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Cardiovascular System: The Heart

Cardiovascular System: The Heart

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Cardiovascular System: The Heart

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  1. Cardiovascular System:The Heart

  2. Functions of the cardiovascular System

  3. Transports O2, nutrients, CO2, cell wastes, etc. to and from body cells • Maintaining body temperature • Homeostatic relationships with all body systems • With the urinary system, regulation of blood volume and pressure

  4. Location of the heart

  5. Thoracic cavity between two lungs • ~2/3 to left of midline Surrounded by pericardium: • Fibrous pericardium - • Inelastic; anchors heart in place • Inside is serous pericardium - double layer around heart • Parietal layer fused to fibrous pericardium • Inner visceral layer adheres tightly to heart • Filled with pericardial fluid - reduces friction during beat.

  6. Heart anatomy

  7. The Heart Wall • Epicardium - outer layer • Myocardium - cardiac muscle • Two separate networks via gap junctions in intercalated discs - atrial & ventricular • Networks- contract as a unit • Endocardium - Squamous epithelium • lines inside of myocardium

  8. The Heart Wall

  9. The Heart Wall

  10. The Heart Wall

  11. Heart Chambers 4 chambers: • 2 upper chambers = Atria • Between is inter-atrial septum • Contains fossaovalis - remnant of foramen ovalis • 2 lower chambers = ventricles • Between is interventricular septum • Wall thickness depends on work load • Atria thinnest • Right ventricle pumps to lungs & thinner than left

  12. External Anatomy

  13. External Anatomy

  14. Internal Anatomy

  15. Great Vessels of the Heart Superior & inferior Vena Cavae • Delivers O2 depleted blood to R. atrium from body • Coronary sinus drains heart muscle veins • R. Atrium  R. Ventricle Pumps through Pulmonary Trunk • R & L Pulmonary Arteries •  lungs

  16. Great Vessels of the Heart Pulmonary Veins from lungs • O2 rich blood • L. atrium Left ventricle ascending aorta body Between pulmonary trunk & aortic arch is the ligamentumarteriosum • fetal ductusarteriosum remnant

  17. Heart Valves Designed to prevent back flow in response to pressure changes • Atrio-ventricular (AV) valves are found between the atria and ventricles • Right AV valve = tricuspid valve (has three flaps, or cusps) • Prevent backflow of blood into the right atrium

  18. Heart Valves • Left AV valve = bicuspid, or mitral valve • Prevents backflow of blood into left atrium Semilunar Valves are found at the base of aorta and pulmonary trunk • Prevent backflow of blood into the ventricles

  19. Heart Valves ChordaeTendinae: • Tiny white cords that anchor the AV valve cusps to the wall of the ventricle • Help to anchor the flaps to prevent a prolapse

  20. Coronary Circulation Blood flow through vessels in myocardium = coronary circulation • Left & right coronary arteries • branch from aorta to carry blood throughout muscle • O2 - depleted blood collected by coronary sinus (posterior) • Empties into right atrium

  21. Coronary Circulation

  22. Heart physiology

  23. Conduction System 1% of cardiac muscle generate action potentials = Pacemaker & Conduction system • Normally begins at sinoatrial (SA) node • Atria & atria contract AV node – slows the signal, then travels along: AV bundle (Bundle of His) bundle branches Purkinje fibers  apex and up- then ventricles contract

  24. Frontal plane Left atrium Right atrium 1 SINOATRIAL (SA) NODE 2 ATRIOVENTRICULAR (AV) NODE 3 ATRIOVENTRICULAR (AV) BUNDLE (BUNDLE OF HIS) Left ventricle 4 RIGHT AND LEFT BUNDLE BRANCHES Right ventricle 5 PURKINJE FIBERS Anterior view of frontal section

  25. Electrocardiogram Recording of currents from cardiac conduction on skin = electrocardiogram (EKG or ECG) • P wave = atrial depolarization • Contraction begins right after peak • Repolarization is masked in QRS • QRS complex = Ventricular depolarization • Contraction of ventricle • T-wave = ventricular repolarization • Just after ventricles relax

  26. Cardiac Cycle After T-wave ventricular diastole • Ventricular pressure drops below atrial pressure & AV valves open  ventricular filling occurs After P-wave atrial systole • Finishes filling ventricle (about 25% of total)

  27. Cardiac Cycle After QRS ventricular systole • Pressure pushes AV valves closed • Pushes semilunar valves open and ejection occurs • Ejection until ventricle relaxes enough for arterial pressure to close semilunar valves Cardiac Cycle Animations

  28. Cardiac Cycle: Flow Terms • Cardiac Output (CO) = liters/min pumped • Heart Rate (HR) = beats/minute (bpm) • Stroke volume (SV) = volume/beat • CO = HR x SV • Average:

  29. Cardiac Cycle: Control of Stroke Volume • Degree of stretch = Frank-Starling law • Increase diastolic volume (stretch) increases strength of contraction increased S.V. • Increased venous return  increased S.V. • Increased sympathetic activity • High back pressure in artery  decreased S.V. • Slows semilunar valve opening • Slow heart rate  increased S.V.

  30. Cardiac Cycle: Control of Heart Rate Pacemaker adjusted by nerves • Cardiovascular Center in Medulla Parasympathetic - ACh slows HR via Vagus nerve Sympathetic - norepinephrine speeds HR Sensory input for control: • Baroreceptors (aortic arch & carotid sinus)- B.P. • Chemoreceptors- O2, CO2, pH

  31. Cardiac Cycle: Other Controls Hormones: • Epinephrine & norepinephrine increase H.R. • Thyroid hormones stimulate H.R. • Called tachycardia (opposite: bradycardia) Ions • Increased Na+ or K+ decrease H.R. & contraction force • Increased Ca2+ increases H.R. & contraction force

  32. Exercise • Aerobic exercise (longer than 20 min) strengthens cardiovascular system • Well trained athlete doubles maximum C.O. • Resting C.O. about the same but resting H.R. decreased

  33. Blood vessels and circulation

  34. Blood Vessels Arteries: carry blood away from heart • Elastic • Muscular: Their smooth muscle helps regulate blood pressure, directs flow • Arterioles: branches of main arteries; distribution to capillaries

  35. Blood Vessels Capillaries: thin-walled for diffusion Veins: carry blood back to heart • Venules: collect blood from capillaries • Veins from tissues  vena cavae heart

  36. Blood Vessel Structure: Arteries, Veins Three Layers: • Tunica externa: connective tissue • Tunica media: smooth muscle • Tunica interna (intima): endothelial tissue

  37. Blood Vessel Structure: Arteries, Veins • Arteries: thicker tunica media • Elastic tissue and/or muscle • Arterioles • Arterioles: control blood pressure, blood flow • Veins • Larger lumen, thinner walls • Contain valves to prevent backflow • Venules • Venules: very thin, no valves

  38. Blood Vessel Structure: Arteries, Veins

  39. Blood Vessel Functions • Muscular arteries, arterioles regulate flow • Sympathetic activity to smooth muscle  vasoconstriction (narrowing) • Decreased sympathetic activity causes relaxation (dilation) • Arterioles adjust flow into capillaries • Capillaries: sites of gas exchange • Systemic venules and veins serve as blood reservoirs (hold ~64% total blood volume)

  40. Venous Return Blood enters veins at very low pressure • Inadequate to overcome gravity and return blood to heart • Skeletal muscle contractions • Contracting skeletal muscles (especially in lower limbs) squeeze veins emptying them • Because of venous valves, flow is  heart

  41. Venous Return • Respiratory pump has similar action • Inhalation decreases thoracic pressure and increases abdominal pressure  blood to heart • Exhalation allows refilling of abdominal veins

  42. Venous Return

  43. Blood Flow Through Vessels Blood flow follows a pressure gradient • Greater gradient  greater flow • BP is highest in aorta: 110/70 mm Hg • BP declines as flows through more vessels • Capillary beds ~35-16 mm Hg • 16 mm Hg at venules  0 at right atrium

  44. Factors Regulating Blood Flow • Blood volume and ventricular contraction  cardiac output • Vascular resistance: opposition to flow (depends on lumen diameter, vessel length, and blood viscosity) • Smaller lumen (vasoconstriction)  greater resistance • Greater vessel length (with weight gain)  greater resistance • Higher viscosity (as with high hematocrit)  greater resistance

  45. Cardiovascular Center • Located in medulla • Helps regulate • Heart rate • Stroke volume • Blood pressure • Blood flow to specific tissues • Mechanisms • By neural mechanisms • By hormonal mechanisms