Ch. 16
Respiratory System
16.4 Control of Breathing
• Normal breathing is a rhythmic, involuntary
act that continues even when a person is
unconscious.
• The respiratory muscles are under voluntary
control.
Respiratory Center
• In the brainstem
• Control both
inspiration and
expiration.
• Neurons scatter
though out the pons
and medulla
oblongata.
Medulla: rhythmicity area
Pons: pneumotaxic area
Medullary rhythmicity Area
• Two neuron groups that extend the length of the medulla
oblongata. 1: Dorsal respiratory group 2: Ventral
respiratory group
1. Dorsal respiratory group
-controls the basic rhythm of inspiration
-neurons emit bursts of impulses that signal the diaphragm
and other inspiratory muscles to contract.
-start out weak and then stengthen and then suddenly stops.
The breathing muscles that contract in response to the
impulses steadily increase the volume of air entering the
lungs.
-neurons remain inactive during expiration. Then start to
inspire again.
2. Ventral respiratory group
-quiet during normal breathing.
-neurons generate impulses that increase
inspiratory movements during forceful
breathing.
-neurons activate muscles that are needed
during forceful breathing.
• Neurons in
pneumotaxic area of
the pons continuously
transmit impulses that
inhibit the inspiratory
bursts originating
from the dorsal
respiratory group.
• Control breathng rate.
• Strong neuron bursts,
breathing rate
increases.
Factors Affecting Breathing
• Chemosensitive areas (chemoreceptors) –
ventral portion of the medulla oblongata,
sense changes in the cerebrospinal fluid (CSF).
• Concentrations of carbon dioxide and
hydrogen ions.
• If concentrations rise, the central
chemoreceptors signal the respiratory center,
respiratory rate and tidal volume increase.
• Result --- more carbon dioxide is exhaled.
Hyperventilation
• Breathing rapidly and deeply.
• Lowers the blood carbon dioxide concentration.
• After hyperventilation, it takes longer than usual
for the carbon dioxide concentration to stimulate
the urge to breath.
• *this can cause abnormally low blood oxygen
levels.
• This should never be done to help hold breath
during swimming --- could lose consciousness
underwater and drown.
16.5 Alveolar Gas Exchanges
• Many capillaries on the alveolus wall.
• Respiratory membrane – between blood and
alveolar air exhange, two layers of epithelial
cells and a layer of fused basement
membrane.
• Consists of the
wall of the
alveolus and the
wall of the
capillary.
• http://www.youtube.com/watch?v=DoSTehS7i
q8&feature=player_embedded
Diffusion Across the Respiratory
Membrane
• Partial pressure: amount of pressure each gas
contributes in a gas mixture.
• Air
– Oxygen 21% (21% of 760 mm Hg or 160mm) = Po2
– Carbon dioxide Pco2 = 0.3mm
Carbon dioxide diffuse from blood where its partial
pressure is higher. (40mm hg)
Oxygen in alveolar is 40mm hg so enters into blood.
16.6 Gas Transport
• Oxygen transport
– 98% of oxygen in blood bind to the iron-containing
protein hemoglobin in RBCs.
– Remainder dissolve in plasma.
– Hemoglobin + oxygen = oxyhemoglobin
– Unstable bond between hemoglobin and oxygen.
– When pressure decreases oxyhemoglobin releases
oxygen, which diffuses into nearby cells.
• More oxygen is released as the blood
concentration of carbon dioxide increases.
• As blood become more acidic, or as blood
temperature increases.
• Explains why more oxygen is released to
skeletal muscles during physical exercise.
• Increase in carbon dioxide, decrease in pH,
and raise temp.
• Hypoxia – deficiency of oxygen reaching the
tissues.
• Hypoxemia – decreased oxygen in blood.
• Anemic hypoxia – diminished ability of the
blood to transport oxygen.
• Ischemica hypoxia – inadequate blood flow.
• Histotoxic hypoxia – defect at the cellular
level.
– Ex. Cyanide poisoning
• http://www.youtube.com/watch?v=WXOBJEX
xNEo&feature=player_embedded#at=44
Carbon Dioxide Transport
• CO2 + hemoglobin = carbaminohemoglobin
• Forms slowly
• Only 23% of the carbon dioxide that blood
transports is in this form.
• Another transport mechanism is the formation of
bicarbonate ions (HCO3-).
• CO2 reacts with water for form carbonic acid.
• Carbonic anhydrase-speeds the reaction between
carbon dioxide and water.
• http://www.youtube.com/watch?v=x26TWL3
VKMg&feature=player_embedded