Circulation and Gas Exchange
Chapter 42
Overview: Trading with the Environment
• Every organism must exchange materials &
energy with environment
• Exchanges ultimately occur at the cellular
level
• In unicellular organisms, exchanges occur
directly with environment
In multicellular organisms, direct exchange with
environment not possible with all internal cells
Diffusion always at cellular level BUT diffusion
over long dist (lung to internal cells) too slow
Therefore developed physiological systems
specialized for transport (circulatory) & exchange
(respiration)
Concept 42.1: Circulatory systems
reflect phylogeny
• Diffusion alone not adequate for transporting
substances over long distances within animals
• Therefore complex animals have internal
transport systems (circulatory systems) that
circulate fluid & connect the organs of
exchange with the body cells for exchg
Invertebrate Circulation
• The wide range of invertebrate body size & form
plus differences in environmental pressures =
diversity in circulatory systems
Gastrovascular
cavities
Open and Closed Circulatory Systems
Complex animals with many cell layers have:
- open circulatory system
- closed circulatory system
Both have 3 components in common:
1. circulatory fluid (blood or hemolymph
2. set of tubes (blood vessels)
3. muscular pump (heart provides pressure
to move fluid)
In insects, other arthropods, & molluscs blood
bathes organs directly in open circ system
no distinction between blood & interstitial fluid;
general body fluid = hemolymph
Closed circulatory system = blood confined to vessels &
distinct from interstitial fluid
Closed systems more efficient at transporting
circ fluids to tissues & cells (worm is an example)
Vertebrate Circulation
Humans & other vertebrates blood flows in
closed circulatory system (blood vessels & 2- 4chambered
heart) = cardiovascular system
- arteries: carry blood to capillaries, sites of
chemical & gas exchange between blood
& interstitial fluid (single cell layer that
gas exchanges)
- veins: return blood from capillaries to heart
Fishes
• 2 main chambers: ventricle & atrium
• Blood pumped from the ventricle travels to the
gills, where it picks up O2 and disposes of CO2
Amphibians
• Frogs and other amphibians have a threechambered heart: 2 atria & 1 ventricle
R atrium
L atrium
Ventricle
Reptiles
Reptiles have double circulation, with a
pulmonary circuit (lungs) and a systemic
circuit
One can say that the reptile heart
has 3 chambers, 2 atria & 1,
partially divided, ventricle. Or one
may argue that reptiles have 4chambered hearts with 2 atria & 2
ventricles, but the wall between
the ventricles is incomplete.
Mammals and Birds
In all mammals & birds, ventricle divided into separate
R & L chambers
L side : pumps & receives only O2-rich blood
R side: receives & pumps only O2-poor blood
A powerful fourchambered heart was
an essential adaptation
of the endothermic
way of life
characteristic of
mammals and birds
Endotherms need 10x
energy as equal-sized
ectotherm so must
deliver more via blood
Concept 42.2: Double circulation in mammals depends on
anatomy & pumping cycle of heart
The human
circulatory
system serves
as a model for
exploring
mammalian
circulation
Mammalian Circulation: The Pathway
• Heart valves dictate a one-way flow of blood
through the heart
• Blood begins its flow with R ventricle pumping
blood to lungs
• In lungs, blood loads O2 & unloads CO2
• O2-rich blood from lungs enters heart at L
atrium & into L ventricle where then pumped
to body tissues
• Blood returns to heart at R atrium
The
Mammalian
Heart:
A
Closer
Look
provides a better understanding of dbl circ
Valves
Cardiac cycle
- contraction, or
pumping, phase =
systole
- relaxation, or
filling, phase =
diastole
Heart sounds, heard with stethoscope,
caused by closing of valves.
“lub-dup, lub-dup”
Lub=close AV
Dub=close semilunar
Heart murmur = defect in valve
detectable as a hissing sound when
blood squirts backward through it
Rheumatic fever
can cause
Heart rate = pulse = beats per minute
Cardiac OP = volume blood pumped into systemic
circ per minute
Stroke vol = amt blood pumped by L ventricle
per contraction
________________________________________
Av stroke vol … 75 ml
Av ht rate ……..70/min
Cardiac OP: 75 * 70 = (5,250 ml) 5.25 L/min
Heart’s Rhythmic Beat
Cardiac muscle stims self = contract without signal from nervous syst
Pacemaker influenced by nerves, hormones, body T, & exercise
Impulses during cardiac cycle can be recorded as an electrocardiogram (ECG or EKG)
Concept 42.3: Physical principles govern
blood circulation
Structure/function: arteries, veins, & capillaries
Velocity blood flow slowest in capillary beds
- arteries: thick wall + muscle
- veins: blood flow result muscle action; valves
5,000
4,000
3,000
2,000
1,000
0
50
40
30
20
10
0
Systolic
pressure
Venae cavae
Veins
Venules
Capillaries
Arterioles
Diastolic
pressure
Arteries
120
100
80
60
40
20
0
Aorta
Pressure (mm Hg)
Velocity (cm/sec)
Area (cm2)
- Exchange materials & gases at capillaries
- BP at capillaries pushes fluid out into tissues
Fluid in tissues & 85% reenters at venous end
Remaining 15% returned via lymphatic system
Critical exchange between blood & interstitial fluid
takes place across thin endothelial walls capillaries
Diff between BP & π drives fluids out capillaries at arteriole end &
into capillaries at venule end
Fluid Return by the Lymphatic System
• The lymphatic system returns fluid to the body
from the capillary beds
• This system role in body defense
• Fluid reenters the circulation directly at the
venous end of the capillary bed & indirectly
through the lymphatic system
5 types Leukocytes
Concept 42.4: Blood is a connective
tissue with cells suspended in plasma
Cellular Elements
Suspended in blood plasma
- red blood cells (erythrocytes) transport O2
- white blood cells (leukocytes) body defenses
- platelets = frags cells & involved in clotting
Stem Cells & Replacement of Cellular Elements
pluripotent stem cells in red marrow of bones
erythropoietin
Blood Clotting
Cascade rxs (fibrinogen to fibrin) = clot
hemophilia
thrombus
Cardiovascular Disease
disorders of heart & blood vessels
account for > half deaths in United States
Artheroscloresis: accumulation cholesterol in
arteries
Chlosterol transported as lipid:prot particles
LDL (low density lipoprot) = “BAD” cholesterol
HDL (high density lipoprot) = “GOOD” cholesterol
Satd fats = ↑ tendency artherosclerotic plaques
• Hypertension, or high blood pressure,
promotes atherosclerosis and increases the risk
of heart attack and stroke
• A heart attack is the death of cardiac muscle
tissue resulting from blockage of one or more
coronary arteries
• A stroke is the death of nervous tissue in the
brain, usually resulting from rupture or
blockage of arteries in the head (can be side
effect of heart attack)
Concept 42.5: Gas exchange occurs across
specialized respiratory surfaces
Gas exchange = uptake O2 from environment &
discharge CO2 (from cell resp) to environment
Animals require large, moist respiratory surfaces
for adequate diffusion of gases between their
cells & the respiratory medium…. air for terrestrial
animals and water for most aquatic animals
Respiratory
medium
(air or water)
Organismal
level
O2
CO2
Respiratory
surface
Circulatory system
Cellular level
Energy-rich
fuel molecules
from food
Cellular respiration
Structure of respiratory surface depends on size of
organism & whether it lives in water or on land
ATP
A. Water Habitat
- Have gills = outfoldings of body surface suspended in water
- Water [O2] low so special processes to ↑ efficiency of exchg
B. Terrestrial Habitat
Tracheal system of insects consists of tiny
branching tubes that penetrate the body
The tracheal tubes supply
O2 directly to body cells
Lungs
Most terrestrial vertebrates have internal lungs
system of branching ducts conveys air to lungs
Air inhaled through the nostrils passes through
pharynx into trachea, bronchi, bronchioles, &
dead-end alveoli, where gas exchange occurs
Mammals ventilate their lungs by neg pressure
Inhale = ↑vol lung = pulls air into the lungs
Exhale = musc relax & elastic fibers retract lung
Main breathing control center in brain which
regulates rate & depth of breathing in response
to pH changes in Cerebrospinal fluid
Sensors in aorta &
carotid arteries
monitor O2 &
CO2 concentration in
blood = exert
2ndary control over
breathing
Gases diffuses
from higher
partial pressure
(conc) to lower
partial pressure
Oxygen Transport
Hemoglobin reversibly binds O2
- loads O2 in lungs
- unloads it in other parts body
Drop in pH
lowers
affinity of
hemoglobin
for O
Carbon Dioxide Transport (mostly as HCO3)
CO2 diffuses into
Red blood cells
where + H2O forms
carbonic acid
which dissoc into
H+ & HCO3H+ binds to
Hemoglobin
HCO3- diffuses into
plasma & carried to
lungs
In lungs, reverse
occurs
CO2 from
respiring cells
diffuses into
blood plasma &
then into red
blood cells
CO2 from
tissues carried
as HCO3- in
plasma of
blood &
released in
lungs
Baby steals O2 from mom’s blood