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Circulatory system
Why is the circulatory system important

Transfer
– Nutrients
– Oxygen
– Waste
– Cells with immune function
*Brain cells die within just a few minutes if
their oxygen supply is interrupted
Path of blood
Arteries – carries blood away from heart
 Arterioles – small vessels that lead to
capillaries (away from heart)
 Capillaries – microscopic vessels with thin
porous walls (these pass within a few cells
of every cell in the body)
 Venules – small vessels that capillaries
lead to (back to the heart)
 Veins – carries blood to the heart

Mammalian Circulation
Blood begins its flow with the right ventricle
pumping blood to the lungs
 In the lungs, the blood loads O2 and unloads
CO2

Fig. 42-6
Superior
vena cava
Capillaries of
head and
forelimbs
7
Pulmonary
artery
Pulmonary
artery
Capillaries
of right lung
Aorta
9
3
Capillaries
of left lung
3
2
4
11
Pulmonary
vein
Right atrium
1
Pulmonary
vein
5
Left atrium
10
Right ventricle
Left ventricle
Inferior
vena cava
Aorta
8
Capillaries of
abdominal organs
and hind limbs

Oxygen-rich blood from the lungs enters
the heart at the left atrium and is pumped
through the aorta to the body tissues by
the left ventricle
Fig. 42-6
Superior
vena cava
Capillaries of
head and
forelimbs
7
Pulmonary
artery
Pulmonary
artery
Capillaries
of right lung
Aorta
9
3
Capillaries
of left lung
3
2
4
11
Pulmonary
vein
Right atrium
1
Pulmonary
vein
5
Left atrium
10
Right ventricle
Left ventricle
Inferior
vena cava
Aorta
8
Capillaries of
abdominal organs
and hind limbs
• Blood returns to the heart through the superior
vena cava (blood from head, neck, and forelimbs)
and inferior vena cava (blood from trunk and hind
limbs)
• The superior vena cava and inferior vena cava flow
into the right atrium
Superior vena cava
Animation
Animation: Path of Blood Flow in Mammals
Inferior vena cava
7
9
6
2
3
3
4
11
1
5
10
8
78
9
7
106
29
3
5
11
10
3
35
4
1
12
14
56
82
Circulation and Evolution