Chapter 23

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CIRCULATION
CHAPTER 23
OPEN AND CLOSED
CIRCULATORY SYSTEMS
• Among the unicellular protists, oxygen and
nutrients are obtained directly by simple
diffusion.
• Cnidarians and flatworms have cells that are
directly exposed to either the external
environment or to a body cavity that
functions in digestion, the gastrovascular
cavity.
Gastrovascular cavity
Pharynx
Mouth
Planaria: gastrovascular cavity
OPEN AND CLOSED
CIRCULATORY SYSTEMS
• Large animals have tissues that are several
cell layers thick so that many cells are too
far away for surface exchange.
• Instead, oxygen and nutrients are transported
from the environment and digestive cavity to the
body cells by an internal fluid within a circulatory
system.
• There are two main types of circulatory systems:
• Open circulatory system
• Closed circulatory system
OPEN AND CLOSED
CIRCULATORY SYSTEMS
• In open circulatory systems, there is no
distinction between the circulating fluid
(blood) and the extracellular fluid of the
body tissues (interstitial fluid or lymph).
• This fluid is called hemolymph.
• Insects have a muscular tube that serves as a
heart to pump the hemolymph through a network
of open-ended channels.
Tubular heart
Insect: open circulation
OPEN AND CLOSED
CIRCULATORY SYSTEMS
• In a closed circulatory system, the
circulating fluid (blood) is always enclosed
within blood vessels that transport blood
away from and back to a heart.
• Annelids and all vertebrates have a closed
circulatory system.
Dorsal blood vessel
Lateral
hearts
Ventral blood
vessel
Earthworm: closed circulation
OPEN AND CLOSED
CIRCULATORY SYSTEMS
• Arteries carry blood away from the heart,
and veins return blood to the heart; blood
passes from the arterial system to the venous
system in capillaries.
• The pressure of the blood forces some fluid
out of the capillary walls.
OPEN AND CLOSED
CIRCULATORY SYSTEMS
• The pressure of the blood forces some fluid
out of the capillary walls.
• This fluid is called interstitial fluid.
• Some of it will return to the blood but some
becomes lymph and travels through the
lymph vessels.
OPEN AND CLOSED
CIRCULATORY SYSTEMS
• The functions of the circulatory system can
be divided into three areas:
• Transportation
• Substances essential for cellular functions are
transported by the circulatory system.
OPEN AND CLOSED
CIRCULATORY SYSTEMS
• Regulation
• The cardiovascular
system participates
in temperature
regulation, such as
by countercurrent
heat exchange.
Core body
temperature
Warm blood
36º C
Veins
Artery
5º C
Temperature
of environment
Capillary
bed
Artery
Cold blood
Veins
OPEN AND CLOSED
CIRCULATORY SYSTEMS
• Protection
• The circulatory system protects against injury
and foreign microbes or toxins introduced into
the body.
ARCHITECTURE OF THE VERTEBRATE
CIRCULATORY SYSTEM
• The vertebrate circulatory system (also
known as the cardiovascular system) is
made up of three elements.
• Heart—a muscular pump that pushes blood
through the body.
• Blood vessels—a network of tubes through which
the blood moves.
• Blood—fluid that circulates through the vessels.
ARCHITECTURE OF THE VERTEBRATE
CIRCULATORY SYSTEM
• Blood moves through the body in a cycle, from the
heart, through a system of vessels.
• Blood leaves the heart in arteries.
• From the arteries, blood passes into smaller arterioles.
• Tiny vessels called capillaries connect arterioles to venules,
or small veins.
• Venules and then veins carry blood back to the heart.
Heart
Arteries
Veins
Arterioles
Venules
Capillaries
ARCHITECTURE OF THE VERTEBRATE
CIRCULATORY SYSTEM
• Although each capillary is very narrow, there are so
many of them that the capillaries have the greatest
total cross-sectional area of any other type of blood
vessel.
ARCHITECTURE OF THE VERTEBRATE
CIRCULATORY SYSTEM
• Capillary beds can be opened or closed based on
the physiological needs of the tissues.
• Precapillary sphincters can contract or relax and
affect whether blood flows into a capillary bed
for exchange of3 gases and metabolites.
Precapillary
sphincters open
Through-flow
channel
Precapillary
sphincters closed
1
2
Arteriole
Capillaries
(a) Blood flows through capillary network
Venule
(b) Blood flow in capillary network is limited
ARCHITECTURE OF THE VERTEBRATE
CIRCULATORY SYSTEM
• An artery is more
than a simple pipe.
• It needs to be able to
expand with and be
strong against the
pressure caused by
contraction of the
heart.
• For this reason,
arteries have both
elastic and smooth
muscle layers.
Connective
tissue
Smooth muscle
Elastic
layer
Endothelial
cells
(a) Artery
ARCHITECTURE OF THE VERTEBRATE
CIRCULATORY SYSTEM
• Arterioles differ from arteries in that they are
smaller in diameter and respond to nervous
and hormonal stimulation.
• They can constrict or expand to affect blood flow
during periods of stress or body activity.
ARCHITECTURE OF THE VERTEBRATE
CIRCULATORY SYSTEM
• Capillaries are where O2
and food molecules are
transferred from the
blood to the body’s cells
and waste CO2 is picked
up.
• Capillaries are narrow
and have thin walls for
exchange.
• Almost all cells of the
vertebrate body are no
more than 100
micrometers from a
capillary.
• The blood pressure is
actually far lower in the
capillaries than in the
arteries.
Endothelium
Endothelial
cells
ARCHITECTURE OF THE VERTEBRATE
CIRCULATORY SYSTEM
• Veins are vessels
that return blood
to the heart.
• The walls of veins
are thinner because
the blood pressure is
not great.
Connective tissue
Smooth muscle
Elastic layer
Endothelium
(c) Vein
ARCHITECTURE OF THE VERTEBRATE
CIRCULATORY SYSTEM
• Veins have
unidirectional
valves that prevent
the flow of blood
backwards.
Blood flows
toward heart
Open
valve
Vein
Contracting
skeletal
muscles
Valve
closed
THE LYMPHATIC SYSTEM:
RECOVERING LOST FLUID
• The cardiovascular system is
Lymph nodes
very leaky.
• From capillary exchange, the
body loses about 4 liters of fluid
each day.
• To collect and recycle this fluid,
the body uses a second
circulatory system called the
lymphatic system.
• The lymphatic system is also a
network of vessels filled with
a fluid called lymph.
• Ultimately the lymph reenters
the bloodstream through
veins in the neck .
Thymus
Spleen
Lymphatic vesse
LYMPHATIC CAPILLARIES RECLAIM
FLUID FROM INTERSTITIAL FLUID
Lymphatic
capillary
Excess interstitial fluid
becomes lymph
Osmosis due to plasma
proteins causes net
absorption
Blood pressure
causes net filtration
Interstitial
fluid
Blood
flow
Capillary
Arteriole
Venule
THE LYMPHATIC SYSTEM:
RECOVERING LOST FLUID
• The lymphatic system has 3 important
functions:
• It returns proteins to circulation.
• If this protein remains in the tissues, it would
cause swelling or edema.
• It transports fats absorbed from the intestine.
• It aids in the body’s defense.
• Swellings along lymph vessels called lymph
nodes and a lymph organ called the spleen are
where bacteria and dead blood cells are
destroyed.
• The thymus produces white blood cells.
BLOOD
• Blood plasma is a complex solution of water
with three kind of substances dissolved in it:
• Metabolites and wastes
• Glucose, vitamins, hormones, wastes.
• Salts and ions
• Sodium, chloride, and bicarbonate.
• Proteins
• Proteins help keep water in the plasma.
• Serum albumin functions in maintaining
osmotic balance.
THREADS OF FIBRIN
• Other proteins
found in blood
include:
antibodies,
globulins, and
fibrinogen.
• Fibrinogen (which
converts into
fibrin) is required
for blood clotting.
BLOOD
• Nearly half the volume of blood is occupied
by cells.
• The three principal cell types are:
• Erythrocytes (red blood cells)
• The blood’s hematocrit is the fraction of the
total volume of the blood that is occupied by
red blood cells.
• In humans, the hematocrit is usually about
45%.
• Leukocytes (white blood cells)
• Platelets (cell fragments)
BLOOD
• Erythrocytes resemble flat disks with a
central depression on both sides.
• Almost the entire interior is packed with
hemoglobin, which carries oxygen.
• Because these cells have no nucleus they are
short-lived and must be replaced by new cells
synthesized in the bone marrow.
BLOOD
• Leukocytes contain no hemoglobin and are
essentially colorless.
• There are several different kinds, all of which help
defend the body against invading
microorganisms and other foreign substances.
BLOOD
• Platelets are cell fragments, pinched from
large cells in the bone marrow, called
megakaryocytes, that play a key role in
clotting.
FISH CIRCULATION
• The chordates that were ancestral to the
vertebrates have simple tubular hearts.
• The evolution of gills by fishes required a
more efficient pump, a true chamber-pump
heart.
FISH CIRCULATION
• The fish heart is essentially a
tube with four chambers
arrayed one after another.
• The sinus venosus (SV) and atrium
(A) are collecting chambers, and
the ventricle (V) and conus
arteriosus (CA) are pumping
chambers.
• The SV and CA chambers are
reduced in higher vertebrates.
• The chambers contract in a
peristaltic sequence.
• The blood that is pumped to the
body is fully oxygenated because
it passes through the gills first, but it
has less pressure.
Sinus
venosus
SV
Atrium
Ventricle
A
V
Conus
arteriosus
CA
(a)
Systemic
capillaries
Respiratory
capillaries
Gills
Body
SV
A
V CA
AMPHIBIAN AND REPTILE
CIRCULATION
• The advent of lungs involved a major
change in the pattern of circulation.
• After blood is pumped by the heart to the lungs, it
does not go directly to the tissues of the body but
instead returns to the heart.
• Pulmonary circulation goes to and from the
heart and lungs.
• Systemic circulation goes to and from the heart
and the rest of the body.
AMPHIBIAN AND REPTILE
CIRCULATION
• The amphibian heart has structural features
to prevent the mixing of deoxygenated
blood from the body with oxygenated
blood from the lungs.
AMPHIBIAN AND REPTILE
CIRCULATION
• The atrium is divided by a
septum that separates the
blood coming from the
body and from the lungs.
• There is a single, common
ventricle, but little mixing
of blood occurs because
• Some species of
amphibians have folds in
the ventricle that direct
the flow of blood from
the atria
• The conus arteriosus is
branched
AMPHIBIAN AND REPTILE
CIRCULATION
• Amphibians in water supplement the
oxygenation of their blood by obtaining
additional oxygen by diffusion across their
skin.
• This is called cutaneous respiration.
AMPHIBIAN AND REPTILE
CIRCULATION
• The reptilian heart is additionally specialized.
• There is a partial septum in the ventricle.
• The conus arteriosus has become incorporated
into the large arteries leaving the heart.
MAMMALIAN AND BIRD
CIRCULATION
• Mammals, birds, and crocodiles have a fourchambered heart with two complete
pumping circuits.
• This increased efficiency of the double circulation
in mammals and birds may have been important
in the evolution of endothermy.
• More efficient circulation is necessary to support
the high metabolic rate required.
MAMMALIAN AND BIRD
CIRCULATION
• In the mammalian heart,
• Oxygen-rich blood
returns from the lungs
through pulmonary
veins to the left atrium of
the heart and flows
through the mitral valve
into the left ventricle.
• The thick-walled left
ventricle contracts,
sending oxygenated
blood through a large
artery called the aorta
and out to the body.
• Backflow of blood
from the aorta is
prevented by the
aortic semilunar valve.
Aorta
Superior
vena cava
Aortic
semilunar
valve
Pulmonary
semilunar valve
Right atrium
Pulmonary
artery
Pulmonary
veins
Left atrium
Bicuspid
(mitral) valve
Tricuspid valve
Left ventricle
Inferior
vena cava
Right ventricle
MAMMALIAN AND BIRD
CIRCULATION
• Blood travels through
the body and returns to
the heart via the vena
cavae, which drain into
the right atrium.
• Blood flows from the
right atrium through the
tricuspid valve to the
right ventricle.
• The right ventricle
contracts, pushing
blood through the
pulmonary valve into
pulmonary arteries that
lead to the lungs.
Aorta
Superior
vena cava
Pulmonary
artery
Aortic
semilunar
valve
Pulmonary
veins
Pulmonary
semilunar valve
Left atrium
Right atrium
Bicuspid
(mitral) valve
Tricuspid valve
Left ventricle
Inferior
vena cava
Right ventricle
http://youtu.be/gn6QmETEm8s
Carotid artery
Jugular vein
Superior
vena cava
Brachial
artery
Aorta
Pulmonary
artery
Heart
Hepatic
portal
system
THE HEART
AND
CIRCULATION
OF MAMMALS
AND BIRDS
Radial
artery
Inferior
vena
cava
Aorta
Femoral
artery
andvein
Femoral
artery
Femoral
vein
Great
saphenous
vein
MAMMALIAN AND BIRD
CIRCULATION
• The simplest way to monitor heartbeat is to
listen using a stethoscope.
– “Lub” is the sound made by the closing of
the bicuspid and tricuspid valves at the
start of ventricular contraction.
– “Dub” is the sound made by the closing of
the pulmonary and aortic valves at the
end of ventricular contraction.
• A heart murmur is heard due to turbulence
created by the valves not closing fully.
MAMMALIAN AND BIRD
CIRCULATION
• Another way to examine the events of the
heartbeat is to monitor the blood pressure.
– A device called a sphygmomanometer is
used to measure the blood pressure in the
brachial artery of the arm.
– Diastolic pressure is the low pressure when
the atria are filling.
– Systolic pressure is the high pressure
associated with the ventricles
contracting.
MEASURING BLOOD PRESSURE
Blood 2
pressure
gauge
1
100
50
150
100
200
0
3
50
250
150
200
0
250
100
50
150
200
0
250
Cuff
Stethoscope
Cuff pressure: 150
No sound:
artery closed
Cuff pressure: 120
Pulse sound:
Systolic pressure
Cuff pressure: 75
Sound stops:
Diastolic pressure
MAMMALIAN AND BIRD
CIRCULATION
• The contraction of the heart consists of a
carefully orchestrated series of muscle
contractions.
• First the atria contract, followed by the ventricles.
• The sinoatrial (SA) node is the pacemaker of the
heart and determines the rhythm of the heart’s
beating.
MAMMALIAN AND BIRD
CIRCULATION
• Contraction of the atria is initiated by the SA
node.
• The wave of depolarization does not
immediately spread to the ventricles
because it must pass first through cardiac
muscle called the atrioventricular (AV)
node.
• This delays the signal for about 0.1 sec until the
atria have finished contracting.
MAMMALIAN AND BIRD
CIRCULATION
• The ventricles finally contract after the signal
passes from the AV node to an
atrioventricular bundle of muscle called the
bundle of His.
• Bundle branches divide into fast-conducting
Purkinje fibers which initiate the almost
simultaneous contraction of the right and
left ventricles.
• The electrical activity of the heart can be
measured by a recording called an
electrocardiogram (ECG or EKG).
HOW THE MAMMALIAN HEART
CONTRACTS
SA node
AV node
LA
RA
LV
RV
1
2
3
4
Bundle of His
Purkinje fibers
QRS wave in ECG
P wave in ECG
R
1 sec
R
ECG
P
T
QS
QRS wave
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