The Cardiovascular System

Pulmonary and Systemic Circuits


Right side of the heart:

  •  receives oxygen poor blood

  • vessels that carry blood to and from the lungs form the Pulmonary Circuit ( Right Ventricle)

Left side of the heart 

  • receives oxygenated blood

  • takes the blood from the lungs and uses it to supply rest of body

  • the Systemic Circuit (Left Ventricle)


  • Right Atrium receives blood returning from the systemic circuit.

  • Left Atrium receives blood returning from the pulmonary circuit


Coverings of the Heart

Pericardium

  • double walled sac surrounding the heart

  • protects the heart

  • anchors it to surrounding structures

  • prevents overfilling

  • serous and fibrous


Pericarditis- inflammation of the pericardium


Layers of the Heart Wall

3 layers- epicardium, myocardium, endocardium

Epicardium

  • visceral layer

  • covers external surface of the heart and parts of its wall

  • contains fat in older people

Myocardium

  • middle layer; cardiac muscle

  • bulk of heart, controls contraction

  • muscle cells are arranged in spiral or circular bundles

Endocardium

  • innermost layer

  • lines the heart chambers and fibrous skeleton of the valves


Chambers and Great Vessels

2 atrias and ventricles

interatrial septum- divides the two atrias longitudinally

Interventricular septum- separates the ventricles

Coronary sulcus- encircles the junction between atria and ventricles, landmark that separates the upper and lower chambers

flow of blood through the chambers of the heart and blood vessels of the body.

Atrium:

Right-

  • receives de-oxygenated blood from 3 veins   

  • handles systemic return

                    - Superior vena cava: blood superior to diaphragm

                    - Inferior vena cava: below the diaphragm

                    -Coronary sinus: collects blood draining from myocardium

Left-

  • smooth and pectinate muscles

  • receives oxygenated blood from the lungs via pulmonary veins

  • handles pulmonary return

Ventricles

Trabeculae carneae: ridges of muscle, mark the internal walls of the ventricles

papillary muscles: play a role in valve function (closing), anchors the atrioventricular valve via chordae tendineae

  • bigger walls and the actual pumps of the heart

Right:

  • pumps blood into the pulmonary trunk to go to the lungs for gas exchange

  • thinner muscle wall, partly wraps around the left ventricle

Left

  • pumps oxygen rich blood into the aorta to the systemic circulation

  • can pump blood at a higher pressure (thicker walls and has to travel longer distances)


Valves

  • open and close due to change in blood pressure

Atrioventricular valves (AV)

  • prevent backflow into the atria when ventricles contract

  • between atria and ventricles

  • Tricuspid valve:

                      -Right AV valve

  • Mitral valve:

                    -Left AV valve (biscuspid valve)

  • Chordae Tendineae:

                    -heart strings, anchor the cusps to the papillary muscles, prevent valves from everting into atria

  • What happens: When heart is relaxed the AV valves hang limply into the ventricles, when blood flows into the atria, it flows through the cusps and into the ventricle, the ventricle contracts and increases pressure, and blood back flows and closes the valves

Structures of the heart valves.

Semilunar Valves (SL)

  • aortic and semilunar valves guard the larger arteries coming from the ventricles (aorta & pulmonary trunk)

  • rising pressure opens these valves, when they relax, blood causes them to close

SL Valve

Coronary Circulation

  • functional blood supply

Coronary Arteries

Left coronary artery branches into 2 parts:

  • anterior interventricular artery: supplies blood to the interventricular septum and anterior walls of both ventricles.

  • circumflex artery: supplies the left atrium and posterior walls of the left ventricle.

Right coronary artery gives rise to:

  • The right marginal artery, serving the lateral right side of the heart.

  • The posterior interventricular artery, supplying posterior ventricular walls

Coronary Veins:

  • After passing through capillary beds, venous blood is collected by cardiac veins that form an enlarged vessel called the coronary sinus, emptying into the right atrium.


Arteries and veins of the hearts.

Angina pectoris:

            -chocked chest, pain due to a deficiency in blood delivered to the heart muscle, cells are weakened but do not die

Myocardial Infarction:

           -heart attacked, prolonged blockage of coronary arteries causing cells to die, permanent damage and replace with scar tissue, damage to left ventricle is most serious


Cardiac v. Skeletal Muscle

Structure/microscopic

  • cardiac cells are short, fat, branched, and interconnected, one or two nuclei while skeletal muscle fibers are independent of one another

  • intercalated dics and gap junctions for electrical coupling

  • desmosomes prevent fibers from separating during contraction (functional syncytium)

  • no recruitment involved in cardiac muscle, contracts as one unit

  • cardiac have more mitochondria (resistent to fatigue)

  • delivering Ca is similar in cardiac muscle, lacks terminal cisterns (no triads)

  • ^ T tubules are wider and less abundant

contraction

  • in skeletal muscle, contractions can sumate (tetanic), cardiac muscle cannot do this because it would not fill properly


Cardiac Muscle Contraction

  • depolarization of the heart rhythmic and spontaneous (self excitable)

  • 1 % have automaticity

  • have long refractory periods

  1. Depolarization- sodium channels open which reverses the membrane potential from -90mv to 30mv, becomes more positive (closing of K+ channels) -occurs when pacemaker potential reaches threshold

  2.  Calcium influx- depolarization flows down T tubules causes SR to release calcium (plateau)

  3. Excitation-Contraction coupling- influx of Ca triggers more release from the SR, calcium binds to troponin and sliding of the filaments occur

  4. Repolarization- occurs when potassium channels open and calcium channels close, returning to RMP

*the long plateau ensures sustained contraction for effective blood ejection and prevents tetanic contractions due to a prolonged refractory period.

Pacemaker cell: depolarize spontaneously, have unstable resting potentials


Sequence of Excitation

  1. Sinoatrial node (SA) (pacemaker): right atrial wall, generates impulses 75 times/minute (sinus rhythm), not others area has a faster depolarization rate

  2. Atrioventricular node (AV): depolarization wave reaches the SA node, impulse is delayed for 0.1 second, allowing atria to respond before the ventricles contract (fewer gap junctions, slowest part

  3. Atrioventricular bundle (bundle of his): atria and ventricles are not connected by gap junctions, AV bundle is the only electrical connection between the chambers

  4. Right and left bundle branches: Impulses travel through these branches within the interventricular septum

  5. Purkinje fibers: depolarizes ventricular walls


Homeostatic Imbalances

  1. Arryhythmias: irregular heart rate

  2. Fibrillation: rapid and irregular heart rate, makes it ineffective as a pump

  3. ischemia: deficiency of blood to the heart muscle, blockage or narrowing of the coronary arteries, can cause anginia (cells dont die) or prolonged (myocaridal infarction)


Electrocardiography

P wave: atrial depolarization from the SA node

QRS complex: ventricular depolarization, proceeds ventricle contraction

T wave: ventricular repolarization, slower then depolarization


Heart sounds

  • first sound is the Av valves closing (systole)

  • second sound is the SL valves closing at the begnining of ventricular diastole

  1. Ventricular filling: blood passively flows into the ventricles, atrial systole (the remaining amount). End diastolic volume (EDV) volume of the blood in each ventricle before contraction

  2. Ventricle systole: atrias relax and ventricles begin to contract. Pressure results in closing of ther AV valves. Isovolumetric contraction phase (brief period where all the valves are closed. Ejection phase- when pressure in the ventricles exceeds those in the arteries, open the SL valves End systolic volume (ESV): volume of blood remaining in each ventricle (whats left after full contraction)


equations:

Cardiac Output- volume of blood pumped by each ventricle in one minute

Stroke volume- volume of blood pumped out by a ventricle with each beat

CO=HRx SV

At rest: HR(75beats/min)

CO is 4-5 times resting CO in nonatheltic people


Regulation of stroke volume:

SV= EDV-ESV


Preload= degree of stretch of cardiac muscle cells