Cardiac Cycle PDF

ATRIOVENTRICULAR (AV) VALVES SEMILUNAR VALVES Atrioventricular (AV) valves - prevent backflow of blood from ventricles to atria during ventricular systole (contraction) Tricuspid valve - located between right atrium & right ventricle Mitral valve - located between left atrium & left v...

ATRIOVENTRICULAR (AV) VALVES SEMILUNAR VALVES Atrioventricular (AV) valves - prevent backflow of blood from ventricles to atria during ventricular systole (contraction) Tricuspid valve - located between right atrium & right ventricle Mitral valve - located between left atrium & left ventricle Semilunar valves - prevent backflow of blood from arteries (pulmonary artery & the aorta) to ventricles during ventricular diastole (relaxation) Aortic valve - located between left ventricle & the aorta Pulmonary valve - located between right ventricle & the pulmonary artery During cardiac cycle heart valves open and close in response to differences in blood pressure on their two sides. Blood flow in the heart is controlled by the pressure changes.  All valves consist of connective tissue (not cardiac muscle tissue) and therefore, open & close passively. Valves open & close in response to changes in pressure:  AV valves - open when pressure in the atria is greater than pressure in the ventricles (i.e., during ventricular diastole) & closed when pressure in the ventricles is greater than pressure in the atria (i.e., during ventricular systole)  Semilunar valves - open when pressure in the ventricles is greater than pressure in the arteries (i.e., during ventricular systole) and closed when pressure in the pulmonary trunk & aorta is greater than pressure in the ventricles (i.e., during ventricular diastole)  Heart Sounds Closing of the valves causes audible sounds  However, when the valves close, the vanes of the valves and the surrounding fluids vibrate under the influence of sudden pressure changes, giving off sound that travels in all directions through the chest.  The first hears a sound caused by closure of the A-V valves. The vibration is low in pitch and relatively long-lasting and is known as the first heart sound.  When the aortic and pulmonary valves close at the end of systole, one hears a rapid snap because these valves close rapidly, and the surroundings vibrate for a short period. This sound is called the second heart sound.  The Function of Valves One way- passively working. Prevent back flow of blood. open closed SL AV systole diastole AV SL SYSTOLE : CONTRACTION, specifically contraction of ventricles. DIASTOLE : RELAXATION, specifically relaxation of ventricles. CARDIAC CYCLE 0,80 sec Blood fills into ventricles. DIASTOLE 0,50 sec 0,30 sec SYSTOLE Blood is ejected from heart.  “Phases” of the Cardiac Cycle 1. Isovolumetric Contraction VENTRICULAR 2. Rapid Ejection SYSTOLE 3. Reduced Ejection 1. Isovolumetric Relaxation VENTRICULAR 2. Rapid Filling DIASTOLE Ventricular Filling 3. Reduced Filling (Diastasis) 4. ATRIAL SYSTOLE  VENTRICULAR SYSTOLE Isovolumetric Contraction Ventricular Ejection Stroke volume (SV) is the volume of blood pumped from At this phase: ventricle per beat The SV= 70 ml ventricular volumes are maximal End-diastolic volume = EDV = 120 ml As the ventricles contract, intraventricular Ventricular ejection starts rising ventricular pressure rises, AV valves closed, briefly, pressure forces semilunar valves open. Blood is ventricles are completely closed chambers. ejected from the heart. VENTRICULAR DIASTOLE Isovolumetric Relaxation The ventricles relax and ventricular pressure drops. AV and SL valves are closed, The ventricles are totally clossed off again. End-Systolic Volume (ESV): the residual volume of blood that remains in a ventricle after ejection ESV = 50 ml  Ventricular Filling Then, Atria contracts AV valves are open, blood flows through ventricles (rapid filling) Forcing the remaining blood into ventricles (reduced filling)  CARDIAC OUTPUT Cardiac output is the amount of blood pumped out by each ventricle in one minute.  Cardiac output is the amount of blood pumped out by each ventricle in one minute. Cardiac Output = Heart Rate X Stroke Volume SV is the amount of blood pumped by each ventricle with each heart beat. 70 mL per beat in adult at Heart rate is the number of the rest. times heart beats in one minute. Averaging 75 bpm in adult at rest.  1. Regulation of heart rate 2. Regulation of stroke volume The key factor regulating heart rate is the balance between sympathetic-parasympathetic stimulation of the heart.  Effects of Autonomic Nervous System on Heart Rhythm NE Na conductance ACh Ca conductance K conductance Tachycardia - 100 ↑ Bradycardia - 60↓  FACTORS EFFECTING STROKE VOLUME “Regulation of Stroke Volume” Intrinsic control Extrinsic control related to amount of venous return, related to amount of sympathetic stimulation. (amount of blood returning to the heart through the veins) sympathetic stimulation release of norepinephrine (NE) increased end-diastolic volume increased permeability of muscle cell increased stretching of cardiac muscle membranes to calcium increased strength of contraction calcium diffuses in and more cross-bridges are activated increased stroke volume stronger contraction increased stroke volume The various factors of the peripheral circulation that affect flow of blood into the heart from the veins, that are the primary controllers of the CO.  BLOOD VESSEL STRUCTURE AND FUNCTION Five types of blood vessels: (1) Arteries Two large arteries are the aorta and pulmonary trunk (2) Arterioles (3) Capillaries (4) Veins (5) Venules The average adult has over 60,000 miles of blood vessels in their body.  Distribution of Blood Volume Systematic arteries and arterioles 15 % Systematic veins and venules 60 % Systematic capillaries 5% Pulmonary blood vessels 12 % Heart chambers 8% Veins and venules contain so much blood, thus certain veins serve as blood reservoirs from which stored blood can be diverted to other parts of the body.  Arteries and Arterioles The lumen is the hollow space through which the blood flows. Three layers surrounding the lumen: Tunica interna Tunica media Tunica externa  Vasoconstriction → decrease in the size of the lumen Vasodilation → increase in the size of the lumen  Capillaries Connect arterioles and venules exchange vessels → permit exchange of nutrients and waste between body cells and blood Areas with high metabolic requirements have extensive capillary networks – muscles, liver, kidneys, nervous system Areas with very low metabolic requirements lack capillaries – cornea and lens of the eye, nails, hair follicles, cuticles, cartilage  Structure of Capillaries Walls consist of single layer of endothelial cells Precapillary sphincters → rings of smooth muscle at meeting point of capillary to arteriole  Capillary Exchange Two methods of exchange – Diffusion – Bulk Flow (A net movement of fluid occurs from blood into tissues)  Diffusion Oxygen and nutrients → down the gradient into interstitial fluid and then into body cells Carbon dioxide and waste → down the gradient from interstitial fluids into the blood for removal Glucose Amino acids Hormones Plasma proteins usually remain in blood; too large to pass through – Exceptions: Sinusoids the smallest blood vessels in the liver have very large gaps in between their endothelial cells to allow proteins (fibrinogen, main clotting protein, and albumin) to enter bloodstream Other areas are very selective: – Blood-brain barrier refers to the tightness of endothelial layer found in brain; allows only a few substances to enter and leave Bulk Flow (Filtration and Reabsorption)  Venules and Veins Capillaries unite to form venules (small veins) Venules receive blood from capillaries and empty it into veins Veins return blood to the heart  Structure of Venules and Veins Venules – little veins; walls thinner at capillary end, thicker as they progress toward heart Veins – structural similar to arteries; middle and inner layers thinner than arteries, outer layers are the thickest Generally, lumen of veins wider than that of corresponding artery  BLOOD FLOW THROUGH BLOOD VESSELS From areas of higher pressure to areas of lower pressure – greater the pressure difference the greater the blood flow Contractions of the ventricles generate blood pressure (BP) Blood pressure is the measure of pressure exerted by blood on the walls of a blood vessel – highest in the aorta and large systemic arteries  Systolic versus Diastolic Systolic (contraction) measures maximum arterial pressure occurring during contraction of the left ventricle of the heart – Average = 120 mmHg – High end begins = 140mmHg Diastolic (relaxation) measures arterial pressure during the interval between heartbeats – Average = 80 mmHg – High end begins = 90mmHg  Resistance Vascular resistance → opposition to blood flow due to friction between blood and the walls of blood vessels – Increase in vascular resistance = increase in BP – Decrease in vascular resistance = decease in BP Vascular resistance is dependent upon: – Size of the blood vessel (lumen) Smaller means greater resistance to blood flow; alternates between vasoconstriction and vasodilation – Blood viscosity Ratio of RBCs to plasma volume Higher viscosity = higher resistance – Total blood vessel length Resistance increase with total length Longer the length = greater contact between vessel wall and blood  Blood Pressure Regulation There are two basic mechanisms for regulating blood pressure. 1. Short- term mechanisms *vessel diameter, *heart rate, *heart contractility 2. Long –term mechanisms *Blood volume  Short term reflexes afferent pathway efferent pathway CVS Coordinating Center Detector heart receptor (-) feedback loop effectors arteries baroreceptor adrenal gland Blood pressure Blood volume  Baroreceptor Arterial blood pressure is regulated through negative feedback systems incorporating pressure sensors (baroreceptors) found in strategic locations within the cardiovascular system. Arterial baroreceptors are found in the carotid sinus (at the bifurcation of external and internal carotids) and in the aortic arch.  Baroreceptor Increased arterial pressure increases the firing rate of individual receptors and nerves  KARDİYOVASKÜLER KONTROL MERKEZİ NTS CI VM + CA (Vagal) (Symp) Nucleus tractus solitarius (NTS) Effectors Vasomotor center (VM) (sympathetic) Cardiac accelator (CA) (sympathetic) Cardioinhibitory center (CI) (parasympathetic) Short term regulation of Rising Blood Pressure *Rising Blood Pressure *Streching of Baroreceptors *Increased impulses to the brain *Increased Parasympathetic activity *Decreased Sypmpathetic activity *Slowing Heart Rate *Increased arteriolar diameter. *Reduction of blood pressure. Cardiac Output = Heart Rate X Stroke Volume Decreased diameter 1. Short- term mechanisms *vessel diameter, *heart rate, *heart contractility 2. Long –term mechanisms *Blood volume 2. Long–term mechanisms *Blood volume  Renin-Angiotensin system Blood pressure Renal perfusion Granular cells in the kidney “Juxtaglomerular cells”sense the alteration of blood pressure and secrete RENIN RENİN From liver to circulation Angiotensin I inactive plasma protein “Angiotensinojen” Angiotensin converting enzyme *Strong vasocontraction (ACE) (Lung capillaries) *Stimulates Angiotensin II (Ang II) “Aldosterone” and ADH release  Angiotensin II *Strong vasocontraction *Stimulates “Aldosterone” release Atrial natriuretic peptide (ANP) Atrial natriuretic peptide (ANP), which is released by the atria primarily in response to atrial stretch, functions as a counter-regulatory mechanism for the renin-angiotensin-aldosterone system. ❖ Therefore, increased ANP reduces blood volume, venous pressure, and arterial pressure. ELECTROCARDIOGRAM (ECG)  ELECTROCARDIOGRAM (ECG) Lead set  ELECTROCARDIOGRAM (ECG) The electrocardiogram (ECG or EKG) is a measurement of potential differences on the surface of the body that reflect the electrical activity of the heart. ECG is useful in diagnosing abnormal heart rates, arrhythmias, and damage of the heart muscle.  ELECTROCARDIOGRAM (ECG) Ventricular depolarization QRS complex Ventricular repolarization Atrial depolarization T wave P wave Rate We can measure rate in two ways. The direct method is to measure the number of small square between waves of the same type, for example, the R-R interval.  17 small square HR= 1500/17 = 88.2bpm HR= 1500/ small square between 2 R wave