HomeBiologyB2: Structures and Functions in Living OrganismsB2.8 Circulatory System

B2: Structures and Functions in Living Organisms

B2.1 Cell Structure and FunctionB2.2 Biological MoleculesB2.3 Enzymes - Biological CatalystsB2.4 Movement Across MembranesB2.5 PhotosynthesisB2.6 RespirationB2.7 Ventilation and Gas ExchangeB2.8 Circulatory SystemB2.9 Coordination and ResponseB2.10 Excretion and Osmoregulation
B2: Structures and Functions

Circulatory System

How blood transports materials around the body

Heart and circulatory system showing blood vessels and chambers

The Body's Transport Network

Heart, blood vessels, and circulation

Interactive Heart Model
Click on any part to learn more. Watch the cardiac cycle animate through all 3 stages.
VENACAVAPULMONARYVEINSRIGHTATRIUMLEFTATRIUMOPENOPENRIGHTVENTRICLE(thinner wall)LEFTVENTRICLE(thicker wall)PULMONARYARTERY→ LUNGSAORTA→ BODYSEPTUMDeoxygenatedOxygenatedValve Open

Stage 1: Diastole (Relaxation)

1 of 3

The heart muscle relaxes. Blood flows passively from the veins into both atria, then through open AV valves into the ventricles.

  • •Vena cava brings deoxygenated blood to right atrium
  • •Pulmonary veins bring oxygenated blood to left atrium
  • •AV valves (tricuspid & mitral) are OPEN
  • •Semi-lunar valves are CLOSED
  • •Pressure in chambers is LOW

Tip: Click on any part of the heart to learn what it does!

Blood Composition
What makes up blood?
55%
44%

Plasma (55%)

Liquid part - transports dissolved substances

Red Blood Cells (44%)

Carry oxygen using hemoglobin

White Blood Cells (0.7%)

Fight infections

Platelets (0.3%)

Help blood clot

Blood Vessel Comparison
How arteries, capillaries, and veins differ
FeatureArteryCapillaryVein
Wall ThicknessThick (muscular + elastic)Very thin (1 cell thick)Thin
Lumen SizeNarrowVery narrowWide
Blood PressureHighLowVery low
ValvesNo (except at heart)NoYes
Direction of FlowAway from heartConnects arteries to veinsTowards heart
Blood TypeUsually oxygenatedExchange occursUsually deoxygenated
Circulatory System Flashcards
Click any card to reveal the definition
Circulatory System Quiz
Test your knowledge of the heart and blood vessels

1. Which blood vessel carries blood away from the heart?

2. What is the function of red blood cells?

3. Which chamber of the heart has the thickest wall?

4. What do valves in the heart prevent?

5. What percentage of blood is plasma?

6. Which blood vessels have valves?

7. What is cardiac output?

8. Which artery supplies the heart muscle with oxygen?