blood leaves the atria and moves into the ventricles. Pressure reduces in the atria and atrioventricular valves close preventing backflow. Pressure increases inside the ventricles which are relaxed. This causes a pressure difference between the ventricles and the aorta and pulmonary artery. This forces the semi lunar valves open triggering Atrial systole. 3. Ventricular systole Ventricles contract and blood leaves ventricles and enter aorta or pulmonary artery. Pressure drops in ventricles and the semilunar valves close preventing backflow. The whole cycle begins again What causes the heart beat sound? The classic lub dub sound comes from the opening and closing of the valves in the heart. The ‘lub’ is from the closing of the atrioventricular valve. The ‘dub’ is from the closing of the semi lunar valves. Cardiac Cycle graph Complete this table Stage Atria Ventricle 1 Diastole Diastole 2 Systole Diastole 3 Diastole Systole Q: Can you match the events of the cardiac cycle to the electrical activity of the heart?  Cardiac Output The amount of blood pumped around the body is called the cardiac output, and depends on two factors: l the stroke volume – the volume of blood pumped by the left ventricle in each heart beat. A typical value for an adult at rest is 75 ml. l the heart rate – the number of times the heart beats per minute. A typical value for an adult at rest is 70 bpm. cardiac output = stroke volume × heart rate A typical resting cardiac output is 4–6 litres per minute. This can rise to as much as 40 litres per minute in highly trained endurance athletes.  Autonomic Innervation of the Heart  THE HEARTBEAT Action Potentials and Muscle Cell Contraction in Skeletal and Cardiac Muscle 1 Rapid Depolarization 2 The Plateau 3 Repolarization Cause: Na+ entry Cause: Ca2+ entry Cause: K+ loss Duration: 3-5 msec Duration: ~175 msec Duration: 75 msec Ends with: Closure of Ends with: Closure of Ends with: Closure of voltage-regulated calcium channels potassium channels sodium channels +30 2 0 mV 1 Stimulus 3 Refractory period –90 0 100 200 300 Time (msec) Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings  The Conducting System Initiates and spreads electrical impulses in heart Two types of cells Nodal cells Pacemaker cells Reach threshold first Set heart rate Conducting cells Distributes stimuli to myocardium Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings  The Conducting System Contraction is controlled my the sino atrial node (SAN) which is also known as the pacemaker. This generates electrical activity in the heart by generating a wave of depolarisation. Waves of depolarisation spreads across the atria which causes them to contract. This is called atrial systole. Excitation doesn’t reach ventricles because walls separating atria and ventricles are non-conducting. Excitation passes from SAN to atrio- Ventricular node (AVN) Excitation moves from the AVN through the septum and spread through the ventricle. There is a small delay which gives the atria time to contract so blood passes through the atrioventricular valves and into the ventricles. The AVN then stimulates the bundle of His which is conducting tissue which pass it onto the purkinje fibres. The purkinje fibres causes the waves of excitation to move upwards around the ventricles initiating ventricular systole. Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings Electrical Activity in Heart Cardiac Cycle graph An Electrocardiogram  An Electrocardiogram Electrocardiograms are used to monitor electrical activity in the heart. Sensors are uses to trace activity that can be interpreted by a medical professional. A normal ECG has the following trace and made up of waves labelled P, Q R, S and T.  An Electrocardiogram P wave – atrial depolarization QRS complex – ventricular depolarization & atrial repolarization T wave – ventricular repolarization All of these wave patterns have specific magnitudes and length of time patterns in a healthy heart Any deviation from these norms may mean a heart defect within the conduction system  An Electrocardiogram P wave represents excitation of atria – showing atrial systole QRS complex represents excitation of the ventricles – ventricular systole T wave represent diastole Stage Atria Ventricle ECG 1 Diastole Diastole T wave 2 Systole Diastole P wave 3 Diastole Systole QRS complex Abnormal ECGs  Cardiovascular Disease (CVD) Congenital Heart defects Atherosclerosis Angina Myocardial Infarction Stroke The role of high blood pressure in CVD  Factors that increase your chances of CVD Genetics – a family history of CVD or genetic predisposition Age – as people age the likelihood of developing CVD increase Gender – CVD death rates are higher in men than women Diet – poor diet containing high saturated fats, high salt intake and lack of vitamins and healthy fats High blood pressure (hypertension) – this naturally increases with age, makes CVD more likely as blood vessels are more likely to get damaged Smoking – exposure to chemicals that increase blood pressure and damage blood vessels Inactivity – lack of regular exercise 1. How many of the above factors are unchangeable? 2. Could some of the above factors be linked with one another or increase the likelihood of getting another? 3. What actions could be taken to lower risk of CVD?  Developmental Aspects of the Heart  Examples of Congenital Heart Defects Coronary Artery Disease Atherosclerosis Heart muscle receiving insufficient blood supply narrowing of vessels--- atherosclerosis, artery spasm or clot atherosclerosis--smooth muscle & fatty deposits in walls of arteries Treatment drugs, bypass graft, angioplasty, stent Chapter 18, Cardiovascular System 59  Coronary Artery Disease Atherosclerosis begins with damage to the endothelial lining damage Leads to inflammatory response chemicals from the blood, including cholesterol causes a fatty deposit known as an atheroma to develop. Fibrous tissue builds up making the plaque harden. artery wall to harden so that it is less elastic.  Problems caused by atherosclerosis The artery lumen becomes very small which causes a increases in blood pressure. This can increase the risk of atherosclerosis occurring elsewhere in the body. Aneurysm: Blood can build up behind a blockage causing the artery wall to bulge and weaken. This increases the chances of the wall splitting and internal bleeding occurring. Aneurysms are often fatal. High Blood Pressure: Can cause damage in other organs such as kidneys, eyes and the brain.  Clinical Problems The two most common forms are angina and Myocardial Infarction (heart attack), but there are many others. These two are closely linked to atherosclerosis. MI = myocardial infarction death of area of heart muscle from lack of O2 replaced with scar tissue results depend on size & location of damage Blood clot use clot dissolving drugs streptokinase or t-PA & heparin balloon angioplasty Angina pectoris heart pain from ischemia (lack of blood flow and oxygen ) of cardiac muscle  Strokes Caused by an interruption to the blood supply in the brain. May be a bleed from a damaged vessel, or a blockage cutting off the blood supply. Blockages in main vessels can cause serious strokes, in smaller arterioles the effects are less severe. Symptoms: Dizziness, confusion, blurred or lost vision, slurred speech and numbness. Severe strokes can cause paralysis down one side of the body and death. By-pass Graft Percutaneous Transluminal Coronary Angioplasty  Artificial Heart- Waiting for a transplant