Download Some animals, such as insects, have an open circulatory system

AS Biology
Circulatory System Overview
SPRING BREAK HW
Name: __________________________________________________________
Class: _______________
Directions:
1) Read over the following article, annotating it for important information.
2) Create a “One-Pager” summary sheet of the information.
FOLLOW THESE 5 STEPS
1. Select 2 quotes from the text that stood out to you in the reading.
2. Illustrate your interpretation. (Literally draw, use clip art, cut our magazines, etc.…) This
can be a small scale or a big scale image.
3. Write at least four single words or thoughts that express the function/purpose of the
human circulatory system
4. Make a 5-sentence summary of the reading.
5. Ask/Write 2 questions you have after reading the text.
The goal is to complete all 5 steps into ONE PAGE, hence a One Pager. Have fun!
**This will be 10 points in your quarter 4, standards-based grade.
Circulatory systems and the cardiac cycle
Article Sources:
www.bbc.co.uk/schools/gcsebitesize/science/triple_ocr_21c/further_biology/circulation/revision/1/ and
http://www.bbc.co.uk/schools/gcsebitesize/science/triple_ocr_gateway/the_living_body/circulatory_systems_cardia
c/revision/6/
Summary: Circulatory systems can be open (as in insects) or closed (as in fish and mammals). Closed
circulatory systems may be single circulatory systems with a two-chambered heart, or double circulatory
systems with a four-chambered heart. The contractions of the heart muscles are controlled by groups of
cells called pacemakers.
The circulatory system in mammals transports essential chemical substances to and from all of the cells
in our bodies. The heart pumps blood along a network of blood vessels to reach our cells, while the lungs
replace the oxygen used during respiration.
Open and closed circulatory systems
Living cells need to absorb nutrients and oxygen, and to release waste products, such as carbon dioxide.
Some animals – such as the single-celled amoeba - are small enough to do this by diffusion from their
surface, and do not require a circulatory system. But larger, multicellular animals need a circulatory
system to transport substances to and from their cells.
A. Open circulatory systems
Some animals, such as insects, have an open circulatory system. Their blood flows freely through their
body cavity, carrying nutrients to their cells. Oxygen is delivered directly to the insect’s tissues through
tiny tubes that open to the outside.
B. Closed circulatory systems
Vertebrates have closed circulatory systems. Their blood flows through blood vessels
(arteries, veins and capillaries) and they have a heart to push the blood around their body. The human
circulatory system is a closed system.
Single and double circulatory systems
Fish have a single circulatory system, but mammals have a double circulatory system.
A. Single circulatory system
In the circulatory system of a fish, the blood travels from the heart to the gills, where it absorbs oxygen
and releases carbon dioxide. It then flows from the gills to the organs and tissues in the rest of the body,
and back to the heart. There is just one circuit from the heart.
B. Double circulatory system
In the circulatory system of a mammal, there are two circuits from the heart:
1. Blood passes from the heart to the lungs - where it absorbs oxygen and releases carbon dioxide then back to the heart
2. Blood passes from the heart to the organs and tissues in the body, and back to the heart
Blood pumps through the heart twice during a complete
journey around the body. Some blood is sent to the lungs
and some blood is sent to the rest of the body each time
the heart beats.
The blood in each circuit is kept separate. This is
called double circulation and is a more efficient way of
delivering oxygen to the tissues than single circulation.
Compared to a single circulatory system, blood in a double
circulatory system is under higher pressure - which allows
materials to be transported more quickly around the body.
Figure 1: The double circulation of mammals


The double circulatory system in humans
Arteries, veins and capillaries
 Arteries are blood vessels that carry blood away from
the heart. (It’s easy to remember this – ‘arteries away’.) Because arteries have to withstand the
high pressure of the blood during each heart beat, they have thick, elastic walls which substances
cannot pass through
Veins carry blood towards the heart.
Veins have thinner walls that are less
elastic, because the blood they transport
is under lower pressure. They still do
not allow substances to pass through
their walls. Veins contain one-way
valves that prevent blood flowing
backwards.
Capillaries are very thin blood vessels
that have walls that are only one cell
thick. This means that substances such
as glucose, oxygen, water and carbon
dioxide can diffuse through between the
blood and the tissues.
How does the circulatory system work?
1. The left side of the heart pumps
oxygenated blood from the lungs,
through the aorta to the body tissues
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(excluding the lungs).
2. Deoxygenated blood returns from the body tissues to the right side of the heart, via the vena cava.
3. It is then pumped to the lungs, via the
pulmonary artery where it is oxygenated.
4. Blood returns to the left side of the heart, via
the pulmonary vein and is pumped to the
body tissues again.
The heart
The heart is mainly made from muscle. The
left ventricle of the heart has a thicker muscle wall
because it needs to pump blood further, and at a
higher pressure, around the body. The right
ventricle is under less pressure, as it only needs to
pump blood to the lungs.
The cardiac cycle
The atria are the top chambers of the heart. They
collect blood as it flows back to the heart through
the veins.
The blood is then pumped into the lower chambers called the ventricles -, which are more muscular.
When the ventricles contract, blood is forced out of the heart through the arteries.
Sets of valves exist between each atrium and ventricle, preventing blood from flowing backwards into the
atria. Another set of valves exists between the ventricle and arteries, preventing blood flow back into the
ventricles.
Veins also have one-way valves stopping blood flowing backwards between each heartbeat.
Deoxygenated blood
Deoxygenated blood passes through these blood
vessels, valves and parts of the heart:
1. Vena cava
2. Right atrium
3. Tricuspid valve
4. Right ventricle
5. Semilunar valve
6. Pulmonary artery
It then moves on to the lungs.
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Oxygenated blood
Oxygenated blood passes through these blood vessels, valves and parts of the heart:
1. Pulmonary vein
5. Semilunar valve
2. Left atrium
6. Aorta
3. Bicuspid valve
It then moves on to the rest of the body.
4. Left ventricle
The coronary artery
The heart needs a continuous supply of oxygen and glucose for respiration. The coronary artery is a
branch of the aorta that transports blood to the heart muscle itself.
A blockage in one of the branches of the coronary artery can severely interrupt blood flow and is called a
heart attack.
Blood pressure
You should be able to interpret pressure changes in arteries, capillaries and veins. The chart shows how
the pressure changes in the circulatory system - starting at the aorta leading from the left ventricle to the
rest of the body, and back to the vena cava leading to the right atrium.
Figure 2: Pressure changes in the circulatory system
Note - the pressure is greatest in the arteries. The regular rise and fall in arterial pressure is due to the
action of the heart. The systolic pressure is the pressure in the arteries when the heart is contracting, and
the diastolic pressure is when the heart’s chambers are refilling with blood.
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Controlling heart beat
The heart is made of powerful muscles. The coronary artery supplies these muscles with oxygen and food
substances such as glucose. The heart needs a constant supply of glucose and oxygen so that its muscle
cells can respire and continue to contract.
The pulse
The pulse is a measure of the heartbeat – the muscle contractions that put the blood under pressure. The
pulse can be felt at various places on the body, including the ear, wrist and temple.
Controlling heart rate
Heart rate is linked to activity. The body’s cells need more glucose and oxygen during exercise, and the
blood supplies this. The heart rate increases as activity increases, and this is detected as a faster pulse
rate. The hormone adrenaline increases heart rate.
The action of the heart can be investigated using:
 Electrocardiograms (ECGs) - which measure the heart’s electrical activity
 Echocardiograms - which use ultrasound to show possible heart defects
Figure 3: An ECG of a normal heart
Pacemakers
The muscles in the heart are stimulated to contract by small electric currents. These are produced by
groups of cells called pacemakers,
which naturally control the heartbeat.
Some people have a heart rate that is
too fast, too slow, or irregular. They may
have an artificial pacemaker fitted to
control their heartbeat.
Pacemaker cells
Two groups of pacemaker cells
coordinate the contractions of the heart
muscles:
 Impulses from the SAN (sinoatrial node) cause the atria to
contract, and stimulate the AVN
 Impulses from the AVN (atrioventricular node) cause the
ventricles to contract
ECG (electrocardiograms) traces show
these impulses.
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Blood and blood cells
The blood transports many useful chemicals around the body. For example, all cells for aerobic
respiration need glucose and oxygen. Carbon dioxide and water are the waste products of respiration and
need to be transported to the lungs so that they can be excreted.
Blood is made from four components:
 Plasma - the liquid part of blood. It transports nutrients (e.g. glucose), amino
acids, antibodies and hormones to tissues that need them. It also transports waste substances:
carbon dioxide and water to the lungs, and water and urea to the kidneys.
 Red blood cells - they transport oxygen, which is bound to hemoglobin.
 White blood cells - they are part of the body’s immune system and fight infection.
 Platelets - they stick together when a blood vessel is damaged in order to help form a clot.
Red blood cells
Red blood cells are highly specialized. They are the only cells in the body that do not have a nucleus. This
gives them more room inside to carry hemoglobin that is the red pigment that binds oxygen (to
form oxyhemoglobin).
Red blood cells are a biconcave shape. This kind of shape (which is disc like) gives them an increased
surface area for oxygen exchange.
Tissue fluid
By the time blood reaches the capillary beds from an artery, it is at high pressure and this forces blood
plasma out. The plasma leaves the capillary and becomes tissue fluid. As the blood plasma moves through
the capillary bed towards the vein, pressure drops and stops plasma being squeezed out.
Figure 4: Tissue fluid, blood, and lymph
Tissue fluid acts as a bridge in the diffusion of chemicals between the capillaries and the cells of the tissue.
Oxygen and glucose diffuse from the blood into the tissue fluid and then into the cells. Carbon dioxide
and urea diffuse from the cells into the tissue fluid and then into the blood.
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