Small Intestine.pptx

The small intestine or small bowel is an organ in the gastrointestinal tract where most of the absorption of nutrients from food takes place. It lies between the stomach and large intestine, and receives bile and pancreatic juice through the pancreatic duct to aid in digestion. The small intestine is about 5.5 metres (18 feet) long and folds many times to fit in the abdomen. Although it is longer than the large intestine, it is called the small intestine because it is narrower in diameter.

The small intestine has three distinct regions – the duodenum, jejunum, and ileum. The duodenum, the shortest, is where preparation for absorption through small finger-like protrusions called villi begins.[2] The jejunum is specialized for the absorption through its lining by enterocytes: small nutrient particles which have been previously digested by enzymes in the duodenum. The main function of the ileum is to absorb vitamin B12, bile salts, and whatever products of digestion that were not absorbed by the jejunum.

1. Small Intestine Dr Mathew Joseph MBBS, MD(AIIMS), BCC(Palliative Medicine) Assistant Professor Department of Anatomy Amala Institute of Medical Sciences , Thriss ur

2. Small Intestine

3. SMALL INTESTINE The small intestine extends from the pylorus to the ileocaecal junction. It is about 6 metres long. It is divided into: 1. An upper, fixed part, called the duodenum , which measures about 25 cm in length; and 2. A lower, mobile part, forming many convolutions The upper two-fifths of the mobile intestine are known as the jejunum , and the lower three-fifths are known as the ileum .

4. RELEVANT FEATURES Large Surface Area a. The great length of the intestine. The presence of circular folds of mucous membrane, villi and microvilli . Intestinal Glands The duodenal glands or Brunner’s glands lie in the submucosa . Lymphatic Follicles Solitary lymphatic follicles Aggregated lymphatic follicles or Peyer’s patches.

5. Arterial Supply The arterial supply to jejunum and ileum is derived from the jejunal and ileal branches of the superior mesenteric artery. Lymphatics The lymphatics (lacteals) have a circular course in the walls of the intestine. Tubercular ulcers and subsequent strictures are due to involvement of these lymphatics. Nerve Supply The nerve supply of the small intestine is sympathetic (T9 to T11) as well as parasympathetic (vagus), both of which pass through the coeliac and superior mesenteric plexuses.

6. Duodenum 1. First or superior part, 5 cm or 2 inches long. 2. Second or descending part, 7.5 cm or 3 inches long. 3. Third or horizontal part, 10 cm or 4 inches long. 4. Fourth or ascending part, 2.5 cm or 1 inch long.

7. Parts of the duodenum

8. Relations of First Part Relations of the first part of the duodenum: (a) Sagittal section viewed from the left side, and (b) posterior relations

9. Relations of Second Part Relations of the second part of the duodenum: (a) Anterior relations, and (b) posterior relations

10. • The interior of the second part of the duodenum shows the following special features. • The major duodenal papilla is an elevation present posteromedially , 8 to 10 cm distal to the pylorus. • The minor duodenal papilla is proximal to major duodenal papilla Relations of Third Part Relations of Fourth Part SUSPENSORY MUSCLE OF DUODENUM OR LIGAMENT OF TREITZ Composed of smooth muscle fibres skeletal fibres and elastic fibres . Arterial Supply of Duodenum (See the Figure)

11. Relations of the third part of the duodenum: (a) Anterior relations, and (b) posterior relations

12. Posterior relations of the fourth part of the duodenum

13. Suspensory muscle of the duodenum

14. Arterial supply of the duodenum

15. JEJUNUM AND ILEUM Features The jejunum and ileum are suspended from the posterior abdominal wall by the mesentery. The differences between the jejunum and the ileum are given in Table 20.1.

16. MECKEL’S DIVERTICULUM ( Diverticulum Ilei ) 1. It occurs in 2% subjects. 2. Usually it is 2 inches or 5 cm long. 3. It is situated about 2 feet or 60 cm proximal to the ileocaecal valve, attached to antimesenteric border of the ileum. 4. Its calibre is equal to that of the ileum.

17. Basic Histological Layers Mucosa: a. Epithelium b. Lamina Propria c. Muscularis Mucosae Submucosa: Submucosal plexus “ Plexus of Meissner ” Muscularis: Myenteric plexus “ Plexus of Auerbach ” Serosa

18. Small Intestine It is divided into duodenum, jejunum and ileum. Mucosa: characteristic features- Plicae circularis (valves of Kerkring) Villi & Microvilli Goblet cells (few) Crypts of Lieberkuhn (intestinal glands) Glands are lined by columnar cells, goblet cells, Paneth cells & enteroendocrine cells

19. Types of Cells

20. Layers of Small Intestine Mucosa: E,LP,MM Submucosa: contains blood vessels, lymphatics and Meissner’s plexus. Muscularis externa: Outer longitudinal and inner circular layers of smooth muscle. Serosa/Adventitia

21. Duodenum Functions Villi have absorptive function Microvilli increase the surface area of absorption Muscularis externa helps in churning food particles i.e peristalsis Serosa is supportive and protective in function Brunner’s glands secrete alkaline fluid rich in HCO3‾ Features of Identification Brunner’s glands present in submucosa Numerous leaf-shaped villi Goblet cells Crypts of Lieberkuhn present

22. Duodenum Presence of Brunner’s glands in submucosa

23. Jejunum Functions Villi have absorptive function Microvilli increase the surface area of absorption Muscularis externa helps in churning food particles i.e peristalsis Serosa is supportive and protective in function Features of Identification Tongue shaped villi lined by simple columnar epithelium. Absence of brunner’s glands in submucosa. Crypts of Lieberkuhn present

24. Ilieum Functions Villi have absorptive function Microvilli increase the surface area of absorption Muscularis externa helps in churning food particles i.e peristalsis Serosa is supportive and protective in function Peyer's patches have an immunologic function Features of Identification Finger-like villi lined by simple columnar epithelium. Villi rich in goblet cells. Crypts of lieberkuhn present. Mucosa containing Peyer’s patches

25. Histology of the Mucosa Organ Epithelium Mouth Nonkeratinized Stratified Squamous Pharynx Nonkeratinized Stratified Squamous Esophagus Nonkeratinized Stratified Squamous Stomach Simple Columnar Small Intestine Simple Columnar Large Intestine Simple Columnar Anus Nonkeratinized Stratified Squamous

26. Histology of the Mucosa Organ Folds of the epithelium Esophagus none Stomach Rugae , G astric pits Small Intestine Plicae circulares, Villi , Crypts of Lieberkuhn, microvilli Large Intestine Haustra , Intestinal glands

27. Histology of the Submucosa Organ Specialized structures Esophagus Submucosal mucous glands Stomach None Duodenum Brunner’s glands Ileum Peyer’s Patches Large Intestine None

28. Histology of the Muscularis Organ Smooth muscle layers Esophagus 2, circular and longitudinal Stomach 3, oblique, circular, and longitudinal Small Intestine 2, circular and longitudinal Large Intestine 2, circular and longitudinal

29. Histology of the Serosa Organ Serosa Esophagus Adventitia due to the fact that the esophagus is not in a cavity Stomach Visceral Peritoneum Small Intestine Visceral Peritoneum Large Intestine Visceral Peritoneum Anus Adventitia

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