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Chapter 42:
Circulation / Gas Exchange
Transport systems connect
organs of exchange with body cells
Diffusion
Lung
Blood
Bulk Flow
(Pressure)
Blood
Cells
100 m 1 s
1 mm 100 s
1 cm 10000 s
d = t2
Chapter 42: Circulation / Gas Exchange
Methods of Fluid Circulation:
1) Gastrovascular Cavities (e.g. cnidarians / flatworms)
Campbell et al. – Figure 42.2
• Digestive cavity also serves to distribute nutrients (diffusion to body cells)
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Methods of Fluid Circulation:
2) Open Circulatory Systems (e.g., insects / arthropods / mollusks)
• No distinction between blood and
interstitial fluid (“blood” = hemolymph)
• Blood is confined to vessels (distinct from interstitial fluid)
Chapter 42: Circulation / Gas Exchange
• Three basic components:
1) Circulatory fluid (= blood)
2) Set of tubes (= blood vessels)
3) Muscular pump (= heart)
3) Closed Circulatory System (e.g., vertebrates)
Campbell et al. – Figure 42.3
Cardiovascular System:
Chapter 42: Circulation / Gas Exchange
Heart
Elastic
Arteries
Muscular
ArteriesArterioles
Capillaries
Veins
1) Arteries (away from heart)
Vessel Types:
Venules
2) Capillaries
3) Veins (toward heart)
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Metabolic rate critical factor in evolution of cardiovascular systems:
( metabolic rate = complexity of system)
Chapter 42: Circulation / Gas Exchange
3 – Chambered Heart
Mixing of oxygen-rich blood
and oxygen-poor blood (= constrains O2 delivery)
(e.g., amphibian)
4 – Chambered Heart
Complete separation of
O2-rich and O2-poor blood (= enhanced O2 delivery)
(e.g., mammals / birds)
2 – Chambered Heart
Slow flow of blood to
systemic circuit (= constrains
O2 movement to tissue)
(e.g., fish)
Campbell et al. – Figure 42.4 / 42.5
Overview of Mammalian Cardiovascular System:
Atria:
• Receiving chambers
• Small, thin-walled
Ventricles:
• Discharging chambers
• Large, thick-walled (Left >> Right)
Chapter 42: Circulation / Gas Exchange
Campbell et al. – Figure 42.6
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Cardiac Cycle (one complete pumping and filling of the heart):
Systole:
Contraction phase of heart
Diastole:
Relaxation phase of heart
• Atrioventricular valves
• Semilunar valves
Heart murmur
Cardiac Output:
Volume of blood / minute
pumped out by a ventricle
CO = HR x SVHeart
Rate
Stroke
VolumeCOaverage = 70 beats / min x 75 ml / beat = 5.25 L / min
Valves supply one-way
flow of blood:
Chapter 42: Circulation / Gas ExchangeCampbell et al. – Figure 42.8
Intrinsic Conduction System (coordinates heart beat):
Step 1: Depolarization wave initiated by sinoatrial node (SA Node = pacemaker)
• Located in right atrial wall; auto-rhythmic cells (100 beats / min)
Step 2: Impulse briefly delayed at atrioventricular node (AV Node)
• Allows for atria to complete contractions
Step 3: Impulses pass down bundle branches to apex of heart before racing
up Purkinje fibers, triggering contraction of ventricles
Chapter 42: Circulation / Gas Exchange
Parasympathetic
control
Campbell et al. – Figure 42.9
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Anatomy of Blood Vessels:
• Elastic Fibers
• Thick muscular layer
• elasticity
• Thin-walled
• Large lumen
• Only endothelium(nutrient exchange)
“Vascular Sink”(~ 65% of blood)
Chapter 42: Circulation / Gas ExchangeSimilar to Campbell et al. – Figure 42.10
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Physical Laws Govern Movement of Blood Through Vessels:
• Law of Continuity: When the diameter of a pipe narrows along its
length, fluids will flow through the narrow section
faster than the wider sections (volume constant)
Blood Flow Velocity:
Thus, blood should move most rapidly through capillaries - Right?
Benefits: 1) Nutrient exchange
2) Damage control
Chapter 42: Circulation / Gas Exchange
Capillaries are arranged in beds…
Total cross sectional area much
larger than found in arteries and veins
WRONG
Campbell et al. – Figure 42.11
Physical Laws Govern Movement of Blood Through Vessels:
• Pressure gradients drive blood flow through body
Blood Pressure:
• Blood Pressure = Force per unit area on wall of vessel (mm Hg)
Systolic Pressure: Pressure from ventricular
contraction (~ 120 mm Hg)
Diastolic Pressure: Pressure from ventricular
relaxation (~ 80 mm Hg)
Blood Pressure = Cardiac Output x Peripheral Resistance
Amount of friction blood
encounters passing
through vessels
• Blood viscosity
• Vessel length
• Vessel diameter
Regulatory mechanisms
adjust CO / PR to keep
relatively constant BP
Chapter 42: Circulation / Gas ExchangeCampbell et al. – Figure 42.11
• Valves
• Muscular pumps
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Transfer of Nutrients Occurs at the Capillaries:
• Capillary bed activity varies over time
time depending on needs of tissues
• Regulatory Mechanisms:
1) Arterioles constrict
• Flow to bed decreased
2) Capillary sphincters constrict
• Flow through bed decreased
Lymphatic System Returns Fluid to Blood:
• ~ 4 L of fluid lost to tissues per day
• Fluid enters lymph capillaries (fluid = lymph)
• Empties into blood near right atrium
• Utilize valves & muscular pumps
Elephantiasis
Chapter 42: Circulation / Gas ExchangeCampbell et al. – Figure 42.15
• Lymph Nodes = Organs that filters lymph
(part of body defense)
Blood Components:
• Erythrocytes (RBC’s)
• Small, bi-concave, anucleate
• Contain hemoglobin (iron-containing protein)
• Transports oxygen
• Erythropoietin (kidney) stimulates production
• Leukocytes (WBC’s)
• Function in defense against disease
• Five types (neutrophils / eosinophils / basophils
lymphocytes / monocytes)
• Use blood for transport
• Platelets
• Cell fragments; function in blood clotting
Formed
Elements
1) Formed Elements (living cells)
Plasma
2) Plasma
• Non-cellular fluid matrix (~90 % water)
• Dissolved proteins (clotting / transport / defense)
Hematocrit
% of whole blood containing
formed elements (~ 45 – 50%)
Chapter 42: Circulation / Gas Exchange
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Blood Clotting:
Chapter 42: Circulation / Gas ExchangeCampbell et al. – Figure 42.18
Gas Exchange in Animals:
Gas Exchange: The uptake of molecular oxygen (O2) from the environment
And the discharge of carbon dioxide (CO2) to the environment
• Respiratory medium = air (~ 21% O2) or water ( than air)
• Respiratory surface = Location where gas exchange occurs
• Thin; large surface area (gases move via diffusion)
• Moist (maintain cellular integrity)
Types of Respiratory Systems:
1) No Specialized System
A) All cells have access to external environment (e.g. sponges, flatworms)
Chapter 42: Circulation / Gas Exchange
B) Skin functions as respiratory surface (e.g. earthworms, amphibians)
• surface area / volume ratio (small, thin, and long / flat)
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Campbell et al. – Figure 42.22
Gas Exchange in Animals:
Types of Respiratory Systems:
2) Gills: Out-folds of body surface that are suspended in water (aquatic animals)
1) Ventilation: Increased flow of respiratory
medium over respiratory surface
• Move appendages (e.g. crayfish)
• Swim / pump operculum (e.g. fish)
2) Counter-current Exchange:
• Advantage: Respiratory surface always moist
• Disadvantage: [O2] in water (system must be efficient)
Chapter 42: Circulation / Gas Exchange
Gas Exchange in Animals:
Types of Respiratory Systems:
3) Tracheal System: Air tubes that branch throughout body to individual
cells (smaller terrestrial animals - insects)
• Circulatory system not involved in gas transport / exchange
• Larger insects ventilate system via muscle contractions (e.g., flight)
Chapter 42: Circulation / Gas ExchangeCampbell et al. – Figure 42.23
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Gas Exchange in Animals:
Types of Respiratory Systems:
4) Lungs: Internal respiratory organs restricted to single location (larger
terrestrial animals – e.g. spiders, land snails, vertebrates)
• Circulatory system required to transport gases to / from body cells
• Size / complexity of lung correlated with animal’s metabolic rate
• Warms, humidifies, & cleans air
• Reinforced with cartilage; vocal cords
• Rings / plates of
cartilage, ciliated
• Dead-end air sacs;
where gas exchange
actually occurs
• ~ 100 m2 (surface area)
Chapter 42: Circulation / Gas Exchange
Similar to Campbell et al. – Figure 42.24
Campbell et al. – Figure 42.25
Ventilation of Lung (= breathing):
Examples of Ventilation Adaptations:
1) Mammals ventilate by negative pressure breathing:
• Air is pulled into lungs via changes in thoracic cavity volume
Boyle’s Law:
P1V1 = P2V2
P = Pressure
V = Volume
Example:
4 mm Hg (2 mm3) = P2 (4 mm3)
P2 = 2 mm Hg
CHANGING THE VOLUME RESULTS
IN INVERSE CHANGE OF PRESSURE!
• Tidal Volume: Volume of air exchanged with each breath
• Vital Capacity: The maximum tidal volume during forced breathing (~ 4.5 L)
• Residual Volume: Air remaining in lungs after forced exhalation
Chapter 42: Circulation / Gas Exchange
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Examples of Ventilation Adaptations:
2) Frogs ventilate by positive pressure breathing:
• Air is pushed into lungs shrinkage of oral cavity size (i.e. swallow air)
3) Birds have air sacs that add complexity to system:
• Air completely exchanged from lung with every breath (no residual volume)
Chapter 42: Circulation / Gas ExchangeCampbell et al. – Figure 42.26
Ventilation of Lung (= breathing):
Regulation of Breathing:
Breathing control centers located in the pons and medulla oblongata:
• Medulla sets basic breathing rhythm
• Measures CO2 level in blood (via pH change in CSF)
• O2 only triggers respiratory response when severely depressed
Gas Exchange at Lungs / Tissues:
Gas exchange at lungs driven by partial pressures of gases:
• PO2 in alveoli = ~ 100 mm Hg
• PO2 in blood = ~ 40 mm Hg
• PCO2 in alveoli = ~ 40 mm Hg
• PCO2 in blood = ~ 45 mm Hg
Net movement of O2 into blood
Net movement of CO2 into alveoli
Reverse is true at tissues…
Chapter 42: Circulation / Gas Exchange
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Transport of Gases in Blood:
Oxygen has low solubility in liquid – needs respiratory pigments for transport:
• Hemocyanin: Hemolymph of arthropods; copper-containing protein
• Hemoglobin: Blood of vertebrates; iron-containing protein (4 O2 / unit)
• Myoglobin: Muscles of vertebrates; iron-containing protein
Cooperative O2 Binding:
Binding of one O2 molecule
causes conformational change
of hemoglobin resulting in rapid
binding of 3 other O2 molecules
Chapter 42: Circulation / Gas Exchange
Dissociation
Curve
Campbell et al. – Figure 42.29
Transport of Gases in Blood:
Carbon dioxide is primarily carried in blood as bicarbonate ion:
• Requires carbonic anhydrase (enzyme)
Chapter 42: Circulation / Gas ExchangeCampbell et al. – Figure 42.30