The document provides detailed notes on the digestive system, focusing on the gastrointestinal tract (GIT), its secretions, and associated glands. It explains the structure and function of digestive organs, highlighting the roles of enzymes and hormones in digestion. Practical illustrations and exa...
THE DIGESTIVE SYSTEM
Organs, structure and function
,INTRODUCTION
• The alimentary/digestive tract provides the body with a continual supply of water,
electrolytes, and nutrients.
• To achieve this requires:
• Movement of food through the alimentary tract;
• Secretion of digestive juices and digestion of the food;
• Absorption of water, various electrolytes, and digestive products;
• Circulation of blood through the gastrointestinal organs to carry away the absorbed substances
• Control of all these functions by local, nervous, and hormonal systems.
• As shown in figure 1, each part is adapted to its specific functions: some to simple
of food, such as the oesophagus; others to temporary storage of food, such as the
and others to digestion and absorption, such as the small intestine.
,FIGURE 1: THE DIGESTIVE TRACT. This
image illustrates the various
components that comprise the digestive
system. All these elements possess a
specific function that allows the
breakdown and uptake of nutrients.
, NERVOUS CONTROL OF GIT
• The gastrointestinal tract has a nervous system all its own called the enteric nervou
system.
• This gastrointestinal nervous system resides in the wall of the gut, beginning in the
oesophagus and extending all the way to the anus.
• The number of neurons in this enteric system is about 100 million, almost exactly e
the number in the entire spinal cord.
• This highly developed enteric nervous system is especially important in controlling
gastrointestinal movements and secretion.
• The enteric nervous system is composed mainly of two plexuses (fig. 2):
• An outer plexus lying between the longitudinal and circular muscle layers, called the m
plexus or Auerbach's plexus,
• An inner plexus, called the submucosal plexus or meissner’s plexus, that lies in the su
• The myenteric plexus increases the tone of the gut and the velocity and intensity o
contractions.
• The submucosal plexus is involved with local conditions and controls local secretion
absorption, and muscle movements.
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