University of Jordan 1

Cardiovascular system L1

Faisal I. Mohammed, MD, PhD

University of Jordan 2

Anatomy of the Heart

Located in the mediastinum – anatomical region extending from the sternum to the vertebral column, the first rib and between the lungs

Apex at tip of left ventricle Base is posterior surface Anterior surface deep to sternum and ribs Inferior surface between apex and right border Right border faces right lung Left border (pulmonary border) faces left lung

Cardiovascular System Anatomy

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Anatomy of the heart

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Anatomy of the heart

Cardiac valves

Cardiac Valves Open and Close

Passively

Importance of Chordae Tendineae

Importance of Chordae Tendineae

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Layers of the Heart Wall

1. Epicardium (external layer) Visceral layer of serous pericardium Smooth, slippery texture to outermost surface

2. Myocardium 95% of heart is cardiac muscle

3. Endocardium (inner layer) Smooth lining for chambers of heart, valves and

continuous with lining of large blood vessels

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Chambers of the Heart

2 atria – receiving chambers Auricles increase capacity

2 ventricles – pumping chambers Sulci – grooves

Contain coronary blood vessels Coronary sulcus Anterior interventricular sulcus Posterior interventricular sulcus

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Internal anatomy of the heart and Cardiac valves

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Right Atrium

Receives blood from Superior vena cava Inferior vena cava Coronary sinus

Interatrial septum has fossa ovalis Remnant of foramen ovale

Blood passes through tricuspid valve (right atrioventricular valve) into right ventricle

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Right Ventricle

Forms anterior surface of heart Trabeculae carneae – ridges formed by raised bundles

of cardiac muscle fiber Part of conduction system of the heart

Tricuspid valve connected to chordae tendinae connected to papillary muscles

Interventricular septum Blood leaves through pulmonary valve (pulmonary

semilunar valve) into pulmonary trunk and then right and left pulmonary arteries

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Left Atrium

About the same thickness as right atrium Receives blood from the lungs through pulmonary

veins Passes through bicuspid/ mitral/ left atrioventricular

valve into left ventricle

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Left Ventricle

Thickest chamber of the heart Forms apex Chordae tendinae attached to papillary muscles Blood passes through aortic valve (aortic semilunar

valve) into ascending aorta Some blood flows into coronary arteries, remainder to

body During fetal life ductus arteriosus shunts blood from

pulmonary trunk to aorta (lung bypass) closes after birth with remnant called ligamentum arteriosum

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Myocardial thickness

Thin-walled atria deliver blood under less pressure to ventricles

Right ventricle pumps blood to lungs Shorter distance, lower pressure, less resistance

Left ventricle pumps blood to body Longer distance, higher pressure, more resistance

Left ventricle works harder to maintain same rate of blood flow as right ventricle

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Heart Valves and Circulation of Blood Atrioventricular valves

Tricuspid and bicuspid valves Atria contracts/ ventricle relaxed

AV valve opens, cusps project into ventricle In ventricle, papillary muscles are relaxed and chordae

tendinae slack Atria relaxed/ ventricle contracts

Pressure drives cusps upward until edges meet and close opening

Papillary muscles contract tightening chordae tendinae Prevents regurgitation

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Movement of blood in the heart

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Semilunar valves

Aortic and pulmonary valves Valves open when pressure in ventricle exceeds

pressure in arteries As ventricles relax, some backflow permitted but

blood fills valve cusps closing them tightly No valves guarding entrance to atria

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Systemic and pulmonary circulation - 2 circuits in series

Systemic circuit Left side of heart Receives blood from lungs Ejects blood into aorta Systemic arteries, arterioles Gas and nutrient exchange in systemic capillaries Systemic venules and veins lead back to right atrium

Pulmonary circuit Right side of heart Receives blood from systemic circulation Ejects blood into pulmonary trunk then pulmonary arteries Gas exchange in pulmonary capillaries Pulmonary veins takes blood to left atrium

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Cardiac Muscle Tissue and the Cardiac Conduction System Histology

Shorter and less circular than skeletal muscle fibers Branching gives “stair-step” appearance Usually one centrally located nucleus Ends of fibers connected by intercalated discs Discs contain desmosomes (hold fibers together) and gap

junctions (allow action potential conduction from one fiber to the next)

Mitochondria are larger and more numerous than skeletal muscle Same arrangement of actin and myosin

Cardiac muscle, like skeletal muscle, is striated. Unlike skeletal muscle, its fibers are shorter, they branch, and they have only one (usually centrally located) nucleus.

Cardiac muscle cells connect to and communicate

with neighboring cells through

gap

junctions in

intercalated

discs.

Cardiac Muscle Tissue

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Cardiac and Skeletal MusclesDifferences

Skeletal muscle• Neurogenic

(motor neuron-end plate-acetylcholine)

• Insulated from each other

• Short action potential

Cardiac Muscle• Myogenic

(action potential originates within the muscle)

• Gap-junctions

• Action potential is longer

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Cardiac Myocyte• 50-100 µm long

• 10-20 µm in diameter

• single central nucleus

• the cell is branched, attached to adjacent cells in an end-to-end fashion (intercalated disc)

– desmosomes (connexons)

– gap junction…… Skeletal Myofiber(Muscle fiber): 10-100 m in diameter and its length 10-30 cm. Hundreds nuclei reside below the sarcolema.

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Action Potentials and Contraction

1. Depolarization – contractile fibers have stable resting membrane potential

Voltage-gated fast Na+ channels open – Na+ flows in Then deactivate and Na+ inflow decreases

2. Plateau – period of maintained depolarization Due in part to opening of voltage-gated slow Ca2+

channels – Ca2+ moves from interstitial fluid into cytosol Ultimately triggers contraction Depolarization sustained due to voltage-gated K+

channels balancing Ca2+ inflow with K+ outflow

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Action Potentials and Contraction

3. Repolarization – recovery of resting membrane potential Resembles that in other excitable cells Additional voltage-gated K+ channels open Outflow K+ of restores negative resting membrane

potential Calcium channels closing

Refractory period – time interval during which second contraction cannot be triggered

Lasts longer than contraction itself Tetanus (maintained contraction) cannot occur

Blood flow would cease

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Depolarization Repolarization

Refractory period

Contraction

Membranepotential (mV) Rapid depolarization due to

Na+ inflow when voltage-gatedfast Na+ channels open

0.3 sec

+ 20

0

–20

–40

– 60

– 80

–100

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Depolarization Repolarization

Refractory period

Contraction

Membranepotential (mV) Rapid depolarization due to

Na+ inflow when voltage-gatedfast Na+ channels open

Plateau (maintained depolarization) due to Ca2+ inflowwhen voltage-gated slow Ca2+ channels open andK+ outflow when some K+ channels open

0.3 sec

+ 20

0

–20

–40

– 60

– 80

–100

2

11

2

Depolarization Repolarization

Refractory period

Contraction

Membranepotential (mV)

Repolarization due to closureof Ca2+ channels and K+ outflowwhen additional voltage-gatedK+ channels open

Rapid depolarization due toNa+ inflow when voltage-gatedfast Na+ channels open

Plateau (maintained depolarization) due to Ca2+ inflowwhen voltage-gated slow Ca2+ channels open andK+ outflow when some K+ channels open

0.3 sec

+ 20

0

–20

–40

– 60

– 80

–100

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1

3

1

2

3

Action Potential in a ventricular contractile fiber

0

12

3

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Electrical Activityof the Heart

Different Expression levels andDifferent types of ion channels

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