Life Processes · Lesson 9 of 13
Transportation in Human Beings
“The heart runs two connected delivery routes without taking a break.”
• Describe the transport roles of plasma and red blood corpuscles. • Trace blood through all four chambers of the heart. • Explain the function of valves and chamber-wall differences. • Explain double circulation and separation of blood. • Compare vertebrate heart designs. • Interpret systolic and diastolic blood pressure.
The lungs obtain oxygen and the intestine absorbs nutrients, but neither process helps a distant cell unless those materials are delivered. Blood forms the moving link between specialised exchange organs and every tissue.
Blood And Its Components
Blood is a fluid connective tissue. Plasma carries dissolved food, carbon dioxide, nitrogenous wastes, salts and many other substances. Red blood corpuscles carry oxygen using haemoglobin. A pumping organ and a network of vessels keep these materials circulating.
| Component | Main transport role |
|---|---|
| Plasma | Carries dissolved nutrients, carbon dioxide, salts and nitrogenous wastes |
| Red blood corpuscles | Carry oxygen using haemoglobin |
| Heart | Creates pressure that drives blood flow |
| Blood vessels | Form routes between the heart and tissues |
Our Pump — The Heart
The heart has two atria above and two ventricles below. Oxygen-rich blood from the lungs enters the left atrium, passes into the left ventricle and is pumped to the body. Deoxygenated blood from the body enters the right atrium, moves into the right ventricle and is pumped to the lungs. Valves prevent reverse flow.
| Step | Chamber or destination | State of blood |
|---|---|---|
| From lungs | Left atrium | Oxygen-rich |
| Left atrium contracts | Left ventricle | Oxygen-rich |
| Left ventricle contracts | Body tissues | Oxygen-rich |
| From body | Right atrium | Deoxygenated |
| Right atrium contracts | Right ventricle | Deoxygenated |
| Right ventricle contracts | Lungs | Deoxygenated |
Ventricles have thicker muscular walls than atria because they pump blood out of the heart. The left ventricle is especially muscular because it must drive blood throughout the body. Atria mainly push blood a short distance into the ventricles.
Double Circulation
Double circulation is a circulation pattern in which blood passes through the heart twice during one complete journey around the body.
One circuit carries deoxygenated blood from the heart to the lungs and oxygenated blood back to the heart. The other sends oxygenated blood from the heart to the body and returns deoxygenated blood. Complete separation supports a high and efficient oxygen supply needed by birds and mammals to maintain body temperature.
| Group | Heart design | Circulation consequence |
|---|---|---|
| Fish | Two chambers | Blood passes through the heart once per complete circuit |
| Amphibians and many reptiles | Three chambers | Some mixing of oxygenated and deoxygenated blood |
| Birds and mammals | Four chambers | Complete separation and efficient double circulation |
Blood Pressure
Blood pressure is the force exerted by circulating blood against the walls of blood vessels.
Systolic pressure is the arterial pressure during ventricular contraction, while diastolic pressure is the pressure during ventricular relaxation. A typical reference value is about 120/80 mm Hg. Blood pressure is measured with a sphygmomanometer. Persistently high pressure can damage vessels and increase the risk of internal bleeding and other disease.
Problem
Trace oxygen-rich blood from the lungs until it returns to the lungs.
- 1.It enters the left atrium from the lungs.
- 2.It passes through a valve into the left ventricle.
- 3.The left ventricle pumps it to body tissues.
- 4.After oxygen delivery, deoxygenated blood returns to the right atrium.
- 5.It passes into the right ventricle.
- 6.The right ventricle pumps it back to the lungs.
Problem
What would happen if a valve allowed blood to flow backward?
- 1.Some blood would reverse direction during chamber contraction.
- 2.Less blood would move forward with each beat.
- 3.The heart would need to work harder to maintain delivery.
- 4.Transport efficiency and tissue oxygen supply could fall.
Problem
Why is mixing of oxygenated and deoxygenated blood less suitable for a bird than for many reptiles?
- 1.Mixing lowers the oxygen concentration of blood sent to tissues.
- 2.Birds have high, continuous energy needs for maintaining body temperature and activity.
- 3.Their cells require an efficient oxygen supply for aerobic respiration.
- 4.A four-chambered heart prevents mixing and supports this high demand.
The right side of a heart diagram may appear on the viewer’s left. Chamber names refer to the person’s anatomical right and left, not the viewer’s position.
Quiz
Which chamber pumps oxygenated blood to the body?
What is the function of heart valves?
Why are ventricular walls thicker than atrial walls?
What does double circulation mean?
What does the first value in 120/80 represent?
Practice Problems
- Trace deoxygenated blood from a toe until it becomes oxygenated and returns toward the body.
- Explain why valves and thick ventricular walls are both needed for efficient pumping.
- Compare circulation in fish with circulation in humans.
- Explain why complete separation of blood is valuable to mammals and birds.
- Interpret a pressure written as 118/76 mm Hg by identifying the systolic and diastolic values.
Key Takeaways
• Plasma carries many dissolved substances while red blood corpuscles carry oxygen. • The right heart sends deoxygenated blood to the lungs. • The left heart sends oxygenated blood to the body. • Valves preserve one-way flow. • Ventricular walls are thick because ventricles pump blood outward. • Double circulation separates pulmonary and body circuits. • Four chambers prevent mixing in birds and mammals. • Blood pressure includes systolic and diastolic values.