Overview: Cardiovascular System and the Heart

Circulatory System = heart, BVs, and blood

Cardiovascular System = passageways for blood = heart, arteries veins, etc.

Two Hearts:1. Pulmonary Circuit

(right side) - takes blood to lungs for gas exchange

2. Systemic circuit (left side)- takes oxygen rich blood to the organs and oxygen poor blood back to the heart

• Right side of heart gets O2 poor blood– Pulmonary artery takes it

away from heart to lungs– Pulmonary veins bring it

back O2 rich

• Left side of heart serves systemic system– Aorta takes O2 rich blood out

to organs– Superior vena cava brings it

back from head, neck, upper limbs

– Inferior vena cava brings it back from organs below diaphragm.

Pericardium

• Double walled sac enclosing heart

• In the pericardial cavity is pericardial fluid that allows the heart to beat without friction

• Pericarditis is the pain caused by friction when the membranes are dry

Heart wall• Epicardium

– outer layer– fatty

• Myocardium– thickest layer– cardiac muscle

that pulls against a fibrous skeleton of fibers

– focuses the movement of electricity

• Endocardium– Smooth inner

lining

Chambers

• Right and left atria receive returning blood– have an easier

workload

• Right and left ventricles eject blood

Heart Valves• Ensure one way flow

• Made of flaps called cusps

• Open & close as a result of pressure changes

• When ventricles relax, valves are open

• Full ventricles contract pressure pushes valves shut

AV valves = between atria + ventriclesRight AV – tricuspid valveLeft AV – bicuspid valve (aka, mitral valve)

Semilunar valves = bet. ventricles + the great arteries

Coronary Circulation

• Getting blood to your heart• ~3 billion beats over an 80

year life span• Heart needs 5% of body’s O2

– delivered by coronary arteries

• Myocardial Infarction: fat deposits blocking arteries leading to necrosis of tissue– Anastomoses: our body’s defense

• Two arteries covering the same area

• If the damage is extensive, theheart beat becomes inefficient- coronary bypass may be necesssary

Cardiac Muscle and The Cardiac Conduction System

• Cardiocytes: short, thick branched cells-mononucleated, striated-myogenic –will beat rythmically w/o CNS stimulation-inherent contractile activity controlled by the ANS

• Intercalated discs join cells

end to end– Gap junctions allow ions to flow

between cells, keep electrical current flowing from one cell to the next

– The action potential travels thru all cells connected together forming a functional syncytium

Cardiac conduction system

• Our brain can modify the heartbeat, but not create it. Disembodied hearts can beat for hours.

• Sinoatrial (SA) node = the pacemaker-initiates heart beat and determines heart rate-damage to SA node results in slower heart rate – implant an artificial pacemaker

• Atrioventricular node = sends signals to the ventricles

Purkinje fibers arise from bundle branches near the apex and then spread throughout the myocardium.

Control of Heart Rate• Without nervous system control, the heart would

beat about 100 times per minute• Both sympathetic and parasympathetic nerves

innervate the SA node• When you are relaxed, your parasympathetic

nervous system (via the vagus nerve) sets a resting heart beat rate at about 70 beats/min

• When exercising or anxious, the sympathetic nervous system ↑ heart beat via hormones like adrenaline – this ↑ flow of O2 blood to muscles

• Average maximum heart rate is 220 minus your age

Electrical & Contractile Activity

Contraction = systoleRelaxation = diastole

These can apply to parts (e.g., atrial systole), or just to the ventricles

Sinus rhythm = normal beat triggered by SA nodeCan have ectopic focus (alternate source of beat, instead of SA node) called nodal rhythm

Arrhythmia = abnormal rhythm

Physiology of the SA node

• The nerves of the SA node are always slowly moving toward an action potential

• As soon as the heart beats it’s already starting toward another beat

• Avg. ~75 beats per minute

• Cardiac muscle has a sustained contraction, and a longer refractory period– This prevents tetanus:

continual contraction

Membrane potential starts around -60mV.Pacemaker potential is a gradual driftupward (slow inflow of Na+ w/o outflow of K+).Fast calcium channels – inflow of Ca+.

Electrocardiogram (ECG/EKG)

• Composite reading of many action potentials

• P wave: atria contract

• QRS complex: AV node fires, ventricles start to contract

• T wave: ventricles repolarizing

• U wave: not always seen – repolarization of papillary muscles or Perkinje fibers

Electrocardiogram

Cardiac cycle

“Lub-dub” sounds are made when the heart valves thatseparate the chambers of the heart open and close in sequence.

Now, you can…

• Identify the chambers and valves of the heart

• Trace the flow of blood through the heart chambers

• Contrast cardiac vs. skeletal muscle• Describe the physiological properties of

cardiac muscle• Describe the heart’s electrical conduction

system• Describe the physiological mechanism of

control of rate of heart beat