PRAC 8 – CIRCULATION IN MAMMALS
Caitlin Bowie 10A
BACKGROUND INFORMATION:
The human heart is the most important muscle in the body. It can beat more than 100,000 times a day
pumping just over 7,500 litres of blood thorough an intricate network of vessels in the body. The human
heart is made up of four major chambers: the right atrium, the right ventricle, the left atrium and the left
ventricle. The right side of the heart receives blood that is low in oxygen from veins all over the body. It
then pumps the blood through the pulmonary artery into the lungs where it will become re-oxygenated.
The left side of the heart receives this oxygen-rich blood from the lungs then it pumps the blood through
the pulmonary vein into the left atrium and left ventricle then to the aorta and back out to the rest of the
body. While blood is circulating through the body it is delivering oxygen and nutrients to tissue through
the capillaries and at the same time picks up carbon dioxide and other waste material. The veins return
the deoxygenated blood to the right atrium and the cycle begins again.
A sheep’s heart is for the most part the same as ours. One of the main differences between a human
heart and a sheep’s heart include the heart being positioned slightly differently in their body. As humans
and sheep are both mammals we share many common similarities in our body systems and organ
function. Some similarities of the heart include having four major chambers and having a similar average
heart rate – humans (60-100 bpm), sheep (60-90 bpm). The average human heart beats 72 times per
minute. In the course of one day it beats over 100,000 times. In one year the heart beats almost 38
million times, and by the time you are 70 years old, on average, it has beat over 2.5 billion beats.
AIM:
For this experiment, the purpose was to examine and identify the major features of a mammalian heart
and how they compare to the characteristics of a human heart and also to relate the different parts of a
heart to their functions.
METHOD:
Please see attached prac sheet.
MATERIALS:
The materials we used in the heart dissection included: apron, gloves, newspaper, heart, pins, dissection
board, probe, forceps, scissors and scalpel.
SAFETY:
To ensure the experiment was safe we had some safety procedures to follow for everyone in the room
and also for the people who would be involved in cleaning up further afterwards. We had to wear gloves
and an apron, avoid direct contact with the heart with your hands, mouth, eyes etc, always cut away
from yourself and others, know what to do and who to tell if you cut yourself, be extremely careful when
using the instruments, when finished wrap the heart inside of the newspaper and dispose of as directed,
put the pins and dissection board on the trolley in the correct place also put all instruments sharp-side
down in the bleach solution. Afterwards we washed our hands thoroughly.
DIAGRAM OF MATERIALS:
DIAGRAM OF RESULTS:
Aorta
Left atrium
Right atrium
Bicuspid valve
Left ventricle
Right ventricle
DISCUSSION QUESTIONS:
1) If you have a heart with the blood vessels attached, note the vena cavae that enter the right atrium
of the heart. From where has the blood in these vessels been transported?
The vena cava that enters the right atrium of the heart is also called the superior vena cava. The superior
vena cava is a vein that carries deoxygenated blood from the upper half of the body to the right atrium in
the heart where it is pumped into the lungs to be re-oxygenated. The blood from the superior vena cava
had been transported from parts of the body higher than the heart and brings de-oxygenated blood back
to the right atrium.
2a) Where does the blood go to after it leaves the right ventricle?
After blood leaves the right ventricle it goes through the pulmonary artery to the lungs where it gets
oxygenated. It then returns to the heart through the pulmonary vein and into the left atrium. It then goes
into the left ventricle and then out to the rest of the body through the aorta. While the blood is
circulating through the body it is delivering vital oxygen and nutrients.
b) What happens to the blood before it returns to the left atrium of the heart?
Before blood returns to the left atrium it becomes oxygenated in the lungs, then the oxygenated blood
goes to the heart via the pulmonary veins which return the blood to the left atrium. Blood becomes
oxygenated when you inhale, you breathe in air which goes down to your lungs. Blood is pumped from
the heart to your lungs where oxygen from the air you've breathed in mixes with the blood, producing
oxygenated blood.
3) In which direction does blood flow through the heart? Draw arrows on the diagram of the heart in
figure 6.2C to show the direction of the flow of blood. Indicate where the blood entering the heart has
come from and where the blood leaving the heart is going to.
Blood flows through the heart by coming in the right side of the heart through the superior and inferior
vena cava, then to the right atrium, through the Tricuspid valve, right ventricle, up the pulmonary artery
to the lungs, through the pulmonary vein from the lungs into the left atrium, through the Bicuspid valve,
left ventricle then through the aorta which distributes the oxygenated blood back out to the rest of the
body. Please see attached prac sheet.
4) What is the function of the semi-lunar valves and the valves between the atrium and ventricle on
each side of the heart?
The main function of the semi-lunar valves is to allow the blood to pass out of the ventricles. The semilunar valves separate the ventricles from major arteries and prevent the back flow of blood within the
heart's chambers. The valves between the atrium and ventricle on either side of the heart are called the
Tricuspid valve (right side) and Bicuspid valve (left side). The Tricuspid valve opens to allow blood to be
pumped from the right atrium in to the right ventricle. Once the blood has passed through the valve it
closes so the blood cannot flow backwards. The Bicuspid valve operates similarly; after the oxygenated
blood flows from the lungs to the left atrium and ventricle the valve closes to prevent the blood from
flowing back.
5) The heart is sometimes likened to a pump. In what way(s) do you think this is a good description of
the heart? Would you disagree in any other way with the comparison?
I think that the description of a heart acting similar to a pump a good description of the heart. Pumps
have an input and an output. Pumps pull in a substance, circulate the substance within and then push it
back out and although the heart is a muscle, not a mechanical pump it accomplishes this. It brings in
deoxygenated blood from the body, and eventually pumps out new oxygenated blood back out to the
rest of the body carrying vital nutrients, causing blood circulation.
6) Sometimes a heart valve may be damaged. What would happen to the efficiency of the pumping
action of the heart when this occurs? Explain.
There are four valves in your heart. These valves act as gates and open and close to make sure that your
blood travels in one direction through your heart and stops blood from leaking backwards. The four
valves are called the Bicuspid valve, Tricuspid valve, Aortic valve and the pulmonary valve. When a heart
valve is damaged it puts extra strain on your heart and causes your heart to pump less efficiently. When
your heart does not pump as efficiently as it should the blood flow being pumped from the heart slows
down and less blood is pumped to the rest of the body, meaning the body’s need for oxygen-rich blood is
not met.
7) When animals hibernate, their heart rates are significantly reduced. For example, when active, North
American squirrels have a heart beat rate of 350 beats per minute. This falls to about 2 or 3 beats per
minute during the squirrel’s hibernation.
a) What is hibernation?
Hibernation is a deep sleep that helps animals survive winter months without eating much. Animals enter
hibernation during winter to conserve energy by going into this sleep-like state. Mammals lower their
metabolism and with a slowed heart rate, breathing less and a lowered body temperature.
b) Suggest why a squirrel is able to survive such a dramatic decrease in heartbeat rate.
While in hibernation, animals can have decreased heartbeat rates of up to 95 percent. Breathing,
thinking, moving and using the body systems all use energy and when a squirrel is in hibernation these
actions are not happening and so the animal is conserving energy. As the squirrel is not moving, it is not
using its muscles so the heart doesn’t have to pump as much blood and oxygen towards the muscles and
brain as fast because it doesn’t need as much oxygen.
8) Study figure 6.20 and 6.21 on page 147. Explain how an open circulatory system differs from a closed
system.
A closed circulatory system is a type of system in which blood flows in a closed circle within the heart,
arteries, veins and blood capillaries. Blood does not flow out of the system into the body and there is a
clear distinction between oxygenated blood and deoxygenated blood. This system is common in
vertebrates including humans. An open circulatory system is where blood is contained in vessels for only
part of its circuit. This system allows all fluid within the organism to mix and this combined fluid is called
hemolymph. This system is common in invertebrates. A closed circulatory system differs from an open
circulatory system because organisms with a closed circulatory system lack veins. Fluids, nutrients and
waste move freely through the body cavity. In a closed circulatory system blood is enclosed in veins and
does not mix with the interstitial fluid. Closed circulatory systems are more effective at transporting fluids
throughout the entire body and it also has the ability to support higher metabolic processes.
9) What role does the lymphatic system play in mammals?
The lymphatic system plays a large role in mammals and is closely related to the immune and circulatory
system. Its main function is to transport lymph which is a clear fluid and contains white blood cells that
help the body get rid of toxins and waste. The lymphatic system consists of lymph fluid, vessels and
lymphoid tissue, for example lymph nodes and the spleen. The lymphatic system collets and transports a
collection of fluids which are found between the cells or actually seep out of the cells. This intracellular
fluid begins to build up and eventually enters the bloodstream. The lymph system gathers these fluids
and returns them to our body.
10) Answer review q4 on page 180.
Two electrocardiograms (ECGs) are shown in figure 6.17. The person with the normal ECG had a heart
rate of 56 beats per minute. The abnormal ECG was of a person with ischaemia, a condition in which a
reduced oxygen supply has weakened heart muscles. This person had a heart rate of 137 beats per
minute. Suggest why the ischaemic heart had a much higher rate than the normal heart.
When a person has ischaemia, they have restricted blood supply to tissues causing a shortage of
oxygen and glucose needed to keep tissue alive. If blood flow to parts of the body are interrupted and
impaired, the heart has to beat faster to make up for the slowed blood flow and make sure that all organs
have enough blood supply. Compared to a normal heart which consistently pumps blood all over our
body, a person’s heart with this condition has to beat faster in order to survive and keep the body
oxygenated.
OBSERVATIONS AND ANALYSIS:
The results showed that a sheep’s heart is very similar to that of a human’s with only a few slight
differences. We observed the left and right side of the heart and the coronary artery. Once the heart was
open, we saw the right atrium and ventricle and the left atrium and ventricle as well as the tricuspid and
bicuspid valves, we also saw how parts of the heart were connected and where different areas of the
heart led to.
The findings in this experiment were to be expected. The aim of this experiment was to examine and
identify the major features of a mammalian heart and how they compare to the characteristics of a
human heart and also to relate the different parts of a heart to their functions and our group achieved
this goal. During this experiment we observed the four major chambers of a sheep’s heart and learnt
more about how the heart pumps blood through the body.
CONCLUSION:
Throughout this experiment we had no specific difficulties as a group. When dissecting the heart we had
a little bit of trouble cutting through the heart as the top section of the heart was still semi-frozen. The
experiment could only be improved by discussing beforehand the different chambers of the heart and
where the different valves that we had to identify were. Also we should have followed the method more
carefully rather than dissecting the heart freely.
In this experiment the patterns and trends between a human’s heart and a sheep’s heart was evident.
The hearts were similar because we are both mammals and so have many of the same features and
functions. We saw how by dissecting a heart we could better understand more about their body and ours
at the same time. The dissection helped me understand more about the heart, how it works and what
makes it work.
In future investigations I would like to learn about how the heart and pumping action is affected when it
is positioned differently in an animal’s body. For example an animal that stands on two legs and an
animal that stands on four legs.