TRANS 4 - Chapter 12 - Heart 1 & 2 PDF

NMD2 GENERAL PATHOLOGY 1ST SEMESTER Lecture / DR. john Patrick padilla prefinals...

NMD2 GENERAL PATHOLOGY 1ST SEMESTER Lecture / DR. john Patrick padilla prefinals [TRANS] CHAPTER 12: THE HEART/CARDIAC PATHOLOGY 1 (PART 1 + PART 2) CARDIAC STRUCTURE AND SPECIALIZATIONS CONDUCTION SYSTEM Heart weight varies with body habitus, averaging ~0.4-0.5% of body Coordinated conduction of the cardiac muscle depends on the initiation weight (250-320 g in the average adult female and 300 to 360 g in the and rapid propagation of electrical impulses—accomplished through average adult male) specialized myocytes in the conduction system Increased heart weight/ventricular thickness indicates hypertrophy, and The frequency of electrical impulses is sensitive to: an enlarged chamber size implies dilation – both reflect compensatory - Neural inputs (e.g. , vagal stimulation) changes in response to volume and/or pressure overloads - Extrinsic adrenergic agents (e.g., circulating adrenaline) Increased cardiac weight/size (or both)—resulting from hypertrophy - Hypoxia and/or dilation – cardiomegaly - Potassium concentration (i.e., hyperkalemia can block signal transmission altogether) MYOCARDIUM The pumping function of the heart occurs through coordinated COMPONENTS OF THE CONDUCTION SYSTEM contraction (during systole) and relaxation (during diastole) of cardiac Sinoatrial (SA) node pacemaker, at the junction of the right atrial myocytes (the myocardium) appendage and superior vena cava Left ventricular myocytes – arranged in a spiral circumferential Atrioventricular (AV) node, located in the right atrium along the orientation to generate vigorous coordinated waves of contraction interatrial system spreading from the cardiac apex to the base of the heart Bundle of His (AV bundle), connecting the right atrium to the Right ventricular myocytes – less structured organization → overall less ventricular septum robust contractile forces Right and left branch divisions that stimulate their respective Contraction – achieved by shortening of serial contractile elements ventricles via further arborization into the Purkinje network (sarcomeres) within parallel myofibrils The heart also has other functions (e.g., endocrine); example: BLOOD SUPPLY - Atrial cardiomyocytes have cytoplasmic storage granules that Cardiac myocytes rely almost exclusively on oxidative phosphorylation contain atrial natriuretic peptide for their energy needs - Ventricular myocytes contain B-type natriuretic peptide Myocardial energy generation also requires a constant supply of - Both of these are protein hormones → released in response to oxygenated blood—rendering myocardium extremely vulnerable to increased stretch ischemia - Both promote arterial vasodilation and stimulate renal salt and water Nutrients and oxygen – delivered via the coronary arteries, with ostia elimination (natriuresis and diuresis) immediately distal to the aortic valve: initially course along the external surface of the heart (epicardial coronary arteries) → branching into VALVES arterioles → forming a rich arborizing vascular network so that each 4 cardiac valves maintain unidirectional blood flow: myocyte contracts roughly 3 capillaries 1. Tricuspid The right and left coronary arteries function as end arteries, although 2. Pulmonary anatomically most hearts have numerous intercoronary anastomoses 3. Mitral (connections called collateral circulation) 4. Aortic Blood flow to the myocardium occurs during ventricular diastole, after Function: depends on the mobility, pliability, and structural integrity of closure of the aortic valve, and when the microcirculation is not the leaflets of the atrioventricular valves (tricuspid and mitral) or cusps compressed by cardiac contraction of the semilunar valves (aortic and pulmonary) At rest, diastole comprises ~2/3 of the cardiac cycle; with tachycardia, Function of semilunar valves – depends on the integrity and coordinated the relative duration of diastole also shortens → potentially movements of the cuspal attachments compromising cardiac perfusion Dilation of the aortic root → valvular regurgitation The competence of the atrioventricular valves depends on the proper CARDIAC REGENERATION function not only of the leaflets but also the tendinous cords and the Myocardium of mammals has a very low replicative potential after fetal attached papillary muscles of the ventricular wall and neonatal life, averaging female there will be thrombosis occurring. It can also be attributed to the Risk factors presence of intramural lesions like vasculitis, amyloidosis, and sickle cell - Major modifiable risk factors disease 1. Presence of Diabetes 🎙️ Vasospasm, or vasoconstriction, can be brought about by the 2. Hypertension presence of circulating adrenergic agonists, platelet release products, 3. Smoking and endothelially released factors 4. Hypercholesterolemia Consequences of Myocardial Ischemia - HRT for postmenopausal females: not cardioprotective Stable angina 🎙️ Females have a cardioprotective effect in their estrogen secretion during Results from increases in myocardial oxygen demand that outstrip their reproductive age. For postmenopausal women, or females in HRT, this the ability of coronary arteries with fixed stenoses to increase oxygen is NOT cardioprotective and will have the same risk factors with males of that delivery age Usually not associated with plaque disruption Unstable angina INCIDENCE Caused by acute plaque change → thrombosis and/or Elderly 45% in