Circulation and Gas Exchange

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Chapter 42

• Circulation and Gas Exchange

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Overview

• Every organism must exchange materials and energy
  with its environment
• Example oxygen in carbon dioxide out

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Circulation in Animals

• Diffusion is not adequate for transportation in
  animals
• Glucose takes 3 hours to diffuse 1 cm
• Circulatory system solves this problem

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Circulatory Systems

• Gastrovascular cavities are present in most
  invertebrates
• Body plan does not call for a circulatory system
• They are only 2 cells thick
• Open and closed circulatory systems
• Animals with many cell layers rely on some system
  to bath all the cells with nutrients
• Three parts
• Fluid blood
• Set of tubes vessels
• Pump - heart

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Cardiovascular System Adaptations
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Mammalian Double Circulation
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Mammalian Heart

• Size of a clenched fist
• Consists of four chamber
• Two atria
• Thin walled collects blood returning to the heart
• Two ventricles
• Thick walled which pumps blood to either lungs or
  the body
• Contracts and relaxes in rhythmic fashion
• As it contracts it pumps blood, and as it relaxes
  it fills with blood
• Called a cardiac cycle
• Contraction phase is systole
• Relaxation phase is diastole
• Volume of blood per minute that the left
  ventricle pumps is called cardiac output

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Mammalian Heart

• Contains four valves
• Preventing the backflow of blood in the heart
• Between each atrium and ventricle is an
  atrioventricular valve (AV)
• Semilunar valves are located at each exit
• Aorta and pulmonary arteries
• Closing of these valves creates the heartbeat
  sound heard with a stethoscope
• Heart murmur a hissing sound caused by a
  malfunctioning valve

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Maintaining Heart Beat

• Heart must beat on its own in other words you
  dont have conscious control over the hearts
  rhythm
• Certain vertebrate cardiac muscle cells are self
  excitable (they contract without any signal from
  the nervous system)
• Region of heart called the sinoatrial (SA) node
  or pacemaker sets the rate and timing at which
  all cardiac muscle cells contract
• Located in the wall of the right atrium
• SA node generates electrical impulses
• Making the atria contract in unison
• Impulses also pass to a relay point called the
  atrioventricular (AV) node
• Located in the wall between the right atrium and
  right ventricle
• Here the impulses are delayed about 0.1 sec
  before spreading to the walls of the ventricles

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Vessels
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Blood Components
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Blood Clotting
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Respiration

• Breathing plus cellular respiration
• need a constant supply of energy to maintain
  yourself
• remember metabolism needs oxygen

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Gas Exchange

• All organisms rely on diffusion of gases
• respiratory surface must be moist
• cells lining the surface are thin
• surface must be large to allow adequate gas
  exchange
• Examples
• nematode
• jellyfish

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Respiratory Systems
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Gills

• many aquatic organisms posses gills
• normally branched or folded to increase surface
  area
• fish gills are covered by the operculum
• pump water in mouth and over the gills

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Terrestrial animals

• Air has a higher O2 concentration than water
• air presents some challenges for gas exchange
• resp. surfaces must remain moist
• cant be on the outside of the body like gills are

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Tracheae

• Internal branching tubes
• large tubes branch into tracheoles which nourish
  the cells
• air enters trachea through spiracles

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Lungs

• Chambers containing moist delicate surfaces
• First lung appeared in freshwater fish as an
  outpocket of digestive system
• Birds have extremely efficient lungs

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Human Respiratory System

• Two parts
• Conducting portion
• carries gases to the gas exchange portion
• Gas exchange portion
• the lungs

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Conducting Portion

• Brings air into the lungs
• Air enters the nose or mouth
• passes into the pharynx
• and then the larynx
• opening to the larynx is guarded by the
  epiglottis
• air then passes into the trachea
• trachea splits into two tubes called bronchi
• into bronchioles
• to the alveoli

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Gas Exchange Portion

• Lungs
• moist surface
• packed with tiny alveoli (2-3 million)
• increases surface area to volume ratio
• Alveoli
• thin walls
• look like tiny bubbles
• completely covered with capillaries

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Gas Transportation

• Oxygen and Carbon Dioxide are carried different
  ways
• Oxygen binds to hemoglobin
• loosely and reversible
• oxygenated blood is bright red
• deoxygenated blood is dark maroon and appears blue

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Gas Transportation

• Carbon Dioxide is carried in three ways
• in the presence of carbonic anhydrase it forms
  HCO3 and diffuses into the plasma
• about 70 of CO2 is carried this way
• some binds to the hemoglobin
• 20 of it is carried this way
• some stays as CO2 in the plasma
• 10 of it is carried this way

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1) O2 diffuses through the lungs
3) O2 diffuses though capillary wall to tissues
2) O2 is carried to tissues bound to hemoglobin
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Inhalation and Exhalation

• Inhalation depends on airtight chest cavity
• Lungs are bordered by neck muscles on top and
  diaphragm on the bottom
• Rib cage surrounds the lungs and is covered by
  the pleural membranes which make an airtight seal
  between the lungs and chest wall

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Inhalation

• Accomplished by expanding the chest cavity
• diaphragm contracts drawing it downwards
• ribs also contract bringing them up and out
• The lungs expand with these motions due to the
  airtight chest cavity

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Exhalation

• Occurs automatically as muscles are relaxed
• More air can be exhaled as abdominal muscles are
  contracted

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Respiratory Control Center

• Breathing occurs automatically due to nerve
  signals from the brain
• Respiratory Center is located in the medulla of
  the brain
• Respiration rate depends on CO2 levels in the
  blood
• monitored by the medulla