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BIOLOGY OLYMPIAD
Oct. 31, 2008
Chapter 42: Circulation and Gas Exchange
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The circulatory system ensures that no substance must diffuse over far lengths
Gastrovascular cavities are enclosed by a body wall and serve for digestion and
distribution of substances
o This is the circulatory system for hydras, cnidarians, planarians, and some
flatworms
o Bathed by fluids
o Digestion begins in cavity, and then diffuse a short distance to outer layers
Open and closed circulatory systems are used by animals with many cell layers
o Open circulatory system: has hemolymph as a general body fluid, which is
pumped into sinuses (spaces surrounding organs)
 For insects and some arthropods, they have a tubular heart
 Less costly in terms of energy used (lower hydrostatic pressure) and less
energy to build and maintain (no blood level system)
o Closed circulatory system: has blood vessels not part of interstitial fluid, and the
heart pumps blood into branching vessels
 For earthworms, squids, octopuses, and vertebrates
 More effective at transporting fluids and more suited for active organisms
Cardiovascular system: closed circulatory system used by humans and some vertebrates
o Three basic components: blood, blood vessels, and heart
o One or two atria: chambers that receive blood
o One or two ventricles: pump blood out
o Three main kinds of blood vessels:
Arteries
Capillaries
Veins
Blood vessels that carry
blood away from the heart
Microscopic vessels with
thin, porous walls. Chemical
exchange occurs here.
Blood vessels that return
blood to the heart
o Fish: One atrium, one ventricle. The gills are where the blood picks up oxygen
and disposes of CO2
o Frogs: Two atria, one ventricle.
o Pulmocutaneous circuit: Gas exchange tissues (skin and lungs)
o Systemic circuit: Oxygen-rich blood is carried to all body organs and
returned to the right atrium
o Birds/Mammals: Two atria, two ventricles
o No mixing of oxygen-rich and oxygen-poor blood.
o The left side deals with oxygen-rich blood (pulmonary)
o The right side deals with oxygen-poor blood (systemic)
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Mammalian Circulation Pathway
o Right ventricle pumps blood into lungs through the pulmonary arteries, which
lead into the capillaries of the left lung (where it takes in O2 and releases CO2)
BIOLOGY OLYMPIAD
Oct. 31, 2008
o Once they have taken in O2, blood returns to lungs from the pulmonary veins into
the left atrium
o The O2 rich blood goes into the left ventricle and is pumped into the body tissues.
o The aorta allows blood to leave the left ventricle by leading to arteries, which lead
into the capillary beds in the forelimbs
o The blood continues to the legs and abdomen, and finally back to the head neck
and forelimbs after the O2 has moved to the tissues
o The O2 poor blood flow to the anterior vena cava, and the posterior vena cava
drains blood from the hind limbs
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o The vena cavas allow the blood to flow back into the right ventricle
Human Heart:
o Contracts: pumps blood (systole), retracts: chambers fill with blood(diastole)
 One cycle = Cardiac cycle
o Cardiac output: volume of blood per minute that is pumped, which depends on the
rate of contraction (heart rate) and stroke volume (blood pumped by left ventricle)
o Atrioventricular (AV) valve: contractions keep blood from flowing back into atria
o Semilunar valves: contractions open the valves, allowing blood to exit through the
aorta (systemic) and pulmonary artery (pulmonary); stops blood from flowing
back into the ventricles
o Sinoatrial (SA) node/pacemaker: set rate and timing of contractions
o Blood pressure: hydrostatic force exerted by blood against the wall of a vessel
 The reason blood moves from heart to the arteries to the capillary beds
Lymphatic system
o Some substances are lost from capillaries, and they are returned to the blood via
the lymphatic system
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Oct. 31, 2008
o Fluid: lymph
o Lymph nodes: filter the lymph – filled with white blood cells to help defend the
body against infection
Plasma: liquid matrix in which blood is suspended in
o 90% water
o Inorganic salts present as dissolved ions
o Plasma proteins: buffer pH changes, contribute to blood thickness
Red blood cells (erythrocytes): most numerous blood cells
o Lack nuclei
o Lack mitochondria
o Carry oxygen; must diffuse across the plasma membranes
o Contains hemoglobin: oxygen-carrying protein containing iron (oxygen binds
with hemoglobin)
White blood cells (leukocytes)
o Monocytes, neutrophils, basophils, eosinophils, and lymphocytes
 Fight infections
Platelets
o Fragments of cells
o Blood clotting
Gas exchange: uptake of O2 and discharge of CO2 necessary for cellular respiration
o Respiratory medium: source of O2 (usually air)
o Respiratory surface: part of organism where gases from environment are
exchanged (supply O2 and expel CO2); occurs entirely through diffusion, thus
tend to be thin and have large surface area
 Gills for fish
 Ventilation: increasing flow of respiratory medium over
respiratory system (ventilated by current of water tat enters the
mouth)
 Blood flows in opposite direction of the water
o Countercurrent exchange: diffusion gradient favoring
transfer of oxygen from the water to the blood
 Tracheal system for insects
 The largest tubes (tracheae) open to the outside, while fine
branches extend all throughout the body
 Open circulatory system is not involved with transporting O2 and
CO2
 Lungs for amphibians and vertebrates
 Restricted to one location
 Circulatory system transports gases to lungs
 Have dense nets of capillaries just under the epithelium which
represents the respiratory surface
 Mammalian lungs
 Food is swallowed, larynx moves upward and allows food to be
digested, all the while the glottis is open (windpipe opening),
which allows breathing to occur
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Oct. 31, 2008
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Breathing
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Air passes into the trachea (windpipe), and forks into two bronchi,
each leading into a lung. The bronchus branches into bronchioles
(smaller and thinner tubes), end in clusters of air sacs called
alveoli.
There the air dissolved across the epithelia and carry out gas
exchange. O2 dissolves and diffuses into the capillaries, while CO2
diffuses in the opposite direction
Positive pressure breathing: (amphibians) air travels through nostrils when
oral cavity floor is lowered, and air is forced down trachea as it rises. Air
is forced out of the lungs by elastic recoil of lungs and compression of
muscular body wall (pushes air into lungs)
 Negative pressure breathing: pulls air into lung
 Lung volume increases due to contractions of rib muscles and
diaphragm (sheet of skeletal muscle that forms the bottom wall of
the chest cavity)
o Contraction of rib muscle expands by pulling ribs upward
and breastbone outward while chest cavity expands and
diaphragm contracts and falls
o Tidal volume: volume of air mammal inhales and exhales
with each breath
 Vital capacity: maximum tidal volume
 Residual volume: amount of air remaining in your
lungs (cannot collapse alveoli completely)
Breathing control center
o Located in medulla oblongata and the pons
 Breathing control center sets rhythm of breathing (in medulla), and is
controlled (pons)
 Nerves send impulses to cause contraction and inflation
 Medulla’s control center also regulates blood CO2 level
 Sensors in the walls of aorta and carotid arteries detect changes in O2
levels and coordinate with medulla (increase breathing when levels are
low)
Respiratory pigments: O2 bound to certain proteins to be transported (instead of dissolved
form)
o Greatly increase amount of O2 carried
o Hemocyanin (found in arthropods and mollusks)
Bohr shift: drop in pH lowers affinity of hemoglobin for O2
o CO2 reacts with water to form H2CO3, which induces hemoglobin to release more
O2