Cardiovascular System F24 - 1 Lecture Only PDF

The Cardiovascular System The Heart - Location in chest just dorsal to the olecranon apex of the heart sits on the sternum Usually found between ribs 3-6 (2-6 for horses) Base tilted cranially (40o) Canine c...

The Cardiovascular System The Heart - Location in chest just dorsal to the olecranon apex of the heart sits on the sternum Usually found between ribs 3-6 (2-6 for horses) Base tilted cranially (40o) Canine chest – lungs removed, right lateral aspect  The Heart – shape – inverted cone se Canine heart left side view Ba ex Ap B A Heart – location in chest cavity Within the mediastinum Mediastinum – a potential space between thin tissue layers (serosa) – divides chest into left and right halves Mediastinum contains trachea, esophagus, nerves, lymph nodes, (thymus in young animals), heart and major vessels (aorta) Heart coverings Pericardium – fibrous sac Sac is lined with membrane called the parietal layer of the pericardium (fused with fibrous tissue layer) Directly on the heart is the visceral layer of the pericardium Space between visceral and parietal layer is pericardial space pericardial fluid in this space  Layers – pericardium plus Insideheart wall heart Endocardium – simple squamous epithelium Myocardium – heart muscle Epicardium = visceral pericardium Pericardial space (cavity) Parietal pericardium fused with fibrous layer Outsi de heart Pericardial effusion Bleeding from a heart tumor is common cause Can be idiopathic Can be drained with needle using ultrasound as guide Vet Emergency Ultraso und: Draining a Perica rdial Effusion Hemangiosarcoma on right atrium of heart – bleeds into pericardial sac making it difficult for the heart to fill and beat properly (pericardial sac has been removed in this image).  https://www.youtube.com/watch?v=u3Gv5YNPUb0 Thoracoscopic surgery to remove some of pericardial sac – Rhodesian ridgeback with recurrent idiopathic pericardial effusion Hardware disease in cows - pericarditis Cardiac muscle cell special characteristics REVIEW Connected via branching and intercalated discs Striations Connections between cardiac muscle cells? _____________ and _____ junctions Autorhythmic  Layout of the heart Cardiac skeleton Inter-atrial septum RA LA LV RV Interventricular septum  Canine heart – dorsal view Inside the heart atria removed Skeleton???? 4 CT rings (ossified in cow) 4 jobs: Separate atria from ventricles Anchor valves Place for myocardium to attach Electrical insulation Canine heart – yellow dash represent Location of cardiac skeleton (fibrous) Bovine cardiac skeleton Simplified diagram showing flow of blood through heart and body  Valves between atria and ventricles Right: right AV Left: left AV (atrioventricular) (atrioventricular) valve aka tricuspid valve valve bicuspid valve Mitral valve orsal view of heart atria removed Wearing a Catholic mitre AV valves Fibrous cords keep the valves from opening up in the wrong direction (i.e. back into atria) Cords attached to papillary muscles 2 other valves Separate ventricles from major outflow vessels – prevent backflow Semilunar valves From right ventricle – pulmonary (or pulmonic) valve From left ventricle – aortic valve dorsal view of heart - atria Valves Ensure one way flow Closure of valves = heart sounds  Heart sounds Pressure Second sound – differences shut “dub” valves Blood pressure in First sound – “lub” large vessels – ventricles greater than contract pushing pressure in AV valves closed ventricles as (prevents backflow ventricles relax into atria) Semilunar valves shut preventing Heart murmur audio backflow into ventricles Murmurs = turbulent blood flow Murmurs – valvular insufficiency vs. valvular stenosis Insufficiency – Stenosis – blood blood flows squirts though backwards as narrow valve or valve doesn’t close valve that won’t properly open all the way Mitral valve Aortic stenosis insufficiency Pulmonic stenosis  Brief digression – avian hearts Relative size of heart inversely proportional to bird size Migrating birds’ hearts can hypertrophy before migration Right AV valve only one cusp of myocardium Left AV valve 3 cusps AV valves connected to Purkinje fibres Heart blood supply – see page 344 and Figure 14-13  Electrical conduction in the heart Sinoatrial node – pacemaker In wall of RA – muscle cells that automatically generate action potentials Heartbeat starts here Systole Electrical conduction in the heart diastole Pathway of electrical signals Spreads AP also SA node across RA travels to generates and LA – AV node in delay AP they AV septum contract AP travels AP travels Ventricles up the down the contract ventricles bundle of apex to via Purkinje His to apex base fibres Measuring the electrical conduction ECG (electrocardio gram) P = contraction of the atria QRS = contraction of the ventricles T = relaxation of the ventricles Control of heart rate Part of the heart that initiates the heartbeat and where is it located? What happens when the sinoatrial node stops working properly? Control of heart rate sympathetic and parasympathetic nervous system input Cardiovascular centre in the medulla (brainstem) Increased HR via sympathetic neurons – norepinephrine Decreased HR via parasympathetic neurons (vagus nerve CN X) – Ach Also reflexes – baroreceptors (pressure sensors), chemoreceptors (pH) Baroreceptors (blood pressure sensors) in aorta and right atrium – along CN X to medulla oblongata Chemoreceptors in carotid arteries (one of the main arteries off the aorta) and aorta (sense CO2  pH) There are also central chemoreceptors in the medulla itself. Sinoatrial node Changing mental gears Slightly….  Blood vessels Inner membrane – endothelium, (simple squamous epithelium) Middle layer – smooth muscle +/or elastic fibres Outer layer – dense irreg. CT, strong, flexible Arteries, veins and capillaries Capillaries Capillaries one cell thick (squamous endothelium) Exchange here In ‘beds’, ‘networks’ Skeletal muscle with capillaries Capillary beds Blood pressure Pressure of the blood on the inner walls of the blood vessels Depends on: HR Stroke volume (SV) Blood volume Diameter of vessel Elasticity of vessel Arteries: Elastic vs. muscular Elastic close to heart Muscular farther from heart No valves elastic muscul arteriol capillari aorta ar arteries es es arteries  Feel the pressure wave: Cats, dogs Sheep, goats, piglets Horse Cow Pig Feeling a pulse on your horse Veins – one way valves – to the heart capillari vena venules veins es cava Veins used to take blood samples Dog Cat Horse Cow Sheep Goats Ferrets Birds  Circulation in the Fetus (A) compared to after born (B) Pulmonary circulation bypass – oxygenated blood from ? Foramen ovale Ductus arteriosus Veins coming back to the heart Major arteries and veins (pages 354, 355) Arteries to know: Pulmonary a. (just one) Brachiocephalic trunk (just one of these) Subclavian – L and R Aorta (just one of these – arches to the left and travels all the way caudally through the chest and abdomen) Common carotid Veins to know: – page 355 in your text cranial and caudal vena cava L and R brachiocephalic veins L and R external jugular veins (circled on previous slide)