The GI tract (Dr Campbell)

Question 1

What are the 5 main functions of the GI tract ?

Answer 1

1. Ingestion
2. Mechanical digestion
3. Chemical digestion (secretion)
4. Absorption
5. Excretion

Question 2

How long is the GI tract ?

Answer 2

8 meters long (muscular tube).

Question 3

What is the GI tract lined w/ ?

What can this lining be specialized for ?

Answer 3

An epithelium –> specialized for protection, absorption and/or secretion

Question 4

What are the four general layers (and their sub-layers) found almost consistently throughout the GI tract ?

Answer 4

From inside to outside:

• mucosa (M) : epithelium, lamina propria, muscularis mucosae
• sub-mucosa (SM)
• muscularis externa (ME): circular muscle (thickest part of musc externa) + longitudinal muscle
• serosa (S): adventitia + epithelium

Question 5

What are the main components of the GI tract and their respective general fcts ?

Answer 5

• Oesophagus –> carry food to stomach
• Stomach –> acid & enzymes, breakdown proteins
• Small intestine –> digestion, absorption of nutrients
• Large intestine –> absorption of water

Question 6

What are the 4 layers of the oesophagus ?

Answer 6

From inside to outside:

• M (E, LP + MM)
• SM
• ME
• A

Question 7

What are the main fcts of the stomach ?

Answer 7

• Storage
• Mechanical breakdown
• Acid & enzyme breakdown
• Intrinsic factor - Vitamin B12
• Hold ~ 4 litres

Question 8

What are the 3 layers of muscle in the stomach ?

Answer 8

From inside to outside:

• oblique
• circular
• longitudinal

Question 9

What are the ruggae w/in the stomach ?

Answer 9

Folds that can flatten –> allows stomach expansion –> increase in available volume

Question 10

What is the stomach lined w/ ?

Answer 10

Simple columnar epithelial cells + gastric pits.

Question 11

What are the four layers of the stomach ?

What do these contain ?

Answer 11

M: 
- columnar/(cuboidal) mucus epithlium
- LP --> capillaries + projctions from lympatic vessels
- MM
SM --> arteries, veins + lymphatic vessels
ME:
- oblique
- circular
- longitudinal
Plexus in CT between circular and longitudinal layer 
S:
- adventitia
- epithelium

Question 12

What is a plexus ?

Answer 12

Plexus = a network of nerves or vessels in the body

Question 13

How many liters of gastric juice are produced by the gastric glands of the stomach each day ?

Answer 13

2-3L/day

Question 14

What are the different cells making up the stomach epithelium ?
What are their respective fcts ?

Answer 14

From “top” to “bottom” of the gastric pit:
- surface mucus cell –> secretes mucus
- mucus neck cell –> secretes mucus
- parietal cell –> secretes HCl + intrinsic factor
- chief cell –> secretes pepsinogen
- hormone-producing G cell –> secretes gastrin
Mucus neck, parietal, chief + G cell –> in the gastric gland

Question 15

In which layer of the stomach are:

• the gastric pits ?
• the gastric glands ?

Answer 15

Gastric pits –> E

Gastric glands –> LP

Question 16

What are the fcts of the small intestine ?

Answer 16

• Digestion –> enzymes from liver & pancreas & microvilli/
brush border
• Absorption –> 90% of nutrients

Question 17

What are plicae in the small intestine ?

Answer 17

Plicae = folds or ridge of inner small intestine

Question 18

What are villi ?

Why are they useful ?

Answer 18

Villi = minute elongated projections set closely together on the inner small intestinal surface –> increasing its surface area for the absorption of substances

Question 19

What are the different layers of the small intestinal wall ?

What do these contain ?

Answer 19

• M –> simple columnar E + LP: villi, intestinal glands (Crypts of Liberkuhn), lympoid nodules
• MM
• SM: submucosal arteries + veins, lymphatic vessels, submucosal plexus
• ME –> circular + smooth layer, myenteric plexus between the 2
• S –> A + E

Question 20

What are lacteal ?

What is their fct ?

Answer 20

Lacteal = the lymphatic vessels of the small intestine that absorb digested fats

Question 21

What epithelial cells make up the villus ?

What are their fcts ?

Answer 21

From “top” to “bottom”:

• enterocytes –> have microvilli to digest + absorb nutrients
• goblet cells –> secrete mucus
• endocrine cells –> secretes secretin, cholecystokinin (CCK) + gastric inhibitory polypeptide (GIP)
• paneth cells –> secrete lysozyme + capable of phagocytosis

Question 22

Where do the venules leaving the villi of the small intestine carry ?
Where do they lead to ?

Answer 22

They carry deoxygenated blood from the villi of the small intestine (containing short chain FAs, monosaccharides and AAs) to the hepatic portal vein (into the liver and subsequently go to the heart).

Question 23

Where do the lymphatic vessels leaving the lacteals of the villi in the small intestine carry ?
Where do they lead to ?

Answer 23

They carry chylomicrons (= droplets of fat present in the lymph after absorption) from the villus to the thoracic duct.

Question 24

What can also be found on the surface of the many villi in the small intestine ?

Answer 24

Microvilli.

Question 25

What are the main fcts of the large intestine ?

Answer 25

• Absorption of water & vitamins
• Digestion –> 10% of nutrients
• Lubrication of contents

Question 26

What are the different layers of the large intestine ?

What do these contain ?

Answer 26

M –> clumnar epthelium + LP: intestinal glands, goblet cells + mucosa associated lympoid tissue, lympoid nodules
SM: veins + arteries
ME –> circular + longitudinal layer
S –> A + E

Question 27

What cells can be found in (large) intestinal glands ?

What are their roles ?

Answer 27

Enterocytes –> absorptive cells (absorb water)

Goblet cells –> secrete mucus

Question 28

What is a lympoid nodule ?

Answer 28

Lympoid nodule = small, localized collection of lymphoid tissue, usually located in the loose CT beneath wet epithelial membranes

Question 29

What is the structure that allows defecation made of ?

Answer 29

• the rectum
• the anal canal
• the anal columns
• the internal and external sphincters
• the anus