Changes

The ruminant stomach occupies most of the left hand side of the abdomen. It is a vast structure, holding up to 60 litres in an adult cow. The rumen holds 80%, reticulum 5%, omasum 8% and abomasum 7% in larger ruminants. In smaller ruminants the proportions are slightly different, with the rumen holding 75%, reticulum 8%, omasum 4% and abomasum 13%.

The ruminant stomach occupies most of the left hand side of the abdomen. It is a vast structure, holding up to 60 litres in an adult cow. The rumen holds 80%, reticulum 5%, omasum 8% and abomasum 7% in larger ruminants. In smaller ruminants the proportions are slightly different, with the rumen holding 75%, reticulum 8%, omasum 4% and abomasum 13%.

The different compartments of the ruminant stomach develop from the foregut spindle in foetal life. During embyogenesis and after birth 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 [[Rumen - Anatomy & Physiology|rumen]] into the abomasum, bypassing the [[Reticulum - Anatomy & Physiology|reticulum]].

The different compartments of the ruminant stomach develop from the foregut spindle in foetal life. During embryogenesis and after birth 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 [[Rumen - Anatomy & Physiology|rumen]] into the abomasum, bypassing the [[Reticulum - Anatomy & Physiology|reticulum]].

==Physiology==

==Physiology==

In most animals, after swallowing, food leaves the [[Oesophagus - Anatomy & Physiology|oesophagus]] and enters the [[Monogastric Stomach - Anatomy & Physiology|stomach]]. In ruminants, food enters the [[Abomasum - Anatomy & Physiology|abomasum]] after fermentation in the forestomach. The [[Monogastric Stomach - 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 [[Monogastric Stomach - Anatomy & Physiology|stomach]]. Gastric juice is highly acidic, and contains: HCl, produced by the parietal cells which maintains gastric pH at 2, which denatures protein. It also contains 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. This 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.  

In most animals, after swallowing, food leaves the [[Oesophagus - Anatomy & Physiology|oesophagus]] and enters the [[Monogastric Stomach - Anatomy & Physiology|stomach]]. In ruminants, food enters the [[Abomasum - Anatomy & Physiology|abomasum]] after fermentation in the forestomach. The 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 stomach. Gastric juice is highly acidic, and contains: HCl, produced by the parietal cells, which maintains gastric pH at 2 which denaturing protein. It also contains 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. This provides protection from the gastric juice. The cells of the mucosa are renewed at different rates. This is an important consideration 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==

==Defense Mechanisms==

'''Secretions'''

'''Secretions'''

Continuous movement discourages persistence of insult at the mucosa.

Continuous movement discourages persistence of insult at the mucosa.

'''Test Yourself with [[The Stomachs of the Ruminant - Anatomy & Physiology - Flashcards|Ruminant Stomachs Flashcards]]'''

'''Test Yourself with [[The Stomachs of the Ruminant - Anatomy & Physiology - Flashcards|Ruminant Stomachs Flashcards]]'''

[[Category:Stomach - Anatomy & Physiology]]

[[Category:Stomach - Anatomy & Physiology]]

[[Category:Alimentary System - Cattle]]

[[Category:Alimentary System - Cattle]]

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