Heart Part 1

What is the function of the pericardium?

Pericardium is a *double-walled sac that encloses the heart*

Name and describe the two main layers of the pericardium.

*Fibrous pericardium: superficial part of sac, dense fibrous CT tissue*

-*Protects heart* (surrounds entire heart)

-*Anchors it to surrounding structures*

-*Prevents overfilling of heart with blood*

*Serous pericardium: forms a closed sac around the heart, thin and slippery*

-*Parietal pericardium: lines the internal surface of fibrous pericardium, attaches to large arteries exiting the heart*

-*Visceral pericardium (epicardium): part of heart wall*

Describe the location and importance of the pericardial cavity

*Pericardial cavity lies between parietal and visceral pericardium - contains pericardial fluid*

-*Serous membranes have the fluid which allow them to glide smoothly past one another* → mobile heart can work in a friction-free environment

-*Prevents injury to heart during contractions*

Name and describe the three tissue layers of the heart wall.

*Epicardium: outer layer*

-*Contains fat* (in older people)

-Also the *visceral pericardium*

-Very *thin, transparent layer of mesothelium that lies on top of areolar/loose CT and anchors to myocardium*

-Has *smooth surface → able to slide freely past parietal pericardium without any friction → protects against abrasion*

-*Secretes serous fluid*

*Myocardium: middle layer, "muscle heart", thickest layer*

-Composed of *cardiac muscle tissue. Layer that contracts. Responsible for heart to push blood to blood vessels*

*Cardiac muscle tissue are in criss cross pattern and arranged in bundles*:

-*Tissue wraps around the outer layer of heart*

-When *myocardium contracts, it creates a twerking motion because of spiral pattern*

-*Forms atrial and ventricular network*. *Superior* network of cardiac muscle cells is associated with *atria*. *Inferior* network associated with *ventricles*

*Cardiac muscle is stabilized by a network of CT called cardiac skeleton*:

-*Collagen and elastic fibers*

-Provides *support where great vessels issue from the heart and around the valves*

-*Stabilizes the junction between atrial and ventricular bundles*

-*Prevents overexpansion of heart*, ensures muscles don't stretch too much

*Endocardium: innermost layer*

-*Composed of endothelium overlying a thin layer of CT*

-*Lines all chambers and covers surface of valves.* Continuous with endothelial lining of blood vessels

-*Protects underlying tissue*

-*Smooth layer so blood can move between heart chambers and blood vessels without too much friction*

What is the function of the fibrous skeleton of the heart?

Fibrous skeleton *anchors cardiac muscle fibers of the atria and ventricles*

Serves as an anchoring point for large blood vessels that enter and leave the heart and for heart valves

*Acts as an insulator between atria and ventricles, limiting the spread of action potentials to specific paths*

Which layer of the heart wall is the thickest?

Myocardium

Which chamber of the heart has the thickest wall?

*Walls of ventricle are thicker than atrium because ventricle contract to pump blood out of heart*

*Left ventricle is thicker than right because left needs to generate force to pump blood into systemic circulation*

*Atria - superior chambers, receive blood returning to the heart*

-Separated by interatrial septum

-*Blood returns to atria via veins*

-*Right atrium receives deoxygenated blood* via superior vena cava, inferior vena cava, and coronary sinus

-*Left atrium receives oxygenated blood* via four pulmonary veins

*Ventricles - inferior chambers, pump blood out of the heart, make up most of the volume of heart*

-Separated by interventricular septum

-*Blood is pumped out of ventricles through large arteries*

-*Right ventricle: forms anterior surface of heart. Pumps blood into pulmonary trunk → starts pulmonary circulation. Pumps deoxygenated blood into circulation*

-*Left ventricle: forms inferorposterior surface of heart and heart apex. Pumps blood into aorta → starts systemic circulation*

Trace the flow of blood through the heart, beginning at the right atrium.

look up a chart

Name the three vessels that return blood to the right atrium. From what general body region is the blood in each of these vessels returning?

*Superior vena cava returns blood from body regions superior to the diaphragm*

*Inferior vena cava returns blood from body areas below the diaphragm*

*Coronary sinus collects blood draining from the myocardium*

Name the vessels that return blood to the left atrium. From what body region is the blood in these vessels returning?

*Pulmonary veins* return blood to left atrium from the lungs back to the heart

Why is the heart referred to as a double pump?

*Right side of the heart pumps deoxygenated blood into pulmonary circuit*

-*Short, low pressure circulation*

*Left side of the heart pumps oxygenated blood into the systemic circuit*

-*Long, high pressure circulation*

What is the function of the heart valves?

*Ensures blood flows in one direction through the heart*

*Open and close in response to pressure difference when contraction happens*

-When myocardium contract, pressure goes up

Describe the mechanism of operation of the atrioventricular (AV) valves and of the semilunar (SL) valves.

*Atrioventricular (AV) valves - prevent backflow of blood into atria when ventricles contract*

-Tricuspid valve: right AV valve, has 3 flexible cusps (flaps of endocardium reinforced by connective tissue cores)

-Mitral valve: left AV valve, has 2 cusps

AV valve mechanics:

-*When heart is relaxed, AV valve flaps hang into ventricular chambers below → blood flows into atria and through open AV valves into ventricles*

-*When ventricles contract, compressing blood in their chambers, intraventricular pressure rises, forcing blood superiorly against the valve flaps → flap edges meet, closing the valve*

*Semilunar (SL) valves - prevent backflow of blood into ventricles when ventricles relax and guard the bases of large arteries, crescent moon shaped*

-Pulmonary valve: right side

-Aortic valve: left side

SL valve mechanics:

-*When ventricles contract and intraventricular pressure rises above the pressure in the aorta and pulmonary trunk, SL valves are forced open and their cusps flatten against arterial walls as blood rushes past them*

-*When ventricles relax, blood flows backward toward the heart, it fills the cusps and closes the valves*

Which valves are associated with the chordae tendineae and papillary muscles?

*Atrioventricular valves use chordae tendineae and papillary muscles to anchor the valve flaps in their closed position*

*Chordae tendineae: "heart strings"*

-*Made of collagen, withstand pulling*

-Attach to fibrous tissue of cusp on one end and papillary muscle on other end

-*Chordae tendineae and papillary muscle anchor cusp to prevent atria from swinging backward → prevent blood from flowing backward*