Download Introduction to the Circulatory System

Introduction to the Circulatory System
Read below about the circulatory system. Answer the questions below attached.
The Importance of a Circulatory System
Your circulatory system carries nutrients to cells, wastes away from cells, and chemical messages
from cells in one part of the body to distant target tissues. It distributes heat throughout the body
and, along with the kidneys, maintains acceptable levels of body fluid.
No cell is further than two cells away from a blood vessel that carries nutrients. Your circulatory
system has 96 000km of blood vessels to sustain your 100 trillion cells. No larger than the size of
your fist and with a mass of about 300g, the heart beats about 70 times/min from the beginning of
life until death. During an average lifetime, the heart pumps enough blood to fill two large ocean
tankers.
Every minute, 5 L of blood cycles from the heart to the lungs, picks up oxygen, and returns to the
heart. Next, the heart pumps the oxygen-rich blood and nutrients to the tissues of the body. The
oxygen aids in breaking down high-energy glucose into low-energy compounds and releases energy
within the tissue cells. The cells use the energy to build new materials, repair existing structures,
and for a variety of other energy-consuming reactions. Oxygen is necessary for these processes to
occur, and the circulatory system plays a central role in providing oxygen.
The circulatory system is also vital to human survival because it transports wastes and helps defend
against invading organisms. It permits the transport of immune cells throughout the body.
The Challenge of Transporting Oxygen and Nutrients
Single-celled organisms, such as an amoeba have
no need for a circulatory system because oxygen
diffuses directly into the cell from the external
environment. The products of cellular respiration
(carbon dioxide and water) can leave the
organism by diffusion as well.
Even simple multicellular organisms such as the
sponge, have no need for a circulatory system in
an acquatic environment. Because the sponge has
only two cell layers, all cells remain in contact
Sponge – transportation of oxygen and nutrients
with water. The flagella pull water into the
sponge, bringing oxygen and nutrients into the
body. Water and wastes are expelled through the large pore, or osculum, at the top of the body.
All things that need to be absorbed or eliminated by the cells can pass directly into or out of each
cell.
Open and Closed Circulatory System
More complex organisms have three cell layers. Relying on diffusion to deliver oxygen and
nutrients is too limiting for more complex animals. The middle cell layer, or mesoderm layer, is
sandwiched between the ectoderm and endoderm and does not come in direct contact with
circulatory fluids or water. Cells of the mesoderm need a circulatory system to bring them into
contact with oxygen and nutrients. For this, there are two circulatory systems; the organism
physiology and functions play a key role as to which type of circulatory system they have.
Open and Closed Circulatory Systems
In an open circulatory system, blood carrying
oxygen and nutrients is not always contained
in blood vessels and is pumped by one or
several hearts towards a central cavity where
all the cells are bathed in the blood. The
blood returns to the heart(s) when the
heart(s) relaxes. This type of circulatory
system is commonly found in snails, insects
and crustaceans. There is no distinction
between the blood and the interstitial fluid
Snail – has an open circulatory system
(refers to fluid between cells) in this system.
The contraction of one or more hearts pushes
blood from one body cavity to another. Muscular movements by the animal during locomotion can
assist blood movement, but diverting blood flow from one area to another is limited. When the
heart relaxes, blood is drawn back toward the heart through open-ended pores.
In a closed circulatory system, the blood does not come in direct contact with all cells. The blood is
separated from other fluids, is transported around the body in blood vessel, and circulates in one
direction only. This system is commonly found in earthworms, squids, octopuses, and vertebrates.
QUESTIONS
1. Describe the main functions of the circulatory system.
2. Differentiate between an open and closed circulatory system.
3. Identify one advantage and one disadvantage to an open circulatory system.
4. Why do large, multicellular animals require a circulatory system?
5. What purpose is served by the respiratory system?
6. Why is the respiratory surface for terrestrial organisms inside rather than outside the body?