The Circulatory System
• The circulatory system moves nutrients,
gases, and wastes to and from cells
• Single-celled organisms obtain oxygen
and nutrients directly across the surface of
the cell
• Multi-cellular organisms require methods
for transporting materials to and from cells
which are far removed from the external
environment
Invertebrate Circulatory Systems
• Sponges and most Cnidarians use water
from the environment as a circulatory fluid
• Pseudocoelomate invertebrates (e.g.,
roundworms) use the fluids of the body cavity
for circulation (=gastrovascular cavity)
• Larger animals have tissues that are several
cells thick, such that many cells are too far
away from the body surface or digestive
cavity to exchange materials with the
environment
• In Cnidarians, respiration occurs via diffusion
directly through their tissues
• A gastrovascular cavity is used for digestion
and transport
Invertebrate Circulatory Systems
Invertebrate Circulatory Systems
• Open circulatory system – No distinction
between blood and the interstitial fluid;
hemolymph
– Most Molluscs and Arthropods
– A tubular muscle, or heart, pumps hemolymph
through a network of channels and body cavities,
before draining back to the central cavity
– Hemolymph directly
bathes the internal
organs
The Circulatory System
• Closed circulatory system – The
circulating fluid, or blood, is enclosed
within blood vessels that transport it away
from – and back to – the heart
– All vertebrates, cephalopod molluscs, and
annelids
– Consists of
heart, blood
vessels and
blood
Vertebrate Circulatory Systems
• Surface area – as the physiological
complexity of animals increased, so too
did the need for more surface area to
transport and exchange nutrients and
oxygen (and remove CO2 and metabolic
wastes)
• Adaptations have allowed the
development of large body size and
locomotion
Vertebrate Circulatory Systems
http://www.amnh.org/exhibitions/permanent/ocean/images/03_oceanlife/features/06_whales/whale.jpg
Check out:
http://www.youtube.com/watch?v=yd_w3biT3TU
http://en.wikipedia.org/wiki/File:Bar-headed_Goose_-_St_James%27s_Park,_London_-_Nov_2006.jpg
Vertebrate Circulatory Systems
• Fish evolved a 2-chambered heart to
increase efficiency of gas exchange in gills
First to contract
2.
1.
3.
4.
Vertebrate Circulatory Systems
• The evolution of lungs in amphibians involved a
major change in the pattern of circulation – a
second pumping circuit
• After blood is pumped from the heart through
pulmonary arteries to the lungs, it is returned to
the heart via pulmonary veins
– Double circulation – gives boost to speed/pressure
at which blood is transported to the rest of the body
– Pulmonary circulation moves blood between the
heart and lungs; Systemic circulation moves blood
between the heart and the rest of the body
Heart
1b.
1. Deoxygenated
blood from
body is pumped
through the
heart and to the
lungs
2. Oxygenated
blood is
returned to
heart to be
pumped to rest
of the body
1a.
2a.
2b.
Vertebrate Circulatory Systems
• Amphibians and most reptiles have a 3chambered heart
– 2 atria and 1 ventricle
– Some mixing of oxygenated and
deoxygenated blood
• Right atrium receives deoxygenated blood from the
systemic circulation, and the left atrium receives
oxygenated blood (pulmonary) from the lungs – no
mixing in the atria
• Separation of pulmonary and systemic incomplete
in ventricle
Amphibian and Reptilian
Circulation
• Amphibians obtain additional oxygen via
diffusion through their (moist) skin
• Reptiles have a septum that partially
subdivides the ventricle
– Separation is complete in Crocodilians
(septum divides ventricle into 2 separate
ventricles; a 4-chambered heart)
– Further reduces mixing of blood in the heart
– Atria receive blood returning to the heart
– Ventricles pump blood out of the heart
Mammalian and Avian (and
Crocodilian) Circulatory Systems
• Oxygenated and deoxygenated blood does
not mix; completely separated
– 4-chambered heart: 2 atria, 2 ventricles
– Right atrium receives deoxygenated blood from
the body and delivers it to the right ventricle
which pumps it to the lungs (pulmonary); the
left atrium receives oxygenated blood from the
lungs and delivers it to the left ventricle, which
pumps it to the rest of the body (systemic)
pulmonary
systemic
RA  RV  LUNGS  LA  LV  REST OF BODY
1b.
1a.
2a.
2b.
1. Deoxygenated blood from body is pumped through the heart and to lungs
2. Oxygenated blood is returned to heart to be pumped to rest of the body
Mammalian and Avian (and
Crocodilian) Circulatory Systems
• The sinus venosus is present, but
reduced, in amphibians and (further
reduced) in reptiles
• In mammals and birds, the sinus venosus
is present only as a remnant of tissue in
the wall of the right atrium = sinoatrial (SA)
node
– Pacemaker, site where the impulses that
initiate the heartbeat originate
The Four-Chambered Heart
• The heart functions as a two-cycle pump
– Both atria fill with blood and simultaneously
contract, emptying the blood into the
ventricles (atrial contraction)
– Both ventricles also contract at the same time,
pushing blood into the pulmonary and
systemic circulations (ventral contraction)
pulmonary
systemic
RA  RV  LUNGS  LA  LV  REST OF BODY
The Four-Chambered Heart
• The cardiac cycle includes the atrial and
ventricular contraction, and the resting period
between these two
• Atrioventricular (AV) valves maintain
unidirectional flow between the atria and the
ventricles: tricuspid (right) and bicuspid (left)
• Semilunar valves maintain unidirectional flow out
of the ventricles to the arterial systems
– Pulmonary valve located at exit of the right ventricle
– Aortic valve located at the exit of the left ventricle
– Valves open and close as the heart goes through its
cycle
The Four-Chambered Heart:
Diastole (resting) phase
• Blood returns to the resting heart through
veins that empty into the right and left atria
• As blood fills the atria and pressure rises,
the AV valves open and blood flows into
the ventricles
• The ventricles become ~80% full from this
process; contraction of the atria fills the
remaining 20%
• Ventricles are relaxed = diastole phase
The Four-Chambered Heart: Systole
(ventricle contraction) phase
• Following a slight delay from the diastole
phase, the ventricles contract = systole
phase
• Contraction of the ventricles increases the
pressure within each chamber, causing
the AV valves to forcefully close; this
forces the semilunar valves open and
blood flows into the arterial systems
• As the ventricles relax, closing of the
semilunar valves prevents backflow
Heart Contraction and Blood Flow
• http://www.nhlbi.nih.gov/health/dci/Diseas
es/hhw/hhw_pumping.html
The Four-Chambered Heart and
the Blood Vessels
• The aorta (and all its branches) are
systemic arteries, carrying oxygen-rich
blood from the left ventricle to all parts of
the body
• Right and left pulmonary arteries deliver
oxygen-depleted blood from the right
ventricle to the right and left lungs
• Pulmonary veins return oxygenated blood
from the lungs to the left atrium of the
heart
The Four-Chambered Heart and
the Blood Vessels
• Arteries – carry blood away from the heart;
branch into arterioles
• Capillaries – where materials (O2, CO2,
nutrients, metabolic wastes) are
exchanged
• Veins – carry deoxygenated blood back
towards the heart
The Four-Chambered Heart and
the Blood Vessels
• Coronary arteries are the first branches off
the aorta and supply the heart muscle with
oxygenated blood
• Blood from the body’s organs (now low in
O2) returns to the heart via systemic veins,
which empty into 2 major veins
– Superior vena cava – drains the upper body
– Inferior vena cava – drains the lower body
– Both empty into the right atrium
Measuring Blood Pressure
• As the ventricles contract, they generate
tremendous pressure, which is transferred
through the arteries once the AV valve
opens
• Arteries contain large amounts of elastin,
an elastic protein which allows for
dilation/stretching and rebound
• A pulse results from changes in pressure
as arteries expand and contract with blood
flow
Measuring Blood Pressure
• Blood pressure is a general indicator of
cardiovascular health
• Arterial blood pressure can be measured with a
sphygmomanometer at the brachial artery on the
inside part of the arm
• A tightened cuff stops the flow of blood to the
lower part of the arm; As the cuff is loosened,
blood begins pulsating through the artery =
systolic pressure; ventricles are contracting
• As the cuff is loosened further, the vessel is no
longer distorted and the pulsing stops = diastolic
pressure; ventricles are relaxed
Measuring Blood Pressure
Measuring Blood Pressure
• Systolic pressure is the peak pressure at
which ventricles are contracting
• Diastolic pressure is the minimum
pressure between heartbeats at which the
ventricles are relaxed
• Written as a ratio of systolic over diastolic
• Typical blood pressure is 120/75; >150
systolic or >90 diastolic = hypertension
Contraction of Cardiac Muscle
• Each cell in heart produces an action
potential (electrical signal that is stimulus
for cell to contract); fairly long in duration;
250 milliseconds from start to finish
• Can’t start another action potential until
the other is completely finished
• The sinoatrial (SA) node located in the
wall of the right atrium acts as a
pacemaker by producing spontaneous
action potentials
Contraction of Cardiac Muscle
• Action potentials are generated by a
constant leakage of Na+ ions into the cell
that depolarize the membrane
• When the threshold is reached, the action
potential occurs
• Allows heart muscle to carry signal over
distance; conducted rapidly over both
ventricles by a network of fibers, including
Purkinje fibers, which spread electrical
activity to rest of heart
Contraction of Cardiac Muscle
• An electrocardiogram (ECG or EKG) records the
electrical activity of the heart
• Illustrates via electrodes how the cells of the
heart depolarize and repolarize during the
cardiac cycle (action potentials)
– Depolarization causes contraction of the heart
– Repolarization causes relaxation
– Depolarization of the atria produces first peak;
depolarization of ventricles produce second, larger
peak
– Repolarization produces third peak
Blood Vessels
• The walls of arteries and veins have three
layers:
– Epithelium (innermost layer)
– Smooth muscle with elastin fibers
– Connective tissue (outermost layer)
• Arteries have thicker walls than veins;
arterioles have less elastin than arteries
• Capillaries only have the inner epithelium
layer (site of gas/nutrient/waste exchange)
Blood Vessels
Blood Vessels: Capillaries
• Blood flows slower through capillaries
because of larger total cross-section
– Enables materials to be exchanged
– By the time blood reaches the end of the
capillary, it releases some of its oxygen and
nutrients and picks up CO2 and waste
products
Blood Vessels: Veins
• Less muscle is needed in veins because
the pressure in veins is only ~1/10th of that
in the arteries
• Venous pressure alone is not sufficient to
return blood to the heart
• Thus, skeletal muscles surrounding the
veins contract to move blood by squeezing
the veins; the venous pump
Blood Vessels: Veins
• Internal valves in veins (venous valves)
ensure that blood continues to heart;
operate as one-way swinging doors
• Skeletal muscles on outside of vein
contracts, pushes against vein, causing
blood to flow towards heart; this opens
one-way valves up, pressure is released
and cannot return through valves (oneway transport to heart)
Blood Vessels: Veins
Components of Blood
• Blood serves to transport, regulate, and
protect
• Blood is composed of a fluid-matrix
known as plasma, within which reside
different cells and other ‘elements’
– Blood cells (red & white) and platelets
– Ions, proteins
– Nutrients, wastes and hormones
Components of Blood
• Red blood cells, Erythrocytes
– Most numerous: 5 million/mL
– Transport O2 and CO2 (hemoglobin in
vertebrates)
– Mammalian erythrocytes lack nuclei
Components of Blood
• White blood cells; Leukocytes
– Fewer in number; 1-2 for every 1000
erythrocytes
– Larger in size, and have nuclei
– Not confined to blood as erythrocytes are; can
migrate out of blood into surrounding
interstitial fluid or into the lymphatic system –
where your body fights infection
– Function in body’s defense
Components of Blood
• Platelets; Thrombocytes
– Cell fragments that pinch off from larger cells in the
bone marrow
– Following injury to a blood vessel, platelets release
clotting factors (proteins) into the blood
– When platelets contact collagen, they stick to it ;
results in release of several factors which activate
other platelets
• Conversion of fibrogen (soluable) to fibrin (insoluable); fibrin
threads cross-link, connecting platelets and trapping other
cells in network = blood clot
Formation of Blood Clot
Prothrombin
Thrombin
Fibrinogen
Thrombin
Fibrin
1. Vessel is
damaged,
exposing
surrounding
tissue to blood.
2. Platelets
adhere and
become
sticky, forming
a plug.
3. Cascade of
enzymatic
reactions is
triggered by
platelets,
plasma factors,
and damaged
tissue.
4. Threads of
fibrin trap
erythrocytes
and form
a clot.
5. Once tissue
damage
is healed,
the clot is
dissolved.
Blood Types
• Three alleles denote presence of specific
glycoproteins on the surface of blood cells
– Type A, B, O (and AB)
– Each contains antibodies of other types
• Rh factor – presence or absence of Rh
protein
– Positive (have) or negative (do not have)
– Negatives will form antibodies against Rh
blood upon exposure