The Heart Flashcards
lecture 7 week 4
Where is the heart located
- the heart is located in the mediastinum of the thoracic cavity in the fibrous pericardium, it is the size of a clenched fist with an apex and a base
- the fibrous membrane tethers the heart in place, it also prevents disease and stops the overfilling of the heart
What is the structure of the heart
- heart wall consists of the endocardium (contact with blood), myocardium (main part of heart wall) and epicardium (outer edge in contact with pericardium)
- there are two atria and two ventricles arranged in pairs separated by the septum
What is the blood flow of the body
- deoxygenated blood returns to the right atrium via the vena cava, blood is pumped to the lungs by the pulmonary artery
- oxygenated blood returns to the left atrium via the pulmonary vein, blood is pumped to the body via the aorta
- the left ventricle has a thicker wall to contract with more force to move blood around the entire body
What are the different valves in the body
tricuspid valve: between right atrium and ventricle
bicuspid (mitral) valve: between left atrium and ventricle
- blood emerges from right ventricle through pulmonary semilunar valve and from left ventricle via the aortic semilunar valve
the atrioventricular valves open when atria and ventricles relax, semilunar valves close
the atrioventricular valves close when ventricles contract, semilunar valves are open
What is coronary circulation
- the vascular network of the heart
- oxygenated blood is delivered to cardiac tissue by coronary arteries and deoxygenated blood is removed by coronary veins - blood drains into coronary sinus into right atrium it is deoxygenated and moves to lungs
What is coronary heart disease (CHD)
- the leading cause of death in the UK, 1 person dies every 7 minutes
- lack of blood to the heart leads to ‘ischemia’ which can lead to a myocardial infection
- blockage of fat in artery going into the heart causes a lack of O2 to areas, plaque can rupture completely stopping blood flow
- CDH can be prevented by diet and exercise, drugs include aspirin and cholesterol lowering agents
What are the treatments of CHD
- nitroglycerine: causes vasodilation reducing blood pressure, this reduces cardiac work which reduces O2 consumption
- B-blockers: activation of beta-adrenergic receptors increases cardiac contractility and heart rate (prevents adrenaline binding). B-blockers are antagonists of beta-adrenergic receptors, they reduce cardiac work reducing O2 consumption
- B1-adrenoceptors: found in the heart, prevents an increased heart rate, and prevents cardiac muscle contractility
- B2-adrenoceptors: found in the lungs, GI tract, uterus, vascular smooth muscle. relaxes smooth muscle
- B3-adrenoreceptors: not given to asthmatic patients, selective B1-adrenoceptor antagonist (Atenolol)
How does nitroglycerine affect vascular smooth muscle contraction
normal smooth muscle contraction
- Ca2+ is released through intracellular stores
- Ca2+ bonds with calmodulin proteins in the cytoplasm forming calcium calmodulin complex
- this activates myosin light chain complex (MLCK) which then phosphorylates the myosin heads causing muscle contraction
Smooth muscle contraction with nitroglycerin
- nitroglycerin produces NO
- NO diffuses into blood vessels
- NO activates the myosin light chain phosphatase (MLCP)
- MLPC causes the myelin head to be depolarised meaning no muscle contraction occurs
What is atenolol
- does not reduce the morbidity or mortality caused by hypertension
- increases mortality, increases type ii diabetes
- still one of most prescribed medicine for hypertension
- does reduce the demand for oxygen in the heart
How is the heartbeat initiated
- the sinoatrial node (SA node) generates an action potential (100 beats/min)
- the action potential propagates throughout the atria to the atrioventricular (AV) node
- a delay occurs at the AV node (-100 ms) to ensure atria fully contracts before ventricles
- impulses conducted through bundle of His which divides into left/right branches in interventricular septum
- bundle branches lead to Purkinje fibtrd, causing contraction up the ventricles
What is an electrocardiogram (ECG)
- standard ECG uses 3,5 or 12 leads: more leads give more information
- three parts of ECG: P wave, QRS complex and T wave
P wave: atrial depolarisation (contraction)
QRS complex: ventricle depolarisation (contraction)
T wave: ventricle repolarisaiton (relaxation)
atrial repolarisaiton occurs during ventricle depolarisation and is masked by QRS complex
What is the cardiac cycle
- electrical excitation causes depolarisation which results in contraction, repolarisation results in relaxation
- the cardiac cycle is an alternating pattern of contraction and relaxation
- two major phases: diastole (chambers relax and fill with blood), systole (the heart contracts ejecting blood into the pulmonary and systematic circulation)
What is atrial systole and diastole
- atrial contraction follows depolarisation (P wave)
- ventricular relaxation accounts for 70-80% of blood filling, atrial contraction the rest
- atrial systole lasts -100ms and ends prior to ventricular systole, as the atrial muscle returns to diastole
What is ventricular systole (depolarisation)
- ventricle systole follows depolarisation of the ventricles (QRS complex)
- ventricles contract and pressure rises but not opening the semilunar valves (isovolumetric contraction)
- the pressure rises further, semilunar valves open and blood is ejected (ventricular ejection)
- stroke volume -70ml leaving and -60ml remaining in ventricle (end systole volume (ESV))
