Heart

Pulmonary circuit

• Blood flows from right heart to lungs

• Gas exchange in lungs (CO2 unloaded, O2 loaded)

Systemic circuit

• Blood flows from left heart to all body organs

• Gas exchange in organs (O2 unloaded, CO2 loaded)

Position, Size, and Shape of the Heart

Heart located in mediastinum, size of fist, base is superior, apex points inferiorly and to left

Pericardium

Double- walled collection of membranes surrounding the heart

• Fibrous pericardium

• Parietal serous layer

• Visceral serous layer

• Pericardial cavity

Fibrous pericardium

Fibrous CT superficial to the serous pericardium

Parietal serous layer

Lies just below fibrous pericardium

Visceral serous layer

epicardium of the heart

Pericardial cavity

Space between walls containing serous fluid

Layers of the Heart Wall

1. Epicardium - visceral layer of serous cavity (serous pericardium)

2. Myocardium - cardiac muscle

3. Endocardium - lines chambers of the heart, made of simple squamous epithelium

Chambers of the Heart

Left and right atria + left and right ventricles

Left and right atria

- Thin-walled, superior portion of the heart

• Separated by interatrial septum

• Receiving chambers

• auricles – earlike extensions seen covering the atria on the surface of the heart

• Pectinate muscles – internal ridges

Left and right ventricles

• Thick-walled, inferior portion of the heart

• Separated by interventricular septum

• Pumping chambers

• Trabeculae carneae – internal ridges

• Chordae tendineae (tendinous cords) attached to papillary muscles (3 in RV, 2 in LV) to hold valves shut

Valves of the Heart

Atrioventricular (AV) valves, semilunar valves

Atrioventricular (AV) valves

close when ventricles contract

• Right AV (tricuspid) valve

• Left AV (bicuspid) valve or mitral valve

Left AV (bicuspid valve)

Chordae tendineae (tendinous chords) tether valves to papillary muscles

Semilunar valves

close when ventricles relax

• Pulmonary valve – at exit of right ventricle

• Aortic valve – at exit of left ventricle

Pathway of Bloodflow (Steps 1-6)

1) Blood enters right atrium from superior and inferior vena cavae.

2) Blood in right atrium flows through right AV valve into right ventricle.

3) Contraction of right ventricle forces pulmonary valve open.

4) Blood flows through pulmonary valve into pulmonary trunk.

5) Blood is distributed by right and left pulmonary arteries to the lungs, where it unloads CO2 and loads O2.

6) Blood returns from lungs via pulmonary veins to left atrium

Pathway of Bloodflow (Steps 7-11)

7) Blood in left atrium flows through left AV valve into left ventricle.

8) Contraction of left ventricle (simultaneous with step 3) forces aortic valve open.

9) Blood flows through aortic valve into ascending aorta.

10) Blood in aorta is distributed to every organ in the body, where it unloads O2 and loads CO2.

11) Blood returns to right atrium via vena cavae

Coronary circulation

the blood supply to the heart (not within the heart). The heart muscle needs O2 to survive. Both the LCA and RCA are the first branches off the aorta. Blockage can cause myocardial infarction (death of heart tissue)

Left coronary artery (LCA)

first branch off the aorta

• Anterior interventricular branch (left anterior descending branch (LAD))

• Circumflex branch → Left marginal branch (posterior)

Right coronary artery (RCA)

first branch off the aorta

• Right marginal branch (anterior)

• Posterior interventricular branch

Venous Drainage of Cardiac Muscle

• Small cardiac veins drain 20% of the blood directly to the chambers

• Most blood (80%) is returned to right atrium through coronary sinus, which receives from: Great cardiac vein (small cardiac vein), posterior interventricular (middle cardiac) vein, left marginal vein

Conduction System

• Non-contractile cells specialized for generating and conducting signals

• Ensure chambers contract at the appropriate time and are coordinated with each other

• Consists of:

-Sinuatrial (SA) node – pacemaker

-Atrioventricular (AV) node

-Atrioventricular (AV) bundle - splits into bundle branches

-Subendocardial conducting network (Purkinje fibers)

Cardiac Conduction System steps

1) SA node fires

2) Excitation spreads through atrial myocardium

3) AV node fires

4) Excitation spreads down AV bundle splitting into right and left bundle branches

5) Subendocardial conducting network (Purkinje fibers) distributes excitation through ventricular myocardium

Special Properties of Cardiac Muscle

Cardiomyocytes are joined at ends by intercalated discs which contain:

• Mechanical junctions

• Fascia adherens

• Desmosomes

• Electrical junctions

• Gap junctions

Changes to the Heart at Birth

• In fetal heart, the foramen ovale and the ductus arteriosus cause most blood to bypass pulmonary circuit (fetus not breathing air)

• However, when lungs inflate at birth, the resistance to blood flow in the lungs decreases

• Seals the foramen ovale with a flap between the right and left atria (eventual fossa ovalis).

• Several hours after birth, ductus arteriosus closes.

• Eventual remnant is ligamentum arteriosum

Coronary atherosclerosis

Myocardial infarction (Heart attack) leading to eventual heart failure

Myocardial hypertrophy or degeneration

high blood pressure

Congenital defects in anatomy

Tetralogy of Fallot, situs inversus, etc.

Inflammation of pericardium or heart wall

pericarditis or myocarditis

Valvular defects

Valve prolapse, regurgitation, stenosis