Chapter 20Chapter 20

The circulatory system The circulatory system IIII

The HeartThe Heart

Circulatory Circulatory systemssystems

Pulmonary circuit:Pulmonary circuit:Blood flows to the Blood flows to the

lungslungsto exchange CO2 for to exchange CO2 for O2 in the alveoli.O2 in the alveoli.

Systemic circuit:Systemic circuit:Provides oxygenated Provides oxygenated

blood to all organs blood to all organs and tissues in the and tissues in the body, including the body, including the heart and lungs.heart and lungs.

The HeartThe Heart Located: in the thoracic cavity in the Located: in the thoracic cavity in the

mediastinum between the lungs and deep mediastinum between the lungs and deep to the sternum.to the sternum.

Function: to pump blood to all tissues and Function: to pump blood to all tissues and cells in the bodycells in the body

StructureStructure: the base of the heart is superior, : the base of the heart is superior, and is where the great vessels are and is where the great vessels are attached. The heart tapers down to the attached. The heart tapers down to the apex (tip) situated immediately above the apex (tip) situated immediately above the diaphragm (left upper quadrant). diaphragm (left upper quadrant).

Size/Orientation – weighs ~300 gm, ~9 cm Size/Orientation – weighs ~300 gm, ~9 cm diameter at base,~13 cm from base to diameter at base,~13 cm from base to apex and 6 cm diameter at the apex.apex and 6 cm diameter at the apex.

Location and OrientationLocation and Orientation

The pericardiumThe pericardium Two coverings that surround the heart, Two coverings that surround the heart,

enclosing it in a sac with a tough outer layer, enclosing it in a sac with a tough outer layer, the fibrous pericardium and a thin serous the fibrous pericardium and a thin serous parietal pericardium, with a serous visceral parietal pericardium, with a serous visceral pericardium (epicardium) attached to the pericardium (epicardium) attached to the myocardium. The pericardial space between myocardium. The pericardial space between these layers is filled with pericardial fluid.these layers is filled with pericardial fluid.

Tissues of the Wall of the Tissues of the Wall of the HeartHeart

The outer layer is epicardium and is a The outer layer is epicardium and is a serous membrane (the visceral serous membrane (the visceral pericardium).pericardium).

The myocardium is cardiac muscle and The myocardium is cardiac muscle and consists of layers circularly and spirally consists of layers circularly and spirally wrapped around each other.wrapped around each other.

The endocardium is a layer of specialized The endocardium is a layer of specialized epithelial cells called endothelium. epithelial cells called endothelium. Endothelial cells cover the heart valves Endothelial cells cover the heart valves and line the entire cardiovascular and and line the entire cardiovascular and lymphatic system.lymphatic system.

Pattern of cardiac muscle Pattern of cardiac muscle wrapwrap

Heart ChambersHeart Chambers The heart contains four chambers: 2 upper The heart contains four chambers: 2 upper

atria and 2 lower ventriclesatria and 2 lower ventricles The right side of the heart (The right side of the heart (right atrium and right atrium and

right ventricleright ventricle) receives oxygen poor blood ) receives oxygen poor blood (high in CO2) from the body and pumps it to (high in CO2) from the body and pumps it to the lungs where exchange of CO2 for O2 takes the lungs where exchange of CO2 for O2 takes place.place.

The left side of the heart (The left side of the heart (left atrium and left left atrium and left ventricleventricle) receives oxygenated blood (high in ) receives oxygenated blood (high in O2) from the lungs and pumps it to every cell in O2) from the lungs and pumps it to every cell in the body.the body.

Heart chambersHeart chambers

Heart StructureHeart Structure The atria (right and left) are separated from The atria (right and left) are separated from

each other by the thin interatrial septum. each other by the thin interatrial septum. The ventricles (left and right) are separated The ventricles (left and right) are separated

from each other by a thick muscular from each other by a thick muscular interventricular septum.interventricular septum.

The atria and ventricles are separated from The atria and ventricles are separated from each other by valves that regulate blood flow each other by valves that regulate blood flow in a one way direction and by dense fibrous in a one way direction and by dense fibrous connective tissue.connective tissue.

The ventricles are separated from their The ventricles are separated from their outflow trunks, the pulmonary trunk and the outflow trunks, the pulmonary trunk and the aorta (great vessels), by semilunar valves.aorta (great vessels), by semilunar valves.

Right AtriumRight Atrium Oxygen poor blood from the entire body and Oxygen poor blood from the entire body and

the heart flows into the right atrium via the the heart flows into the right atrium via the superior and inferior vena cavae and the superior and inferior vena cavae and the coronary sinus.coronary sinus.

Occupies most of upper right side of heartOccupies most of upper right side of heart Right auricle is conspicuous, looks like a Right auricle is conspicuous, looks like a

serrated dogs ear.serrated dogs ear. Externally right atrium is separated from right Externally right atrium is separated from right

ventricle by right coronary sulcus containing ventricle by right coronary sulcus containing the right coronary artery.the right coronary artery.

Internally, theInternally, the right atrioventricular (tricuspid) right atrioventricular (tricuspid) valvevalve separates the right atrium and right separates the right atrium and right ventricle.ventricle.

Right AtriumRight Atrium

Right ventricleRight ventricle Receives blood from RA via tricuspid valve.Receives blood from RA via tricuspid valve. Externally it occupies most of anterior right Externally it occupies most of anterior right

side of heart.side of heart. Internally the RV exhibits muscular ridges Internally the RV exhibits muscular ridges

((trabeculaetrabeculae carneaecarneae) and ) and papillary musclespapillary muscles with with chordae tendonaechordae tendonae that anchor the that anchor the tricuspid valve. The chordae tendonae tricuspid valve. The chordae tendonae prevent the valve from flopping (prolapsing) prevent the valve from flopping (prolapsing) back into the right atrium when RV pumps back into the right atrium when RV pumps and assures a one way flow of the blood.and assures a one way flow of the blood.

Pumps blood through pulmonary semilunar Pumps blood through pulmonary semilunar valve into pulmonary trunk for delivery to the valve into pulmonary trunk for delivery to the lungs.lungs.

Right ventricleRight ventricle

Left atriumLeft atrium Receives oxygen rich blood from the lungs via Receives oxygen rich blood from the lungs via

2 to 5 pulmonary veins (right and left).2 to 5 pulmonary veins (right and left). Separated from right atrium by the interatrial Separated from right atrium by the interatrial

septum, with the fossa ovale, a remnant of septum, with the fossa ovale, a remnant of fetal foramen ovale.fetal foramen ovale.

Left auricle is on the upper left side of heart Left auricle is on the upper left side of heart and is the only part of LA visible from front of and is the only part of LA visible from front of heart.heart.

Separated externally from the left ventricle by Separated externally from the left ventricle by the left coronary sulcus and internally by the the left coronary sulcus and internally by the left atrioventricular (left atrioventricular (bicuspid bicuspid or or mitral) valvemitral) valve..

Pumps oxygen rich blood into left ventricle.Pumps oxygen rich blood into left ventricle.

Left auricle of left atriumLeft auricle of left atrium

Left ventricleLeft ventricle Large thick walled pumping chamber of the heart.Large thick walled pumping chamber of the heart. Receives oxygen rich blood from LA via bicuspid Receives oxygen rich blood from LA via bicuspid

valve (left atrioventricular valve).valve (left atrioventricular valve). Contains Contains trabeculae carneae, papillary muscles trabeculae carneae, papillary muscles

and chordae tendonaeand chordae tendonae similar to right ventricle. similar to right ventricle. Occupies anterior inferior wall of heart down to Occupies anterior inferior wall of heart down to

apex.apex. Pumps oxygen rich blood through Pumps oxygen rich blood through Aortic valveAortic valve

(left semiliunar valve) into the aorta.(left semiliunar valve) into the aorta. Externally anterior interventricular sulcus Externally anterior interventricular sulcus

separates RV from LV and contains left anterior separates RV from LV and contains left anterior descendens (LAD) coronary (anterior descendens (LAD) coronary (anterior interventricular) artery.interventricular) artery.

Left ventricleLeft ventricle

Ventricular wall thicknessesVentricular wall thicknesses The left ventricular wall is much thicker The left ventricular wall is much thicker

than the right, as it must pump blood to than the right, as it must pump blood to the entire body and back again, whereas the entire body and back again, whereas the right ventricle pumps blood at lower the right ventricle pumps blood at lower pressure through the lungs and back to pressure through the lungs and back to the left atrium.the left atrium.

The right side is a lower pressure side as The right side is a lower pressure side as compared to the left side of the heart compared to the left side of the heart (~20mm Hg vs 120 mm Hg).(~20mm Hg vs 120 mm Hg).

Comparison of wall Comparison of wall thicknessthickness

Heart ValvesHeart Valves The four heart valves assure one way flow of The four heart valves assure one way flow of

blood through the heart.blood through the heart. Atrioventricular valves are tricuspid (right side) Atrioventricular valves are tricuspid (right side)

and bicuspid or mitral (left side). Attached to and bicuspid or mitral (left side). Attached to ventricular walls by chordae tendonae to prevent ventricular walls by chordae tendonae to prevent prolapse.prolapse.

The pulmonary (right side) and aortic (left side) The pulmonary (right side) and aortic (left side) semilunar valves contain three half moon-shaped semilunar valves contain three half moon-shaped cusps each.cusps each.

All valves are made of flaps of endocardium and All valves are made of flaps of endocardium and are reinforced by dense connective tissue. are reinforced by dense connective tissue.

The heart valves open and close depending on The heart valves open and close depending on the pressure exerted on them within each the pressure exerted on them within each chamber.chamber.

Papillary muscle connected to Papillary muscle connected to chordae tendonaechordae tendonae

Heart ValvesHeart Valves

Heart Valves/Open-ClosedHeart Valves/Open-Closed

Papillary muscle connected to Papillary muscle connected to chordae tendonaechordae tendonae

Heart Valves/Open-ClosedHeart Valves/Open-Closed

Blood flow in heartBlood flow in heart

Blood flow to the heartBlood flow to the heartLeft and right Left and right

coronary arteries coronary arteries come off of aorta come off of aorta behind cusps.behind cusps.

Venous return from Venous return from heart drains into heart drains into great cardiac vein great cardiac vein and into coronary and into coronary sinus and into right sinus and into right atrium atrium

Coronary arteriesCoronary arteries

Coronary veinsCoronary veins

Coronary stenosisCoronary stenosis

Cardiac conduction systemCardiac conduction system For the heart to pump it must be For the heart to pump it must be

activated by an electrical impulse activated by an electrical impulse generated from its own pacemaker generated from its own pacemaker tissue. This site is the sinoatrial (SA) tissue. This site is the sinoatrial (SA) node located in the right atrium. The node located in the right atrium. The impulse spreads through the atrial impulse spreads through the atrial muscle to the atrioventricular (AV) node muscle to the atrioventricular (AV) node → AV bundle → the right and left bundle → AV bundle → the right and left bundle branches → Purkinje fibers → ventricular branches → Purkinje fibers → ventricular depolarization and contraction.depolarization and contraction.

Cardiac tissueCardiac tissueThe myocardium is a syncitium of muscle The myocardium is a syncitium of muscle

fibers that interdigitate at intercalated fibers that interdigitate at intercalated discs discs

Cardiac tissueCardiac tissue

Cardiac conduction systemCardiac conduction system

Conduction pathwaysConduction pathways Sinoatrial Node (SA Node)Sinoatrial Node (SA Node)-“sinus rhythm” – rate -“sinus rhythm” – rate

generated by the sinoatrial node in right atriumgenerated by the sinoatrial node in right atrium Atrioventricular Node (AV Node)- Atrioventricular Node (AV Node)- located near located near

tricuspid valve; AV node acts as electrical gateway tricuspid valve; AV node acts as electrical gateway to ventriclesto ventricles

Atrioventricular Bundle/”Bundle of His”-Atrioventricular Bundle/”Bundle of His”- pathway by which impulses leave AV node. Forks pathway by which impulses leave AV node. Forks into right and left bundles branches which enter into right and left bundles branches which enter interventricular septum and descend to the apex.interventricular septum and descend to the apex.

Right/Left Bundle Branches- Right/Left Bundle Branches- continuation of continuation of Bundle of His which descend to apex and gives rise Bundle of His which descend to apex and gives rise to the purkinje fibers.to the purkinje fibers.

Purkinje Fibers- Purkinje Fibers- conductingconducting fibers which turn fibers which turn upward and extend into ventricular myocardium. upward and extend into ventricular myocardium. They form a more elaborate network in LV than RV.They form a more elaborate network in LV than RV.

Cardiac conduction systemCardiac conduction system

Cardiac innervationCardiac innervation Although the heart can beat without neural Although the heart can beat without neural

control, it receives both sympathetic and control, it receives both sympathetic and parasympathetic input from the autonomic parasympathetic input from the autonomic nervous system.nervous system.

The parasympathetic input is via CN - X The parasympathetic input is via CN - X (Vagus)(Vagus)

Sympathetic input is from the medullary Sympathetic input is from the medullary cardioacclerator center → sympathetic chain cardioacclerator center → sympathetic chain (paravertebral) ganglia → the sympathetic (paravertebral) ganglia → the sympathetic nerve.nerve.

The heart can also be regulated by neuro-The heart can also be regulated by neuro-humors circulating in the blood. humors circulating in the blood.

Sympathetic and Sympathetic and parasympathetiparasympathetic input to the c input to the heart.heart.