Small And Large Intestine Anatomy Question And Answers

Small And Large Intestine

Question 1. Discuss the general features, parts, and functions of the small intestine in brief.
Answer:

Small Intestine General features:

• The small intestine is the longest part of the gastrointestinal tract (6 m long) being greater in males than in females.
• It extends from the pylorus to the ileocecal junction.

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Small Intestine Parts:

• The upper fixed part is called the duodenum, 25 cm long.
• The lower mobile part is further divided into 2 parts:
  • The upper 2/5th is called jejunum.
  • The lower 3/5th is called the ileum.

Small Intestine Functions:

The structure of the small intestine is adapted to:

• Digestion of food
• Absorption of nutrients

Small And Big Intestine

Question 2. Give the differences between jejunum and ileum in the tabular form.
Answer:

The differences are given in Table

Small Intestine Anatomy

Differences Between Jejunum and Ileum:

Question 3. Write a short note on the mesentery.
Answer:

The mesentery is a broad fan-shaped fold of the peritoneum, which suspends the coils of the jejunum and ileum from the posterior abdominal wall. The breadth of the mesentery is maximum (8˝) in its central part and gradually diminishes toward the ends.

Mesentery Features:

• Two borders – attached and free
• Number of pleats

Small And Big Intestine

Mesentery Borders:

• The attached border (the root of mesentery) is 15 cm (6˝) long.
  • Directed obliquely downward and to the right.
  • Extends from the duodenojejunal flexure (located on the left side of L2 vertebra) to the right sacroiliac joint.
• The free border/intestinal border is 6 m long.
• Forms fold or pleats.

Note: The root of the mesentery is 15 cm(6′) long, while its ferr border is 6 m long hence, it is thrown into a number of please like that of a full skirt.

Mesentery Contents:

• Jejunum and ileum
• 100–200 lymph nodes
• Lacteals (lymphatics)
• Autonomic nerves
• Connective tissue and fat

Mesentery Development:

The small intestine develops from the midgut loop. The apex of the midgut loop communicates with the yolk sac through the narrow vitellointestinal duct (stalk of the yolk sac). The midgut loop is divided into pre- and post-arterial segments by the superior mesenteric artery.

The parts of the small intestine derived from the midgut loop are as under:

• Whole of jejunum, from the pre-arterial segment
• The whole of the ileum except its terminal part, from the pre-arterial segment
• The terminal part of the ileum, from the post-arterial segment

Small Intestine Anatomy

Question 4. Give the histological differences between the jejunum and ileum in a tabular form.
Answer:

These are given in Table.

Histological differences between jejunum and ileum:

Question 5. Write a short note on Meckel’s diverticulum (diverticulum ilei).
Answer:

• It is a persistent proximal part of the vitellointestinal duct, which is normally present in the embryo but disappears during 6th week of intrauterine life (IUL).
• It is a small diverticulum (if present) seen at the antimesenteric border of the ileum.
• Its caliber is equal to that of the ileum.
• Its apex may be free/attached to the umbilicus by a fibrous band.
• It is the most common congenital anomaly of the gastrointestinal duct.

Meckel’s diverticulum General features:

They follow the rule of “2”:

• Length: 2˝ long.
• Location: 2 feet away from the ileocecal junction.
• Occurrence: 2% of subjects.

Meckel’s diverticulum Applied anatomy:

When connected to the umbilicus by a fibrous band, the intestine may rotate around it and get obstructed. It is often the site of heterotrophic pancreatic tissue and gastric mucosa with oxyntic cells. It may enter into the hernia sac. It may present a discharge from the umbilicus/bulging umbilicus/cystic umbilical tumor. If remains patent, the contents of the small intestine are discharged at the umbilicus.

Large Intestine

Question 6. Describe parts and functions of the large intestine. Give its cardinal features.
Answer:

The large intestine:

• Is 1.5 m long
• Extends from the ileocecal junction to the anus.

Large Intestine Parts:

The large intestine is divided into 7 parts:

1. Caecum
2. Ascending colon
3. Transverse colon
4. Descending colon
5. Sigmoid colon
6. Rectum
7. Anal canal

Large Intestine Functions:

• Absorption of water and electrolytes
• Lubrication of feces by mucus
• Normal bacterial flora of the colon synthesize vitamin B
• The mucus of the colon contains IgA antibodies, which protect it from invasion by microorganisms
• Storage of feces
• Microvilli of columnar cells of the lining epithelium serve as a sensory function

Large Intestine Cardinal features:

The large intestine presents 3 cardinal features:

1. Presence of appendices epiploicae: These are peritoneal sacs filled with fat.
2. Presence o the taeniae coli: These are three longitudinal muscular bands.
3. Presence of sacculations: These are sacculated dilatations in the wall. They are formed Taeniae coli are shorter in length than the intestine itself.

Question 7. What are the differences between the small and large intestines? 
Answer:

These are given in Table.

Differences between Small and Large Intestines:

Small Intestine Anatomy

Question 8. Describe the appendix under the following headings:

1. General Features
2. Positions
3. Relations
4. Development and
5. Applied anatomy.

Answer:

1. Appendix General Features:

It is a narrow worm-like tubular diverticulum arising from the posteromedial wall of the caecum, about 2 cm below the ileocecal valve.

• It resembles a roundworm, hence called a vermiform appendix.
• It is located in the right iliac fossa.
• Its length varies from 2 to 20 cm with an average length of 9 cm.
• Its length increases in young adults but gradually diminishes after middle age.
• All the taenia of the colon converges on the base of the appendix.
• The appendix is suspended by a small triangular fold of the peritoneum called a mesoappendix.

2. Appendix Positions:

The appendix lies in the right iliac fossa with the base fixed/attached to the posteromedial wall of the caecum. The location of the base corresponds to a point 2 cm below the intersection of transtubercular and right lateral planes.

Although the base of the appendix is fixed, its tip may point in any direction, thus defining the position of the appendix. These positions are often compared to those of the hour needle of a time clock.

The positions are as follows:

• Paracolic (11 o’clock) position: The appendix lies in the paracolic gutter, right to the ascending colon.
• Retrocaecal/retro colic (12 o’clock) position: The appendix lies behind the caecum or ascending colon (the commonest position, 65%).
• Splenic (2 o’clock) position: The appendix lies in front of or behind the terminal ileum and is directed toward the spleen. It is the most dangerous position because if inflamed, its infection spreads to the general peritoneal cavity.
• Promonteric (3 o’clock) position: Appendix passes horizontally to the left towards the sacral promontory.
• Pelvic (4 o’clock) position: The appendix passes over the pelvic brim to descend into the pelvis near the ovary in females (2nd commonest position, 30%).
• Subcecal (6 o’clock) position: The appendix lies below the caecum.

Note: The appendicular orifice is situated on the posteromedial wall of the caecum 2 cm below the ileocecal orifice.

3. Appendix Arterial supply:

• By appendicular artery, a branch of the inferior division of the ileocolic artery. It runs behind the terminal part of the ileum and enters the mesoappendix.
• Here, it gives a recurrent branch that forms an anastomosis with the posterior cecal artery. The tip of the appendix is the least vascular.

4. Appendix Development:

The appendix develops from the narrow part of the caecal diverticulum of the midgut loop.

5. Appendix Applied anatomy:

• Appendicitis: It is the inflammation of the appendix. It usually occurs due to obstruction of its lumen by a fecolith.

Clinically, it is present as:

• Pain in the umbilical region, which later gets localized in the right iliac fossa
• Vomiting
• Fever
• Tenderness of McBurney’s point
• Muscle guarding and rebound tenderness over the appendix

Note: Appendicitis is rare, at extreme ages because in children lumen of the appendix is wide, while in old age it gets obliterated. Thus, it cannot be obstructed by a fecolith.

• Appendectomy: It is the surgical removal of the appendix, which is often required in chronic appendicitis.
• McBurney’s point: It is the point that lies at the junction of the lateral 1/3rd and medial 2/3rd of the line joining the umbilicus with the right anterior superior iliac spine (spinoumbilical line). For exposure of the appendix, a gridiron incision is given at a right angle to this line at this point.
• Referred pain of appendix: The appendicular pain is referred to the umbilicus because both the appendix and umbilicus are supplied by T10 spinal segment (appendix by sympathetic fibers and umbilicus by somatic fibers).

Question 9. Give the histological features of the appendix.
Answer:

The histological features of the appendix are:

The appendix shows a small angulated lumen and its wall consists of four coats, viz. mucosa, submucosa, muscularis externa, and serosa.

• Mucosa:
  • Lining epithelium: It is a simple columnar with plenty of goblet cells.
  • Lamina propria: It contains a few intestinal glands (crypt of Lieberkuhn) and a ring of lymphoid follicles.
  • Muscularis mucosae: It is often interrupted by lymphoid follicles.
• Submucosa: It contains a ring of large lymphoid follicles with germinal centers extending from lamina propria. Hence, the appendix is commonly considered as an abdominal tonsil.
• Muscularis externa: It consists of outer longitudinal and inner circular layers of smooth muscle.
• Serosa: It is made up of the visceral peritoneum.

Large vessels of the gut

Question 10. Write a short note on the coeliac trunk.
Answer:

It is the artery of the foregut. It is a short trunk (1.25 cm long) and supplies the alimentary canal up to the opening of the bile duct and its derivatives.

Small Intestine Anatomy

Coeliac trunk Origin:

It arises from the front of the aorta just below the aortic orifice of the diaphragm, at the level of the L1 vertebra.

Coeliac trunk Branches:

It gives 3 branches:

1. Left gastric artery, smallest branch.
2. Common hepatic artery, larger than the left gastric artery.
3. The splenic artery is the largest and remarkably tortuous.

1. Left gastric artery:

It is the smallest branch of coeliac trunk but supplies the largest areas of the stomach.

• Branches
• Esophageal branch
• Gastric branches

2. Common hepatic artery: It passes to the right over the upper border of the pancreas.

Branches:

• Gastroduodenal artery
• Right gastric artery
• Duodenal branch
• Terminal Branches
  • Right gastric hepatic artery
  • left hepatic artery

Note: The gastroduodenal artery passes behind the first part of the duodenum and divides into:

• Right gastroepiploic artery
• Superior pancreaticoduodenal artery

3. Splenic artery:

It is the largest branch of the coeliac trunk. It is remarkably tortuous and runs toward the left behind the stomach to reach the hilum of the spleen where it ends by dividing into 5–7 splenic branches.

Note: It is the main source of arterial supply to the pancreas.

Branches and distribution:

• Pancreatic branches to the body of the pancreas
• Five to six short gastric arteries to the fundus of the stomach
• Left gastroepiploic artery to left half of body of the stomach near the greater curvature and to the greater omentum
• Five to six splenic branches to the spleen

Small Intestine Anatomy

Question 11. Give a brief account of the superior mesenteric artery.
Answer:

It is the artery of the midgut.

Superior mesenteric artery Origin:

From the front of the aorta at the lower border of L1 vertebra. It courses downward and to the left to reach right iliac fossa where it terminates by anastomosing with a branch of the ileocolic artery.

Superior Mesenteric Artery Syndrome

Branches and distribution:

• Jejunal and ileal arteries (12 or more) from its convex aspect to jejunum and ileum.
• Inferior pancreaticoduodenal artery to lower half of the head of the pancreas and adjoining part of duodenum.
• Middle colic artery to the transverse colon.
• Right colic artery to ascending colon, right colic flexure, and proximal part of the transverse colon.
• Ileocolic artery to caecum, vermiform appendix, the beginning of the ascending colon, and termination of the ileum.

Question 12. Give a brief account of the inferior mesentery artery.
Answer:

It is the artery of the hindgut.

Inferior mesentery artery Origin:

From front of the aorta at the level of the L3 vertebra. It courses downward left to the aorta, crosses the left common iliac artery, and then continues as the superior rectal artery.

Branches and distribution:

• Left colic artery to the terminal part of transverse colon, left colic flexure, and upper part of descending colon.
• Sigmoid arteries (2 to 4 in number) to the lower part of descending colon and sigmoid (pelvic) colon.
• Superior rectal artery to the upper part of the rectum.

Superior Mesenteric Artery Syndrome

Question 13. Describe the marginal artery of Drummond.
Answer:

• It is a circumferential anastomotic channel located near the inner margin of the colon which it supplies.
• It is formed by the anastomoses between colic branches of superior and inferior mesenteric arteries

Marginal artery of DrummondClinical significance:

It provides collateral supply to the colon. When there is a blockage of one of the mesenteric arteries. If the marginal artery of Drummond is absent, ischemia of the colon can occur.

Question 14. Describe the caecum under the following headings:
Answer:

1. Introduction
2. Shapes
3. Relations
4. Arterial supply and
5. Applied anatomy.

Answer:

1. Caecum Introduction:

It is a large blind sac forming the commencement of the large intestine below the ileocolic junction. It is situated in the right iliac fossa above the lateral half of the inguinal ligament. It has a greater width than length.

Large Intestine Size: Length, 6 cm; breadth, 7.5 cm.

It communicates:

• Superiorly with ascending colon
• Medially with ileum
• Posteromedially with appendix

2. Caecum Shapes:

There are 3 types of caecum according to shape:

1. Conical type (13%): When the caecum is conical and the appendix arises from the apex of the caecum.
2. Intermediate type (9%): When right and left caecal pouches are of equal size and the appendix arises from a depression between them.
3. Ampullary type (78%) (commonest): When the right caecal pouch is much larger than the left and the appendix arises from the medial side.

small intestine size

Superior Mesenteric Artery Syndrome

3. Caecum Relations:

• Anterior:
  • Coils of the small intestine
  • Anterior abdominal wall
• Posterior:
  • Right psoas major and iliacus muscles
  • Retrocaecal peritoneal recess
  • Right gonadal vessels
  • Right external iliac vessels
  • Genitofemoral, femoral, and lateral cutaneous nerves of the thigh

Above: Continuous with an ascending colon.

Below: Lateral half of inguinal ligament.

4. Caecum Arterial supply: By the anterior and posterior caecal arteries from the inferior division of the ileocecal artery (terminal branch of the superior mesenteric artery).

5. Caecum Applied Anatomy:

Caecum acts as a guide: Caecum acts as a guide to localize the site of intestinal obstruction in barium enema study. The dictum is that:

• If the caecum is distended, the obstruction is in the large intestine.
• If the caecum is empty, the obstruction is in the small intestine.
• Tuberculosis: Tuberculosis of the intestine is common at the ileocecal junction.
• Intussusception: It is a telescopic invagination of the ileum into the caecum and ascending colon. It is not uncommon.

Question 15. What are embryological subdivisions of primitive gut give the derivatives of midgut?
Answer:

Embryological Subdivisions of the primitive gut. These are:

• Foregut, supplied by the coeliac artery
• Midgut, supplied by the superior mesenteric artery
• Hindgut, supplied by the inferior mesenteric artery

Derivatives of midgut:

• The lower half of the duodenum
• Jejunum and ileum
• Caecum and appendix
• Colon up to proximal 2/3rd of the transverse colon

Question 16. Briefly describe the rotation of the midgut.
Answer:

Rotation Introduction:

• The midgut loop is U-shaped.
• It is supplied by the superior mesenteric artery.
• It consists of two segments: The arterial segment and post arterial segment
• The apex (center) of this loop communicates with the yolk sac through the vitellointestinal duct
• The posterior segment near the apex of the loop possesses a caecal bud.
• By the end of 6th week of intrauterine life, the gut elongates greatly and can no longer be accommodated within the abdominal cavity.
• As a result, the midgut extrudes/herniates into the umbilical cord called a physiological hernia.

Superior Mesenteric Artery Syndrome

Mechanism of rotation of midgut/midgut loop:

• Before rotation the arterial segment, mesenteric artery, and post-arterial segment lie in the vertical plane in the umbilical cord.
• The rotation of the midgut loop occurs during 3rd month of IUL when it tries to return back into the abdominal cavity.
• First, it undergoes 90° anticlockwise rotation in the umbilical cord itself before entering the abdomen.
• Now the arterial segment lies to right and the post arterial segment to the left.
• The arterial segment increases in length to form coils of jejunum and ileum.
• Now jejunum and ileum (arterial segment) return to the abdominal cavity. As they do so the midgut loop again undergoes 90° anticlockwise rotation.
• Lastly, post arterial segment returns to the abdominal cavity. As it does so it also rotates 90° anticlockwise. Thus there is a total rotation of 270° anticlockwise.
• Out of which 90° rotation occurs in the umbilical cord (i.e. outside the abdominal cavity) and 180° rotation inside the abdominal cavity.