Chapter 23
Facilitating Exchanges
 Circulatory systems ensure O2, CO2, nutrients, and
wastes get to their specific sites in the body
 Important for animals to large to survive by diffusion
alone
 Cnidarians and flatworms have gastrovascular cavities
that serve in digestion and distribution
 Cells can exchange directly with water surrounding them
 Animals with multiple layers of cells need a true
circulatory system
 Muscular pump (heart) and circulatory fluid (blood)
Molecular Exchange
 O2 and nutrients must
enter cells
 CO2 and wastes must exit
 Larger organisms have
smaller outer surfaces than
inner
 All cells must be in an
aqueous environment
 Folds and alternate
structures within to
facilitate
Circulatory Systems
 Direct exchange not between blood and body cells
 Cells bathed in interstitial fluid that diffusion must pass
 Open circulatory system
 Many invertebrates including molluscs and all arthropods
 Closed circulatory system
 Often called a cardiovascular system
 Earthworms, squids, octopuses, and vertebrates
Open Circulatory System
 Fluid pumped through
open-ended vessels out to
cells
 No distinction between
blood and interstitial fluid
 Body movements circulate
fluid to allow exchange
 Heart with pores that
allows fluid return and
prevents backflow
 Respiratory exchange
through tracheal system
Cardiovascular System
 Blood confined to vessels
 Separate from interstitial
fluid
 3 kinds of vessels
 Arteries (red) blood Away
from heart
 Veins (blue) blood to heart
 Capillaries transport blood
between the 2
 Heart with atrium and
ventricle pumps blood to
body cells
 Arteries to arterioles to
capillaries in capillary beds to
venules to veins back to heart
Cardiovascular System Evolution
 Single Circuit pumps blood to capillaries which
diffuses to body tissues
 Double circulation pumps blood a second time after
losing pressure in the capillaries
 Pulmonary circuit carries blood between the heart and
lungs
 Systemic circuit carries blood between the heart and rest
of the body
Single Circuit
 2 chambered heart
 Blood to gill capillaries
where pressure is
reduced considerably
 Flow maintained by
organism’s movements
 Pressure to low for
complex circulation
Double Circulation
 Amphibians have 3
chambered heart
 Pulmocutaneous circuit
because gas exchange in
lungs and across skin
 Mixing occurs, but most
blood to proper location
 Birds and mammals have 4
chambered hearts
 Supports higher metabolic
rates
 Different ancestral
evolution so demonstrates
convergent evolution
Human Cardiovascular System
 R. ventricle to lungs via
pulmonary arteries
 CO2 and O2 exchange
 Pulmonary veins back to L.
atria to L. ventricle
 Through aorta to systemic
circuit
 Branches to upper body and
lower body separately
 O2 poor blood back to R.
ventricle via S. and I. vena
cava
(heart to lungs to heart to
body tissue to heart)
Cardiac Cycle
 Sequence of pumping and
filling of the heart
 Heart pumps O2 poor
blood to lungs and O2 rich
blood to body
 Diastole=entire heart
relaxed, ventricles fill with
blood
 Systole=atria then
ventricle contraction
 Left stronger because
blood to body, but volume
is same in both
sides=cardiac output
The Beating Heart
 Heart rate and cardiac rhythm can vary
 Age and fitness can effect
 Both increase with increasing activity levels
 Blood flow controlled by internal valves
 Open when pushed from behind and close when pushed
from in front
 Heart beat sounds = lub-dub

AV and semilunar valves’ closing respectively
 Heart murmur sound when blood squirts backwards
Beating to its Own Rhythm
 Cardiac muscle tissue cycle without neural input
 Pacemaker sets the contraction rate
 AV node coordinates, delay to ventricle
 Electric shock can be used to reset pacemaker during a heart attack
 Artificial pacemaker when self system fails
Cardiovascular disease
 Disorders of heart and blood vessels
 Heart attack is the damage or death of cardiac tissue
from blockage of coronary arteries
 Stroke is death of brain tissue from vessel blockage to
the head
 Most caused by arterosclerosis, or plaque build up,
which narrows vessel openings
 Clots trapped or blood flow is slowed
 Anti-inflammatories, angioplasty, and clot-dissolving
 Tendency to be inherited, but smoking can increase
while exercise and low cholesterol diets can decrease
Blood Vessel Functions
 Must connect with all
body tissues
 Remarkable length,
close enough for
diffusion to occur
 Into interstitial fluid
first
 Transport blood,
nutrients, and wastes to
disposal organs
 Role in homeostasis and
the environment of cells
Blood Vessel Structure
 Capillaries
 Thin walls of single layer epithelial tissue
 Wrapped in a basal lamina
 Larger structures
 Same epithelial structure, but reinforced
 Supported by elastic fiber layer and smooth muscle
 Arteries and arterioles

Thicker and sturdier to accommodate high pressure from heart
 Veins and venules


Blood to heart at lower pressure
One way valves to prevent backflow
Blood Flow
 Blood pressure is the force blood exerts against vessel
walls
 Pumped to arteries faster than it can flow = stretching
of vessels, detected as pulse
 Pressure reduces from arteries to capillaries as
resistance from vessel walls decreases
 Smaller, but more numerous vessels
 Relaxing muscles allows vessel dilation = drop pressure
 Pressure almost zero at veins
 1 way valves and muscle to propel back to heart
Digestive System
Muscle Control
 Every part of body has
blood supply at all times
 Certain areas always full,
others are rationed by
need
While eating
 Smooth muscle controls
arteriole flow
 Precapillary sphincters
control
 Thoroughfare channel is
always open
 Relaxed vs. contracted
While exercising
Capillaries
 Only vessels that can allow diffusion between blood
and interstitial fluid
 Exchange of substances by diffusion (O2 and CO2),
carried by endocytosis and released by exocytosis, or
leaks in wall (water, sugars, and salts)
 Direction of movement depends on osmotic and blood
pressure differences
 Arteriole end blood pressure drives fluid out of capillary
 Venous end blood pressure drops so osmotic drives into


Fluid that leaves one end generally reenters at other
Rest returned via lymphatic system
Blood Composition
RBC Count
 Set number needed for healthy organisms
 Broken down and recycled every 3-4 months
 Fe returned to bone marrow to form new RBCs
 Low RBC count = anemia
 Excessive tiredness due to lack of O2
 Most commonly due to low Fe (women more likely); also blood
loss, vitamin and mineral deficiency, or cancers
 Negative feedback sensitive to O2
 Low O2, kidneys produce erthropoietin (EPO) to stimulate bone
marrow production of RBCs
 Increased RBC production in individuals at high altitudes
 Connections to athletic training, blood doping, and artificial EPO
injections
Blood Clots
 Blood platelets and plasma protein fibrinogen prevent death
from minor cuts, enable clotting
 Upon damage vessel constricts to reduce blood loss
 Platelets adhere to epithelium and form a sticky plug to halt
blood loss
 Clotting factors released from plug to form reinforced patch
 Fibrinogen converted to fibrin which traps other blood cells
Stem Cells
 Unspecialized cells in red marrow of bones that can
differentiate into different blood cells
 Lymphoid stem cells produce lymphocytes for immune
system
 Myeloid stem cells produce RBCs, WBCs, and plaelets
 Formed in early embryo and make all blood cells for life
Leukemia
 Cancer of white blood cells or leukocytes
 Protect against infections and cancers
 Cells become cancerous, grow uncontrollably, and crowd
RBCs and platelets
 Severe anemia and impaired clotting results
 Usually fatal unless treated
 Not all responsive to radiation and chemo
 Bone marrow transplant, often from a sibling


Lifelong treatment with drugs to avoid rejection of cells
Can treat infected marrow to remove most cancer cells and re-inject
 Umbilical cord blood has potential, but unsuccessful so far