Mechanical activity moves food through the gut and aids digestion

In most vertebrates, including humans, food entering the mouth is chewed and mixed with saliva. A muscular tongue then pushes a chunk, or bolus, of chewed food toward the back of the mouth cavity. By making contact with the soft palate at the back of the throat, the bolus of food initiates swallowing, which is a complex series of autonomic reflexes. If you stand in front of a mirror and gently touch this tissue at the back of your throat with a cotton swab, you will experience an uncontrollable urge to swallow. Swallowing propels the food through the pharynx (where the mouth cavity and the nasal passages join) and into the esophagus (the food tube). To prevent the food from entering the trachea (windpipe), the larynx (voice box) closes, and a flap of tissue called the epiglottis covers the entrance to the trachea (Figure 50.12).

Once the food is in the esophagus, a wave of smooth muscle contraction, called peristalsis, takes over and pushes it toward the stomach. The smooth muscle layers of the gut contract in response to being stretched. Swallowing a bolus of food stretches the upper end of the esophagus, and this stretching initiates a wave of contraction that moves progressively down the gut from the pharynx toward the anus.

The movement of food from the stomach into the esophagus is normally prevented by the lower esophageal sphincter, a thick ring of circular smooth muscle at the junction of the esophagus and the stomach. This sphincter is normally constricted, but waves of peristalsis cause it to relax enough to let food pass from the esophagus into the stomach. Sphincter muscles are found elsewhere in the digestive tract as well. The pyloric sphincter governs the passage of stomach contents into the intestine. Another important sphincter surrounds the anus.

Submucosal gland

(a) Swallowing

Brain stem reflex center and nerves controlling swallowing

(a) Swallowing

Brain stem reflex center and nerves controlling swallowing

Epiglottis CloseEpiglottis And Esophagus

Esophageal sphincter

2l The soft palate is pulled up as the vocal cords close the larynx.

The larynx is pulled up and forward and is covered by the epiglottis. The esophageal sphincter relaxes. the bolus of food enters the esophagus.

(b) Peristalsis

Food bolus

Esophagus

Circular muscles___||

contract

Previous bolus

Epiglottis Glottis Vocal cords

Esophageal sphincter

2l The soft palate is pulled up as the vocal cords close the larynx.

Food bolus

Previous bolus

Pyloric sphincter

Food Bolus Picture

I Peristaltic contractions propel the food to the stomach.

Circular muscles relax

Longitudinal muscles' contract

Pyloric sphincter

I Peristaltic contractions propel the food to the stomach.

50.12 Swallowing and Peristalsis Food pushed to the back of the mouth triggers the swallowing reflex. Once food enters the esophagus, peristalsis propels it through the gut.

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Responses

  • claudia reiniger
    Which nerve is controlling the epiglottis?
    8 years ago
  • stefan
    What moves food through the gut?
    8 years ago
  • petri
    How does the food enters into the oesophagus?
    8 years ago

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