Circulatory Systems
in Animals
Basic Components of All
Circulatory Systems
• A fluid, blood, that serves as a medium of
transport
• A system of channels, or vessels, that
conduct the blood throughout the body
• A pump, the heart, that keeps the blood
circulating
Types of Circulatory Systems
1) Open Circulatory System
example: arthropods and mollusks
2) Closed Circulatory System
example: earthworms, vertebrates
Open Circulatory System
• Have an open space, the hemocoel
• Vessels empty blood into and pick blood
up from the hemocoel
• Tissues within the hemocoel are bathed
directly in the blood
Hemocoel
Blood Vessel
Blood
Closed Circulatory System
• Blood is confined to the heart and a
continuous system of blood vessels
• Each body cell has a direct blood vessel
connection
Functions of the Vertebrate
Circulatory System
1. Transport of oxygen from lungs to tissues
2. Transport of carbon dioxide from tissues to
lungs
3. Transport of nutrients from digestive
system to all body cells
4. Transport of waste products from all body
cells to the liver, then kidney
Functions of the Vertebrate
Circulatory System
5. Distribution of hormones from gland to target
organ
6. Regulation of body temperature by adjustments
in blood flow
7. Prevention of blood loss by means of clotting
8. Protection of body from microbes by circulating
white blood cells and antibodies
Evolution of Vertebrate Heart
• Two distinctly different chambers:
1) atrium (pl. atria)
thin walls and very elastic
designed to collect blood from the body
2) ventricle
thick walls and very muscular
designed to pump blood to the body
Atrium
Ventricle
Evolution of Vertebrate Heart
1. Fish have a 2 chambered heart = one
atrium and one ventricle
2. Amphibians and reptiles have a 3
chambered heart = two atria and one
ventricle
3. Birds and mammals have a 4 chambered
heart = two atria and two ventricles
Fish
Amphibian, Reptile
Bird, Mammal
Fish Circulatory System
• Single loop circulatory system
1. Atrium collects blood from
body
2. Atrium transfers blood to
ventricle
3. Ventricle pumps blood to gills
4. Gills pick up oxygen and give
off carbon dioxide
5. Blood travels to body cells and
gives off oxygen and picks up
carbon dioxide
Amphibian and Reptile Circulatory
System
• Two loop circulatory system
1. Right atrium collects low
oxygen/ high carbon dioxide
blood from body
2. Left atrium collects high
oxygen/ low carbon dioxide
blood from lungs
3. Both atria empty into the
common ventricle
4. Deoxygenated and oxygenated
blood mix in ventricle and is
pumped to body and lungs
Bird and Mammal Circulatory
System
• Two distinct loops circulatory
system
1. Right loop= pulmonary
circulation
2. Left loop = systemic circulation
Low O2
High O2
Deoxygenated blood is always
kept separate from oxygenated
blood
Low O2
High O2
The Blood Vessels
•
1.
2.
3.
There are 3 types of blood vessels:
Arteries (and smaller arterioles)
Capillaries
Veins (and smaller venules)
Artery
Capillary
Vein
The Blood Vessels: ACV
Arteries
Arterioles
Heart
Capillaries
Veins
Venules
Arteries and Arterioles
• Carry blood under
pressure away from
the heart towards the
capillaries
• Middle tissue layer of
arteries is thick
smooth muscle
Lumen
Thick layer of smooth muscle
Arteries and Arterioles
• Smooth muscle contractions regulate
blood flow and blood pressure in arteries
• Contraction of arteries and arterioles
increases blood pressure
• Relaxation of arteries and arterioles
decreases blood pressure
Capillaries
Capillary wall
Lumen
• Capillaries have
cell walls one cell
thick 🡪 easy
diffusion of
molecules between
blood in capillaries
and cells in body
CO2
O2
RBC
Body
Cell
Capillary Bed
• While individual
capillaries are small,
capillaries form large
capillary beds in
tissues 🡪 very large
total area which
slows down blood
flow 🡪 increases the
rate of diffusion
Capillary Bed
Capillary Bed and Total Area
Blood Shunting in Capillary Bed
• Body regulates the flow of
blood through capillary
beds
• When precapillary
sphincters are closed,
blood is moved in bulk
through a thoroughfare
channel called the
arteriovenous shunt
• This prevents diffusion
between blood in
capillaries and cells in
tissue
Blood Shunting in Capillary Bed
• Example: after eating, precapillary
sphincters in digestive system capillary
beds are open while precapillary
sphincters in muscle capillary beds are
closed 🡪 priority is for the blood to pick up
the nutrient molecules from digestive
system
Veins and Venules
• Veins (and smaller venules) drain blood
from the capillaries and return it to the
heart under low blood pressure
• Veins have the same tissue layers as
arteries, but have less smooth muscle in
the middle layer 🡪 walls of a vein are thin
in comparison to arteries
Veins and Venules
Connective Tissue
Smooth Muscle
Veins and Valves
• Theoretically, because veins are thin
walled and blood pressure is low in veins,
blood should tend to move slowly through
the veins
• Actually, the flow of blood in the veins
increases due to the presence of one-way
valves in veins and skeletal muscle
contraction around veins
Veins, Blood Pressure and Velocity
Cross-section of Vein
Summary of Blood Vessels
Artery
Capillary
Vein
Flow of Blood
From heart to
capillaries
Diffusion
between
capillary and
body tissue
From capillaries
to heart
Blood Pressure
High
Low
Lowest
Smooth Muscle
Layer
Thick
None
Thin
Valves
None
None
Yes
Summary of Blood Vessels
Total
Cross-sectional
area
Blood Velocity
Artery
Capillary
Vein
Low
High
Low
High
Low
High
The Human Heart
• The human heart weighs
between 200 to 425
grams and is a little larger
than the size of your fist
• The heart is located
between your lungs in the
middle of your chest,
behind and slightly to the
left of your sternum
• The apex of the heart is
oriented to the left side of
the body
Right
Side
Left
Side
Rat Dissection
Left Side
Lungs
Heart
Liver
Lungs
Right Side
Diaphragm
Pericardium
• A double-layered
membrane sac called the
pericardium surrounds
the heart
• The outer parietal
pericardium surrounds
the roots of your heart's
major blood vessels and
is attached by ligaments
to your spine, diaphragm,
and other parts of your
body
• The inner visceral
pericardium is attached to
the heart muscle
(myocardium)
Pericardium
• A coating of fluid
separates the two
layers of membrane,
letting the heart move
as it beats, yet still be
attached to your body
• This space between
the visceral and
parietal pericardium is
the pericardial cavity
Myocardium
• The major portion of the heart is composed of cardiac
muscle cells, collectively called the myocardium
• Myocardium has a "stringy" look compared to skeletal
muscle
• Striated skeletal muscle cells are large and lie next to
each other in more or less parallel bundles
Myocardium
• Cardiac muscle cells are
small, butted together at
their ends, irregularly
shaped, and have
numerous blood vessels
(BV) between them
• Intercalated disks are
specialized cell-to-cell
adhesion/communications
sites and are found only
in cardiac muscle.
Heart Chambers
• Your heart has 4 chambers
• The upper chambers are called the left
and right atria ( atrium, singular) and have
protruding appendages called auricles
• The lower chambers are called the left and
right ventricles
Heart Septum
• A wall of muscle
called the septum
separates the left and
right atria and the left
and right ventricles 🡪
the right side of the
heart is a pump for
pulmonary circulation
and the left side of the
heart is a pump for
systemic circulation
Left Ventricle
Right
Ventricle
Heart Valves
• The heart has two types of valves: atrioventricular valves
and semilunar valves
• The tricuspid and mitral (or bicuspid) valves are
atrioventricular valves
• They have fibrous strands called chordae tendineae on
their leaflets that attach to papillary muscles located on
the respective ventricular walls
• The papillary muscles contract during ventricular
contraction and generate tension on the valve leaflets via
the chordae tendineae to prevent the AV valves from
bulging back into the atria 🡪 no back flow
• The pulmonary and aortic valves are called semilunar
valves and do not have chordae tendineae
Blood Flow Through the Heart
• The right atrium receives
deoxygenated blood from the
body via the superior and
inferior vena cava
• Deoxygenated blood flows
from the right atrium, across
the atrioventricular tricuspid
valve, and into the right
ventricle
• The right ventricle contracts
and pumps deoxygenated
blood to the lungs via the
pulmonary artery
• The semilunar pulmonary
valve prevents back flow of the
blood into the right ventricle
Blood Flow Through the Heart
•
•
•
•
Oxygenated blood returns to the
heart from the lungs via four
pulmonary veins that enter the left
atrium
Oxygenated blood flows from the
left atrium, across the
atrioventricular mitral (or bicuspid)
valve, and into the left ventricle
The left ventricle has a very thick
muscular wall so that it can
generate high pressures during
contraction
Oxygenated blood from the left
ventricle is pushed across the
semilunar aortic valve and into the
aorta for transport to the body
Human Circulatory System
Two distinct loops circulatory
system
1. Right loop= pulmonary
circulation
2. Left loop = systemic circulation
Low O2
High O2
Deoxygenated blood is always
kept separate from oxygenated
blood
Low O2
High O2
Heartbeat and Cardiac Cycle
• When surgically removed from the body, the
heart will continue to beat for several hours
provided it is supplied with the appropriate
nutrients and salts
• This is possible because the heart possesses its
own specialized conduction system and can beat
independently even after being separated from
its nerve supply
• The extrinsic (arising external to the heart) nerve
supply coming from the nervous system serves
to modify and control the intrinsic (inherent to the
heart itself) beating established by the heart
Heart Conduction System
SA node
Atrioventricular
Bundle
Inter-nodal
Fiber Bundle
AV node
Purkinje
fibers
Heartbeat and Cardiac Cycle
• There are five basic components to the
heart's intrinsic conduction system
• (1) sinoatrial node (SA node)
• (2) inter-nodal fiber bundle
• (3) atrioventricular node (AV node)
• (4) atrioventricular bundle
• (5) Purkinje fibers
SA Node
• The sinoatrial (SA) node is a
small mass of specialized
cardiac muscle situated in the
upper dorsal surface of the
right atrium
• Because the SA node is able
to initiate each beat of the
heart, it is often referred to as
the pacemaker of the heart
• The excitation impulse occurs
every 0.85 seconds 🡪
approximately 72 times per
minute
SA Node
• Excitation of the SA node
sends a nerve impulse to:
(1) the muscles of the
atria causing them to
contract (atrial systole)
while the ventricles relax
(ventricular diastole), and
(2) the AV node along the
inter-nodal fiber bundle
• Atrial systole takes 0.15
seconds of the 0.85
second cardiac cycle
AV Node
• From the SA node, inter-nodal
fiber bundles conduct the
nerve impulse to the
atrioventricular (AV) node
• The AV node is located in the
right atrium near the lower part
of the interatrial septum
• There is a short delay in
transmission of the impulse to
the ventricles
• This is important because it
permits the atria to complete
their contraction and empty
their blood into the ventricles
before the ventricles contract
Purkinje Fibers
• Once the nerve impulse leaves
the AV node, it enters
specialized muscle fibers
called Purkinje fibers
• Purkinje fibers permit a very
rapid and simultaneous
distribution of the nerve
impulse throughout the
muscular walls of both
ventricles
• This results in a contraction of
the ventricles that proceeds
upward from the apex of the
heart toward its base
• Ventricle contraction (systole)
and atria relaxation (diastole)
takes 0.30 seconds of the
cardiac cycle
Purkinje Fibers
• Once the ventricles have contacted, there
is a period of atrial and ventricular
relaxation
• This recovery period occupies the final
0.40 seconds of the cardiac cycle
Cardiac Cycle
Atrial
Ventricular
Systole Systole
0.15 sec
0.30 sec
Atrial &
Ventricular
Diastole
0.40 sec
Review of Cardiac Cycle
1. The spontaneous generation of a nerve impulse within the SA node
represents the start of the cardiac cycle. This electrical impulse
spreads throughout the atrial muscle and leads to contraction of the
two atria.
2. As the atria contract, the AV valves remain open and blood is forced
into the ventricles. The aortic and pulmonary semilunar valves
remain closed, keeping blood in the ventricles.
3. After the atria have contracted and the ventricles have filled, the AV
valves close.
4. The nerve impulse reaches the AV node, travels through the
Purkinje fibers and the ventricles begin their contraction.
5. Ventricular contraction forces blood through the semilunar valves
into the aorta and pulmonary arteries.
6. As the ventricles begin to relax, the aortic and pulmonary valves
close, the AV valves open, and blood flows into the ventricles to
begin another cycle.
Vascular Pathways
• The human heart has two pumps:
1) right atrium and ventricle pump
deoxygenated blood from the body cells to
the heart 🡪 pulmonary circulation
2) left atrium and ventricle pump
oxygenated blood from the lungs to the
body cells 🡪 systemic circulation
Major Blood Vessels
Arteries
1. Aorta🡪body
2. Subclavian🡪arms
3. Carotid🡪brain
4. Pulmonary🡪lungs
5. Mesenteric🡪intestines
6. Renal🡪kidneys
7. Iliac🡪lower body
8. Femoral🡪legs
9. Cardiac🡪heart
Veins
1. Body🡪vena cavae
2. Arms🡪subclavian
3. Brain🡪jugular
4. Lungs🡪pulmonary
5. Intestines🡪hepatic portal
6. Liver🡪hepatic
7. Kidneys🡪renal
8. Lower body🡪iliac
9. Legs🡪femoral
10. Heart🡪cardiac
Blood Flow
• Blood pressure, the pressure of blood
against the wall of a blood vessel, keeps
the blood moving through the circulatory
system
• Blood pressure is measured with a
sphygmomanometer, usually around the
brachial artery in the arm
Blood Pressure
• Systolic pressure = the highest blood
pressure in the arteries is reached when
the ventricles contract
• Diastolic pressure = the lowest blood
pressure in the arteries is reached when
the ventricles are relaxed
Blood Pressure
• The ratio of systolic pressure to diastolic
pressure is commonly referred to as
“blood pressure”
• For the average human, “blood pressure”
is 120 mm mercury systolic pressure to 80
mm mercury diastolic pressure 🡪 120/80
Blood Pressure and Velocity
Fetal Circulation
Fetal Circulation
• The developing human fetus has several
features that are not present in adult
human circulation
• These differences exist because the fetus
is not using its lung for gas exchange
• Gas exchange for the fetus is
accomplished by the mother via the
umbilical blood vessels
Fetal Circulation Features
1. Foramen ovale = oval opening
Shunts blood from right to left atrium in
order to bypass inoperable lungs
2. Ductus arteriosus = arterial duct
Shunts blood from right ventricle and
pulmonary artery to aorta in order to
bypass inoperable lungs
Fetal Circulation Features
3. Umbilical arteries carry low oxygen blood
and waste from fetus to placenta
4. Placenta allows gas, waste and nutrient
exchange between the mother and fetus
5. Umbilical veins bring high oxygen blood
and nutrients from placenta to fetus
Fetal Circulation Features
6. Ductus venosus = venous duct
Shunts blood from umbilical vein and fetal
liver to the inferior vena cava of fetus