Small and Large Intestine Flashcards
Functions of the small intestine
- Mechanical digestion and mixing chyme from stomach with various secretions – segmentation
- Secretions – water, ions, mucus (and receives bile and pancreatic juice)
- Chemical digestion of nearly all nutrients (enzymes from pancreas and small intestine, bile emulsifies fats and solubilises hydrophobic digestion products)
- Absorption of nearly all nutrients, most water, ions
- Move chyme along to large intestine – **peristalsis **
Folds of the SI
- Circular folds= plicae circulares (mucosa and submucosa)
- Villi (mucosa)
- Brush border = microvilli (on epithelial cells)
Parts of the SI
- Duodenum–first 20-25cm
- Jejunum – proximal 2/5 of small intestine after duodenum
- Ileum–dista l3/5
Anatomy of the duodenum
- From pyloric sphincter to duodenojejunal flexure, where the suspensory muscle of the duodenum (ligament of Treitz) is located
- 4 parts of duodenum: superior, descending, horizontal, ascending
- Descending part receives bile duct and pancreatic duct at major duodenal papilla on left (medial) side
Functions of the duodenum
- Receives chyme from stomach – highly acidic
- Neutralised by duodenal gland secretions, bile from liver & gallbladder, pancreatic juice from exocrine pancreas
- Involved in regulating gastric emptying, gallbladder contraction, secretion by pancreas and liver (endocrine, neural)
- Digestion and absorption
Functions of jejunum
- Mixes chyme with bile and pancreatic juice and small intestine secretions – segmentation
- Peristalsis–moves contents along
- Most chemical digestion
- Most absorption
Functions of the ileum
- Segmentation, peristalsis
- Some chemical digestion
- Some absorption
Surface anatomy of the small intestine
Duodenum
- the right upper and left upper quadrants.
- epigastric, right and left hypochondriac and umbilical.
Jejunum and ileum
- All quadrants
- All regions
Movements in the SI
- Segmentation
- Peristalsis
Segmentation
Segmentation serves to mix digestive tract contents. This movement consists of contraction and relaxation of short lengths of inner circular muscle (1-5cm), and is controlled by the enteric nervous system. Slow wave potentials control segmentation, and consist of depolarization/repolarization, at about 12-15 (in duodenum) and 6-9 (in ileum) cycles per minute – action potentials cause contraction (segmentation).
Peristalsis SI
Peristalsis is waves of relaxation and contraction of circular muscle, with leading wave of contraction of longitudinal muscle, which propels contents along the length of the small intestine. Peristalsis occurs over 10-70 cm of the small intestine.
Regulation of motility in the SI
Regulation of motility of the small intestine is via local mechanisms and chemical stimuli e.g. distension, low pH, digestion products etc. which are detected by the nervous system, which stimulate smooth muscle contraction (local reflexes). 3-5 hours is the typical transit time through the small intestine.
Iliocaecal sphincter
The ileocaecal sphincter is located at the junction of the ileum and caecum of the large intestine. It relaxes to allow chyme from the ileum to the caecum and tonically contracts to prevent reflex, with stronger contractions as the caecum distends.
Functions of the large intestine
The large intestine has several functions:
- It provides important secretions (primarily mucus)
- It absorbs most of the remaining water and ions, as well as some nutrients, remaining from the small intestine.
- Bacteria in the large intestine perform some digestion
- Compaction of remaining luminal contents
- Peristalsis to move faeces along
- Storage and defecation (elimination) of faeces
Describe the parts of the LI
Structurally, there are four major regions of the large intestine: the cecum, colon (ascending, transverse, descending, sigmoid), rectum and anal canal. Additionally, there is the appendix which is a twisted, coiled tube, measuring about 8cm in length, that is attached to the caecum.