1 Lecture #10 – Animal Circulation and Gas Exchange Systems.

Lecture #10 – Animal Circulation and Gas Exchange Systems

Key Concepts:

• Circulation and gas exchange – why?• Circulation – spanning diversity• Hearts – the evolution of double circulation• Blood circulation and capillary exchange• Blood structure and function• Gas exchange – spanning diversity• Breathing – spanning diversity• Respiratory pigments

Animals use O2 and produce CO2

• All animals are aerobicLots of oxygen is required to support active

mobilitySome animals use lots of oxygen to maintain

body temperature• All animals produce CO2 as a byproduct of

aerobic respiration• Gasses must be exchanged

Oxygen must be acquired from the environmentCarbon dioxide must be released to the

environment

Except……breaking news!http://www.biomedcentral.com/1741-7007/8/30

Abstract – 6 April 2010BackgroundSeveral unicellular organisms (prokaryotes and protozoa) can live under permanently anoxic conditions. Although a few metazoans can survive temporarily in the absence of oxygen, it is believed that multi-cellular organisms cannot spend their entire life cycle without free oxygen. Deep seas include some of the most extreme ecosystems on Earth, such as the deep hypersaline anoxic basins of the Mediterranean Sea. These are permanently anoxic systems inhabited by a huge and partly unexplored microbial biodiversity.ResultsDuring the last ten years three oceanographic expeditions were conducted to search for the presence of living fauna in the sediments of the deep anoxic hypersaline L'Atalante basin (Mediterranean Sea). We report here that the sediments of the L'Atalante basin are inhabited by three species of the animal phylum Loricifera (Spinoloricus nov. sp., Rugiloricus nov. sp. and Pliciloricus nov. sp.) new to science. Using radioactive tracers, biochemical analyses, quantitative X-ray microanalysis and infrared spectroscopy, scanning and transmission electron microscopy observations on ultra-sections, we provide evidence that these organisms are metabolically active and show specific adaptations to the extreme conditions of the deep basin, such as the lack of mitochondria, and a large number of hydrogenosome-like organelles, associated with endosymbiotic prokaryotes.ConclusionsThis is the first evidence of a metazoan life cycle that is spent entirely in permanently anoxic sediments. Our findings allow us also to conclude that these metazoans live under anoxic conditions through an obligate anaerobic metabolism that is similar to that demonstrated so far only for unicellular eukaryotes. The discovery of these life forms opens new perspectives for the study of metazoan life in habitats lacking molecular oxygen.

Animals use O2 and produce CO2

• Circulation systems move gasses (and other essential resources such as nutrients, hormones, etc) throughout the animal’s body

• Respiratory systems exchange gasses with the environment

Circulation systems have evolved over time

• The most primitive animals exchange gasses and circulate resources entirely by diffusionProcess is slow and cannot support 3-D large

bodies• Sponges, jellies and flatworms use diffusion

Critical Thinking

• Why isn’t diffusion adequate for exchange in a 3D large animal???

Critical Thinking

• Why isn’t diffusion adequate for exchange in a 3D large animal???

Critical Thinking

• But…..plants rely on diffusion for gas exchange…..how do they get so big???

Critical Thinking

• But…..plants rely on diffusion for gas exchange…..how do they get so big???

• The most primitive animals exchange gasses and circulate resources entirely by diffusionProcess is slow and cannot support 3-D large

bodiesSurface area / volume ratio becomes too small

• Sponges, jellies and flatworms use diffusion alone

Diagram of sponge structure

Virtually every cell in a sponge is in direct contact with the water – little circulation is

required

Diagram of jellyfish structure, and photos

• Jellies and flatworms have thin bodies and elaborately branched gastrovascular cavitiesAgain, all cells are very close to the external

environmentThis facilitates diffusionSome contractions help circulate (contractile

fibers in jellies, muscles in flatworms)

Diagram of open circulatory system in a grasshopper

Metabolic energy is used to pump hemolymph through blood vessels into the body cavity

Hemolymph is returned to vessels via ostia – pores that draw in the fluid as the heart relaxes

• Most invertebrates (esp. insects) have an open circulatory system

Diagram of a closed circulatory system, plus a diagram showing an earthworm circulatory system

Metabolic energy is used to pump blood through blood vessels

Blood is contained within the vessels

Exchange occurs by diffusion in capillary beds

• Closed circulatory systems separate blood from interstitial fluid

Open vs. Closed…both systems are common

Open systems…. • Use less metabolic

energy to run• Use less metabolic

energy to build• Can function as a

hydrostatic skeleton

• Most invertebrates (except earthworms and larger mollusks) have open systems

Closed systems….• Maintain higher

pressure • Are more effective

at transport• Supply more

oxygen to support larger and more active animals

• All vertebrates have closed systems

All vertebrates have a closed circulatory system

• Chambered heart pumps bloodAtria receive bloodVentricles pump blood

• Vessels contain the bloodVeins carry blood to atriaArteries carry blood from ventricles

• Capillary beds facilitate exchangeCapillary beds separate arteries from veinsHighly branched and very tinyInfiltrate all tissues in the body We’ll go over these

step by step

Diagram of a chambered heart

Chambered heart pumps blood• Atria receive blood

• Ventricles pump blood

• One-way valves direct blood flow

Critical Thinking

• Atria receive blood; ventricles pump• Given that function, what structure would

you predict???

Critical Thinking

• Atria receive blood; ventricles pump• Given that function, what structure would

you predict???

Diagram of a chambered heart

Chambered heart pumps blood• Atria receive blood

Soft walled, flexible• Ventricles pump

bloodThick, muscular

walls• One-way valves

direct blood flow

Diagram showing artery, vein and capillary bed

Vessels contain the blood• Arteries carry blood

from ventriclesAlways under pressure

• Veins carry blood to atriaOne-way valves

prevent back flowBody movements

increase circulationPressure is always low

Diagram of blood circulation pattern in humans

Note that blood vessel names reflect the direction of flow, NOT the amount of

oxygen in the blood

• Arteries carry blood AWAY from the heartArterial blood is always

under pressureIt is NOT always

oxygenated• Veins carry blood TO

the heart

Capillary beds facilitate exchange

• Capillary beds separate arteries from veins• Highly branched and very tiny• Infiltrate all tissues in the body• More later

All vertebrates have a closed circulatory system – REVIEW

• Chambered heart pumps bloodAtria receive bloodVentricles pump blood

• Vessels contain the bloodVeins carry blood to atriaArteries carry blood from ventricles

• Capillary beds facilitate exchangeCapillary beds separate arteries from veinsHighly branched and very tinyInfiltrate all tissues in the body

Diagram showing progression from a 1-chambered heart to a 4-chambered heart. This diagram is used in the next 12 slides.

Evolution of double circulation – not all animals have a 4-chambered heart

Fishes have a 2-chambered heart

• One atrium, one ventricle• A single pump of the heart

circulates blood through 2 capillary beds in a single circuitBlood pressure drops as blood

enters the capillaries (increase in cross-sectional area of vessels)

Blood flow to systemic capillaries and back to the heart is very slow

Flow is increased by swimming movements

Two circuits increases the efficiency of gas exchange = double circulation

• One circuit goes to exchange surface• One circuit goes to body systems• Both under high pressure – increases flow rate

Amphibians have a 3-chambered heart• Two atria, one ventricle• Ventricle pumps to 2 circuits

One circuit goes to lungs and skin to release CO2 and acquire O2

The other circulates through body tissues

• Oxygen rich and oxygen poor blood mix in the ventricleA ridge helps to direct flow

• Second pump increases the speed of O2 delivery to the body

Most reptiles also have a 3-chambered heart

• A partial septum further separates the blood flow and decreases mixingCrocodilians have a complete

septum• Point of interest: reptiles have

two arteries that lead to the systemic circuitsArterial valves help direct blood

flow away from pulmonary circuit when animal is submerged

Critical Thinking

• What is a disadvantage of a 3 chambered heart???

Critical Thinking

• What is a disadvantage of a 3 chambered heart???

Mammals and birds have 4-chambered hearts

• Two atria and two ventricles• Oxygen rich blood is completely

separated from oxygen poor bloodNo mixing much more efficient gas

transportEfficient gas transport is essential

for both movement and support of endothermy

Endotherms use 10-30x more energy to maintain body temperatures

• Mammals and birds are NOT monophyletic

• What does this mean???

Phylogenetic tree showing the diversification of vertebrates

• Four-chambered hearts evolved independently

• What’s this called???

• Four-chambered hearts evolved independently

Review: evolution of double circulation

Blood Circulation

• Blood vessels are organsOuter layer is elastic connective tissueMiddle layer is smooth muscle and elastic

fibersInner layer is endothelial tissue

• Arteries have thicker walls• Capillaries have only an endothelium and

basement membrane

Critical Thinking

• Arteries have thicker walls than veins• Capillaries have only an endothelium and

basement membrane• What is the functional significance of this

structural difference???

Critical Thinking

• Arteries have thicker walls than veins• Capillaries have only an endothelium and

basement membrane• What is the functional significance of this

structural difference???

Form reflects function…

• Arteries are under more pressure than veins

• Capillaries are the exchange surface

Graph showing relationships between blood pressure, blood velocity, and the cross-sectional area of different kinds of blood vessels – arteries to capillaries to veins. This same graph is on the next 3 slides.

Blood pressure

and velocity drop as

blood moves through

capillaries

Total cross-sectional area

in capillary beds is much higher than in

arteries or veins; slows

Velocity increases as blood passes

into veins (smaller cross-

sectional area);

pressure remains

dissipated

One-way valves and

body movements force blood back to right heart atrium

Critical Thinking

• What makes rivers curl on the Coastal Plain???

Critical Thinking

• What makes rivers curl on the Coastal Plain???

Emphasize the difference

between velocity and pressure!!!

Velocity increases in the venous system; pressure does

Capillary Exchange

• Gas exchange and other transfers occur in the capillary beds

• Muscle contractions determine which beds are “open”Brain, heart, kidneys and liver are generally

always fully openDigestive system capillaries open after a mealSkeletal muscle capillaries open during

exerciseetc…

Diagram showing sphincter muscle control over capillary flow. Micrograph of a capillary bed.

Bed fully open

Bed closed, through-flow only

Note scale – capillaries are very tiny!!

Capillary Transport Processes:

• Endocytosis exocytosis across membrane• Diffusion based on electrochemical gradients• Bulk flow between endothelial cells

Water potential gradient forces solution out at arterial end

Reduction in pressure draws most (85%) fluid back in at venous end

Remaining fluid is absorbed into lymph, returned at shoulder ducts

• Endocytosis exocytosis across membrane• Diffusion based on concentration gradients• Bulk flow between endothelial cells

Bulk Flow in Capillary Beds

• Remember water potential: Ψ = P – s• Remember that in bulk flow P is dominant

No membranePlus, in the capillaries, s is ~stable (blood

proteins too big to pass)• P changes due to the interaction between

arterial pressure and the increase in cross-sectional area

Diagram showing osmotic changes across a capillary bed

Bulk Flow in Capillary BedsRemember: Ψ = P – s

• Endocytosis exocytosis across membrane• Diffusion based on concentration gradients• Bulk flow between endothelial cells

Blood structure and function• Blood is ~55% plasma and ~45% cellular

elementsPlasma is ~90% waterCellular elements include red blood cells, white

blood cells and platelets

Chart listing all blood components – both liquid and cellular

Blood Components

Plasma Solutes – 10% of plasma volume• Solutes

Inorganic salts that maintain osmotic balance, buffer pH to 7.4, contribute to nerve and muscle function

Concentration is maintained by kidneys• Proteins

Also help maintain osmotic balance and pHEscort lipids (remember, lipids are insoluble in water)Defend against pathogens (antibodies)Assist with blood clotting

• Materials being transportedNutrientsHormonesRespiratory gassesWaste products from metabolism

Cellular Elements • Red blood cells, white blood cells and

plateletsRed blood cells carry O2 and some CO2

White blood cells defend against pathogensPlatelets promote clotting

Red Blood Cells

• Most numerous of all blood cells• 5-6 million per mm3 of blood!• 25 trillion in the human body• Biconcave shape• No nucleus, no mitochondria

They don’t use up any of the oxygen they carry!• 250 million molecules of hemoglobin per cell

Each hemoglobin can carry 4 oxygen moleculesMore on hemoglobin later…

Critical Thinking

• Tiny size and biconcave shape do what???

Critical Thinking

• Tiny size and biconcave shape do what???

White Blood Cells• All function in defense against pathogens• We will cover extensively in the chapter on

immune systems

Platelets

• Small fragments of cells• Formed in bone marrow• Function in blood clotting at wound sites

Diagram showing the clotting process

The Clotting Process

Diagram showing blood cell production from stem cells in bone marrow

Blood Cell Production

• Blood cells are constantly digested by the liver and spleenComponents are re-

• Pluripotent stem cells produce all blood cells

• Feedback loops that sense tissue oxygen levels control red blood cell production

Fig 42.16, 7th ed

Key Concepts:

Hands On

• Dissect out the circulatory system of your rat

• Start by clearing the tissues around the heart

• Be especially careful at the anterior end of the heart – this is where the major blood vessels emerge

• Trace the aorta, the vena cava, and as many additional vessels as possible – use your manual and lab handout for direction!

Hands On

• Feel and describe the texture of the atria vs. the ventricles

• Take cross sections of the heart through both the atria and the ventricles

• Examine under the dissecting microscope• Do the same with aorta and vena cava• Try for a thin enough section to look at

under the compound microscope too

Gas Exchange

• Gas Exchange ≠ Respiration ≠ BreathingGas exchange = delivery of O2; removal of

Respiration = the metabolic process that occurs in mitochondria and produces ATP

Breathing = ventilation to supply the exchange surface with O2 and allow exhalation of CO2

Diagram showing indirect links between external environment, respiratory system, circulatory system and tissues.

Gas Exchange Occurs at the Respiratory Surface

• Respiratory medium = the source of the O2

Air for terrestrial animals – air is 21% O2 by volume

Water for aquatic animals – dissolved O2 varies base on environmental conditions, especially salinity and temperature; always lower than in air

Gas Exchange Occurs at the Respiratory Surface

• Respiratory surface = the site of gas exchangeGasses move by diffusion across membranesGasses are always dissolved in the interstitial

fluid• Surface area is important!

Evolution of Gas Exchange Surfaces

• SkinMust remain moist – limits environmentsMust maintain functional SA / V ratio – limits

3D size• Gills

Large SA suspended in water• Tracheal systems

Large SA spread diffusely throughout body• Lungs

Large SA contained within small space

Skin Limits

• Sponges, jellies and flatworms rely on the skin as their only respiratory surface

3D size• Gills

Diagrams and photos of gills in different animals.

Invertebrate Gills

• Dissolved oxygen is limited

• Behaviors and structures increase water flow past gills to maximize gas exchange

Fig 42.20, 7th ed

Diagram of countercurrent exchange in fish gills

Countercurrent Exchange in Fish Gills• Direction of blood flow allows for maximum

gas exchange – maintains high gradient

Fig 42.21, 7th ed

Figure showing countercurrent vs co-current flow effects on diffusion

How countercurrent flow maximizes diffusion

3D size• Gills

Diagram and micrograph of insect tracheal system.

Tracheal Systems in Insects

• Air tubes diffusely penetrate entire body• Small openings to the outside limit

evaporation• Open circulatory system does not transport

gasses from the exchange surface• Body movements ventilate

Tracheal Systems in InsectsRings of chitin

Look familiar???

Critical Thinking

• Name 2 other structures that are held open by rings

Critical Thinking

3D size• Gills

Lungs in Spiders, Terrestrial Snails and Vertebrates

• Large surface area restricted to small part of the body

• Single, small opening limits evaporation• Connected to all cells and tissues via a

circulatory systemDense capillary beds lie directly adjacent to

respiratory epithelium• In some animals, the skin supplements

gas exchange (amphibians)

Mammalian Lungs• Highly branched system of tubes – trachea,

bronchi, and bronchioles• Each ends in a cluster of “bubbles” – the

alveoliAlveoli are surrounded by capillariesThis is the actual site of gas exchangeHuge surface area (100m2 in humans)

• Rings of cartilage keep the trachea open• Epiglottis directs food to esophagus

Figure and micrograph of lung and alveolus structure.

Figure of vascularized alveolus

Breathing Ventilates Lungs

• Positive pressure breathing – amphibiansAir is forced into trachea under pressureMouth and nose close, muscle contractions

force air into lungsRelaxation of muscles and elastic recoil of lungs

force exhalation

force exhalation• Negative pressure breathing – mammals

Air is sucked into trachea under suction• Circuit flow breathing – birds

Air flows through entire circuit with every breath

Diagram of negative pressure breathing

Negative Pressure Breathing

forces exhalation• Negative pressure breathing – mammals

Air is sucked into trachea under suction• Circuit flow breathing – birds

Air flows through entire circuit with every breath

Diagram of circuit flow breathing in birds

Flow Through Breathing• No residual air left in lungs• Every breath brings fresh O2 past the exchange

surface• Higher lung O2 concentration than in mammals

Critical Thinking

• What is the functional advantage of flow-through breathing for birds???

Critical Thinking

• What is the functional advantage of flow-through breathing for birds???

Respiratory pigments – tying the two systems together

• Respiratory pigments are proteins that reversibly bind O2 and CO2

• Circulatory systems transport the pigments to sites of gas exchange

• O2 and CO2 molecules bind or are released depending on gradients of partial pressure

Partial Pressure Gradients Drive Gas Transport

• Atmospheric pressure at sea level is equivalent to the pressure exerted by a column of mercury 760 mm high = 760 mm HgThis represents the total pressure that the

atmosphere exerts on the surface of the earth• Partial pressure is the percentage of total

atmospheric pressure that can be assigned to each component of the atmosphere

Atmospheric pressure at sea level is equivalent to the pressure exerted by

a column of mercury 760 mm high = 760 mm Hg (29.92” of mercury)

• Atmospheric pressure at sea level is equivalent to the pressure exerted by a column of mercury 760 mm high = 760 mm HgThis represents the total pressure that the

atmosphere exerts on the surface of the earth• Partial pressure is the percentage of total

atmospheric pressure that can be assigned to each component of the atmosphere

• Each gas contributes to total atmospheric pressure in proportion to its volume % in the atmosphereEach gas contributes a part of total pressureThat part = the partial pressure for that gas

• The atmosphere is 21% O2 and 0.03% CO2

Partial pressure of O2 is 0.21x760 = 160 mm Hg

Partial pressure of CO2 is 0.0003x760 = 0.23 mm Hg

• Each gas contributes to total atmospheric pressure in proportion to its volume % in the atmosphereEach gas contributes a part of total pressureThat part = the partial pressure for that gas

• The atmosphere is 21% O2 and 0.03% CO2

Partial pressure of O2 is 0.21x760 = 160 mm Hg

Partial pressure of CO2 is 0.0003x760 = 0.23 mm Hg

• Atmospheric gasses dissolve into water in proportion to their partial pressure and solubility in waterDynamic equilibriums can eventually develop

such that the PP in solution is the same as the PP in the atmosphere

This occurs in the fluid lining the alveoli

Critical Thinking

• If a dynamic equilibrium exists in the alveoli, will the partial pressures be the same as in the outside atmosphere???

Critical Thinking

• If a dynamic equilibrium exists in the alveoli, will the partial pressures be the same as in the outside atmosphere???

Diagram showing partial pressures of gasses in various parts of the body. This diagram is used in the next 3 slides.

• Inhaled air PP’s = atmospheric PP’s

• Alveolar PP’s reflect mixing of inhaled and exhaled airLower PP of O2 and

higher PP of CO2 than in atmosphere

• O2 and CO2 diffuse based on gradients of partial pressureBlood PP’s reflect supply

and usageBlood leaves the lungs

with high PP of O2

Body tissues have lower PP of O2 because of mitochondrial usage

O2 moves from blood to tissues

• Same principles with CO2 Blood leaves the lungs

with low PP of CO2

Body tissues have higher PP of CO2 because of mitochondrial production

CO2 moves from tissues to blood

• When blood reaches the lungs the gradients favor diffusion of O2 into the blood and CO2 into the alveoli

Diagram of hemoglobin structure and how it changes with oxygen loading. This diagram is used in the next 3 slides.

Oxygen Transport

• Oxygen is not very soluble in water (blood)• Oxygen transport and delivery are

enhanced by binding of O2 to respiratory pigments

Fig 42.28, 7th ed

Oxygen Transport• Increase is 2 orders of magnitude!• Almost 50 times more O2 can be carried this

way, as opposed to simply dissolved in the blood

Oxygen Transport

• Most vertebrates and some inverts use hemoglobin for O2 transport

• Iron (in heme group) is the binding element

Oxygen Transport

• Four heme groups per hemoglobin, each with one iron atom

• Binding is reversible and cooperative

Critical Thinking

• Binding is reversible and cooperative• What does that mean???

Critical Thinking

• Binding is reversible and cooperative• What does that mean???

Oxygen Transport

• Reverse occurs during unloading• Release of one O2 induces shape change

that speeds up the release of the next 3

Graph showing how hemoglobin oxygen saturation changes with activity.

Oxygen Transport

• More active metabolism (ie: during muscle use) increases unloading

• Note steepness of curveO2 is unloaded

quickly when metabolic use increases

Graph showing the Bohr Shift

Oxygen Transport – the Bohr Shift

• More active metabolism also increases the release of CO2

Converts to carbonic acid, acidifying blood

pH change stimulates release of additional O2

Fig 42.29, 7th ed

Figure showing how carbon dioxide is transported from tissues to lungs. This figure is used in the next 3 slides.

Carbon Dioxide Transport

• Red blood cells also assist in CO2 transport7% of CO2 is transported

dissolved in plasma23% is bound to amino groups of

hemoglobin in the RBC’s70% is converted to bicarbonate

ions inside the RBC’s

• CO2 in RBC’s reacts with water to form carbonic acid (H2CO3)

• H2CO3 dissociates to bicarbonate (HCO3

-) and H+

• Most H+ binds to hemoglobinThis limits blood

acidification

• HCO3- diffuses

back into plasma for transport

• Reverse occurs when blood reaches the lungsConversion back to

CO2 is driven by diffusion gradients as CO2 moves into the lungs

REVIEW – Key Concepts:

Hands On

• Dissect out the respiratory system of your rat

• Trace the trachea into the lungs• Examine trachea and lungs under the

dissecting microscope• Try for thin enough sections to also

examine with the compound microscope

1 Lecture #10 – Animal Circulation and Gas Exchange Systems.

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