transport systems connect organs of exchange with body cells

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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)


• Three basic components:

1) Circulatory fluid (= blood)

2) Set of tubes (= blood vessels)

3) Muscular pump (= heart)

3) Closed Circulatory System (e.g., vertebrates)


Cardiovascular System:


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)


3 – Chambered Heart

Mixing of oxygen-rich blood

and oxygen-poor blood (= constrains O2 delivery)

(e.g., amphibian)


Complete separation of

O2-rich and O2-poor blood (= enhanced O2 delivery)

(e.g., mammals / birds)


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)



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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


Parasympathetic

control


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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


Capillaries are arranged in beds…

Total cross sectional area much

larger than found in arteries and veins

WRONG


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


• 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


• 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%)


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Blood Clotting:


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)


B) Skin functions as respiratory surface (e.g. earthworms, amphibians)

• surface area / volume ratio (small, thin, and long / flat)

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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)




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)


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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)


Similar to Campbell et al. – Figure 42.24


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


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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)


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…


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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


Dissociation

Curve


Transport of Gases in Blood:

Carbon dioxide is primarily carried in blood as bicarbonate ion:

• Requires carbonic anhydrase (enzyme)


transport systems connect organs of exchange with body cells

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