Chapter 42 Circulation and Gas Exchange

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Chapter 42Circulation and Gas Exchange

• Barbara Musolf
• Clayton State University
• AS Building G 110-G
• 678-466-4851

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Objectives

• Circulatory systems and phylogeny
• Vertebrate circulatory systems
• Physical principles that govern blood circulation
• External and internal respiration
• Ventilation
• The respiratory pigments that bind and transport
  gases

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Role of the circulatory system

• Replaces diffusion when substances need to be
  transported long distances.
• Functionally connects the aqueous environment of
  body cells to the organs to supply O2 and
  nutrients and collect metabolic waste.
• Allows the distribution of hormones and other
  chemical signals.

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Invertebrate circulation gastrovascular cavities

• In cnidarians sea water is held in the
  gastrovascular cavity, so that the epithelial
  cells are bathed in sea water.
• Diffusion of materials occurs to outer layer.
• Flatworms also exchange fluids through an
  extensive gastrovascular cavity.

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Invertebrate circulation open systems

• Components
• Blood
• Vessels
• Pump or heart
• Blood pressure provides the force for transport.
• No distinction between blood and interstitial
  fluidshemolymph
• Sinuses surround organs and allow for exchange of
  materials.
• Relaxation of the heart draws in blood through
  ostia.

Found in arthropods and most molluscs
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Invertebrate circulation closed systems

• Blood is distinct from interstitial fluids.
• Vessels branch into smaller ones.
• Material is exchanged between interstitial fluid
  and blood.
• Found in annelids, cephalopods, and all
  vertebrates.

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Closed vs open circulation

• Open systems
• Are less costly in energy expenditure
• Require less energy to build and maintain
• Can function as a hydrostatic skeleton
• Closed systems
• Can produce higher pressures and more efficient
  transport to meet high metabolic needs.

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Vertebrate circulation

• Heart has receiving chamber(s)atrium
• Heart has a pumping chamber(s)ventricle
• Blood vessels are arteries? ? arterioles
  ?capillaries ?venules ?veins
• Arteries carry blood to capillaries
• Exceptions are portal systemsthe hepatic vein
  which carries blood to capillary beds in the
  liver
• Animals with higher metabolic rates have more
  complex circulatory systems and more powerful
  hearts.

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Fish circulation

• Has one atrium and one ventricle.
• Blood from the ventricle travels to gill
  capillaries to pick up O2 and discard CO2
• From the gill the blood enters into systemic
  circulation.
• Blood passes through 2 capillary beds per cycle

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Amphibian circulation

• 3 chambered heart with 2 atria and one ventricle
• Pulmocutaneous circuit and systemic circuit
• Blood flows to lungs and skin to pick up O2 and
  discard CO2
• Some mixing of blood occurs but a ventricular
  ridge provides some separation.
• Double circulationblood is pumped twice to
  maintain pressure

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Reptile circulation

• Have a pulmonary and systemic circuit
• 3 chambered heart with a septum dividing the
  ventricle.
• Crocodilians have complete division of ventricle
• 2 arteries lead from the heart to systemic circuit

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Mammalian and avian circulation

• 4 chambered heart
• Right side receives O2 poor blood and pumps to
  lungs
• Left side receives O2 rich blood and pumps to
  system
• Double system helps maintian high pressure
• 4 chambers ensures no mixing of blood.
• Helps maintain endothermy

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Cardiac cycle

• Systole is contraction
• Diastole is relaxation
• Cardiac output heart rate X stroke volume

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Autorhytmic fibers

• Heart muscle cells have an inherent rhythmical
  electrical activity.
• Electrical activity comes from autorhythmic
  fibers that generate repeated action potentials.
• During embryonic development 1 of the fibers
  develop autorhythmicity.
• Act as pacemakers
• Form the conduction system which ensures
  coordinated rhythmic contraction of the heart

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Heart conduction system
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Conduction system

• Sino-atrial (SA) node
• Atrial contraction
• Atrio-ventricular (AV) node
• AV Bundle of His

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Conduction system

• Left and right bundle branches
• Purkinje fibers
• Ventricular contraction

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ECG

• P wave-atrial depolarization
• QRS-ventricular depolarization
• T waveventricular repolarization
• P-Q interval
• S-T segment
• Q-T interval

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Blood
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Blood vessels

• Plumbing physical principles (resistance
  principles) apply to flow of blood.
• Flow of blood is faster in smaller vessels than
  in larger vessels.
• Flow is from areas of high pressure to low.
• All blood vessels are lined with endothelium.
• The outside layers of blood vessel vary according
  to their size and function.
• Arteries specialize in moving blood at higher
  velocities than veins.

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Blood flow

• Law of continuityfluid flowing through narrow
  segments of a tubular network flows faster than
  through wider segments.
• This also applies to cross-sectional areas
• Why is blood flow slower in capillaries?

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Blood flow

• As cross-sectional area increases, blood velocity
  decreases.
• Flow is slow through the capillaries and speeds
  up in the venules and veins

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Venous flow

• Muscle contractions in leg muscles help propel
  blood towards the heart.
• Valves prevent the backward flow of blood and
  counteract force of gravity.
• Pressure differences between the abdomen and
  thorax also propel blood towards the heart.

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Blood pressure

• Blood enters the aorta faster than at any point
  along the circulatory system.
• This rapid pumping of blood stretches the
  arteriesthe snapping back of the arteries is
  diastole.
• Blood pressure is a combination of cardiac output
  and peripheral resistance.
• Pressure is regulated by hormones, neuronal
  input, and elasticity of the vessels.

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Measuring blood pressure
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Measuring blood pressure
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Capillaries

• Brain, heart, kidneys, and liver generally have
  full capillaries.
• Other tissues have varying amounts of blood
  flowing through capillary beds.
• Capillary blood flow between arterioles and
  venules is controlled by
• Constriction and dilation of arterioles
• Precapillary sphincters (rings of smooth muscle)

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Capillaries
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Capillary exchange

• Exchange of materials between blood and
  interstitial fluid takes place across the
  endothelium of capillaries.
• Endocytosis and exocytosis
• Diffusion (gases and lipophilic materials)
• Bulk flow of materials relies on osmotic and
  fluid pressure differences.
• 85 of the fluid that leaves blood at the
  arterial end reenters at the venous end.
• The remaining 15 enters into the lymph system
  which drains into the venous system near the R
  atrium.