Breathing
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7.1 Air enters the exterior nares and passes into the nasal cavity, and on through the internal nares into the pharynx (Applegate, 2000, 308-312). It is filtered, warmed and moistened as it passes through the nasal cavity. From the pharynx it passes over the soft palate and uvula, down the oropharynx, over the epiglottis into the laryngopharynx and on into the trachea. The air flows down to the trachea, which divides at the level of the fifth thoracic vertebra into the right and left primary bronchi, and enters the lungs. The air flows down the bronchi, which then further divide into smaller and smaller passages to form the bronchial tree. The primary bronchi divide into secondary (lobar) bronchi, which branch into tertiary (segmental) bronchi. Branching continues until the bronchial tree gives rise to the bronchioles. The air flows through the bronchial trees to the bronchioles. The air follows the bronchioles as they get smaller and smaller, to the terminal bronchioles, and then the respiratory bronchioles, which lead into the alveolar ducts which terminate in clusters of minute air sacs - the alveoli (Applegate, 2000, 300-312). Here the air exchanges its oxygen for carbon dioxide across the alveolar squamous epithelium, and across the walls of the capillaries in the alveolar ducts and respiratory bronchioles. The alveoli, alveolar ducts, and respiratory bronchioles are structures in the respiratory zone because this is where gaseous exchange takes place. The
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ial cells that resemble astrocytes of the CNS. Each glial cell wraps around an entire bundle of ENS axons. The ENS is also vulnerable to typical brain lesions, such as the neurfibrillary tangles of Alzheimer's and the Lewy bodies of Parkinson's disease. The gut ENS also contains interstitial cells of Cajal (ICC), which tend to be isolated between nerve terminals and smooth muscle cells, which they may activate. ICC are also thought to act as pacemakers, establishing the rhythm of bowel contractions. The entire ENS is arranged in two ganglionated plexuses - the larger Auerbach's plexus and the smaller, submucosal Meissner's plexus.
Within the enteric plexuses are three types of neurons: sensory neurons of at least five different types, which respond to mechanical, thermal, osmotic, and chemical stimuli; motor neurons which control gastrointestinal motility and secretion; and interneurons which integrate information from sensory neurons and provide it to enteric motor neurons (The Enteric, 2004). Enteric neurons also secrete many neurotransmitters, including acetylcholine, norepinephrine, dopamine, and serotonin. Although the ENS can function autonomously, normal digestive function requires communication links between the
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Some common words found in the essay are:
Rovalino Vidal, Type II, Cajal ICC, Romrell Kaye, , applegate 2000, Hyperventilation Retrieved, gaseous exchange, Ed Retrieved, digestive tract, Alzheimer's Lewy, Hospital Practice, gastric secretions, acid chyme, alveolar ventilation rate, alveolar ventilation, connective tissue, alveolar ducts, ventilation rate, enteric nervous, Ross Romrell, romrell kaye 1995, enteric nervous system, ross romrell kaye, air breathed minute,
Approximate Word count = 2912
Approximate Pages = 12 (250 words per page)
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