Chapter 20Chapter 20

The circulatory system The circulatory system IIII

The HeartThe Heart

Circulatory systemsCirculatory systems

Pulmonary circuitPulmonary circuit

Blood flow to the lungsBlood flow to the lungs

to blow off CO2 and picksto blow off CO2 and picks

up O2 in lungs.up O2 in lungs.

Systemic circuitSystemic circuit

Provides blood to all Provides blood to all

organs an tissues in organs an tissues in

body.body.

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

mediastinum between the lungs and mediastinum between the lungs and beneath the sternumbeneath the sternum

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

StructureStructure: the base of the heart is on top : the base of the heart is on top 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 Size/Orientation – weighs ~300 gm, ~9 cm diameter at base,~13 cm from base cm diameter at base,~13 cm from base to apex and 6 cm diameter at the apex.to 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 Enclosing it in a sac with a tough outer layer, the Fibrous pericardium and a thin layer, the Fibrous pericardium and a thin Serous (Parietal and Visceral) Serous (Parietal and Visceral) pericardium (epicardium) attached to the pericardium (epicardium) attached to the myocardium. Pericardial space between myocardium. Pericardial space between these layers is filled with pericardial these layers is filled with pericardial fluid.fluid.

Myocardial muscleMyocardial muscle The heart is made of cardiac muscle and The heart is made of cardiac muscle and

consists of layers circularly and spirally consists of layers circularly and spirally wrapped around each other.wrapped around each other.

Outer layer is epicardium and is a serous Outer layer is epicardium and is a serous membranemembrane

Myocardium proper is cardiac muscle Myocardium proper is cardiac muscle Endocardium is a layer of specialized Endocardium is a layer of specialized

epithelial cells called endothelium. epithelial cells called endothelium. Endothelial cells make up the heart Endothelial cells make up the heart valves and line the entire cardiovascular valves and line the entire cardiovascular and lymphatic system.and 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 for blowing off CO2 and taking up the lungs for blowing off CO2 and taking up O2.O2.

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 O2) from the lungs and pumps it to every cell in the body.in 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 each other by valves that regulate blood flow in a one way directionflow in a one way direction

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

Right AtriumRight Atrium Receives oxygen poor blood from entire body Receives oxygen poor blood from entire body

and heart. Blood returns via superior and and heart. Blood returns via superior and inferior vena cava and coronary sinus to inferior vena cava and coronary sinus to right atrium.right atrium.

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 Externally right atrium is separated from

right ventricle by right coronary sulcus (right right ventricle by right coronary sulcus (right coronary artery).coronary artery).

Internally, theInternally, the Tricuspid (right Tricuspid (right atrioventricular) valveatrioventricular) valve separates right atrium separates right atrium and right ventricleand right 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 to delivery to valve into pulmonary trunk for to delivery to lungs.lungs.

Right ventricleRight ventricle

Left atriumLeft atrium Receives oxygen rich blood from the lungs via 2 Receives oxygen rich blood from the lungs via 2

pulmonary veins (right and left).pulmonary veins (right and left). Separated from right atrium by interatrial Separated from right atrium by interatrial

septum (fossa ovale) a remnant of fetal foramen septum (fossa ovale) a remnant of fetal foramen ovale.ovale.

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

Separated externally from left ventricle by left Separated externally from left ventricle by left coronary sulcus and internally by coronary sulcus and internally by Bicuspid valveBicuspid valve or or Mitral valveMitral valve (left atrioventricular valve). (left atrioventricular 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 Large thick walled pumping chamber of the

heart.heart. Receives oxygen rich blood from LA via Receives oxygen rich blood from LA via

bicuspid valve (left atrioventricular valve).bicuspid 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 artery.descendens (LAD) coronary 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 an back again, whereas the entire body an back again, whereas the right ventricle pumps blood through the right ventricle pumps blood through the lungs and back to the left atrium.the lungs and back to 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 semilunar valves: Pulmonic (right side) and The semilunar valves: Pulmonic (right side) and Aortic (left side) contain three half moon shaped Aortic (left side) 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 The heart valves open and close depending on the pressure exerted on them within each chamber.pressure exerted on them within each 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 heart

Left 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 in sinoatrial (SA) node tissue. This site is in sinoatrial (SA) node in the right atrium. The impulse spreads in the right atrium. The impulse spreads through the atrial muscle to the through the atrial muscle to the atrioventricular (AV) node → AV bundle atrioventricular (AV) node → AV bundle → →the right and left bundle branches → → →the right and left bundle branches → Purkinje fibers → → ventricular Purkinje fibers → → ventricular depolarization and contraction.depolarization and contraction.

Cardiac tissueCardiac tissue

The 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 and pathway by which impulses leave AV node and forks into right and left bundles branches which forks into right and left bundles branches which enter interventricular septum and descends to the enter interventricular septum and descends to the apexapex

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

Purkinje Fibers- Purkinje Fibers- electricalelectrical 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 Although the heart can beat without

neural control, it receives both neural control, it receives both sympathetic and parasympathetic input sympathetic and parasympathetic input from the autonomic nervous system.from the autonomic 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 cardioacclerator center → sympathetic chain ganglia → the sympathetic nerve.chain ganglia → the sympathetic nerve.

The heart can also be regulated by The heart can also be regulated by neurohumors circulating in the blood. neurohumors circulating in the blood.

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