What is Anatomy┃Human Cell┃Cardiovascular System┃Urinary system┃Skeletal System┃Eye Function┃Respiratory system┃Endocrine system┃Human Body┃The Small Intestine┃Muscular System┃Abdominal Organs┃
The Small Intestines:
The small intestine is the longest part of the digestive system. It extends from the stomach (pylorus) to the large intestine (cecum) and consists of three parts: Duodenum, Jejunum and Ileum.
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| Human Intestines |
Together with the esophagus, large intestine, and the stomach, it forms the gastrointestinal tract.
In living humans, the small intestine alone measures about 6 to 7 meters long.
The main functions of the small intestine are to complete digestion of food and to absorb nutrients.
The main functions of the small intestine are to complete digestion of food and to absorb nutrients.
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| Small Intestine |
Duodenum:
- Together these parts form a 'C' shape, that is around 25cm long, and which wraps around the head of the pancreas.
- The first section of the duodenum is known as 'the cap'. The duodenum can be divided into four parts: superior, descending, inferior and ascending.
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| Duodenum |
Arteries supply and venous drainage of the duodenum
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| Arteries supply and venous drainage of the duodenum |
Jejunum:
- The jejunum is the middle of the three parts of the small intestine between the duodenum and ileum.
- It's arterial supply is provided by the jejunal arteries, while the innervation by the celiac and superior mesenteric plexi together with the vagus nerve.
- It plays an important role for digestion as 40% of the whole small intestine is jejunum. Its functions include absorbing water and nutrients
Definition--Part of the small intestine found between the duodenum and ileum
Blood supply-
- Arterial arcades of the superior mesenteric artery
- Superior mesenteric vein
Innervation-
- Coeliac plexus
- Superior mesenteric plexus
- Vagus nerve (CN X)
Histology-
- Mucosa - simple columnar epithelium; contains crypts of Lieberkuhn and intestinal villi
- Submucosa - loose connective tissue containing neurovasculature
- Tunica muscularis - an inner circular and outer longitudinal smooth muscle layer
- Tunica serosa - simple squamous epithelium
- Mnemonic: M.S.M.S
Function-
- Digestion of nutrients
- Absorption of lipophilic nutrients
- Absorption of water
ileum:
- The small intestine is composed of three distinct parts, the last one being the ileum.
- At the distal end, the ileum is separated from the large intestine, into which it opens, by the ileocecal valve.
- The ileum itself is very rich in lymphoid follicles and is attached to the abdominal wall by the mesentery. Its vascular supply is provided by the ileal arteries and its innervation via the coeliac and superior mesenteric plexi.
Definition--Last of the three parts of the small intestine, found between the jejunum and large intestine
Blood supply-
- Straight arteries (branches of the superior mesenteric artery)
- Superior mesenteric vein
Innervation-
- Coeliac plexus
- Superior mesenteric plexus
- Vagus nerve
Histology-
- Mucosa: Simple columnar epithelium; also contains Peyer's patches
- Submucosa: Contains neurovasculature
- Tunica muscularis: Circular and longitudinal muscle layers
- Tunica serosa: Simple squamous epithelium
Function-Jejunum and Ileum
- Enzymatic digestion of nutrients
- Absorption of vitamin B12, fats and bile salts
- Immunological function
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| Function-Jejunum and Ileum |
Key facts about the small intestine
Definition--A part of the alimentary tract which extends from the stomach (pyloric orifice) to the large intestine (ileal orifice)
Parts--Duodenum, jejunum, ileum
Blood supply-
- Arteries: celiac trunk, superior mesenteric artery
- Veins: hepatic portal vein, superior mesenteric vein
Innervation-
- Parasympathetic: vagus nerve (CN X) (through the submucosal (Meissner’s) and myenteric (Auerbach’s) nervous plexuses)
- Sympathetic: Thoracic splanchnic nerves
Function-
- Final stages of food digestion
- Absorption of nutrients and water
Clinical relations--Diarrhea, obstructive disorders, infectious diseases, neoplastic growths, congenital conditions, duodenal ulcer