Department of medical physiology 7 th week and 8 th week

Transcription

1 Department of medical physiology 7 th week and 8 th week Semester: winter Study program: Dental medicine Lecture: RNDr. Soňa Grešová, PhD. Department of medical physiology Faculty of Medicine PJŠU

2 Cardiovascular system 1. The basic properties of the myocardium 2. Excitation and conduction of the heart impulse 3. Metabolism and energetics of the heart

3 Cardiovascular system function Functional components of the cardiovascular system: Heart Blood Vessels Blood General functions these provide Transportation Everything transported by the blood Regulation Of the cardiovascular system Intrinsic v extrinsic Protection Against blood loss Production/Synthesis

4 Three layers Cardiovascular system Heart Wall Epicardium (outer layer) Myocardium (middle) Endocardium (inner layer)

5 Copyright: d=0ahukewjf5y6t2zvqahwhbhqkhcjxaqsq_auibigb#imgrc=8t9wfe7ll-r6gm%3a Myocardial cells (working cells) Contraction Cardiovascular system Electrical conduction system cells Initiate and carry electrical impulses throughout heart Heart Cells

6 Cardiovascular system Working Cells Myocytes Enclosed in sarcolemma Composed of : Actin filaments (thin) Myosin filaments (thick)

7 Intercalated discs Cardiovascular system the cell membranes fuse with one another (gap junctions) Myocardial Cells ions move with ease in the intracellular fluid along the longitudinal axes

8 Cardiovascular system Heart consists of four chambers 2 atria collect blood and deliver to ventricles 2 ventricles pump blood to pulmonary and systemic circulation Septum separates heart into two functional units Internal Heart Copyright: Hall, J. E., & Guyton, A. C. (2006). Guyton and Hall textbook of medical physiology. Philadelphia, PA: Saunders Elsevier.

9 Cardiovascular system Heart Valves Function is to prevent backflow - Mitral and bicuspid valve (AV valve) Prevent backflow to the atria Prolapse is prevented by the chordae tendineae Tensioned by the papillary muscles - Tricuspid valve (AV valve) - Aortic and pulmonic valves (semilunar valves) Prevent backflow into ventricles Copyright: Hall, J. E., & Guyton, A. C. (2006). Guyton and Hall textbook of medical physiology. Philadelphia, PA: Saunders Elsevier.

10 Cardiovascular system Fibrous tissue : Forms fibrous rings around AV and semilunar valves Provides firm support for valves and separates atria from ventricles Cardiac muscle Attached to fibrous connective tissue Contract ventricles in a wringing motion Skeleton of Heart Copyright: Hall, J. E., & Guyton, A. C. (2006). Guyton and Hall textbook of medical physiology. Philadelphia, PA: Saunders Elsevier.

11 Cardiovascular system Heart s Conduction System Consists of pacemaker cells and conduction pathways Coordinate the contraction of the atria and ventricles Copyright: Hall, J. E., & Guyton, A. C. (2006). Guyton and Hall textbook of medical physiology. Philadelphia, PA: Saunders Elsevier.

12 SA node is primary pacemaker site of heart Normal rate times per minute Cardiovascular system Pacemaker Sites Other cardiac cells lower in conduction pathway play a backup role AV node (rate times per minute) Purkinje fibers (rate times per minute) Copyright: Hall, J. E., & Guyton, A. C. (2006). Guyton and Hall textbook of medical physiology. Philadelphia, PA: Saunders Elsevier.

13 Resting membrane potential Inside of myocardial cells more negatively charged in relationship to outside where it is more positively charged Copyright:

14 Depolarization Occurs when positively charged ions move inside cells causing interior to become positively charged Change in electrical charge over time referred to as cell s action potential Copyright:

15 Autorhythmic Cells (Pacemaker Cells) Characteristics of Pacemaker Cells

16 Excitation and conduction of the heart impulse Phases 4 resting membrane potential -90mV 0 depolarization Due to gap junctions or conduction fiber action Voltage gated Na+ channels open close at 20mV 1 temporary repolarization Open K+ channels allow some K+ to leave the cell 2 plateau phase Voltage gated Ca2+ channels are fully open (started during initial depolarization) 3 repolarization Ca2+ channels close and K+ permeability increases as slower activated K+ channels open, causing a quick repolarization Copyright: the-heart/deck/

17 Excitation and conduction of the heart impulse Plateau phase prevents summation due to the elongated refractory period - absolute refractory period - the relative refractory period No summation capacity = no tetanus Copyright: Copyright:

18 Contractile Cells Plateau phase

19 Repolarization Follows depolarization and occurs when: Potassium leaves cell causing positive charge to lower Sodium and calcium are removed by special transport systems Copyright: the-heart/deck/

20 Key Properties of Myocardial Automaticity (Chronotropic effect) Can produce electrical activity without outside nerve stimulation Conductivity (Dromotropic effect) Ability to transmit an electrical stimulus from cell to cell throughout myocardium Excitability (Batmotropic effect) Ability to respond to an electrical stimulus Contractility (Inotropic effect) Ability of myocardial cells to contract when stimulated by an electrical impulse Cells Copyright: Hall, J. E., & Guyton, A. C. (2006). Guyton and Hall textbook of medical physiology. Philadelphia, PA: Saunders Elsevier.

21 Electrocardiography (ECG or EKG) The EKG device detects and amplifies the tiny electrical changes on the skin that are caused when the heart muscle depolarizes during each heartbeat. During each heartbeat a healthy heart will have an orderly progression of a wave of depolarisation that is triggered by the cells in the sinoatrial node, spreads out through the atrium, passes through "intrinsic conduction pathways" and then spreads all over the ventricles. A 12-lead EKG is one in which 12 different electrical signals are recorded at approximately the same time and will often be used as a one-off recording of an EKG, traditionally printed out as a paper copy.

22 Electrocardiography (ECG or EKG) Copyright: Hall, J. E., & Guyton, A. C. (2006). Guyton and Hall textbook of medical physiology. Philadelphia, PA: Saunders Elsevier.

23 Electrocardiography (ECG or EKG) Heartbeat initiated by an electrical impulse that arises from SA node Impulse travels through atria (P wave) generates a positive waveform on ECG and contraction of atria Copyright: Hall, J. E., & Guyton, A. C. (2006). Guyton and Hall textbook of medical physiology. Philadelphia, PA: Saunders Elsevier.

24 Electrocardiography (ECG or EKG) Impulse slows as it passes through AV node from atria to ventricles (PR segment) Allows atria time to finish filling ventricles Impulse then rapidly travels through His- Purkinje system Seen as a flat line following P wave Copyright: Hall, J. E., & Guyton, A. C. (2006). Guyton and Hall textbook of medical physiology. Philadelphia, PA: Saunders Elsevier.

25 Electrocardiography (ECG or EKG) Depolarization of septum and ventricular walls generates QRS complex and contraction of ventricles Copyright: Hall, J. E., & Guyton, A. C. (2006). Guyton and Hall textbook of medical physiology. Philadelphia, PA: Saunders Elsevier.

26 Electrocardiography (ECG or EKG) Repolarization of ventricles is represented on ECG by ST segment (plateau phase) and T wave Copyright: Hall, J. E., & Guyton, A. C. (2006). Guyton and Hall textbook of medical physiology. Philadelphia, PA: Saunders Elsevier.

27 Electrocardiography (ECG or EKG) Waves - P - QRS - T Segments - PR - ST Intervals - PR - QRS - QT Copyright: Hall, J. E., & Guyton, A. C. (2006). Guyton and Hall textbook of medical physiology. Philadelphia, PA: Saunders Elsevier.

28 Cardiac axis orientation Pregnant women, people older than 40y, small fat people ( ) People older than 30y, ( ) People younger than 30y, ( ) Children ( ) Copyright: Hall, J. E., & Guyton, A. C. (2006). Guyton and Hall textbook of medical physiology. Philadelphia, PA: Saunders Elsevier.

29 3. Metabolism and energetics of the heart Heart muscle is highly oxidative tissue. Mitochondrial respiration produces more than 90% of energy Mitochondria occupy 30% of cardiomyocyte space >95% of ATP formation comes from oxidative phosphorylation in mitochondria 60-70% of ATP hydrolysis is used for muscle contraction, 30-40% for the sarcoplasmatic reticulum (SR) Ca 2+ -ATPase and other ion pumps.