I. Two Circuits!A. Pulmonary circuit- about 20% of blood volume!1. Oxygen poor blood returning from the systemic circuit is delivered to pulmonary capillaries and CO2 exchanged for O2, O2 rich blood goes back to heart!2. blood froms from R ventricle --> pulm. arteries --> lung capillaries --> pulmonary veins --> L atrium!B. Systemic circuit- about 80% of blood V!1. O2 rich blood delivered via arts to capillary beds in body where exchanges occur, O2 poor blood is returned to heart via veins!2. blood flow: L ventricle --> conducting arteries (large/elastic) --> distributing arteries (medium/muscular) --> resistance arteries (arterioles) --> exchange vessels (capillaries) --> capacitance vessels (venules--> medium v. --> large v.) --> R atrium of heart!3. Ateriovenous (AV) shunts/anastomoses divert blood from cap. beds !- blood flows from arteriole --> post. capillary venule!- func. in thermoreg., helps to retain heat since no heat lost at capillaries close to skin!4. Portal systems: blood flows thru 2 cap. networks before going back to heart!- allow for directly delivery of substances from 1 organ to another or 1 region of organ to a 2nd region of that organ!- Arterial portal systems: !cap. beds connect by an artery - Venous portal systems: cap. beds connect by a vein (ex. hepatic portal system)!II. Heart!A. Heart chambers!1. Atria receive blood from systemic and pulmonary circuits --> send to ventricles!- Right atrium: receives O2 poor blood from tissues (systemic) thru inferior and superior venae cavae, delivers blood to R ventricle - Left atrium: receives O2 rich blood from lungs (pulm circuit) thru 4 pulmonary veins!- Atria have thinner walls than ventricles, this allows them to stretch for flow of incoming blood!- Atrial cardiomyocytes (cardiac m. cells) have storage granules w/atrial natriuretic factor (ANF) which is a diuretic hormones released into blood when atria are OVER-stretched (signal to kidney) --> leads to decreased blood V!- Posterior lumenal walls of atria= smooth, here walls of blood vessels delivering blood to atria are continuous w/the endocardium!- Anterior lumenal walls lined by pectinate m. 2. Ventricles pump blood into pulm. and systemic circuits!- R ventricle receives blood thru tricuspid valve, pumps blood to lungs thru pulmonary a.!- L ventricle receives blood thru biscuspid/mitral valve and pumps blood to aorta for distribution to tissues!- Trabeculae carnae (irreg. ridges of m.) line the lumenal walls!- Papillary m. project from walls into lumen and attach to atrioventricular valves via chordae tendinae!3. R and L sides of heart separated by interatrial and interventricular septa!- septa cores: cardiac muscle (in most regions) or CT of cardiac skeleton (in membranousparts)!- lumenal surfaces covered by endocardium!B. Layers of the heart wall!1. Endocardium: lines the chambers of heart, has 3 layers!- Endothelium (simple squamous) w/underlying basement membrane!- Subendothelial connective tissues - Subendocardial layer MAY be present and contains 1 or more: blood vessel insertions (atria), cardiac skeleton, Purkinje fibers (ventricles) 2. Myocardium: thickest layer of heart, thicker in ventricles!- Bundles of cardiac m. cells= cardiomyocytes that spiral around the heart chambers, many bundles insert into cardiac fibrous skeleton!- Cardiac m. cells of atria are separated and insulated by cardiac m. cells of ventriles by cardiac skeleton --> this limits the transmission of impulses between atria and ventricles!- Cardiac m. cells connected by gap junctions --> rapid transmission of impulses throughout atria and ventricles!- Cardiac m. cells of atria and ventricles act as single units= functional atrial syncytium and functional ventricular syncytium 3. Epicardium!- Heart enclosed in triple-layer sac= pericardium - Fibrous pericardium: layer of dense CT that holds heart in place and keeps it from overfilling - Serous pericardium: double-layered, closed sac under fibrous pericardium, made of: - Parietal layer: adheres to inner surfaces of fibrous pericardium - Visceral layer: forms the epicardium, is part of the heart wall. Has 2 layers:!1) Mesothelium: single layer of squamous cells covering outer surface of heart 2) Subepicardium: layer of loose CT under mesothelium. Coronary a., cardiac v., nerves, and ganglia are present in this layer w/fat cells.!- Between visceral and parietal pericardium is lubricating serous fluid --> faciliates the heart's movements!C. Cardiac Skeleton: dense, fibrous CT (+/- fibrocartilage)!1. Components!- 4 rings surrounding the atrioventricular and semilunar valves!- 2 fibrous trigones!- R trigone: between tricuspid and pulmonary valves - L trigone: between mitral/biscusp and aortic valves!- Membranous portions of the interventricular and interatrial septa!2. Functions!- Provide support for attachment of valves!- Provide indep. attachment sites for atrial and ventricular myocardium!- CT around cardiac m. cells inserts into it!- Physically separates and insulates atria from ventricles!- Cardiac skeleton is non-conducting so transmission of cardiac impulses between atria and ventricles is prevented EXCEPT at opening for atrioventricular bundles of His!D. Cardiac Valves 1. Cardiac valves are one way gates that prevent the backflow of blood!- tricuspid valve: prevents backflow from R ventricle to R atrium - mitral (bicuspid) valve: prevents backflow from L ventricle to L atrium - aortic valve: prevents backflow from aorta to L ventricle - pulmonary valve: prevents backflow from pulm. trunk to R ventricle!2. Histology !- Core made of dense, fibro-elastic tissues cont. w/cardiac skeleton!- Endothelium cont. w/that of endocardium covers outer surface!- Valves= avascular, receive O2/nutrients by diffusion!- Valve cusps connected thru chordae tendinae to papillary muscles !3. Opening and closing of seminular valves!- Systole: blood pushes against semilunar valves and forces open!- Diastole: intravent. P drops which pulls blood back towards ventricles, blood flows into cusps and forces valves closed!4. Opening and closing of atrioventricular valves!- Diastole: AV valves open and hang down into ventricles!- Systole: blood flows into cusps and forces valves closed !5. Less of 'flexibility' results in valves that don't open efficiently and or close completely --> increase workload on heart --> can lead to heart failure!- Marfan's Syndrome: congenital disease affecting elastic tissue, valve leaflets enlarge (esp. mitral valve), lose
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