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Chapter 6 – Homeostasis: Internal Fluids And Respiration
CHAPTER
6
HOMEOSTASIS: INTERNAL FLUIDS AND
RESPIRATION
CHAPTER OUTLINE
6.1.
6.2.
Internal Fluid Environment (Figures 6.1, 6.2)
A. Fluids
1. Body fluid of a single-celled organism is cellular cytoplasm.
2. In multicellular organisms, body fluids are intracellular and extracellular.
3. Intracellular fluids are the collective fluids inside all the body’s cells.
4. Extracellular fluids are outside and surrounding the cells.
5. Extracellular fluid buffers cells from harsh physical and chemical changes outside the body.
6. In vertebrates, annelids and a few others, extracellular fluid is further divided into blood plasma and
interstitial fluid.
7. Blood vessels of a closed circulatory system contain the plasma while interstitial fluid is between the
cells and organs of the body.
8. Nutrients and gases passing between vascular plasma and cells must traverse this fluid separation.
9. Interstitial fluid is constantly formed from plasma by movement of fluid from microscopic vessels in
close proximity to cells.
B. Composition of the Body Fluids
1. Plasma, interstitial and intracellular fluids are mostly water.
2. Animals range from 70% to 90% water.
3. Humans are 70% water by weight; 50% is cell water, 15% is interstitial and 5% is blood plasma.
4. Plasma is the pathway of exchange between cells and the kidney, lung or gill, and alimentary canal.
5. Body fluids contain many inorganic and organic substances in solution.
a. Sodium, chloride and bicarbonate are the chief extracellular electrolytes.
b. Potassium, magnesium, and phosphate ions and proteins are major intracellular electrolytes.
c. Concentrations are maintained despite continuous flow of materials into and out of cells.
6. Plasma and interstitial fluids have similar composition except that plasma has more large proteins.
Composition of the Blood (Figures 6.3, 6.4)
A. Elements
1. Flatworms and cnidarians lack a circulatory system and do not have a true “blood.”
2. Invertebrates with an open circulatory system have a more complex “hemolymph.”
3. Closed circulatory systems keep blood contained in blood vessels separate from tissue fluids.
4. In vertebrates, blood is a complex liquid tissue of formed elements suspended in plasma.
5. When separated by centrifugation, blood is 55% plasma and 45% formed elements.
6. Plasma
a. Water constitutes 90%.
b. Dissolved solids include plasma proteins (e.g. albumin, globulins, fibrinogen), glucose, amino
acids, electrolytes, various enzymes, antibodies, hormones, metabolic wastes, etc.
c. Dissolved gases include oxygen, carbon dioxide and nitrogen.
7. Cellular Components
a. Red blood cells contain hemoglobin and transport oxygen and carbon dioxide.
b. White blood cells are scavengers and defend the body against foreign material.
c. Cell fragments function in blood coagulation.
8. Plasma proteins are a diverse group with many functions.
a. Albumins are 60% of plasma proteins and help maintain osmotic equilibrium.
b. Globulins are high-molecular weight proteins and include immunoglobulins.
c. Fibrinogen is a very large protein that is involved in clot formation.
d. Blood serum is plasma minus the proteins.
9. Red Blood Cells (Erythrocytes)
a. Red blood cells occur in enormous numbers in the blood.
b. In mammals and birds, they form from large, nucleated erythroblasts in red bone marrow.
c. In other vertebrates, kidneys and spleen are the major sites of red blood cell production.
d. In mammals, the nucleus shrinks and disappears during development.
e. Human red blood cells also lose ribosomes, mitochondria and most enzyme systems.
f. The human cell is biconcave in shape; this provides the greatest surface area for gas diffusion.
g. Each cell holds about 280 million molecules of hemoglobin.
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Chapter 6 – Homeostasis: Internal Fluids And Respiration
6.3.
h. About 33% of the weight is hemoglobin.
i. In non-mammal vertebrates, red blood cells have a nucleus and are ellipsoidal.
j. Erythrocytes have an average life of four months and may travel 11,000 kilometers.
k. When it is worn out and fragments, it is engulfed by macrophages in the liver.
l. Iron from hemoglobin is salvaged and used again.
m. The rest of the heme molecule is converted to bilirubin, a bile pigment.
n. About 10 million erythrocytes are destroyed every second, and that number must be replaced.
10. White Blood Cells (Leukocytes)
a. White blood cells form a part of the immune system.
b. In human adults, they number about 7.5 million per milliliter of blood, about one per 700 RBCs.
c. Varieties include: granulocytes (neutrophils, basophils, and eosinophils) and agranulocytes
(lymphocytes and monocytes).
B. Hemostasis; Prevention of Blood Loss (Figures 6.5, 6.6)
1. Blood flows under considerable hydrostatic pressure; it is important to prevent blood loss after
injury.
2. When a vessel is damaged, smooth muscle in the wall of the vessel contracts and the lumen narrows.
3. In both vertebrates and invertebrates, this constriction may totally prevent blood loss.
4. Vertebrates and larger, active invertebrates have special cellular elements to form clots.
5. Blood coagulation is the dominant hemostatic defense in vertebrates.
6. Blood clots form as a tangled network of fibers from one of the plasma proteins, fibrinogen.
7. Transformation of fibrinogen into a fibrin meshwork is catalyzed by the enzyme thrombin.
8. Thrombin is present in the blood in the inactive form prothrombin.
9. Platelets and damaged cells of blood vessels play a vital role in clotting.
10. Platelets
a. Platelets form in red bone marrow from large cells that pinch off bits of cytoplasm.
b. Platelets are fragments of cells; ~150,000 to 300,000 per cubic millimeter of blood.
c. Platelets adhere to any disruption in the normally smooth inner surface of a blood vessel.
d. They release thromboplastin and other clotting factors.
e. These factors and calcium ions initiate conversion of prothrombin to active thrombin.
f. This involves a long and complex catalytic sequence; each reactant cascades into release of
much more of the next reactant.
g. 13 different plasma coagulation factors are known; a deficiency of one factor can stop the
process.
h. This provides a balance between providing emergency clotting and avoiding unnecessary clots.
11. Hemophilia is one of several clotting abnormalities; it is caused by a mutation on the X
chromosome.
Circulation (Figure 6.7)
A. General Design
1. Sponges and ciliates utilize the water medium around them for transport.
2. Flattened animals can utilize diffusion across their thin surfaces, but only to a limit.
3. Larger animals cannot rely on diffusion to support respiratory and metabolic needs.
4. A full circulatory system has a propulsive organ, arteries, capillaries and a venous reservoir.
5. An earthworm demonstrates this basic system with a distributed pumping system.
B. Open and Closed Circulations (Figures 6.8, 6.9)
1. A closed circulatory system confines blood to a journey through the vascular system.
2. An open circulation system lacks connecting blood vessels and capillaries.
3. In arthropods, molluscs and some other invertebrates, sinuses collectively form the hemocoel.
4. Open System
a. During development, the blastoderm is not filled by mesoderm but becomes the hemocoel.
b. The blood or hemolymph washes through this primary body cavity or hemocoel.
c. There is no distinction between blood plasma and lymph, as is the case in closed circulation.
d. Hemolymph is 20–40% of body volume in open systems; blood is 5–10% in closed systems.
e. In arthropods, the heart and all organs lie in the hemocoel bathed by blood.
f. Blood enters the heart through valved openings to the side or ostia.
g. Forward-moving waves propel blood forward to the head where it washes into the hemocoel.
h. It is routed through the body by baffles and membranes before returning back into the heart
ostia.
i. Blood pressure is very low in open systems, rarely over 4–10 mm Hg.
j. Therefore, arthropods have auxiliary hearts or contractile vessels to boost blood flow.
k. Insects and other terrestrial arthropods do not use their circulatory system for respiratory gas
transport, rather a separate respiratory system has evolved for this purpose.
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Chapter 6 – Homeostasis: Internal Fluids And Respiration
5.
Closed Systems
a. In embryonic development of animals with closed systems, the coelom increases to obliterate
the blastocoel and forms a second body cavity.
b. The system of continuously connected blood vessels develops within the mesoderm.
c. The heart pumps blood into arteries that branch into arterioles that enter a vast capillary system.
d. Blood leaves the capillaries in converging venules and larger veins to return to the heart.
e. Capillary walls are thin to allow transfer of materials between blood and tissues.
f. Such a closed system allows large animals to shunt blood to tissues needing it.
g. However, blood pressure is much higher in closed systems; fluid is pushed across capillary
walls.
h. Fluid lost into tissues and interstitial spaces is returned by osmosis and the lymphatic system.
C. Plan of Vertebrate Circulatory Systems (Figures 6.10–6.11)
1. Comparative Anatomy
a. The principal difference in vertebrate systems is the separation of the heart into two pumps.
b. These changes occurred as vertebrates converted from gill breathing to lungs.
c. The Fish Heart
1) The heart has two main chambers in series: the atrium and ventricle.
2) The atrium is preceded by an enlarged sinus venosus that collects blood and smooths
delivery.
3) Elasmobranchs have a fourth heart chamber, the conus arteriosus and teleost fish have a
bulbous arteriosus that dampens blood pressure oscillations before blood flows into
capillaries.
4) Blood makes one circuit, flowing first to gills and then on to the aorta and body.
5) Oxygenated blood is provided to the body organs before the veins return to the heart.
6) However, gill capillaries offer much resistance, and blood pressure to the body tissues is
low.
d. Double Circulation
1) Terrestrial animals evolved lungs instead of gills between heart and aorta.
2) This provided a high pressure system that provided oxygenated blood to capillary beds and
a pulmonary circuit to serve the lungs.
3) This change is seen in lungfishes and amphibians.
4) Modern amphibians have separate atria.
5) The right atrium receives venous blood from the body.
6) The left receives oxygenated blood from the lungs.
7) The ventricle is undivided but venous and arterial blood do not heavily mix.
8) Ventricles are nearly separate in nonavian reptiles and completely separate in crocodilians,
birds and mammals.
9) Systemic and pulmonary circulations are served by one half of a dual heart.
2. Mammalian Heart (Figures 6.12, 6.13)
a. The mammalian heart is located in the thorax and enclosed in the pericardial sac.
b. Blood returning from the lungs collects in the left atrium and passes to the left ventricle.
c. The left ventricle pumps the blood to the body in the systemic circuit.
d. Blood returns from the body into the right atrium and passes to the right ventricle.
e. The right ventricle pumps the blood to the lungs in the pulmonary circuit.
f. The bicuspid valves are between the left atrium and ventricle to prevent backflow of blood.
g. The tricuspid valves separate the right atrium and right ventricle to prevent backflow of blood.
h. Semilunar valves stop backflow from the pulmonary to right ventricle and aorta to left ventricle.
i. Contraction of the heart is systole.
j. Relaxation of the heart is diastole.
k. When the atria contract, the ventricles relax; ventricular systole is accompanied by atrial
diastole.
l. Cardiac output is the amount of blood moved through the heart; exercise can increase it fivefold.
m. Heart rates can vary from an ectothermic codfish at 30 beats per minute to a rabbit at 200.
n. Smaller animals have a faster heart rate than larger animals, reflecting the increase in metabolic
rate that occurs with decreased body size.
o. An elephant has a heart rate of about 25 beats per minutes, humans around 70, cats around 125,
a mouse has 400 and a tiny shrew has 800 beats per minute.
3. Excitation of the Heart (Figure 6.14)
a. The vertebrate heart is a muscular pump composed of cardiac muscle.
b. Cardiac muscle fibers are branched and striated, but do not depend on nerve activity to contract.
c. Specialized pacemaker cells initiate nerve contractions.
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Chapter 6 – Homeostasis: Internal Fluids And Respiration
d.
In a nonavian reptile, bird, or mammal heart, the pacemaker is the sinus node, a remnant of the
ancestral sinus venosus still found in fish.
e. Electrical activity of the pacemaker spreads over the muscle of the two atria and then the muscle
of the ventricles.
f. Electrical activity is conducted through the atrioventricular bundle to the apex of the ventricle
and then continues through the specialized Purkinje fibers to the apex of ventricles.
g. This causes the contraction to begin at the tip and pushes blood out efficiently at the same time.
h. A cardiac center in the medulla sends out two sets of nerves.
1) The vagus nerves brake the heart rate.
2) The accelerator nerves speed up the heart rate.
3) Both terminate at the sinus node for direct guidance of the pacemaker.
i. The cardiac center receives sensory information from pressure and chemical receptors.
j. Myogenic hearts have heartbeat initiated in specialized muscle cells.
k. In a neurogenic heart, as is found in decapods, a cardiac ganglion serves as a pacemaker and
the heart stops beating without this stimulation.
l. Isolated myogenic hearts continue to beat for hours; neurogenic hearts do not.
4. Coronary Circulation
a. A constantly active heart needs a generous blood supply.
b. Small fish and frog hearts are heavily channeled; the heart’s pumping action suffices to provide
oxygen.
c. Larger fish, frogs, and nonavian reptile hearts are thicker and need a dedicated vascular supply
(coronary circulation).
d. Coronary arteries divide into an extensive capillary network.
e. Heart muscle has a high oxygen demand and uses 70% of the oxygen from the blood.
f. When the heart is working hard during exercise, the blood supply must increase up to nine
times.
g. Partial or complete blockage of circulation will cause heart cells to die from lack of oxygen.
5. Coronary artery disease (CAD)
a. CAD is currently the #1 killer in the U.S.
b. Risk factors can be divided into those that cannot be modified and those that can.
c. Risk factors that cannot be modified include family history, being a male or postmenopausal
female, or age.
d. Modifiable risk factors include smoking, high blood cholesterol levels, high blood pressure,
uncontrolled diabetes, and others.
D. Arteries (Figure 6.15)
1. All vessels leaving the heart are arteries.
2. Arteries must withstand high, pounding pressures and have thick, elastic walls.
3. The wall bulges during systole and compresses the fluid column during ventricular diastole.
4. The next heartbeat surges the blood pressure before it drops to zero.
5. Blood pressure varies between systole and diastole: 120 mm Hg over 80 mm Hg in humans, or
120/80.
6. Arteries branch into narrower arterioles with smooth muscle walls.
7. Arterioles can dilate or constrict diverting blood flow to body organs where it is most needed.
8. Blood pressure is measured as the force required to support a column of mercury.
9. A sphygmomanometer compresses arteries in the upper arm; pressure is released until blood spurts
through under systolic pressure; when pressure drops below diastolic, blood flow is no longer heard.
E. Capillaries (Figures 6.16, 6.17)
1. Structure
a. Marcello Malpighi confirmed capillaries existed in 1661 by inspecting living frog lung tissue.
b. Huge numbers of capillaries infuse most tissues; muscle has over a million per square inch.
c. At rest, fewer than one percent are open; during exercise, all capillaries may be open.
d. Capillaries are extremely narrow, averaging about 8 micrometers in diameter in mammals.
e. Red blood cells are almost this wide and must pass through single-file.
f. Capillary walls are composed of a single layer of endothelial cells held together by a basement
membrane.
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Chapter 6 – Homeostasis: Internal Fluids And Respiration
2.
6.4.
Capillary Exchange
a. Blood pressure forces fluids out through the permeable capillary walls into interstitial spaces.
b. Fluid may pass between the endothelial cells via water-filled clefts or through endothelial cells.
c. Lipid-soluble substances can diffuse easily through the plasma membrane of endothelial cells.
d. Plasma protein molecules are too large and the filtrate is nearly protein-free.
e. Fluid exchange across a capillary wall is a balance of hydrostatic pressure and osmotic pressure.
f. If fluids leave the capillaries and do not reenter circulation, the tissues accumulate fluid
(edema).
g. In a capillary, blood pressure is higher at the arteriole end and declines toward the venule side.
h. However, osmotic pressure is created by proteins that cannot pass across the capillary wall.
i. As a result, water and solutes are filtered out at the arteriole end and drawn in at the venule end.
j. However, outflow exceeds inflow and the excess fluid is lymph that remains in interstitial
spaces.
k. This excess is removed by lymph capillaries and eventually returned to the circulatory system.
F. Veins
1. Venules and veins are thinner walled, less elastic, and larger than arteries and arterioles.
2. Blood pressure is low (10 mm Hg) where capillaries drain into venules and nearly zero at the heart.
3. Venous blood is assisted back to the heart by valves in veins, body muscles surrounding veins,
suction created during diastole of the heart, and movement of the lungs.
4. Blood would pool in the long extremities without the veins to segment the blood column.
5. Valves are formed as infoldings of the endothelial cell layer and underlying connective tissue.
6. Skeletal muscle action squeezes the veins, and valves keep the flow going toward the heart.
7. Negative pressure in the thorax, created by breathing, speeds venous return by sucking blood up the
large vena cava.
G. Lymphatic System (Figure 6.18)
1. Thin-walled vessels extend into most body tissues to collect lymph.
2. Lymphatic vessels merge into larger vessels that drain into veins in the lower neck.
3. Lymph has a lower concentration of protein but carries some fat molecules absorbed from the gut.
4. Lymph nodes are located along the lymph vessels and trap and remove foreign particles.
5. Lymph nodes are also a center, along with bone marrow and thymus gland, for lymphocytes.
Respiration
A. Processes
1. Cellular respiration is defined as the oxidative processes that occur inside a cell.
2. External respiration is an exchange of oxygen and carbon dioxide between organism and
environment.
B. Problems of Aquatic and Aerial Breathing
1. Water and land are vastly different in their physical characteristics.
2. Air contains about 20 times more oxygen than does water; fully saturated water contains 9 ml of
oxygen per liter compared to 209 ml of oxygen per liter in air.
3. Water is 800 times more dense and 50 times more viscous than air.
4. Gas molecules diffuse about 10,000 times more rapidly in air than in water.
5. Advanced fishes still must use up to 20% of their energy to extract oxygen from water.
6. Mammals use only 1–2% of their resting metabolic energy to breathe.
7. Respiratory surfaces must be thin and moist; this is not a problem for aquatic animals.
8. Air breathers have respiratory surfaces invaginated, and pumping actions move air in and out.
9. Evaginations of the body surface, such as gills, are used for aquatic respiration.
10. Invaginations such as tracheae and lungs are used for air breathing.
C. Respiratory Organs
1. Gas Exchange by Direct Diffusion
a. Protozoans, sponges, cnidarians and many worms use direct diffusion to exchange gases.
b. Cutaneous respiration is not sufficient if the body exceeds 1 mm in diameter.
c. However, flatworms extend a thin body to achieve adequate gas exchange.
d. Larger animals can use cutaneous respiration as a supplement to gills or lungs.
e. Eels secure 60% of their oxygen and carbon dioxide exchange through highly vascular skin.
f. During winter hibernation, frogs and turtles can meet their lowered respiratory requirements.
g. Lungless salamanders usually lack lungs as adults; they are limited in body size.
2. Gas Exchange Through Tubes (Figure 6.19)
a. Insects and some other arthropods have a direct and efficient system of tracheae.
b. Air enters through valve-like spiracles.
c. Tracheal channels narrow to fluid-filled tracheoles 1 micrometer in diameter embedded in
tissues.
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Chapter 6 – Homeostasis: Internal Fluids And Respiration
d. Air enters and leaves the tracheal system through valvelike openings (spiracles).
e. The spiracle opening is regulated to reduce water loss.
f. Oxygen diffuses in along a gradient as oxygen is absorbed by tissues.
g. Carbon dioxide diffuses out along a gradient as carbon dioxide builds up in tissues.
h. Some insects ventilate the tracheal system with body movements.
i. The tracheal system is independent of the hemolymph that has no direct role in respiration.
3. Efficient Exchange in Water (Figure 6.20)
a. Gills, or branchia, may be simple external extensions of the body surface (e.g., dermal papulae
of sea stars or branchial tufts of marine worms).
b. The dorsal lobe of parapodia may also serve as an external respiratory surface for some
polychaete worms.
c. Internal gills of fishes and arthropods are thin filamentous structures supplied with vessels.
d. In gills, blood flow is opposite the flow of water to provide the maximum extraction of oxygen;
this is countercurrent flow.
e. Water is washed over the gills in a steady stream, pulled and pushed by an efficient, two-valved,
branchial pump.
f. The fish’s forward movement through water assists some gill ventilation.
4. Lungs (Figures 6.21–6.22)
a. Despite the high oxygen levels in air, gills do not function in air because they dry out.
b. Some invertebrates including snails, scorpions, some spiders, etc. have inefficient “lungs.”
c. Terrestrial vertebrates generally have lungs that can be ventilated by muscle movements.
d. The most rudimentary lungs exist in lungfishes.
1) The lungfish lung has a rich supply of capillaries on unfurrowed walls.
2) A tube connects it to the pharynx.
3) It uses a primitive ventilating system to move air in and out of the lung.
e. Amphibian lungs vary from smooth-walled, bag-like salamander lungs to divided lungs of frogs.
f. Reptiles’ lungs have greater surface area because they are subdivided further into air sacs.
g. The mammalian lung has millions of small sacs, called alveoli.
h. Human lungs have 1000 kilometers of capillaries and 50–90 square meters of surface area.
i. However, in contrast to flow over a gill, the air does not continuously enter a lung.
j. About one-sixth the air in human lungs is replenished each inspiration.
k. Bird Lungs
1) Bird lungs have an extensive system of air sacs as reservoirs during ventilation.
2) On inspiration, 75% of air bypasses the lungs to enter the air sacs.
3) At expiration, the fresh air flows through lung passages providing continuous gas exchange.
l. Amphibians and lungfishes force air into their lungs by positive pressure breathing; this requires
external nares and the ability to seal nostrils and mouth.
m. Most nonavian reptiles, birds and mammals ventilate lungs by negative pressure, sucking air in
by expanding the thoracic cavity.
D. Structure and Function of the Mammalian Respiratory System (Figure 6.23)
1. Structure
a. Air enters the mammalian respiratory system through nostrils.
b. It passes through nasal chambers lined with mucus-secreting epithelium.
c. The internal nares are openings leading to the pharynx where the pathway crosses with
digestion.
d. Inhaled air passes out a narrow opening, the glottis, while food crosses to enter the esophagus.
e. The glottis opens into the larynx or voice box and then into the trachea or windpipe.
f. The trachea branches into two bronchi, one to each lung.
g. The bronchus divides and subdivides into small bronchioles that lead to alveoli.
h. Alveolar walls are made of single-layered endothelium.
i. Air passageways are lined with mucus-secreting and ciliated epithelial cells.
j. Partial cartilage rings in the tracheae, bronchi, and bronchioles prevent collapsing.
k. During this passage, inhaled air is filtered free from most dust, warmed, and moistened.
l. The lungs are mostly elastic tissue and a little muscle.
m. A thin layer of visceral pleura encloses the lung; parietal pleura lines the inner wall of the chest.
n. The two layers are lubricated and slide past each other during ventilation.
o. The spine, ribs and breastbone surround the thoracic cavity.
p. The diaphragm forms the floor, and a muscular diaphragm is only found in mammals.
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Chapter 6 – Homeostasis: Internal Fluids And Respiration
2.
Ventilating the Lungs (Figure 6.24)
a. The chest cavity is an airtight chamber.
b. In inspiration, the ribs are pulled upward and the diaphragm flattens; this enlarges the chest.
c. The increase in volume causes intrapleural pressure to fall to a more negative value and
intrapulmonary pressure to fall below atmospheric pressure.
d. Air rushes in through the air passageways to equalize the pressure.
e. Tidal volume is the amount of air that is moved during this process.
f. Normal expiration involves relaxation of ribs and diaphragm that return to the normal position.
g. Chest cavity size decreases and air exits.
h. During forced expiration, the ribs are pulled down and inward by the internal intercostal
muscles, abdominal muscles force the diaphragm upward to a greater degree; these mechanisms
expel more air and enhance inspiratory volume.
E. Coordination of Breathing
1. Breathing is normally involuntary and automatic but can come under voluntary control.
2. Neurons in the medulla of the brain regulate normal, quiet breathing.
3. They produce regular spontaneous bursts that stimulate the external intercostal muscles.
4. Respiration must increase dramatically when there is a high requirement for oxygen.
5. However, the body cues on the increasing carbon dioxide level rather than the decrease in oxygen.
6. As carbon dioxide increases, an increase in hydrogen ions makes the cerebrospinal fluid acidic.
7. Carbon dioxide combines with water to form carbonic acid that releases hydrogen ions.
F. Gaseous Exchange in Lungs and Body Tissues: Diffusion and Partial Pressure (Figure 6.25)
1. Air is a mixture of 71% nitrogen, 20.9% oxygen, 0.03% carbon dioxide and a few other gases.
2. Gravity attracts the mass of atmosphere to the earth; total air pressure is 760mm Hg.
3. Each component gas contributes to this total; each component gas therefore has a partial pressure.
(Table 6.1)
4. Partial pressure of oxygen is 0.209 x 760 or 159mm Hg.
5. Partial pressure of carbon dioxide is 0.0003 x 760 or 0.23mm Hg in dry air.
6. Water vapor likewise exerts a partial pressure.
7. Air entering the respiratory tract changes in composition; it becomes wet and mixes with residual air.
8. The partial pressure of oxygen in the lung alveoli is greater (100mm Hg) than in the venous blood of
lung capillaries (40mm Hg), oxygen diffuses into the lung capillaries.
9. The carbon dioxide in the blood of lung capillaries has a higher concentration (46mm Hg) than in the
lung alveoli (40mm Hg) and carbon dioxide diffuses from blood to alveoli.
10. In tissues, respiratory gases continue to move along concentration gradients.
G. Respiratory Gas Transport (Figure 6.26)
1. In some invertebrates, respiratory gases are merely dissolved in body fluids.
2. Only animals with low metabolism can survive on such low levels of oxygen.
3. Only one percent of the human oxygen requirement could be provided by dissolved oxygen.
4. In many invertebrates and all vertebrates, respiratory pigments are used to transport oxygen.
5. In most animals and in all vertebrates, the pigments are packaged in blood cells.
6. Hemoglobin
a. Hemoglobin is the most widespread respiratory pigment among animals.
b. Each molecule is made of 5% heme, an iron-compound and 95% globin, a colorless protein.
c. The heme portion has a great affinity for oxygen; each gram can carry 1.3 ml of oxygen.
d. Heme also holds oxygen in a loose enough chemical state that tissues can take it away.
7. Hemoglobin has a 200 times greater affinity for carbon monoxide than for oxygen and can displace
oxygen, resulting in death.
8. Hemoglobin Saturation Curves
a. Also called oxygen dissociation curves, they show the relationship to surrounding oxygen
levels.
b. The lower the surrounding oxygen is tension, the more oxygen released.
c. This allows more oxygen to be released to tissues that need it most.
d. Carbon dioxide shifts the hemoglobin saturation curve to the right; this is the Bohr effect.
e. Therefore, as carbon dioxide enters the blood from respiring tissues, it causes hemoglobin to
unload more oxygen.
f. The opposite occurs in the lungs and more oxygen is loaded onto hemoglobin.
9. Other Pigments
a. Hemocyanin is a blue, copper-containing protein present in crustaceans and most molluscs.
b. Hemerythrin is a red pigment found in some polychaete worms; it does not have a heme group
and it has lower oxygen-holding properties.
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Chapter 6 – Homeostasis: Internal Fluids And Respiration
10. Carbon Dioxide Transport (Figure 6.27)
a. About 7% of carbon dioxide is carried dissolved in the blood.
b. The remainder diffuses into red blood cells where 70% of it becomes carbonic acid through the
action of the enzyme carbonic anhydrase.
c. Carbonic acid immediately dissociates into hydrogen ions and bicarbonate ions.
d. Several systems buffer the hydrogen ions to prevent blood acidity.
e. About 23% of the carbon dioxide combines reversibly with hemoglobin, not with the heme, but
with the amino acids to form carbaminohemoglobin.
f. The reaction is reversible and the carbon dioxide diffuses into alveoli in the lungs.
g. Increased carbon dioxide in the blood lowers blood pH, as does addition of acid to the blood.
Lecture Enrichment
1.
2.
3.
4.
5.
6.
7.
8.
Note that the short four-month lifetime of the red blood cell is directly related to its inability to repair itself since it
has lost nuclear DNA, ribosomes, mitochondria, etc.
Red blood cells become damaged and fragment from wear-and-tear because, unlike other cells, they cannot repair
themselves. Therefore, they are pulled from circulation by macrophages as they pass through the liver and some
components are recycled, a process that can be compared with worn out money being pulled from circulation as it
passes through banks.
In discussion of the heart structures, the terms “right” and “left” are particularly important. This is a point where
you can remind students that directions and positions are named from the perspective of the organism that
possesses the structure, not right and left as an observer would designate viewing the organism or person head-on.
It can be noted that pulmonary circulation is not used for oxygen before birth in placental mammals because
oxygenated blood is received from the umbilical connection to the placenta. Therefore, it is not critical that the
heart have a completely separated septum before birth, and this is indeed the case where the foramen ovale, or
opening across the heart wall, does not close until late in pregnancy. If it fails to close, the baby is a “blue baby”
which reflects the lower level of oxygenated blood; and the inability of this baby to live very long without an
operation to close the opening is obvious evidence of our need to completely separate pulmonary and systemic
circulation.
The historical notes of Stephan Hales (blood pressure of a mare) and Marcello Malpighi (capillaries in living frog
lung) are just a few of many critical breakthrough experiments that relied on experiments with living animals.
Such examples may elicit revulsion from students who have been sheltered from meat processing farm
experiences and surgical and emergency room procedures. While discussion of these historical discoveries may
provide an intellectual perspective on reality-based laboratory work, only actual labwork by students will give
them a fuller understanding of the concepts and the need for such research practices.
An instructor can illustrate a simple diagnostic test of edema. Pressing on the surface of soft tissue in the hand,
arm, ankle, etc. with a thumb will leave a white thumbprint for about 3–5 seconds as blood has been pressed out
of the capillaries in the surface tissue and takes this much time to return. However, if there is fluid in these
tissues, the thumbprint depression will remain long after the white blanched area has returned to pink. Note that
you are using a teaching technique and not practicing medicine.
Some zoology teachers are accomplished at simulating positive pressure breathing of a frog by taking a mouthful
of air, sealing the nose and lips, and pressing the bloated cheeks so the air appears to be forced into the lungs.
Gases dissolved in fluids are not beyond student experience; the difference between a fizzy soda and a flat soda is
dissolved carbon dioxide, and the bubbles of gas can be seen sparkling off the top of a newly poured drink.
Commentary/Lesson Plan
Background: To the extent students have participated in blood drives and given blood, they will have experiences
with some blood properties, the speed of replenishment, the viscosity, and the equipment involved, including the long
tube that is crimped to provid samples for cross-matching. Students who have run on a cold, dry winter day have
experienced a mild pleurisy where the pleural membranes stick together from dryness.
Misconceptions: Sadly, blood has moved from a public image of “river of life” to potential “river of death.” With the
advent of AIDS and greater awareness of hepatitis (a far greater infection risk than AIDS), the fear is overblown and a
rational discussion of its biology may help restore some objectivity. A few people still believe that some aspects of
heredity including temperament “run in the blood line”; this is ironic since red blood cells are the only common body
cells that lack hereditary material and this old concept could not be farther from the truth. Some students have the
wrong perception that humans have the “best” or “most advanced” of all systems and yet the bird has a far more
efficient lung. Such a high efficiency lung is not needed by a lower metabolism human, just as an alveolar lung is not
useful to an ectothermic frog.
Schedule:
6-8
Chapter 6 – Homeostasis: Internal Fluids And Respiration
HOUR 1 6.1.
6.2.
6.3.
Internal Fluid Environment
A. Fluids
B. Composition of the Body Fluids
Composition of the Blood
A. Elements
B. Hemostasis; Prevention of Blood
Loss
Circulation
A. General Design
B. Open and Closed Circulations
C. Plan of Vertebrate Circulatory
Systems
HOUR 2
6.4.
D. Arteries
E. Capillaries
F. Veins
G. Lymphatic System
Respiration
A. Processes
B. Problems of Aquatic and Aerial
Breathing
C. Respiratory Organs
D. Structure and Function of the
Mammalian Respiratory System
E. Coordination of Breathing
F. Gaseous Exchange in Lungs and Body
Tissues: Diffusion and Partial Pressure
G. Respiratory Gas Transport
ADVANCED CLASS QUESTIONS:
1. What factors limit the size and life span of a red blood cell? How could an experiment be constructed that
demonstrated the inability of a red blood cell to repair itself?
2. If there is no DNA in red blood cells, then how do forensic scientists identify the blood from a crime scene and
establish the DNA match with the accused? [This involves students comprehending that RBC proteins are placed
on the membrane when the cells are formed and that there are nuclei present in the WBCs of a blood sample.]
3. Why is an opening across the heart septum, called the foramen ovale and a normal fetal condition, not a problem
before birth?
4. Arteries and veins are named by their relationship in blood flow from or to the heart. Generally, arteries carry
oxygenated blood and veins carry deoxygenated blood, but the pulmonary arteries and veins are the reverse of
this. What other human circulatory circuit has such a reversal? [Answer: the umbilical cord leading to the
placenta, before birth.]
5. Why would a heavier person be more likely to have higher blood pressure?
6. Why are the substantial plasma proteins found in blood not used by cells as a source of metabolic energy?
7. Some terrestrial mammals ignore declining oxygen levels, and cue on to the reciprocal increase in carbon dioxide
to regulate breathing. However, some diving marine mammals pace breathing on oxygen sensors. Why would
this have evolved?
Fifteenth Edition Changes:
1.
2.
Changes in this chapter are relatively minor.
With respect to circulatory fluid, the term “formed elements” has been replaced by the term “cellular
components.”
One reference by Glass and Wood (2009) has been added.
Source Materials
[Bold = recommended]
Asthma (FH), 19-min. video
Blood (FH) (IM), 22-min. video
Blood: Composition and Functions (IM), 15-min. video
Blood and Immunity (CAM) (Cyber) (Q), Mac, MS-DOS CD
Blood Is Life (FH), 45-min. video
Blood: The Microscopic Miracle (EBE), 22-min. video
Blood: River of Life, Mirror of Health (HRM), video
Body Atlas: Breath of Life (AVP) (JLM), 30-min. video
Body Atlas: The Human Pump (AVP) (JLM), 30-min. video
Body Language: Respiratory System (PLP), Apple, MS-DOS, Mac
Breath of Life (FH), 26-min. video
Breaths of Life: Respiratory Challenges of Animals (Biology: Form and Function) (CPB) (IM), 24-min. video
The Cardiac Cycle (JB) (Q), Mac, Win CD
Cardiac Muscle Mechanics (Q) (SciT) (TS), MS-DOS
Cardiovascular Disease (series) (Ch-F), 45-min. video
Cardiovascular Fitness Lab (CBSC), Apple, MS-DOS
6-9
Chapter 6 – Homeostasis: Internal Fluids And Respiration
Cardiovascular Function (PLP), MS-DOS
Cardiovascular Programs (C-E-G) (JB), MS-DOS
Cardiovascular Physiology Part I: Pressure/Flow Relations (C-BE), MS-DOS
Cardiovascular Physiology Part II: Reflex (C-BE), MS-DOS
Cardiovascular Simulation Program: Computer Rabbit (INT), Mac
Cardiovascular System (CBSC) (PLP), Apple, MS-DOS, Mac
Cardiovascular System (CAM), Mac, Win CD
Cardiovascular System by Logal (WARDS), Mac, Win CD
Cellular Respiration (ei), slides
Comprehensive Review in Biology: Circulation and Respiration (Q), Mac, Win
CIRCSIM: A Teaching Exercise on Blood Pressure Regulation (C-BE), MS-DOS
CIRCSYST 2.0 (C-E-G) (JB), MS-DOS
Circulation (ei), video or filmstrip
Circulation (IM), 29-min. video
Circulation of the Blood (AIMS), Mac, Win CD, 24-min. video, laserdisc
Circulatory and Respiratory Systems (IM) (NGS), 17-min. video
Circulatory System (PHO), 16-min. video
Circulatory System and Its Functions (ei), slides
Circulatory System: Breath of Life (FH), 26-min. video
Circulatory System: Hot and Cold (FH), 26-min. video
The Circulatory System: Life under Pressure (FH), 26-min. video
Circulatory System: Two Hearts That Beat as One (FH), 26-min. video
Comprehensive Review in Biology: Circulation and Respiration (Q), Mac, Win
Coronary Heart Disease: Clinical Aspects (PYR), 17-min. video
Cycles of Life: Exploring Biology–Circulation: A River of Life (A-CPB), 30-min. video
Cycles of Life: Exploring Biology–Respiration (A-CPB), 30-min. video
Diffusion (IM), 29-min. video
EKGTUTOR (C-E-G), MS-DOS
Electrophysiology of the Heart (Q), Mac, Win CD
FICKSYST (C-E-G) (JB), MS-DOS
Frog Heart (INT) (JB), Mac
GASP: A Teaching Exercise on Chemical Control of Ventilation (C-BE), MS-DOS
Growing Old in a New Age–How the Body Ages (A-CPB), 1-hr. video
Growing Old in a New Age–Illness and Disability (A-CPB), 1-hr. video
The Heart (IM), 29-min. video
Heart (NEB), 14-min. video
Heart Abnormalities and EKGs: A Simulation (PLP), Apple
Heart Attack: The Unrelenting Killer (MF), 28-min. video
Heart Dissection and Anatomy (IM), 14-min. video
Hearts and Circulatory Systems (PHO), 14-min. video
How Blood Clots (PHO), 13-min. video
Heart: the Engine of Life (Q), MS-DOS CD
Human Body Series: Circulatory System (PHO), 16-min. video
Human Body Series: Respiratory System (PHO), 13-min. video
Human Circulatory System (EME), Apple II, Mac, MS-DOS
Human Electrocardiogram (INT) (SciT), Mac
Human Lung (INT), Mac
Human Physiology: Circulation (CBSC) (PH), 9-min. filmstrip
Human Physiology: Respiration (CBSC), filmstrip
Hypertension: Your Blood Pressure Is Showing (MF), 28-min. video
Incredible Voyage (CRM), 26-min. video
The Interactive Heart (Q), MS-DOS CD
Introduction to General Biology: The Human Body I (Q), Mac, DOS
Leukemia (FH), 22-min. video
Living Body: Breath of Life (FH), video
Lungs (Revised) (AIMS), Mac, Win CD, 10-min. video, laserdisc
Lymphatic System, The (IFB), 15-min. video
MacFrog Academic (INT), Mac
MacPig (INT), Mac
The Mammalian Heart (AIMS), Mac, Win CD, 15-min. video, laserdisc
Nerves and Heartbeat Rate (BSCS Classic Inquiry) (MDA), videodisc
6-10
Chapter 6 – Homeostasis: Internal Fluids And Respiration
The Nose: Structure and Function (EBE), 11-min. video
NOVA: Cut to the Heart (NEB) (WGBH), 60-min. video
NOVA: Dying to Breathe (NEB), 60-min. video
NOVA: Heart-to-Heart: The Truth About Heart Disease (NEB), 60-min. video
Our Nation’s Blood Supply: The Next Threshold for Safe Blood (FH), 22-min. video
Physiology of Exercise (CBSC), 26-min. filmstrip
Respiration (IM), 29-min. video
Respiration and Waste (WARDS), 8-min. video
Respiration in Man (EBE), 26-min. video
Respiratory Programs (C-E-G) (JB), MS-DOS
Respiratory System (PLP), MS-DOS
Respiratory System (CAM), Mac, Win CD
The Respiratory System [Simulations in Physiology] (NRCLSE), MS-DOS, Apple and Mac
Respiratory System and Its Function (ei), slides or filmstrip
RESPSYST 2.0 (C-E-G), MS-DOS
RESPWIN 3.0 (JB), Win
SimHeart (THIEME), Mac, Win CD
SimVessel (THIEME), Mac, Win CD
Tuberculosis (FH), 50-min. video
Two Hearts that Beat as One (FH), 28-min. video
VENTROL (C-E-G) (JB), MS-DOS
William Harvey (IM) (UC), 19-min. video
William Harvey and the Circulation of Blood (FH), 29-min. video
The World of Chemistry–The Precious Envelope (A-CPB), 30-min. video (atmosphere)
Young Hearts (HE), 27-min. video
6-11