Lecture 22: The Gastrointestinal Tract

Question 0

Localisation of pain and embryological origin

• Pain arising from the foregut derivatives localised in the ____
• pain arising from midgut localises in the _____
• pain arising from hindgut derivatives localises in the ___

Answer 0

Localisation of pain and embryological origin

• Pain arising from the foregut derivatives localised in the __(epigastric region)
• pain arising from midgut localises in the ___(periumbilical region)
• pain arising from hindgut derivatives localises in the ___(hypo gastric region)

Question 1

Adult hindgut derivatives

Answer 1

Slide 5
Supplied by inferior mesenteric artery 
-distal portion of transverse colon 
-descending colon 
-sigmoid colon 
-rectum
Be able to label slide 5 
-anal canal 
-epithelial of urinary bladder 
-most of uretha

Question 2

Large intestine

Answer 2

1. 5m long
   - absorbs water and important ions from faeces
   - compacts faeces for delivery to rectum

Features:
Teniae coli: 3 longitudinal bands of smooth muscle on colon surface
Haustra: sacculations of colon created by contracting taeniae coli
Omental appendices: small fat accumulations that hang from colon
-greater luminal diameter

Look at slide 9- memorise

Question 3

Tell me about the teniae coli

Answer 3

• 3 longitudinal bands of smooth muscle
• originate at base of appendix
• broaden and terminate as a continuous layers around rectum
• tonic contraction causes sacculations known as “haustra”

Question 4

Caecum

Answer 4

7. 5 x 7.5
   - receives terminal portion of ileum
   - inferior to ileocaecal junction
   - continuous with ascending colon
   - right iliac fossa > greater pelvis provides protection

Question 5

Ascending colon

Answer 5

-retroperitoneal
-ascends on right flank to reach liver
-bends into right colic (hepatic) flexure
-site of most of water reabsorption in large intestine
Slide 12

Question 6

Transverse colon

Answer 6

-runs transversely from right to left hypochondrium
-attachement to posterior abdominal wall by transverse mesocolon
-bends to form the left colic (splenic) flexure.
Slide 13

Question 7

Descending colon

Answer 7

-Secondarily retroperitoneal
-commences at left colic (splenic flexure)
-descends along left flank to join sigmoid colon in left iliac fossa
Slide 14

Question 8

Sigmoid colon

Answer 8

-between descending colon and rectum
-extends from left iliac fossa to S3 vertebrae
-suspended by sigmoid mesocolon
15 slide

Question 9

Rectum slide 16

Function:

Answer 9

• accumulates and temporarily stores faeces
• primary retroperitoneal and sub peritoneal
• extends from S3 vertebrae to anal canal
• ends anteroinferior to tip of coccyx as GIT pierces the pelvic diaphragm
• anterior and lateral reflections of peritoneum create
• anterior and lateral reflections of peritoneum create recto vesical pouch in males and rectouterine pouch in females.
• arterial perfusion via branches of inferior mesenteric artery and internal iliac artery

Venous drainage:

• anastomosis between portal and systemic veins in wall of anal canal.
• superior rectal vein drains back to the inferior mesenteric vein (➡splenic➡ portal vein)
• middle rectal veins drains back to internal iliac veins
• anastomosis between rectal veins

Question 10

How is the rectum innervated?

Answer 10

Sympathetic: lumbar splanchnic nerves
Parasympathetic: pelvic splanchnic nerves
Visceral afferent: rectum inferior to pelvic pain line so all visceral afferent fibres follow pelvic splanchnic nerves retrogradely back to S2-S4 spinal sensory ganglia.

Question 11

Male rectum exam.

In males the following structures can be palpate through the walls of the rectum:

Answer 11

• prostate gland
• seminal vesicles
• pelvic surface of coccyx and sacrum

Question 12

Female rectal examination.

What structures can be palpate a through wall of the rectum?

Answer 12

• cervix

- pelvic surface of sacrum and coccyx

Question 13

Anus

Answer 13

2.5-3.5cm long.
-internal anal sphincter: smooth involuntary (contraction stimulated by sympathetic fibres; parasympathetic fibres from pelvic splanchnic nerves inhibit sympathetic contraction and evoke peristaltic contraction for defaecation.
Importance of tonic contraction?

External anal sphincter: large voluntary sphincter innervated by inferior anal nerve- branch do pudendal nerve
-external haemorrhoids (piles)
-anal fissures
➡Distal anal canal is sensitive to touch, pain and temperature

All visceral afferent fibres travel retrogradely with parasympathetic fibres to S2-S4 spinal sensory ganglia.
Anal canal perforates levator ani muscle

Question 14

Puborectalis muscle. Slide 26

Answer 14

Has a major role to play maintaining faecal continence

Question 15

Haven’t finished..only 3 more slides, couldn’t do it. Piece out negro