CH 20 - The Heart

Pulmonary Circuit

• blood flows from the right heart to the lungs

• gas exchange in lungs

  • carbon dioxide unloaded

  • oxygen loaded

Systemic Circuit

• blood flows from the left heart to all body organs

• Gas Exchange in organs

  • oxygen unloaded

  • carbon dioxide loaded

mediastinum

location of the heart

Heart Size and Shape

• size of a fist

• base id superior

• apex points interiorly to the 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

AKA epicardium of the heart

Pericardial Cavity

space between walls containing serous fluid

Layers of the Heart Wall

• Epicardium

• Myocardium

• Endocardium

Epicardium

Visceral layer of serous cavity (serous pericardium)

Myocardium

cardiac muscle

Endocardium

• lines chambers of the heart

• made of simple squamous epithelium

Chambers of the Heart - Atria

• thin-walled, superior portion of the heart

• separated by interatrial septum

• considered the receiving champers

• Auricles

• Pectinate muscles

Auricles

ear-like extensions are seen covering the atria on the surface of the heart

Pectinate muscles

internal ridges

Chambers of the Heart - Ventricles

• thick-walled, inferior portion of the heart

• separated by interventricular septum

• considered the pumping chambers

• trabeculae carneae

• chordae tendinae

Trabeculae carneae

internal ridges

Chordae tendineae

tendinous cords attached to papillary muscles

• 3 in RV and 2 in LV

  • to hold valves shut

Atrioventricular valves

close when ventricles contract

• Right AV (tricuspid)

• Left AV (bicuspid) or mitral valve

  • Chordae Tendineae

Chordae Tendineae

tendinous chords tether valves to papillary muscles

Semilunar valves

close when ventricles relax

• pulmonary valve

• aortic valve

pulmonary valve

at exit of RV

Aortic valve

at exit of LV

Blood Pathway: Step 1

blood enters right atrium from superior and inferior vena cavae

Blood Pathway: Step 2

Blood in right atrium flows through right AV valve into right ventricle

Blood Pathway: Step 3

Contraction of right ventricle forces pulmonary valve open

Blood Pathway: Step 4

Blood flows through the pulmonary valve into the pulmonary trunk

Blood Pathway: Step 5

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

Blood Pathway: Step 6

Blood returns from lungs via pulmonary veins to left atrium

Blood Pathway: Step 7

Blood in left atrium flows through left AV valve into left ventricle

Blood Pathway: Step 8

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

Blood Pathway: Step 9

Blood flows through aortic valve into ascending aorta

Blood Pathway: Step 10

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

Blood Pathway: Step 11

Blood returns to right atrium via vena cavae

Coronary circulation

blood supply to the heart (not within the heart). The heart muscle needs O2 to survive.

• Both LCA and RCA are the first branches off the aorta

  • Blockage can cause myocardial infraction

myocardial infraction

death of heart tissue

heart attack leading to eventual heart faliure

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

small cardiac veins

drain 20% of the blood directly to the chambers

Coronary sinus

through this, most blood (80%) is returned to right atrium which recieves from

• Great cardiac vein

  • small cardiac vein

• Posterior interventricular (middle cardiac) vein

• Left marginal vein

Conduction System

• noncontractile cells specialized for generating and conducting signals

• ensure chambers contact 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: Step 1

SA node fires

Cardiac Conduction System: Step 2

excitation spreads through atrial myocardium

Cardiac Conduction System: Step 3

AV node fires

Cardiac Conduction System: Step 4

Excitation spreads down the AV bundle splitting into right and left bundle branches

Subendocardial conducting network

(Purkinje Fibers) distributes excitation through ventricular myocardium

Special Properties of cardiac muscle

cardiomyocytes are joined at ends by intercalated discs

contain:

• mechanical junctions

  • fascia adherens

  • desmosomes

• Electrical junctions

  • gap junctions

Changes of Heart at Birth

• foramen ovale and the ductus arteriosus cause most blood to bypass the pulmonary circuit (fetus does not breathe air)

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

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

• several hours after birth, ductus ateriosus closes

• eventual remnant if ligamentum arteriosum

Heart Disease

leading cause of death in US

Coronary atherosclerosis

most common form of heart disease

Congenital defects in anatomy

• Tetralogy of Fallot

• situs inversus

• etc

Myocardial hypertrophy

aka degeneration or high blood pressure

pericarditis/myocarditis

inflammation of pericardium or heart wall