The small intestine extends from the pylorus to the ileocecal junction. It has three parts - the duodenum, jejunum, and ileum. Key features that aid absorption include its length of 6 meters, presence of circular folds, villi, microvilli, intestinal glands, and lymphatic follicles. The duodenum is the shortest and most fixed part, located behind the head of the pancreas. It has four parts that differ in length, course, and peritoneal attachments. The duodenum contains Brunner's glands and openings for the bile and pancreatic ducts.

1. SMALL INTESTINE
Presented By – Ashish Ranjan

2. Introduction
◦It extends from the pylorus to the ileocaecal junction.
◦About 6 metres long.
◦Length of small intestine – male>female
◦Length of small intestine is greater in cadaver, due to
loss of tone than in the living
◦It has basically two parts
1. Upper part (fixed duodenum 25cm length)
2. Lower part {mobile part (⅖ jejunum, ⅗ ileum)}

4. RELEVANT FEATURES
1. Large surface area(absorption)
◦ Greater length of intestine
◦ Presence of circular folds of mucous membrane villi and microvilli.
◦ Circular folds of mucous membrane, plicae circulares or valves of kerckring from
complete or incomplete circles. These folds are permanent and are not obliterated
by distension.
◦ Folds -*begin- 2nd part of duodenum(large and closely set below the
level of major duodenal papilla and continue to proximal half of jejunum)
*diminish progressively (size and no.)- distal half of jejunum & proximal half of ileum
*absent- distal half of ileum
◦ Intestinal villi are finger like projection of mucous membrane, just visible to naked
eye. It gives velvety appearance to the surface of intestional mucosa. Each villus
covered by a layer of absorptive columnar cells.

6. 2.Intestinal glands or Crypts of liberkühn
◦ Simple tubular glands distributed over the entire mucous membrane of jejunum
and ileum.
◦ Crypts of liberkühn get open by small circular aperture on the surface of mucous
membrane between the villi.
◦ It secrete digestive enzyme and mucous.
◦ Epithellial cell between Crypts show high level of mitotic activity. These cells get
replaced every two to four days.
★Duodenal glands or Brunner’s glands
◦ Lies in submucosa.
◦ Small, compound tubuloacinar glands
◦ Secrete mucus

8. 3. Lymphatic follicles
◦ Mucous membrane contain 2 type of lymph node.(most numerous in puberty but no.
decreases during old age)
(1)solitary lymphatic follicles.
◦ 1 to 2 mm in diameter
◦ Distributed throughout the small and large intestine.
(2) Aggregated lymphatic follicles or Peyer’s patches.
◦ Form circular or oval patches
◦ Length 2 to 10 cm and containing 10 to over 200 follicles.
◦ Largest and most numerous in the ileum.
◦ Small circular and fewer- distal jejunum
◦ Get ulcerated(oval ulcers) in typhoid fever.
◦ Each villus has central lymph vessel called as lacteals. Lymph from lacteals drains into
plexuses in the walls of the gut and from there to regional lymph node.

10. •Lymphatics(lacteals)
◦ Circular course in the wall of the intestine.
◦ Tubercular ulcers and subsequent strictures are due to involvement of these
lymphatics
◦ Large lymphatic vessels formed at the mesenteric border pass to the mesenteric
lymph node.

11. •Nerve supply
◦ Sympathetic (T9 to T11) as well as parasympathetic (vagus), both pass through the coelic
and superior mesenteric plexuses.
◦ Nerves from myenteric plexus of Auerbach, contain.
.parasympathetic ganglia between circular and longitudinal muscle coats
◦ Fibres from myenteric plexus form the submucous plexus of Meissner contain –
parasympathetic ganglia
◦ Sympathetic nerves-
.motor – sphincter and muscularis mucosae
.inhibitory- peristaltic movements
◦ Parasympathetic nerves.
.stimulate- peristalsis
. Inhibit- sphincter
◦ Nerve plexuses and neurotransmitter of the gut are quite complex called Enteric nervous
system

12. 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
◦ Submucosa: contains blood vessels, lymphatics
and Meissner’s plexus.
◦ Muscularis externa: Outer longitudinal and
inner circular layers of smooth muscle.
◦ Serosa/Adventitia

13. DUODENUM
Defination and location
◦ Shortest, widest and most fixed part of small intestine
◦ Extends from pylorus to duodenojejunal flexure
◦ Curved around the head of pancrease in the form of letter c
◦ It lies above the level of umbilicus, opposite L1 , L2, L3.
Length parts and peritoneal relations
◦ 25 cm long and divided into 4 parts
1.First or superior part, 5cm or 2inches long
2. Second or descending part, 7.5cm or 3inches long
3.Third or horizontal part, 10cm or 4 inch long
4. Fourth or ascending part, 2.5cm or 1inch long.
◦ retroperitoneal and fixed except at its two ends where it is suspended by folds of peritoneum
◦ Anteriorly, the duodenum is only partly covered with paeritoneum.

15. First/superior part
It begins at the pylorus and passes backwards, upwards and to the right to meet the
second part at the superior duodenal flexure.
peritoneal relations:
◦ Proximal 2.5cm is movable.
◦ Attached :Above – lesser omentum
below- greater omentum
◦ Distal 2.5cm fixed, retroperitoneal, anterior aspect covered with paeritoneum.
Visceral relations:
◦ Anteriorly- quadrate love of liver and gallbladder
◦ Posteriorly- gastroduodenal artery, bile duct and portal vein
◦ Superiorly – epiploic foramen
◦ Inferiorly- head and neck of pancreas.

17. Second/Descending part
Course:
◦ 7.5 cm Long .
◦ Begins at superior duodenal flexure, passes downwards to reach
the lower border of the third lumbar vertebra, where it curves
towards the left at the inferior duodenal flexure, to become
continuous with the third part
Peritoneal relations:
◦ Retroperitoneal and fixed.
◦ Anterior surface is covered with peritoneum, except near the
middle, directly related to colon.
Visceral relations:
Anteriorly Posteriorly-
1.Right love of the liver 1. Anterior surface of the
right kidney near medical border
2.Transverse colon 2. Right renal vessels
3.Root of the transverse mesocolon 3. Right edge of the inferior
vena cava
4.Small intestine 4. Right psoas major
Medially-
1.Head of the pancreas
2. The bile duct
Laterally-
.right colic flexure

19. Special features of Second part of the duodenum (interior)
a. Major duodenal papilla is an elevation present posteromedially, 8
to 10 cm distal to the pylorus. The hepatopancreatic ampulla opens
at the summit of the papilla.
b. The minor duodenal papilla is present 6 to 8cm distal to the
pylorus, and presents the opening of the accessory pancreatic duct
c. Below major duodenal papilla, a longitudinal fold called plica
longitudinal is seen

20. Third/ Horizontal part
Course:
◦ Begins at inferior duodenal flexure, on the right side of the lower border of the L3.
◦ It passes almost horizontally and slightly upwards in front of the IVC
◦ Ends by joining the 4th part in front of the abdominal aorta
Peritoneal Reations:
◦ Retroperitoneal and fixed.
◦ Anterior surface is covered with peritoneum, except in median plane, it crossed by superior mesenteric vessels and by root of
mesentery.
Visceral relations:
Anteriorly:
1. Superior mesenteric
vessels
2. Root of mesentery
Posteriorly:
1. Right ureter
2. Right psoas major
3. Right testicular or
ovarian vessels
4. IVC
5. Abdominal aorta
with origin of
inferior mesenteric
artery
Superiorly:
Head of the pancreas with
uncinate process
Inferiorly:
Coils of jejunum

22. Fourth/ Ascending part
Course:
◦ It runs upwards on or immediately to the left of the aorta, up to the upper border of the second lumbar vertebra, where it turns forwards to
become continuous with the jejunum at the duodenojejunal flexure.
Peritoneal relations:
. It is mostly retroperitoneal, and covered with peritoneum only anteriorly.
.The terminal part is suspended by the uppermost part of the mesentery, and is mobile.
Visceral relations:
Posteriorly
◦ 1 Left sympathetic chain
◦ 2 Left renal artery
◦ 3 Left gonadal artery
◦ 4 Inferior mesenteric vein
To the right: Attachment of the
upper part of the root of the
mesentery
To the left
◦ 1 Left kidney and
◦ 2 Left ureter.
Anteriorly:
1 Transverse colon
2 Transverse mesocolon
3 Lesser sac
4 Stomach
Superiorly: Body of pancreas

23. Suspensory Muscle of Duodenum or Ligament of Treitz
◦ fibromuscular band which suspends and supports the duodenojejunal flexure.
◦ Arises from the right crus of the diaphragm, close to the right side of the oesophagus, passes downwards behind the
pancreas, and is attached to the posterior surface of the duodenojejunal and the third and fourth parts of the
duodenum
◦ It is made up of:
a. Striped muscle fibres in its upper part
b. b. Elastic fibres in its middle part
c. c. Smooth muscle fibres in its lower part
• Normally, its contraction increases the angle of the
duodenojejunal flexure. Sometimes it is attached only to the
flexure, and then its contraction may narrow the angle of the
flexure, causing partial obstruction of the gut.

24. Arterial Supply
◦ Duodenum develops partly from the foregut and partly from the midgut.
◦ Opening of the bile duct into the second part of the duodenum represents the junction of the foregut and the
midgut.
◦ Up to the level of the opening, the duodenum is supplied by the superior pancreaticoduodenal artery, and below
it by the inferior pancreaticoduodenal artery
★The first part of the duodenum receives additionalsupply from:
a. The right gastric artery.
b. The supraduodenal artery of Wilkie, which is
usually a branch of the common hepatic artery.
c. The retroduodenal branches of the gastroduodenal artery.
d. Some branches from the right gastroepiploic artery.

25. Venous Drainage
◦ The veins of the duodenum drain into the splenic, superior mesenteric and portal veins.
Lymphatic Drainage:
◦ lymph vessels from the duodenum end in the pancreaticoduodenal nodes present along the inside
of the curve of the duodenum, i.e. at the junction of the pancreas and the duodenum.
◦ Lymph passes partly to the hepatic nodes, and through them to the coeliac nodes; and partly to the
superior mesenteric nodes and ultimately via intestinal lymph trunk into the cisterna chyli.
◦ Some vessels from the first part of the duodenum drain into the pyloric nodes, and through them to
the hepatic nodes. All the lymph reaching the hepatic nodes drains into the coeliac nodes.
Nerve Supply:
◦ Sympathetic nerves from thoracic ninth and tenth spinal segments and parasympathetic nerves from
the vagus, pass through the coeliac plexus and reach the duodenum along its arteries.

26. Histology of Duodenum
◦ Mucous membrane shows evaginations in the
form of villi and invaginations to form crypts
of Lieberkühn.
◦ Lining of villi is of columnar cells with
microvilli.
Muscularis mucosae comprises two layers:
*Submucosa is full of mucus-secreting
Brunner’s glands.
◦ The muscularis externa comprises outer
longitudinal and inner circular layer of muscle
fibres.
◦ Outermost layer is mostly connective tissue.

27. CLINICAL ANATOMY
◦ • In the skiagram taken after giving a barium meal, the first part of the duodenum
is seen as a triangular shadow called the duodenal cap.
◦ First part of the duodenum commonest sites for peptic ulcer, because direct
exposure of this part to the acidic contents reaching it from the stomach.
◦ ulcer pain located at the right half of epigastrium is relieved by meals and
reappears on an empty stomach.
◦ First part of duodenum is overlapped by liver and gallbladder may become
ulcerated by a duodenal ulcer.
◦ Duodenal diverticula are fairly frequent. They are seen along its concave border,
generally at points where arteries enter the duodenal wall.
◦ Congenital stenosis and obstruction of the second part of the duodenum may
occur at the site of the opening of the bile duct. Other causes of obstrartion are:
a. An annular pancreas
b. Pressure by the superior mesenteric artery the third part of duodenum
c. Contraction of the suspensory muscle of the duodenum

28. JEJUNUM AND ILEUM
FEATURES:
◦ jejunum and ileum are suspended from the posterior abdominal wall by the mesentery therefore considerable
mobility.
◦ Jejunum begins at the duodenojejunal flexure.
◦ ileum terminates at the ileocaecal junction.
BLOOD SUPPLY:
◦ supplied by branches from the superior mesenteric artery.
◦ Drained by corresponding veins.
Lymphatic Drainage:
◦ Lymph from lacteals drains into plexuses in the wall of the gut. It passes into lymphatic vessels in the mesentery.
◦ Passing through numerous lymph nodes present in the mesentery, and along the superior mesenteric artery, it
ultimately drains into nodes present in front of the aorta at the origin of the superior mesenteric artery.
Nerve Supply:
Sympathetic nerves are from T9 to T11 spinal segments and parasympathetic nerve is from vagus.

29. Histology
JEJUNUM
1.Mucus membrane
-epithelium- Simple columnar
- intestinal villi
-lamina propria
intestinal glands (crypts of lieberkuhn)
-solitary Lymphoid nodule
-muscularis mucosae
2.Submucosa
-NO gland
3.Musculalis layer
-inner circular
-outer longitudinal
4. Serosa

30. ILEUM:
1.Mucus membrane
-Epithelium
- Simple columnar
- intestinal villi
-Lamina propria
intestinal glands (crypts of lieberkuhn)
- Muscularis mucosae
2.Submucosa
-aggregated Lymphoid nodule (peyers patches)
- mircofold cells (“M” Cell)
3.Musculalis layer
-inner circular
-outer longitudinal
4. Serosa

32. MECKEL’S DIVERTICULUM (DIVERTICULUM ILEI)
◦ Meckel’s diverticulum is the persistent proximal part of the vitellointestinal duct.
◦ Present in the embryo, and normally disappears during the 6th week of intrauterine life.
Some points about MECKEL’S DIVERTICULUM:
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.
5 Its apex may be free or may be attached to the
umbilicus, to the mesentery, or to any other
abdominal structure by a fibrous band.

33. CLINICAL ANATOMY
◦Meckel’s diverticulum may cause intestinal obstruction.
◦Occasionally, it may have small regions of gastric
mucosa/pancreatic tissue.
◦Acute inflammation of the diverticulum may produce
symptoms that resemble those of appendicitis.
◦ It may be involved in other diseases similar to those of the
intestine.