1. 34
Circulation and Gas Exchange

2. Open Circulatory Systems
Circulatory systems have different-sized vessels that facilitate bulk flow and diffusion.
The O2 carried by hemoglobin is transported to tissues throughout the body by the circulatory system. Circulatory systems can be classified as closed or open
Closed systems: Closed circulatory systems are made up of a set of internal vessels and a pump—the heart—to transport the blood to different regions of the body. Closed circulatory systems have two conflicting requirements: They must produce enough pressure to carry the circulating blood to all the tissues, yet once the blood reaches smaller vessels that supply the cells within the tissues the blood pressure and flow rate must not be too high. High pressure would cause the blood to flow so quickly through smaller vessels that there would not be enough time to exchange gases.
Open systems: Generally, smaller animals, such as insects and many mollusks, have open circulatory systems that contain few blood vessels. Most of the circulating fluid, the hemolymph, is contained within the animal’s body cavity. The hemolymph bathes the animal’s tissues and organs.
Open circulatory systems have limited control of where the fluid moves. Muscles that are active in locomotion can assist circulation of the hemolymph, and some invertebrates have simple hearts with openings that help pump fluid between different regions of the animal’s body cavity.
Open circulatory systems: no vessels to transport hemolymph (blood & interstitial fluid)
Mollusks (snails, oysters, clams), Arthropods (insects, spiders, lobsters)

3. Closed Circulatory Systems
Closed circulatory systems: also called cardiovascular systems
Well-defined blood vessels
Earthworms, echinoderms, chordates, all vertebrates
Comparing closed and open circulatory systems:
Animals with closed circulatory systems tend to be larger and more active. A closed circulatory system delivers O2 at high rates to exercising tissues.
Animals with open circulatory systems are less active. That is because open circulatory systems generally operate under low pressure and have limited transport capacity. However, insects can be very active despite having an open circulatory system because they obtain O2 by their tracheal system independently of the circulatory system.
Closed circulatory systems can control blood flows to specific regions of the body by varying the resistance to flow. For example, wading birds reduce blood flow to their legs when they are in cold water to lessen heat loss, and vertebrates can increase blood flow to their muscles to deliver O2 and nutrients during exercise.
The ability of open circulatory systems to control the delivery of respiratory gases and metabolites to specific tissues and regions is limited.

4. Vessel Size
Artery: away from the heart;(NOTE: most arteries carry oxygenated blood, but not always)
Arterioles: smaller
Capillaries: consist only of endothelium for diffusion of gases
Venule: small vein
Vein: to heart (NOTE: usually carries deoxygenated blood, but not always)
Arteries and veins are composed of 3 layers:
Outer: connective tissue with elastin fibers
Middle: smooth muscle (more elastin fibers; thicker in arteries than veins)
Inner: endothelium (only layer in capillaries)
NOTE: veins are much thinner than arteries
Gas exchange
In order to pump blood through a set of closed interconnected vessels, a muscular heart is needed to produce sufficient pressure to overcome the flow resistance of the vessels.
For a fluid like blood to flow through a set of pipes, pressure (P) is required to overcome the resistance (R) to flow. The rate of blood flow is governed by P/R. That is, the rate of blood flow increases with an increase in pressure and decreases with an increase in resistance. The resistance to flow is determined
in part by the fluid’s stickiness (its viscosity) and by the vessel’s length. Longer vessels of a given size impose greater resistance.
mainly by the vessel’s radius (r). Resistance is proportional to 1/r 4, which means that if a vessel’s radius is reduced by half, its resistance to flow increases 16 times.
The high resistance of narrow vessels presents a challenge. To keep diffusion distances short, gas exchange between cells and blood requires narrow vessels. Animal circulatory systems are organized to have blood flow over longer distances in a relatively few large-diameter vessels with low resistance to flow.
Arteries are the large, high-pressure vessels that move blood flow away from the heart to the tissues.
Veins are the large, low-pressure vessels that return blood to the heart.
Arteries branch into blood vessels of progressively smaller diameter called arterioles, and arterioles ultimately connect to finely branched networks of very small blood vessels called capillaries. It is at the capillaries that gases are exchanged by diffusion with the surrounding tissues.
The number of smaller-diameter vessels at each branching point in the circulatory system greatly exceeds the number of larger diameter vessels. The reverse organization is found on the return side of circulation: Numerous capillaries drain into vessels of progressively larger diameter called venules, and the venules drain into a few larger veins that return blood to the heart.

5. LM Vein Artery Red blood cells 100 mm Basal lamina Valve Endothelium
Figure 34.9 LM
Vein
Artery
Red blood
cells
100 mm
Basal lamina
Valve
Endothelium
Endothelium
Smooth
muscle
Smooth
muscle
Connective
tissue
Connective
tissue
Capillary
Figure 34.9 The structure of blood vessels
Arteriole
Venule
Capillary bed
15 mm
Red blood cells
in capillary LM
© 2016 Pearson Education, Inc.

6. Vessel Area Vs. Flow Velocity
Capillaries in total have largest area, therefore slowest velocity (blood flow comes to a standstill in capillaries)
Arteries have faster velocities than veins
BP: main force driving blood from heart to capillaries; BP is highest in aorta and arteries; lowest in veins
SO, how does blood flow in veins?
Contracting skeletal muscles of veins
Have one-way valves
Keeps blood moving to the heart
If we sit or stand too long, the lack of muscular activity make our feet swell, with stranded fluid
Must avoid DVT (Deep Vein Thrombosis)
This organization has two advantages.
It maintains the same volume of blood flow at all levels within the circulatory system: The increased resistance to flow in the capillaries is offset by the large increase in the number of capillaries.
It enables the blood to flow more slowly in smaller vessels, providing time for gases and metabolites to diffuse into and out of the neighboring cells. The diameter of a capillary is so small that red blood cells pass through one at a time, and must be flexible to do even that.

7. Direction of blood flow in vein (toward heart)
Figure 34.11
Direction of blood flow
in vein (toward heart)
Valve (open)
Skeletal muscle
Figure Blood flow in veins
Valve (closed)
© 2016 Pearson Education, Inc.

8. Velocity (cm/sec) Pressure (mm Hg)
Figure 34.10
Area (cm2)
4,000
2,000
Velocity
(cm/sec) 40 20
120
Pressure
(mm Hg)
Systolic
pressure
Figure The interrelationship of cross-sectional area of blood vessels, blood flow velocity, and blood pressure 80 40
Diastolic
pressure
Aorta
Arteries
Arterioles
Capillaries
Venules
Veins
Venae
cavae
© 2016 Pearson Education, Inc.

9. BLOOD FLOW IN CAPILLARY BEDS
Pre-capillary sphincters regulate passage of blood into capillary beds
If sphincters relaxed, blood flows into beds
I.e. into digestive system after we eat
If sphincters contracted, capillary beds are closed; blood flow reduced to thoroughfare channel
I.e. into skeletal muscles after we eat
Therefore, might have a leg cramp swimming too soon after eating
Blood collected from local capillary networks returns to the heart through progressively larger veins. These veins ultimately drain into the two largest veins, the venae cavae. The venae cavae drain blood from the head and body into the heart.
There is little pressure available to push the blood forward in the veins because pressure has been lost to the resistance of the arterioles and capillaries. Consequently, veins are thin walled and have little smooth muscle or elastic connective tissue. Because of the low pressure, blood tends to accumulate within the veins: As much as 80% of your total blood volume resides in the venous side of your circulation at any one time. When you stand or sit for a long time, blood may pool within the veins of your limbs.
How does blood get back to the heart?
Veins located in the limbs and in the body below the heart have one-way valves that help prevent blood from pooling.
The most important aid to returning blood to the heart is the voluntary muscle contraction that occurs during walking and exercise, which exerts pressure on the veins.
Above the level of the heart, the return of blood to the heart is assisted by gravity.

10. Pressure
Water, certain ions, and other small molecules move from capillaries into the surrounding interstitial fluid by filtration, forced by blood pressure. Why doesn’t the blood plasma lose all its fluid and ions over time? The lost fluid and ions are mostly restored through osmosis.
As fluid is filtered out of the capillaries, some ions, proteins, and other large compounds remain inside, increasing in concentration. As a result, there is a tendency of fluid to flow back into the capillary by osmosis. At the same time, blood pressure decreases because of the flow resistance imposed by the capillaries. When the pressure is no longer high enough to counter osmosis, fluid moves back into the capillaries.
In vertebrates, excess extracellular fluid is also returned to the bloodstream by means of the lymphatic system, a network of vessels distributed throughout the body. The fluid that enters the lymphatic system is called the lymph. Small lymphatic vessels merge with progressively larger thin-walled vessels, draining the lymph into lymphatic ducts. The lymphatic ducts empty into the venous system. Lymphatic vessels have one-way valves, similar to those in the veins, that assist the return of lymph to the circulatory system.

11. Fish Heart & Circulatory System
The evolution of animal hearts reflects selection for a higher metabolic rate, achieved by increasing the delivery of oxygen to metabolically active cells.
Fish: 2-chambered heart and 1 circuit of blood flow
A fish heart has two chambers, the atrium and ventricle.
Deoxygenated blood returning from the fish’s tissues enters the atrium, which fills and then contracts to move the blood into a thicker-walled ventricle.
The muscular ventricle pumps the blood through a main artery to the gills for uptake of O2 and elimination of CO2.
Oxygenated blood collected from the gills travels to the tissues through a large artery called the aorta.
The small gill capillaries impose a large resistance to flow. As a result, much of the blood pressure is lost in moving blood through the gills. This loss of pressure limits the flow of oxygenated blood to body tissues.

12. Amphibian Heart & Circulatory System
Amphibians and reptiles: 3-chambered heart and a partially divided circulatory path
As animals moved onto land, the transition from breathing water to breathing air had important consequences for the organization of vertebrate circulatory systems. Land vertebrates evolved hearts that separated the circulation of deoxygenated blood pumped to their gas exchange organs from circulation of oxygenated blood delivered to their body tissues. Gas exchange became more efficient and O2 delivery increased. Metabolic rates rose, and animals became capable of greater activity.
Amphibians evolved an additional atrium, dividing their heart into two separate atria and a single ventricle. This arrangement partially separates the pulmonary and systemic circulations, so in amphibians freshly oxygenated blood can be pumped under higher pressure to the body than is the case in fishes. However, because amphibians have a single ventricle, oxygenated blood returning to the heart from the gills or lungs mixes with deoxygenated blood returning from the animal’s body before being pumped from the ventricle.

13. Pulmocutaneous circuit Pulmonary circuit
Figure 34.4
(a) Single circulation: fish
(b) Double circulation: amphibian
(c) Double circulation: mammal
Pulmocutaneous
circuit
Pulmonary
circuit
Gill
capillaries
Lung
and skin
capillaries
Lung
capillaries
Artery
Atrium
(A)
Atrium
(A)
Heart: A A
Atrium (A) V V
Ventricle (V)
Right
Left
Right
Left
Vein V
Systemic
capillaries
Systemic
capillaries
Figure 34.4 Examples of vertebrate circulatory system organization
Body
capillaries
Systemic circuit
Systemic circuit
Oxygen-rich blood
Oxygen-poor blood
© 2016 Pearson Education, Inc.

14. Mammalian Heart & Circulatory System
Birds and mammals:
4-chambered heart
Fully divided pulmonary and systemic circulations
Pulmonary circulation:
From heart to lungs
Systemic circulation:
From heart to rest of body
Mammals and birds evolved four-chambered hearts with separate atria and separate ventricles. This arrangement completely separates blood flow to the lungs from blood flow to the tissues. As a result, these animals can pump blood to their lungs under lower pressure, allowing increased uptake of O2, while at the same time supplying blood gases and nutrients to their tissues at high pressure. Metabolic rates increased, and endothermic lifestyles became possible in birds and mammals.
1.Deoxygenated blood enters the right atrium from the venae cavae.
2. When the atrium contracts, the deoxygenated blood moves through an atrioventricular (AV) valve into the right ventricle.
3. When the right ventricle contracts, blood is pumped through the pulmonary valve into the pulmonary trunk, which divides into the left and right pulmonary arteries. The blood travels to the lungs for oxygenation. The walls of the right ventricle are thinner than those of the left ventricle, and its weaker contractions eject blood at a lower pressure. As a result, the blood of the pulmonary circulation moves at a slower rate, allowing greater time for gases to diffuse into and out of the lungs.
4. The oxygenated blood returns from the lungs through the pulmonary veins and enters the left atrium.
5. When the left atrium contracts, blood is pumped through a second atrioventricular valve into the left ventricle.
6. The thick muscular walls of the left ventricle eject the blood under high pressure to the body. Oxygenated blood leaving the left ventricle passes through the aortic valve and then flows to the head and the rest of the body through a large artery called the aorta.

15. Superior vena cava Capillaries of head and forelimbs Pulmonary artery
Figure 34.5
Superior vena
cava
Capillaries of
head and
forelimbs
Pulmonary
artery
Pulmonary
artery
Capillaries
of right lung
Aorta
Capillaries
of left lung
Pulmonary
vein
Pulmonary vein
Right atrium
Left atrium
Figure 34.5 The mammalian cardiovascular system: an overview
Right ventricle
Left ventricle
Inferior vena
cava
Aorta
Capillaries of
abdominal organs
and hind limbs
© 2016 Pearson Education, Inc.

16. FLOW OF BLOOD THROUGH PULMONARY & SYSTEMIC SYSTEMS
From body (deoxy)
Down from superior vena cavae and up from inferior vena cavae (deoxy)
Right atrium (deoxy)
Right ventricle (deoxy)
To lungs (via Pulmonary Arteries: deoxygenated)
Back to left atrium (via Pulmonary Veins: oxygenated)
Left ventricle (oxy)
Arch of aorta (oxy)
To body

17. Figure 34.6 Pulmonary artery Aorta Pulmonary artery Right atrium Left
Semilunar
valve
Semilunar
valve
Figure 34.6 The mammalian heart: a closer look
Atrioventricular
(AV) valve
Atrioventricular
(AV) valve
Right
ventricle
Left
ventricle
© 2016 Pearson Education, Inc.

18. HEART Heart: mostly cardiac muscle; striated and branched
Cone-shaped organ; size of clenched fist, just under sternum
Enclosed in pericardial sac
Atrium/atria: receive blood to heart
Top 2 chambers, thinner walled….only pump to ventricles
Right atrium: received deoxygenated blood from body
Left atrium: receives oxygenated blood from lungs
Ventricles: pump blood out of heart
Bottom 2 chambers; thicker walled
Right ventricle: pumps deoxygenated blood to lungs
Left ventricle: pumps oxygenated blood to body

19. Heart Valves
Between right atrium and right ventricle: Tricuspid AV Valve
Between left atrium and left ventricle: Bicuspid or Mitral AV Valve
Between right ventricle and lungs: Pulmonary Semilunar Valve
Between left ventricle and aorta: Aortic Semilunar Valve
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20. BLOOD PRESSURE
Blood pressure: pushing force exerted by blood against walls of blood vessels
Greatest in major arteries attached directly to heart (aorta, pulmonary artery)
Decreases with distance from heart
BP is main force driving blood flow
Creates a blood pressure gradient (I.e. blood flows into lower pressure arteries from higher pressure ones)
Brachial artery: on upper arm; most frequent site for taking BP using stethescope and sphygmomanometer (mm Hg)

21. Cardiac Cycle
The contraction of the two atria followed by contraction of the two ventricles makes up the cardiac cycle.
The cardiac cycle is divided into two main phases. Systole is the contraction of the ventricles, and diastole is the relaxation of the ventricles.
During systole, blood is pumped from the heart into the pulmonary and systemic circulations.
During diastole, the atria contract and the ventricles fill with blood.

22. Atrial systole and ventricular diastole Atrial and ventricular
Figure 34.7-s3
Atrial systole and
ventricular diastole
Atrial and
ventricular
diastole
0.1
sec
Figure 34.7-s3 The cardiac cycle (step 3)
0.3 sec
0.4
sec
Ventricular systole
and atrial diastole
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23. Blood Pressure Cont’d Systolic BP: upper number Average 120 mm Hg
Caused by systole (contracting and emptying); lasts 0.4 secs
Diastolic BP: lower number
Average 80 mm Hg
Caused by diastole (relaxing and filling); lasts 0.4 secs
Entire cardiac cycle lasts 0.8 secs, giving a pulse (heart beat) of about 75 beats/min
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24. Hypertension versus Hypotension
Hypotension (low BP): below normal BP; <100/60
i.e. accidentally cut an artery
Hypertension (high BP): above normal BP, >140/90
High BP may overstretch, thin out arterial walls
May create aneurysms…….abnormally widened out arteries that will rupture
Arteriosclerosis: hardening of walls of artery with calcium
Hypertension and arteriosclerosis worsen each other; called positive feedback mechanisms (just continues to get worse)

25. Heart Beat Basics
The cardiac muscle cells that make up the walls of the atria and ventricles must contract in a coordinated fashion. Thus, these cells must be depolarized in unison by an action potential.
Cardiac muscle cells are distinct from skeletal muscle cells in two ways:
Specialized cardiac muscle cells can generate action potentials on their own, independently of the nervous system.
Cardiac muscle cells are in electrical continuity with one another, meaning that they can pass their action potentials to adjacent cells.
These two features ensure that all muscle cells in a region surrounding a heart chamber are activated and contract in unison. The specialized cardiac muscle cells capable of generating action potentials independently function as a pacemaker that causes the heart to beat with a basic rhythm. These cells stimulate neighboring cells to contract in synchrony. They are found in two specialized regions of the heart—the sinoatrial (SA) and atrioventricular (AV) nodes.
Control of Heart Beat: initiated by SA (sino-atrial) node ; also called natural pacemaker
SA node controls contraction of atria
AV node controls contraction of ventricles

26. Heart Beat Process Heart Rate: same as pulse
Number of times the heart beats/min; usually about 75 beats/min at rest
Increases during anxiety and/or exercise
Decreases severely in seniors (they may need a pacemaker)
The heartbeat is initiated at the sinoatrial node, located at the junction of the vena cava and right atrium.
When the pacemaker cells in the SA node fire an action potential, action potentials spread rapidly from one cell to the next throughout the right and left atria, causing them to contract in unison.
Because there is no electrical contact between the atria and ventricles, the ventricles do not contract. Instead, the depolarization in the atria reaches a second set of pacemaker cells, located in the atrioventricular (AV) node.
3a. A modified set of cardiac muscle fibers transmits action potentials from the AV node to the base of the ventricles.
3b. The depolarization spreads throughout the ventricle walls, causing the ventricles to contract in unison. The delay in transmission from the AV node and through the conducting fibers ensures that the ventricles do not contract until they are fully filled with blood from the atria.

27. EKG & Cardiac Output Heart Sounds: detected by stethoscope
Electrodes placed over the surface of the chest and other body regions can record the electrical currents produced by the depolarization of the heart while it beats. This type of recording is called an electrocardiogram. Cardiologists use EKGs to diagnose heart problems or to determine what region of the heart has been damaged following a heart attack.
The volume of blood pumped by the heart over a given interval of time is its cardiac output (CO). This quantity is the key measure of heart function. Cardiac output is determined by calculating the product of heart rate (HR) and the volume of blood pumped during each beat, the stroke volume (SV):
CO = HR X SV
For example, if heart rate increases 50% and the heart’s stroke volume increases 10%, the heart’s cardiac output increases 65% [(1.5 x 1.1) - 1 X 100%].
Cardiac output rises or falls in response to the metabolic demand for O2. Stroke volume depends on how much blood returns to fill the heart and how strongly the heart contracts. The strength of the heartbeat is adjusted in order to match heart filling to heart emptying: when exercise increases the return of blood to the heart, the ventricles contract more forcefully.
The correspondence of changes in stroke volume to changes in heart filling is described by Starling’s Law. It provides the means by which cardiac is are adjusted to meet changing rates of blood supply.
Heart Sounds: detected by stethoscope
Lub: 1st low pitch; contraction of ventricles and closing of AV valves
Dupp: 2nd high pitch; closing of semilunar valves

28. Atherosclerosis, Heart Attacks, and Stroke
Damage or infection can roughen the lining of arteries and lead to atherosclerosis, the hardening of arteries due to accumulation of fatty deposits
Cholesterol is a key player in the development of atherosclerosis
Low-density lipoprotein (LDL) delivers cholesterol to cells for membrane production
High-density lipoprotein (HDL) scavenges excess cholesterol for return to the liver
Risk for heart disease increases with a high LDL to HDL ratio
Inflammation, the body’s reaction to injury, is also a factor in cardiovascular disease
© 2016 Pearson Education, Inc. 28

29. Coronary arteries supply oxygen-rich blood to the heart muscle
A heart attack, or myocardial infarction, is the death of cardiac muscle tissue resulting from blockage of one or more coronary arteries
Coronary arteries supply oxygen-rich blood to the heart muscle
A stroke is the death of nervous tissue in the brain, usually resulting from rupture or blockage of arteries in the head
Angina pectoris is caused by partial blockage of the coronary arteries and may cause chest pain
© 2016 Pearson Education, Inc. 29

30. Risk Factors and Treatment of Cardiovascular Disease
A high LDL to HDL ratio increases the risk of cardiovascular disease
The proportion of LDL relative to HDL is increased by smoking and consumption of trans fats and decreased by exercise
Drugs called statins reduce LDL levels and risk of heart attacks
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31. Inflammation plays a role in atherosclerosis and thrombus formation
Aspirin inhibits inflammation and helps reduce the risk of heart attacks and stroke
Hypertension (high blood pressure) contributes to the risk of heart attack and stroke
Hypertension can be reduced by dietary changes, exercise, medication, or some combination of these
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32. Figure 34.16 Endothelium Lumen Thrombus Plaque 1 mm 1 mm
Figure Atherosclerosis
1 mm
1 mm
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33. Lymphatic System Interstitial Blood fluid capillary Adenoid Tonsils
Figure 34.12
Lymphatic System
Interstitial
fluid
Blood
capillary
Adenoid
Tonsils
Lymphatic
vessels
Thymus
(immune
system)
Lymphatic
vessel
Tissue cells
Lymphatic
vessel
Spleen
Lymph
nodes
Figure The human lymphatic system
Appendix
(cecum)
Masses of
defensive
cells
Lymph node
Peyer’s patches
(small intestine)
© 2016 Pearson Education, Inc.

34. LYMPHATIC SYSTEM Circulatory function
Collect excess fluids/plasma proteins (stranded fluid) from surrounding tissue and return them to deoxygenated blood in right atrium
Immune function
Filters lymph…has WBC waiting in lymphatic organs and lymph nodes to trap antigens and lyse them
Consists of the following components:
Lymph…..has the same composition as interstitial fluid (also known as stranded fluid, or edema); composed of fluid, plasma proteins, escaped blood cells
Lymph vessels….returns excess fluid to blood ; drains into right atrium; has one-way valves
Lymphatic organs: thymus, spleen, tonsils/adenoids, appendix, Peyer’s patch on small intestines
Lymph nodes: small bodies interspersed along lymph vessels; act as cleaning filters and immune centers against infection; get large with infections or cancer

35. SPLEEN
Largest lymphatic organ; on left side; between diaphragm and stomach
4 functions:
Filters blood for immune function; has macrophages waiting inside
Destroys old RBC/recycles iron (overlaps with liver)
RBC do not mitose. Old ones are destroyed and new ones made in bond marrow every 120 days. Iron is recycled for use in liver. The rest of hemoglobin is converted to bilirubin, the chief component of bile.
Provides a reservoir of blood
Retains large quantities of blood; contains about 33% blood platelets
Spleen (and liver) produce blood cells during fetal development (before bone takes over)

36. Mammalian Blood Plasma 55% Cellular elements 45% Constituent
Figure 34.13
Mammalian Blood
Plasma 55%
Constituent
Major functions
Cellular elements 45%
Water
Solvent
Number
per mL (mm3)
of blood
Cell type
Functions
Ions (blood
electrolytes)
Osmotic balance,
pH buffering,
and regulation
of membrane
permeability
Separated
blood
elements
Leukocytes (white blood cells)
5,000-10,000
Defense and
immunity
Sodium
Potassium
Calcium
Magnesium
Chloride
Bicarbonate
Lymphocytes
Basophils
Plasma proteins
Albumin
Osmotic balance,
pH buffering
Eosinophils
Immunoglobulins
(antibodies)
Defense
Monocytes
Figure The composition of mammalian blood
Neutrophils
Apolipoproteins
Lipid transport
Fibrinogen
Clotting
Platelets
250, ,000
Blood clotting
Substances transported by blood
Nutrients (such as glucose, fatty
acids, vitamins)
Waste products of metabolism
Respiratory gases (O2 and CO2)
Hormones
Erythrocytes (red blood cells)
5,000,000-
6,000,000
Transport
of O2 and
some CO2
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37. COMPOSITION OF MAMMALIAN BLOOD
Blood is a type of connective tissue
About 5 liters in body; pH
55% Plasma (fluids)
Water, ions, hormones, fibrinogen, antibodies
45% cellular elements
Erythrocytes, RBC; transport O2; non-nucleated; 1 loop RBC = 20 secs
Leukocytes, WBC: defense & immunity
Monocytes:/macrophages: phagocytic
Lymphocytes: primary immune system cells
Basophils
Eosinophils
Neutrophils
Platelets, also called thrombocytes. Blood clotting

38. Figure 34.13-1 The composition of mammalian blood (part 1: plasma)
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39. Cellular elements 45% Number per mL (mm3) of blood Cell type Functions
Figure
Cellular elements 45%
Number per mL
(mm3) of blood
Cell type
Functions
Leukocytes (white blood cells)
5,000-10,000
Defense and
immunity
Lymphocytes
Basophils
Eosinophils
Monocytes
Neutrophils
Figure The composition of mammalian blood (part 2: cellular)
Platelets
250, ,000
Blood clotting
Erythrocytes (red blood cells)
5,000,000-6,000,000
Transport of O2
and some CO2
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40. DIFFERENTIATION OF BLOOD CELLS
All blood cells originate from stem cells in red marrow of bones (ribs, vertebrae, pelvis, breastbone)
These differentiate into lymphoid stem cells & myeloid stem cells
Lymphoid stem cells give rise to:
B and T lymphocytes ( a type of leukocyte)
Myeloid stem cells:
RBC
Platelets
Other 4 WBC

41. Differentiation of Blood Cells
Figure 34.14
Differentiation of Blood Cells
Stem cells
(in bone marrow)
Lymphoid
progenitor
cells
Myeloid
progenitor
cells
B cells T cells
Figure Differentiation of blood cells
Erythrocytes
Basophils
Neutrophils
Lymphocytes
Monocytes
Eosinophils
Platelets
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42. BLOOD CLOTTING
Caused by appearance of rough spot in lining of blood vessel
Platelets stick; get platelet plug
Finally fibrin clot

43. Fibrin clot formation Collagen fibers Platelet plug Fibrin clot
Figure
Collagen
fibers
Platelet
plug
Fibrin clot
Platelet
Clotting factors from:
Fibrin clot
formation
Platelets
Damaged cells
Plasma (factors include calcium, vitamin K)
Figure Blood clotting (part 1: detail)
Enzymatic cascade
Prothrombin
Thrombin
Fibrinogen
Fibrin
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44. Gas Exchange by Diffusion
Respiration and circulation depend on diffusion over short distances and bulk flow over long distances.
Human Gas Exchange System:
Called respiration or breathing
Uptake of O2 from air; release of CO2
Animals have evolved mechanisms to acquire O2 from their environment and to eliminate excess CO2 from their body. These mechanisms make up the process known as animal respiration—or “breathing.” The transport of O2 and CO2 between an animal and its environment is referred to as gas exchange.
Single-celled organisms and simple animals and plants exchange gases by diffusion. Diffusion is the random movement of individual molecules. Diffusion results in the net movement of molecules from regions of higher concentration to regions of lower concentration until the substance is evenly distributed.
Given a large enough surface, diffusion is an extremely effective way to exchange gases and other substances over short distances between two compartments. The rate of diffusion is directly proportional to the surface area over which exchange occurs and to the concentration difference, and inversely proportional to the distance over which the molecules move.
Because effective transport by diffusion is limited to short distances, some of the earliest and simplest invertebrate animals are composed of thin sheets of cells with a large surface area. For example, sponges and sea anemones have a thin body with a central cavity through which water circulates, and flatworms have a flattened body surface.

45. Gas Exchange Organs
Respiration provides oxygen and eliminates carbon dioxide in support of cellular respiration.
All animals obtain O2 from the surrounding air or water.
Aquatic animals like crabs, aquatic salamanders, and fish that take in O2 from water breathe through gills, highly folded delicate structures that facilitate gas exchange with the surrounding water.
Many terrestrial animals, such as reptiles, birds, and mammals, have internal lungs for gas exchange.
Terrestrial insects evolved a system of air tubes called tracheae that branch from openings along their abdominal surface into smaller airways. These smaller airways, termed tracheoles, supply air directly to the cells within their body.
Gas exchange organs are shaped and folded to provide large surfaces for gas exchanges. These surfaces are only one or two cell layers thick, providing a diffusion distance of as little as 1 to 2 μm.
Aquatic animals exchange gases with water thru gills
Terrestrial animals breathe air by internal trachae or lungs.

46. Diffusion
Diffusion: net movement of molecules from regions of higher concentration to regions of lower concentration
Unicellular organisms
Simple plants & animals
Effective only over short distances and requires large surface areas with thin barriers
I.e. sponges, sea anemones, flatworms
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47. BULK TRANSPORT
Bulk transport: physical movement of fluid and gases over a given distance
Occurs in 2 steps:
Ventilation: movement of respiratory medium (air or water) past a specialized respiratory surface
Circulation: movement of specialized body fluid that carries O2 and CO2
Circulatory fluid in invertebrates: hemolymph
Circulatory fluid in vertebrates: blood
O2 delivered to tissues in 4 steps:
Bulk flow of water or air past lungs or gills
Diffusion of O2 across lungs into circulatory system
Bulk flow thru circulatory system
Diffusion of O2 into tissues/cells

48. PARTIAL PRESSURE OF A GAS
With a gas, we discuss its partial pressure instead of concentration
pp = the concentration of a gas in air/dissolved water
At sea level: the pp of O2 = 160 mm Hg
Calculated as: O2 makes up 21% of atmosphere; 0.21 x 760 mm Hg (atmospheric pressure at sea level) = 160 mm Hg
Therefore, for O2 to diffuse from the air into cells, the pp of O2 inside cells must be less than the pp of O2 in the atmosphere (<160 mm Hg).
Pp of CO2 = 0.23 mm Hg
When talking about the diffusion of a gas, we usually consider its partial pressure rather than its concentration. The partial pressure (p) of a gas is defined as its fractional concentration relative to other gases present, multiplied by the overall (that is, the atmospheric) pressure exerted on the gases.
Pressure is measured in units of millimeters of mercury (mmHg). Oxygen makes up approximately 21% of the gases in air. At sea level, atmospheric pressure is approximately 760 mmHg. Thus O2 in the atmosphere exerts a partial pressure (pO2) of about 160 mmHg (0.21  760).
For O2 to diffuse from the air into cells, the partial pressure of O2 inside the cells must be lower than the partial pressure of O2 in the atmosphere.
Gas will diffuse from a region of higher pp to lower pp 48

49. Countercurrent exchange
Figure 34.18
O2-poor blood
Lamella
Gill
arch
O2-rich blood
Blood
vessels
Gill arch
Water
flow
Operculum
Water flow
Blood flow
Countercurrent exchange
P (mm Hg) in water O2
Figure The structure and function of fish gills
Gill filaments
Net
diffu-
sion
of O2
P (mm Hg)
in blood O2
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50. Respiration by Fish Gills
Countercurrent flow of water relative to blood in gills enhances O2 extraction from water
Fish need sufficient O2 to meet the energy demands of swimming. Their respiratory organ, the gills, is located in a chamber behind the mouth cavity. Fish actively pump water through their mouth and over the gills. Fish greatly reduce the energy cost of moving dense, viscous water by maintaining a continuous, unidirectional flow of water past their gills. In bony fishes, a protective flap overlying the gills, called the operculum, expands laterally to draw water over the gills while the mouth is refilling before its next pumping cycle.
Gills consist of a series of gill arches located on either side of the animal behind the mouth cavity and, in bony fishes, beneath the operculum. Each gill arch consists of two stacked rows of flat, leaf-shaped structures called gill filaments. Numerous lamellae, thin sheetlike structures, are evenly but tightly spaced along the length of each gill filament. The lamellae extend upward from the filament’s surface.
A series of blood vessels brings O2-poor blood from the heart to the lamellar surfaces. The lamellae are composed of flattened epithelial cells and are extremely thin, so the water passing outside and blood passing inside the lamellae are separated by only about 1 to 2 mm. The lamellae give the gills an enormous surface area for their size.
The lamellae are oriented so that the blood flowing through them in a capillary network moves in a direction opposite to the flow of water past the gill. This type of organization, in which fluids with different properties move in opposite directions, is called countercurrent flow. It is an efficient way to exchange properties between the two fluids. The property can be a chemical property, such as O2 concentration, or a physical property, such as heat.

51. Concurrent & countercurrent Exchange
Used widely in nature
i.e. fish gills
Two fluids exchange properties efficiently (such as oxygen, carbon dioxide, heat, etc)
Consider for a moment two tubes right next to each other, one carrying hot water and the other carrying cold water. If we want to make the hot water cold and the cold water hot, the efficiency of heat transfer between the two tubes depends on the direction of flow. When the water in the tubes flows in the same direction (concurrent flow), the hot water gets colder and the cold water gets hotter since heat is transferred between the two tubes. Given enough distance, the water will be at an intermediate (warm) temperature at the end of the tubes, reaching the same average temperature in both tubes.
Now consider what happens when the water in the two tubes flows in opposite directions (countercurrent flow). In this case, the cold water encounters increasingly hot temperatures and, given enough distance, becomes nearly as hot as the hot water entering the other tube. Similarly, the hot water encounters increasingly cold temperatures, and becomes nearly as cold as the cold water entering the other tube. With countercurrent flow, the two flows essentially exchange properties (heat, in this example).
This mechanism, known as countercurrent exchange, is used widely in nature. As a result of countercurrent exchange, fish gills can extract nearly all the O2 in the water that passes over them. At the same time, CO2 readily diffuses out of the blood vessels and into the water that leaves the gill chamber. A set of blood vessels carries the O2-rich blood away from the gills to supply the fish’s body.

52. Lung Anatomy
Despite the limitations of tidal respiration, mammalian lungs are well adapted for breathing air. They have an enormous surface area and a short diffusion distance for gas exchange. Consequently, the lungs of mammals supply O2 quickly enough to support high metabolic rates.
Except in the case of birds, the lungs of air-breathing vertebrates are blind-ended sacs located within the thoracic cavity.
Air is taken in through the mouth and nasal passages, and then passes through the larynx.
Air then enters the trachea, the central airway leading to the lungs. The trachea divides into two airways, called primary bronchi, one of which supplies each lung. The trachea and bronchi are supported by rings of cartilage that prevent them from collapsing during respiration, ensuring that airflow meets with minimal resistance.
The primary bronchi divide into smaller secondary bronchi and again into finer bronchioles. This branching continues until the terminal bronchioles have a diameter of less than 1 mm.
The very fine bronchioles end with clusters of tiny thin-walled sacs called the alveoli. Here diffusive gas exchange takes place. As a result of this branching pattern, each lung consists of several million alveoli, providing a large surface area.
Small blood vessels, called pulmonary capillaries, supply the alveolar wall. Each alveolus is lined with thin epithelial cells in intimate contact with the endothelium of these small blood vessels.
The alveoli are lined with mucus-secreting cells. These cells keep the inside surface of the alveoli coated with a fluid film. The moisture in the film helps O2 molecules move from the air into solution and thus diffuse across the alveolar wall. Other alveolar epithelial cells produce a compound called surfactant, which acts like soap to reduce the surface tension of the fluid film. The surfactant allows the lungs to be inflated easily at low volumes when the alveoli are partially collapsed and small. It also ensures that alveoli of different sizes inflate with similar ease, enabling uniform ventilation of the lung.
The mucus-secreting cells also trap and remove foreign particles and microorganisms that an animal may breathe in. Beating cilia on the surface of these cells move the mucus and foreign debris out of the lungs and into the throat, where it is swallowed and digested.

53. Gas Transport & Exchange
Coordination of Circulation and Gas Exchange
Blood (deoxy) entering capillaries of lungs has a lower pO2 and a higher pCO2 than air in alveoli
Therefore, O2 diffuses into capillaries and CO2 diffuses out
In tissue capillaries, oxygenated blood diffuses O2 into tissues and CO2 into blood
Larger, more-complex animals transport O2 and CO2 longer distances to cells within their body. These animals rely on bulk flow in addition to diffusion. Bulk flow is the physical movement of fluid over a given distance. Specialized pumps, like the heart, generate the pressure that is required to move the fluid.
Bulk flow occurs in two steps to meet the gas exchange needs of cells in larger animals:
The first is ventilation. Ventilation is the movement of the animal’s respiratory medium—water or air—past a specialized respiratory surface.
The second is circulation. Circulation is the movement of a specialized body fluid that carries O2 and CO2. The circulatory fluid is called hemolymph in invertebrates and blood in vertebrates. This fluid delivers O2 to cells within different regions of the body and carries CO2 back to the respiratory exchange surface.
Gas exchange in complex multicellular organisms can be viewed as a series of four linked steps. To deliver O2 to the mitochondria within their cells:
Animals move fresh air or water past their respiratory exchange surface in the process of ventilation (the first part of bulk flow). Ventilation maximizes the concentration of O2 in the air or water on the outside of the respiratory surface.
The buildup of O2 favors the diffusion of O2 into the animal across its respiratory surface. O2 diffuses into the blood.
O2 is transported by the circulation to the tissues. Internal circulation again serves to maximize the concentration of O2 outside cells.
Oxygen diffuses from the blood across the cell membrane and into the mitochondria, where it burns fuels for ATP production.
The same four steps occur in reverse to remove CO2 from the body.

54. Tidal Ventilation
Terrestrial vertebrates inflate/deflate lungs by bidirectional tidal ventilation driven by changes in pressure
Called a Negative Pressure System
Inhalation: lungs & rib cage expand, intercostal muscles of diaphragm contract/move down; air is pulled into lungs
Exhalation: lungs & rib cage compress, muscles of diaphragm relax/move up; forces air out
Unlike fish gills, the lungs of most land vertebrates inflate and deflate to move fresh air with O2 into the lungs and expire stale air with CO2 out of the lungs. The low density and viscosity of air enables these animals to breathe by tidal ventilation without expending too much energy. Air is drawn into the lungs during inhalation and moved out during exhalation.
Inhalation: Mammals and reptiles expand their thoracic cavity to draw air inside their lungs on inhalation. The expansion of the lungs causes the air pressure inside lungs to become lower than the air pressure outside the lungs. The resulting negative pressure draws air into the lungs. In contrast, amphibians inflate their lungs by pressure produced by their mouth cavity.
Exhalation: In most animals, exhalation is passively driven by elastic recoil of tissues that were previously stretched during inhalation. The contraction of the lungs causes the air pressure inside the lungs to become higher than the air pressure outside the lungs. The resulting positive pressure forces air out of the lungs.
The diaphragm is a domed sheet of muscle located at the base of the lungs that separates the thoracic and abdominal cavities. In mammals, inhalation during normal, relaxed breathing is driven by contraction of the diaphragm. Exhalation occurs passively by elastic recoil of the lungs and chest wall.
During exercise, other muscles assist with inhalation and exhalation. For example, the intercostal muscles are attached to adjacent pairs of ribs. These muscles assist the diaphragm by elevating the ribs on inhalation and depressing the ribs during exhalation. The action of the intercostal muscles helps to produce larger changes in the volume of the thoracic cavity, increasing the negative pressure that draws air into the lungs during inhalation and assisting elastic recoil of the lungs and chest wall to pump air out of the lungs during exhalation.

55. enveloping alveoli (SEM)
Figure 34.20
Branch of
pulmonary artery
(oxygen-poor
blood)
Branch of
pulmonary vein
(oxygen-rich
blood)
Terminal
bronchiole
Nasal
cavity
Pharynx
Left
lung
Larynx
(Esophagus)
Alveoli
Trachea
50 mm
Right lung
Bronchus
Capillaries
Figure The mammalian respiratory system
Bronchiole
Diaphragm
(Heart)
Dense capillary bed
enveloping alveoli (SEM)
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56. RESPIRATORY SYSTEM Nose: warms and moistens air
Trachea: cartilaginous tube that leads to lungs
Epiglottis: flap of tissue that prevents food from entering trachea
Swallowing blocks lungs: trachea moves up, covered by epiglottis
Bronchi: 2 smaller tubes in lungs; from trachea; have primary bronchi, secondary and tertiary
Bronchioles: even smaller tubes in lungs; terminal bronchioles end in air sacs called alveoli
Alveoli: site of gas exchange
Coated with surfactants, which keep them from sticking closed
Right lung: has 3 lobes; Left lung: has 2 lobes
Diaphragm

57. Tidal Volume 0.5 l of air every cycle
Tidal Volume: volume of air inhaled and exhaled during normal breathing
0.5 l of air every cycle
Ventilation Rate: breathing frequency x tidal volume
I.e. with a breathing rate of 12 breaths/min, ventilation rate = 6 l/min
When more O2 is needed during exercise, both breathing frequency and tidal volume increase
At rest, we inhale and exhale about 0.5 liter of air every cycle. This amount represents the tidal volume of the lungs. The ventilation rate is
breathing frequency  tidal volume
With a breathing frequency of 12 breaths per minute, the ventilation rate is 6 liters per minute. When more O2 is needed during exercise, both breathing frequency and tidal volume increase to elevate ventilation rate.
The fresh air inhaled during tidal breathing mixes with O2-depleted stale air that remains in the airways after exhalation. As a result, the pO2 in the lung (approximately 100 mmHg in humans) is lower than the pO2 of freshly inhaled air (approximately 160 mmHg at sea level). Consequently, the fraction of O2 that can be extracted is lower than the fraction that can be extracted by the countercurrent flow of fish gills, which can reach 90% or more.
Typically, mammalian lungs extract less than 25% of the O2 in the air, and reptile and amphibian lungs extract even less. Nevertheless, the disadvantages of tidal respiration are offset by the ease of ventilating the lung at high rates and the high O2 content of air.

58. Exhaled air Inhaled air Alveolar spaces Alveolar epithelial cells CO2
Figure 34.UN02
Exhaled air
Inhaled air
Alveolar
spaces
Alveolar
epithelial
cells
CO2 O2
Alveolar
capillaries
Pulmonary
arteries
Pulmonary
veins
Systemic
veins
Systemic
arteries
Figure 34.UN02 Summary of key concepts: double circulation
Heart
Systemic
capillaries
CO2 O2
Body tissue
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59. Homeostasis in Breathing
Breathing Control Centers; pons and medulla oblongata in brain
Autonomically regulate breathing
Respond first to high CO2 levels, then lowered pH, then low O2 levels
Animals adjust their respiratory rate to meet their cells’ changing demand for O2. Respiration is unique in that it is controlled by both the voluntary and involuntary components of the nervous system. In sleep, breathing is maintained at a resting rate by the involuntary part of the nervous system. In most circumstances, breathing is controlled unconsciously.
Homeostasis often depends on sensors that monitor the levels of the chemical being regulated. In the case of breathing, the sensors are chemoreceptors located within the brainstem and in sensory structures called the carotid and aortic bodies.
The carotid bodies sense O2 and proton (H+) concentrations of the blood going to the brain.
The aortic bodies monitor their levels in blood moving to the body.
Chemoreceptors in the brainstem sense CO2 and H+ concentrations.
The most important factor in the control of breathing is the amount of CO2 in the blood. If the concentration of CO2 in the blood is too high, chemoreceptors in the brainstem stimulate motor neurons that activate the respiratory muscles to contract more strongly or more frequently. Stronger or faster breathing rids the blood of excess CO2 and increases the supply of O2 to the body.
Breathing can also be controlled voluntarily.
Holding the breath makes it possible for humans and marine mammals to dive under water.
Sound is produced by voluntarily adjusting the magnitude and rate of airflow over the vocal cords of mammals, the syrinx of songbirds, or the glottal folds of calling amphibians, such as some toads and frogs.

60. NORMAL BLOOD pH (about 7.4) Blood CO2 level falls and pH rises.
Figure s4
NORMAL BLOOD pH
(about 7.4)
Blood CO2 level falls
and pH rises.
Blood pH falls
due to rising levels of
CO2 in tissues (such as
when exercising).
Medulla detects
decrease in pH of
cerebrospinal fluid.
Cerebrospinal
fluid
Carotid
arteries
Aorta
Sensors in major
blood vessels
detect decrease
in blood pH.
Signals from
medulla to rib
muscles and
diaphragm
increase rate
and depth of
ventilation.
Figure s4 Homeostatic control of breathing (step 4)
Medulla
oblongata
Medulla receives
signals from
major blood
vessels.
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61. Structure of Hemoglobin & Myoglobin
Red blood cells produce hemoglobin, greatly increasing the amount of oxygen transported by the blood.
Blood plasma is the fluid portion of blood without the cells. It can hold only as much O2 or CO2 as can be dissolved in solution. How much O2 goes into solution at a given partial pressure is a measure of its solubility. Because O2 is about 30 times less soluble than CO2, only about 0.2 ml of O2 can be carried in 100 ml of blood.
In both vertebrates and invertebrates, hemoglobin evolved as a specialized iron-containing, or heme, molecule for O2 transport. Hemoglobin gives the cells and the blood their red appearance. By binding O2 and removing it from solution, hemoglobin increases the amount of O2 in the blood a hundredfold.
After O2 diffuses into the blood, it diffuses into the red blood cells and binds to the heme groups in hemoglobin.
Hemoglobin’s binding of O2 removes O2 from solution, keeping the pO2 of the red blood cell below that of the blood plasma so that O2 continues to diffuse into the cell.
The removal of O2 from the plasma, in turn, keeps the pO2 of the plasma below that of the lung alveolus, so O2 continues to diffuse from the lungs into the blood.
Because of its greater solubility, CO2 is transported in solution within the blood. Most of the CO2 (about 95%) in the blood is converted to carbonic acid, which dissociates to form bicarbonate ions (HCO3–) and protons.
Hemoglobin’s 3-dimensional structure was determined in the 1950s by Max Perutz and John Kendrew using X-ray crystallography. They showed that adult hemoglobin consists of four subunits, two α (alpha) and two β (beta) subunits. Each subunit contains a heme group that contains iron, which is the site of O2 binding.
Blood plasma cannot hold very much O2 in solution due to its low solubility
Hemoglobin: specialized respiratory pigment found in all vertebrate RBCs
RBC contain hemoglobin with iron-containing heme groups that reversibly bind and release O2
Myoglobin: binds and stores O2 in muscle cells; has greater affinity for O2 than hemoglobin; it will give up its O2 only when concentrations get very low

62. O2 saturation of hemoglobin (%) O2 saturation of hemoglobin (%) 100
Figure 34.26
O2 saturation of hemoglobin (%)
O2 saturation of hemoglobin (%)
100
100
O2 unloaded
to tissues
at rest
pH 7.4 80 80
pH 7.2
O2 unloaded
to tissues
during
exercise
Hemoglobin
retains less
O2 at lower pH
(higher CO2
concentration) 60 60 40 40 20 20 20 40 60 80
100 20 40 60 80
100
PO2 (mm Hg)
Figure Dissociation curves for hemoglobin at 37°C
Tissues during
exercise
Tissues
at rest PO2 (mm Hg)
Lungs
(a) PO2 and hemoglobin dissociation at pH 7.4
(b) pH and hemoglobin dissociation
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63. O2 saturation of hemoglobin (%) 100
Figure
O2 saturation of hemoglobin (%)
100
pH 7.4 80
pH 7.2
Hemoglobin
retains less
O2 at lower pH
(higher CO2
concentration) 60 40 20
Figure Dissociation curves for hemoglobin at 37°C (part 2: variable pH) 20 40 60 80
100
PO2 (mm Hg)
(b) pH and hemoglobin dissociation
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