NDA TBL 4 - Colon

Which embryonic region gives rise to the descending colon and rectum?

Hindgut

Which artery supplies the hindgut?

Inferior mesenteric artery

What structure divides the cloaca into the urogenital sinus and anorectal canal?

Urorectal septum

What marks the junction between endodermal and ectodermal parts of the anal canal?

Pectinate line

Above the pectinate line

venous blood drains into which system?

Below the pectinate line

venous drainage enters which system?

Which lymph nodes drain the area above the pectinate line?

Inferior mesenteric and internal iliac nodes

Which lymph nodes drain the area below the pectinate line?

Superficial inguinal nodes

Which nerve provides parasympathetic innervation to the descending colon and rectum?

Pelvic splanchnic nerves (S2–S4)

What are the three longitudinal muscle bands on the colon called?

Teniae coli

What causes the sacculated appearance of the colon?

Tonic contraction of teniae coli forming haustra

What are the small fat-filled pouches on the colon’s surface called?

Appendices epiploicae

What type of epithelium lines the colon?

Simple columnar epithelium with goblet cells

Does the colon have villi?

No

Which cells secrete mucus in the colon?

Goblet cells

What is the main function of mucus in the colon?

Lubrication and protection of mucosa

What are haustral contractions responsible for?

Mixing and slow propulsion of contents

What triggers mass movements in the colon?

Gastrocolic reflex

Which reflex causes relaxation of the internal anal sphincter when the rectum is distended?

Rectoanal inhibitory reflex

What type of muscle makes up the internal anal sphincter?

Smooth muscle

What type of muscle makes up the external anal sphincter?

Skeletal (voluntary) muscle

Which nerve controls the external anal sphincter?

Pudendal nerve

Which plexus regulates colonic secretion and local blood flow?

Submucosal (Meissner’s) plexus

Which plexus controls colonic motility?

Myenteric (Auerbach’s) plexus

What is the primary function of the colon?

Absorption of water and electrolytes

Which electrolyte is actively absorbed by the colon?

Sodium

Which ion is mainly secreted by the colon?

Bicarbonate

Why does the colon secrete bicarbonate?

To neutralize acidic bacterial products

Which bacteria-produced molecules feed colon cells?

Short-chain fatty acids (like butyrate)

What produces short-chain fatty acids in the colon?

Bacterial fermentation of dietary fibre

What is the function of butyrate in the colon?

Energy source for colonocytes and promotes mucosal health

What happens when colonic transit is too slow?

Constipation

What happens when colonic transit is too fast?

Diarrhoea

What is the main cause of constipation?

Decreased motility and excess water absorption

Name a congenital cause of severe constipation.

Hirschsprung’s disease (aganglionic colon)

What is the main neurotransmitter that increases colonic motility?

Acetylcholine

Which neurotransmitter decreases colonic motility?

Noradrenaline

What type of diarrhoea occurs due to excess chloride secretion?

Secretory diarrhoea

Which toxin causes secretory diarrhoea by activating cAMP?

Cholera toxin

What type of diarrhoea occurs due to unabsorbed solutes?

Osmotic diarrhoea

Give an example of osmotic diarrhoea.

Lactose intolerance

What type of diarrhoea occurs when the mucosa is damaged?

Inflammatory diarrhoea

Name the two main types of inflammatory bowel disease.

Ulcerative colitis and Crohn’s disease

Which part of the GI tract is always involved in ulcerative colitis?

Rectum

What is the pattern of spread in ulcerative colitis?

Continuous from rectum proximally

What layers of bowel wall are affected in ulcerative colitis?

Mucosa and submucosa

What are crypt abscesses?

Collections of neutrophils in colonic glands

What radiologic sign is seen in chronic ulcerative colitis?

Lead-pipe colon (loss of haustra)

What serious complication can occur in ulcerative colitis?

Toxic megacolon

How does Crohn’s disease differ from ulcerative colitis?

It has skip lesions and transmural inflammation

What type of granulomas are seen in Crohn’s disease?

Non-caseating granulomas

Which part of the bowel is most often affected in Crohn’s disease?

Terminal ileum and colon

What gross appearance is typical of Crohn’s disease?

Cobblestone mucosa with deep fissures

What complications are more common in Crohn’s than UC?

Fistulas and strictures

What kind of diet predisposes to diverticular disease?

Low-fibre diet

Which part of the colon is most often affected by diverticulosis?

Sigmoid colon

What causes diverticulosis?

Increased intraluminal pressure and wall weakness

What layer herniates through the muscle wall in diverticulosis?

Mucosa and submucosa

What is diverticulitis?

Inflammation of diverticula

What are common symptoms of diverticulitis?

Left lower quadrant pain

What are possible complications of diverticulitis?

Abscess

What is the most common type of colorectal cancer?

Adenocarcinoma

What is the typical pathway for colorectal cancer development?

Adenoma–carcinoma sequence

What is the first gene usually mutated in the adenoma–carcinoma sequence?

APC gene

Which gene mutation causes progression to carcinoma?

p53 mutation

Which oncogene is commonly activated in colon cancer?

KRAS

What alternative molecular pathway leads to colorectal cancer?

Microsatellite instability (MMR defect)

Which genes are defective in microsatellite instability pathway?

MLH1 or MSH2

What histologic feature is typical of colonic adenocarcinoma?

Gland formation with “dirty necrosis”

Which side of the colon cancer causes iron-deficiency anaemia?

Right-sided (ascending) colon

Which side of the colon cancer commonly causes obstruction?

Left-sided (descending) colon

What classic imaging sign is seen in left-sided colon cancer?

Apple-core lesion

What is the gold-standard screening test for colorectal cancer?

Colonoscopy

At what age should average-risk individuals begin colon cancer screening?

45 years

Which stool test detects hidden blood for cancer screening?

Faecal immunochemical test (FIT)

Which inherited condition causes hundreds of colonic polyps?

Familial adenomatous polyposis (FAP)

Which condition causes early-onset CRC due to MMR defects?

Lynch syndrome (HNPCC)

What type of adenoma has the highest cancer risk?

Villous adenoma

Which dietary factor increases CRC risk?

High red-meat

Which drug reduces CRC risk?

NSAIDs (COX-2 inhibitors)

What is toxic megacolon?

Massive colonic dilatation with paralysis of the wall

What nerve plexus is affected in Hirschsprung’s disease?

Myenteric (Auerbach’s) plexus

What is the embryologic cause of Hirschsprung’s disease?

Failure of neural crest cell migration

What happens to the colon proximal to the aganglionic segment in Hirschsprung’s disease?

It becomes massively dilated (megacolon)

What part of the colon lacks teniae coli?

Rectum

Which anal sphincter is under voluntary control?

External anal sphincter

Which anal sphincter is under involuntary control?

Internal anal sphincter

What reflex relaxes the internal sphincter when the rectum fills?

Rectoanal inhibitory reflex

Which artery supplies the rectum?

Superior rectal artery (branch of IMA)

Which arteries supply the anal canal?

Middle and inferior rectal arteries

What is the function of the colon in electrolyte balance?

Absorbs sodium and secretes potassium/bicarbonate

How does the colon protect itself from bacterial acid?

Secretes bicarbonate and mucus

Which structure provides a collateral link between SMA and IMA?

Marginal artery of Drummond

Which region of colon is prone to ischaemic colitis?

Splenic flexure (watershed area)

What is the typical cause of ischaemic colitis?

Reduced blood flow in low-perfusion states

What type of necrosis occurs in ischaemic colitis?

Mucosal and submucosal coagulative necrosis

What cells are most abundant in the colonic lamina propria?

Lymphocytes and plasma cells

Which structural feature increases colonic wall strength?

Circular muscle layer

What change is seen in chronic diverticular disease?

Hypertrophy of circular muscle

What substance produced by colonic bacteria benefits epithelial health?

Butyrate (a short-chain fatty acid)