19 Cardiovascular System The Heart Taft College Human Physiology

Transcription

1 19 Cardiovascular System The Heart Taft College Human Physiology

2 Cardiovascular System Oxygenated blood Introduction A primary function of the circulatory system is transportation of: 1. nutrients 2. respiratory gases 3. hormones 4. waste products Components of the Cardiovascular System 1. Muscular Pump = Heart An amazing ability to do work. With every heartbeat, sends blood throughout the body. Continues to beat second by second, every minute. Continuously working whether you are working or not. At rest, pumps 5 L/min of blood = total blood volume of body gallons/day or recycles total blood volume 1500/day. More amazing is the hearts ability to pump 5x resting volume upon demand, due to heavy exercise. 2. Tubing = Blood Vessels 60,000 miles of blood vessels. Arteries Arterioles Capillaries Venules Veins 3. Transporting Medium - Blood We have already discussed. Deoxygenated blood

3 Veins Basic Introduction to Blood Circulation Arteries No exceptions! Veins always serve to return blood to the heart, arteries always serve to carry blood away from the heart. The purpose of the heart is to pump blood (transporting medium) to the tissues. This accomplished as follows:

4 O 2 Lungs Heart Arteries w/ Plasma Arterioles CO 2 Tissue Fluid w/ Cardiovascular Water Veins w/ Plasma System Capillaries w/ Plasma Oxygen Nutrients Hormones Body Tissues Venules Lymph ducts w/ Lymph Lymph nodes Lymphatic System Lymph vessel Wastes CO2 Tissue Fluid Lymph capillaries w/ Lymph

5 2 Circulatory Patterns There are 2 circulation systems within the body: 1. Pulmonary Circulation Pulmonary circulation carries blood from the heart to the lungs and back to the heart again. The pulmonary circuit will carry oxygen poor blood from the right ventricle > pulmonary artery > lungs, where the blood becomes oxygenated. The oxygenated blood will travel from the lungs > pulmonary vein > left atrium. 2. Systemic Circulation Systemic circulation serves to carry blood from the heart to the body tissues (systems) and back to the heart again. The systemic circuit will carry oxygen rich blood from the left ventricle > aorta artery > body tissues, where the oxygen will be utilized. Oxygen poor blood will travel from the body tissues > right atrium. RV LV > Lungs > > Body > Tissues LA RA

6 Lungs Pulmonary circuit > Lungs > Heart Systemic circuit Body Tissues > Body > Tissues oxygen poor oxygen rich

7 The Anatomy of the Heart The human heart, which is a dual pump, consists of 4 chambers, and is divided into right and left halves. Each half of the heart consists of an upper chamber = atrium. And a lower chamber called a ventricle. Atria = receiving chambers, receiving blood from various parts of body. Ventricles = pumping chambers, pumping blood to various portions of body. Every time blood leaves a chamber, it passes through a one way valve that prevents back flow.

8 Lungs Pulmonary circuit Systemic circuit Body Tissues oxygen poor oxygen rich

9 Lungs Right atrium = receiving chamber Left atrium = receiving chamber Pulmonary circuit Right ventricle = pumping chamber Left ventricle = pumping chamber Systemic circuit Body Tissues oxygen poor oxygen rich

10 Pulmonary vein From RV 6 Lungs 7 Blood Flow by the Numbers 14 Superior Vena Cava Inferior Vena Cava Coronary Sinus Atrioventricular valve - tricuspid Right atrium 1 2 Right ventricle 3 Left atrium 8 9 Left ventricle 10 Atrioventricular valve bicuspid or mitral To lungs Aortic semilunar valve 5 Pulmonary artery Aorta To body Pulmonary semilunar valve 13 Body Tissues oxygen poor oxygen rich

11 Diagram of Blood Flow -Review 6 Lungs 1. Right Atrium 2. Rt. Atrioventricular valve = =Tricuspid valve 3. Right Ventricle 4. Pulmonary Semilunar valve Pulmonary artery 6. Lungs 7. Pulmonary veins Left Atrium 9. Lt. Atrioventricular valve = =Bicuspid = Mitral valve Left Ventricle 11. Aortic Semilunar valve 12. Aorta artery Body Tissues 14. Superior vena cava, Inferior vena cava, Coronary sinus? Which numbers make up the pulmonary circuit?? Systemic circuit? 13 Body Tissues

12 6 Lungs Pulmonary Circuit 5 7 How do the arteries and veins of the pulmonary and systemic circuits differ? Systemic arteries are oxygenated Systemic veins are deoxygenated Pulmonary arteries are deoxygenated Pulmonary veins are oxygenated Systemic Circuit Body Tissues

13 Lungs Interventricular septum 1. Right Atrium 2. Rt. Atrioventricular valve 3. Right Ventricle 4. Pulmonary Semilunar valve (Pulmonary trunk) 5.Pulmonary arteries 6.Lungs 7.Pulmonary veins 8.Left Atrium 9.Lt. Atrioventricular valve 10. Left Ventricle 11. Aortic Semilunar valve 12. Aorta artery 13. Body Tissues 14. Superior vena cava Inferior vena cava Coronary sinus

14 Heartbeat (Nodal Tissue) The heart can beat by itself, that is, it is independent of any outside source. It possesses autorhythmicity. This autorhythmicity is due to specialized tissue of the heart known as nodal tissue. There are 2 very specialized areas of nodal tissue: SA node (sinoatrial node)- also known as the "pacemaker". AV node (atrioventricular node). Both of these nodes can produce their own action potentials spontaneously. They exhibit spontaneous electrical activity, independent of any nerve supply. The SA node produces about action potentials/minute. The AV node about 50/minute. Because of this difference the SA node is the "pacemaker" and stimulates the AV node to continue the message before it can initiate an AP of its own. Experiment: cut the heart of a turtle out and it will continue to beat. Cut it into pieces and the pieces will continue to beat, but not simultaneously. Those pieces closest to the pacemaker will beat fastest.

15 The Pacemaker and Conduction System of the Heart Intra-atrial path Atria Contract Simultaneously Sinoatrial node Right atrium Left atrium Atrioventricular node Right ventricle Left ventricle Atrioventricular bundle (of His) Left and Right bundle branches Conduction myofibers (purkinje) Ventricles Contract Simultaneously

16 The Pacemaker and Conduction System of the Heart Both Atria Contract Both Ventricles Contract

17 Heartbeat Heartbeat is initiated in sinoatrial node,sa node = pacemaker. SA node sends out electrical impulse through heart muscle of the atria. Causes atrial walls to contract simultaneously. Atrial contraction increases amount of blood in ventricles only %. The ventricles are primarily filled by the negative pressure of the ventricles relaxing, not by the contraction of the atria. Impulse from SA node cannot pass beyond atria by itself. However, right atrium contains another node atrioventricular node, AV node. AV node receives impulse and after short pause, sends electrical impulse down specialized conducting cells to ventricles. Ventricles contract simultaneously from apex and travels upward toward base of heart where outgoing vessels are located. SA node atria contract simultaneously. AV node interventricular septum ventricles sends contract blood to the body and lungs.

18 Cardiac Muscle Cardiac muscle forms the contractile tissue of the heart. It contains intercalated discs, thickenings of the sarcolemma, that connects the muscle fibers together. The intercalated discs contain gap junctions that are channels between cells that allow action potentials (ions) to pass from one cell to the next. This ensures that a wave of depolarization passes throughout the heart tissue, causing a coordinated contraction. The muscle fibers of the heart are divided into 2 networks: 1 network surrounds the atria and, 1 surrounds the ventricles. The 2 networks are separated by an insulating layer of C.T., so atrial and ventricular contraction occur separately.

19 3 Characteristics of Cardiac Muscle The heartbeat, once triggered, is all or none. If one cell fires in one of the networks, all the rest follow. 1. Stimulation of one part of the cardiac muscle affects all parts, that is, it acts like a single cell. 2. Cardiac muscle cells exhibit a length-tension relationship = law of the heart". As a cardiac fibers are elongated or stretched (to a point), strength of contraction will increase. Unlike skeletal muscle, cardiac muscle fibers are normally shorter than their optimal length. Example: Greater filling during exercise causes elongation of ventricles with blood -- a stronger contraction that empties the greater quantity of blood. 3. Cardiac muscle has a long refractory period. This insures filling of the chambers prior to contraction.

20 The Heart as a Pump Cardiac Output Cardiac output is measured as the volume of blood to leave one ventricle per minute. Equal amounts of blood are ejected from each ventricle with each beat of the heart. Cardiac output is determined by 2 things: Heart Rate (HR) and Stroke Volume (SV) CO (L/min) = Heart Rate (HR) (beats/min) X Stroke Volume (SV) (L/beat) Normal Resting Heart may have a: Heart of about 75 beats/min, and a Stroke volume of 0.07 L/beat CO (L/min) = Heart Rate (HR) (beats/min) X Stroke Volume (SV) (L/beat). 75 beats/min X 0.07 L/beat =5.25 L/min = CO of approx L/min = 3600 gallons/day CO may be measured in several ways, usually invasive. For example : echocardiagram/doppler or thermodilution/dilution techniques. Note 1= CO at rest is approx equal to pumping your total blood volume each minute. Note 2 = the ventricles do not empty completely when they contract % of blood remains in the ventricles at resting heart rate. This is a reserve of sort, and allows stroke volume to increase during exercise as more of the reserve is ejected.

21 The Heart as a Pump Exercising Heart Heart rate = 120 beats/min X Stroke volume 0.16 L/beat = Active CO of 20 L/min note increased HR & SV Non athletic person = Active CO = L/min = (4-5x resting CO) Athletes = Active CO = 35 L/min (=7x CO at rest) Why? Trained athletes usually have a greater SV due to larger heart. ** If heart rate > 140 beats/min, cuts down on amount of time for ventricular filling. Therefore, at heart rates >140 see a decrease in stroke volume and therefore cardiac output. CO does not show a linear relationship to heart rate. Why is stroke volume greater in the heart during exercise? Increased blood returned to the heart during exercise stretches the muscle cells - they contract with more force, ejecting greater volume of blood (increased SV) with each stroke = Law of the Heart.

22 Alterations of Heart Rate and Rhythm of Heart Beat Variations in normal rhythm (irregularity) = arrhythmia. Causes of Arrhythmia 1. Alteration of rate of node activity Tachycardia = increased heart rate Bradycardia = decreased heart rate Can be due to drugs and response to physical activity. 2. Interference with conduction of impulse along nodal tissue = Heart Block Conduction of SA node signal is interrupted on its way to the AV node to some degree. Atria and ventricles will beat independently. Install pacemaker to AV node to control the most important part, the ventricle pump. 3. Areas other than nodal tissue assume pacemaker role. Heart flutter = coordinated heart beats of /min (what happens to SV? decreases) Heart fibrillation = Uncoordinated beats and contraction. Cardiac muscle cell contractions are no longer synchronized. Ventricular pumping will cease. Can use external shock (defibrillation) to correct. External with paddles and large current, smaller shock if an internal defibrillator is installed. Defibrillator resynchronizes contractions of cardiac muscle cells necessary for pumping action.

23 Heart Pathology Cardiovascular disease causes more deaths in the U.S. than accidents and all other diseases combined. Recent estimates show that 18% (40 million people) of the U.S. population have cardiovascular disease of some form. 65% of cardiovascular related deaths are caused by heart attack. A heart attack is the result of insufficient blood supply through the coronary arteries that supply the cardiac muscle. With the 0 2 supply cutoff, the cardiac muscle cells die = myocardial infarction (MI). About 1.5 million MI/year in U.S.

24 Causes of Heart Attack 1. Thrombus or Embolus = blood clot Ischemia = Reduced 02 supply to tissues. Can lead to tissue dysfunction and cell death. Lack of blood and 02 in cardiac muscle may lead to angina pectoris = chest pain that accompanies myocardial ischemia. Symptoms of angina pectoris include a tight or squeezing sensation as though the chest were in a vice. The pain is often referred to the neck, chin, or down the left arm to the elbow. Sometimes ischemic events occur without pain and are called silent myocardial ischemia. Heart attack without angina pectoris events are more common in women. When cardiac cells die, their contents leak into the blood. Cardiac enzymes (CPK, LDH), troponin, and myoglobin in circulating blood can be measured to detect recent cardiac damage. Chemical tests for these cardiac markers can be determined within 30 minutes along with an ECG which can assist the physician in determining that cardiac muscle damage has occurred.

25 Causes of Heart Attack 2. Atherosclerosis- thickening of the lining of the arteries formed by deposition of fatty material (cholesterol and lipids), smooth muscle cells, and fibrous tissue, called plaque. Surface of cardiac arteries become roughened by deposits of cholesterol, collagen and elastin, and cellular debris which reduce the inner diameter of the vessel. Symptoms of coronary artery disease begin at about 75% narrowing of coronary arteries. Arteriosclerosis hardening of the arteries may subsequently occur as cells in the plaque die (lack of nutrient deliver) and calcium salts deposit in the artery walls. This stiffens the artery further and increases the chance of a thrombus forming or and embolus getting stuck.

26 Risk factors for developing heart disease High blood cholesterol level, high blood pressure, cigarette smoking, obesity, lack of regular exercise, diabetes mellitus, genetic pre-disposition (family history of early heart disease), male gender (until age 70). Female hormones seem to protect against arteriosclerosis until menopause. This is a major reason why women live longer than men on average, about ten years longer. Recovery from heart attack Recovery depends on how much cardiac tissue has been damaged and whether other near by blood vessels can enlarge their area of supply. t-pa is can really help here. The dead tissue will be replaced by non-contractile scar tissue and the heart will lose some of its strength. If nodal tissue (especially SA node) is damaged, a pacemaker may need to be installed. If AV node is damaged, ventricular fibrillation may result with sudden death as an outcome.

27 Life Saving Measures What is CPR? Cardiopulmonary Resuscitation How successful is CPR in saving life of a heart attack victim? CPR success is about 3%. Why? CPR typically does not resynchronize cells of a fibrillating heart. It does improve O2 in the tissues moves some blood. Success improves to >40% with a defibrillator. $3,000 portable defibrillators are becoming more common in airports, casinos, and in police cars in some cities.

28 Repair of Heart Coronary Artery/ Heart Disease 1. Coronary Artery Bypass- a surgical procedure where a blood vessel (usually a piece of the saphenous vein is removed from the thigh/leg) is sutured between the aorta and the unblocked portions of the coronary artery. More than 1 bypass may be needed to establish adequate blood supply to the heart. 2. Coronary Angioplasty- coronary artery cleaning or opening procedures- in these procedures an attempt is made to open clogged arteries. The catheter is inserted into the artery of an arm or leg and guided into a coronary artery. Dyes are used to locate closures (plaques). Then a balloon may be inflated to squash the plaque, a laser may be used to remove plaque, or a drill may be used to shave off plaque. Sometimes a stent (some coated with antibiotics) may be inserted to keep the artery open.

29 Repair of Heart Coronary Artery/Heart Disease 3. Diet changes and rehabilitation exercise. If diagnosed early. Eat less fat/cholesterol. Exercise under medical care. 4. Other remedies Experimental use of vascular endothelial growth factor (an injected protein) is being tested as an alternative to bypass surgery to grow new blood vessels. Experimental gene insertion to grow new blood vessels. Heart transplant, artificial heart, cardiac assist devices. Stroke Caused by interference of blood supply to the brain. May be result of thrombus (cerebral thrombosis), embolus, or from bursting of a blood vessel (hemorrhage) that supplies brain tissue. The outcome depends upon severity of damage in where it occurs in the brain. 6 minutes without 02 and the brain begins to die.

30 The Cardiac Cycle Cardiac cycle = one complete series of events during one heartbeat. Timing of cardiac cycle The cycle begins with an AP originating in the SA node that spreads across both atria. Resting heart rate = 70 beats/min. One complete cycle = 0.8 sec. Systole Diastole Diastasis contraction relaxation rest Atria 0.1 sec 0.1 sec 0.6 sec = 0.8 sec Ventricles 0.2 sec 0.2 sec 0.4 sec = 0.8 sec SA Node fires

31 The Electrocardiogram (ECG or EKG) The ECG is a graph of the electrical activity (action potentials) of the heart muscle cells during each heartbeat. The ECG measures voltage in relation to time. A clinical ECG will use 12 different leads and give a comprehensive set of views of the heart s electrical activity. An experienced professional can interpret heart pathology by various patterns of electrical activity seen in the ECG recording. The ECG may provide info on size and position of heart, electrolyte balance or imbalance, electrical activity, and timing of heart activities. The 3 major waves that appear in a normal lead II ECG: 1. P wave = excitation (depolarization) of atria. 2. QRS complex = excitation (depolarization) of ventricles and repolarization of the atria. 3. T wave = repolarization of the ventricles Occasionally, in some individuals a 4th wave may appear: 4. U wave = possible slower repolarization of papillary muscles. It appears just after the T wave and before the P wave of the next cycle. Abnormal ECG Alterations of voltage appear in the vertical plane. Alterations of timing appear in the horizontal plane. A stress test (ECG performed under moderate exercise) may uncover abnormalities that may otherwise be missed. (Effects of reduced O2 as a result of coronary artery disease)

32 The Electrocardiogram (ECG or EKG) The 3 major waves that appear in a normal lead II ECG: 1. P wave = excitation (depolarization) of atria. 2. QRS complex = excitation (depolarization) of ventricles and repolarization of the atria. 3. T wave = repolarization of the ventricles Occasionally, in some individuals a 4th wave may appear: 4. U wave = possible slower repolarization of papillary muscles. It appears just after the T wave and before the P wave of the next cycle. Abnormal ECG Alterations of voltage appear in the vertical plane. Alterations of timing appear in the horizontal plane.

33 Peak Pressures and Volume Changes in the Heart Cycle Pulmonary artery RA RV Pulmonary semilunar valve LA 7 mm 10 mm LV 30 mm 130 mm 18 mm to open Peak Pressures produced by each chamber and Pressure to open semilunar valves. 80 mm to open Aortic semilunar valve Aorta To body The force imparted on the blood by the atria is of minimal importance in ventricular filling. Increases volume of blood in ventricles by only 20%. Most ventricular filling occurs when ventricles relax, lowering pressure and draining blood into expanding chamber. Filling continues during diastasis (rest) and stops with beginning of systole (contraction). AV valves close during ventricular contraction but blood does not leave ventricles until pressure opens semilunar valves. Thicker wall of left ventricle allows for greatest pressure. Normal BP = 120/80 Volume of ventricle = ml/chamber. At rest- about 2/3 of this is emptied as ventricles contract. Therefore, there is a blood reserve with greater emptying during increased activity levels.

34 Heart sounds- Lubb - dupp Lubb = 1 st heart sound due to closing of AV valves. Signals the onset of ventricular contraction. Dupp (dubb) = 2 nd heart sound due to the closing of semilunar valves. Signals the end of ventricular contraction. Intensity depends on force of heartbeat. Ventricular systole (contraction) is occurring between the heart sounds.