Ch. 16 Respiratory System Sec. 4 - 6

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 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.

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=DoSTehS7iq8&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 http://www.youtube.com/watch?v=WXOBJEXxNEo&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=x26TWL3VKMg&feature=player_embedded