Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Heart failure wikipedia , lookup
Management of acute coronary syndrome wikipedia , lookup
Coronary artery disease wikipedia , lookup
Electrocardiography wikipedia , lookup
Cardiac surgery wikipedia , lookup
Cardiac contractility modulation wikipedia , lookup
Myocardial infarction wikipedia , lookup
BIOENGENHARIA MÉDICA MÚSCULO CARDÍACO Abril 31, 2008 Eduardo Infante de Oliveira Instituto de Fisiologia, FML FACULDADE MEDICINA LISBOA MÚSCULO CARDÍACO l Abril 31, 2008 l 2 FACULDADE MEDICINA LISBOA MÚSCULO CARDÍACO l Abril 31, 2008 l 3 FACULDADE MEDICINA LISBOA MÚSCULO CARDÍACO l Abril 31, 2008 l 5 Orientation of cardiac muscle fibres: Unlike skeletal muscles, cardiac muscles have to contract in more than one direction. Cardiac muscle cells are striated, meaning they will only contract along their long axis. In order to get contraction in two axis, the fibres wrap around. FACULDADE MEDICINA LISBOA MÚSCULO CARDÍACO l Abril 31, 2008 l 7 TYPES OF MUSCLE LOCATION MICROSCOPIC APPEARANCE RELATIONSHIP WITH THE NERVOUS SYSTEM VOLUNTARY SPEED OF CONTRATION SKELETAL HEAVYILY STRIATED SLOW TO FAST CONTRACTIONS VISCERAL NONSTRIATED INVOLUNTARY VERY SLOW (SMOOTH) CONTRACTIONS CARDIAC LIGHTLY STRIATED AUTORHYTHMIC SLOW CONTRACTIONS Characteristics of Skeletal, Cardiac, and Smooth Muscle Table 10–4 Cardiac Tissue • Cardiac muscle is striated, found only in the heart • 7 Characteristics of Cardiocytes • Unlike skeletal muscle, cardiac muscle cells (cardiocytes): – are small – have a single nucleus – have short, wide T tubules – have no triads – have SR with no terminal cisternae – are aerobic (high in myoglobin, mitochondr – have intercalated discs Figure 10–22 Intercalated Discs • Are specialized contact points between cardiocytes • Join cell membranes of adjacent cardiocytes (gap junctions, desmosomes) • Functions – Maintain structure – Enhance molecular and electrical connections – Conduct action potentials • Because intercalated discs link heart cells mechanically, chemically, and electrically, the heart functions like a single, fused mass of cells FACULDADE MEDICINA LISBOA MÚSCULO CARDÍACO l Abril 31, 2008 l 14 Structure of Cardiac Muscle Cell 15 Cardiac muscle Cardiac muscle – section – H&E – 40x objective striations intercalated disc centrally-located nucleus One distinguishes cardiac muscle from skeletal muscle by the branching fibers, presence of intercalated discs, and centrally-placed single nuclei/cell. Cardiac muscle Cardiac muscle –section – silver – 20x objective branching intercalated disc nucleus This stain clearly shows the single central nucleus, branching fibers, intercalated discs, and striations. T: T tubules mit: mitochondria g: glycogen contractile unit: sarcomere Z line: the actin filaments are attached I: band of actin filaments, titin and Z line A: band of actin-myosin overlap H: clear central zone containing only myosin AP-contraction relationship: AP in skeletal muscle is very short-lived AP is basically over before an increase in muscle tension can be measured. AP in cardiac muscle is very long-lived AP has an extra component, which extends the duration. The contraction is almost over before the action potential has finished. Cardiac myocyte action potential: Refractory Period Absolute: Cardiac muscle cell completely insensitive to further stimulation Relative: Cell exhibits reduced sensitivity to additional stimulation Long refractory period prevents tetanic contractions Cardiac vs. Skeletal Muscle Contraction Cardiac Muscle Action Potential Extracellular Calcium Ions Type of contraction Skeletal Muscle Duration: 250-300 msec Duration: 10 msec Delay repolarization & initiate contraction Initiate contraction Long refractory period Tetanus occurs which continues while because short relaxing = no tetanus! refractory period Cardiac conducting system: Pacemaker potential: Pacemaker regulation: Once the pacemaker cells reach threshold, the magnitude and duration of the AP is always the same. In order to change the frequency, the time between APs must vary. The interval can only be changed in two ways. The rate of depolarization can be changed The amount of depolarization required to reach threshold can be changed. The conduction system of the heart. EE-515 Bioelectricity & Biomagnetism 2002 Fall - Murat Electrophysiology of the heart The different waveforms for each of the specialized cells EE-515 Bioelectricity & Biomagnetism 2002 Fall - Murat • Principle of Continuity: • • • • Conservation of mass in a closed hydraulic system Blood is an incompressible fluid Vascular system is a closed hydraulic loop Vol ejected from left heart = vol received in R heart Pressure relationships: Curva Pressão-Volume Ventricular Cardiac Output and EDV Regulation of the Heart Intrinsic regulation: Results from normal functional characteristics, not on neural or hormonal regulation Starling’s law of the heart Extrinsic regulation: Involves neural and hormonal control Parasympathetic stimulation Supplied by vagus nerve, decreases heart rate, acetylcholine secreted Sympathetic stimulation Supplied by cardiac nerves, increases heart rate and force of contraction, epinephrine and norepinephrine released Heart Homeostasis Effect of blood pressure Effect of pH, carbon dioxide, oxygen Chemoreceptors monitor Effect of extracellular ion concentration Baroreceptors monitor blood pressure Increase or decrease in extracellular K+ decreases heart rate Effect of body temperature Heart rate increases when body temperature increases, heart rate decreases when body temperature decreases