Lower GI Tract

Question 1

1. what is the role of intestinal goblet cells?
2. what facilitates venous drainage of the intestine?
3. what is the lymphatic drainage of a villus called?
4. describe the turnover of intestinal mucosal cells
5. what cells are important for immune defence in the intestine?

Answer 1

1. secrete mucous that protects the intestine from damage by gastric acid and proteolytic enzyme
2. hepatic portal vein - transports nutrients to the liver
3. lacteal
4. epithelial cells are shed due to friction by food
   stem cells proliferate at the bottom of the crypt and migrate to the tip of the villus
5. paneth cells. contain eosinophillic granules

Question 2

1. which part of the small intestine comprises of the jejunum?
2. which part of the small intestine comprises the ileum?
3. what are:
   a) plicae circulares?
   b) arterial arcades?
   c) vasa recta?
   d) payer’s patches?
4. how do the jejunum and illeum differ in terms of:
   a) diameter and wall thickness?
   b) arterial arcades
   c) vasa recta
   d) arterial supply
5. Which parts of the small intestine have:
   a) Plicae circulares?
   b) payer’s patches?
6. What are Mekel’s diverticulum?

Answer 2

1. proximal 2/5
2. distal 3/5
   3a) folds that circle into the lumen to increase surface area
   3b) anastomoses of the jejunal and ileal arteries
   3c) arteries coming off arcades.
   3d) lymphatic tissue
   4a) jejunum - thick wall and large diameter. ileum - small diameter and thin wall
   4b) jejunum - less prominent; ileum - more prominent
   4c) jejunum - long; ileum - short
   4d) jejunum - jejunal arteries; ileum - ileal arteries
   5a) jejunum
   5b) ileum
3. a remnant of the vitelline duct present as a slight bulge in the small intestine. It is present in 2% of the population and containst 2 types of ectopic tissue - gastric and pancreatic. It can become inflamed (diverticulitis)

Question 3

1. which parts of the large intestine are:
   a) intraperitoneal?
   b) retroperitoneal?
2. Describe the 3 distinguishing features of the large intestine
3. which part of the large intestine is the appendix connected to?

Answer 3

1a) caecum, transverse colon, sigmoid colon, superior rectum
1b) ascending colon; descending colon
2. tenia coli - segregation of longitudinal muscle into 3 narrow bands
haustra - bulges
appendix epiploica - peritoneal covered accumulations of fat
3. caecum

Question 4

1. at what level is the rectum found?
2. what rectal structures support the weight of the faecal matter?
3. what type of muscle makes up the:
   a) internal anal sphincter?
   b) external anal sphincter?
4. what does the pectinate line demarate?
5. what is the blood supply and histology of:
   a) internal anus
   b) external anus
6. what is the neural supply of
   a) smooth muscle of rectum and anal canal
   b) external anal sphincter

Answer 4

1. between S3 and pelvic floor
2. transverse rectal folds

3a) smooth
3b) skeletal
4. transition between internal and external anus
5a) columnar epithelium; superior rectal artery
5b) stratified squamous epithelium; middle and inferior rectal artery
6a) parasymp fibres from S2-4
symp fibres from T11-L2
6b) pudenal nerve or sacral plexus

Question 5

Describe the process of defaecation

Answer 5

1. faeces stretches the rectum and stimulates stretch receptors that relay signal to spinal cord
2. spinal reflex stimulates contraction of rectum and relaxes internal anal sphincter
3. impulses from brain prevent untimely defaecation by keeping external anal sphincter contracted.
4. Defaecation occurs under voluntary contraction of external anal sphincter

Question 6

What are the embryonic derivatives of:

1. embryonic foregut
2. embryonic midgut
3. embryonic hindgut
4. what is the blood supply of these derivatives derivatives?

Answer 6

1. oesophagus > proximal duodenum. Liver, gall bladder, pancreas
2. distal duodenum > proximal 2/3 of transverse colon
3. distal 1/3 of transverse colon > proximal anal canal
4. foregut - celiac trunk
   midgut - superior mesenteric artery
   hindgut - inferior mesenteric artery

Question 7

1. what is the superficial fascia?
2. Describe the layers it forms beneath the umbilicus
3. Name the 4 abdominal muscles, the direction of their fibres and origins and insertions
4. what forms the rectus sheath?
5. how are the layers of the rectus sheath arranged:
   a) above the arcuate line
   b) below the arcuate line

Answer 7

1. a layer of fatty connective tissue that is the most superficial abdominal tissue
2. superficial layer - contains fat, varies in thickness, continuous over inguinal ligament
   deep layer - thin membranous layer that has no fat.
3. external oblique - inferiomedial. inferior 8 ribs > linea alba, iliac crest and pubic tubercle
   internal oblique - superiomedial. iliac crest, inguinal ligament and lumbar fascia > linea alba and ribs
   transversus abdominus - transversely; iliac crest, costal cartilages and inguinal ligament > pubic crest and linea alba
   rectus abdominis - paired muscle running longitudinally. Contained in rectus sheath. crest of pubis and pubic symphysis > costal cartilages
4. layering of aponeuroses of external and internal oblique and transverse abdominis

5a) anterior sheath composed of external oblique and half of internal oblique.
posterior sheath composed of half of internal oblique and transversus abdominis
5b) aponeuoses of all 3 muscles.

Question 8

1. what is the peritoneum?
2. what are intraperitoneal organs?
3. what are retroperitoneal organs?
4. what is the mesentery?
5. what is the omentum?
   a) greater omentum
   b) lesser omentum

Answer 8

1. serous membrane that forms the lining of the abdominal cavity
2. organs completely covered in visceral peritoneum
3. organs that located behind the intraperitoneal space
4. a double fold of peritoneum that attaches organs to the abdominal walls. Provides a pathway for vessels and nerves and allows movement
5. a fold of peritoneum that connects the stomach to other structures
   a) connects stomach to transverse colon. Has a free edge and an immune role
   b) connects the lesser curvature of stomach to liver.

Question 9

1. what is the inguinal canal?
2. what structures make up the following?
   a) floor
   b) roof
   c) posterior wall
   d) anterior wall
3. What is contained within the inguinal canal?
4. How does the inguinal canal develop?
5. Why does an inguinal hernia develop?

Answer 9

1. slit like passage that extends in an inferiomedial direction, above and parallel to the inguinal ligament.
   2a) inguinal ligament
   2b) transversus abdominis and internal oblique
   2c) transversalis fascia
   2d) aponeuroses of external and internal oblique muscles
2. genitofemoral nerve
   spermatic cord
   round ligament of uterus
3. peritoneal outpocket (processus vaginalis) forms, protruding through various layers of abdominal wall, acquiring coverings from transversalis fascia, internal oblique and aponeurosis of external oblique. This tubular structure forms the basis of the inguinal canal.
   In men, testes decend through the processus vaginalis
   in both sexes, the processus vaginalis obliterates
4. if obliteration of processus vaginalis is incomplete, a potential weakness exists.