Question

Describe the major activities during each phase of GI function: Cephalic/Oral, Gastric, Intestinal (Small and Large Intestines). Trace the passage of food in order through each section of the anatomical regions.

Answer 1

Cephalic/Oral,
MASTICATION
Mastication or chewing is the first mechanical process in the gastrointestinal (GI) tract, by which the food substances are torn or cut into small particles and crushed or ground into a soft bolus.   
DEGLUTITION Definition
Deglutition or swallowing is the process by which food moves from mouth into stomach.
Stages of Deglutition
Deglutition occurs in three stages:
I. Oral stage, when food moves from mouth to
pharynx
II. Pharyngeal stage, when food moves from
pharynx to esophagus
III. Esophageal stage, when food moves from
esophagus to stomach.

Gastric phase
Activities of smooth muscles of stomach increase during gastric digestion (when stomach is filled with food) and when the stomach is empty.
Types of movements in stomach
1. Hunger contractions
2. Receptive relaxation
3. Peristalsis.
When food enters the stomach, the peristaltic contrac- tion or peristaltic wave appears with a frequency of 3 per minute. It starts from the lower part of the body of stomach, passes through the pylorus till the pyloric sphincter.
Initially, the contraction appears as a slight indenta- tion on the greater and lesser curvatures and travels towards pylorus. The contraction becomes deeper while traveling. Finally, it ends with the constriction of pyloric sphincter. Some of the waves disappear before reaching the sphincter. Each peristaltic wave takes about one minute to travel from the point of origin to the point of ending.
This type of peristaltic contraction is called digestive peristalsis because it is responsible for the grinding of food particles and mixing them with gastric juice for digestive activities.   
While taking food, it arranges itself in the stomach in different layers. The first eaten food is placed against the greater curvature in the fundus and body of the stomach. The successive layers of food particles lie nearer, the lesser curvature, until the last portion of food eaten lies near the upper end of lesser curvature, adjacent to cardiac sphincter.
The liquid remains near the lesser curvature and flows towards the pyloric end of the stomach along a V-shaped groove. This groove is formed by the smooth muscle and it is called magenstrasse. But, if a large quantity of fluid is taken, it flows around the entire food mass and is distributed over the interior part of stomach, between wall of the stomach and food mass.
Gastric emptying is the process by which the chyme from stomach is emptied into intestine. Food that is swallowed enters the stomach and remains there for about 3 hours. During this period, digestion takes place. Partly digested food in stomach becomes the chyme.

Intestinal phase

Movements of small intestine are essential for mixing the chyme with digestive juices, propulsion of food and absorption.
Types of Movements of Small Intestine
Movements of small intestine are of four types: 1. Mixing movements:
i. Segmentation movements ii. Pendular movements.
2. Propulsive movements:
i. Peristaltic movements
ii. Peristaltic rush.
3. Peristalsis in fasting – migrating motor complex 4. Movements of villi.
MOVEMENTS OF LARGE INTESTINE
Usually, the large intestine shows sluggish movements. Still, these movements are important for mixing, propulsive and absorptive functions.
Types of Movements of Large Intestine
Movements of large intestine are of two types:
1. Mixing movements: Segmentation contractions 2. Propulsive movements: Mass peristalsis.