Chapter 18 - The Cardiovascular System - Heart
- Size - Approximately the size of your fist
- Location
- Superior surface of diaphragm
- Left of the midline
- Anterior to the vertebral column, posterior to the sternum
- Coverings of the Heart
- Pericardium - a double-walled sac around the heart composed of:
- A superficial fibrous pericardium
- A deep two-layer serous pericardium
- The parietal layer lines the internal surface of the fibrous pericardium
- The visceral layer or epicardium lines the surface of the heart
- They are separated by the fluid-filled pericardial cavity
- Protects and anchors the heart
- Prevents overfilling of the heart with blood
- Allows for the heart to work in a relatively friction-free environment
- An inflammation of the pericardium is known as pericarditis. Associated bleeding into the pericardial cavity compresses the heart (cardiac tamponade) and is potentially lethal.
- Heart Wall
- Epicardium - visceral layer of the serous pericardium
- Myocardium - cardiac muscle layer forming the bulk of the heart
- Fibrous skeleton of heart - crisscrossing, interlacing layer of connective tissue
- Endocardium - endothelial layer of the inner myocardial surface
- Trabeculae carneae
- Pectinate muscle
- Anterior View
- Vessels returning blood to the heart include:
- Superior and inferior venae cavae
- Right and left pulmonary veins
- Vessels conveying blood away from the heart include:
- Pulmonary trunk , which splits into right and left pulmonary arteries
- Ascending aorta - brachiocephalic, left common carotid, subclavian arteries
- Vessels that Supply/Drain the Heart (Anterior View)
- Arteries - right and left coronary (in atrioventricular groove), marginal, circumflex, and anterior interventricular arteries
- Veins - small cardiac, anterior cardiac, and great cardiac veins
- Note the ligamentum arteriosum
- Remnant of the fetal ductus arteriosus
- Purpose?
- Posterior View
- Vessels returning blood to the heart include:
- Right and left pulmonary veins
- Superior and inferior venae cavae
- Vessels conveying blood away from the heart include:
- Right & left pulmonary arteries
- Aorta
- Vessels that Supply/Drain the Heart (Posterior View)
- Arteries - right coronary artery (in atrioventricular groove) and the posterior interventricular artery (in interventricular groove)
- Veins - great cardiac vein, posterior vein to left ventricle, coronary sinus, and middle cardiac vein
- Atria are the receiving chambers of the heart
- Each atrium has a protruding auricle
- Blood enters left atria from pulmonary veins
- Blood enters right atria from sup & inf venae cavae, coronary sinus
- Fossa ovalis which is a remnant of fetal foramen ovale
- Ventricles are the discharging chambers of the heart
- Papillary muscles & trabeculae carneae muscles mark ventricular walls
- Right ventricle pumps blood into the pulmonary trunk
- Left ventricle pumps blood into the aorta
- Heart valves ensure unidirectional blood flow through the heart
- Atrioventricular (AV) valves lie between the atria and the ventricles
- Right AV valve - tricuspid
- Left AV valve - bicuspid (Mitral)
- AV valves prevent backflow into the atria when ventricles contract
- Chordae tendineae anchor AV valves to papillary muscles
- Semilunar valves prevent backflow of blood into the ventricles
- Aortic semilunar valve lies between the left ventricle and the aorta
- Pulmonary semilunar valve lies between the right ventricle and pulmonary trunk
- Heart sounds (lub-dup) are associated with closing of heart valves
- First sound: AV valves close and signifies beginning of systole
- Second sound: SL valves close beginning of ventricular diastole
- Incomplete closure produces a __________.
- Interactive Review
- Right atrium --> tricuspid valve --> right ventricle
- Right ventricle --> pulmonary semilunar valve -->
- To Pulmonary Circulation-->
- pulmonary arteries --> Lungs --> pulmonary veins --> left atrium
- Left atrium --> bicuspid valve --> left ventricle
- Left ventricle --> aortic semilunar valve --> aorta
- Aorta --> To Systemic circulation
- Trace the circulation
- Coronary circulation is the functional blood supply to the heart muscle itself
- Collateral routes ensure blood delivery to heart even if major vessels are occluded
- Poor circulation due to clots, fatty atherosclerotic plaques results in
- Cardiac muscle is striated, short, fat, branched, and interconnected
- The connective tissue endomysium acts as both tendon and insertion
- Purkinge fibers conduct action potential
- Intercalated discs anchor cardiac cells together and allow free passage of ions
- Heart muscle behaves as a functional syncytium
- lnability to develop an 02 debt
- many mitochondria
- intense capillary network (anastomoses)
- uses fatty acids and lactic acid
- Cardiac Muscle Contraction
- Heart muscle:Is stimulated by nerves and is self-excitable (automaticity)
- Contracts as a unit
- Has a long (250 ms) absolute refractory period
- Cardiac muscle contraction is similar to skeletal muscle
Heart Physiology
- Intrinsic Conduction System
- Contraction Autorhythmic cells:
- Initiate action potentials
- Have unstable resting potentials called pacemaker potentials
- Use calcium influx (rather than sodium) for rising phase of the action potential
- Sequence of Excitation
- Sinoatrial (SA) node generates impulses about 75 times/minute
- Atrioventricular (AV) node delays the impulse approximately 0.1 second
- Impulse passes from atria to ventricles via the atrioventricular bundle (bundle of His)
- AV bundle splits into two pathways in the interventricular septum (bundle branches)
- Bundle branches carry the impulse toward the apex of the heart
- Purkinje fibers carry impulse to the heart apex and ventricular walls
- Extrinsic Innervation of the Heart
- Heart is stimulated by the sympathetic cardioacceleratory center
- Norepinephrine increase rate
- Accelerator nerves connected to SA & AV nodes
- Heart is inhibited by the parasympathetic cardioinhibitory center
- ACh decreases rate
- Vagus nerve connected to SA and AV nodes
- Sends pulses continuously (brake)
- Arterial pressure detected in carotid sinus and aortic arch
- Venous pressure detected in venae cavae
- Increased pressure in the venae cavae will affect which reflex center?
- Increased pressure in the carotid sinus will effect which reflex center?
- Electrocardiography
- Cardiac cycle refers to all events associated with blood flow through the heart
- Systole - contraction of heart muscle
- Diastole - relaxation of heart muscle
- Phases of the Cardiac Cycle
- Ventricular filling- mid-to-late diastole
- Heart BP is low as blood enters atria and flows into ventricles
- AV valves are open, then atrial systole occurs
- Ventricular systole
- Atria relax
- Rising ventricular pressure results in closing of AV valves
- Isovolumetric contraction phase
- Ventricular ejection phase opens semilunar valves
- Isovolumetric relaxation - early diastole
- Ventricles relax
- Backflow of blood in aorta and pulmonary trunk closes SL valves
- Dicrotic notch - brief rise in aortic pressure caused by backflow of blood rebounding off semilunar valves
- Cardiac Output
- CO is the amount of blood pumped by each ventricle in one minute
- CO is the product of heart rate (HR) and stroke volume (SV)
- HR is the number of heart beats per minute
- SV is the amount of blood pumped out by a ventricle with each beat
- SV = EDV - ESV
- EDV = amount of blood collected in a ventricle during diastole
- ESV = amount of blood remaining in a ventricle after contraction
- Ejection Fraction (EF) = Stroke Volume / End Diastolic Volume
- Example of Cardiac Output
- CO (ml/min) = HR (75 beats/min) x SV (70 ml/beat)
- CO = ______________________
- Factors Affecting Stroke Output
- Preload - amount ventricles are stretched by contained blood
- Contractility - cardiac cell contractile force due to factors other than EDV
- Increase in contractility comes from:
- Increased sympathetic stimuli
- Certain hormones
- Ca2+ and some drugs
- Agents/factors that decrease contractility:
- Acidosis
- Increased extracellular K+
- Calcium channel blockers
- Afterload -back pressure exerted by blood in the large arteries leaving the heart
- Frank-Starling Law of the Heart
- Preload, or degree of stretch, of cardiac muscle cells before they contract is the critical factor controlling stroke volume
- Slow heartbeat and exercise increase venous return to the heart, increasing SV
- Regulation of Heart Rate
- Autonomic Nervous System
- Sympathetic nervous system (SNS) stimulation is activated by stress, anxiety, excitement, or exercise
- Parasympathetic nervous system (PNS) stimulation is mediated by acetylcholine and opposes the SNS
- PNS dominates the autonomic stimulation, slowing heart rate and causing vagal tone
- Atrial (Bainbridge) reflex - a sympathetic reflex initiated by increased blood in the atria
- Causes stimulation of the SA node
- Stimulates baroreceptors in the atria, causing increased SNS stimulation
- Chemical Regulation of Heart
- The hormones epinephrine and thyroxine increase heart rate
- Intra- and extracellular ion concentrations must be maintained for normal heart function
Risk factors in heart disease:
- high blood pressure
- cigarette smoking
- obesity & lack of regular exercise.
- diabetes mellitus
- genetic predisposition
- male gender
- high blood levels of fibrinogen
- left ventricular hypertrophy
- Risk factor for developing heart disease is high blood cholesterol level.
promotes growth of fatty plaques
- Most lipids are transported as lipoproteins
- HDLs remove excess cholesterol from circulation
- LDLs are associated with the formation of fatty plaques
- VLDLs contribute to increased fatty plaque formation
- There are two sources of cholesterol in the body:
in foods we ingest & formed by liver
- Congestive heart failure (CHF) is caused by:
- Coronary atherosclerosis
- Persistent high blood pressure
- The pressure that must be overcome before a semilunar valve can open is the afterload.
- In congestive heart failure, blood begins to remain in the ventricles increasing the preload and ultimately causing an overstretching of the heart and less forceful contraction
- Left ventricular failure results in pulmonary edema
- Right ventricular failure results in peripheral edema.
- Dilated cardiomyopathy (DCM)
Age-Related Changes Affecting the Heart
- Sclerosis and thickening of valve flaps
- Decline in cardiac reserve
- Fibrosis of cardiac muscle
- Atherosclerosis
References
Lab Exercises for Cardiovascular (Homework)
- Heart Anatomy
- Conduction System of the Heart/Electrocardiogram
- Anatomy of Blood Vessels – (stop at Fetal Circulation)
- Blood
Class Activities for Credit- only if you are present for the activity
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