Evolution of Systems for Exchange

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What Characteristic Define an Animal?

• Eukaryotic cells
• Multicellular
• Ingestive Heterotroph

2

• How did the animal kingdom evolve?
• Oldest fossils are 700 million years old
• Animals probably evolved from an ancestor of a
  colonial choanoflagellate
• protist
• One hypothesis for the origin of animals

3
Major Trends in Animal Evolution

• Development of Tissue Layers
• Patterns of Body Symmetry
• Development of a Body Cavity
• Body Segmentation
• Specialization

4
Development of Tissue Layers

• Most animals have tissues that arise from three
  embryologic tissues layers
• Ectoderm produce skin and nervous system
• Endoderm produces GI tract
• Mesoderm produces muscle, skeleton and most
  organs

5
Patterns of Body Symmetry

• Asymmetrical
• Bilateral symmetry
• Radial symmetry

6
Development of a Body Cavity

• Allows independent movement of body wall
• Cushions internal organs
• Provides a hydrostatic skeleton
• Increases flexibility and mobility

Protostomes mesoderm forms from mass of cells
between endoderm and ectoderm
Deuterostomes mesoderm forms as outpocketing of
gastrulation cavity
Visualizing Protostome Deuterostome Development
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Body Segmentation

• Most animals have segmented bodies
• Segmentation increases body flexibility and
  mobility

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Evolution of Systems for Exchange with the
Environment

• The maintenance of constant conditions in the
  internal environment is called homeostasis.
  Homeostasis is an essential feature of complex
  animals.
• Animals have evolved variable adaptations to
  maintain homeostasis, that depend on their
  environment and level of sophistication

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Evolution of Systems

• Every organism must exchange materials energy
  with environment, which ultimately occurs at the
  cellular level.

• Most animals have organ systems specialized for
  exchanging materials, and many have an internal
  transport system that conveys fluid
  (blood/interstitial fluid) throughout the body.

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Evolution of the Circulatory System

• The bulk transport of fluids throughout the body
  connects aqueous environment of body cells to
  organs that exchange gases, absorb nutrients, and
  dispose of wastes.
• For animals with many cell layers, gastrovascular
  cavities are insufficient, due to the amount of
  transports.

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• Open Circulatory System
• There is no distinction between blood and
  interstitial fluid, collectively called
  hemolymph.
• One or more hearts pump the hemolymph into
  interconnected sinuses surrounding the organs,
  allowing exchange between hemolymph and body
  cells.

• Closed Circulatory System
• Blood is confined to vessels and is distinct from
  the interstitial fluid.
• One or more hearts pump blood into large vessels
  that branch into smaller ones cursing through
  organs.
• Materials are exchanged by diffusion between the
  blood and the interstitial fluid bathing the
  cells.

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• Arteries carry Away
• Veins Veturn
• Blood Arrives at Atria
• Blood Vacates Ventricles
• Left oxygenated
• Right deoxygenated

Fig. 42.4
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Evolution of the Nervous System
3 evolutionary trends in nervous system
development 1-bilateral 2-cephalization 3-increas
ed numbers of neurons
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Evolution of Nervous Systems

• The nervous system monitors and controls almost
  every organ system through a series of positive
  and negative feedback loops.

16
Evolution of Respiratory Systems

• Large animals cannot maintain gas exchange by
  diffusion across their outer surface. They
  developed a variety of respiratory surfaces that
  all increase the surface area for exchange, thus
  allowing for larger bodies.
• A respiratory surface is covered with thin, moist
  epithelial cells that allow oxygen and carbon
  dioxide to exchange. Those gases can only cross
  cell membranes when they are dissolved in water
  or an aqueous solution, thus respiratory surfaces
  must be moist.

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Evolution of Respiratory Surfaces

• Single-celled organisms exchange gases directly
  across cell membrane. However, the slow diffusion
  rate of oxygen/carbon dioxide limits size. Simple
  animals lack specialized exchange surfaces have
  flattened, tubular, or thin shaped body plans
• Earthworms have a series of thin-walled blood
  vessels known as capillaries. Gas exchange occurs
  at capillaries located throughout the body as
  well as those in the respiratory surface.
• Many terrestrial animals have their respiratory
  surfaces inside the body and connected to the
  outside by a series of tubes.
• Tracheae tubes carry air directly to cells for
  exchange. Spiracles openings at surface that
  lead to tracheae that branch into smaller tubes.
  Body movements or contractions speed up the rate
  of diffusion. Does not function well in animals
  whose body gt 5 cm.
• Amphibians use skin as a respiratory surface.
  Frogs eliminate carbon dioxide 2.5 times as fast
  through their skin as they do through their
  lungs. Eels (a fish) obtain 60 of their O2
  through their skin. Humans exchange only 1 of
  CO2 through skin. Constraints of water loss
  dictate that terrestrial animals must develop
  more efficient gas exchange.

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Gills

• Gills greatly increase the surface area for gas
  exchange.
• Gills typically are convoluted outgrowths
  containing blood vessels covered by a thin
  epithelial layer.
• Gills are very efficient at removing oxygen from
  water there is only 1/20 the amount of oxygen
  present in water as in the same volume of air.
  Water flows over gills in one direction while
  blood flows in the opposite direction through
  gill capillaries. This countercurrent flow
  maximizes oxygen transfer.

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Lungs

• Lungs are ingrowths of the body wall and connect
  to the outside by as series of tubes and small
  openings. Lung breathing probably evolved about
  400 million years ago. Lungs are not entirely the
  sole property of vertebrates, some terrestrial
  snails have a gas exchange structures similar to
  those in frogs.

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Evolution of Excretory System

• Osmoregulation balances the uptake and loss of
  water and solutes.
• An animal's nitrogenous wastes reflect its
  phylogeny and habitat.
• Diverse excretory systems are variations on
  tubular theme
• The nephron is organized for stepwise processing
  of blood filtrate.
• Hormonal circuits link kidney function, water
  balance, and blood pressure.

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Evolution of Digestive System

• Diffusion?ingestion?gastrovascular cavity?1 way
  digestive system.

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Evolution of Digestive System

• Diffusion?ingestion?gastrovascular cavity?1
  opening digestive system.

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Evolution of Digestive System
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Resources

• Architecture of Animals
• Milestones of Life
• External Environment I