BIO 203 Lecture Notes - Lecture 1: Sodium Chloride, Nephron, Duodenum

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Motility serves 2 purposes: moving food from mouth to anus, mechanically mixing food and breaking down to smaller particles. Mixing maximizes exposure to enzymes by increasing sa. Gi smooth muscle exhibits different patterns of contraction. Migrating motor complex is a fxn that sweeps food and bacteria out of upper gi and into larger intestine. Muscle contractions during a mean follow one of two patterns: Peristalsis, progressive waves of contraction that move from one section of gi to the next receiving segment. Circular muscles contract behind bolus (mass of food), and pushes into. Segmental contractions, short segments of intestine alternately contract and relax. In contracting segments, circular muscles contract while longitudinal muscles relax. Alternating contractions churn contents and mix them and keeps it in contact with absorptive epithelium. Most of gi is composed of single unit smooth muscle, with groups of cells electrically connected by gap jxns to create contracting segments.

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