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Ruminant Stomach - Anatomy & Physiology (view source)
Revision as of 12:40, 29 May 2010
, 12:40, 29 May 2010no edit summary
The different compartments of the ruminant stomach develop from the foregut spindle in foetal life. During embyogenesis and after birth the [[The Abomasum - Anatomy & Physiology|abomasum]] is the largest of the compartments (over half of the weight and capacity of the four stomachs) due to the [[oesophageal groove|Oesophageal Groove]] directing milk from the oesophagus to the [[The Rumen - Anatomy & Physiology|rumen]] into the [[The Abomasum - Anatomy & Physiology|abomasum]], bypassing the [[The Reticulum - Anatomy & Physiology|reticulum]].
The different compartments of the ruminant stomach develop from the foregut spindle in foetal life. During embyogenesis and after birth the [[The Abomasum - Anatomy & Physiology|abomasum]] is the largest of the compartments (over half of the weight and capacity of the four stomachs) due to the [[oesophageal groove|Oesophageal Groove]] directing milk from the oesophagus to the [[The Rumen - Anatomy & Physiology|rumen]] into the [[The Abomasum - Anatomy & Physiology|abomasum]], bypassing the [[The Reticulum - Anatomy & Physiology|reticulum]].
* In most animals, after swallowing, food leaves the [[Oesophagus - Anatomy & Physiology|oesophagus]] and enters the [[Forestomach - Anatomy & Physiology|stomach]]. In ruminants, food enters the [[The Abomasum - Anatomy & Physiology|abomasum]] after fermentation in the forestomach.
* The [[Forestomach - Anatomy & Physiology|stomach]] acts as a reservoir in which a semi-solid mass (chyme) is formed from the ingested food before passing into the [[Duodenum - Anatomy & Physiology|duodenum]].
* With the exception of water, little absorption occurs in the [[Forestomach - Anatomy & Physiology|stomach]].
* Gastric juice is highly acidic, and contains:
** HCl, produced by the parietal cells
*** Maintains gastric pH at 2, which denatures protein.
** Pepsin, derived from pepsinogen, produced by zymogen cells
*** The action of HCl facilitates this.
* Surface epithelial cells and mucous neck cells produce mucus which forms an alkaline sheet over the epithelial surface.
** Provides protection from the gastric juice.
* The cells of the mucosa are renewed at different rates. This is an important considerination in the pathogenesis of certain gastric diseases.
** Surface epithelial cells and mucous neck cells are replaced about every 3 days.
** Parietal cells and zymogen cells are produced at a slower rate; the parietal cells have a half-life of 23 days.
===Defence Mechanisms===
# Secretions :
#* Mucus (inhibits contact with mucosa, protects surface).
#* Acid (parietal cells)
#* Digestive enzymes (pepsin from gastric chief cells)
# Epithelium:
#* Provides a barrier
#** Stratified squamous epithelium; multilayered, high cell turnover
# Movement:
#* Continuous movement discourages persistence of insult at mucosa.
[[The Rumen - Anatomy & Physiology|The Rumen]]
[[The Rumen - Anatomy & Physiology|The Rumen]]