Circulation
and Gas
Exchange
AP Biology
Invertebrate Open Circulatory System
• Arthropods and mollusks
• Blood and interstitial fluid
are the same (hemolymph)
• Tubular heart pumps
hemolymph through a dorsal
vessel out into sinuses
• Hemolymph bathes cells and
allows for exchange of
nutrients
• When heart relaxes,
hemolymph flows back into
vessels through ostia
• Body movements squeeze
sinuses to aid circulation
Invertebrate Closed Circulatory System
• Annelids (earthworms) have
closed circulatory system
• 5 Aortic arches or ‘hearts’
force blood down to the
ventral vessel, which carries
blood to posterior and up to
complete the circuit
• Blood carries O2 and CO2
between cells and the skin
where gas exchange takes
place
• Blood also circulates
nutrients from digestive
tract to the rest of the body
Vertebrate Circulatory
System
• Closed system with a chambered heart that
pumps blood through arteries that lead away
from the heart to capillaries.
• Capillaries—small vessels in tissues where
exchange of materials take place
• Blood is carried back to heart through veins
Fish
• 2 chamber heart
– One artrium
– One ventricle
• Blood from ventricle
picks up O2 in gills, then
is collected into a large
artery to pass directly to
the rest of the body
before returning to the
atrium
Amphibian
• 3 chamber heart
– Two artria
– One ventricle
• Ventricle pumps blood to both the
lungs and the rest of the body
simultaneously through 2 different
major arteries
• Allows oxygenated blood from
lungs and deoxygenated blood
from the body to mix in the
ventricle before it is delivered
back to the body
• Allows higher arterial pressure in
blood pumped to vessels
Birds and Mammals
• 4 chamber heart
– Two artria
– Two ventricle
• Higher metabolic need met by
division of heart into 2 pumps
• Right atrium and ventricle pumps
deoxygenated blood to lungs
through pulmonary circulation
• Left atrium and ventricle pumps
oxygenated blood to the rest of the
body through systemic circulation
• Avoids mixing of oxygenated and
deoxygenated blood
• Allows high arterial pressure
required for quick delivery
Human Heart
•
•
•
•
Located beneath the sternum
About the size of your fist
Composed mostly of cardiac muscle tissue
2 atria have thin walls and function as
collection chambers for returning blood
• 2 ventricles have thick, powerful walls that
pump blood to the organs
Four valves function to prevent backflow of blood
–Atrioventricular
valves
• Prevent backflow
when ventricles
contract
–Semilunar valves
• Prevent backflow
when ventricles
relax
Cardiac Cycle
–Systole—heart
muscles contract
and the chambers
pump blood
–Diastole—heart
muscles relax and
fills with blood
–Cardiac output—
volume of blood
per minute that the
left ventricle
pumps into the
systemic circuit
Control of Heart Rhythm
• Sinoatrial (SA) node—cells are selfexcitable—generate electrical impulses
• Cardiac muscle cells are electrically
coupled by intercalated discs b/w cells
Control of Heart Rhythm
• Atrioventricular (AV) node—receives signal
from atria, delays 0.1 sec, and then sends
signal throughout walls of ventricle via the
bundle branches and Purkinje fibers
Blood Vessels
• Arteries—carry blood away from the heart
to the tissues
– Branch into smaller arterioles, which supply
blood to tissues via capillaries
– Thick-walled, muscular (smooth muscle), and
elastic, transporting blood at high pressure
– Blood is oxygenated, except the pulmonary
artery that carries deoxygenated blood from
tissues to lungs through the right atrium and
ventricle
• Veins—carry blood to the heart from the capillaries
– Capillaries branch into larger venules, which supply blood to
veins and back to the heart
– Thin-walled, little smooth muscle, transporting blood at low
pressure, and contain many valves to prevent backflow
– Veins have no pulse and carry deoxygenated blood, except
the pulmonary vein which carries oxygenated blood from
the lungs
– Skeletal muscle contraction aids in systemic circulation
• Capillaries—thinwalled vessels (simple
squamous)
• Permit exchange of
materials between
blood and body cells
• Controlled by
precapillary
sphincters
• Capillaries
• Fluid containing water
with nutrients and
hormones seep from
capillaries into tissues,
driven by pressure
• Cells and proteins are
retained in the
capillaries and draw
water back into the
capillaries by osmosis
• Excess fluid in tissue
can enter lymphatic
system to be filtered
and cycled back to the
circulatory system
Capillary Exchange
Regulation of Blood Flow
• Regulated to match the metabolic needs
• Smooth muscle in walls of arterioles
constrict to reduce blood flow to capillaries
• Smooth muscle relaxes when blood leaving
capillaries is low in O2, allowing more
blood to flow through capillary bed
Regulation of Blood Flow
• Secretion of epinephrine by adrenal glands  heart
rate and constricts arteries to  arterial pressure
• Angiotensin secreted from the kidney acts on
smooth muscle in the arterioles and arteries to
cause constriction and  arterial pressure
• Vasopressin secreted by posterior pituitary in
response to stretch sensors causes constriction in
arterioles and arteries to  arterial pressure
Erythrocytes: Red Blood Cells
• Primary function to carry
oxygen
• Production in red bone
marrow of bones stimulated
by erythropoietin (produced
by kidneys)
• Mature cells lack nuclei and
circulate ~4mos.
• Mature cells lack
mitochondria—produce ATP
without oxygen through
glycolysis
• Contain hemoglobin-pigment
that binds oxygen
Erythrocytes: Red Blood Cells
• Red blood cells (rbc)
manufacture 2 antigens,
antigen A (Blood Type A)
and antigen B (Blood
Type B)
• Plasma carries antibodies
for the antigens that are
not present on the rbcs
Leukocytes: White Blood Cells
• Involved in immune
functions in the body
– Phagocytes—engulf
bacteria
• Neutrophils—1st to arrive at
site of inflammation
• Macrophages and
Monocytes
– Lymphocytes (B and T
cells)—immune response
• B cells produce antibodies
• Helper T cells kill infected
cells
Leukocytes: White Blood Cells
• Platelets—cell
fragments produced
in marrow
– Involved in blood
clotting mechanism
– Activation of
protease thrombin
cleaves fibrinogen
protein in the blood
to make fibrin that
polymerizes to for a
net across the
wound, trapping
more cells and
blocking the flow of
blood
Cardiovascular Disease
• Heart attack—death of
cardiac muscle tissue
resulting from artery
blockage of one or more
coronary arteries which
supply oxygen to the heart
• Stroke—death of nervous
tissue in the brain resulting
from artery blockage in the
head
Cardiovascular Disease
• Atherosclerosis—plaques develop on inner
walls of arteries
– Forms where smooth muscle thickens
abnormally and is infiltrated by fibrous
connective tissue
• Arteriosclerosis—hardening of the arteries
by calcium deposits
• Hypertension—high blood pressure
Cardiovascular Disease
• Hypertension and atherosclerosis have
genetic component and environmental
component (smoking, lack of exercise, high
fat and cholesterol diet)
– Low-density lipoproteins (LDLs)—add
deposits of cholesterol in arterial plaques
– High-density lipoproteins (HDLs)—may reduce
cholesterol deposition
• Exercise increases HDL concentration
• Smoking increases LDL concentration
Gas
Exchange
• Involves both
Respiratory
system and
Circulatory
system
Invertebrate Gas Exchange
• Water contains less oxygen than air
• As an adaptation, most aquatic
animals have gills
• Total surface area of gills is often
larger than that of the rest of the
body
Invertebrate Gas Exchange
• Arthropods respiratory system consists of a
series of respiratory tubules, tracheae
– Open to the outside in the form of pairs of
orifices called spiracles
– Tracheae subdivide into smaller and smaller
branches, to make close contact with most cells
– Direct diffusion through tracheae is one factor
that limits body size in arthropods
Fish
Countercurrent Exchange
• Maximizes exchange of gases between
blood inside the gills and the water flowing
over the gills
• Blood flows through capillaries in direction
opposite of water flowing across gills
Amphibians
• Simple air sac with little surface area
• Must supplement gas exchange in lungs
with exchange across the thin moist skin
http://www.answersingenesis.org/home/area/magazines/images/v22frogR.jpg
• Air sacs permit a
unidirectional flow of
air through the lungs
• Unidirectional flow
means that air moving
through bird lungs is
largely 'fresh' air &
has a higher oxygen
content
http://people.eku.edu/ritchisong/RITCHISO/birdrespiration.html
http://numbat.murdoch.edu.au/Anatomy/avian/fig3.2.GIF
Avian Respiration
Air Flow through Avian System
1.
2.
3.
4.
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On first inhalation, air flows through the trachea & bronchi &
primarily into the posterior (rear) air sacs
On exhalation, air moves from the posterior air sacs & into the lungs
With the second inhalation, air moves from the lungs & into the
anterior (front) air sacs
With the second exhalation, air moves from the anterior air sacs
back into the trachea & out
Air flow is driven by changes in pressure within the respiratory
system:
So, it takes two respiratory cycles to move one 'packet' of air
completely through the avian respiratory system
http://people.eku.edu/ritchisong/RITCHISO/birdrespiration.html
Ventilating Lungs: Breathing
Automatic Control of Breathing
• Breathing control center
in brain = medulla
oblongata and pons
• Monitors CO2 levels in
blood by changes in pH
– CO2 + H2O  Carbonic acid
–  pH =  depth and rate of
breathing
• altitude =  O2 levels
• Sensors in aorta and
carotid arteries detect and
signal control center to 
breathing rate
Loading and
Unloading of
Respiratory Gases
Oxygen Transport
• Oxygen carried by respiratory pigments
– Invertebrates utilize hemocyanin—Cu is the
oxygen-binding component
– Vertebrates utilize hemoglobin—four heme
groups surrounding an Fe atom
• Can carry four oxygen atoms
Oxygen Dissociation Curves for
Hemoglobin
Bohr Shift:
Active tissue releases CO2
CO2 reacts with H2O to form
carbonic acid
This ↓ pH which induces
hemoglobin to release more O2
Carbon Dioxide Transport
• Hemoglobin transports CO2 and assists with
buffering the blood—prevents dramatic
changes in pH
• 7% CO2 released by cells transported as
dissolved CO2
• 23% binds to amino group of hemoglobin
• 70% transported in form of bicarbonate ions
in red blood cells