Alimentary System

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The alimentary system (Lt. alimentum :nourishment ) includes all the body structures involved in preparing food for absorption into the body and excretion of waste products ie.
oral cavity

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Тheme   :  «Alimentary System.»




                                                                         Выполнила:Сапаргалиева Ольга.

                                                            028-2 ОМ






               Alimentary System


The alimentary system (Lt. alimentum :nourishment ) includes all the body structures involved in preparing food for absorption into the body and excretion of waste products ie.

  • oral cavity
  • pharynx
  • oesophagus
  • stomach
  • small intestine
  • large intestine
  • anus

The gastrointestinal system is (strictly speaking) composed of only the stomach and small and large intestines but is commonly deemed to include the oesophagus as well.

A knowledge of the normal microanatomy of the gastrointestinal system is vital to the understanding of:

  • the normal function of the gastrointestinal system
  • the pathology of gastrointestinal disease
  • staging of gastrointestinal tumours

Normal function of the gastrointestinal system

The main functions of the gastrointestinal system are:

  • absorption of nutrients from ingested food
  • protection against ingested pathogens

Absorption of nutrients from ingested food occurs in four main phases within defined regions of the gastrointestinal tract

1. fragmentation

  • starts in the oral cavity, continues in the stomach
  • aided by secretion of saliva from salivary glands

2. digestion

  • starts in the stomach, continues in the duodenum
  • aided by pancreatic enzymes, bile salts, brush border enzymes

3. absorption

  • occurs mainly in the jejunum and ileum
  • aided by the large surface area produced by mucosal villi and microvilli
  • absorbed nutrients are transported away from the mucosa via lacteals and capillaries

4. elimination of waste products

  • liquid residue passes into the large intestine where water is progressively absorbed from it
  • resultant solid faeces are expelled through the anal canal

In order for food to be properly absorbed, it must be propelled smoothly from one segment to another. This occurs via:

  • voluntary muscular action
    • striated muscle in the oral cavity, pharynx and upper oesophagus
  • involuntary muscle contraction (peristalsis)
    • smooth muscle of the muscularis propria
    • modulated by autonomic nerves in the submucosal and myenteric plexuses

Protection against ingested pathogens occurs as a result of

  • lymphoid aggregates distributed throughout the gastrointestinal tract (mucosa-associated lymphoid tissue or MALT)
  • IgA secreted into the gut lumen


Structure of the gastrointestinal system  
The gastrointestinal system (or tract) is essentially a muscular tube which has the same basic structure throughout. Four layers are recognised, from inside out:

  1. mucosa
  2. submucosa
  3. muscularis propria
  4. serosa

The mucosa varies greatly in the different regions of the gastrointestinal tract while the other layers are essentially the same.

Structure of GI tract


  • is composed of
    • epithelium
    • lamina propria (loose connective tissue)
    • muscularis mucosae (thin layer of smooth muscle)
  • changes abruptly from one type to another at several points along the tract


  • is composed of fairly dense connective tissue containing blood vessels, lymphatics and nerves

Muscularis propria

  • is divided into two layers
    • inner circular layer
    • outer longitudinal layer
  • has inherent rhythmicity which results in peristalsis






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