Circulation and Gas Exchange

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Circulation and Gas Exchange

• Chapter 44

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Gas Exchange and Circulation

• Gas exchange involves two things
• Oxygen consumed during cellular respiration must
  be brought to tissues
• Carbon dioxide produced during cellular
  respiration must be removed
• Done with the aid of the circulatory system and
  the respiratory surface

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Air and Water as Respiratory Media

• Gas exchange involves ventilation (the movement
  of air or water through the lungs or gills)
• circulation (the transportation of dissolved
  gases throughout the circulatory system)
• and respiration (the exchange of O2 and CO2
  between cells and the blood as mitochondria use
  O2 and release CO2

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Organs of Gas Exchange

• Some animals have organs for gas exchange,
  others use direct diffusion across the body
  surface
• Surface must be moist for diffusion

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Simple Circulation

• Wide range of body types and great diversity in
  circulatory systems
• Gastrovascular cavity- cnidarians
• Functions in both digestion and distribution of
  substances throughout the body
• Some cnidarians, such as jellies
• Have elaborate gastrovascular cavities

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Simple Circulation
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Complex Animal Circulation

• More complex animals
• Have too many cell layers for a simple cavity to
  be sufficient
• Have one of two types of circulatory systems
  open or closed
• Both of these types of systems have three basic
  components
• A circulatory fluid (blood)
• A set of tubes (blood vessels)
• A muscular pump (the heart)

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Gas Exchange
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Tracheae

• Extensive system of tubes located well within
  the body of insects
• Connect to the exterior through openings called
  spiracles
• Can be closed to minimize the loss of water by
  evaporation
• Transports air close enough to cells for gas
  exchange to take place directly

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Tracheal Systems

• The tracheal system of insects
• Consists of tiny branching tubes that penetrate
  the body

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• The tracheal tubes
• Supply O2 directly to body cells

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Gills

• Outgrowths of the body surface used for gas
  exchange in aquatic animals
• Extremely large surface area for oxygen to
  diffuse across an extremely thin epithelium
• Structure of gills in invertebrates is diverse
• Gills of bony fish are similar in structure

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Gills

• Movement of water over the gills is
  unidirectional
• Gill filaments extend from each gill arch
• Gill filament is composed of hundreds or
  thousands of gill lamellae
• Sheetlike structures through which a bed of
  capillaries runs.

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Countercurrent Exchange System

• Flow of blood through the capillary bed is in the
  opposite direction to the flow of water over the
  gill surface
• Ensures that the difference in the amount of O2
  and CO2 in water versus blood is large over the
  entire respiratory surface.
• Countercurrent exchange system

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Countercurrent Exchange System
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Lungs

• Spiders, land snails, and most terrestrial
  vertebrates
• Have internal lungs
• Lungs require a circulatory system
• Respiratory surface not in direct contact with
  the cells
• Amphibians have small lungs so the use their skin
  as a respiratory surface
• Trachea carries inhaled air to narrower tubes
  called bronchi. The bronchi branch off into even
  narrower tubes called bronchioles

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Mammalian Respiration

• Air is inhaled through the nostrils where it is
  warmed and cleaned
• Passes pharynx and larynx
• Where the vocal chords are
• Then to the trachea (windpipe)
• Trachea forks into two bronchi
• Bronchi enter the lungs and split into
  bronchioles
• Then to the alveoli where gas exchange occurs

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Mammalian Respiratory Systems

• A system of branching ducts
• Conveys air to the lungs

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Ventilation

• Simple lungs of snails and spiders, air movement
  takes place by diffusion only
• Frogs and related animals push air into their
  lungs via positive pressure ventilation.
• Humans and other mammals pull air into their
  lungs via negative pressure ventilation.

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Breathing

• Mammals ventilate their lungs
• By negative pressure breathing, which pulls air
  into the lungs

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Control of Breathing

• The main breathing control centers
• Are located in two regions of the brain, the
  medulla oblongata and the pons

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Control of Breathing

• The centers in the medulla
• Regulate the rate and depth of breathing in
  response to pH changes in the cerebrospinal fluid
• The medulla adjusts breathing rate and depth
• To match metabolic demands
• Sensors in the aorta and carotid arteries
• Monitor O2 and CO2 concentrations in the blood
• Exert secondary control over breathing

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Blood

• Blood in the circulatory systems of vertebrates
• Is a specialized connective tissue
• Blood consists of several kinds of cells
• Suspended in a liquid matrix called plasma
• The cellular elements
• Occupy about 45 of the volume of blood

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Blood Elements

• Blood plasma is about 90 water
• Among its many solutes are
• Inorganic salts in the form of dissolved ions,
  sometimes referred to as electrolytes
• Another important class of solutes is the plasma
  proteins
• Which influence blood pH, osmotic pressure, and
  viscosity

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Blood Elements

• Various types of plasma proteins
• Function in lipid transport, immunity, and blood
  clotting and buffering

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Blood Elements

• Suspended in blood plasma are two classes of
  cells
• Red blood cells, which transport oxygen
• White blood cells, which function in defense
• A third cellular element, platelets
• Are fragments of cells that are involved in
  clotting

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Blood Elements
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Erythrocytes

• Red blood cells, or erythrocytes
• Are by far the most numerous blood cells
• Transport oxygen throughout the body

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Leukocytes

• The blood contains five major types of white
  blood cells, or leukocytes
• Monocytes, neutrophils, basophils, eosinophils,
  and lymphocytes, which function in defense by
  phagocytizing bacteria and debris or by producing
  antibodies

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Leukocytes
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Platelets

• Platelets function in blood clotting
• Pinched off cytoplasmic fragments of large cells
  in the bone marrow

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Stem Cells and Cell Replacement

• The cellular elements of blood wear out
• And are replaced constantly throughout a persons
  life
• Erythricytes, leykocytes and platelets all
  develop from a common source
• Pluripotent stem cells in the red bone marrow of
  ribs, vertebrae, breatsbone, and pelvis

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Pluripotent Stem Cells
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Blood Clotting

• When the endothelium of a blood vessel is damaged
• The clotting mechanism begins
• A cascade of complex reactions
• Converts fibrinogen to fibrin, forming a clot
• Fibrin aggregates into threads which form the clot

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Blood Clotting
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Respiratory Pigments

• Respiratory pigments
• Are proteins that transport oxygen
• Greatly increase the amount of oxygen that blood
  can carry
• The respiratory pigment of almost all vertebrates
• Is the protein hemoglobin, contained in the
  erythrocytes
• Like all respiratory pigments
• Hemoglobin must reversibly bind O2, loading O2 in
  the lungs and unloading it in other parts of the
  body

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Respiratory Pigments
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Circulation
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The Circulatory System

• The function of a circulatory system is to carry
  a transport fluid such as blood into close
  contact with cells
• Sophisticated systems have hearts and complicated
  systems of various vessels to carry gas and
  nutrients to cells
• Some animals lack some or all of these or have
  no circulatory system

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Open Circulatory Systems

• Hemolymph is actively pumped throughout the body
• Bloodlike tissue that transports wastes and
  nutrients in most invertebrates
• not confined exclusively to blood vessels,
• Pressure in the system is low, favors sedentary
  animals

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Closed Circulatory Systems

• Blood is completely contained within blood
  vessels
• Flows in a continuous circuit through the body
• Under pressure generated by the heart

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Vertebrate Circulation

• Humans and other vertebrates have a closed
  circulatory system
• Often called the cardiovascular system
• Blood flows in a closed cardiovascular system
• Consisting of blood vessels and a two- to
  four-chambered heart
• Arteries carry blood to capillaries
• The sites of chemical exchange between the blood
  and interstitial fluid
• Veins
• Return blood from capillaries to the heart

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Blood Vessels
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Blood Vessel Structure and Function

• The infrastructure of the circulatory system
• Is its network of blood vessels
• All blood vessels
• Are built of similar tissues
• Have three similar layers

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Blood Vessel Structure and Function

• Structural differences in the vessels correlate
  with their different functions
• Arteries have thicker walls
• To accommodate the high pressure of blood pumped
  from the heart
• Capillaries are very thin-walled to allow for
  flow of things between the blood and tissues

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Blood Vessel Structure and Function

• In the thin-walled veins
• Blood flows back to the heart mainly as a result
  of muscle action

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Blood Flow Velocity

• The velocity of blood flow varies in the
  circulatory system
• And is slowest in the capillary beds as a result
  of the high resistance and large total
  cross-sectional area

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Blood Pressure

• Fluids exert hydrostatic pressure against the
  surfaces they contact
• Blood pressure is the hydrostatic pressure that
  blood exerts against the wall of a vessel
• Systolic pressure
• Is the pressure in the arteries during
  ventricular systole
• Is the highest pressure in the arteries
• Diastolic pressure
• Is the pressure in the arteries during diastole
• Is lower than systolic pressure

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Capillary Function

• Capillaries in major organs are usually filled to
  capacity
• But in many other sites, the blood supply varies
• Depends on where the blood is needed
• Two mechanisms
• Regulate the distribution of blood in capillary
  beds
• In one mechanism
• Contraction of the smooth muscle layer in the
  wall of an arteriole constricts the vessel

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Capillary Function

• In a second mechanism
• Precapillary sphincters control the flow of blood
  between arterioles and venules

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Capillary Function

• The critical exchange of substances between the
  blood and interstitial fluid
• Takes place across the thin endothelial walls of
  the capillaries
• The difference between blood pressure and osmotic
  pressure
• Drives fluids out of capillaries at the arteriole
  end and into capillaries at the venule end

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Capillary Function
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The Heart
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The Heart

• Atrium receives blood returning from circulation
• Ventricle generates force to propel the blood
  through the system
• Number of distinct heart chambers has increased
  as vertebrates diversified

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Vertebrate Circulatory Systems
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Fish

• A fish heart has two main chambers
• One ventricle and one atrium
• Blood pumped from the ventricle
• Travels to the gills, where it picks up O2 and
  disposes of CO2

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Amphibians

• Frogs and other amphibians
• Have a three-chambered heart, with two atria and
  one ventricle
• The ventricle pumps blood into a forked artery
• That splits the ventricles output into the
  pulmocutaneous circuit and the systemic circuit

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Reptiles (Except Birds)

• Reptiles have double circulation
• With a pulmonary circuit (lungs) and a systemic
  circuit
• Turtles, snakes, and lizards
• Have a three-chambered heart with a septum

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Mammals and Birds

• In all mammals and birds
• The ventricle is completely divided into separate
  right and left chambers
• The left side of the heart pumps and receives
  only oxygen-rich blood
• While the right side receives and pumps only
  oxygen-poor blood
• A powerful four-chambered heart is essential for
  endothermic animals

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Mammalian Circulation

• Blood begins its flow with the right ventricle
  pumping blood to the lungs
• In the lungs the blood loads O2 and unloads CO2
• Oxygen-rich blood from the lungs enters the heart
  at the left atrium and is pumped to the body
  tissues by the left ventricle

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Mammalian Circulation

• Blood returns to the heart through the right
  atrium
• Oxygen-rich blood from the lungs
• Enters the heart at the left atrium and is pumped
  to the body tissues by the left ventricle
• Blood returns to the heart
• Through the right atrium

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Mammalian Cardiovascular System
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The Mammalian Heart

• About the size of a clenched fist and made
  primarily of cardiac muscle
• The heart contracts and relaxes
• In a rhythmic cycle called the cardiac cycle
• The contraction, or pumping, phase of the cycle
• Is called systole
• The relaxation, or filling, phase of the cycle
• Is called diastole

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The Mammalian Heart
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The Mammalian Heart

• The heart rate, or pulse is the number of beats
  per minute
• The cardiac output
• Is the volume of blood pumped into the systemic
  circulation per minute
• Affected by heart rate and stroke volume
• Increases during exercise

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Heart Valves

• Four valves in the heart prevent backflow to keep
  blood moving in the right direction
• Atrioventricular valves (AV) between each atrium
  and ventricle
• Semilunar valves located at the exits of the
  heart
• Where aorta and pulmonary artery leave the heart

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Maintaining the Hearts Rhythmic Beat

• A region of the heart called the sinoatrial (SA)
  node, or pacemaker
• Sets the rate and timing at which all cardiac
  muscle cells contract
• Impulses from the SA node
• Travel to the atrioventricular (AV) node
• At the AV node, the impulses are delayed
• And then travel to the Purkinje fibers that make
  the ventricles contract

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The Cardiac Cycle

• The contraction phase of the atria and the
  ventricles, called systole, is closely
  coordinated with their relaxation phase, or
  diastole.