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6.2 – The
Blood
System
Essential Idea: The blood system continuously transports substances to cells and
simultaneously collects waste products.
6.2
The Blood System
Understandings:
 Arteries convey blood at high pressure from the ventricles to the tissues of the body
 Arteries have muscle cells and elastic fibers in their walls
 The muscle and elastic fibers assist in maintaining blood 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
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Applications:
Skills:
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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
William Harvey’s discovery of the circulation of the blood with the heart acting as the pump
Pressure changes in the left atrium, left ventricles and aorta during the cardiac cycle
Causes and consequences of occlusion of the coronary arteries
Identify blood vessels as arteries, capillaries or veins from the structure of their walls
Recognize the chambers and valves of the heart and the blood vessels connected to it in dissected
hearts or in diagrams of heart structure
I. Blood vessels
A.Arteries – carry blood away from the heart
1.Walls of smooth muscle and elastic fibers - Helps
maintain and withstand high pressure
2. Branch into arterioles, which branch into
capillaries
B. Veins – carry blood to the heart
1. Form from merged venules
2. Have valves to prevent backflow due to low
pressure and gravity
C. Capillaries
1.Form “beds” to allow gas exchange in all areas
of the body - diffusion of O2 and CO2 from high
concentration to low
2.Merge to form venules
Arteries
Capillaries
Veins
Carry blood away
from heart
Exchange of gases
with tissues
Carry blood back to
the heart
Thick walled
1 cell thick
Thin walled
No exchange
All exchange
No exchange
No valves
No valves
Valves
High pressure
Low pressure
Low pressure
Small lumen
Lumen 1 cell wide
Larger lumen
II.
The Heart -2 side-by-side
pumps that take blood in
and pump it out, creating
2 circuits (William Harvey
– 1628)
1. Pulmonary – to
lungs and back, O2
poor blood received on
right side and pumped
to the lungs
2. Systemic – to rest
of body and back, O2
rich blood received on
left and pumped to the
body
-From body, blood enters heart through vena cava
-Collects in right atrium
-Atria contract and move blood through atrioventricular valve to right
ventricle
-Ventricle contracts – closes atrioventricular valve to prevent backflow –
increase pressure in ventricle and opens semilunar valve, pushing blood into
pulmonary artery
-Blood goes to lungs where it drops off CO 2 and picks up O2-Returns to heart
through pulmonary veins
-Enters left atrium, through atrioventricular valve to left ventricle, through
semilunar valve to aorta
-Aorta branches to send blood to rest of body where it drops of O 2 and picks
up CO2
III. Blood
– NOT blue!
A. Components
1. Plasma – liquid portion, mostly water
2. Erythrocytes – Red blood cells, carry O2 & CO2
3. Leucocytes – White blood cells
4. Platelets – cell fragments for clotting
B. Transports
1. Nutrients – glucose, amino acids, etc.
2. O2 – reactant for cellular respiration
3. CO2 – waste product of cellular respiration
4. Hormones – transported from glands to target cells
5. Antibodies – proteins for immunity
6. Urea – nitrogenous waste
7. Heat- skin arterioles open/dilate to gain/lose heat
IV.
Control of Heart Rate
A. Myogenic muscle contractions – contracts and
relaxes without nervous system control
B. Sinoatrial node (SA node) – mass of tissue
located in the right atrium
1. acts as a natural pacemaker
2. initiates contraction of both
atria and sends out signals to AV
node after .8 seconds
C.
Atrioventricular Node (AV Node)
1. Also in right atrium
2. Receives signal from SA node, waits .1 sec and
sends out its own signal to ventricles to contract
D.
If there is an increased demand
for O2 and to get rid of CO2 (ex.
during exercise), brain gets
involved
1. Medulla oblongata senses
increase in CO2, sends signal
through cardiac nerve to SA
node to increase rate at which
heart contracts
2. Once demand returns to
normal, medulla sends
message through vagus
nerve for SA node that take
back control
E.
Chemicals can also increase heart rate
1. Adrenaline (epinephrine)
a. Secreted by adrenal glands (which sit on
top of kidneys) when stressed or excited
b. Causes SA node to fire more rapidly
V.
Pressure & Volume in the heart
A. Diastole – not contracting
B. Systole – contracting
C. As blood enters the atria, the atrioventricular valves
are closed. The increase in volume increases pressure.
D. Systole of atria pushes open atrioventricular valves
and moves blood into ventricles
E. Systole of ventricles forces atrioventricular valves
closed to prevent backflow (“lub”)
F. As ventricle contracts, pressure increase until
semilunar valves are forced open, pushing blood into
aorta/pulmonary artery
G. As contraction finishes, semilunar valve closes
(“dub”)
Heart Health
A. Artherosclerosis – build-up of plaque in the arteries
1. Plaque is composed of lipids, cholesterol, cell
debris, calcium
2. Causes arteries to be less flexible
VI.
B.
Heart attacks
1. Coronary arteries – 3, branch off aorta, blood
supply of heart muscle itself
2. Occlusion – when blood flow in an artery is
obstructed by plaque
3. Myocardial
Infarction – blood
supply to the heart
blocked -> dead
heart muscle