Circulation in Animals

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Circulation in Animals

• All organisms exchange materials and energy with
  their environment
• Materials move across the cell membrane to
  cytoplasm and wastes move out of cell.
• Most animals have specialized organ systems to
  exchange materials with the environment.

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Cnidarian Body PlanA gastrovascular cavity
instead of a circulatory system
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Circulation in Animals

• Hydra and other cnidarians do not have a
  circulatory system.
• Their body wall only two cells thick
• Have a central gastrovascular cavity used for
  digestion and diffusion of substances throughout
  body.

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Circulation in Animals

• Animals with many cell layers diffusion is
  insufficient
• Internal distances are too great.
• Glucose diffuses 1 cm in three hours in a human
• In more complex animals, two types of circulatory
  systems have evolved
• open circulatory systems
• closed circulatory systems
• Both have a circulatory fluid, a set of tubes,
  and a muscular pump (the heart). Heart circulates
  blood by applying pressure

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• Open circulatory system - circulatory fluid not
  always in a vessel. Blood and fluid around cells
  (interstitial fluid) mix and called hemolymph
• Found in arthropods and most mollusks
• One or more hearts pump hemolymph into spaces
  around organs for exchange between hemolymph and
  body cells.
• heart contracts hemolymph pumped out into body
• heart relaxes, draws hemolymph into vessels

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Open Circulatory System
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Closed Circulatory System

• In a closed circulatory system, blood is confined
  to vessels
• Found in some invertebrates (earthworm, squid,
  octopus) and vertebrates

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Blood Vessels In a Closed System

• Same
• layer of elastic connective tissue
• smooth muscle
• endothelium lining
• Different
• Capillaries lack connective tissue and smooth
  muscle
• Arteries have thicker smooth muscle layer
• Veins have valves and skeletal muscle aids in
  blood circulation in veins

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Metabolic Rate and Evolution of Cardiovascular
Systems.

• In general, animals with high metabolic rates
  have more complex and powerful circulatory
  systems than animals with low metabolic rates.
• From low to high metabolic rate compare closed
  circulatory systems of
• Fish
• Amphibian
• Crocodilians, Birds, and Mammals

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Fish Circulatory System

• Blood pumped from ventricle to gills (picks upO2
  and disposes of CO2)
• The gill capillaries lead to a vessel that
  carriesoxygenated blood to body and then back
  to heart

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Fish Circulatory System

• In fish, blood passes through two capillary beds,
  the gill capillaries and systemic capillaries.
• When blood flows through a capillary bed, blood
  pressure (the force pushing circulation)
  decreases
• Oxygen-rich blood leaving gills flows to
  systemic circulation slowly

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Amphibian Circulatory System

• Three-chambered heart with two atria and one
  ventricle.
• Has double circulation pulmocutaneous and
  systemic circulation.

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Amphibian Circulatory System

• Advantage is vigorous blood flow to brain,
  muscles, and organs because blood pumped a second
  time after has lost pressure in capillaries
• BUT some O2 poor blood mixes with O2 rich blood
  in ventricle

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Bird, Crocodilian and Mammal Circulatory System

• Four chambered heart.
• The left side receives and pumps O2 rich blood,
  while right side handles O2 poor blood.
• Double circulation restores pressure to systemic
  circuit and prevents mixing of O2 rich and O2
  poor blood.

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Comparative Anatomy of 3 Closed Circulatory
Systems
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Human Heart
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Cardiac Cycle
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Control of the heart beat
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Blood Flow Velocity and Pressure

• Blood velocity fastest in arteries, slows down in
  capillaries and speeds up a little in veins
• Caused by large total cross sectional area of
  capillaries
• Blood pressure (pressure blood exerts on vascular
  tissue) is highest in arteries

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Capillary Exchange

• Exchange of substances between blood and
  interstitial fluid occurs in capillary bed
• Exocytosis across endothelial cells
• Diffusion across endothelial cells
• Pressure differences force some materials out of
  clefts between adjoining endothelial cells

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Pressure Differences between Capillaries and
Interstitial Fluid

• At arteriole end of capillary net movement out
  because blood pressure is greater than osmotic
  pressure, and venule end of capillary net
  movement in because osmotic pressure is greater
  than blood pressure

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Lymphatic System

• Not all fluid returned to blood at vein end of
  capillary bed
• Net loss of 4 L of fluid a day
• Fluid enters lymph capillaries that are embedded
  around blood capillaries
• Fluid called lymph and similar to interstitial
  fluid
• Lymph Vessels have valves, contract rhythmically
  to move fluid but also rely on voluntary muscle
  contractions

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Lymphatic System

• Lymph nodes filter lymph and fight infection
• Lymph returned to blood by a duct between the
  vena cava and right atrium

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Blood