TOPIC 7: GASEOUS EXCHANGE AND ITS CONTROL

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TOPIC 7 GASEOUS EXCHANGE AND ITS CONTROL

• DURATION 5 HOURS

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7.3 Role of chemoreceptors in
controlling rate of breathing
1 hour
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• CHAPTER OUTLINES
• Students should be able to
• describe
• detail structure of an alveolus
• basic structure of haemoglobin and its
• characteristics (as respiratory pigments)
• explain
• transport of oxygen and carbon dioxide
• characteristics of oxygen dissociation curve
• compare oxygen dissociation curves fetus and
  adult.
• explain
• Bohr effect
• role of chemoreceptors in controlling rate of
• breathing
• describe structure and functions of guard cells
• explain regulation of stomatal opening and
  closing

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1st hour

• By the end of the class, students should be able
  to describe
• detail structure of an alveolus
• basic structure of haemoglobin and its
• characteristics (as respiratory pigments)

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Mammalian Respiratory Systems

• In mammals, air inhaled through the nostrils
• passes through the pharynx into the trachea,
  bronchi, bronchioles, and dead-end alveoli, where
  gas exchange occurs

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The human respiratory system
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Structure of an alveolus

• each lung packed with 1.5-2.5 million alveoli
• diameter is 0.2 millimeter each enmeshed in
  capillaries
• wall of each alveolus is only one cell thick
• thin layer of watery fluid lining each alveolus

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Detailed structure of an alveolus
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Adaptation of the lungs for gaseous exchange

• consists of millions alveoli to maximize
  respiratory surface area
• thin-walled alveoli resemble tiny bubbles,
  therefore provided enormous surface areas of
  diffusion

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• alveolis surface remains moist, thus gasses can
• easily dissolve in thin fluid and diffuse
  through
• the alveolar and capillary membranes
• both alveolar wall and the adjacent capillary
  walls are only one cell thick, the air is
  extremely close to the blood in the capillaries

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Respiratory Pigments

• Respiratory pigments
• are proteins that transport oxygen
• greatly increase the amount of oxygen that blood
  can carry
• The respiratory pigment of almost all vertebrates
• is the protein hemoglobin, contained in the
  erythrocytes
• Like all respiratory pigments
• hemoglobin must reversibly bind O2, loading O2 in
  the lungs and unloading it in other parts of the
  body

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Basic structure of haemoglobin

• oxygen-carrying protein in red blood cells
• consists of two pairs of very similar peptides,
  held together by hydrogen bonds
• each peptide holds an iron-containing organic
  molecule called a haem that can bind one molecule
  of oxygen
• therefore, one haemoglobin (Hb) molecule binds up
  to four oxygen molecules

O2 loaded in lungs
Haem group
Iron atom
O2
O2 unloaded In tissues
O2
Polypeptide chain
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Characteristics of haemoglobin as respiratory
pigment

• Loading and unloading of O2
• depends on cooperation between the subunits of
  the hemoglobin molecule
• The binding of O2 to one subunit induces the
  other subunits to bind O2 with more affinity
• Cooperative O2 binding and release
• is evident in the dissociation curve for
  hemoglobin
• A drop in pH
• lowers the affinity of hemoglobin for O2

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Thank your for your attention

• Next lecture
• explain
• transport of oxygen and carbon dioxide
• characteristics of oxygen dissociation
• curve
• Question to ponder
• What is partial pressure?

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