Chapter 31- Cardiac and lymph system

Circulatory System Functions

• The circulatory system delivers oxygen, nutrients, hormones, immune cells, and other substances to body tissues.
• It also removes waste products from cellular metabolism.
• A complex network of blood and lymphatic vessels connected to the heart serve these functions.
• The heart pumps blood through these vessels, with regulation from the nervous and endocrine systems.
• The immune, digestive, and respiratory systems supply essential components, while the lungs, kidneys, and digestive tract remove waste.
• A functional vascular endothelium is crucial for vascular and hemostatic physiology; its dysfunction contributes to various diseases.

Heart as a Double Pump

• The heart is composed of two conjoined pumps powering two separate circulatory circuits.
• The right side of the heart (right heart) pumps blood to the lungs through pulmonary circulation.
• The left side of the heart (left heart) pumps blood to the rest of the body (excluding the lungs) through systemic circulation.
• These two systems are serially connected, with the output of one pump becoming the input of the other.

Blood Vessel Network

• Arteries carry blood away from the heart, branching into arterioles and then capillaries.
• Capillaries facilitate exchange between the blood and the interstitial space (interstitium).
• Veins carry blood from capillaries back to the heart.
• Lymph, derived from plasma, is returned to the cardiovascular system via the lymphatic system.
• The lymphatic system is a vital part of the immune system.

Blood Flow Through Pulmonary and Systemic Circulation

• The right heart chambers pump unoxygenated blood through the pulmonary circulation.
• The left heart propels oxygenated blood through the systemic circulation.
• Blood flow starts at the left ventricle, moving through arteries, arterioles, and capillaries of each organ.
• The blood then flows through venules, veins, to the right atrium, right ventricle, pulmonary artery, lung capillaries, and pulmonary veins, before returning to the left atrium and finally the left ventricle.

Heart Functions

• Structural support of heart tissues and circulation, including the:
  • Heart wall
  • Fibrous skeleton
  • Four chambers
  • Valves
  • Great vessels
• Maintenance of heart cells through coronary circulation and lymphatic vessels.
• Stimulation and control of heart action:
  • Nerves
  • Specialized muscle cells for rhythmic contraction and relaxation, pushing blood throughout pulmonary and systemic circuits.

Heart Wall Layers and Pericardium

• The heart wall has three layers: epicardium, myocardium, and endocardium.
• The heart is enclosed by the pericardium, a double-walled membranous sac.
• The pericardial sac:
  • Prevents heart displacement during acceleration or deceleration.
  • Acts as a physical barrier against infection and inflammation.
  • Contains pain and pressure receptors that can affect blood pressure and heart rate.

Pericardial Layers

• The outer layer of the pericardium is the parietal pericardium, composed of mesothelium over connective tissue.
• The inner layer of the pericardium is the visceral pericardium, or epicardium.
• The visceral pericardium folds back to become continuous with the parietal pericardium, allowing large vessels to enter and leave.
• The space between the visceral and parietal pericardia is called the pericardial cavity, which contains lubricating pericardial fluid.
• Inflammation can alter the amount and character of pericardial fluid.
• The outer epicardium layer of the heart provides a smooth surface for contraction and relaxation within the pericardium.
• The myocardium, the heart wall's thickest layer, is made of cardiac muscle anchored to the fibrous skeleton;its thickness varies by chamber based on pumping resistance.
• The endocardium, the internal lining of the myocardium, is made of connective tissue and squamous cells and connects with the endothelium lining blood vessels, creating a closed circulatory system.

Heart Chambers

• The four heart chambers include the right atrium (RA), left atrium (LA), right ventricle (RV), and left ventricle (LV), forming two pumps in series.
  • The right heart is a low-pressure system pumping blood through the lungs.
  • The left heart is a high-pressure system pumping blood through the rest of the body.
• Wall thickness depends on the pressure or resistance each chamber must overcome to eject blood.
• The mean pulmonary capillary pressure is 15 mmHg, whereas the mean arterial pressure is 92 mmHg.
• Due to the pressure difference, the LV's myocardial wall is thicker than the RV's.
• Blood typically does not flow between the right and left chambers, except in the fetus before birth.
• The atria are separated by the interatrial septum, and the ventricles by the interventricular septum.

Atria

• Atria are smaller than ventricles and have thinner walls (2mm thick).
• They act as low-pressure storage units and conduits for blood emptying into the ventricles.
• There is normally little resistance to flow from the atria to the ventricles.
• The foramen ovale, an opening between the atria present before birth, usually closes shortly after birth.

Ventricles

• The right ventricle's wall is 5 mm thick and shaped like a crescent or triangle.
• This shape enables it to function like a bellows, ejecting large blood volumes into the low-pressure pulmonary system.
• The left ventricle is the most muscular chamber, with a 15 mm thick wall.
• Its bullet shape helps it eject blood into the high-pressure systemic circulation.
• The left ventricle's myocardial wall is significantly thicker due to these pressure differences.
• The ventricles consist of muscle fibers originating from the fibrous skeleton at the base of the heart.
• The ventricular myocardium must be strong enough to pump against pulmonary or systemic vessel pressures.
• Ventricles have a structurally more complex than the atria.
• The interventricular septum, an extension of the heart's fibrous skeleton, has endocardial indentations forming valves that separate the atria from the ventricles and the ventricles from the aorta and pulmonary arteries.

Fibrous Skeleton Functions

• Four dense connective tissue rings provide anchorage for atrial and ventricular musculature and valvular tissue.
• Adjacent fibrous rings form a central supporting structure called the annuli fibrosis cordis.

Heart Valves Function

• Four heart valves along with pressure gradients ensure one-way blood flow.
• During ventricular relaxation, the atrioventricular valves open, and blood flows from the high-pressure atria into the low-pressure ventricles.
• Valves close with increasing ventricular pressure, preventing backflow into the atria.
• Semilunar valves open when intraventricular pressure exceeds aortic and pulmonary pressures, allowing blood to flow into systemic and pulmonary circulations.
• After ventricular contraction, intraventricular pressure falls, closing the pulmonic and aortic semilunar valves due to higher vessel pressure.

Atrioventricular Valves

• Atrioventricular (AV) valve openings (tricuspid and mitral) consist of tissue flaps called leaflets or cusps.
• Leaflets attach to fibrous skeleton rings at the upper end and to papillary muscles via chordae tendineae at the lower end.
• Papillary muscles are myocardial extensions that prevent backward cusp expulsion during ventricular contraction.
• The RIGHT AV valve, the tricuspid valve, has three cusps.
• The tricuspid opening has the largest diameter of all heart valves.
• The LEFT AV valve, the mitral valve, is bicuspid (two cusps).
• The mitral valve resembles a cone-shaped funnel extending into the cusps, connected by the commissure.
• The anterior cusp of the mitral valve is continuous with the aortic semilunar valve cusps.
• Tricuspid and mitral valves function as a unit with atrium, fibrous rings, valvular tissue, chordae tendineae, papillary muscles, and ventricular walls.
• These six structures are the mitral and tricuspid complex. Any damage to these components significantly alters function.

Semilunar Valves

• Blood leaving the LV goes through the pulmonic semilunar valve, and also leaves through the aortic semilunar valve.
• Both valves have three cup-shaped cusps from the fibrous skeleton but the pulmonic cusps are slightly thinner.

Valves Suspension and Function

• The lower edges of cusps are suspended from the root of the pulmonary artery or aorta, with upper valve edges projecting into vessel lumen.
• Cusps behave like one-way swinging doors during ventricular contraction, propelled outward by the blood force.
• During ventricular relaxation, blood fills the cusps, meeting at the vessel's middle, closing the valve, and prevents backflow.

Great Vessels and Blood Flow

• Blood moves in/out of the heart through large vessels.
• The right heart receives venous deoxygenated blood from systemic circulation through the superior and inferior vena cava, entering the right atrium.
• Blood exiting the RV enters the pulmonary circulation through the pulmonary artery.
• The pulmonary artery splits into right and left arteries to transport unoxygenated blood to the lungs.
• Pulmonary arteries branch into capillary beds for oxygen to enter and carbon dioxide to exit.
• Four pulmonary veins (two from each lung), carry oxygenated blood from the lungs to the heart's left side.
• Oxygenated blood moves through the left atrium and left ventricle to the aorta, delivering it to systemic vessels.

Cardiac Cycle Blood Flow

• Heart pumping action: Contraction and relaxation of the heart muscle, or myocardium.
• Each ventricular contraction and relaxation constitutes one cardiac cycle.
• During diastole (relaxation), blood fills the ventricles.
• During systole (contraction), blood propels out of the ventricles into the pulmonary and systemic circulations.
  • LV contraction occurs slightly before RV contraction.
• During ventricular systole: systemic veins fill the right atrium, and coronary venous blood enters the right atrium via the coronary sinus
• During ventricular diastole: the RA fills, LV pressure falls, the mitral valve opens, and blood flows into the LV; LA contraction increases LV volume.

Cardiac Cycle Phases

• Phase 1: Ventricular diastole or atrial systole:
  • Begins with mitral and tricuspid valves opening, ventricles fill from atria (rapidly in early diastole, again when atria contract in late diastole).
• Phase 2: Ventricular systole starts with "isovolumetric contraction"
  • Ventricular volume is constant (AV and semilunar valves closed), pressure rises, AV valves shut-cusps prevented from opening back by chordae tendineae.
• Phase 3: Ventricular pressure exceeds pulmonary artery and aorta pressure :
  • Semilunar valves open, then ventricular ejection occurs as intraventricular pressure and ventricular volume rapidly drop.
• Phase 4: Ventricular relaxation occurs:
  • Aortic valve closes as ventricular pressure decreases, termed "isovolumetric relaxation", both AV and semilunar valves are closed.
• Phase 5: Mitral/tricuspid valves open:
  • Passive ventricular filling occurs when LV pressure dips below atrial pressure.

Contraction Location

• Blood flows through inflow/outflow tracts, around the crista supraventricularis, and mixes through trabeculae carneae strands.

Intracardiac Pressures

• Measured by venous pressure pulses containing three waves, which are:
  • The a wave where atrial contraction actively fills the right ventricle.
  • The c wave in early systole from the bulging of closed tricuspid valve in the right atrium.
  • The v wave, that is the increase in pressure/ volume in the right atrium
• The x descent reflects right atrium movement toward the right ventricle in ventricular systole's final phases
• The y descent corresponds to early diastole termination and the opening of the tricuspid valve/ ventricular passive filling.

Electrocardiogram Readings

• The P wave atrial depolarization.
• The PQ segment - time for the SA node to reach the AV node
• The Q wave Intreventricular septum depolarization.
• The R wave - Ventricle mass depolarization.
• The S wave represents the final phase of ventricle depolarization.
• ThePR interval measures time from atrial activation to ventricular activation(0.12 – 0.20 seconds) travels from SA node through the atrium and AV node.
• QRS is depolarization of the ventricular muscle cells
• During the ST interval the ventricle contracts and pumps blood whilst depolarized
• T wave is ventricular repolarization

Coronary Artery Blood FLow

• RCA(Right Coronary Artery ) & LCA ( Left Coronary Artery) Main coronary arteries
• Arteries enter the Myocardium and capillary
• Coronary arteries of women are smaller that that of men

Coronary Artery Branches

• LAD (Left anterior descending )artery delivers blood to ventricles and septum.
• The artery is located in-between the right and left ventricles and goes down to the anterior portion and apex of the heart.
• Circumflex Artery- is located by the coronary sulcus, seperates the left ventricle and atrium supplies blood to the lateral wall, often brances off to the posterior.
• New vessels form through Arteriogenesis & Angiogenesis when there is gradual coronary occlusion
• There is a shift through blood flow velocity if there is a stenosis
• Occlusion fo artery leads to a MI: anterior, posterior, lateral, subendocardial, or transmural. based on tissue and location damage.

Vasopressin

• AHD hormone that is a analog is for peripheral splanchnic constriction
• Vasopressin can treat GI hemorrhage and causes hypertension and bradycardia

Nitroprusside

• Light sensitive, special infustion set/ Cover if slow infustion/Thicyanate
• Give lower rates w/ Renal Issues