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 aerobic Lots of oxygen is required to support active mobility Some 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 environment Carbon dioxide must be released to the environment

Except……breaking news! http://www.biomedcentral.com/1741-7007/8/30 Abstract – 6 April 2010 Background Several 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. Results During 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. Conclusions This 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 diffusion Process is slow and cannot support 3-D large bodies Sponges, jellies and flatworms use diffusion alone

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???

Circulation systems have evolved over time The most primitive animals exchange gasses and circulate resources entirely by diffusion Process is slow and cannot support 3-D large bodies Surface area / volume ratio becomes too small Sponges, jellies and flatworms use diffusion alone

Virtually every cell in a sponge is in direct contact with the water – little circulation is required Diagram of sponge structure

Jellies and flatworms have thin bodies and elaborately branched gastrovascular cavities Again, all cells are very close to the external environment This facilitates diffusion Some contractions help circulate (contractile fibers in jellies, muscles in flatworms) Diagram of jellyfish structure, and photos

Circulation systems have evolved over time Most invertebrates (esp. insects) have an open circulatory system 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 Diagram of open circulatory system in a grasshopper

Circulation systems have evolved over time Closed circulatory systems separate blood from interstitial fluid Metabolic energy is used to pump blood through blood vessels Blood is contained within the vessels Exchange occurs by diffusion in capillary beds Diagram of a closed circulatory system, plus a diagram showing an earthworm circulatory system

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 Open – insects!!!

All vertebrates have a closed circulatory system Chambered heart pumps blood Atria receive blood Ventricles pump blood Vessels contain the blood Veins carry blood to atria Arteries carry blood from ventricles Capillary beds facilitate exchange Capillary beds separate arteries from veins Highly branched and very tiny Infiltrate all tissues in the body We’ll go over these step by step

Chambered heart pumps blood Atria receive blood Ventricles pump blood One-way valves direct blood flow Diagram of a chambered heart

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???

Chambered heart pumps blood Atria receive blood Soft walled, flexible Ventricles pump blood Thick, muscular walls One-way valves direct blood flow Diagram of a chambered heart

Vessels contain the blood Arteries carry blood from ventricles Always under pressure Veins carry blood to atria One-way valves prevent back flow Body movements increase circulation Pressure is always low Diagram showing artery, vein and capillary bed

Note that blood vessel names reflect the direction of flow, NOT the amount of oxygen in the blood Arteries carry blood AWAY from the heart Arterial blood is always under pressure It is NOT always oxygenated Veins carry blood TO the heart Diagram of blood circulation pattern in humans

Capillary beds facilitate exchange Capillary beds separate arteries from veins Highly branched and very tiny Infiltrate all tissues in the body More later Diagram showing artery, vein and capillary bed

All vertebrates have a closed circulatory system – REVIEW Chambered heart pumps blood Atria receive blood Ventricles pump blood Vessels contain the blood Veins carry blood to atria Arteries carry blood from ventricles Capillary beds facilitate exchange Capillary beds separate arteries from veins Highly branched and very tiny Infiltrate all tissues in the body

Evolution of double circulation – not all animals have a 4-chambered heart Diagram showing progression from a 1-chambered heart to a 4-chambered heart. This diagram is used in the next 12 slides.

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 circuit Blood 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 ventricle A 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 mixing Crocodilians have a complete septum Point of interest: reptiles have two arteries that lead to the systemic circuits Arterial 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 blood No mixing  much more efficient gas transport Efficient gas transport is essential for both movement and support of endothermy Endotherms use 10-30x more energy to maintain body temperatures

Mammals and birds have 4-chambered hearts Mammals and birds are NOT monophyletic What does this mean???

Mammals and birds have 4-chambered hearts Mammals and birds are NOT monophyletic Phylogenetic tree showing the diversification of vertebrates

Mammals and birds have 4-chambered hearts Mammals and birds are NOT monophyletic Four-chambered hearts evolved independently What’s this called???

Mammals and birds have 4-chambered hearts Mammals and birds are NOT monophyletic Four-chambered hearts evolved independently

Review: evolution of double circulation

Blood Circulation Blood vessels are organs Arteries have thicker walls Outer layer is elastic connective tissue Middle layer is smooth muscle and elastic fibers Inner 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 Diagram showing artery, vein and capillary bed

Blood pressure and velocity drop as blood moves through capillaries 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.

Total cross-sectional area in capillary beds is much higher than in arteries or veins; slows flow

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 Emphasize the difference between velocity and pressure!!! Velocity increases in the venous system; pressure does NOT

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 open Digestive system capillaries open after a meal Skeletal muscle capillaries open during exercise etc…

Bed fully open Bed closed, through-flow only Note scale – capillaries are very tiny!! Diagram showing sphincter muscle control over capillary flow. Micrograph of a capillary bed.

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

Capillary Transport Processes: Endocytosis  exocytosis across membrane Diffusion based on concentration 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

Bulk Flow in Capillary Beds Remember water potential: Ψ = P – s Remember that in bulk flow P is dominant No membrane Plus, 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

Bulk Flow in Capillary Beds Remember: Ψ = P – s Diagram showing osmotic changes across a capillary bed

Capillary Transport Processes: Endocytosis  exocytosis across membrane Diffusion based on concentration 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

Blood structure and function Blood is ~55% plasma and ~45% cellular elements Plasma is ~90% water Cellular elements include red blood cells, white blood cells and platelets

Blood Components Chart listing all blood components – both liquid and cellular

Plasma Solutes – 10% of plasma volume 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 pH Escort lipids (remember, lipids are insoluble in water) Defend against pathogens (antibodies) Assist with blood clotting Materials being transported Nutrients Hormones Respiratory gasses Waste products from metabolism

Cellular Elements Red blood cells, white blood cells and platelets Red blood cells carry O2 and some CO2 White blood cells defend against pathogens Platelets 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 molecules More on hemoglobin later… Produce ATP by glycolysis

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

The Clotting Process Diagram showing the clotting process

Blood Cell Production Blood cells are constantly digested by the liver and spleen Components are re-used Pluripotent stem cells produce all blood cells Feedback loops that sense tissue oxygen levels control red blood cell production Diagram showing blood cell production from stem cells in bone marrow Fig 42.16, 7th ed

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

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 ≠ Breathing Gas exchange = delivery of O2; removal of CO2 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 exchange Gasses move by diffusion across membranes Gasses are always dissolved in the interstitial fluid Surface area is important!

Evolution of Gas Exchange Surfaces Skin Must remain moist – limits environments Must 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

Evolution of Gas Exchange Surfaces Skin Must remain moist – limits environments Must 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

Invertebrate Gills Dissolved oxygen is limited Behaviors and structures increase water flow past gills to maximize gas exchange Diagrams and photos of gills in different animals. Fig 42.20, 7th ed

Countercurrent Exchange in Fish Gills Direction of blood flow allows for maximum gas exchange – maintains high gradient Diagram of countercurrent exchange in fish gills Fig 42.21, 7th ed

How countercurrent flow maximizes diffusion Figure showing countercurrent vs co-current flow effects on diffusion

Evolution of Gas Exchange Surfaces Skin Must remain moist – limits environments Must 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

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 Diagram and micrograph of insect tracheal system.

Tracheal Systems in Insects Rings of chitin Look familiar???

Critical Thinking Name 2 other structures that are held open by rings

Name 2 other structures that are held open by rings Critical Thinking Name 2 other structures that are held open by rings

Evolution of Gas Exchange Surfaces Skin Must remain moist – limits environments Must 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

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 system Dense 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 alveoli Alveoli are surrounded by capillaries This is the actual site of gas exchange Huge 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.

Mammalian Lungs Highly branched system of tubes – trachea, bronchi, and bronchioles Each ends in a cluster of “bubbles” – the alveoli Alveoli are surrounded by capillaries This is the actual site of gas exchange Huge surface area (100m2 in humans) Rings of cartilage keep the trachea open Epiglottis directs food to esophagus

Figure of vascularized alveolus

Mammalian Lungs Highly branched system of tubes – trachea, bronchi, and bronchioles Each ends in a cluster of “bubbles” – the alveoli Alveoli are surrounded by capillaries This is the actual site of gas exchange Huge surface area (100m2 in humans) Rings of cartilage keep the trachea open Epiglottis directs food to esophagus

Breathing Ventilates Lungs Positive pressure breathing – amphibians Air is forced into trachea under pressure Mouth and nose close, muscle contractions force air into lungs Relaxation of muscles and elastic recoil of lungs force exhalation

Breathing Ventilates Lungs Positive pressure breathing – amphibians Air is forced into trachea under pressure Mouth and nose close, muscle contractions force air into lungs Relaxation of muscles and elastic recoil of lungs 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

Negative Pressure Breathing Diagram of negative pressure breathing

Breathing Ventilates Lungs Positive pressure breathing – amphibians Air is forced into trachea under pressure Mouth and nose close, muscle contractions force air into lungs Relaxation of muscles and elastic recoil of lungs 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

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 Diagram of circuit flow breathing in birds

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 Hg This 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)

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 Hg This 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

Partial Pressure Gradients Drive Gas Transport Each gas contributes to total atmospheric pressure in proportion to its volume % in the atmosphere Each gas contributes a part of total pressure That 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

Partial Pressure Gradients Drive Gas Transport Each gas contributes to total atmospheric pressure in proportion to its volume % in the atmosphere Each gas contributes a part of total pressure That 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

Partial Pressure Gradients Drive Gas Transport Atmospheric gasses dissolve into water in proportion to their partial pressure and solubility in water Dynamic 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???

Inhaled air PP’s = atmospheric PP’s 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 air Lower PP of O2 and higher PP of CO2 than in atmosphere

O2 and CO2 diffuse based on gradients of partial pressure Blood PP’s reflect supply and usage Blood 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

Oxygen Transport Oxygen is not very soluble in water (blood) Oxygen transport and delivery are enhanced by binding of O2 to respiratory pigments Diagram of hemoglobin structure and how it changes with oxygen loading. This diagram is used in the next 3 slides. 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

Oxygen Transport More active metabolism (ie: during muscle use) increases unloading Note steepness of curve O2 is unloaded quickly when metabolic use increases Graph showing how hemoglobin oxygen saturation changes with activity.

Oxygen Transport – the Bohr Shift Graph showing 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

Carbon Dioxide Transport Figure showing how carbon dioxide is transported from tissues to lungs. This figure is used in the next 3 slides. Red blood cells also assist in CO2 transport 7% of CO2 is transported dissolved in plasma 23% is bound to amino groups of hemoglobin in the RBC’s 70% is converted to bicarbonate ions inside the RBC’s

Carbon Dioxide Transport CO2 in RBC’s reacts with water to form carbonic acid (H2CO3) H2CO3 dissociates to bicarbonate (HCO3-) and H+

Carbon Dioxide Transport Most H+ binds to hemoglobin This limits blood acidification HCO3- diffuses back into plasma for transport

Carbon Dioxide Transport Reverse occurs when blood reaches the lungs Conversion back to CO2 is driven by diffusion gradients as CO2 moves into the lungs

REVIEW – 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

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