Functional histology of intestines

Question 1

Identify the main histological features of the small intestine

Answer 1

Question 2

Adaptations which maximise the surface area of the small intestine

Answer 2

1. Long (6-7 cm)
2. Highly folded (circular folds)
3. Villi
4. Microvilli

Question 3

Three regions of the small intestine

Answer 3

duodenum

jejunum

ileum

Question 4

Describe the main features of villi

Answer 4

Finger-like/ leaf-like projections of mucosa

Lamina propria forms the ‘core’,

Rich supply of blood vessels and lacteals (for lipid transport)

Simple columnar epithelium

Microvilli further increase surface area and create a brushborder

Crypts of Lieberkuhn open at the base of villi

Question 5

What are the cells of the small intestine?

Answer 5

Enterocytes: main cells of villi, make up the columnar epithelium. Main function is absorption

Goblet cells: produce mucus

Enteroendocrine cells: produce peptide hormones such as secretin and cholecystokinin.

Paneth Cells: located at crypts of Leiberkuhn, produce lysozyme

Stem cells: found towards the base of intestinal glands. Allow regeneration of epithelial cells every 3-4 days

Lymphocytes: immune surveillance and protection

Question 6

Where does the blood supply to the small intestine originate?

Answer 6

Superior mesenteric artery: has jejunal, ileal and ileocolic branched.

Proximal half of duodenum supplied by coeliac trunk

Question 7

Where are Brunner’s glands found?

Answer 7

In the submucosal layer of the duodenum. Glands produce an alkaline secretion which neutralises the acidic chyme

Question 8

Where are Peyer’s patches found?

Answer 8

In the lamina propria of the ileum: Large collections of lymphoid tissue

Question 9

How can you distinguish between the different regions of the small intestine?

Answer 9

Duodenum: C-shaped structure. Simple columnar epithelium, villi, Brunner’s glands. Widest part of the small intestine, approx 25cm long. Mostly retroperitoneal

Jejunum: Intraperitoneal, prominent circular folds, thicker walled and wider lumen than ileum. The less prominent arterial arcades and longer vasa recta (straight arteries) compared to those of the ileum.

Ileum: narrowest part of small intestine, intraperitoneal, Peyer’s patches

Question 10

Name two diseases which affect the small intestine and two which affect the large intestine

Answer 10

Small intestine: Coeliac disease, Chron’s disease

Large intestine: Appendicitis, Ulcerative colitis, diverticular disease

Question 11

Features of coeliac disesase

Answer 11

Autoimmune disorder

Caused by intolerance to proteins in cereal crops (particularly gluten), triggers an immune reaction.

Inflammation and damage to duodenum and jejunum leads to blunting and loss of villi

Question 12

Features of Chron’s disease

Answer 12

Inflammatory bowel disease

Patchy chronic inflammation which can affect any part of the GI tract. Commonly affects areas whith high concentration of lymphoid follicles e.g. peyer’s patches. Most common in terminal ileum.

Transmural inflammation

Causes strictures, fistula formation, symptoms due to malabsorption.

Question 13

Function of small intestine

Answer 13

Further digestion of food and absorption into the blood

Question 14

Function of large intestine

Answer 14

Absorption of water and formation of faeces

Question 15

Distinctive features of the large intestine

Answer 15

Taenia coli: three thickened bands formed by condensations of longitudinal muscle layer present in the caecum and colon

Appendices epiploicae: fatty tages found on the outside of the colon

Haustrations: Visible saculations of the colon

Semilunar folds: Incomplete folds of smooth muscle

Question 16

Four main regions of the large intestine

Answer 16

Caecum, appendix, colon, rectum, anal canal

Question 17

Describe the histological features of the large intestine

Answer 17

Smooth mucosal surface - no vill or circular folds

Simple columnar epithelium (except for anal canal) form glands which exist in an organised ‘test tube rack’ arrangement.

No Paneth cells

Absorptive cells

Goblet cells - more numerous than small intestine, mucus aids passage of semi-solid material

Stem cells

Lymphocytes

Question 18

Blood supply of large bowl

Answer 18

Superior mesenteric artery branches supplies caecum, ascending colon and proximall 2/3 of transverse colon

Inferior mesenteric artery branches supplies distal 1/3 of transverse colon, rectum and part of anal canal.

Marginal arteries connect the branches of superir and inferior mesenteric. This ensures that there is continued blood supply to the bowl if there is occlusion in one area.

Note. Watershed area between sup/inf crossover

Question 19

How would you locate the caecum?

Answer 19

Blind ending pouch inferior to the ileocaecal junction. Intraperitoneal

Question 20

Why can it be difficult to locate the appendix surgically?

Answer 20

The appendix is a narrow blind ending muscular tube approximately 8-13cm long that arises from the posteromedial surface of the caecum.

The tip is mobile and so can be found in a variety of positions.

Question 21

What is McBurney’s point?

Answer 21

Defined point used for locating the appendix in surface anatomy.

Lies 1/3 of the way along the line from the ASIS to the umbilicus

Question 22

How can you identify each region of the colon?

Answer 22

Ascending colon: runs from the caecum to the hepatic flexure

Transverse colon: runs between hepatic and splenic flextures

Descending colon: runs from the splenic flecture to the sigmoid colon

Sigmoid colon: Meets descending colon at the pelvic brim, joins rectum in from of S3

Question 24

Features of appendicitis

Answer 24

Inflammation of the appendix due to inital obstruction of the lumen. Swelling compresses the blood vessels, exacerbating inflammation and creating a ‘visious feedback cycle’

Appendix can then become infected.

Complications include perforation and peritonitis. Requires surgical removal.

Clinical presentation: Pain initially referred to umbilicus then as the appendix becomes more inflammed and the parietal peritoneum is irritated it becomes localised to the right iliac region.

Question 25

Features of ulcerative colitis

Answer 25

Inflammatory bowel disease where diffuse chronic inflammation affects the mucosa of the large intestine.

Failure to absorb water from waste material results in diarrhoea, ulceration can cause bleeding.

Question 25

Features of diverticular disease

Answer 25

Outpouchings of mucosa into the wall of the colon between the taenia coli and alongside perforating blood vessels.

Predominantly occurs in the descending and sigmoid colon

Causes diverticulitis if inflamed, which results in bleeding and perforation.

Question 26

Describe the blood supply of the duodenum

Answer 26

Upper part from branches the coeliac trunk (namely branches of the gastroduodenal artery), lower half is supplied by branches of the superior mesenteric artery.

Question 27

What are the ileocaecal folds?

Answer 27

Two musclular flaps that surround the opening between the ileum and the large intestine forming a sphincter.

Possible functions regulating the passage of contents from the ileum to the cecum and preventing reflux.

Question 28

Where do you find the paracolic gutters?

Answer 28

Paracolic gutters are found immediately lateral to the ascending and descending colon. They are formed during development when the ascending and descendign colon attach to the posterior abdominal wall. The peritoneum fuses to the abdominal wall, forming the right and left paracolic gutters.

These allow material to pass from one area of the peritoneal cavity to another. Particularly impotant for draining of fluid.

Question 29

Why can chemotherapy drugs have adverse effects on the small intestine?

Answer 29

There is normally a very rapid turnover of enterocytes due to the division of stem cells so that the intestinal epithelium is replaced every three to four days. Chemotherapy drugs target rapidly proliferating cells which are commonly found in tumours. This inhibits stem cell division, causing mucositis, and malabsorption.

Question 30

Which type of peptic ulcer is most common?

Answer 30

Ulcers in the first part of the duodenum are much more common that gastic ulcers.

The squiring of acidic chyme into the duodenum is considered an importatn factor in the aetiology.

Question 31

Which part of the duodenum is intraperiotneal?

Answer 31

The first part of the duodenum is intraperiotneal, and is connected to the liver by the hepatoduodenal ligament, which is part of the lesser omentum.