لخّصلي

Introduction A. Digestion refers to the mechanical and chemical breakdown of foods so that nutrients can be absorbed by cells.d. The outer layer, or serosa, is composed of the visceral peritoneum that protects underlying tissues and secretes serous fluid to keep the canal from sticking to other tissues in the abdominal cavity.(The lumen is the space inside the intestine) b. The next layer is the submucosa, which is made up of loose connective tissue housing blood lymph vessels and nerves; it nourishes the surrounding layers of the canal.a. The inner layer is the mucosa, which is lined with epithelium attached to connective tissue; it protects tissues of the canal and carries on secretion and absorption.The wall of the alimentary canal consists of the same four layers throughout its length, with only slight variations according to the functions of specific sections of the canal.C. Movements of the Tube 1.2.3.

Introduction
A. Digestion refers to the mechanical and chemical breakdown of foods so that nutrients can be absorbed by cells.
B. The digestive system carries out the process of digestion.
C. The digestive system consists of the alimentary canal, leading from mouth to anus, and several accessory organs whose secretions aid the processes of digestion.
General Characteristics of the Alimentary Canal
A. The alimentary canal is a muscular tube about 9 meters long that passes through the body’s ventral cavity.
B. Structure of the Wall
1. The wall of the alimentary canal consists of the same four layers throughout its length, with only slight variations according to the functions of specific sections of the canal.
a. The inner layer is the mucosa, which is lined with epithelium attached to connective tissue; it protects tissues of the canal and carries on secretion and absorption. (The lumen is the space inside the intestine)
b. The next layer is the submucosa, which is made up of loose connective tissue housing blood lymph vessels and nerves; it nourishes the surrounding layers of the canal.
c. The muscular layer consists of inner circular fibers and outer longitudinal fibers that propel food through the canal.
d. The outer layer, or serosa, is composed of the visceral peritoneum that protects underlying tissues and secretes serous fluid to keep the canal from sticking to other tissues in the abdominal cavity.
C. Movements of the Tube
1. The motor functions of the alimentary canal are of two types-mixing movements and propelling movements.
2. Mixing movements occur when smooth muscles contract rhythmically in small sections of the tube. Segmentation, in the SI, aids by alternately contracting and relaxing the smooth muscle.
3. Propelling movements include a wavelike motion called peristalsis, which is caused by contraction behind a mass of food as relaxation allows the mass to enter the next segment of the tube.