CFR 5 Heart WT 2024-25 PDF

Cardiovascular System, Biological Fluids, Renal Function CFR.5 The Heart, structure and physiology, Cardiac cycle, Arterial blood pressure; Cardiac failure. NAME SURNAME DAT E : 2 9 J a n 2 0 2 5 Learning outcomes At the end of this lecture, the learner will be able to: Describe the fea...

Cardiovascular System, Biological Fluids, Renal Function CFR.5 The Heart, structure and physiology, Cardiac cycle, Arterial blood pressure; Cardiac failure. NAME SURNAME DAT E : 2 9 J a n 2 0 2 5 Learning outcomes At the end of this lecture, the learner will be able to: Describe the features of the human heart and its essential role in the systemic and pulmonary circulatory systems. Explain and identify the external features of the human heart; major arteries, veins, compartments, cardiac muscle, orientation and location in the body. Describe the internal features of the human heart; atria, ventricles, septum, bicuspid and tricuspid valves, semilunar valves, sinoatrial node. Explain the stages of the cardiac cycle understanding terms such as systole, diastole, stroke volume, cardiac output, and the Frank-Starling law. Discuss and explain blood pressure measurements and the different levels detected in different parts of the systemic circulation eg. aorta vs vena cava. CFR.5 The Heart, structure and physiology; Cardiac cycle; Arterial blood pressure; Cardiac failure. 2 The heart The heart is the organ responsible for the circulation of the blood. Found in the thorax in a cavity of its own called the pericardial cavity. The heart is attached to the walls of the pericardium only where the great vessels enter and leave. The pericardium is lined by a layer of simple squamous epithelium called mesothelium- forming part of the pericardial membrane. The outer covering of the heart, the epicardium, is covered by a mesothelium. CFR.5 The Heart, structure and physiology; Cardiac cycle; Arterial blood pressure; Cardiac failure. 3 The heart CFR.5 The Heart, structure and physiology; Cardiac cycle; Arterial blood pressure; Cardiac failure. 4 Structure of the heart 1. Deoxygenated blood enters right atrium through superior and inferior vena cava. 2. Blood enters right ventricle through tricuspid valve. 8 3. Blood exits right ventricle through pulmonary valve and enters pulmonary artery. 4 4. Left and right pulmonary arteries send blood 5 to the lungs, where gas exchange occurs 7 3 1 5. Oxygenated blood returns to heart via the 6 pulmonary veins and enters left atrium. 2 6. Blood enters left ventricle through mitral valve. 7. Blood exits left ventricle through aortic semilunar valve to enter aorta. 8. Aorta distributes blood to body. CFR.5 The Heart, structure and physiology; Cardiac cycle; Arterial blood pressure; Cardiac failure. 5 Systemic and pulmonary circulation Carotid A. Jugular V. Sup. Vena Cava Pulmonary A. Aorta Inf. Vena Cava CFR.5 The Heart, structure and physiology; Cardiac cycle; Arterial blood pressure; Cardiac failure. 6 Cardiac muscle physiology Co-ordination of muscular contraction is vital for proper heart function. Cardiac muscle is striated but arranged into individual cells separated by areas of intercalated discs: - These are special membranes with numerous gap junctions allowing a free diffusion of ions from cell to cell. To allow proper timing of the heart-beat, cardiac muscle: -Is myogenic i.e., it can contract rhythmically and continuously without external stimulation. -Functions as a syncytium, action potentials spreading from cell to cell. -Cardiac muscle has a long refractory period during which no further contraction may take place (0.25 – 0.3 sec). CFR.5 The Heart, structure and physiology; Cardiac cycle; Arterial blood pressure; Cardiac failure. 7 Nervous control of the heart- CV center Heart rate is regulated by the cardiovascular/ cardiac centre in the medulla oblongata which responds to pressure receptors in the walls of blood vessels and other stimuli. CFR.5 The Heart, structure and physiology; Cardiac cycle; Arterial blood pressure; Cardiac failure. 8 Heart rate  The rate of heart-beat varies widely in different mammals, generally being lower in larger animals. elephant 25/min mouse 500/min The adult human heart: – Normally contracts at about 72 beats/min – It may rise to 195 beats/min under stress – Trained athletes tend to have lower resting heart rates (50/min) CFR.5 The Heart, structure and physiology; Cardiac cycle; Arterial blood pressure; Cardiac failure. 9 Physiology of the heart Contraction of the heart muscle begins spontaneously in an area called the sino-atrial (SA) node, in the right atrial wall near the entry of the superior vena cava. The SA node or pacemaker consists of a modified cardiac muscle mixed with nerve fibres of the autonomic nervous system (i.e. Sympathetic and Parasympathetic- vagus nerve). CFR.5 The Heart, structure and physiology; Cardiac cycle; Arterial blood pressure; Cardiac failure. 10 Physiology of the heart The heart-beat originates spontaneously at the SA node because of the myogenic nature of cardiac muscle (the SA node generates ‘100 beats per min’ ) It is normally made to ‘slow down’ or ‘speed up’ (i.e. change frequency) by nervous input from the autonomic nervous system (ANS). Sympathetic fibres normally discharge at a slow rate but can increase heart rate by up to 100%. Parasympathetic fibres can reduce the heart rate by 30%. Contraction wave spreads at 0.3-0.45 metres/sec from the SA node to the entire atrial muscle mass; so the two atria contract simultaneously like a single cell. CFR.5 The Heart, structure and physiology; Cardiac cycle; Arterial blood pressure; Cardiac failure. 11 Excitatory and conductive system The SA node is normally made to ‘slow down’ or ‘speed up’ (i.e. change frequency) by the autonomic nervous system (ANS): Sympathetic fibres normally discharge at a slow rate but can increase heart rate by up to 100%. Parasympathetic fibres can reduce the heart rate by up to 30%. Sympathetic stimulation raises cardiac output and blood pressure. CFR.5 The Heart, structure and physiology; Cardiac cycle; Arterial blood pressure; Cardiac failure. 12 Excitatory and conductive system The two atria contract siumultaneously as a single cell/ unit. The atria are separated from the ventricles by the connective tissue of the annulus fibrosus (cannot carry the action potential acts as electrical insulation) so the contraction wave stops. Because of the annulus fibrosus there is a delay of 0.11 sec between atrial and ventricular contraction. Impulses travelling to the base of the right atrial wall near the centre of the heart, stimulate another special region, the Atrio-Ventricular (AV) node. Normally the AV node is the only electrical link between the atria and ventricles. CFR.5 The Heart, structure and physiology; Cardiac cycle; Arterial blood pressure; Cardiac failure. 13 Excitatory and conductive system The AV node transmits an impulse to the muscles of the ventricles, via the ‘His-Purkinje system’ of specialized fibres, The His-Purkinje system consists of the following parts: Bundle of His/atrioventricular bundle (the start of the system) Right bundle branch Left bundle branch Purkinje fibres (the end of the system Purkinje fibres conduct impulses at about 4 metres/ second. This allows an almost immediate transmission of the cardiac impulse to the muscle and the ventricles contract simultaneously. CFR.5 The Heart, structure and physiology; Cardiac cycle; Arterial blood pressure; Cardiac failure. 14 Excitatory and conductive system Annulus fibrosus – Yellow Passage of electrical signal – Green CFR.5 The Heart, structure and physiology; Cardiac cycle; Arterial blood pressure; Cardiac failure. 15 Excitatory and conductive system CFR.5 The Heart, structure and physiology; Cardiac cycle; Arterial blood pressure; Cardiac failure. 16 Cardiac cycle Contraction of heart chambers is known as systole, relaxation is called diastole. The period from the end of one contraction to the end of the next is called the cardiac cycle. The frequency of the cardiac cycle is described by the heart rate, which is typically expressed as beats per minute. Typically, the heart beats 70 times per minute (slowed from 100 bpm by the parasympathetic nervous system). One complete cardiac cycle is about 0.8 sec. The human heart beats some 2,600 billion times in an average life. CFR.5 The Heart, structure and physiology; Cardiac cycle; Arterial blood pressure; Cardiac failure. 17 Cardiac cycle Starts with the contraction of the two atria, the impulse originating in the sino- atrial node, causing the blood to be pumped into the ventricles. Blood normally flows continuously into the atria from vena cavae and pulmonary vein. 70% of atrial blood flows directly into the ventricles from the atria, the remaining 30% is pushed by atrial systole, thus the atria act as primer pumps for the ventricles. Because of the delay in transmission through the AV node, a pause occurs between atrial systole and ventricular systole. CFR.5 The Heart, structure and physiology; Cardiac cycle; Arterial blood pressure; Cardiac failure. 18  Cardiac cycle During ventricular diastole the chambers fill to a volume of 120-130 ml blood in each. At the start of ventricular systole the rise in pressure causes the atrioventricular valves to close, followed 0.02 to 0.03 sec later by the sudden opening of the semilunar valves. 70 ml of blood is ejected from the ventricle which is called the stroke volume, this can increase with exercise. The remaining volume in each ventricle is called the end-systolic volume, usually 50 – 60 ml. https://www.youtube.com/watch?v=5tUWOF6wEnk CFR.5 The Heart, structure and physiology; Cardiac cycle; Arterial blood pressure; Cardiac failure. 19 Cardiac output Cardiac output is defined as the volume of blood ejected into the aorta by the left ventricle in a time period of 1 minute, but normally it is also the amount of blood pumped into the pulmonary circulation by the right ventricle. Cardiac output is measured as follows: Stroke volume x Heart rate = 70 ml x 72/min = 5040 ml / minute  ~ 5 litres / min. Cardiac output varies with changes in either stroke volume or heart rate; under stress this can rise to 25 litres/ min. CFR.5 The Heart, structure and physiology; Cardiac cycle; Arterial blood pressure; Cardiac failure. 20  Frank Starling Law of the Heart Stroke volume depends mainly on venous return to the atria. Frank - Starling Law of the heart explains the intrinsic ability of the heart to adapt to changing loads of inflowing blood. The ventricles are elastic and so can expand to accommodate a larger volume of blood pumped by the atria. This also results in a larger force when the ventricle contracts. “within physiological limits, the heart pumps all the blood that comes to it without allowing excessive damming of blood in the veins” http://www.cvphysiology.com/Cardiac%20Function/CF003.htm CFR.5 The Heart, structure and physiology; Cardiac cycle; Arterial blood pressure; Cardiac failure. 21 Frank Starling Law of the Heart Stroke Volume Left Ventricle End-Diastolic Pressure http://www.cvphysiology.com/Cardiac%20Function/CF003.htm CFR.5 The Heart, structure and physiology; Cardiac cycle; Arterial blood pressure; Cardiac failure. 22  Note that the curve shifts upwards and to the left with exercise, demonstrating an increase in cardiac output. In the failing heart cardiac output declines and more blood remains in the heart after contraction. Damming of blood in the veins results in dyspnea (difficulty breathing) and subsequently oedema, especially pulmonary oedema. Heart failure: The pumping of the heart and cardiac output decline so that the heart does not meet the needs of the body. CFR.5 The Heart, structure and physiology; Cardiac cycle; Arterial blood pressure; Cardiac failure. 23 Electrocardiogram An electrocardiogram (ECG) may be used to record the electrical activity of the heart. CFR.5 The Heart, structure and physiology; Cardiac cycle; Arterial blood pressure; Cardiac failure. 24 Excitatory and conductive system CFR.5 The Heart, structure and physiology; Cardiac cycle; Arterial blood pressure; Cardiac failure. 25 Heart sounds 'Lub' and 'Dub' refer to the two heart sounds heard using a stethoscope. The first sound is due to the closing of the bicuspid and tricuspid valves between the left and right atria and ventricles respectively, during ventricular systole. The second sound is caused by the closing of semilunar valves in the pulmonary artery and the aorta, at the beginning of ventricular diastole. Damaged valves, heart murmurs, can be detected by listening to the sounds. CFR.5 The Heart, structure and physiology; Cardiac cycle; Arterial blood pressure; Cardiac failure. 26 Measurement of blood pressure The left ventricle drives the blood around the arteries under pressure. Arterial blood pressure is measured using a sphygmomanometer. The blood pressure in a young, healthy adult being about 120 mmHg at systole dropping to 80 mmHg at diastole. Written as: 120/80. In all mammals the systolic pressure lies between 100 – 200 mmHg whereas in the lower vertebrates it is only about 40 mmHg. CFR.5 The Heart, structure and physiology; Cardiac cycle; Arterial blood pressure; Cardiac failure. 27 Measurement of blood pressure CFR.5 The Heart, structure and physiology; Cardiac cycle; Arterial blood pressure; Cardiac failure. 28 Blood pressure Mean Arterial Pressure = Diastolic + 1/3rd Systolic – Diastolic) Mean pressure in the aorta is 100 mmHg. Since resistance in the aorta is minimal, it is still 100mmHg at start of the large arteries. Resistance increases particularly in the small arteries, so that at start of the arterioles blood pressure is 85 mm Hg. Resistance is greatest in the arterioles at start of the capillaries, where pressure drops to 30 mm Hg. Pressure is about 25 mm Hg at the start of the arterial capillary bed. The venous capillary pressure is 10 mmHg and it continues to drop in the venous system being almost exactly 0 mmHg in the vena cava at the right atrium. CFR.5 The Heart, structure and physiology; Cardiac cycle; Arterial blood pressure; Cardiac failure. 29 Blood pressure 100 mmHg at start of the large arteries 0 mmHg in the vena Arterioles it is 85 mmHg; cavae 10mmHg venous capillary 25 mmHg at start of the capillaries; CFR.5 The Heart, structure and physiology; Cardiac cycle; Arterial blood pressure; Cardiac failure. 30 Blood pressure- Systemic circulation Pulse pressure is the difference between the systolic and diastolic pressure readings. The pulse pressure curve of high systolic and low diastolic pressures becomes less as blood passes through the smaller arteries until it almost disappears in the capillaries (1mm Hg). See Solomon 9th Edition p953, Fig 44- 14b. CFR.5 The Heart, structure and physiology; Cardiac cycle; Arterial blood pressure; Cardiac failure. 31 Blood pressure A The maximal systolic pressure is terminated by a sharp drop or incisura (or dicrotic notch) at the commencement of ventricular diastole. B This notch is explained by a falling intraventricular pressure causing a backflow of blood from the aorta into the ventricles which causes a sharp drop in aortic pressure (A). The rapid closure of aortic semi-lunar valves causes a brief rebound in aortic pressure produces the notch (B). CFR.5 The Heart, structure and physiology; Cardiac cycle; Arterial blood pressure; Cardiac failure. 32  Sherwood. Human Physiology. Chapters 9 and 10. Learning Solomon. Biology. Chapter 44 Resources Chiras. Human Biology 6th Edition. Chapters 5 and 6. CFR.5 The Heart, structure and physiology; Cardiac cycle; Arterial blood pressure; Cardiac failure. 33 Thank you F O R M O R E I N F O R M AT I O N P L E A S E C O N TA N T NAME SURNAME EMAIL: [email protected] 34