Cardiovascular System Lecture Notes PDF

The Cardiovascular System Dr. Eman Alsultan Department of Physiology College of Medicine Imam Abdulrahman Bin Faisal University Lecture-1  The 3 Components of the circulatory system  The Heart A hollow muscular organ Located...

The Cardiovascular System Dr. Eman Alsultan Department of Physiology College of Medicine Imam Abdulrahman Bin Faisal University Lecture-1  The 3 Components of the circulatory system  The Heart A hollow muscular organ Located in the thoracic cavity midline between sternum anteriorly and vertebrae posteriorly Divided into two halves Each half has 2 chambers : an atrium and a ventricle Right & Left Atrium Right & left Ventricle Atria receive blood returning to the heart Right Atrium receives deoxygenated blood from all of the body Left Atrium receives oxygenated blood from the Lungs Ventricles pump the blood from the heart. Right ventricle to the lungs (deoxygenated blood) Left ventricle to all the rest of the body (oxygenated blood) Oxygenated & Unoxygenated blood  The Two major divisions of the Circulation Systemic Circulation Pulmonary Circulation Deoxygenated Right atrium. Oxygenated Left ventricle Left Atrium→ Right ventricle → → Veins → Pulmonary superior & Aortic valve Pulmonary valve → inferior vena → aorta→ Pulmonary Veins → cava→ Artery→ Arteries → Lungs Arterioles → Capillaries → Pulmonary venules → Capillaries→ Technically heart is a dual (double) pump The Right Pump & The Left Pump  The function of the heart is to Pump Heart pumps all the blood coming into it, with sufficient pressure, around the body, in cycles.  The Cardiac Cycle The cardiac events that occur from the beginning of one heartbeat to the beginning of the next. Transport (The function of circulation) Blood cells (RBC , WBC, Platelets) O2 & CO2 Nutrients delivery Metabolic wastes removal Water & electrolytes balance Hormones, enzymes and other proteins Immune defense Thicker left ventricular wall Both sides of the heart simultaneously pump equal amounts of blood. The left side of the heart performs more work because it pumps blood at a higher pressure against higher resistance. The heart muscle on the left side is therefore much thicker than the muscle on the right side.  Blood must flow through the heart in a fixed direction Presence of 4 one-way heart valves ensure this unidirectional flow  Mechanism of working of one-way valves When pressure is greater behind When pressure is greater in front the valve, it opens. of the valve, it closes The Heart is made up of Cardiac Muscle Cells  Cardiac muscle cells There are two specialized types of cardiac muscle cells: Contractile cells (99 %): they do mechanical work of pumping (contraction) Autorhythmic cells (1 %): they are specialized for initiating and conducting the action potentials responsible for contraction of the contractile cells.  Adjacent cardiac muscle cells join end-to- end by intercalated discs. Intercalated discs have desmosomes & gap junctions. Desmosomes mechanically hold cardiac cells together and convey the force of contraction. Gap junctions are the areas of low electrical resistance that allow the action potential to spread from cell to cell atria and ventricles are separate pumps There are no gap junctions between atria and ventricles They communicate only through the specialized junctional tissue (AV node)  Heart is a functional syncytium Syncytium is an arrangement of muscle fibers in which the fibers fuse to form an interconnected mass of fibers. This leads to all fibers contracting and relaxing together. Both the atria contract (systole) together first, after a little while both the ventricles contract together while atria are relaxing (diastole). This is followed by relaxation of ventricles Both the gap junctions and the fast-conducting system between the atria and ventricles make the heart a functional syncytium  Origin & spread of cardiac impulse SA NODE TO BOTH ATRIA Origin & spread of cardiac impulse INTERNODAL PATHWAYS AV NODE AV BUNDLE BUNDLE BRANCHES PURKINJE FIBRES  The cells with the fastest rate of action potential are located in the SA node SA node is therefore the pacemaker of the heart Rate of action potential discharge / minute SA node 70-80 AV node 40-60 Bundle of His 20-40 Purkinje fibers 20-40 Conduction velocity (m/Sec) (AV node) nodal fibers 0.02 - 0.1 (Slowest) Bundle of His 0.3 - 1 Purkinje fibers 4.0 (Fastest)  AV node has the slowest conduction velocity The impulse in the AV node is delayed for about 0.1 second This is called AV nodal delay AV nodal delay To allow the atria to be excited and to contract completely before the impulse reaches His bundle Meanwhile the ventricles get enough time to be completely filled Purkinje fibers The fastest conducting cells To ensure rapid and simultaneous excitation and contraction of both the ventricles  ECG (also called EKG)- Electrocardiogram It is the record of the heart’s electrical activity, recorded from the surface of the body. Because the body is a very good conductor therefore the small currents generated in the heart can be detected at the body surface. The ECG is a recording of these small currents and reflects the depolarization (contraction) and repolarization (relaxation) of different regions of the heart.  A typical ECG tracing Waves P, Q, R, S, T P wave: Atrial Depolarization QRS complex: Ventricular Depolarization T wave: Ventricular Repolarization A normal heart always beats in a Rhythm An abnormal rhythm of the heart is called Arrhythmia  Cardiac Output & Lecture-2 Autonomic Regulation of Heart DIASTOLE & SYSTOLE  Diastole vs Systole The blood is The blood is received by pumped out the heart by the heart during in systole diastole  End Diastolic The volume of blood in the ventricle at the end of diastole i.e., ventricular relaxation and filling Volume (EDV): (135 ml). End Systolic The volume of blood remaining in the ventricles after ejection of blood is completed at the end Volume (ESV): of systole i.e., ventricular contraction (65 ml)  It is the amount of blood pumped out of each ventricle in one heart-beat (one systole). Stroke Volume SV is usually 70 ml/ beat. (SV) SV = End Diastolic Volume – End Systolic Volume SV = 135 ml – 65 ml = 70 ml/ beat  It is the number of heart beats per minute (BPM) It is established by the SA node HR = 70–75 BPM on the average (Range is 60–100 ) Heart Rate (HR) HR is greater in females than males HR is greater in children than in adults HR is greater in sedentary people than in athletes  Tachycardia HR greater than Normal (100 BPM) Examples Fever, anemia, hyperthyroidism, sympathetic Heart Rate stimulation (HR) Bradycardia HR less than Normal (60 BPM) Examples Athletes, hypothyroidism, parasympathetic stimulation  It is the volume of blood pumped through the circulatory system by each ventricle per minute. The CO of the left ventricle = CO of the right ventricle. Cardiac output It is an important medical indicator of how efficiently the heart can meet the demands of the body. (CO) HR and SV are two key factors which contribute to CO CO = HR X SV  Example What would be the Cardiac output (CO) if Heart Rate (HR) is 70 BPM & Stroke Volume is 70 ml/beat CO = HR x SV = 70 beats / min x 70 ml / beat = 4900 ml / min (about 5 liters) Normal resting cardiac output (5L) equals to the normal blood volume in an individual Factors that control heart rate & stroke volume also control cardiac output  Regulation of Cardiac Output Cardiac output has to be regulated to meet the body needs under various conditions. This is achieved by regulation of: Heart rate Stroke volume  Heart rate can be regulated by regulating SA node activity since it is the pacemaker of the heart. Factors Increasing heart rate Sympathetic stimulation on SA node Regulation of Presence of circulating epinephrine hormone Increased body temperature Heart rate Anxiety Young children Factors decreasing heart rate Parasympathetic stimulation on SA node Decreased body temperature Advanced age During rest (parasympathetic discharge is dominant)  Regulation of Stroke Volume The stroke volume can be increased by increasing the force of contraction of heart. Force of contraction increased by: Autonomic nervous system (Sympathetic stimulation) Increased venous return “Frank Starling mechanism”  Primary control of stroke volume Intrinsic Control Extrinsic Control (venous return) (Autonomic nervous system)  Intrinsic Control (venous return) Frank-Starling’s law of heart states that “ increased venous return to the heart will result in an increased stroke volume’’. Frank-Starling’s law of heart  Intrinsic control venous return results Greater More the theblood initial returns length of Frank-Starling’s law cardiac to themuscle heart, greater fiber greater is itsthe force stroke of contraction volume ↑ EDV causes ↑ pressure in ventricle ↑ pressure stretches heart muscle fibers ↑ length in muscle fibers allows ↑ force of contraction Which results in an  Stroke volume  Extrinsic control (Sympathetic and parasympathetic activity) AUTONOMIC REGULATION ▪ The autonomic nervous system DOES NOT initiate the heart beat ▪ SA-node does this spontaneously, but it does modulate it.  Heart Strength of Cardiac Autonomic Rate pumping Output Sympathetic Increase Increase Increase Regulation of Parasympathetic Decrease Decrease Decrease the heart for atria No effect on ventricles.  Control of the radius of the arterioles Sympathetic nervous system can affect vascular tone. Sympathetic stimulation → vasoconstriction. Sympathetic inhibition→ vasodilation.  Control of Blood Pressure Short-term Long-term (within seconds) (within minutes-days) Renal compensation Baroreceptor Ref lex (by controlling urine output) (by controlling CO & TPR)  Hypertension BP > 140/90 mmHg Primary hypertension (essential hypertension): the cause of this type of hypertension is not known. Secondary hypertension: means that hypertension is secondary to some other factor. Hyperlipidemia: narrowing of vessels ➔ increased total peripheral resistance ➔ increased blood pressure. Increased blood glucose levels: hyperlipidemia ➔ increased blood pressure. Renal problems: increased release of angiotensin and aldosterone (kidneys) ➔ increased retention of salt and water ➔ hypertension Hypotension: BP < 100/60 mmHg  Heart Failure Is the inability of the heart to supply adequate blood flow and therefore oxygen delivery to peripheral tissues and organs. Under perfusion of organs leads to reduced exercise capacity, fatigue, and shortness of breath. It can also lead to organ dysfunction (e.g., renal failure) in some patients. Reference Human Physiology, 9th Edition Lauralee Sherwood Thank you