Changes

==Introduction==

==Introduction==

[[Image:smalllargeintestine.jpg|thumb|right|150px|Illustration of the jejunum, caecum, transverse and ascending colon - © RVC 2008]]

[[Image:smalllargeintestine.jpg|thumb|right|150px|Illustration of the jejunum, caecum, transverse and ascending colon - © RVC 2008]]

The large intestine extends from the [[Ileum - Anatomy & Physiology|ileum]] of the [[Small Intestine - Anatomy & Physiology|small intestine]] to the [[Anus - Anatomy & Physiology|anus]]. Water, electrolytes and nutrients are absorbed which concentrates the ingesta into faeces. Faeces are stored prior to defeacation. There is no secretion of enzymes and any digestion that takes place is carried out by microbes. All species have a large microbial population living in the large intestine, which is of particular importance to the [[Hindgut Fermenters - Anatomy & Physiology|hindgut fermenters]]. For this reason, hindgut fermenters have a more complex large intestine with highly specialised regions for fermentation.

The large intestine extends from the [[Ileum - Anatomy & Physiology|ileum]] of the [[Small Intestine Overview - Anatomy & Physiology|small intestine]] to the [[Anus - Anatomy & Physiology|anus]]. Water, electrolytes and nutrients are absorbed which concentrates the ingesta into faeces. Faeces are stored prior to defeacation. There is no secretion of enzymes and any digestion that takes place is carried out by microbes. All species have a large microbial population living in the large intestine, which is of particular importance to the [[Hindgut Fermenters - Anatomy & Physiology|hindgut fermenters]]. For this reason, hindgut fermenters have a more complex large intestine with highly specialised regions for fermentation.

===Development===

===Development===

The caecum, ascending and part of the transverse colon have already been considered in the [[Small Intestine - Anatomy & Physiology|development of the small intestine]]. The hindgut forms the portion of the transverse [[Colon - Anatomy & Physiology|colon]] that lies to the left of the midline, the descending [[Colon - Anatomy & Physiology|colon]] and [[The Avian Vent and Cloaca - Anatomy & Physiology#The Cloaca|cloaca]]. The anal membrane breaks down to allow communication with the exterior.     

The caecum, ascending and part of the transverse colon have already been considered in the [[Small Intestine Overview - Anatomy & Physiology|development of the small intestine]]. The hindgut forms the portion of the transverse [[Colon - Anatomy & Physiology|colon]] that lies to the left of the midline, the descending [[Colon - Anatomy & Physiology|colon]] and [[The Avian Vent and Cloaca - Anatomy & Physiology#The Cloaca|cloaca]]. The anal membrane breaks down to allow communication with the exterior.     

                                                                                            

                                                                                            

The large intestine can be divided into:

The large intestine can be divided into:

''Cell-mediated and humoural defences''

''Cell-mediated and humoural defences''

*The lamina propria contains macrophages, B and T lymphocytes, plasma cells, and [[Mast Cells|mast cells]].

*The lamina propria contains macrophages, B and T lymphocytes, plasma cells, and [[Mast Cells|mast cells]].

*Lymphoid aggregates known as [[Peyer's Patches - Anatomy & Physiology|Peyer's patches]] within the [[Small Intestine - Anatomy & Physiology|small intestine]] aid in immunity.

*Lymphoid aggregates known as [[Peyer's Patches - Anatomy & Physiology|Peyer's patches]] within the [[Small Intestine Overview - Anatomy & Physiology|small intestine]] aid in immunity.

*Secretory [[IgA]] and [[IgM]] provide humoural immunity and help prevent attachment of pathogens to the intestinal epithelium.

*Secretory [[IgA]] and [[IgM]] provide humoural immunity and help prevent attachment of pathogens to the intestinal epithelium.

*Lysozyme from Paneth cells inhibits bacterial growth (McGavin & Zachary, 2007).

*Lysozyme from Paneth cells inhibits bacterial growth (McGavin & Zachary, 2007).

==Innervation==

==Innervation==

*Similarly to the [[Small Intestine - Anatomy & Physiology|small intestine]], there are pacemaker cells that generate an action potential.

*Similarly to the [[Small Intestine Overview - Anatomy & Physiology|small intestine]], there are pacemaker cells that generate an action potential.

*Cells are able to function as a syncytium due to gap junctions, allowing the action potential to spread.

*Cells are able to function as a syncytium due to gap junctions, allowing the action potential to spread.

**Contractions are generated in the forward (peristaltic) and backward (antiperistaltic) directions. Antiperistaltic contractions move ingesta into the caecum in some species.

**Contractions are generated in the forward (peristaltic) and backward (antiperistaltic) directions. Antiperistaltic contractions move ingesta into the caecum in some species.

*The formation of action potentials is under a much stronger neural influence than in the [[Monogastric Stomach - Anatomy & Physiology|stomach]] and [[Small Intestine - Anatomy & Physiology|small intestine]].  

*The formation of action potentials is under a much stronger neural influence than in the [[Monogastric Stomach - Anatomy & Physiology|stomach]] and [[Small Intestine Overview - Anatomy & Physiology|small intestine]].  

*The large intestine recieves '''sympathetic''' and '''parasympathetic''' innervation.

*The large intestine recieves '''sympathetic''' and '''parasympathetic''' innervation.

**The sympathetic have coeliac, cranial mesenteric and caudal mesenteric ganglia.

**The sympathetic have coeliac, cranial mesenteric and caudal mesenteric ganglia.

*Lymphatic nodules are present in the mucosa of the large intestine.

*Lymphatic nodules are present in the mucosa of the large intestine.

*Lymph nodes of the large intestine drain into one of two centres, the '''cranial mesenteric centre''' or the '''caudal mesenteric centre'''.  

*Lymph nodes of the large intestine drain into one of two centres, the '''cranial mesenteric centre''' or the '''caudal mesenteric centre'''.  

**The '''cranial mesenteric centre''' includes lymph nodes of the [[Small Intestine - Anatomy & Physiology|small intestine]] and the following lymph nodes of the large intestine:

**The '''cranial mesenteric centre''' includes lymph nodes of the [[Small Intestine Overview - Anatomy & Physiology|small intestine]] and the following lymph nodes of the large intestine:

**'''Caecal''' - drains the [[Caecum - Anatomy & Physiology|caecum]].

**'''Caecal''' - drains the [[Caecum - Anatomy & Physiology|caecum]].

**'''Colic''' - drains the ascending and transverse [[Colon - Anatomy & Physiology|colon]].

**'''Colic''' - drains the ascending and transverse [[Colon - Anatomy & Physiology|colon]].

*The mucosa of the large intestine is smooth; there are '''no villi or microvilli'''.

*The mucosa of the large intestine is smooth; there are '''no villi or microvilli'''.

*Mucosal glands are much longer and straighter.

*Mucosal glands are much longer and straighter.

*The number of goblet cells in the mucosa is increased compared to the [[Small Intestine - Anatomy & Physiology|small intestine]].

*The number of goblet cells in the mucosa is increased compared to the [[Small Intestine Overview - Anatomy & Physiology|small intestine]].

**Mucus is very important for lubrication of the ingesta as it passes through the intestine, particularly as more water is absorbed from the lumen making chyme drier.

**Mucus is very important for lubrication of the ingesta as it passes through the intestine, particularly as more water is absorbed from the lumen making chyme drier.

*There are numerous scattered lymph nodules.

*There are numerous scattered lymph nodules.

**The number of lymph nodules increases compared to the [[Small Intestine - Anatomy & Physiology|small intestine]].

**The number of lymph nodules increases compared to the [[Small Intestine Overview - Anatomy & Physiology|small intestine]].

*The submucosa is much reduced in thickness.

*The submucosa is much reduced in thickness.

*'''Taenia''' may be present.

*'''Taenia''' may be present.