Biology • Form 4 • Chapter 10
Transport in Humans and Animals
10.1 - Types of Circulatory System
The Necessity for Transport Systems in Complex
Multicellular Organisms
All living organisms require the exchange of substances such as nutrients,
waste products and respiratory gases constantly in order to survive. The
exchange of these substances usually occurs through diffusion. However, in
large multicellular organisms, diffusion alone is not enough to make sure
constant supply of oxygen and nutrients to the cells due to
Their small total surface area to volume (TSA/V) ratio, and
Great distance between the source of the substances and the cells.
In order to overcome these problems, they require a circulatory system to help
with the distribution of nutrients and oxygen as well as the removal of waste
products.
Types of Circulatory Systems in Multicellular
Organisms
The circulatory system of large multicellular organisms can be categorized into
two:
Open circulatory system
Closed circulatory system
Figure 1 - In an open circulatory system (left), hemolymph is pumped directly
into the hemocoel which contains the body cells. In a closed circulatory
system (right), the blood flows continuously within the heart and vessels.
The exchange of substances occurs through the blood capillaries walls.
Figure 2 - Insects have an open circulatory system. One or more hearts
pump the hemolymph into the hemocoel. When the heart contracts,
hemolymph flows from the heart into the hemocoel. Here, chemical
exchange occurs between the hemolymph and body cells. When the hearts
relax, the hemolymph is drawn back into the hearts through pores called
ostia (singular, ostium).
Figure 3 - A fish has a heart with one atrium and one ventricle. Blood that
leaves the ventricle goes to the gill capillaries first for gaseous exchange.
The gill capillaries carry oxygenated blood to the systemic capillaries. In
systemic capillaries, oxygen diffuses in while carbon dioxide diffuses out of
the body cells. Since the circulatory system of fish has only one circuit, it is
called a single circulatory system.
Figure 4 - In amphibian such as frogs, they have a heart which consist of two
atria and one ventricle. Deoxygenated blood enters the right atrium, while
oxygenated blood goes into the left atrium. The blood then enters into a
single ventricle. Although there is some mixing of oxygenated and
deoxygenated blood , most of the oxygenated blood tends to remain on the
left side of the ventricle, while the deoxygenated blood tends to remain on
the right side. The ventricle then pumps the blood to the pulmocutaneous
and systemic circulations. Since the blood flows in 2 separate circuits, the
system is known as a double circulatory system.
Figure 5 - Humans have a heart that consist of two atria and two completely
separate ventricles. In pulmonary circulation , deoxygenated blood in the
right ventricle is pumped into the pulmonary arteries and transported to the
lungs to be oxygenated. In the systemic circulation , blood is pumped from
the heart to the rest of the body. Oxygenated blood flows into the left
ventricle to be pumped into the systemic capillaries via aorta. Since it
involves 2 separate circulations, this is called a complete double circulatory
system.
Comparison between circulatory systems of insects, fish,
amphibians and humans
Similarities
Present in all multicellular organisms
Consist of a heart to pump blood throughout the body or hemolymph
(in insects)
Function in transporting nutrients and waste products
The heart has valves to prevent backflow of blood
Differences
Insects
Types of circulatory system: Open circulatory system
Separation of oxygenated and deoxygenated blood: Number of circulations: Number of heart cavities: Many
Fish
Types of circulatory system: Closed circulatory system
Separation of oxygenated and deoxygenated blood: Number of circulations: Single (blood flows through the heart once
in a complete circulation)
Number of heart cavities: Two (one atrium and one ventricle)
Amphibians
Types of circulatory system: Closed circulatory system
Separation of oxygenated and deoxygenated blood: Incomplete
(mixture of oxygenated and deoxygenated blood in the ventricle)
Number of circulations: Double (blood flows through the heart
twice in a complete circulation)
Number of heart cavities: Three (two atria and one ventricle)
Humans
Types of circulatory system: Closed circulatory system
Separation of oxygenated and deoxygenated blood: Complete (no
mixture of oxygenated and deoxygenated blood in the ventricle)
Number of circulations: Double
Number of heart cavities: Four (two atria and two ventricles)
Answer practice questions to test your knowledge
Practice
10.1 - Types of Circulatory System
10.2 - Circulatory System of Humans
10.3 - Mechanism of Heartbeat
10.4 - Mechanism of Blood Clotting
10.5 - Blood Groups of Humans
10.6 - Health Issues Related to the Human Circulatory System
10.7 - Lymphatic System of Humans
10.8 - Health Issues Related to the Human Lymphatic System
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