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Digestive Physiology: Motility, Digestion, and Absorption

The function of the digestive system is to break down the foods you eat, release their nutrients, and absorb those nutrients into the body. Although the small intestine is the workhorse of the system, where the majority of digestion occurs, and where most of the released nutrients are absorbed into the blood or lymph, each of the digestive system organs makes a vital contribution to this process (Figure 23 2). As is the case with all body systems, the digestive system does not work in isolation; it functions cooperatively with the other systems of the body.

Figures (10)

Areas of the stomach
Schematic drawing of bacterial conjugation. 1- Donor cell produces pilus. 2- Pilus attaches to recipient cell, bringing the two cells together. 3- The mobile plasmid is nicked and a single strand of DNA is transferred to the recipient cell. 4- Both cells recircularize their plasmids, synthesize second strands, and reproduce pili; both cells are now viable donors.
Upper and lower human gastrointestinal tract
Peristalsis animation
Adult digestive system
3D medical illustration explaining the oral digestive system
The main salivary glands
Esophagus shown in yellow passing behind the trachea and the heart
Liver and gall bladder
Gallbladder shown in green below the liver

Key Points

  • Peristalsis is the rhythmic contraction of muscles that begins in the esophagus and continues along the wall of the stomach and the rest of the gastrointestinal tract.
  • The peristalsis and segmentation, detailed below and pendular movement are famous examples of distinct patterns of GI contraction.
  • The duodenum is the first and shortest section of the small intestine.
  • From here it passes into the first of the three sections of the small intestine, the duodenum (the next section is the jejunum and the third is the ileum).
  • The myenteric plexus and submucosal plexus are both located in the gut wall and receive sensory signals from the lumen of the gut or the CNS.
  • The submucosal plexus (plexus of Meissner) lies in the submucosal layer and is responsible for regulating digestive secretions and reacting to the presence of food (see Figure 23.3).

Terms

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