Anatomy and physiology of the cardiovascular system.pptx

Notes

1. Anatomy and physiology of the cardiovascular system Dr. Okuku

2. Outline anatomy important history physical exam investigations

3. Anatomy of the heart Difficult to represent in a 2 dimensional structure 4 chambers, 4 valves, a handful of great vessels and a muscular wall Entrance into the heart-right side by the vena cava (inferior and superior) left side- pulmonary veins Exit from the heart-pulmonary arteries and aorta for the right and left sides respectively De-oxygenated blood is maroon in color not blue as often represented in illustrations Left ventricle has a thick muscular wall because it pumps blood against higher pressures than the right

4. cont; Myocardial cells constitute 75% of the heart mass but only about 25% of the cell number. Myocardial cells play 2 Fundamental functions: initiation and conduction of electrical impulses and contraction. Majority of the cells are predominantly contractile cells (myocytes) and a small number are specifically electrical cells (conducting systems). The electrical cells , are not nervous tissue but modified myocytes lacking in myofibril components. N umerous factors including autonomic input and stretch, modify the electrical activity and contractility of the myocardial tissue. Three epicardial coronary arteries supply blood to the myocardium, and a more complex network of veins is responsible for drainage.

5. Valves Consist of leaflets or cusps that allow movement of blood in one direction All the valves have 3 cusps except the mitral which has 2 cusps The atrioventricular valves have fibrous threads called chordea tendinea which attach to the respective ventricular walls( tricupid and mitral valves) Semi-lunar valves named because of their cusps are reminiscent of a half moon when viewed from above (aortic and pulmonary valves)

6. Great vessels Superior vena cava Inferior vena cava Pulmonary artery Aorta-divided into 4parts Ascending aorta, aortic arch, descending thoracic aorta and abdominal aorta Pulmonary vein (4 in number)

7. Conducting system Delivers electrical impulses to different chambers at different times Originates from the SAN (pace maker)- located in the superior posterior aspect of the right atrium Frequency of its impulse is governed by the balance between the sympathetic and parasympathetic systems-resulting in a rate between (60-100bpm) Impulse travels into the two atria, triggering contraction and ejection of blood into the respective ventricles AVN - acts a gate keeper (located with the inferior part of the inter- atrial septum) The AVN conducts relatively slowly (holds the impulse for about 100mS) to allow time for blood to move into the relaxed ventricles

8. Conducting system Impulse travels from the AVN to the bundle of his that divides into the left and right bundle branches The bundle branches travel to right and left ventricles respectively This terminate into the purkinje fibers which rapidly deliver the signal to the ventricles This results in a rapid and nearly simultaneous contraction of both ventricles in a wave form that starts at the cardiac apex travels upwards towards the valves

9. Coronary arteries Supply the heart muscles They are two (left and right) Branch off the aorta above the aortic valve Right-supplies the right ventricle and the SAN Left –bifurcates into the Left anterior descending artery supplies the anterior interventricular septum and anterior wall of the left ventricle and Left circumflex artery wraps around behind to supply the lateral wall of the left ventricle A number of distal connections occur between the two coronary arteries allowing continuous supply incase of obstruction in one

10. Cardiac cycle A series of events in the heart that occur between one heart beat to another. consists of precisely timed rhythmic electrical and mechanical events that propel blood into the systemic and pulmonary circulations Triggered by the firing of the SAN-atrial contraction (atrial systole or atrial kick) – results in emptying of the atria into the ventricles Signal at AVN-undergoes AV delay-allows time for filling of the ventricles during the atrial kick Signal is after propagated through the bundle of his to the purkinje system triggering ventricular contraction- results in increased intra-ventricular pressure forcing the AV-valves to snap shut (first heart sound-S1)-ventricular systole Blood is ejected from the ventricles thru the open semi lunar valves Ventricles relax, pressure in the pulmonary artery and aorta causing the semilunar valves the snap shut (second heart sound S2)-ventricular systole-QRS complex on the ECG Systolic is usually shorter than the diastolic, but as the heart rate increases the diastolic shortens

11. Blood vessels Arteries, arterioles, capillaries, venules , veins Arteries-thick walled with much elastic tissue to resist higher pressures Arterioles-sites of greatest resistance to blood flow Capillaries-point of gas exchange occurs-so many to increase their area, blood flows here most slowly Venules -equivalence of arterioles Veins –thin walled and lack much elastic tissue Note: lymphatic vessels – return the interstitial fluid

12. Histology of the heart 3 layers- thin inner endocardium beneath it is the subendocardium Myocardium (thick)-composed predominantly of cardiomyocytes (high density of mitochondria, connected to each other by intercalated discs-allow easy flow of electrolytes necessary for rapid transmission of signals -necessary for coordinated contraction Pericardium-thin fibrous structure encases the heart and roots of the great vessels-its tethered to diaphragm and sternum keeping the heart in place. Has two layers-parietal and visceral pericardium creating a potential space that contains serous fluid to prevent friction-in pathological events may accumulate to form a pericardial effusion

13. Blood vessel control and functions of th e vascular endothelium The central control of blood vessels is achieved via the neuroendocrine system. Sympathetic vasoconstrictor and parasympathetic vasodilator nerves regulate vascular tone in response to daily activity. Where neural control is impaired, or in various pathological states, e.g. haemorrhage , endocrine control of blood vessels mediated through epinephrine (adrenaline), angiotensin and vasopressin takes over At a local level, tissue perfusion is maintained automatically and by the effect of various factors synthesized and/or released in the immediate vicinity This process of autoregulation at the local level, is a consequence of: The Bayliss myogenic response – the ability of blood vessels to constrict when distended The vasodilator washout effect – the vasoconstriction triggered by a decrease in the concentration of tissue metabolites.

14. Summary component Associated disease valves Endocarditis, valvular heart disease myocardium Myocarditis, heart failure pericardium Pericarditis, pericardial effusion Conducting system arrhythmias coronary arteries Coronary artery disease arteries Peripheral arterial disease Veins Venous insufficiency Lymphatics vessels lymphoedema

15. Approach to a patient with a cardiac disease Dr. Okuku Mmed.Surgery

16. History Thoughtful taken history is fundamental Can never be replaced by testing Thinks to note include: Family history-many cardiac diseases have a heritable basis: CAD & HTN Major cardiac symptoms are also seen in non cardiac disorders Medical history-including number and reasons for hospitalizations, previous and current treatments e.g., thyroid disorders, DM and dyslipidemias(coronary artery disease), Smoking is a major risk factor for coronary artery disease Alcohol abuse predisposes to cardiac arrhythmias and cardiomyopathy­

17. Symptoms of a cardiac disorder Chest pain Breathlessness dyspneoe- abnormal awareness of breathing occurring either at rest or at an unexpectedly low level of exertion orthopnea, PND Palpitations, - increased awareness of the normal heart beat or the sensation of slow, rapid or irregular heart rhythms. Syncope- a transient loss of consciousness due to inadequate cere­ral ­lood flow Fatigue Extremity swelling

18. EXAMINATION OF THE CARDIOVASCULAR SYSTEM p atient’s well­eing should be noted as well as the presence of conjunctival pallor, obesity, jaundice and cachexia. clubbing, splinter hemorrhages, cyanosis pulse (rate, rhythm, character) blood pressure, JVP apex beat w/c may be displaced to left ot right heart sounds and murmurs (graded 1-6)

19. CARDIAC INVESTIGATIONS Routine haematology, urea/creatinine and electrolytes, liver biochemistry, cardiac enzymes, thyroid function and brain natriuretic peptides (BNP). Chext x-ray- AP (heart size ECG Echocardiography

20. References Merck manual Kumar and Clark’s Clinical Medicine Hutchison’s clinical methods