Ch 31 Hard--Heart Structure and Function

• The circulatory system’s functions are to deliver oxygen, nutrients, hormones, and immune cells to body tissues, and remove cellular waste products.
• These functions are achieved through a network of tubing (blood and lymphatic tissues) connected to the heart.
• The heart constantly pumps blood through vessels, regulated by the nervous and endocrine systems.
• The vascular endothelium is a critical component, essential for normal vascular and hemostatic physiology.

Heart Structure

• The heart has two conjoined pumps for two separate circulatory systems: one to the lungs and one to the rest of the body.
• The right side of the heart pumps blood to the lungs for pulmonary circulation.
• The left side of the heart sends blood through systemic circulation, supplying the entire body except the lungs.
• These systems are serially connected, where the output of one pump becomes the input of the other.
• Arteries carry blood from the heart, branching into arterioles and then capillaries.
• Capillaries facilitate exchange between blood and the interstitial space where cells live.
• Veins carry blood back to the heart from capillaries.
• Lymph, derived from plasma, returns to the cardiovascular system via lymphatic vessels.
• The lymphatic system is an important element of the immune system.
• Blood flow starts at the left ventricle, moves to arteries, arterioles, capillaries of body organs, venules, veins, right atrium/ventricle, pulmonary artery, lung capillaries/veins, and left atrium, then returns to the left ventricle.

Heart Function

• Supports heart tissues, circulates blood, maintains cells via coronary/lymphatic vessels, and stimulates/controls heart action through nerves and muscle cells for rhythmic contraction.
• The heart wall has three layers: epicardium, myocardium, and endocardium, enclosed by the pericardium
• The pericardial sac prevents displacement, protects against infection, and contains receptors for pain/blood pressure regulation.
• The parietal pericardium, is the sac’s outer layer of mesothelium
• The visceral pericardium (epicardium) is the inner layer of the pericardium.
• The pericardial cavity is a fluid-filled space between the visceral and parietal pericardia that reduces friction as the heart beats.
• The epicardium, the heart's outer layer, allows contraction/relaxation within the pericardium with minimal friction.
• The thickest layer, the myocardium, is cardiac muscle anchored to the heart’s fibrous skeleton and varies in thickness based on the resistance needed to pump blood.
• The endocardium, the internal lining, connects with the endothelium of all body vessels, creating a closed circulatory system.

Heart Chambers

• The heart has four chambers: right/left atria and right/left ventricles, 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 to the rest of the body.
• Wall thickness depends on the pressure needed to eject blood, with the left ventricle being thicker due to higher systemic pressure.
• Pulmonary capillary pressure is 15 mmHg, whereas mean arterial pressure is 92 mmHg.
• In adults, blood doesn't flow between sides of the heart, unlike in fetuses.
• The atria, smaller than ventricles with thinner walls (2mm), are storage units for blood entering the ventricles.
• Atria have little resistance to flow.
• The right ventricle (5 mm thick) is crescent-shaped, functioning like a bellows to eject blood into the pulmonary system.
• The left ventricle (15 mm thick) is bullet-shaped ejection into the systemic circulation
• Ventricles pump blood through pulmonary or systemic circulation, needing strong myocardium.
• The interventricular septum is a fibrous skeleton extension.

Fibrous Skeleton

• Four dense connective tissue rings provide anchorage for atrial/ventricular muscles and valves, forming a central supporting structure.
• Valves ensures one-way blood flow via pressure gradients
• During ventricular relaxation, atrioventricular valves open, allowing blood flow from higher atrial pressure to lower ventricular pressure.
• Semilunar valves open when intraventricular pressure exceeds aortic/pulmonary pressures, directing blood into pulmonary/systemic circulations.
• After ventricular ejection, pulmonic/aortic semilunar valves close when vessel pressure exceeds ventricular pressure.
• Atrioventricular (AV) (tricuspid and mitral) valve openings have tissue flaps (leaflets/cusps) attached to the fibrous skeleton and papillary muscles by chordae tendineae.
• The papillary muscles prevent backward expulsion into the atria during contraction.
• The right AV valve, the tricuspid valve, has three cusps.
• The left AV valve, the mitral valve, is a bicuspid (two cusps) valve
• The mitral valve resembles a cone-shaped funnel connected by the commissure.
• Damage to the continuous tissue can affect aortic and mitral valve functions.
• The atrium, fibrous rings, valvular tissue, chordae tendineae, papillary muscles, and ventricular walls form a functional unit.
• Damage to members of the tricuspid and mitral complex can significantly affect heart function.

Semilunar Valves

• Blood exits the left ventricle via the pulmonic/aortic semilunar valves with three cup-shaped cusps from the fibrous skeleton.
• Pulmonic cusps are slightly thinner than aortic cusps.
• Each cusp is suspended from the artery/aorta root, projecting valve edges into the vessel lumen.
• Ventricle contraction force propels valve cusps outward against the vessel wall, while relaxation fills the cusps, closing the valve to prevent backflow.

Great Vessels

• Blood enters/exits the heart through large vessels.
• The right atrium receives deoxygenated blood from systemic circulation via the superior/inferior vena cava.
• Blood exits the right ventricle via the pulmonary artery to be transported to the right and left lungs where oxygen enters and carbon dioxide leaves.
• Four pulmonary veins transport oxygenated blood to the left side of the heart. Oxygenated blood moves through the left atrium/ventricle/aorta and then to system vessels.

Cardiac Cycle

• Pumping consists of heart muscle contraction/relaxation. Ventricular contraction and relaxation is one cardiac cycle.
• During diastole (relaxation), ventricles fill with blood.
• Then systole (contraction that propels blood). Left ventricle contracts slightly before right.
• During cycle, venous blood enters the right atrium, and during diastole, the tricuspid valve opens and fills the right ventricle.
• Pulmonary cycle events occur a split second earlier in the left heart.
• Pulmonary veins carry blood to the left atrium, opening the mitral valve when left ventricular pressure falls, increasing blood volume.

Cardiac Cycle Phases

• Phase 1: Atrial systole and ventricular diastole begins with the opening of the mitral and tricuspid valves and then ventricular filling.
• Phase 2: Ventricular systole begins with “isovolumetric contraction,” where the AV and semilunar valves are closed, and the ventricular volume remains constant.
• Phase 3: When ventricular pressure slightly exceeds that of the pulmonary artery and aorta, the semilunar valves open and ventricular ejection takes place; intraventricular pressure and volume decrease swiftly
• Phase 4: Ventricular relaxation and decreased ventricular pressure, the aortic valves close and ventricular pressure decreases
• Phase 5: When left ventricle pressure falls below atrial pressure, mitral and tricuspid valves open and passive ventricular filling occurs.
• Blood moves through tracts around the muscle separating inflow/outflow and strands of the trabeculae carneae

Intracardiac Pressures

• Venous pressures pulses are atrial contraction, causing pressure in end-diastole.
• The c wave means the tricuspid valve bulging into the right atrium during systole.
• The v wave is pressure/volume increase in the right atrium during late systole/early diastole.

Electrical Activity

• P wave represents atrial depolarization.
• PQ segment is the signal from the SA node to the AV node.
• The Q wave means interventricular septum depolarization.
• The R wave represents mass ventricles depolarization.
• The S Wave represents ventricular depolarization.
• PR interval activation time of atrial/ventricular activation (0.12 – 0.20 seconds).
• The QRS complex all ventricular muscle cell depolarizations (0.06 – 0.10 seconds).
• During the ST-interval, the ventricular myocardium is depolarized.
• T-wave means ventricular repolarization.
• The QT interval is the "electrical systole" of the ventricles, meaning time for ventricular depolarization/repolarization (0.04 seconds but inversely with heart rate).

Coronary Arteries and Blood Flow

• The major coronary arteries are Right Coronary Artery (RCA) and Left Coronary Artery (LCA).
• The arteries enter myocardium/endocardium, branching arterioles/capillaries.
• The Left Coronary Artery arises from a single opening behind the aortic valve and divides into two branches
• The Right Coronary Artery extends around the heart to the heart’s posterior surface.
• Gradual occlusion causes collateral's (new vessels)
• Arteriogenesis is new artery growth from pre-existing arteries
• Angiogenesis is growth of capillaries.

Sympathomimetics Effects

• Dobutamine increases cardiac contractility.
• Dopamine effects predominate, increase filtration and urine.
• Epinephrine adrenergic effects/bronchoconstriction
• Vasopressin, Antidiuretic hormone receptors vasoconstriction/ splanchnic
• Phos inhib improved heart contractility vasodilations
• Vasodilators arterial Nitroglycerin and venodilator

Heart Beta Receptors

• Found in Beta 1 (mostly heart and specifically conduction system)
• Found in Beta 2 (also vascular smooth muscle) and heart
• Beta 3 found in myocardium and coronary vessel
• Cardiovascular structures dominated by beta receptors.
• Adrenergic receptor blockers reduce heart.
• Hypertension, caused by elevated blood can be caused by cardiac output or peripheral resistance.
• Genetics and environment cause HTN.

HTN Risk Factors

• Family history
• Age
• Gender
• Race
• High dietary sodium
• Glucose intolerance
• Smoking
• Obesity
• Alcohol consumption
• HTN, dyslipidemia, and glucose often found together in a condition called metabolic syndrome.

HTN and Smoking

• Nicotine vasoconstriction elevates BP.
• Habitual smoking high severe hypertension and heart disease.
• HTN related to high alcohol (increases pressure)
• Healthy RAAS needed
• HTN and high sodium intake

Anti HTN medications

• ACE and ARB oppose the RAAS
• Early HTN (elevated BP).
• Primary hypertension increases with age
• Clinical manifestations caused by hypertension. The Lack of signs/symptoms is why early hypertension is undetected
• Complicated hypertension attacks heart and major organ

HTN treatment

• Elevated BP needs measurement
• Elevated measurement means no HTN.
• Evaluation of HTN lifestyle and assessment
• Physical exam needed
• Lifestyle modification can prevent BP / treatment
• DASH diet recommended in HTN reduces risk
• Exercise promotes endurance/reduces relaxation.
• Thiazide beta blockers