Functional histology of intestines Flashcards

1
Q

Identify the main histological features of the small intestine

A
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2
Q

Adaptations which maximise the surface area of the small intestine

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

Three regions of the small intestine

A

duodenum

jejunum

ileum

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4
Q

Describe the main features of villi

A

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

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5
Q

What are the cells of the small intestine?

A

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

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6
Q

Where does the blood supply to the small intestine originate?

A

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

Proximal half of duodenum supplied by coeliac trunk

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7
Q

Where are Brunner’s glands found?

A

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

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8
Q

Where are Peyer’s patches found?

A

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

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9
Q

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

A

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

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10
Q

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

A

Small intestine: Coeliac disease, Chron’s disease

Large intestine: Appendicitis, Ulcerative colitis, diverticular disease

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11
Q

Features of coeliac disesase

A

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

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12
Q

Features of Chron’s disease

A

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.

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13
Q

Function of small intestine

A

Further digestion of food and absorption into the blood

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14
Q

Function of large intestine

A

Absorption of water and formation of faeces

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15
Q

Distinctive features of the large intestine

A

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

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16
Q

Four main regions of the large intestine

A

Caecum, appendix, colon, rectum, anal canal

17
Q

Describe the histological features of the large intestine

A

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

18
Q

Blood supply of large bowl

A

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

19
Q

How would you locate the caecum?

A

Blind ending pouch inferior to the ileocaecal junction. Intraperitoneal

20
Q

Why can it be difficult to locate the appendix surgically?

A

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.

21
Q

What is McBurney’s point?

A

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

22
Q

How can you identify each region of the colon?

A

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

24
Q

Features of appendicitis

A

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.

25
Q

Features of ulcerative colitis

A

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.

25
Q

Features of diverticular disease

A

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.

26
Q

Describe the blood supply of the duodenum

A

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

27
Q

What are the ileocaecal folds?

A

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.

28
Q

Where do you find the paracolic gutters?

A

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.

29
Q

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

A

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.

30
Q

Which type of peptic ulcer is most common?

A

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.

31
Q

Which part of the duodenum is intraperiotneal?

A

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.