Cardiovascular Lectures 3 & 4 PDF

2025-01-24 Important Dates BIOM*3200 Practice test 1 (last year’s) now posted. Ask your TA if you have any specific questions re: this! Tues Jan 21 – CV lecture 1 Thurs Jan 23 – CV lecture 2 Fri Jan 24 – office hours Mon Jan 27 – office hours Tues...

2025-01-24 Important Dates BIOM*3200 Practice test 1 (last year’s) now posted. Ask your TA if you have any specific questions re: this! Tues Jan 21 – CV lecture 1 Thurs Jan 23 – CV lecture 2 Fri Jan 24 – office hours Mon Jan 27 – office hours Tues Jan 28 – CV lecture 3 – Distinguished Clinician Scientist Thurs Jan 30 – test #1 1 2 Cardio-Respiratory Cardio-Respiratory Version 12: 449 (distribution of blood pie chart) Version 13: 525-527 (structure of the respiratory system) 455 (distribution of blood pie chart) 530-533 (from physical properties of the lungs – to - 533-535 (structure of the respiratory system) mechanics of breathing); 538-544 (from physical properties of the lungs – to – 535-536 (lung volumes and capacities) pulmonary disorders) 545-546 (oxygen toxicity, nitrogen narcosis, hyperbaric 552-553 (Disorders caused by High Partial Pressures of oxygen therapy, decompression sickness) Gases) 552 (hemoglobin) 559 (hemoglobin) 558-560 (carbon dioxide transport - to - ventilation and 565-568 (carbon dioxide transport - to - ventilation and acid-base balance) acid-base balance) 563-566 (high altitude to end of chapter) 571-573 (high altitude to end of chapter) 3 4 1  2025-01-24 Cardio-Respiratory Cardio-Respiratory Version 14: Version 15: 455 (distribution of blood pie chart) 455 (distribution of blood pie chart) 533-535 (structure of the respiratory system) 533-535 (structure of the respiratory system) 538-544 (from physical properties of the lungs – to – 536-544 (from physical properties of the lungs – to – pulmonary disorders) pulmonary disorders) 552-553 (Disorders caused by High Partial Pressures of 552-553 (Disorders caused by High Partial Pressures of Gases) Gases) 559 (hemoglobin) 559 (hemoglobin) 565-568 (carbon dioxide transport - to - ventilation and 565-568 (carbon dioxide transport - to - ventilation and acid-base balance) acid-base balance) 573 (respiratory adaptations to high altitude) 573 (respiratory adaptations to high altitude) 5 6 Cardio-Respiratory Learning Objectives Version 16: Distribution of blood in the circulatory 454 (distribution of blood pie chart) system at rest 532-535 (The respiratory system, section 16.1) 537-543 (from physical properties of the lungs – to – Structure of the respiratory system pulmonary disorders) Physical Aspects of Ventilation 551-552 (Disorders caused by High Partial Pressures of Mechanics of breathing Gases) 558-559 (hemoglobin) Hemoglobin and Oxygen Transport 564-566 (carbon dioxide transport - to - acid-base balance) 570 (Acclimatization to High Altitude) 7 8 2  2025-01-24 Distribution of blood within the circulatory Distribution of blood within the circulatory system at rest system at rest Notice that the venous system contains most of the blood; it functions as a reservoir from which more blood can be added to the circulation under appropriate conditions (such as exercise). 9 10 Structure of Blood Vessels Veins Most of blood volume is in the venous system. Unlike arteries, which provide resistance to the flow of blood from the heart, veins are able to expand as they accumulate additional amounts of blood. The average pressure in veins is only 2 mmHg, compared to a much higher average arterial pressure of 100 mmHg Text Fig. 13.26 11 12 3  2025-01-24 Veins The venous pressure is Veins too low to return blood To help venous blood from the abdominal and to the heart. thoracic regions, the act of breathing + contraction of the diaphram + pressure in the To help veins of the abdomen from breathing squeezes the veins lower limbs return blood, and helps the venous blood return to the heart. the veins pass between skeletal muscle groups which provide contractions to help move blood back. (called – “skeletal muscle pump”) 13 14 Arteries Arteries In the aorta and other larger arteries, there The elastic recoil drives blood during the are numerous layers of elastin fibers between diastolic phase when the heart is resting and the smooth muscle cells of the tunica media. not providing pressure. These large elastic arteries expand when the pressure of the blood rises as a result of the ventricle’s contraction. They recoil like a stretched rubber band when the blood pressure falls during relaxation of Small arteries and arterioles are less elastic the ventricles. and so their diameter only changes slightly. 15 16 4  2025-01-24 Capillaries Over 40 billion capillaries in the body. Number is so great that scarcely any cell in the body is more than 60-80 um away from a blood capillary. Decellularized heart 17 18 Capillaries Capillaries Vasoconstriction decreases blood flow to the capillary bed, vasodilation increases it. Unlike the arterial and venule tissues, the walls of the capillaries are composed of just one cell layer. Lack SM and CT – makes it easier to exchange materials between blood and tissues. 19 20 5  2025-01-24 Air passageways The pharynx and the larynx Nasal The nasal cavity leads into the pharynx cavity (throat), a muscular passage connecting the Pharynx nasal cavity with the larynx Oral cavity Larynx The larynx is where air is diverted toward the lungs and food is diverted to the Bronchus esophagus to the stomach Trachea The larynx also contains the vocal “cords"; despite their name, these so-called cords are folds in the lining tissue of the larynx Lung 21 22 Inside the Voice – Larynx – Distribution of blood within the circulatory just showing image of a moving voicebox system at rest Capillary beds of lungs where gas exchange occurs Pulmonary artery* Pulmonary vein* Right atrium Left atrium Left ventricle Right ventricle Aorta Vena cava (carries de-oxygenated Capillary beds of blood to the hearts all body tissues right atrium) where gas exchange occurs * Vein but highly oxygenated – vein because traveling TO heart 23 24 6  2025-01-24 Distribution of blood within the circulatory The Respiratory System system at rest Pulmonary Pulmonary artery* vein* *Artery but * Vein but low O2 – highly artery oxygenated because – vein traveling because AWAY from traveling TO heart heart 25 26 Physical Properties of the Lungs: 1. The Respiratory System Inspiration & Compliance SEM of lung tissue. Left – bronchiole passes between many alveoli. Right – alveoli seen under higher power, showing pores through which air can pass from one alveolus to another. 27 28 7  2025-01-24 Physical Properties of the Lungs: 1. Physical Properties of the Lungs: 2. Inspiration & Compliance Expiration & Elasticity In order for inspiration to occur, the lungs must be able to expand when stretched – they must have high compliance (distensiblity, stretchability). This means the ease with which the lungs can expand, under pressure. Lung compliance is change in lung volume per change in transpulmonary pressure = dV/dP. So at any given transpulmonary pressure, there will be greater or lesser expansion, depending on the compliance of the lungs. Lung disease reduces compliance – anything that produces a resistance to distention. 29 30 Physical Properties of the Lungs: 2. Lungs are normally attached to the Expiration & Elasticity chest wall For Expiration to occur, the lungs must get smaller when tension is released. They must have elasticity. so they are Elasticity is the tendency of a structure to return to always in a state its initial size after being distended. of elastic tension Because of the high content of elastin proteins, the lungs are very elastic and resist distension. The lungs are normally stuck to the chest wall, so they are always in a state of elastic tension. This tension increases during inspiration when the lungs are stretched, and is reduced by elastic recoil during expiration. 31 32 8  2025-01-24 Lungs are normally attached to the Expansion of the lungs chest wall Although contraction of the diaphragm and intercostal muscles cause the chest cavity to increase in volume, the lungs cannot inflate unless they are attached to the inner wall of the chest cavity [A person who has a chest wounded cannot inflate the lung on the wounded side, even though she/he continues to ventilate] This attachment of the outer lung surface to the inner surface of the chest cavity is made with membranes called pleural Changes in lung volume during breathing. Radiographs membranes during a) expiration, and b) inspiration. 33 34 The pleural membranes Chest wall The pleural membranes (PMs) consist of one membrane layer attached to the surface of the lung, and one membrane layer Lung attached to the inner wall of the chest cavity The PMs produce a mucous-rich lubricating fluid (pleural fluid) PS into the space between the two membranes (it is called the pleural space (PS), but it really isn’t a PMs space because the membranes lie close to one another) 35 36 9  2025-01-24 The pleural membranes Physical Properties of the Lungs: 3. Surface Tension The pleural fluid holds the two pleural membranes together; consequently, as the size of the thoracic cavity changes, so Surface tension is exerted by fluid in the alveoli. does the volume of the lungs; it is the “glue” that holds the lungs attached to The fluid contains surfactant, a mixture of the inner wall of the thoracic cavity. phospholipids and hydrophobic surfactant proteins, secreted into the alveoli by type II alveolar cells. The pleural fluid is also the lubricant that Surfactant lowers surface tension in the alveoli, which allows the lungs to slide easily within the prevents the alveoli from collapsing during expiration. thoracic cavity as they inflate and deflate. 37 38 bronchiole Physical Properties of the Lungs: Alveoli Respiratory Distress Syndrome smooth muscle fibers Type II pneumocyte capillary Pulmonary artery Surfactant is Pulmonary produced late in vein fetal life. Premature babies are sometimes born with lungs that lack sufficient surfactant and their alveoli are collapsed as a result. alveoli have tendency to surfactant prevents collapse collapse 39 40 10  2025-01-24 Physical Properties of the Lungs: 4. Physical Properties of the Lungs: 4. Lung volumes and capacities Lung volumes and capacities VOLUMES: Tidal Volume: volume of gas inspired or expired in an unforced respiratory cycle (~500 mls) Inspiratory reserve: max vol of gas that can be inspired during forced breathing in addition to tidal volume Expiratory reserve: max vol of gas that can be expired during forced breathing in addition to tidal volume Residual volume: vol of gas remaining in lungs after max expiration. 41 42 Physical Properties of the Lungs: 4. Physical Properties of the Lungs: 4. Lung volumes and capacities Lung volumes and capacities Anatomical Dead Space (Dead Volume): Nose, mouth, larynx, trachea, bronchi, bronchioles – where no gas exchange occurs Lung Capacities: Total lung capacity: total amount of gas in the lungs after a max inspiration. about 150 mls Vital capacity: max amount of gas expired after a max inspiration. Inspiratory capacity: max amount of gas that can be inspired after a normal tidal expiration. Functional residual capacity: amount of gas remaining in the lungs after a normal tidal expiration. 43 44 11  2025-01-24 Physical Properties of the Lungs: 4. Lung volumes and capacities Critical Thinking What is the percentage of fresh air reaching the alveoli, if … Zombies i) the anatomical dead space is 150 mls, and (Walking Dead) ii) tidal volume is 500mls? Vampires (Twilight) Answer: 150 is dead space therefore 500 – 150 = 350 reaches the alveoli… 350 / 500 x 100% = 70% The percentage of fresh air reaching the alveoli is 70% 45 46 Physical Properties of the Lungs: 4. Lung volumes and capacities What is the percentage of fresh air reaching the alveoli, if the tidal volume is increased to 2000 ml?… Answer: 150 is STILL the dead space in humans therefore 2000 – 150 = 1850 that reaches the alveoli… 1850 / 2000 x 100% = 93% The percentage of fresh air reaching the alveoli is 93% 47 48 12  2025-01-24 The role of hemoglobin Hemoglobin is contains iron, and it is present in the cytoplasm of red blood cells; it has interesting properties: Not only does it chemically combine with O2, but it can also release the gas when cells need it Hemoglobin acts as an O2 shuttle from the lungs to body tissues 49 50 The role of CO2 in regulating the binding of O2 with hemoglobin In the lungs: CO2 diffuses from the blood to the alveoli and blood CO2 levels are low – this Carbon Dioxide / Oxygen reduces the acidity of blood in the lungs (e.g. higher pH). transport in blood In the tissues, the opposite is the case: blood CO2 levels are high because the cells produce the gas as an excretory product, and O2 levels are low because it is being used by cells – this increases the acidity of blood in the tissues (e.g. lower pH). 51 52 13  2025-01-24 The role of CO2 in regulating the O2 uptake in the lungs binding of O2 with hemoglobin In the lungs, O2 is entering the blood and CO2 is The acidity of the plasma (which is related leaving the blood: directly to plasma CO2 content) determines O2 dissolves in the lining fluid film of the alveoli, whether O2 combines with hemoglobin to form diffuses through the walls of the alveoli and oxyhemoglobin (low acidity/ higher pH in the blood capillaries into the plasma. lungs), or whether O2 is released from oxyhemoglobin (high acidity/lower pH in the tissues). O2 then diffuses into RBCs and combines chemically with Hb to form oxyhemoglobin. [Hemoglobin also has binding sites for CO2; it acts as a CO2 shuttle from body tissues to Oxyhemoglobin formation occurs in the lungs lungs]. because blood CO2 levels in the lung are low 53 54 O2 release in the tissues O2 and CO2 movements in the lung In the body tissues, O2 is being used by the cells O2 Capillary and CO2 is being produced: + vessel Hb O2 is released from oxyhemoglobin, and Alveolar air O2 ¯ diffuses into body tissues sac Red blood HbO2 cells Disassociation of Hb and O2 occurs in the CO2 tissues because plasma CO2 levels in the body tissues are high (and pH decreases – is more CO2 acidic). [The following 2 slides summarize in figure Blood acidity decreases (pH up!) as CO2 diffuses format the processes described in the last from the plasma to the alveolar sac allowing O2 few slides] to combine with Hb to form oxyhemoglobin (HbO2) 55 56 14  2025-01-24 O2 and CO2 movement in the tissues O2 Capillary Body cell + vessel O2 Hb ­ Red blood How exactly is Carbon dioxide HbO2 cells CO2 transported in blood? CO2 Blood acidity increases (pH lowers!!) as CO2 diffuses from body cells to the plasma causing oxyhemoglobin (HbO2) to dissociate into Hb and O2; the O2 diffuses into the body cells 57 58 CO2 transport CO2 transport CO2 is a byproduct of metabolism; it is As CO2 diffuses from body cells into the plasma, constantly produced and there is a constant it diffuses into RBCs and is converted into movement, by diffusion, from body cells into bicarbonate ion (HCO3-) by the enzyme, carbonic the blood plasma. anhydrase, that is present in the RBCs The gas has low solubility and only very little A small amount of CO2 is also carried attached can be carried in simple solution. chemically to Hb; these are called carbamino compounds 59 60 15  2025-01-24 CO2 conversion to bicarbonate in red CO2 transport blood cells; the bicarbonate equation In the general body tissues, the constant Spontaneous production of CO2 causes the bicarbonate reaction equation in the red blood cells to go in the direction indicated in the previous slide (i.e., from left to right). CO2 + H2O H2CO3 H+ + HCO3- In the lungs, CO2 is being lost to the alveolar air sacs, and the equation moves from the right Bicarbonate to the left, as shown in the following slide. Enzyme action ion (carbonic Hydrogen anhydrase) ion Note that the enzyme-regulated step works in both directions 61 62 CO2 conversion to bicarbonate in red O2 and CO2 transport: Summary blood cells; the bicarbonate equation Spontaneous reaction The next two slides, and a summary slide provide an overview of the O2 and CO2 interactions with hemoglobin in the lungs and in the general body tissues CO2 + H2O H2CO3 H+ + HCO3- Bicarbonate Enzyme action ion (carbonic Hydrogen anhydrase) ion 63 64 16  2025-01-24 O2 and CO2 movement in the **LUNG** O2 and CO2 movement in the **TISSUES** Blood Start Blood capillary here!!! capillary O2 O2 HCO3- + HCO3- O2 + Cell O2 Hb Hb nucleus ­ Alveolar air ¯ HCO3- HCO3- sac HbO2 HbO2 + + CO2 H+ H+ CO2 ¯ CO2 ­ CO2 CO2 + H2O CO2 + H2O Body cell Incr. pH- or - Acidity decreases Start Decreased pH (Incr. Acidity) (Hb affinity for oxygen increases) here!!! -Hb affinity for Oxygen decreases 65 66 O2 and CO2 movement in the lungs Summary: and tissues Learning Objectives Distribution of blood in the circulatory system at rest Structure of the respiratory system Physical Aspects of Ventilation Mechanics of breathing Hemoglobin and Oxygen Transport LUNGS TISSUE LEVEL 67 68 17  2025-01-24 Cardiovascular Lectures 3 & 4 Learning Objectives: Readings Version 12: Blood vessels: 427-431 How does our Heart -- beat? Structure of the Heart: 414-415 (end at Heart sounds). Include Figures 13.10, 13.11, 13.12, The whole heart? 13.14 The electrical activity of the heart? Cardiac Cycle, ECG: 418-425 (Include figures in The cells of the heart? lecture notes) Cardiac Muscle: 387-391 The cellular sarcomere? Mechanism of Contraction: 360-368 Critical thinking 69 70 Cardiovascular Lectures 3 & 4 Cardiovascular Lectures 3 & 4 Readings Version 13: Readings Version 14: Blood vessels: 432-436 (end at atherosclerosis) Blood vessels: 432-436 (end at atherosclerosis) Structure of the Heart: 418-419. Include Structure of the Heart: 418-419. Include Figures 13.10, 13.11, 13.12, 13.14 Figures 13.10, 13.11, 13.12, 13.14 Cardiac Cycle, ECG: 422-429 (Include figures in Cardiac Cycle, ECG: 422-429 (Include figures in lecture notes) lecture notes) Cardiac Muscle: 392-393 Cardiac Muscle: 392-393 Mechanism of Contraction: 364-373 Mechanism of Contraction: 364-373 71 72 18  2025-01-24 Cardiovascular Lectures 3 & 4 Cardiovascular Lectures 3 & 4 Readings Version 15: Readings Version 16: Blood vessels: 432-436 (end at atherosclerosis) Blood vessels: 430-435 (end at atherosclerosis) Structure of the Heart: 418-420. Include Structure of the Heart: 417-420. Include Figures 13.10, 13.11, 13.12, 13.14 Figures 13.10, 13.11, 13.12, 13.14 Cardiac Cycle, ECG: 422-429 (Include figures in Cardiac Cycle, ECG: 421-428 (Include figures in lecture notes) lecture notes) Cardiac Muscle: 392-393 Cardiac Muscle: 391-392 Mechanism of Contraction: 364-373 Mechanism of Contraction: 363-372 73 74 3D animation of working heart Cardiac Muscle http://www.youtube.com/watch?v=NF68qhyfcoM Cardiac cycle: Systole & Diastole http://www.youtube.com/watch?v=jLTdgrhpDCg The Cardiac Cycle http://www.youtube.com/watch?v=rguztY8aqpk Anatomy & Physiology Online. Cardiac Conduction System and it’s relationship with ECG. http://www.youtube.com/watch?v=v3b- YhZmQu8 Excitation-Contraction Coupling in Cardiac Muscle (Video, All Things Science - Heart excitation contraction coupling) (No links, just google the topics) Myosin is thick and Actin is thin http://www.youtube.com/watch?v=xhgDbjrrmFg Non-cardiac muscle contraction https://www.youtube.com/watch?v=RcweKl4_OVw 75 76 19  2025-01-24 3D ANIMATION OF WORKING OF HEART Cardiac Anatomy http://www.youtube.com/watch?v=NF68qhyfcoM 77 78 Cardiac Anatomy Cardiac Anatomy Atria and Ventricles are separated Because the amount of work performed by the into 2 functional units by a sheet LV is much greater (by a factor of 5-7) than of connective tissue, and there are that performed by the RV, it is not surprising one-way atrioventricular (AV) that the LV wall is thicker (8-10 mm) vs. the RV valves. Valves prevent backflow wall (2-3 mm). of blood into atria. AV valve between the RA and RV has 3 flaps = tricuspid valve. AV valve between LA and LV has 2 flaps = bicuspid valve – or sometimes called the “mitral valve” 79 80 20  2025-01-24 Cardiac Anatomy Cardiac Anatomy One-way semilunar When the ventricles are contracted, these valves are located at valves open so blood is pumped through the origin of the them. pulmonary artery (pumps deoxygenated During ventricular relaxation, the blood to the lungs) and semilunar valves snap shut so blood doesn’t aorta (pumps flow back into the ventricles. oxygenated blood to the body). 81 82 The Heart Valves The Heart Valves 83 84 21  2025-01-24 The Heart Valves The Cardiac Cycle Both atria fill with blood then contract simultaneously sending blood to ventricles. This is followed by simultaneous contraction of both ventricles, about 0.1-0.2 seconds later. (one of which sends blood to the lungs or pulmonary system, the second of which sends blood to the body or systemic system). Aortic and pulmonary semilunar valves, flaps in closed position. 85 86 The Cardiac Cycle The Cardiac Cycle Contraction of ventricles in systole ejects Therefore, STROKE VOLUME is the amount about 2/3rds of the blood they contain – an of blood coming from the ventricle in 1 heart amount called the STROKE VOLUME – leaving beat. 1/3rd the initial amount in the ventricles as the end-systolic volume. 87 88 22  2025-01-24 End Diastolic – filled: End Systolic - pumped 89 90 The Cardiac Cycle At an average What happens to Cardiac Output if your heart is cardiac rate of beating faster? 75 bpm, each cycle lasts 0.8 What happens to Cardiac Output if you have seconds… heart disease that prevents your heart from ejecting as much in systole? 0.5 sec = time spent in diastole CO = HR x SV 0.3 sec = time spent in systole 91 92 23  2025-01-24 Title: Cardiac Cycle - Systole & Diastole. Active link 2025 Putting it all together: Title: Cardiac Cycle. Link active 2025 http://www.youtube.com/watch?v=rguztY8aqpk http://www.youtube.com/watch?v=jLTdgrhpDCg 93 94 Electrical Activity of the Heart Electrical Activity of the Heart The electrical activity of the heart facilitates its pumping ability. 3 regions of the heart can Action potentials originate at the SA node: spontaneously generate action potentials: They spread to adjacent myocytes in RA and 1. Sinoatrial node (SA node) LA through gap junctions between these cells. (functions as pacemaker, located in the RA, near the opening of the superior vena cava) However the atria and ventricles are separate *Vagus nerve innervates the SA node, can so specialized cells are needed to move the adjust HR impulse atria to ventricles 2. AV Node These are the specialized myocardial cells in the AV node 3. Purkinje fibers 95 96 24  2025-01-24 Electrical Activity of the Heart Electrical Activity of the Heart Impulse starts at SA node Goes to AV node Continues through AV bundle (or “bundle of His”) Descends down the intraventricular septum, divides right & left with Purkinje fibers in the ventricle wall Spreads from endocardium to epicardium causing both ventricles to contract simultaneously 97 98 Timing Electrical Activity Starts at the SA node Impulse starts at SA node Sinoatrial – spreads quickly (0.8-1.0 meter/sec) (SA) node Left atrium Goes to AV node – conduction rate slows (0.03 to 0.05 m/sec) Right atrium Continues through AV bundle (or “bundle of His”) - Conduction rate increases SA node cells directly contact Descends down the intraventricular septum, atrial muscle cells divides right & left with Purkinje fibers in the ventricle wall - Conduction rate peaks at 5m/sec 99 100 25  2025-01-24 Moves to the Atrioventricular Node Moves to the Atrioventricular Bundle (His) Left Left atrium located in the atrium Right posterior septal Conduction rate atrium starts to increase wall of the right Right atrium AV Bundle and atrium, Node are only conduction rate connection slows, allowing AV between Bundle AV atria to contract AV node atria and node and fill ventricles ventricles 101 102 Purkinje Fibres/Bundle Branches The Electrocardiogram Potential differences generated by the heart are conducted to body surfaces where they can be Conduction rate peaks rapid conduction recorded by electrodes placed on the skin. caused by more positive resting membrane The recording is called an electrocardiogram (ECG Right potential and many gap or EKG). ventricle junctions synapse directly with ventricular myocytes ECG is not the recording of a single action potential, but it does result from the production Left and Right bundle branches and conduction of action potentials in the heart. Purkinje fibres 103 104 26  2025-01-24 The Electrocardiogram Anatomy & Physiology Online - Cardiac conduction system and its relationship with ECG http://www.youtube.com/watch?v=v3b-YhZmQu8 105 106 CRITICAL THINKING CVD is a leading cause of death worldwide. - 17 million people die each year (WHO). - A major contributor to this coronary heart disease, which leads to heart failure. - There is no known cure for HF - 50% of patients with HF die within 5 years. - USA estimates, $32.4 billion treating HF - USA estimates, $77.7 billion by 2030 107 108 27  2025-01-24 What is Coronary Artery Disease? What is Coronary Artery Disease? Occurs when you have plaque build-up in one or more of the 3 coronary If it partly restricts blood flow to the heart, it causes chest pain or arteries. angina 109 110 What is Coronary Artery Disease? Myocardial Infarction When build up of atherosclerosis is sufficient to interrupt blood flow it causes a myocardial infarction or heart attack…. Death of the heart muscle cells. 111 112 28  2025-01-24 ECG & Heart Disease ECG & Heart Disease S-T segment as a result of myocardial ischemia (heart attack) S-T segment as a result of myocardial ischemia (heart attack) Signal is heading out of the ventricles, they are relaxing, heading to diastole, but there-in lies the problem because of the infarct region 113 114 ECG & Heart Disease MORE CLINICAL PROBLEMS: 115 116 29  2025-01-24 117 118 Cardiac Muscle Heart muscle cells = myocardial cells Striated Contain actin filaments & myosin filaments arranged in the form of sarcomeres They contract via a sliding mechanism 119 120 30  2025-01-24 Cardiomyocytes beat in culture Cardiac Muscle Striations 121 122 Cardiac Muscle Cardiac Muscle Myocytes connected via gap junctions, at the ends of each myocardial cell, which permits electrical impulses to be conducted cell to cell (so heart Myocytes are organized into fibers cells beat in synchrony). These gap junctions stain (groups of myocytes) along with 2 as “intercalated discs”. major organelles – mitochondria for energy, and sarcoplasmic reticulum (SR) for calcium (Ca2+ handling). 123 124 31  2025-01-24 Cardiac Muscle Cardiac action potentials originate in the SA-node How does an electrical signal cause a (pacemaker). heart muscle cell to contract? Contraction follows Ca2+-induced Ca2+ release: Ca2+ enters myocyte cytoplasm through voltage-gated channels, then stimulates opening of the Ca2+ release channels in the sarcoplasmic reticulum SR. So Ca2+ from the voltage channels serves as a messenger for Ca2+ release channels In order for the heart muscles to relax, the Ca2+ in the cytoplasm must be pumped back into the SR. 125 126 Excitation-Contraction Coupling in Cardiac Excitation-Contraction Coupling in Cardiac Muscle Muscle Voltage gated calcium channels open… 1. Ca2+ diffuses from ECF to cytoplasm 2. Ca2+ release channels on SR open 3. Ca2+ released from SR binds to sarcomere, stimulates contraction 4. Ca2+ ATPase pumps calcium back into SR 5. Myocardial cell relaxes TEXT FIGURE 12.34 127 128 32  2025-01-24 Excitation-Contraction Coupling in Cardiac Muscle (Video, All Things Science - Heart excitation contraction How does all this lead to the heart coupling.flv, 0-1:30) cell contracting? We already know that muscle fibers are made up of thin (actin) filaments & thick (myosin) filaments Link active 2025: https://www.youtube.com/watch?v=0bEfAd8gJWM Lets look closer at how muscles are arranged…. 129 130 Microanatomy of muscle Microanatomy of muscle Cells are arranged into The Z-discs are proteins that act as anchors long, rod-shaped organelles that are called myofibrils for thin protein filaments; these consist of a protein called actin, and other proteins that The myofibril rods have a will be introduced later distinct striated pattern of alternating light and dark bands And z-discs Myofibril 131 132 33  2025-01-24 Microanatomy of muscle Microanatomy of muscle Myofibril Titin/cap myosin Z-disc Each myofibril is separated into Sarcomere separate sections by protein structures call “Z-discs”; the section of the fibre between Z-discs is called a sarcomere Z-discs 133 134 Microanatomy of muscle Microanatomy of muscle Lying in between the thin filaments are thicker filaments Thick of another protein called myosin Relaxed filament Muscles contract myofibril when the thin and thick filaments slide past one another, and the Z- discs move closer Contracted together myofibril Thin filaments 135 136 34  2025-01-24 Microanatomy of muscle Microanatomy of muscle H-zone Z-disc Z-disc The overlapping of the thin and thick filaments gives the striated pattern A-band I-band A-band I-band A-band The light bands are called “I-bands” The dark bands are called “A-bands” The Z-discs lie in the middle of the I-bands In the centre of the A-band is a narrow light band, called the “H-zone” 137 138 Microanatomy of muscle And there are 2 few more major molecules in play… in addition to the actin and myosin: The thick filaments (TF) are made up rod-shaped proteins, that have an TF angular head at one end The contraction of muscle is caused by the swiveling of the head TF Actin Head Tropomyosin - attached to actin. Rod-shaped myosin Troponin complex of 3 subunits is attached to tropomyosin protein 139 140 35  2025-01-24 The myosin head has an actin- Putting it all together: Excitation-Contraction Coupling in binding site and an ATP-binding Cardiac Muscle (Video, All Things Science - Heart site. When ATP is hydrolyzed to excitation contraction coupling.flv – entire video this ADP, myosin head becomes activated and changes orientation. time) Attachment of Ca2+ to troponin causes movement of the troponin- tropomyosin complex, exposing binding sites on the actin. Myosin cross bridges can then attach to actin and undergo a power stroke. Link active 2025: https://www.youtube.com/watch?v=0bEfAd8gJWM 141 142 Myosin filaments on a plate of Actin Decreased Ca2+ Increased Ca2+ Dawson Lab 143 144 36  2025-01-24 Number #1 NOTE: there are 3 main differences - Skeletal Muscles require external between Cardiac & Skeletal muscle stimulation by somatic motor nerves contraction are: vs. - Cardiac Muscle produces action potentials automatically (SA node) 145 146 Number #2 Number #2 - Skeletal muscles are long and fibrous …… vs. - Myocardial cells are short, branched, and interconnected. Cells are tubular in structure and adjoined to adjacent myocardial cells by electrical synapses (gap junctions). 147 148 37  2025-01-24 Number #3 Muscle contraction video Muscle Contraction Pearson - Skeletal muscles have direct excitation- contraction coupling between the transverse tubules and SR vs. - Cardiac cells the voltage gated Ca2+ channels in the plasma membrane and the Ca2+ release channels in the SR do not directly interact, instead it is Ca2+- https://www.youtube.com/watch?v=RcweKl4_OVw induced Ca2+ release 149 150 Do animals get coronary heart disease? Congenital heart problems? Congestive heart failure? CLINICAL Are treatments in humans are relevant to animals? PROBLEMS Do they have other conditions as well e.g. insufficient taurine in : diet (cats) – heart failure - Humans do not produce taurine and need dietary sources. - Cats do produce taurine but also need a well-balanced diet so commercial cat foods have added taurine (in the 1980’s when the deficiency became well recognized) 151 152 38  2025-01-24 Why don’t cats get coronary heart disease? They do have congenital heart problems, congestive heart failure, treatments in humans are relevant to animals. Doberman Pinscher Insufficient taurine in diet (cats) – heart failure Video 153 154 155 156 39  2025-01-24 Summary of Learning Objectives: How does our Heart -- beat? The whole heart? The electrical activity of the heart? The cells of the heart? The cellular sarcomere? Critical thinking 157 158 40