29 Questions
What is the primary function of the esophagus?
To conduct food from the pharynx to the stomach
How long does the primary peristaltic wave take to pass from the pharynx to the stomach?
5 to 10 seconds
What triggers secondary peristaltic waves in the esophagus?
The distention of the esophagus by retained food
Where do secondary peristaltic waves originate?
In the esophagus itself
What is the relationship between primary and secondary peristaltic waves?
They are essentially the same, except for their origin
What is the primary function of the stomach in terms of food intake?
Storage of large quantities of food
What is the name of the semifluid mixture formed by the mixing of food with gastric secretions in the stomach?
Chyme
What is the purpose of the slow emptying of food from the stomach into the small intestine?
To ensure proper digestion and absorption by the small intestine
What is the anatomical part of the stomach that is often considered separate from the body by anatomists?
Fundus
Where is the newest food located in the body of the stomach?
Closest to the esophageal opening
What is the purpose of the muscular wall of the stomach being relatively thin?
To enable the stomach to accommodate greater quantities of food
What is the frequency of the mixing waves along the stomach wall?
Approximately every 20 seconds
What happens to the food and secretions in the antrum?
They become more mixed with a greater degree of fluidity
What is the main function of the peristaltic movements in the antral part of the stomach?
To mix the food and secretions
What is the result of the mixing caused by the waves in the body of the stomach and the peristaltic movements in the antral part?
A fluid mixture of food and secretions
What happens to the chyme in the stomach?
It becomes more fluid
When does the stomach empty?
When the stomach is empty
What is the function of the peristaltic constrictive ring in the stomach?
To mix food with stomach secretions
What is the resulting mixture of food and stomach secretions called?
Chyme
What is the frequency of strong peristaltic waves in the antrum of the stomach?
About 20% of the time
What is the pressure exerted by the peristaltic waves?
Up to 50 to 70 cm of water pressure
What happens to the antral contents with each peristaltic wave?
Most of the antral contents squirt backward through the peristaltic ring
What is the appearance of chyme?
A murky, milky semi-fluid or paste
How much more powerful is the usual mixing wave compared to the peristaltic wave in the antrum?
One-sixth as powerful
What normally prevents the flow of chyme into the duodenum?
The mild tonic contraction of the Pylorus
What is the primary factor that determines the rate of emptying of the stomach?
The degree of activity of the antral peristaltic waves
What is the purpose of the 'pumping' action of the antral portion of the stomach?
To force several milliliters of chyme into the duodenum
What is the main regulator of the pyloric pump activity?
Signals from the duodenum
What is the effect of signals from the duodenum on the pyloric pump activity?
They depress the pyloric pump activity
Study Notes
Movement of Food Through the Alimentary Tract
- The pylorus is small enough to only allow a few milliliters of antral contents to pass into the duodenum with each peristaltic wave.
- Instead, most of the antral contents are pushed backward through the peristaltic ring towards the body of the stomach.
- This reflux action, combined with the moving peristaltic constrictive ring, is an important mixing mechanism in the stomach.
Chyme
- Chyme is the mixture of food and stomach secretions that passes through the gut.
- The degree of fluidity of chyme depends on the relative amounts of food and stomach secretions, as well as the degree of digestion that has occurred.
- Chyme appears as a murky, milky semi-fluid or paste.
Propulsion of Food Through the Stomach
- Strong peristaltic waves occur about 20% of the time in the antrum of the stomach.
- These waves occur about once every 20 seconds and exert as much as 50-70 cm of water pressure.
- As the stomach becomes more empty, the intense waves begin farther up the body of the stomach, gradually pinching off the lowermost portions of stored food and adding it to the chyme in the antrum.
Motor Functions of the Stomach
- The motor functions of the stomach are threefold: storage, mixing, and slow emptying of food into the small intestine.
- The stomach can be divided into two major parts: the corpus (or body) and the antrum.
Storage Function of the Stomach
- Food enters the stomach and forms concentric circles in the body of the stomach, with the newest food closest to the esophageal opening and the oldest food closest to the wall of the stomach.
- The body of the stomach has a relatively weak muscular wall, allowing it to expand outward and accommodate greater and greater amounts of food up to a limit of about 1 liter.
Mixing in the Stomach
- The digestive juices of the stomach are secreted by the gastric glands, which cover almost the entire outer wall of the body of the stomach.
- Weak contractions, also called mixing waves, occur along the stomach wall about once every 20 seconds, mixing the gastric secretions and the outermost layer of food.
- In the antrum, the waves become stronger and mix the food and secretions with a greater degree of fluidity.
Pyloric Pump
- The pyloric pump is the pumping action of the antral portion of the stomach that forces chyme into the duodenum.
- With each peristaltic wave, several milliliters of chyme are forced into the duodenum.
- The rate of emptying of the stomach is determined principally by the degree of activity of the antral peristaltic waves.
- The degree of activity of the pyloric pump is regulated mainly by signals from the duodenum that depress pyloric pump activity.
Test your knowledge about the functions of the esophagus and its peristaltic movements, including primary and secondary peristalsis, and how they facilitate food movement from the pharynx to the stomach. Learn about the different stages of swallowing and how the esophagus works. Evaluate your understanding of human anatomy and physiology!
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