Digestive System 2

Question 1

Describe the oesophagus?

Answer 1

A muscular tube about 25cm long, extending pharynx to stomach, travels posterior to the trachea, tube is normally empty with its lumen collapsed, and expands to accomodate food/water

Question 2

Functions of the oesophagus?

Answer 2

Transport (travel time 5 seconds for food, 1 second for fluid, due to peristalsis)
Protection
No absorption, little secretion, no digestion

Question 3

Differences in the oesophagus to the four layers of the gut tube?

Answer 3

1. Epithelium of mucous membrane
2. External muscle
3. Serosa

Question 4

What is the epithelium of the mucous membrane like?

Answer 4

• thick many layered (stratified squamous) with sacrificial outer layers for protection against abrasive fragments
• cells are replaced by division in basal layers, then slow migration outwards. Old cells are shed from the surface. Entire epithelium is renewed every 7 days

Question 5

What is the external muscle in the oesophagus like?

Answer 5

Contains, in addition to the usual smooth muscle, some skeletal muscle in the upper third of the oesophagus to allow rapid contraction and voluntary control of swallowing

Question 6

Does the oesophagus have a serosa?

Answer 6

No. Over most of its length the oesophagus does not lie in a body cavity, so lacks a serosa- instead, it is covered with a fibrous adventitia which attaches it to neighbouring organs eg trachea

Question 7

What does the stomach look like?

Answer 7

A j-shaped bag on the left side, an enlargement of the gut tube. About 1.5 litre capacity

Question 8

Function of the stomach?

Answer 8

Storage, since food can be eaten more quickly than it can be digested and absorbed

Question 9

Regions of the stomach?

Answer 9

Four; cardia, fundus, body, pylorus

Question 10

What’s at the outlet of the stomach?

Answer 10

A well developed muscular pyloric sphincter

Question 11

What’s the stomach like when empty?

Answer 11

Lines with longitudinal folds

Question 12

Differences in the stomach to the typical four layers of the gut tube?

Answer 12

1. Epithelium of mucosa; forms many pits lined with mucus-secreting cells, plus gastric glands which open into pits
2. External muscle; three layers rather than two (with addition of innermost oblique layer)

Question 13

Functions of the stomach?

Answer 13

1. Secretion of acid, enzymes, mucus (total volume 2-3 litres per day). Food+gastric juices= chyme
2. Digestion of protein by pepsin (active form of enzyme)
3. Absorption of water, ions, some drugs (aspirin, alcohol)
4. Transport (mixing waves, every 20 seconds)
5. Protection (against its own secretion and microbes)

Question 14

Purpose of surface mucous cells?

Answer 14

To secrete insoluble alkaline mucus which protects the mucosa from acid and pepsin

Question 15

Purpose of undifferentiated cells?

Answer 15

Stem cells dividing to generate new epithelium

Question 16

Purpose of parietal cells?

Answer 16

To secrete HCl which kills microbes and living cells. Also secretes intrinsic factors, important for absorption of B12

Question 17

Purpose of mucous neck cells?

Answer 17

Secrete soluble acid mucus at meal times

Question 18

Purpose of chief cells?

Answer 18

Secrete pepsinogen (inactive form of pepsin) and gastric lipases. Pepsinogen is converted into the protein splitting enzyme pepsin by acid in the lumen of the gland

Question 19

Purpose of gastric cells?

Answer 19

(Enteroendocrine)
Gastrin enters the bloodstream as a hormone, stimulates secretion of acid and pepsinogen, increases muscular contractions of stomach releases pyloric sphincter

Question 20

What precedes chief cells?

Answer 20

Mucous neck cells then stem cells

Question 21

Two parts of mucosa of stomach?

Answer 21

Gastric pit (upper) 
Gastric gland (lower)

Question 22

What is the liver made of?

Answer 22

Epithelial cells (hepatocytes) derived from embryonic endoderm

Question 23

What carries out liver function?

Answer 23

Hepatocytes

Question 24

What are hepatocytes and what do they do?

Answer 24

Multitalented cells which perform more than 500 different metabolic functions, including: glycogen/glucose storage and release, recycling of red blood cells, bile synthesis and secretion, synthesis of plasma proteins and removal of toxins from blood

Question 25

What do hepatocytes require?

Answer 25

Access to nutrient-laden blood drained from the intestinal wall
Access to oxygenated blood from the systemic circuit
Access to ducts which drain bile to the gall bladder

Question 26

What do fenestrated endothelial cells of the liver sinusoid do?

Answer 26

Act as a filter and allow passage of the watery part of the blood (lymph) but exclude red blood cells

Question 27

What in the liver is like a brick?

Answer 27

Hepatocytes

Question 28

What is a plate of hepatocytes stacked together called?

Answer 28

Liver lobules-each lobule is hexagonal in cross-section, about 2mm long by 1mm wife

Question 29

Where is outgoing bile from in the liver lobule?

Answer 29

Canaliculis leading into the bile duct