Circulatory System

Heart

• central pump

• maintains blood flow

  • 5 quarts per minute

Arteries

carry oxygenated blood away from heart

Veins

return deoxygenated blood

Capillaries

• tiny vessels

• crucial exchange of oxygen, nutrients, hormones, and waste products

  • move between blood and body tissues

Right Atria

receives deoxygenated venous blood from body via superior and inferior vena cava

Left Atria

receives deoxygenated blood from lungs via pulmonary veins

Right Ventricle

pumps deoxygenated blood to lungs via pulmonary arteries

Left Ventricle

pumps oxygenated blood to rest of body via aorta

What do valves do and how many are there?

• prevents back flow of blood

• four main valves

Tricuspid Valve

located between right atrium and ventricle

Mitral (bicuspid) Valve

located between left atrium and ventricle

Pulmonary Valve

right ventricle to pulmonary arteries

Aortic Valve

left ventricle to aorta

What is the cardiac cycle?

• it goes one heartbeat to the next heartbeat

• diastole and atrial systole

STEP ONE: Diastole (relaxation)

• heart relaxes

• atria fills with venous blood returning from body and lungs

• tricuspid and mitral valves close

• pressure increases in the atria

  • valves open

STEP TWO: Atrial Systole

• atria contracts, pushes blood into ventricles to complete ventricular filling

• 20% of blood volume is in the ventricles

  • ensures that they get filled before contraction

STEP THREE: Ventricular Systole (contraction)

• Isovolumetric contraction: ventricles contract, but the pressure isn’t high enough to open the semilunar valves (pulmonary and aortic) 

• All heart valves close to create pressure

• Ventricular ejection: pressure exceeds pressure in pulmonary arteries and aorta, causing semilunar valves to open

  1. Blood is ejected into the pulmonary arteries from the right and aorta from the left

STEP FOUR: Isovolumetric Relaxation

• After blood is ejected, ventricles begin to relax

  • Semilunar valves close up

• Atria fills up and the cycle restarts 

Pericardium

• Heart is enclosed by protective, double layered pericardium

  • Visceral pericardium (epicardium): inner layer that directly covers the heart

  • Parietal pericardium: outer layer, sac around the heart 

Pericardial Cavity

• between layers

• containing fluid to reduce friction as heart beats

Myocardium

• muscle tissue of heart, contracts and pumps blood

  • Consists of striated muscle fibers

Endocardium

• smooth lining inside the heart chambers

• Ensures smooth blood flow

Conduction System

• Coordinates cardiac cycle by generating impulses and spreading them through the myocardium 

Sinoatrial Node

• Small patch of tissue

• Acts as pacemaker for heart

• Impulse for contraction initiates at SA node, spreads over atria, and passes to the ventricles via conductive tissue called the atrioventricular node (AV node)

  • Continues along left and right bundle branches and terminates in the Purkinje fibers (further branch throughout ventricle walls) 

Atrioventricular Node

• Junction of atria and ventricles

• Delays electrical impulses so ventricles can fill with blood before contraction

Bundle of His

• Electrical impulse travels here

• Located in interventricular septum 

• Left and right bundle branches

Purkinje Fibers

• Spread electric impulse through ventricular myocardium, triggers contraction

Coronary Circulation

• Heart has own blood supply via coronary arteries

  • Provides oxygen and nutrients to myocardium

Left Coronary Artery

Anterior interventricular artery: supplies left ventricle

Circumflex artery

Supplies left atrium and side of left ventricle

Right coronary artery

Supplies right atrium, right ventricle

Cardiac Veins

• Collect deoxygenated blood from myocardium and returns it to the coronary sinus

• Drains into the right atrium 

Vascular System

• Closed transport system

• Supply tissues with oxygenated blood and nutrients

• Takes waste products to an excretory organ

• Includes arteries, capillaries, veins

• Blood vessel walls composed of three layers

1. Tunica intima: smooth thin endothelium, allows minimal friction with flowing blood

2. Tunica media: smooth muscle and elastic tissue under control of sympathetic nervous system

3. Tunica externa: connective tissue, creates support and protection for vessels 

• Arterial walls much thicker than venous walls

Lymphatic System

• Critical role in immune system (fights infections)

• Includes lymphatic vessels, tissues (nodes, tonsils, thymus) and lymph

• Vessels carry lymph fluid aided by muscle contractions