
Circulation is the flow of blood
throughout your body. It distributes
oxygen and minerals to the cells, and
also removes waste.
› The circulatory system is vital! Without it, cells
and tissues would die
 Lead to death of organism and eventually a
species

There are two main types of circulatory
systems:
› Open systems
› Closed systems

Some invertebrates don’t have one at
all; can simply diffuse in/out of the cells
right from the environment
› Doesn’t work for vertebrates!

Lack a heart or capillaries.
› Instead of a heart, there are blood vessels to
pump the blood along
› Instead of capillaries, blood vessels join
directly with open sinuses
› Blood “bathes” the organs directly, then
goes back into the vessels



Very inefficient
Works for arthropods,
insects, mollusks
(animals with lots of
openings in body to
let blood have
contact with the air)
More complex
organisms needed
something different

Has a closed system of capillaries,
arteries, and veins
› Capillaries surround organs to ensure all cells
will be nourished

Complexity of these systems varies
› Can be very simple, like annelids, or very
intricate, like humans



Much more efficient
Keeps oxygenated
and deoxygenated
blood separate
Found in most
vertebrates
(annelids, humans,
fish, frogs, etc.)

Our circulatory system consists of three
main things
› Heart
› Blood
› Blood vessels

Our heart consists of
fiber, strong muscle,
and valves
› Valves divide into 4
chambers and 2
pumps

Approximately the
size of your fist, and
weighs less than 1
pound

When resting, it beats 70 times per min.
› Each beat pumps 1/15 of a pint of blood

Individual heart cells beat at their own
tempo; as soon as two or more are
touching, they’ll synchronize.
› Coordinated by the “pacemaker”, a group
of nerves that send currents and receive
signals

The body contains 15 gallons
of blood
› Carries oxygen, minerals,
food, etc. to the cells
› Carries waste and carbon
dioxide away from the cells
› Fights disease


1/5 of our blood is always in
the lungs
Has a blue tinge when low on
oxygen

R.B.C. are responsible for carrying O
through body, and give blood its color
› Without, blood would be pale yellow
Every pinprick of blood contains about 5
million R.B.C!
 250,000,000,000 in the body; about 40 for
every other cell



Arteries, veins,
capillaries
Allow blood to travel
through body
› Like a network of
roads leading to the
body’s internal
organs, tissues, cells

Keep the blood from
flowing backwards;
has distinct
pathways to follow
The first process, systemic circulation,
starts in upper left chamber of the heart
(left atrium)
 Oxygenated blood flows down to the
lower left chamber (left ventricle)

› Once full, the L.V. squeezes, forcing the
blood out of the heart and through the body
 Valves keep blood from flowing backwards
 Have to use enough pressure to get the blood
all the way through the body!

Blood flows through the arteries
› Travels down through the body to all the
muscles and organs

All arteries eventually end in capillaries
› Very small; only 1/40 of an inch long (less
than the width of a human hair)
› The small size forces blood to slow
 R.B.C. sometimes have to bend to get through

While in the
capillaries, the blood
does its job
› Drops off O and
food for cells
› Picks up waste
› Picks up carbon
dioxide

After leaving the capillaries, blood enters
the veins
› Veins push the deoxygenated blood back
up the body towards the heart and lungs
 Valves keep blood from flowing down
 60% of blood is always headed back towards
heart
› Veins have to flow at the same rate as
arteries, but without the initial acceleration!
(fighting gravity + capillaries slowed)
 Have to be wider than the arteries

Sometimes, veins will get a little extra
help
› Leg muscles will contract to make pressure
› Once near the lungs, blood will be pushed
along by our breathing

Deoxygenated blood reaches the heart
again
› If the heart is resting, the entire process takes
about 40 seconds

The second process (pulmonary
circulation) is a much shorter journey.
› Deoxygenated blood enters the right
ventricle
› R.V. pushes blood to the lungs
› Blood picks up O and gets rid of carbon
dioxide
› Blood goes back to L.V. and everything starts
over

Mitral Valve Prolapse: one of the heart’s
valves doesn’t work, so blood can flow
backwards
› Seems to be genetic

Temporal Arteritis: inflammation of the
arteries, esp. in the head, neck, upper
body, and arms
› Can cause blindness and strokes

Endocarditis:
infection of the inner
lining of the heart
› Treatments may
include antibiotics
or surgery

The circulatory system is constantly
working with the:
› Respiratory system (getting O and getting rid
of carbon dioxide)
› Endocrine system (blood carries hormones
through the body)

Oxygenated blood travels down the
body through arteries
› Arteries end in capillaries
› Drop off food and O, pick up waste and
CO2

Deoxygenated blood travels back up
through veins
› Go back to heart, gets pushed to lungs,
picks up O

No C.S. = no life!