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Heart+Mediastinum
Organisation of the Body
| Question | Answer |
|---|---|
| Function of the heart | Acts as a double pump Right side - pulmonary circulation - low resistance pressure 20mmHg Left side - systemic circulation - high, variable resistance pressure 130mmHg |
| Requirements of heart structure | Chambers to receive blood Chambers to eject blood Valves Muscle Vascular system Pacemaker Conducting system Fibrous skeleton Autonomic innervation Pericardial activity |
| What can you see on an exterior view from anterior | Right atrium - venae cavae and coronary sinus Right ventricle Left ventricle Left atrium - mainly only left auricle Pericardium |
| Development of aorta and pulmonary trunk | Begin as a single vessel Spilt during development, leading to a twisted structure |
| Key features of internal right heart | Crista terminalis - rough patch of the atrium from different embryonic origin Sino-atrial node Fossa ovalis - where the atria are connected during development Tricuspid valve - septal, anterior and posterior cusps Chordae tendineae to anchor valve |
| Left atrium | Receives oxygenated blood via 4 pulmonary veins Forms the posterior surface of the heart in front of the posterior mediastinum Smooth walled interior formed by incorporation of primitive pulmonary veins in development Leaves via bicuspid valve |
| Left auricle | Extends onto the anterior surface of the heart to the left base of the pulmonary trunk Rough walled, formed from primitive atrium |
| Interventricular septum | Separates the ventricles Made of muscle At the base it is made of membrane - a common congenital abnormality is the failure of this to form |
| Why may the muscle be too thick | Pathological reasons for hypertrophy of muscle Leads to hypertension, reduced capacity and fibrillation - change in precise arrangement of muscle fibres leads to abnormal contraction |
| Atrio-ventricular valves | Flattened sheets Reflux prevented by cordae tendinae and papillary muscles Tricuspid and bicuspid valves |
| Outflow tract valves | 3 semilunar cusps with thickened margins Reflux prevented by blood bulging cusps and pushing them together Pulmonary and aortic valves |
| Fibrous skeleton of the heart | Supports the valves Provides electrical disconnect between atrial and ventricular muscle |
| Arterial supply of the heart | Coronary arteries arise above the aortic valve, from aortic sinuses Although the right coronary artery usually provides the posterior interventricular artery, this branch can come from the left coronary artery - left dominant Left coronary artery-larger |
| Venous drainage of the heart | A small amount of blood drains directly into the right atrium through venae cordis minimae Rest drains into coronary sinus which then drains back into circulation |
| Pacemaker and conduction in the heart | SAN acts as a pacemaker; impulses spread through atria to AVN Fibrous skeleton prevents spread from atria to ventricles AVN excites the bundle of HIs which passes through the fibrous skeleton and the membranous part of the septum to pukinje fibres |
| ECG | P wave - atria contracting P-Q interval - delay in AVN QRS complex - contraction of the ventricles T wave - repolarisation of the ventricles |
| Cardiac plexus | Receives nerves from both the sympathetic and parasympathetic systems Located beneath the arch of the aorta As the heart develops in the cervical region of the embryo many fibres innervating the cardiac plexus arise in the neck |
| Sympathetic innervation | Innervate both SA and AV nodes as well as the cardiac muscle Sympathetic activation causes an increase in heart rate and force of contraction |
| Parasympathetic innervation | Vagal fibres end primarily on the SAN and cause slowing of the heart |
| Basic imaging of the heart | Apex should be on the left and not extend further laterally than the mid-clavicular line Cardiac size is an important indicator of pathology |
| Situs inversus | When all visceral organs position is mirrored to normal Tends to not cause any harm |
| Major veins | The superior vena cava is formed in the superior mediastinum from the right and left brachiocephalic veins Each of which is formed from the confluence of an internal jugular vein draining the head and a subclavian vein draining the upper limb |
| Aorta | The ascending aorta passes up and to the right into the superior mediastinum to form the aortic arch, which passes to the left and is continuous with the descending aorta in the posterior mediastinum |
| Major branches of the aortic arch | Brachiocephalic Left + right common carotid Left + right subclavian arteries Internal thoracic Vertebral |
| Transverse sinus | Situated between the aorta and pulmonary trunk anteriorly and venous structures (superior vena cava and pulmonary veins) behind It is formed when the dorsal mesocardium breaks down during development |
| Oblique sinus | An extension of the pericardial sac between the four pulmonary veins It allows the left atrium to move on the pericardium and posterior mediastinum |
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