THE HEART

Cardiovascular System• series of tubes-blood vessels• filled with a fluid-blood• connected to a pump-heart• Arteries

– carry blood away from heart• Veins

– carry blood to heart• pressure generated in heart

pumps blood continuously through system

• Blood flow– movement of blood through

heart & around body to peripheral tissues

• Circulation

Circulation• right side of body-

Pulmonary Circuit– carries blood to & from

lungs for gas exchange• Systemic Circuit

– carries newly oxygenated blood from lungs to body & back to heart

• each circuit begins & ends at heart

Heart Anatomy• hollow, small organ• about size of clenched fist• weighs from 250-350 grams• located in middle of chest in

mediastinum• surrounded by pericardial cavity• lining of pericardial cavity is

pericardium– visceral & parietal part

• visceral pericardium -epicardium– superficial layer that covers

surface of heart• parietal pericardium

– lines inner surface of pericardial sac which surrounds heart

• between these two-pericardial cavity

• filled with pericardial fluid • to lubricate & reduce friction

Heart Wall• 3 layers

• Epicardium-visceral pericardium

– covers outer surface

• Myocardium

– muscular wall

• Endocardium

– simple squamous epithelium

Microscopic Anatomy• different from skeletal muscle

in several ways• cells are smaller• uninucleated• have branching

interconnections between have intercalated discs– location of gap junctions &

desmosomes– convey action potentials

from cell to cell – ensure cells contract

simultaneously

Heart Anatomy• top of heart-base• pointed, lower part-apex• 4 chambers

– 2 atria & 2 ventricles• coronary sulcus

(atrioventricular sulcus)

• anterior & posterior interventricular sulci– mark external

boundary of right & left ventricle

Coronary Sulcus

Heart Anatomy• each atrium has expandable

extensions- auricles– hold extra blood

• right atrium receives blood from systemic circuit via superior & inferior vena cavae & coronary sinus

• superior vena cava– returns blood from body areas

superior to diaphragm

• inferior vena cava– drains areas below diaphragm

• coronary sinus– delivers blood from myocardium

of heart

Internal Heart Anatomy• blood passes into right

ventricle via right AV (atrioventricular) valve or tricuspid valve– keeps blood flowing in one

direction from atrium to ventricle

– prevents backflow into atrium

• tiny, white collagen cords-chordae tendineae attach to each flap

• originate at papillary muscles– help to close valves

• chordae tendineae & papillary muscles anchor flaps in closed position

Internal Heart Anatomy• pectinate muscles-right

atrium• fossa ovalis also found here• muscular ridges- ventricles-

trabeculae carnae• moderator band extends

horizontally from right ventricle wall– coordinates contraction

of muscle cells– insures chordae tendinae

tense before ventricles contract

Internal Anatomy• from right ventricle blood is pumped to

pulmonary circuit• valves between ventricles & vessels-

semilunar valves– prevent back flow into ventricles

• each made of 3 pocket-like flaps shaped like crescent moons

• blood travels via pulmonary semilunar valve into pulmonary trunk– start of pulmonary circuit

• from pulmonary trunk, blood goes to left & right pulmonary arteries and to lungs for gas exchange

• after being oxygenated, blood reenters heart via 2 left & 2 right pulmonary veins-open into left atrium

• blood goes from left atrium to left ventricle via left AV valve

• bicuspid or mitral valve• from here blood is ejected through

aortic semi lunar valveinto aortic arch

Heart Anatomy• left ventricle

– discharging chamber• contractsblood propelled into

circulation• equal volumes are pumped to both

circuits• right pumps blood to pulmonary circuit

through pulmonary trunk– short path with low pressure

• left pumps blood through systemic circuit– long path-runs through entire body– 5X more resistance to flow – functional difference between left &

right ventricle is reflected in anatomy• left ventricle walls are 3X as thick as

right ventricle wall– allows left ventricle to generate more

pressure• pulmonary trunk is attached to aortic arch

by ligamentum arteriosum

Ligamentum arteriosum

Coronary Circulation• heart muscle must have its own

source of oxygenated blood• supplied by coronary arteries

– originate at base of ascending aorta

– blood pressure• right coronary artery follows coronary

sulcus & supplies right atrium, parts of both ventricles & parts of conducting system

• left coronary artery supplies: left ventricle, left atrium & interventricular septum

• great cardiac vein– begins anterior surface of

ventricles along interventriuclar sulcus

• curves around left side of heart in coronary sulcus

• empties into coronary sinus

Heart Beat• myocytes-autorhythmic

– depolarize spontaneously at regular time intervals

– initiate contraction without signals from brain

• each beat begins with action potential generated at SA node (sino-atrial)-pacemaker– generates impulses at regular

intervals• to ensure four chambers of heart are

coordinated electrical signals travel through cardiac conduction system

• sympathetic & parasympathetic connections to heart can modify heart beat– not involved in normal contractions