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Circulation Volunteer State Community College


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									Circulation & Gas Exchange

      Chapter 42, Campbell, 6th edition
                          Nancy G. Morris
        Volunteer State Community College
Exchange of materials
between organism and environment:

     always occurs across a moist

     nutrients, gases, and wastes
      diffuse across membrane

     molecules must be dissolved in
      water in order to diffuse
Exchange of materials…

     In protozoans, the entire surface is
      used for exchange.
     Simple animals like sponges and
      cnidarians are constructed so that
      each cell is exposed to the
      surrounding water. (What pattern
      of construction permits this?)
What about triploblastic animals?

     some cells are isolated from the
      surrounding environment
     they require specialized organs for
      exchange with the environment
     AND special systems for internal
      transport through body fluids to the
What are the advantages of specialized
organs with an internal transport system?

       1) reduces distance over which
        molecules must diffuse to enter
        & leave a cell AND

       2) permits regulation of internal
        body fluids
Circulation in Animals
 Transport systems functionally connect body
    cells with the organs of exchange.
    Diffusion alone is too slow for complex
     multicellular animals.
    The time of diffusion is proportional to
     the square of the distance the chemical
     must travel:
        if a glucose molecule takes 1 second
         to diffuse 100µm, it will take 100
         seconds to diffuse 1 mm.
The presence of a circulatory system
reduces the distance a substance must

    because it connects the aqueous
     environment of the cell with organs
     specialized for exchange.
For example,

   O2 diffuses from air across thin epithelium
    in the lung into the blood.
   Oxygenated blood is carried via the
    circulatory system to all parts of the body.
   As blood passes through capillaries in the
    tissues, O2 diffuses from the blood into the
    cells across the plasma membrane.
   CO2 is produced by the cells and moves in
    the opposite direction.
The circulatory system…

    not only moves gases, but is a
     critical component in maintaining
     homeostasis of the body.

    Blood passes from cells through
     organs (liver, kidneys) that
     regulate the nutrient and waste
     content of the blood.
Circulation in Animals

   Invertebrates have either a
     gastrovascular cavity or a
     circulatory system for
     internal transport.
    In sponges & cnidarians, nutrients have
     only a short distance to diffuse to the
     outer cell layer.   (Figure 42.1)

    In flatworms & other platyhelminthes, no
     cell is more than a few mm away from the
     body surface.

    Complex multicellular animals require some
     type of circulatory system.
    Hemolymph bathes the internal organs directly
     while moving through sinuses (Figure 42.2a)

    Hemolymph acts as both blood and interstitial

    Relaxation of the heart draws hemolymph
     through the ostia into the vessel.

    Insects, arthropods, mollusks
     Blood is confined to vessels and interstitial
      fluid is present
     Heart (or hearts) pumps blood into large
     Major vessels branch into smaller ones which
      supply blood to organs (Figure 42.2b)

     In the organs, materials are exchanged
      between the blood and the interstitial fluid
      bathing the cells.

     Annelids and vertebrates

   A closed circulatory system
   consists of
            1) a heart
            2) blood vessels
            3) blood
    Closed cardiovascular systems
     A heart has one atrium or two atria, chambers
      that receive blood, and one or two ventricles,
      chambers that pump blood out.

     Arteries carry blood away from the heart to
      organs where they branch into smaller arterioles
      that give rise to microscopic capillaries.

     Capillaries rejoin to form venules, which converge
      to form veins that return blood to the heart.
    Capillaries have thin, porous walls and
     are arranged into networks called
     capillary beds that infiltrate each
    The capillary wall is a single cell
    This is the site of chemical exchange
     between blood & interstitial fluid.
Fish: 2-chambered heart

   one atrium & one ventricle. (Fig 42.3a)
   Blood pumped from the ventricle goes to the
    gills. O2 diffuses into the gill capillaries and
    CO2 diffuses out.

   Gill capillaries converge into arteries that
    carry blood to capillary beds in other organs.
    Blood from the organs travels through veins to
    the atrium, then into the ventricle.
Fish: 2-chambered heart
   Blood flows through two capillary beds during
    each complete circuit: one in the gills and the
    second in the organ systems (systemic

   As blood flows through a capillary bed, blood
    pressure drops substantially (due to the
    resistance of the numerous small vessels).

   Blood flow to the tissues and back to the
    heart is aided by swimming motions.
2-chambered heart
 1 atrium & 1 ventricle
 in fish
Amphibians: 3-chambered heart
   two atria and one ventricle (Fig. 42.3b)
   Blood flows in a double circulation scheme
    1) pulmocutaneous circuit (to lungs and skin)
    2) systemic circuit (to all other organs)
   Blood flow pattern: ventricle -> lungs &
    skin-> left atrium -> ventricle -> all other
    organs -> right atrium
• 2 atria & 1 ventricle of amphibian
Amphibians: 3-chambered heart

    There is some mixing of oxygen-rich
     and oxygen-poor blood in the single
    A ridge present in the ventricle
     diverts most of the oxygenated blood
     to the systemic circuit and most of
     the deoxygenated blood to the
     pulmonary circuit.
Reptiles: 3-chambered heart
   most reptiles (except crocodilians)
   ventricle is partially divided
   providing for double circulation:
       1) a systemic circuit
       2) a pulmonary circuit

   partial division of ventricle reduces mixing of
    oxygenated and deoxygenated blood
Birds & mammals: 4 chambers
    Double circulation:
        1) systemic
        2) pulmonary
    complete septum eliminates mixing of
     oxygenated and deoxygenated blood
    separation greatly increases the efficiency
     of O2 delivery to the cells
4-chambered heart
• 2 atria & 2 ventricles
• complete seperation of oxygenated
       and deoxygenated blood
• right heart drives pulmonary
• left heart dives systemic
• complete separation of oxygenation
       & deoxygenated blood
Human heart:
    located beneath the sternum
    cone-shaped about size of fist
    surrounded by pericardium (2 layers)
    cardiac muscle tissue
    atria collect blood returning to heart
    ventricles are powerful pumps
Four valves of human heart.
   Valves are flaps of connective tissue.
   Atrioventricular valves –
       found between atria & ventricles
       prevent backflow of blood
   Semilunar valves-
       located where aorta leaves left ventricle
       located where pulmonary arteries leave
        the right ventricle
A heart murmur

       is a defect in one or
        more of the valves that
        allows backflow of blood.
Heart’s rhythmic beat:
   Cardiac muscle is myogenic   (self-excitable).

   contracts without input from the
    nervous system

   tempo is controlled by the sinoatrial
    node (SA) sometimes called the
SA node
    located in right atrium near the entrance
     of the superior vena cava
    composed of specialized muscle tissue
     with characteristics of both muscle and
     nervous tissue
    contraction of SA causes a wave of
     excitation to spread rapidly from the
     node causing the two atria to contract in
AV node
   second mass of specialized tissue

   receives the wave of excitation from SA

   impulse is delayed at the AV node for 0.1
    second to ensure that the atria are
    completely empty before the ventricles
   impulse is then carried by a mass of
    specialized fibers, Bundle of His,
    throughout the ventricle walls
Heart rate
   controlled by SA
   influenced by:
     1) two antagonistic sets of nerves– one
         speeds contractions and the other slows
     2) hormones influence the SA node –
         epinephrine increases heart rate
     3) other factors: body temperature &
         exercise influence heart rate

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