Cardiovascular System: BDS108, Ajman University

• The cardiovascular system is the topic of study in the Integrated Biological Sciences - II, BDS108 course, taught by Dr. Jayaraj at Ajman University.

Learning Outcomes related to the Heart

• Describe the location of the heart.
• Detail the wall structure, and anatomy of the heart.
• Explain the pacemaker potential.
• The timing of heart sounds, systole and diastole can be explained.
• Cardiac output and the structure/function of blood vessels are defined and described.
• Blood pressure changes and regulation can be outlined.
• You should understand the different types of circulatory shock that can occur.

Heart Anatomy

• The heart is about 12 cm long, 9 cm wide, and 6 cm thick.
• It weighs 250g on average in adult females, and 300g on average in adult males.

Heart Location and Important Surfaces & Borders

• The heart is located in the mediastinum.
• It is oriented anteriorly, inferiorly, and to the left.
• Approximately 2/3 of the heart's mass lies to the left of the body's midline.
• The apex is formed by the tip of the left ventricle, resting on the diaphragm.
• The base is the posterior surface of the heart.
• The heart has several distinct surfaces and borders.
• The anterior surface is deep to the sternum and ribs.
• The inferior surface rests mostly on the diaphragm, between the apex and right border.
• The right border faces the right lung and extends toward the base.
• The left border looks toward the left lung and extends toward the apex.

Pericardium

• A membrane that surrounds and protects the heart.
• It confines the heart's position in the mediastinum, but allows sufficient freedom of movement.
• The pericardium consists of fibrous and serous layers.
• The fibrous pericardium is the superficial, tough, inelastic, dense irregular connective tissue layer.
• It rests on and attaches to the diaphragm, with the open end fused to the connective tissues of the blood vessels.
• It prevents overstretching and provides protection, anchoring the heart in the mediastinum..
• The serous pericardium is a thinner, more delicate membrane forming a double layer around the heart.
• It is comprised of the Outer parietal layer fused to the fibrous pericardium and the Inner visceral layer, which adheres tightly to the heart's surface.
• The pericardial cavity lies between the parietal and visceral layers of the serous pericardium.
• The pericardial fluid is a thin film of lubricating serous fluid that reduces friction between the layers.

Heart Wall Layers

• The heart wall has 3 layers: epicardium, myocardium, and endocardium.
• The epicardium is the thin, transparent outer layer, composed of mesothelium and delicate connective tissue.
• The myocardium, the middle layer, is made of cardiac muscle tissue, making up about 95% of the heart and responsible for its pumping action.
• The endocardium is the inner layer consisting of a thin layer of endothelium overlying a thin layer of connective tissue.
• It covers the valves and provides a smooth lining for the chambers, continuous with the endothelial lining of the blood vessels, and reducing surface friction.

Heart Chambers

• The heart has four chambers: atria and ventricles.
• The atria are the two superior receiving chambers.
• Auricles increase capacity of atria and hold greater blood volume.
• Auricles are wrinkled pouch-like structures on the anterior surface of each atrium.
• The ventricles are the two inferior pumping chambers.

Sulci of the Heart

• Series of grooves on the heart's surface contain coronary blood vessels and a variable amount of fat.
• The deep coronary sulcus marks the external boundary between the atria and ventricles.
• The anterior interventricular sulcus is the external boundary between the right and left ventricles (anterior aspect).
• The posterior interventricular sulcus marks the external boundary between the ventricles (posterior aspect).

Right Atrium

• Forms the right border of the heart with an average thickness of 2-3 mm.
• Its posterior wall is smooth, while the anterior wall is rough due to pectinate muscles.
• The right atrium receives blood from three veins: superior vena cava, inferior vena cava, and coronary sinus.

Atria: Interatrial Septum and Fossa Ovalis

• The Interatrial septum is a thin partition between the right and left atria.
• The Fossa ovalis is an oval depression on the septum, a vestige of the former foramen ovale.
• Blood passes from the right atria into the right ventricle
• Blood passes into the right ventricle through the tricuspid valve (Right atrioventricular valve).
• The tricuspid valve consists of three dense connective tissue leaflets or cusps covered by endocardium.

Left Atrium

• Has an average thickness of 2-3 mm and forms most of the base of heart.
• It contains a smooth posterior and anterior wall, with pectinate muscles confined to the auricle.
• Receives blood from the lungs through four pulmonary veins and passes blood into the left ventricle.
• Blood passes into the left ventricle through the bicuspid (mitral) valve, also known as the left atrioventricular valve, which has two cusps.

Ventricles

• The right ventricle has an average thickness of 4-5 mm and forms most of the anterior surface of the heart.
• Trabeculae are cardiac muscle fibers inside of the right ventricle, some taking part of the conduction system.
• Blood passes from the left ventricle into the pulmonary trunk and divides it into right and left pulmonary arteries.
• The interventricular septum separates the right ventricle from the left ventricle.
• The cusps of the tricuspid valve connect to the chordae tendineae which in turn attach to papillary muscles.

Left Ventricle

• It's the thickest chamber of the heart, with an average thickness of 10-15 mm, forming the apex of the heart.
• It receives blood from the left atria and passes it into the ascending aorta.
• Some blood flows into the coronary arteries, while the remainder passes into the arch of the aorta, descending aorta (thoracic and abdominal), and is carried throughout the body.
• The left ventricle contains trabeculae carneae and chordae tendineae to anchor the cusps of the bicuspid valve to papillary muscles.

Systemic and Pulmonary Circulations

• The systemic circulation receives bright red oxygen-rich blood from the lungs and the Pulmonary veins.
• The systemic circulation ejects blood from the left ventricle into the aorta and smaller systemic arteries, then to arterioles.
• Systemic capillaries transport blood to all organs throughout the body, exchange nutrients and gases, then enter a systemic venule.
• Deoxygenated blood is carried from the venule away from tissues, merging into larger systemic veins and flowing back to the right atrium.
• The pulmonary circulation is a system where the heart receives all the dark red, deoxygenated blood.
• Blood is ejected from the right ventricle into the pulmonary trunk and then flows into the pulmonary arteries to the lungs.
• In capillaries of the lungs, blood unloads CO₂ and loads O₂ and then oxygenated blood flows into the pulmonary veins which returns blood to the heart(left atrium).

Coronary Circulation

• The coronary circulation has a network of blood vessels for the myocardium.
• Coronary arteries branch from the ascending aorta and encircle the heart like a crown.
• The left coronary artery is divided into the anterior interventricular and circumflex artery.
• The anterior interventricular artery supplies blood to the walls of both ventricles.
• The circumflex artery supplies blood to the walls of the left ventricle and left atrium.
• The right coronary artery supplies small branches to the right atrium and is divided into the posterior interventricular and marginal arteries.
• The posterior interventricular artery supplies blood to the walls of two ventricles.
• The marginal artery supplies blood to the walls of the right ventricle.
• Anastomoses are provided to the heart (collateral circuits that provide alternate routes for blood such as in the myocardium).

Coronary Veins

• The heart has major veins such as the great cardiac vein, the middle cardiac vein, the small cardiac vein, and the anterior veins
• The Great cardiac vein drains both ventricles and the left atrium.
• The Middle cardiac vein drains the both ventricles.
• The Small cardiac vein drains right atrium and right ventricle.
• The Anterior cardiac veins drain the right ventricle
• All Cardiac veins drain to the coronary sinus which empties into the right atrium

Conductive System

• Autorhythmic fibers spontaneously and rhythmically generate action potentials that trigger heart contractions
• The Sinoatrial (SA) node begins the conduction of AP
• The AV node, Bundle of His, bundle branches, and Purkinje fibers conduct AP through the heart and stimulate heart contractions
• The SA node is located in the right atrial wall just inferior and lateral to the opening of the superior vena cava.
• Spontaneous depolarization is a action potential that is a pacemaker potential begins here

Pacemaker Potential and Nodal Rhythmicity and Action Potentials

• Fast Na+ channels are closed at RMP -55 mV, with both Na+ and transient calcium channels being open.
• The Pacemaker potential (Slow depolarization) occurs in between two heartbeats when cells reaches a threshold of -40 mV.
• Action potential begins in the SA node in the right atrial wall.
• Action potentials propagate throughout the atria via gap junctions.

Steps of Action Potential

1. Depolarization occurs when the cardiac muscle cells have action potential reach -40mv, long lasting Ca2+ is activated, Ca2+ influx occurs,
2. Repolarization: Ca2+ & Na+ channels deactivate with K+ channels being open, with net Efflux of K+.
3. Hyperpolarization: K+ channels remain open which cases the action potential to have a higher negative polarity.

Ionic Basis

• A slow influx of Ca2+ occurs through transient Ca2+ channels, coupled with Na+ influx through slow Na+ channels.
• Influx of Ca²+ through long lasting Ca2+ channels in Depolarization.
• Repolarization via Efflux of K+.
• Hyperpolarization via Excess efflux of K+.

Resting Heart Rate

• An action potential initiated by the SA node travels along the conduction system.
• The speed of the action potential is controlled by the atria.
• Impulses are delayed at the AV node, which is important at to fill the atrias
• The heart can beat anywhere from 20-100 beats per minute

Transmission of Cardiac Impulse

• The delay of impulse conduction from the atria to the ventricles is a total delay of 0.16 sec, which allows the atria to empty their blood into the ventricles before ventricular contraction begins.
• Cardiac excitation begins in the sinoatrial node and propagates along atrial muscle fibers to the atrioventricular node.
• The AV node is the only site for conduction of AP from atria to ventricles.

Heart Impulses

• AP propagates along the AV bundle with fiber rapidly conducting AP from apex to ventricular myocardium.
• Cardiac muscle cells that develop spontaneous automaticity are called ectopic pacemakers.
• The ectopic pacemaker does not follow heart rhythm.

Regulation of Rhythmicity and Impulse Conduction

• It can be stimulated by the sympathetic neurons which causes Norepinephrine.
• Norepinephrine increases Ca2+ & Na+ permeability which causes Depolarerization.
• Parasympathetic neurons cause release of Acetylcholine.
• Parasympathetic neurons increase permeability of K+ (efflux of K+) and causes Hyperpolarizing

Action Potentials in Cardiac Muscle

• Membrane potential is at a resting state between -85 to -90mv which is Phase 4, and then goes into threshold to begin bringing contractile fiber to threshold
• During Phase 0 also known as rapid depolarization, this is when voltage gated fast Na+ channels open
• During Phase 1Also known as initial Rapid Repolarization this causes fast Na+ channels to open (The fast Na+ channels inactive)
• During Phase 2 also know as plateau, the opening of voltage gated slow Ca2+ channels with Ca2+ channels slower to open and remain open for a long time
• • During Phase 3 repolarization, large More voltage gated K+ channels open.
• The resting membrane potential is restored by Phase 4, where theres resting membrane, and Efflux of 3 Na+ and influx of 2 K+ by Na+/K+ ionic pump

Mechanical Properties of the Heart

• Refractory Period: The period during and following an action potential; cardiac muscle cannot be re-excited
• Ventricle action is between 0.25 to 0.30 sec, while Atria actions are between 0.15 sec
• Absolute refractory period at 0.2 is when Cardiac re-stimulation during action is impossible
• Relative refractory period at 0.05 is when cardiac muscle Can be re-excited by very strong electrical stimuli

Excitation-Contraction Coupling

• Action potential in cardiac muscles then Inward spread of depolarization along T tubules
• Causes activation of dihydropyridine receptors which causes the ryanodine receptors of the sarcoplasmic reticulum.
• Ca2+ diffuses into the heart sarcoplasm from the Ttubules, then diffuses thich thick filaments and thin filaments until it exposes the binding sites
• During the Ca2+ is transported out of the cell

Issues around Cardiovascular

• Heart valves may fail from Stenosis.
• There may also be Myocardial ischemia (reduced blood flow to the myocardium caused by Ischemia).
• Myocardial infarction (heart attack) is due to a complete obstruction of heart blood flow.

Cardiac Cycle

• Consists of diastole which is the period of heart relaxation.
• Consists of systole which is the period of heart contraction pumps blood
• 1 Cardiac Beats =0.8 sec. Systole=0.3 sec while Diastole=0.5 sec

Atria/Ventricular Systole Timeline

• Atrial systole/kick delivers last 20% of volume to ventricles (A-V valves open; Semilunar valves closed).
• Ventricular diastole (blood accumulates from atria with the A-V valves open) causes A-V pressures to open..
• Ventricular systole (contraction of ventricles causes the A-V valves close with Tension increases muscle fiber length by +80 mm Hg
• Ventricular Ejection: 1/3 is empties 70%, while 2/3 is around 30%.
• End of systole aka Ventricular systole causes A-V to close to begin a new cycle
• EGC reads composite action potentials.
• The ECG can be read because of electricity travelling throughout the heart

Cardiovascular Sounds

• Normal heart only the first and second sounds aka (S1 and S2) and heart thumping action is caused by fluid turbulence.
• S1 first sounds comes from LUB sound when the heart is louder.
• S2 Second heart sounds come from the closure of AV valve
• S4 Sounds stem from turbulent blood flow during atrial systole.

Ventricular Ejection

• Ventricular pressure rises above 80 mm Hg with ventricular pressures push the semilunar valves
• In relation to heat: Repolarization occurs as the heat is cooling
• During Atrial diastole the p wave of electrical activity
• During atrium emptying the ventricles begins systole action

Cardiac Output

• The volume of blood ejected from left ventricle/right ventricle into the aorta /pulmonary trunk each minute
• The blood volumes ejects due to the ventricles during each contraction In a the number of heart beats per minutes times volume 70mL times beat 75 BPM = 5.25

Blood Vessels and Vascular Resistance

• The five main types of vessels Arterioles, arteries, and aorta, Medium artery capillaries, then large vessels, Then last Vena Cava Veins.
• To be a main Vascal there you must 3 layers tunics- externa intima media
• Size of blood vessel lumen and opposition to blood flow due to opposition between walls between vessels is Vascal resisatnce

Hemodynamics

• Volume of blood =time and then you have the blood flow amount _Cardiac Output is important aspect of hemodynamic flow rate- and it goes from large pressure to normal pressure rate

Regulation

• Hydrostatic pressure exerted by blood on the walls of of vessel is the bloods vessels
• Vasoconstrticiton lowers blood cells but increases tension in vessel
• Heart helps regulate heart rate and and stroke by blood flow

Blood Circulation

• Sympathetic increases force in heart muscle and decreases back blood volume
• Low BP is from emotional increases in activity
• Blood returns to pulmonary, VR(vencacva) is from heart returning it.
• Blood pressure sensotive receptors and senesory impulse
• Pressure reglated thru harmones Aldosteorne is sected in kidneys and harmoses Nat and h ions- are at the cell levels
• Autoregulation: Body temperature and K, H lactic acids and cause vasdilation