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Digestive Physiology: Motility, Digestion, and Absorption

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Terms you will need

  • peristalsisPeristalsis is the wave-like muscle movements that push food through the digestive system.
  • segmentationSegmentation is the mixing of food in the intestines through muscle contractions, which helps digestion and absorption.
  • gastric emptyingGastric emptying is the process of food moving from the stomach into the small intestine.
  • duodenumThe duodenum is the first part of the small intestine where food mixes with digestive enzymes and bile.
  • jejunumThe jejunum is the middle part of the small intestine where most nutrients are absorbed.
  • ileumThe ileum is the last part of the small intestine where remaining nutrients and vitamin B12 are absorbed.

How this topic runs

  1. 1Start here
  2. 2How it works
  3. 3At competition depth

Digestive physiology involves the processes of motility, digestion, and absorption that enable the body to break down food and extract nutrients. The digestive system transforms ingested food into smaller components through mechanical and chemical means, allowing the body to absorb essential nutrients. This system includes the alimentary canal, which runs from the mouth to the anus, and accessory organs such as the liver, pancreas, and gallbladder. These organs work together to ensure efficient digestion and nutrient absorption. The process begins in the mouth with chewing and saliva, continues in the stomach with acid and enzymes, and concludes in the small intestine where most nutrients are absorbed. The digestive system also interacts with other systems, such as the cardiovascular and endocrine systems, to regulate digestion and nutrient metabolism.

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

Digestive physiology covers how the body moves food, breaks it down, and takes in nutrients. This happens through three main actions: motility, digestion, and absorption. Motility is the movement of food through the digestive tract using muscle contractions like peristalsis and segmentation.

Digestion is the chemical and physical breakdown of food into smaller parts. Absorption is how the body takes in these small parts into the bloodstream. The alimentary canal is a long tube from the mouth to the anus.

Along the way, food is chewed, mixed with enzymes, and pushed forward by muscle waves. Accessory organs help by making enzymes and bile that break down food further. For example, the liver makes bile to help digest fats, and the pancreas releases enzymes to break down proteins and carbs.

The digestive system also relies on nerves and hormones to control when and how much to digest. The enteric nervous system, often called the 'second brain,' manages local reflexes in the gut. Hormones like gastrin and secretin signal the stomach and pancreas to release acids and enzymes.

These signals help the body respond to food and keep digestion running smoothly. It starts in the mouth, gets broken down in the stomach, and is fully processed in the small intestine. Along the way, muscles push it forward, enzymes break it apart, and the body absorbs what it needs.

The rest becomes waste and leaves the body.

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.
  • Segmentation contractions act to mix and move the chyme more slowly in the small intestine allowing more time for absorption.
  • The duodenum is the first and shortest section of the small intestine.
  • The jejunum, the midsection of the small intestine contains circular folds, flaps of doubled mucosal membrane which partially encircle and sometimes completely encircle the lumen of the intestine.
  • The ileum is the last part of the small intestine and this also contains villi and vitamin B12; bile acids and any residue nutrients are absorbed here.

Terms

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