THE HEART

• Location: Thoracic cavity directly behind the breastbone(sternum)

• Surrounded by the pericardium

• 4 Chambers: 2 atria and 2 ventricles

• Blood vessles: – Veins:

• Superior vena cava • Inferior vena cava • Pulmonary veins – left and right

• Arteries:– Aorta– Pulmonary

• Blood is pumped through the chambers, aided by four heart valves

• The valves open and close to let the blood flow in only one direction

• Valves: – Atrioventricular valves:

• Tricuspid• Bicuspid (mitral)

– Semilunar valves• Aortic• Pulmonary

• Where

• are the four heart valves?– The tricuspid valve is between the right atrium

and right ventricle– The pulmonary (semilunar) valve is between the

right ventricle and the pulmonary artery

– The bicuspid (mitral) valve is between the left atrium and left ventricle.

– The aortic valve is between the left ventricle and the aorta.

• Valves open when the pressure in the preceding chamber is higher than that in the next chamber and they close when pressure in the preceding chamber falls below that in the next chamber.

• What causes the familiar “lubb-dupp” sounds associated with the heart?

• The closing of the heart valves causes blood to splash against the valves. This causes the heart sounds.

• Each heart beat is one cardiac cycle.

• There are three parts to each cycle:– Part 1: two atria contract (systole) at once.

two ventricles are relaxed (diastole).– Part 2: two ventricles contract at once.

two atria are relaxed

• Part three: all chambers relax

• The heart contracts and relaxes through this cycle on average about 70 times a minute

• Each heart beat lasts just under a minute.

• Blood flow during the beat:

• Atrial systole – ventricular filling

• Ventricular systole – blood forced through semilunar valves into circulation

The Meaning of Blood Pressure

• Pressure = force of blood pushing against blood vessel wall

• Example: 120/80

• Systolic number = pressure of ventricular contraction

• Diastolic number = pressure when heart is relaxed

Intrinsic Control of Heartbeat

• Cardiac conduction system• SA node• AV node• AV bundle • Left and right bundle branches• Purkinge fibers• Allows impulse conduction to spread first to atria

and then after delay to ventricles• Allows for adequate filling of all chambers

Extrinsic Control of Heartbeat

• Medulla oblongata (in the brain stem)

• Norepinephrine – released by the adrenal medulla (on top of kidney) during exercise, can increase heart beat

Electrocardiogram

• P wave: occurs just before the atria contract

• QRS complex: occurs just before ventricular contraction

• T wave: ventricular relaxation

Blood Vessels

• Arteries– Take blood away from the heart– Thick (three layers) and muscular– Blood enters arteries under pressure

• Veins– Channel blood towards the heart– Thinner walls

• Capillaries– Walls are only one cell thick– Precapillary sphincters regulate flow into capillary

beds

Blood Flow back to the Heart

• How does blood get back to the heart with such little pressure?– Valves play a big role– Muscular pumps

• Pathway of the Blood– Pulmonary circuit (to lungs)– Systemic circuit (to body tissues)

– Coronary arteries supply heart muscle with blood

Pulmonary Circulation

• Right atrium – from superior vena cava

• Right ventricle

• Pulmonary trunk – semilunar valve

• Pulmonary arteries

• Lungs (pulmonary capillaries)

• Pulmonary veins – oxygen rich

• Left atrium

Systemic Circulation

• Left atrium• Left ventricle• Aorta• System arteries• Systemic capillaries• Systemic veins• Superior vena cava• Right atrium

• Cardiovascular disease– #1 killer; 1 in 2 Americans die of it– High blood pressure ( hypertension)

• Damages organs, especially heart, kidneys • Contributes to atherosclerosis, stroke risk

– Heart disease – atherosclerosis• Narrowing of arteries – lipid buildup, thickening of

walls• Coronary arteries especially susceptible• Restricted blood flow angina• Blocked flow heart attack• Treatments: balloon angioplasty, coronary bypass

– Heart muscle dies after 2 hrs without oxygen– Signs of heart attack: chest pains, nausea,

and dizziness

• Stroke = cutoff of oxygen to brain cells –

cell survival – only 5 minutes

• Taking care of your heart– Exercise (aerobic, at least 20 minutes)– Good nutrition (control fats & body weight)– QUIT SMOKING

Summary of Main Points

• The heart is a double pump that operates continuously

• Arteries take blood away from the heart• Veins take blood back to the heart• Capillaries are the exchange vessels• Pulmonary and systemic circulations serve the

lungs and body respectively• Blood consists of plasma, oxygen-carrying red

blood cells, and defensive white blood cells• Cardiovascular disorders can be genetic or a

result of poor decisions