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Circulatory System
Objectives
• Identify the function of the circulatory system
• Describe the structure and function of the
human heart
• Describe the three types of blood vessels
• Describe the function of the lymphatic system
Parts of the Circulatory System
• The circulatory system is made
up of:
– The cardiovascular system
– The lymphatic system
• The cardiovascular system is
made up of:
– Blood
– Heart
– Blood vessels
• The lymphatic system is made
up of:
– Lymph
– Lymph nodes
– Lymph vessels
Functions of the Circulatory System
• Brings oxygen, nutrients, and
hormones to cells
• Fights infection
• Removes cell wastes
• Helps to regulate body
temperature
The Heart
• The heart is a hollow organ
composed almost entirely
of muscle
• It is about the size of your
fist
• Pericardium is a tough,
saclike membrane that
surrounds the heart and
secretes a fluid that reduces
friction as the heart beats
• Myocardium is a thick
muscle layer that surrounds
the heart
The Heart
• The septum vertically
divides the heart into
two sides
• The right side pumps
oxygen-poor blood to
the lungs
• The left side pumps
oxygen-rich blood to
other parts of the body
The Heart
• Each side is divided into an
upper and lower chamber
• Atrium – upper chamber
(plural is “atria”)
• Ventricle – lower chamber
• The heart has 4 chambers
– two atria
– two ventricles chambers
Circulation Through The Heart
• Blood high in CO2 and low
in O2 enters the heart
through the right atria
• Right atria pumps the
blood to the right ventricle
• Right ventricle pumps
blood to the lungs
• Blood has CO2 removed
and receives O2 in the
lungs
Circulation Through The Heart
• Blood high in O2 re-enters
the heart through the left
atria
• Left atria pumps blood to
the left ventricle
• Left ventricle pumps
blood to the rest of the
body
• Aorta – largest artery in
the human body that
pumps blood from the
left ventricle to the rest of
the body
Circulation Through The Heart
• Valves – connective tissue
between the atria and
ventricles that prevents the
backflow of blood
• Blood moving from the
atria holds the valves open
• When the ventricles
contract, the valves close
– This prevents blood from
flowing back into the atria
Heartbeat
• Not this one…
Heartbeat
• Two networks of muscle
fibers in the heart
– One in the atria
– One in the ventricles
• When a single fiber is
stimulated, all the fibers
are stimulated, and the
network contracts as a
whole
Heartbeat
• Each contraction begins in the
sinoatrial (SA) node
– Sinoatrial node – the nerve tissue
in the right atrium that regulates
the contraction rate of the heart
– Also called the pacemaker
• The impulse sent by the SA
node reaches the
atrioventricular (AV) node
– The AV node, located in the
septum, sends the impulse to the
ventricles, which causes them to
contract
Heartbeat
• Heartbeat has two phases:
– Systole – occurs when
ventricles contract
• Pumps blood out of the heart
– Diastole – occurs when
ventricles relax and blood
flows into the atria
Blood Vessels
• When blood leaves the left
ventricle, it passes through the
aorta
• The aorta is the first of a series
of blood vessels that carry blood
throughout the circulatory
system
• There are 3 types of blood
vessels:
– Arteries
– Capillaries
– Veins
Arteries
• Arteries are large vessels
that carry blood from the
heart to the tissues of the
body
• All arteries carry oxygenrich blood
– Except for pulmonary
arteries
• Arteries have thick walls
to withstand pressure
• Arteries branch off into
smaller arteries called
arterioles
Capillaries
• Arterioles branch off into
capillaries
• Capillaries are the smallest
blood vessels in the body
– Walls are only one cell thick
• They carry O2 and nutrients
to cells and absorb CO2 and
other wastes
Veins
• Veins – blood vessels
that carry blood back to
the heart
• Large veins have valves
in them to keep blood
moving towards the
heart
• Venules are smaller veins
that collect blood from
the capillaries
Pulmonary Circulation
• Pulmonary circulation –
pathway of circulation
between the heart and the
lungs
• The right side of the heart
pumps blood to the lungs
• CO2 is removed from the
blood and O2 is absorbed
• Oxygen-rich blood returns
to the heart
Systemic Circulation
• Systemic circulation – the
movement of blood between
the heart and all parts of the
body except the lungs
• The left side of the heart pumps
oxygen-rich blood to the rest of
the body
• Coronary circulation supplies
blood to the heart itself
• Renal circulation supplies blood
to the kidneys
• Hepatic portal circulation moves
nutrient-rich blood from the
small intestine to the liver
The Lymphatic System
• The lymphatic system is a
network of vessels, nodes, and
organs that collects the fluid
that is lost by the blood and
returns it back to the
circulatory system
– The fluid lost by the blood is
called lymph
• Lymph collects in lymphatic
capillaries and slowly flows into
larger and larger lymph vessels
• Ducts collect the lymph and
return it to the circulatory
system
The Lymphatic System
• Lymph nodes are bean-shaped
enlargements in lymph vessels
• Lymph nodes act as filters that
trap bacteria and other
microorganisms that cause
disease
• Lymphocytes are white blood
cells stored in lymph nodes
that are specialized to fight
disease
Review Questions
• Identify the functions of the circulatory system
– The circulatory system brings oxygen, nutrients, and
hormones to cells, fights infection, removes cell
wastes, and helps to regulate body temperature
• Describe the structure and function of the human
heart
– The upper chamber that receives the blood is called the
atrium
– The lower area that pumps blood out is called the ventricle
– The heart pumps blood
Review Questions
• Name the three types of blood vessels.
– Arteries
– Veins
– Capillaries
• Describe the role of the lymphatic system.
– The lymphatic system collects the fluid that is lost
by the blood and returns it back to the circulatory
system