The document describes the structure and function of the blood system, including the three main types of blood vessels (arteries, capillaries, and veins), how blood flows through the circulatory system from the heart to tissues and back again, and some pathologies that can occur like atherosclerosis and heart attacks. The heart functions as a pump to circulate blood through the arteries and veins, with capillaries allowing for exchange of oxygen, nutrients, and waste between the blood and body tissues. Valves in the veins and heart prevent backflow of blood and ensure forward circulation.

1. 6.2: The Blood System
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2. Understandings
Arteries convey blood at high pressure from the ventricles to the tissues of the body.
Arties have muscle cells and elastic fibers in their walls.
The muscle and elastic fibers assist in maintaining pressure between pump cycles.
Blood flows through tissues in capillaries. Capillaries have permeable walls that allow exchange of materials
between cells in the tissue and the blood in the capillary.
Veins collect blood at low pressure from the tissues of the body and return it to the atria of the heart.
Valves in veins and the heart ensure circulation of blood by preventing backflow.
There is a separate circulation for the lungs.
The heart beat is initiated by a group of specialized muscle cells in the right atrium called the sinoatrial node.
The sinoatrial node acts as a pacemaker.
The sinoatrial node sends out an electrical signal that stimulates contraction as it is propagated through the walls
of the atria and then the walls of the ventricles.
The heart rate can be increased or decreased by impulses brought to the heart through two nerves from the
medulla of the brain.
Epinephrine increases the heart rate to prepare for vigorous physical activity.

3. Applications and Skills
A: William Harvey’s discovery of the circulation of the blood with the heart acting as the pump.
A: Pressure changes in the left atrium, left ventricle, and aorta during the cardiac cycle.
A: Causes and consequences of occlusion of the coronary arteries.
S: Identification of blood vessels as arteries, capillaries, or veins from the structure of their walls.
S: Recognition of the chambers and valves of the heart and the blood vessels connected to it in
dissected hearts or in diagrams of heart structure.

4. Blood Vessels
There are three main types of blood vessel:
Arteries carry high pressure blood away from the
heart to tissues that need it
Capillaries are very small (< 10 μm diameter) and
therefore can penetrate virtually every tissue in
the body. Blood moves slowly through them
under low pressure providing opportunities for
the exchange of substances.
Veins carry the low pressure blood back to the
heart using valves to ensure blood flows in the
correct direction.
Arteries and veins tend to be large structures; smaller arteries are known as arterioles and correspondingly
smaller veins are venules.
Arteries have a relatively
thick smooth muscle layer
to change the inside
diameter of the lumen.
A capillary bed is a network of capillaries
that drain into a single venule.

5. Muscle contracts to decrease the size of the
lumen. This causes an increase blood pressure
and therefore maintains high blood pressure
between the pulses of high pressure blood
travelling from the heart.
Elastic fibers stretch to increase the lumen with
each pulse of blood. After the pulse of blood
passes the fibers recoil decreasing the lumen
size and therefore helping to maintain a high
blood pressure.
Relatively small lumen maintains high blood
pressure.
The structure of arteries
Thick muscular wall and fibrous outer
layer help the artery to withstand
high pressure
https://commons.wikimedia.org/wiki/File:Blausen_0055_ArteryWallStructure.png

6. https://commons.wikimedia.org/wiki/File:Capillary_system_CERT.jpg
The structure of capillaries
Capillaries are the smallest blood vessels and are adapted for the exchange of
substances to and from the blood.
This enables tissues to gain nutrients and molecules such as oxygen and to rid
themselves of waste material.
Capillaries also allow substances to enter and leave the organism, e.g. gas exchange
of oxygen and carbon dioxide in the lungs.
Wall is one cell thick allows easy diffusion
of substances in and out of the capillary
due to the short diffusion distance.
Blood travels slowly under low
pressure allowing more opportunity for
exchange.
Basement membrane is
permeable to many
substances
The walls and membrane can contain
pores to further aid the diffusion of
substances
Due the the massive number of
capillaries present and the small
lumen the surface area available for
the exchange of substances is very
large.
Image adapted from: https://commons.wikimedia.org/wiki/File:Capillary.svg

7. The structure of veins
https://commons.wikimedia.org/wiki/File:Venous_valve.svghttp://40.media.tumblr.com/tumblr_m0dwjt3WKQ1qzcf71o1_500.jpg
Veins return blood to the heart for recirculation.
Because of the low pressure valves are required to
prevent back-flow of the blood and therefore
ensure that the blood moves towards to heart.
Because there is less pressure to resist the walls of
the veins are thinner and less elastic than arteries.
They also contain less muscle than the arteries.
The large lumen (compared to arteries and the
thickness of the wall) means that the blood is
under low pressure.

8. Artery Capillary Vein
Thick walled Wall is 1 cell thick Thin walled
No exchanges All exchanges occur No exchanges
No internal valves No internal valves Internal valves
present
Internal pressure
high
Internal pressure
low
Internal pressure
low
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/http://cdn2.hubspot.net/hub/256273/file-407424614-png/images/Arteries_vs_Veins.png?t=1386888253000

9. http://www.kscience.co.uk/animations/blood_system.swf
Circuit through blood
vessels:
- A large artery
- Smaller artery branches
- An arteriole (small artery)
- A capillary bed
- A venule (small vein)
- A larger vein
- Large vein which takes
back to the heart
- Begins again

10. Now try to label this heart: http://sciencelearn.org.nz/Contexts/See-through-Body/Sci-Media/Animation/Label-the-heart
Left atrioventricular
valve
Right atrioventricular valve

11. http://www2.estrellamountain.edu/
faculty/farabee/Biobk/heartbeat.gif

12. http://goo.gl/YeoeJ
adrenalin is also known as epinephrine

13. WHEN BOTH CHAMBERS ARE AT REST
(Diastole)
- Atrial pressure is slightly higher (keeps AV valve
open)
- Pressure in aorta is higher than in left ventricle
(keeps semilunar valve closed to prevent
backflow)
http://goodfoodeating.com/wp-content/uploads/2014/06/Systolic-diastolic-heart-actions.jpg

14. WHEN ATRIA ARE IN SYSTOLE
- Ventricles in diastole
- Pressure produced is not very high since the
muscle of the atria are relatively thin.
- Much of the blood has already accumulated
passively into the ventricle.

15. WHEN VENTRICLES ARE IN SYSTOLE
- Atria are in diastole
- Pressure in atrium greater than ventricle (causes
AV valve to close)
- Pressure in aorta still higher, SL valve remains
closed
- Ventricle highly muscular pressure build up
- Pressure in ventricle becomes higher than aorta,
SL valve opens, ventricle pumps blood into aorta
- Pressure drops, SL valve closes
Both chambers go back into diastole and the
cardiac cycle repeats.

16. ATHEROSCLEROSIS
- Build up of plaque in the arteries
- Arteries become harder, less flexible
- Genetics and eating habits influence plaque build up
http://www.health-choices-for-life.com/images/arterialplaque.jpg

17. Partial or complete occlusion can lead to a heart attack
- Coronary arteries supply oxygen rich blood to cardiac muscle
- Blockage decreases blood supply
- This deprives the muscle of oxygen
- Leads to coronary muscle tissue death

18. Identify the labeled structures using your understanding of blood vessels.
a
b
https://www.ouhsc.edu/histology/Text%20Sections/Cardiovascular.html

20. Homework
VOCAB
Arteries, veins, capillaries, pulmonary arteries,
pulmonary veins, atria, ventricles, blood
pressure, pulmonary circulation, systemic
circulation, cardiac muscle, myogenic muscle
contraction, sinoatrial node, atrioventricular
node, medulla, cardiac nerve, vagus nerve,
myogenic heart rate, epinephrine, adrenal
glands, diastole, systole, cardiac cycle,
semilunar valve, atrioventricular valve,
atherosclerosis, plaque, endothelium, aorta,
coronary arteries, occlusion, coronary
thrombosis, acute myocardial infarction
Challenge yourself: 1 (pg 279), 2 (pg280)
Nature of Science (pg 283) Summarize how
ideas about blood flow have changed over
time. How did Harvey come to his conclusion
about a closed circulatory system?
Exercises 4-6 (pg 283)