Download CHAPTER 52: CIRCULATION

CHAPTER 49: The Circulatory and Respiratory Systems
WHERE DOES IT ALL FIT IN?
Chapter 49 builds on the foundations of Chapter 32 and provides detailed information about animal
form and function Students should be encouraged to recall the principles of eukaryotic cell structure
and evolution associated with the particular features of animal cells. Multicellularity should also be
reviewed. The information in chapter 49 does not stand alone and fits in with the all of the chapters
on animals. Students should know that animals and other organisms are interrelated and originated
from a common ancestor of all living creatures on Earth
SYNOPSIS
Simple, small organisms transport nutrients and gases directly across the membrane of each cell.
Other organisms are too large and complex for such exchange and need a circulatory system to
transport nutrients, gases, and other materials to their cells and remove waste materials from
those cells to disposal organs. In open systems there is no distinction between the circulating
fluid and the body fluid. In a closed system the circulating fluid is restricted to tubular vessels
throughout the animal. In vertebrates, oxygen diffuses into the blood in the gills or lungs,
accumulates in the erythrocytes and is carried to all tissues. Waste carbon dioxide is collected at
metabolizing tissues and transported back to the gills or lungs for release. Nutrients enter the
circulation through the wall of the small intestine and are transported to the liver. The blood
transports nutrients to the tissues while metabolic wastes are collected from them and carried to
the kidneys for removal. Hormones are also transported through the circulatory system to various
target tissues. Heat produced in body tissues is distributed through the bodies of homeothermic
birds and mammals. Plasma proteins and platelets are involved in the clotting mechanism that
protects against blood loss. White blood cells provide immunity against disease.
Blood is composed of various metabolites, waste, salts, ions, hormones, nutrients, and proteins
in solution in the plasma. Circulating cells include erythrocytes, granular and non-granular
leukocytes, and platelets. Arteries carry blood away from the heart; veins carry it back.
Capillaries lie between the two and are the location of exchange with individual cells since they
have only a single thin layer if endothelial cells. The walls of all other blood vessels are
composed of four layers, an innermost endothelium, a layer of elastic fibers, a layer of smooth
muscle, and an outer layer of connective tissue. The muscle layer of arteries and arterioles is
thicker than that in venules and veins. As a result the resistance and flow of blood in these
vessels changes through vasoconstriction or vasodilation. The velocity of the blood in the
capillaries is less than in the arteries due to differences in overall vessel area coupled with a
constant flow rate. The lymphatic vessels constitute an open system to collect blood fluid lost to
the tissues and return it to the closed circulation.
The vertebrate heart originated as a simple peristaltic pump in early chordates. Fish evolved the
first true heart composed of four consecutive chambers that pumped blood from the heart to the
gills to the body and back to the heart. The first separation of systemic and pulmonary circulation
is seen in amphibians and reptiles. A complete two-cycle pump evolved independently in birds
and mammals. The right side of the heart pumps deoxygenated blood to the lungs while the left
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side pumps oxygenated blood to the body tissues. The sinoatrial (SA) node, a remnant of the
sinus venosus, is the heart’s pacemaker. The wave of depolarization passes through cardiac cell
gap junctions. There is a slight delay between atrial and ventricular contractions as the wave of
depolarization cannot pass through the connective tissue between the chambers. The wave is
conducted via the atrioventricular (AV) node and across both ventricles through the bundle of
His and through Purkinje fibers. Cardiac performance is monitored by recording the wave of
depolarization in an electrocardiogram. Cardiac output, the volume of blood pumped by each
ventricle per minute increases greatly with exercise, the rate at which the heart fills and empties
is increased and the ventricles contract more strongly and empty more completely.
Blood flow, pressure, and blood volume are regulated by several homeostatic systems.
Baroreceptors are located in the walls of the aortic arch and carotid artery. Their rate of firing
decreases when blood pressure falls, which increases sympathetic activity, decreases
parasympathetic activity, and restores normal pressure and cardiac output. Blood volume is also
regulated by four homeostatic endocrine systems. Antidiuretic hormone (ADH), secreted by the
hypothalamus of the brain and stored in the posterior pituitary, reduces the amount of water lost
in the urine, increasing blood volume. The renin-angiotensin-aldosterone system stimulates
contraction of blood vessel smooth muscle (vasoconstriction) and increases body sodium, both
which serve to increase blood volume and pressure. Atrial natriuretic hormone production
increases when the atrium is stretched by high blood volume. This increases the excretion of
sodium and water in the urine, lowering blood volume. Nitric oxide (NO) produced by blood vessel
endothelial cells is a gas that acts as a hormone causing vessel muscles to relax, dilating the blood
vessel. Nitroglycerine causes the release of NO gas. Cardiovascular diseases are the leading cause of
death in the U.S.
Heterotrophs obtain energy by oxidizing carbon compounds utilizing oxygen and producing
carbon dioxide. Oxygen passively diffuses into the layer of water surrounding the epithelial
layers and is driven by the difference in oxygen concentration between the interior of the
organism and the environment. This relationship is described by Fick’s law of diffusion. Many
animals increase their diffusion constant by circulating fresh water around their bodies. Other
animals increase the diffusion surface via special respiratory organs. External gills are the
simplest aquatic gas exchange organs.
Fish circulate water past their gills and out the opercular openings. Most fish possess moveable
gill covers that pump water past their gills, ensuring a constant flow of oxygen to maintain a high
diffusion constant. The structure of the gill and its blood supply create a countercurrent flow;
maximal diffusion occurs the entire length of the gill. Air-oriented respiratory systems are far
less efficient. Insects evolved tubular tracheae; other animals evolved lungs. Amphibians breathe
with simple sac lungs augmented by cutaneous respiration. Reptile lungs are more complex as
their water-tight skin prevents diffusion. Mammal lungs are highly branched with terminal
alveoli. They increase their diffusion surface area to meet the demand for more oxygen with
greater metabolic activity. Birds evolved a super efficient system with unidirectional air flow by
utilizing posterior and anterior air sacs. Gas exchange in birds occurs across parabronchi, minute
air vessels rather than the blind-ended alveoli of mammals. Avian respiration requires two cycles
of inspiration and exhalation to move a single volume of gas through their respiratory system.
Their respiration is nearly as efficient as a fish’s due to the 90o cross-current flow between the air
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and the blood.
The mammalian respiratory system is contained within the thoracic cavity. A single trachea
connects to two bronchi, each divides into bronchioles that branch into alveoli. Human inhalation
is a one-cycle pumping system, there is a small residual volume of air that remains within the
lungs. Intrapleural fluid supports the lungs within the pleural cavity and enables the lungs to
inflate as a result of pressure changes associated with changes in the size of that cavity. Reptiles,
birds, and mammals possess negative pressure breathing (air is sucked into the lungs) while
amphibians have positive pressure breathing (air is pushed into the lungs). Breathing in humans
is dependent on regular contractions of the thoracic muscles and the diaphragm. The amount of
air exchanged in passive inspiration and expiration is the tidal volume: vital capacity is the
amount of air expired after a forceful, maximum inspiration equal to three to four times the tidal
volume.
Breathing is initiated by the respiratory center in the brain. It sends signals to the diaphragm and
intercostal muscles to contract. This process is ultimately not under direct conscious control, you
cannot asphyxiate yourself by holding your breath. The speed and depth of breathing is
dependent on the level of CO2 in the blood. Chemoreceptors sensitive to blood pH are located in
the aorta and carotid artery. The central chemoreceptors in the brain sense changes in pH in the
cerebrospinal fluid. Blood pH changes occur as CO2 forms carbonic acid and further dissociates
into hydrogen and bicarbonate ions.
Respiratory gases are transported via the carrier protein hemoglobin. An animal’s oxygenhemoglobin dissociation curve correlates partial pressure of oxygen and its ability to bind to
hemoglobin. Oxygen diffuses into the blood plasma within the alveoli and then into the red blood
cells. As the oxygen binds with hemoglobin it is removed from the plasma, allowing a greater
amount to diffuse. Oxygen is unloaded from capillaries in metabolically active tissues as a result
of the Bohr effect. Carbon dioxide is simultaneously absorbed by the blood and is bound to
hemoglobin and the red cell cytoplasm. The carbon dioxide is unloaded at the alveoli where
hemoglobin preferentially associates with oxygen. Carbon dioxide is carried in the red blood
cells through the formation of carbonic acid and bicarbonate. Hemoglobin also transports nitric
oxide (NO), a regulatory gas that causes dilation of blood vessels.
LEARNING OUTCOMES
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Compare the anatomy and efficiency of open and closed circulatory systems.
Understand the three primary functions of the vertebrate circulatory system.
Identify and describe the function(s) of each of the cellular and non-cellular components of
blood.
Describe the anatomy of the major kinds of blood vessels.
Explain the relationship between blood vessel diameter and flow resistance including the effects
resistance has on the efficient operation of a closed circulatory system.
Describe the vertebrate lymphatic system and indicate its importance.
Understand the evolution of the vertebrate heart from primitive fish to amphibians and reptiles
through birds and mammals in terms of structure and overall circulatory efficiency.
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Describe the structure of a human heart and the flow of blood through it.
Explain how the mammalian heart contracts.
Understand how the heart’s performance is monitored.
Explain how exercise affects cardiac output.
Describe how blood flow, pressure, and volume are regulated.
Describe Fick’s law of diffusion and understand how animals alter the variables to evolve
more efficient respiratory systems.
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Understand how primitive invertebrate, advanced vertebrate, and vertebrate respiratory systems
each maximize the rate of diffusion.
Explain the countercurrent flow exchange in fish gills and indicate which parameters of Fick’s
equation are optimized.
Describe the two major respiratory systems possessed by terrestrial animals and the evolutionary
adaptations of each.
Compare respiration in amphibians, reptiles, and mammals.
Explain the unique respiratory system of birds, their need for a highly efficient
system, and the similarities with a fish respiratory system.
Describe the anatomy of the human respiratory system and the mechanics of breathing.
Understand how breathing and blood gas levels are regulated.
Understand the importance of gas carrier molecules in the circulatory system of vertebrates.
Describe how oxygen is transported from the alveoli to metabolically active tissue, how carbon
dioxide returns, and how the Bohr effect augments this gaseous exchange.
Describe carbon dioxide and nitric oxide transport.
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COMMON STUDENT MISCONCEPTIONS
There is ample evidence in the educational literature that student misconceptions of information
will inhibit the learning of concepts related to the misinformation. The following concepts
covered in Chapter 49 are commonly the subject of student misconceptions. This information on
“bioliteracy” was collected from faculty and the science education literature.
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Students believe that all land animals use lungs
Students do not know will gills are found in aquatic animals
Students believe the circulatory system and respiratory system are not tightly integrated
Students confuse breathing and respiration
Students believe all animals have red blood cells
Students do not associate diffusion with respiratory system function
Students think that all animals evolved at about the same time
Students believe that most animals are vertebrates
Students do not equate humans with being animals
Students believe that all animals have identical organ system structures
INSTRUCTIONAL STRATEGY PRESENTATION ASSISTANCE
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Compare the countercurrent analogy with a heat pump. If very cold air meets very warm air a lot
of exchange will occur, but only over a short distance.
Most students are relatively familiar with the circulatory system and shouldn’t have much
difficulty with this chapter. The most confusing thing is which ventricle pumps blood to the
lungs (the right side) and which pumps to the rest of the body (the left side). Since the left
ventricle pumps blood through the systemic circulation, it is the largest chamber of the
mammalian heart.
Stress that circulation is not directional with respect to individual organs, with the exception of
circulation to the lungs and from the small intestine to the liver. Blood flows throughout the body
reaching every cell in its own good time, like riding a circular subway system. You can’t get
from point a to point c without going through point b. Once you’ve passed b, you have to go
around the entire circuit again to get back to it.
Stress why a two-cycle pump is more effective for terrestrial circulation than a one-cycle pump.
Discuss the mammal diving reflex and its effects on children accidentally submerged in cold
water.
Very active fish (i.e., trout) require large amounts of oxygen and live in cold moving water.
Other fish have adapted to water low in oxygen by reducing metabolism (catfish) or by evolving
special labyrinth organs (Bettas).
Many aquatic turtles significantly increase the time that they can remain submerged by utilizing
cloacal respiration. Oxygen in the water diffuses across the cloacal membrane, similar to
cutaneous respiration in amphibians and sea snakes.
Discuss why birds need the most efficient respiratory systems, especially with regard to their
body metabolism and flight altitude.
HIGHER LEVEL ASSESSMENT
Higher level assessment measures a student’s ability to use terms and concepts learned from the
lecture and the textbook. A complete understanding of biology content provides students with the
tools to synthesize new hypotheses and knowledge using the facts they have learned. The
following table provides examples of assessing a student’s ability to apply, analyze, synthesize,
and evaluate information from Chapter 49.
Application
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Have students explain path of an oxygen molecule through an open and
closed circulatory system.
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Have students explain how the circulatory system responds to different
needs of the respiratory system.
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Ask students to explain path of oxygen through a gill and a lung.
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Analysis
Synthesis
Evaluation
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Have students explain why certain birds can live at very high altitudes at
which no other animal can survive.
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Have students explain why pollutants that contain iron are harmful to
aquatic organisms.
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Ask students compare the adaptations needed for a gill to be used by a
land animal.
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Ask students to come up with the criteria needed for designing an
artificial lung.
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Have students come up with a commercial application for a chemical that
improves the blood’s ability to dissolve oxygen in the fluid component.
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Ask students to come up with the criteria needed for designing artificial
blood.
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Ask students evaluate the effectiveness and safety sports supplements that
increase the rate of the circulatory system.
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Ask students evaluate the effects of drugs that interfere with
baroreceptors.
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Ask students evaluate the accuracy of using fish to study human heart
disease
VISUAL RESOURCES
Obtain a fresh heart from a butcher or a slaughter house to demonstrate the various anatomical
structures. The bigger the better so try for a cow or an ox. As last resort, purchase a preserved
heart from a biological supply company.
Construct a transparent circulatory system with plastic chambers and tygon tubing. Alternately,
purchase and assemble one of the many kits available. Most kits, though, rely on only a single
pump to push the “blood” through both systemic and pulmonary circulations.
Make a super inexpensive model lung using a balloon and an empty 1 or 2 liter plastic bottle.
Depress the bottle slightly, place the balloon inside the stem of the bottle (but don’t drop it!). It
takes a little dexterity to get the lip of the balloon on the stem of the bottle, but it is possible.
When the bottle is released the lung balloon will inflate, when the bottle is depressed it will
deflate. This model best exemplifies a garter snake system. They have only a single functional
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lung in their elongate bodies, the other lung is a mere bubble at the end of the bronchus.
Compare the volume of walnuts versus smaller hazelnuts in a jar. Similarly an animal with
smaller, more numerous alveoli has a greater lung volume than one with few, large alveoli.
Several biological supply companies sell a respiratory model that uses a specially prepared actual
cow lung. It is elastic enough that it can be expanded and deflated by breathing into and out of it.
IN-CLASS CONCEPTUAL DEMONSTRATIONS
A. Digestive System Histology
Introduction
This demonstration uses respiratory system histology images to help students understand
the cellular composition of the respiratory system. It is a good demonstration for reinforcing
histological form and function.
Materials
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Computer with Media Player and Internet access
LCD hooked up to computer
Web browser linked to Boston University histology website at
http://www.bu.edu/histology/m/t_respir.htm
Procedure & Inquiry
1. Ask the class what they know about form and function in cell and tissue structure of the
respiratory system and associated blood vessels.
2. Load up the Boston University histology website and click on Respiratory system
histology images in order of the major respiratory structures and then discuss the finer
details:
a. Trachea (H&E)
b. Extrapulmonary bronchus (PAS/Pb hematoxylin)
c. Lung (sheep), intrapulmonary bronchus (H&E)
d. Lung (mouse) (PAS/Pb hematoxylin/resorcin-fuchsin)
e. Lung (human), intrapulmonary bronchus (PAS/Pb hematoxylin)
f. Alveolar sac
g. Bronchioles
h. Ciliated cell
i. Pulmonary artery
j. Pulmonary capillary
k. Pulmonary vein
3. Have students describe the cells and tissue composition.
4. Then see if the students can confirm the function of the organ based on the cellular
structure.
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USEFUL INTERNET RESOURCES
1. The University of Alberta has a valuable homeostasis animations website for
supplementing lectures on the respiratory system. The site is available at
http://www.biology.ualberta.ca/facilities/multimedia/index.php?Page=252
2. A discussion about researchers who created artificial blood vessels is a way to promote
an interest in the circulatory system. A study called “Construction of an Artificial Blood
Vessel Wall from Cultured Endothelial and Smooth Muscle Cells” presents attempts at
building artificial blood vessels. The article is available at:
http://www.pnas.org/cgi/reprint/76/4/1882
3. Faculty and students will find value in websites that simplify animal anatomy and
physiology concepts. The information can be used for projects that educate children and
civic groups about animals. Biology-4-kids is a model website for animal education. The
website can be found at http://www.biology4kids.com/files/systems_digestive.html.
4. Case studies are an effective tool for stimulating interest in a lesson on animals. The
University of Buffalo has a case study called “A Friend in Need Is a Friend Indeed: A
Case Study on Human Respiratory Physiology” which has students investigating the
physiology of the respiratory system. The case study can be found at
http://www.sciencecases.org/respiration/respiration.pdf.
LABORATORY IDEAS
A. Brine Shrimp as a Respiratory System Model
This activity has students has students investigate the effects of caffeine and tobacco and
respiratory rate using a brine shrimp model.
a. Explain to the students that many natural substances affect the respiratory rate of animals.
b. Then explain that they will be using brine shrimp to look at effects of various .
c. Provide students with the following materials:
a. Petri dishes
b. Microscopes
c. Microscope slides
d. pH Indicators ( phenol red or bromothymol blue)
e. Large brine shrimp
f. Brine shrimp medium
g. Test reagents:
i. Chewing tobacco
ii. Coffee
iii. 20% ethanol
d. Tell students to design an experiment to investigate the effects of alcohol, coffee, and
tobacco water on the respiratory system of the shrimp. Stress that they must do the
experiments in a way that they can quantify the results under controlled conditions.
e. Then have them prepare an oral report or a poster session of their findings and
conclusions that can presented to the class.
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LEARNING THROUGH SERVICE
Service learning is a strategy of teaching, learning and reflective assessment that merges the
academic curriculum with meaningful community service. As a teaching methodology, it falls
under the category of experiential education. It is a way students can carry out volunteer projects
in the community for public agencies, nonprofit agencies, civic groups, charitable organizations,
and governmental organizations. It encourages critical thinking and reinforces many of the
concepts learned in a course.
1. Have students do an education program on the effects of smoking on respiratory system
health for elementary school students.
2. Have students tutor high school students studying animal anatomy and physiology.
3. Have students volunteer at a local air quality or lung associate agency.
4. Have students volunteer at the educational center of a zoo or marine park.
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