Circulatory Systems
Chapter 34
Circulatory Systems
Internal Transport in Animals
The Problem:
All animal cells need to acquire nutrients &
oxygen from the environment & give off carbon
dioxide & other wastes to the environment.
How is this problem solved in different animals?
Unicellular protists (Amoeba, Paramecium)
- Use cell membrane to do these functions.
- Have high surface area-to-volume ratio which
allows sufficient materials to enter & exit
Small multicellular animals
- May use exterior surface or branches of inside
cavities (gastrovascular cavities) to do their
exchanges
Ex: Sea anemones & flatworms
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Aquatic Organisms
Without a Circulatory System
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Circulatory Systems
Other Invertebrate Solutions
Roundworms
Use fluids in their body cavity as a means of
transporting substances
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Circulatory Systems
Other Invertebrate Solutions
Echinoderms (Starfish)
Also use fluids in their body cavity
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Circulatory Systems
Invertebrate Circulation
All other animals have a circulatory system in
which a pumping heart moves a fluid into blood
vessels.
Two types of circulatory fluids:
Blood - which is always contained within blood
vessels.
Hemolymph - blood analogue. It is a mixture of
water, inorganic compounds & organic
compounds. There are no blood cells.
- Hemolymph flows within a body cavity called a
hemocoel.
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Open vs. Closed
Invertebrate Circulation
Circulatory Systems
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Open Circulatory System (Arthropods & most Mollusks)
Heart pumps hemolymph via vessels
Vessels empty into tissue spaces
Eventually hemolymph drains back to the heart
Grasshopper circulation (arthropod):
- Dorsal tubular heart pumps hemolymph into dorsal
aorta which empties into hemocoel.
- When heart contracts, openings called ostia, are closed
- When heart relaxes, hemolymph is sucked back into
heart by way of ostia.
- Hemolymph of insects is colorless due to lack of
hemoglobin & it does NOT carry oxygen. Use trachea.
Open vs. Closed Circulatory Systems
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Open vs. Closed
Invertebrate Circulation
Circulatory Systems
Closed Circulatory System
Found in segmented worms (annelids = earthworm) &
molluscs like octopus & squid
Heart pumps blood to system of blood vessels.
Valves prevent backwards flow of blood.
Blood is enclosed in either heart or blood vessels at all
times.
Blood eventually reaches tiny capillaries where gases
and materials diffuse to and from nearby cells
Veins return blood to heart for re-pumping
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Open vs. Closed Circulatory Systems
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Open vs. Closed
Invertebrate Circulation
Circulatory Systems
11
Earthworms have red blood.
Blood contains respiratory pigment, hemoglobin.
Hemoglobin is dissolved in blood; not contained in cells
There is no specialized gas exchange surface.
Gas exchange takes place across the body wall, which
must remain moist to function.
Circulatory Systems
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Transport in the Vertebrates
All vertebrates have a closed cardiovascular system
Vertebrate heart:
Atria - chamber(s) of heart that receive blood from
general circulation of body
Ventricles - chamber(s) of heart that pump blood out to
the body through blood vessels
Vertebrate vessels:
Arteries - Carry blood away from heart
Arterioles – Small arteries whose diameters can change
Capillaries - Exchange materials with body tissue fluid
Venules - Small veins that lead back to veins
Veins - Return blood to heart
Transport in Birds and Mammals
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Circulatory Systems
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Blood Vessels in the Vertebrates
•Arteries
- Have thick walls. Have thick muscles in wall & elastic.
- Able to expand & contract to accommodate increased
flow of blood after heart beats.
Capillaries
- Extremely narrow, microscopically small tubes
- Walls composed of only one layer of epithelial cells
- No cell is more than 60-80 m from a capillary
- Only about 5% of capillary beds are open at once
- Blood cells must pass through in single file
- Allow exchange of materials across their thin walls
Transport in Birds and Mammals
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Circulatory Systems
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Blood Vessels in the Vertebrates
•Venules
- Collect blood from capillary beds
- Join to form veins
Veins
- Walls of veins much thinner than in arteries
- Thinner muscle layer
- Have lower blood pressure than arteries
- Have valves which open towards the heart. These keep
the blood from flowing backwards.
Transport in Birds and Mammals
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Circulatory Systems
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Comparison of Circulatory Pathways
Two types of circulatory paths are seen:
Fish - Blood follows a one-circuit (single-loop)
pathway through the body
Heart has a single atrium and single ventricle
- Ventricle pumps blood to gills
- Gas exchange occurs in gills
- Blood returns to aorta which brings blood to
body. Blood pressure is lower here.
- Veins return oxygen-poor blood to an enlarged
chamber called the sinus venosus that leads to
the atrium.
- Atrium pumps blood back to ventricle.
Comparison of Circulatory Circuits
in Vertebrates
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Circulatory Systems
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Comparison of Circulatory Pathways
All other vertebrates have a two-circuit (doubleloop) pathway.
Heart pumps blood to two places:
•to the body tissues, called the systemic circuit.
•to the lungs, called the pulmonary circuit.
This double pumping system is an adaptation to
breathing air on land.
Comparison of Circulatory Circuits
in Vertebrates
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Circulatory Systems
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Two-circuit Circulatory Pathways
Amphibians
Two atria with a single ventricle
Sinus venosus collects oxygen-poor, deoxygenated,
blood & pumps it to right atrium.
Oxygen-rich, oxygenated, blood coming back from lungs
passes to left atrium.
Both atria empty into single ventricle
Oxygenated & deoxygenated blood is somewhat kept
separate because O2 poor blood is pumped out of
ventricle before O2 rich blood enters.
- Deoxygenated blood is pumped to lungs.
- Oxygenated blood is pumped to the body.
Comparison of Circulatory Circuits
in Vertebrates
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Circulatory Systems
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Two-circuit Circulatory Pathways
Reptiles
A septum partially divides ventricle.
Mixing of oxygen-poor & oxygen-rich blood is
minimal
Crocodiles & alligators have a complete septum &
thus have a true 4-chambered heart
Comparison of Circulatory Circuits
in Vertebrates
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Circulatory Systems
Two-circuit Circulatory Pathways
Birds & Mammals
A septum completely divides heart into left and
right halves.
Right ventricle pumps blood to lungs
Larger left ventricle pumps blood to rest of body
This provides good blood pressure in both the
pulmonary and systemic circuits.
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Comparison of Circulatory Circuits
in Vertebrates
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Circulatory Systems
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Transport in Humans
Human Heart
Fist-sized; cone-shaped
Major portion is called myocardium, and is
composed of cardiac muscle.
- Muscle fibers are branched & tightly joined
Heart lies within a fluid-filled sac, the pericardium
Inner surface of heart is lined with endocardium,
composed of connective & epithelial tissue.
External Heart Anatomy
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Human Heart:
Gross Anatomy
Circulatory Systems
Septum separates heart into left & right halves
Each half has two chambers
Upper two chambers are the atria
- Thin-walled
- Wrinkled protruding appendages called auricles
- Receive blood from rest of circulation
Lower two chambers are the ventricles
- Thick-walled
- Pump blood away from heart
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Internal View of the Heart
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Human Heart:
Valves
Circulatory Systems
Valves open and close to direct blood flow
through heart & prevent backward movement.
Two atrioventricular valves:
- Tricuspid - between right atrium & right ventricle
This valve has three flaps of tissue.
- Bicuspid (mitral) - between left atrium & ventricle
This valve has two flaps of tissue.
Two semilunar valves:
- Pulmonary - between right ventricle & pulmonary
trunk (artery)
- Aortic - between left ventricle & aorta
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Internal View of the Heart
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Circulatory Systems
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Transport in Humans
Blood returning to heart from systemic circuit
Enters right atrium
Right atrium pumps through tricuspid valve to right
ventricle
Right ventricle pumps blood through pulmonary valve to
the pulmonary circuit
Blood returning to heart from pulmonary circuit
Enters left atrium
Left atrium pumps through mitral valve to left ventricle
Left ventricle pumps blood through aortic valve to the
systemic circuit
Deoxygenated blood NEVER mixes with oxygenated
blood (in humans)
Circulatory Systems
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Blood Flow Circuit in Humans
Right atrium  tricuspid valve  right ventricle 
pulmonary valve  pulmonary artery  capillaries
around lung air sacs  pulmonary veins  left atrium
 bicuspid (mitral) valve  left ventricle  aortic valve
 aorta  arteries to all parts of body  capillaries in
body tissues  veins  vena cava (superior or
inferior)  right atrium
Blue writing means deoxygenated blood
Red writing means oxygenated blood
Circulatory Systems
Heartbeat & Cardiac Cycle
The average heart contracts, or beats, about 70
times a minute.
•Each heartbeat lasts about 0.85 seconds.
Systole - Contraction of heart chambers
Diastole - Relaxation of heart chambers
***See Cardiac Cycle Transparency here***
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Circulatory Systems
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Cardiac Cycle
1. Atria contract (while ventricles relax)
2. Ventricles contract (while atria relax)
3. All the chambers rest
•The word systole, when used alone, refers to the left
venticular systole.
- The volume of blood that is pumped out of left
ventricle per minute is called the cardiac output.
- This is about 5.25 liters per minute; almost the
amount of blood in the body.
- During exercise cardiac output can increase
manyfold
Circulatory Systems
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Heart Sounds
When the heart beats a familiar “lub-dub” sound is
heard. This is due to the valves of the heart
closing.
•The longer & lower pitched “lub” is due to the
atrioventricular valves closing.
•The shorter & sharper “dub” is due to the semilunar
valves closing.
A heart murmur is a slight slush sound after the lub.
It is often due to ineffective valves, which allows
blood to flow backwards.
Circulatory Systems
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Conduction System of Heart
Rhythmic contraction of heart is due to its cardiac
conduction system
Nodal tissue, which has both nervous & muscular
characteristics, is located in two regions of
heart:
Sinoatrial node (SA), found in wall of right atrium,
initiates the heartbeat & keeps it regular
- Every 0.85 seconds it sends out an excitation
impulse which causes the atria to contract
- Thus, it is called the cardiac pacemaker.
Conduction System of the Heart
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Circulatory Systems
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Conduction System of Heart
•Atrioventricular node (AV), found in base of right
atrium near septum, receives signal from SA
node.
- The AV node then signals the ventricles to
contract
- It does this with the aid of special large fibers,
called the bundle of His, which terminate in
smaller Purkinje Fibers
- This allows both ventricles to contract
simultaneously and very quickly.
Although the heartbeat is intrinsic it can be
regulated by the nervous system to increase or
decrease when necessary.
Conduction System of the Heart
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Circulatory Systems
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Conduction System of Heart
Electrocardiogram (ECG)
A recording of electrical changes that occur in
myocardium during cardiac cycle
When SA node triggers an impulse, the atrial fibers
produce an electrical change called the P wave. This
signals that the atria are about to contract.
The QRS complex signals that the ventricles are about to
contract & the atria are relaxing.
The T wave is produced during the electrical changes
that occur as the ventricles are recovering.
Conduction System of the Heart
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Ventricular fibrillation - caused by uncoordinated contraction of
the ventricles. Most common cause of sudden cardiac death in
seemingly healthy people.
Circulatory Systems
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Vascular Pathways
Human cardiovascular system includes two major
circular pathways:
Pulmonary Circuit
- Takes deoxygenated blood to the lungs via
pulmonary artery and returns oxygenated blood to
the heart via the pulmonary veins. Only artery that
carries deoxygenated blood & only vein that carries
oxygenated blood.
Systemic Circuit
- Takes blood throughout the body from the aorta to
body & then back in the vena cava
Path of Blood
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Circulatory Systems
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Vascular Pathways
Coronary Arteries
- Arise from aorta & come back to serve the heart.
- Lie on exterior surface of heart & then branch into
arterioles & capillaries.
Portal System
- A blood vessel system that begins & ends in
capillaries.
1. Hepatic Portal System – takes blood from
intestines to liver without going back to heart in
between.
Circulatory Systems
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Blood Pressure
The beat of the heart supplies pressure that
keeps blood moving in the arteries
Systolic Pressure results from blood being forced
into the arteries during ventricular systole
Diastolic Pressure is the pressure in the arteries
during ventricular diastole
Blood pressure
Normally measured with a sphygmomanometer
on the brachial artery in the upper arm.
Expressed in the form: Systolic “over” Diastolic
- Normal blood pressure is 120/80 mmHg.
Velocity and Blood Pressure
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Circulatory Systems
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Blood Pressure
As blood flows from aorta into various arteries &
arterioles, the blood pressure falls.
- The difference between systolic & diastolic
gradually becomes less.
In capillaries there is a slow even flow of blood
without systolic & diastolic differences.
Blood pressure in the veins is low & cannot move
blood back to the heart from the limbs on its
own.
- Skeletal muscle contraction pushes blood in
the veins toward the heart with help of valves.
Velocity and Blood Pressure
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Cross Section of a Valve in a Vein
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Circulatory Systems
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Cardiovascular Disorders
Hypertension - High blood pressure. Can lead to
stroke or heart attack.
Atherosclerosis - Accumulation of fatty materials,
including cholesterol, in inner linings of arteries.
These deposits are called plaque.
- This interferes with flow of blood. Can also
lead to blood clots. Stationary clots are called
a thrombus. If clot dislodges & moves it is
called an embolus.
Circulatory Systems
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Cardiovascular Disorders
Stroke - Cranial arteriole bursts or is blocked by
an embolus. Lack of oxygen causes part of brain
to die. Paralysis or death could result.
Heart attack – (Myocardial infarction) Due to
coronary artery becoming completely blocked.
Affected part of heart dies.
Angina pectoris –Due to partial blockage of
coronary artery. Painful squeezing sensation
from myocardial oxygen insufficiency.
Circulatory Systems
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Prevention of Cardiovascular Disease
Don’t:
- Smoke. Nicotine causes arteries to constrict &
blood pressure to rise.
- Abuse drugs. Cocaine & amphetamines cause
irregular heartbeats & can lead to heart attacks
& strokes.
- Drink too much alcohol. Can destroy just about
any organ in body. 2-4 drinks a week might
lower risk of heart disease.
- Gain too much weight. Heart has to work
harder & blood pressure will rise.
Circulatory Systems
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Prevention of Cardiovascular Disease
Do:
- Eat a healthy diet. Diet influences amount of
cholesterol. Two types plasma proteins “ferry”
cholesterol:
HDL – “good” lipoprotein, transports cholesterol out
of tissues to the liver.
LDL – “bad” lipoprotein, associated with high
levels of plaque.
Eating food high in saturated fats (red meat,
cream, butter) & trans-fats (margarine, baked & fried
foods) raises LDL.
Eat more “healthy” fats: mono- & polyunsaturated fats (canola oil, cold water fish)
Eat at least five servings of fruits & vegetables a day.
Circulatory Systems
Prevention of Cardiovascular Disease
Do:
-Exercise regularly.
- Helps to keep weight under control, minimize
stress, reduce hypertension.
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Blood:
Homeostasis Functions
Circulatory Systems
58
1. Transports gases, nutrients, wastes &
hormones to and from capillaries for exchange
with tissue fluid
2. Helps to destroy pathogens
3. Distributes antibodies for immune system
4. Helps to regulate body temperature
5. Helps maintain water balance & pH
6. Carries platelets & factors to help clot blood
Composition of Blood
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Circulatory Systems
Composition of Blood
4-6 liters of blood in normal human
Liquid part of blood is called plasma
90% water
10% is salts, nutrients, wastes & proteins
Formed elements (cells) make up ~45% of blood
Red blood cells (erythrocytes)
White blood cells (leucocytes)
Platelets (thrombocytes)
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Circulatory Systems
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Red Blood Cells (RBCs)
Small, biconcave disks that lack a nucleus
Most numerous blood cells (approximately 25 trillion
in average adult).
Contain hemoglobin, a respiratory pigment
Hemoglobin contains
- Four globin protein chains
- Each associated with an iron-containing heme
which binds loosely with oxygen
- Manufactured continuously in bone marrow of skull,
ribs, vertebrae, and ends of long bones
- Destroyed in liver & spleen after ~120 days.
Lack of RBCs or low hemoglobin leads to anemia
Circulatory Systems
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White Blood Cells (WBCs)
Usually larger than red blood cells & contain a
nucleus. Lack hemoglobin.
Usually ~5-10,000 white cells per mL of blood
Important in inflammatory response
Neutrophils, macrophages & monocytes are
phagocytes that eat foreign cells or materials
Lymphocytes play a role in fighting infection
- T cells attack infected cells
- B cells produce antibodies which combine with
foreign antigens (part of an invader)
Circulatory Systems
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White Blood Cells (WBCs)
Other white blood cells:
Eosinophils release enzymes that fight parasites
& destroy allergens (substances that start an
allergic reaction)
Basophils contain the anticoagulant heparin which
prevents blood clotting
- They also dilate blood vessels
Circulatory Systems
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Platelets (Thrombocytes)
Platelets result from fragmentation of large cells
called megakaryocytes in the red bone marrow
Produce 200 billion a day.
Involved in blood clotting, coagulation
12 clotting factors are involved in making a clot
Hemophilia - due to mutation in one clotting factor
Can bleed into joints, muscles or the brain.
Circulatory Systems
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Coagulation of Blood
Steps involved:
Platelets clump at site of vessel puncture. They
partially seal the leak
Platelets & injured tissues release a clotting factor
called prothrombin activator.
- Converts prothrombin to thrombin. Needs Ca2+.
Thrombin acts as an enzyme that turns fibrinogen
into long threads of fibrin.
- These threads wind around platelet plug and
also trap red blood cells.
Blood Clotting
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Circulatory Systems
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Capillary Exchange
Two forces control movement of fluid through the
capillary walls & allow exchange of materials:
1. Osmotic pressure
•Tends to cause water to move from tissue fluid
to blood
•Due to fact that blood has higher
concentration of solutes than tissue fluid
2. Blood pressure
•Tends to cause water to move from blood to
tissue fluids
Circulatory Systems
Capillary Exchange
At arterial end of capillary bed:
•Blood pressure (~32 mmHg) exceeds osmotic
pressure (~22 mmHg)
Water exits a capillary at this end.
In middle of capillary bed:
•Osmotic pressure equals blood pressure
Solutes move due to concentration gradients
- Oxygen & nutrients move out of capillary into
surrounding tissues.
- Carbon dioxide & wastes move back into
capillary from the surrounding tissues.
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Capillary Exchange
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Circulatory Systems
Capillary Exchange
At venule end of capillary bed:
•Osmotic pressure (~22 mmHg) exceeds blood
pressure (~15 mmHg)
Water enters a capillary at this end.
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Capillary Exchange
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Circulatory Systems
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Capillary Closures
Not all capillary beds are open at the same time:
•Capillary bed open when precapillary sphincters
(circular muscles) are relaxed.
•Capillary bed closed when the sphincters are
contracted
Then blood flows through a shunt directly from
arteriole into a venule.
Capillary Bed
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