Stack #123096
| Description: | Cardiac Physiology |
| Category: | Physiology |
| Created by: | zeenat on 2008-03-02 |
| Question | Answer |
| Properties of Cardiac Muscle | -Striated -contraction occurs using same sliding filament mechanism. -cardiac are diff b/c they are short, fat, branched + interconnected -Cardiac muscle fibers have only 1-2 nuclei. More mitochondria. |
| Properties of Cardiac Muscle II | Desmosomes - hold cells together + prevent separation during contraction Gap Junctions - Allow for AP to pass freely from cell to cell so whole heart contracts instead of a few cells -all cells in heart are coupled electrically by gap junctions |
| Cardiac Action Potential | 1% cardiac muscle = authorhymic -> start own depolarizations which leads to dp of rest of the Heart (pacemaker cells) -Cardiac muscle = all or none effect -abs refractory period of card. musc. longer - almost as long as contraction. |
| Cardiac Muscle Contraction | 90%- contractile - resp. for pumping heart 10-20% Ca need for contraction enters extracellular space. Depolarization -> Na channels opened Slow Ca opened ->influx of Ca K+ enters = repolarization * READ NOTES |
| Excitation + Electrical Events: Intrinsic Conduction System of Heart | - heart does not depend on nervous system to depolarize/contract. inbuilt mechanism = intrinsic cardiac conduction system. Pacemake cells→self excitory + initiate/distribute impulses. |
| Cardiac Conduction System | Sinoatrial Node→R atrium where superior vena cava enters. Internodal Pathways→direct pathway from SA node to AV - no gap junctions. AV Node→ fibrous septum btwn R atrium + R vent. Purkinje Fibres→branch off AV bundle |
| Cardiac Conduction System II STEP 1 | Activation of an AP in the SA node first Time = 0 |
| Cardiac Conduction System II STEP 2 | Transmitted into the atrial myosites -Reaches AV Node Time = 50 sec |
| Cardiac Conduction System II STEP 3 | 100-second delay @ AV Node. Atrial Contraction begins. Time = 150 sec |
| Cardiac Conduction System II STEP 4 | Impulse travels along the interventricular septum within AV bundle. Bundle branches into Purkinje Fibres via moderater band to papillary muscles of R ventricle time = 175 sec |
| Cardiac Conduction System II STEP 5 | Impulse distributed by Purkinje fibres. relayed thruout ventricular myocardium. Atrial contraction completed. Vent. contraction begins time = 225 seconds |
| Cardiac Conduction System III | No gap junctions between cardiomyocites of atria/ventricles. Av Bundle - only electrical connection btwn atria/ventricles. Branches into 2 paths -connects to purkinje fibres - rapid conduction b/c large fibres + large gap junctions Defects = arrhymias |
| Electrocardiography | -diagnostic tests records electrical activity in heart by placing electrodes on body P-wave-dp of atria, QRS complex-dp of ventricle+rp of atria at same time, T-wave-small rp of ventricle |
| Electrocardiography II | P-R Interval = time it takes for impulse to travel from SA>AV thru penetrating fibres down AV bundle Purkinje fibres O-T Interval - time it takes for ventricle to contract + relax again |
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General Characteristics of the Cardiovascular System Humans possess a closed circulatory system. Structure: series of tubes (i.e. blood vessels), fluid (i.e. blood), and a pump (i.e. heart) Function: transportation Blood flow is described by 2 equations: Ohm’s law Blood flow (Q) = change in Pressure/Resistance Poiseuille’s law: Blood flow (Q) = change in P p r4/8 x viscosity x length Resistance – the tendency of the cardiovascular system to oppose blood flow Due to blood vessel length and diameter and blood viscosity Blood velocity = flow rate / cross-sectional area Heart is enveloped by the pericardium Composition cardiac muscle Prominent myocardium Cardiac myocytes Small, branched fibers Mononucleated Gap junctions within intercalated disks Prominent t-tubules, small SR Numerous mitochondria Heart is an autorhythmic organ Specialized myocytes serve as pacemakers Einthoven’s triangle Einthoven’s Law: lead I + lead III = lead II Stroke volume = 135 – 65 = 70 mL Cardiac output = 70 mL x 70 bpm = 5 L/min Walls of blood vessels contain large numbers of vascular smooth muscle cells Contraction or relaxation of vascular smooth muscle results in changes in blood vessel diameter vasoconstriction + vasodilation SM is sensitive to a variety of chemical stimuli Vasoconstrictors: Norepinephrine Endothelin Serotonin Vasopressin Angiotensin II Vasodilators: Prostacyclin Histamine Epinephrine Acetylcholine Bradykinin Adenosine Capillaries are the site of exchange between the blood and interstitial fluid. Angiogenesis is the process by which new blood vessels develop Definition – the force imposed on the walls of blood vessels by blood as it travels throughout the circulatory system BP = CO x TPR CO = cardiac output TPR = total peripheral resistance BP = CO x TPR Influenced by blood volume and vessel diameter Hypertension Hypotension Definition – the return of blood to the right atrium via the vena cava Facilitated by skeletal muscle pump and respiratory pump Regulation of blood flow is local! Blood flow is autoregulated There are 2 major mechanisms for regulating local blood flow: Myogenic autoregulation Metabolic autoregulation Mechanisms of capillary exchange: 1. Diffusion 2. Transcytosis 3. Bulk flow – mass movement of fluid due to osmotic or hydrostatic gradients; filtration or absorption |
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