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REVIEW: cardiovascular system o Components: Heart Blood vessels Lymphatic vessels o Circulation: Pulmonary circulation: De-O2 blood in heart pulmonary aa lungs O2 blood from lungs pulmonary vv heart Systemic circulation: O2 blood from arteries other tissues Nutrient XΔ occurs in capillaries De-O2 blood from tissues veins heart o Tunics/layers (can have up to 3) General: Number of tunics, cellular & extracellular compenents varies w/ size & fxn of diff’t bv’s Heart wall layers (discussed later) are analogous with vessel tunics Layers: Tunica Intima - innermost layer of bv wall o Endothelium = simple squamous o Subendothelial layer o Internal elastic lamina Tunica Media – middle layer of bv wall o Predominate element is variable, but is either: Circumferentially arranged smooth muscle Elastic lamellae Tunica Adventitia – outermost CT layer of bv wall o Longitudinally arranged: Collagen Elastic fibers Smooth muscle cells Fibroblasts PERICARDIUM & HEART o General: Heart is located in middle mediastinum & is surrounded by pericardial sac o Pericardium Three layers of pericardial sac (1) External Fibrous layer: DCT Serous pericardium (layers continues via “reflection”): o (2) Parietal layer: LCT Layer of squamous epithelium (mesothelium) o (3) Visceral layer LCT Layer of squamous epithelium (mesothelium) = epicardium Pericardial cavity Space b/w the parietal & visceral pericardium Contains: pericardial fluid Fxn: allows the heart to beat without restriction Pericarditis (infection in pericardial cavity) restricts heart from beating properly o Chambers of the heart Four chambers = RA & LA and RV & LV Path of blood flow: De-O2 blood from tissues IVC/SVC RA (tricuspid valve) RV (pulmonary semilunar valve) pulmonary artery lungs gas XΔ in alveoli O2 blood O2 blood from lungs pulmonary veins LA (bicuspid valve) LV (aortic semilunar valve) aorta atrial tree systemic circulation (tissues) capillary beds gas XΔ De-O2 blood Separations: Atria = interatrial septum (mostly cardiac muscle cells) Ventricles = interventricular septum (thick) AV compartments = cardiac skeleton & valves CARDIAC SKELETON o General Features iDCT Central supporting structure of the heart Supports valves Cardiac muscle fibers attach o Components Annuli Fibrosi Surrounds/stabilizes ea. of the 4 cardiac valves Valve cusps arise from this CT Trigona Fibrosi (right & left fibrous trigones) Triangular “islands” of CT Location: superior to AV valves; sides of aoric valve Strengthen the annuli fibrosi Rt trigona contains AV bundle Septum Membranaceum (membranous part of the interventricular septum) Extension of cardiac skeleton (┴ annuli fibrosi) into interventricular septum Associated w/ a segment of the AV bundle o Functions Separates atrial musculature from the ventricular musculature Fxn’s as origin (pnts of insertion) of cardiac muscle Localizes & stabilizes valves Limits the diameter of valves Prevents spread of electrical impulses (except via the conducting system) HEART WALL o Epicardium – external layer of heart wall Analogous to tunica adventitia of bv’s aka visceral reflection layer Consists of: Mesothelium o Simple squamous epithelium o With associated BL Subepicardial CT o Fat storage of heart (a lot) o Collagen fibers o Elastic fibers o Coronary arteries (supply heart) o Caridac veins (supply heart) o Nerves (supply heart) o Myocardium – middle layer of the heart wall (analogous to tunica media) Cardiac muscle cells (myocytes, cardiomyocytes) One (usually) or two nuclei Packed with myofibrils & lg mitochondria Intercalated discs o Connection b/w cardiac muscle cells o Connections or Communications: Fascia adherens – binds actin thin filaments of two cardiac mm cells Desmosomes – connect 2 cardiac mm cells via desmin/vimentin intermediate filaments with desmoplakin/plakoglobin anchors Gap jxns – provide for ionic communication & coupling (impulse “passed”) Myocardial thickness differences Atrial myocardium <<< ventricular myocardium LV myocardium = 3X thickness of RV myocardium o Cardiac muscle cells differ b/w atriums & ventricles Atrial (relative to ventricular myocardial cells): o Smaller o Less elaborate T-tubule system o More gap jxns Atrial myocardial cells o Contain e- dense granules that contain atrial atriuretic factor (ANF) o ANF (“stretch” is biggest stimulator of ANF release) aka atrial natriuretic polypeptide or atriopeptin Produced, stored, secreted by atrial myocardial cells Secreted into surrounding capillaries Receptors found in adrenal cortex, kidney, & vascular smooth mm Stimulates: Kidney excretion of Na+ in urine (water follows; ↓ blood volume) Regulation of fluid balance Regulation of electrolyte balance (Na+ levels) Regulation of BP (↓ in atrial BP) Arrangement of muscle cells (fibers): Ventricular Wall o Trabeculae Carnae – complex spiral & helical pattern o Papillary Muscle – Ventricular wall projections into lumen Atrial Wall o Pectinate musculature aka musculi pectini Innermost mm fiber bundles in lattice arrangement (gives ridged appearance) Endocardium – internal layer of the heart wall Analogous to tunica intima of bv’s Ventricular <<< Atrial Lines: Cardiac valves Papillary muscles Inner walls of atria Inner walls of ventricles Consists of: Endothelium with associated BL (vascular endothelium makes contact w/ blood) Subendothelial (subendocardial) CT o Collagen fibers o Elastic fibers o Smooth muscle cells o Small blood vessels o Nerves o Components of impulse conduction system IMPULSE CONDUCTION SYSTEM o Characteristics Specialized cardiac mm fiber Initiate & conduct electrochemical impulses Coordinated contraction & relaxation of the heart Control of contractions Heart able to contract w/o any CNS stimulation CNS modulates heart rate o SS stimulation = ↑ heart rate o PS stimulation = ↓ heart rate Impulse pathway: SA node (pacemaker) initiates impulse atrial mm (p wave) AV node (PQ interval) Bundle of His left & right bundle branches purkinje fibers cardiac ventricular muscle (apex) spiral/upwrd contraction (QRS wave) Electrocardiogram – conduction of electrical impulse thru the heart voltage trace recorded as EKG/ECG: PQ interval P wave Q R S P wave = atrial contraction PQ interaval = AV node (“delayed”) QRS wave = ventricular contraction o o o o Sinoatrial (SA) Node Location: Wall of RA close to orifice of the SVC Often surrounds a branch of the coronary artery SA nodal cells Modified cardiac muscle cells Histology o Smaller than typical cardiac mm cells o Exhibit paler staining appearance Myofibrils – fewer (in #’s) & less organized than normal cardiac mm cells Not joined by intercalated discs AKA Pacemaker Initiates impulse Spreads along tracts of modified cardiac muscle fibers to AV node Atrioventricular (AV) Node (slowest – “delayed”) RA floor just above tricuspid valve Similar in appearance to SA nodal cells Appear as a mass of small, pale-staining cells isolated by CT Bundle of HIS (AV bundle) & left & right bundle branches Runs RA traversing right fibrous trigone RV along septum membranaceum margin interventricular septum & divides into rt & lft branches terminate in subendocardial layer as purkinje fibers Purkinje fibers (fast) Location: subendocardial CT of ventricular endocardium Transmit impulses to cardiac muscle cells of apex of the heart Characteristics (of purkinje fibers): Relative to normal cardiac muscle cells: o 2 – 3 times larger o Nuclei more rounded Lg amt of glycogen o Appear pale-staining o Appear vaculated o Fxn: resistant to ischemia (important when conducting electrical impulse Contain few myofibrils Lack T tubule system Cells connected via desmosomes & gap jxns (rather than intercalated discs) VALVES OF HEART o Four Valves – cusps come off of annuli fibrosi Left AV (mitral or bicuspid) valve = 2 cusps Right AV (tricuspid) valve = 3 cusps Pulmonary semilunar valve = 3 cusps Aortic semilunar valve = 3 cusps o Structure Cardiac valves extend from the cardiac skeleton Consist of Fibrosa Fibrous iDCT Covered by endocardium on free atrial & free venricular surfaces o Chordae Tendinae Fibrous cords From free edge of valves to papillary muscles of ventricular wall Fxn: prevention valve leaflets from flapping back into the atrium during ventricular contraction