The Digestive System

Question 1

What are the four layers of the gut wall?

Answer 1

• Mucosa (innermost)
• Submucosa
• Muscularis externae (external muscle layers)
• Serosa (outermost)

Question 2

What is the submucosa?

Answer 2

A layer of connective tissue bearing glands, arteries, veins and nerves.

Question 3

What is the muscularis externa?

Answer 3

Two layers of smooth muscle

Question 4

How does the muscularis externa help move luminal contents along the gut?

Answer 4

By creating peristaltic waves

Question 5

What is in the serosa?

Answer 5

A simple squamous epithelium (mesothelium) and connective tissue

Question 6

What are the differences between the inner and outer layer of smooth muscle in the muscularis externa?

Answer 6

Inner layer = circular with nuclei in the centre of the cell.

Outer layer = longer and flattened with cigar shaped nuclei.

Question 7

What’s are the major functions of the GI tract?

Answer 7

• To provide a port of entry for food into the body
• To mechanically disrupt the food
• To temporarily store the food
• To chemically digest the food
• To kill pathogens in the food
• To move food along the tract
• To absorb nutrients from the resultant solution
• To eliminate residual waste material

Question 8

Characteristics of Saliva:

Answer 8

• Starts digestion (amylase and lipase)
• Bacteriostatic (contains IgA)
• High calcium
• Alkaline
• Assists swallowing
• Protects the mouth

Question 9

Upper end Oesophagus

Answer 9

Voluntary control (some striated skeletal muscle)

Question 9

Lower end Oesophagus

Answer 9

Involuntary control (solely smooth muscle)

Question 10

How does the Oesophagus work?

Answer 10

Rapid peristaltic transport transports bolus to stomach (8-9s)

(Fastest GI transport is on entry and exit)

Question 11

Innervation in the Oesophagus

Answer 11

Myenteric plexus

Submucosal plexus

Question 12

What is in the mucosa?

Answer 12

Epithelium

Lamina propria - loose connective tissue bearing blood is and lymph vessels, some smooth muscle cells and immune cells

Muscularis mucosae - thin layer of smooth muscle cells

Question 13

Stomach storage:

Answer 13

Acts as a necessary food store (we eat faster than we digest)

Wall relaxes so pressure doesn’t rise (receptive relaxation)

Question 14

Stomach initial disruption:

Answer 14

Contracts rhythmically to mix and disrupt

Question 15

Stomach disinfection

Answer 15

Stomach secretes acid and proteolytic enzymes to break down tissues and disinfect

Question 16

Stomach final action

Answer 16

Produces hypertonic chyme by combined action of acid, enzymes and agitation

Delivers incompletely digested chyme slowly, and in a controlled way to the duodenum

Question 17

What is the name of the folds of gastric mucosa in the stomach?

Answer 17

Rugae (pronounced roojie)

Question 18

Describe the gastric glands of the mucosa:

Answer 18

Long, straight tubular gastric glands extending from the gastric pits to the muscularis mucosa

Question 19

Describe the gastric pits of the mucosa of the stomach

Answer 19

Shallow, lined by mucous cells

Question 20

How does the mucus secreted by surface mucous cells protect the stomach lining?

Answer 20

The mucus contains HCO3- which neutralises the H+ ions.

It is also resistant to pepsin degradation

Question 21

Constituents of the gastric gland:

Answer 21

• Gastric pit - lined by mucus secreting cells
• Isthmus - where stem cells divide to populate the gland by up/downward migration
• Parietal cells - secrete H ions into the lumen and HCO3 ions into capillaries
• Chief cells - secrete pepsinogens
• Enteroendocrine cells - include G cells which secrete gastric

Question 22

Shape of duodenum:

Answer 22

20-25cm long, C shaped, proximal portion of small intestine

Curves around head of pancreas

Question 23

Steps of dilution in the duodenum:

Answer 23

• Water drawn in from the ECF
• Liver releases bile (water, alkali, bike salts)
• Pancreas and liver secrete alkalis
• Pancreas, liver and intestine secrete enzymes which with bile complete digestion

Question 24

Completion of digestion with enzymes from pancreas and intestine steps:

Answer 24

* Cleave peptides to amino acids * Cleave polysaccharides to monosaccharides * Break down and re-form lipids * Break down nucleic acids

Question 25

Requirements for absorption

Answer 25

* Requires a lot of energy * Requires a large surface area (gut is folded, villi, micro-villi) * Adequate contact time * Good blood supply/drainage (liver/hepatic portal vein)

Question 26

Dimensions of Small Intestine

Answer 26

22 feet/7 meters 2.5 cm in diameter SA of 25 (meters squared)

Question 27

What is the name of the folds of the Jejunum?

Answer 27

Plicae circulares

Question 28

What does the Duodenum absorb?

Answer 28

Iron

Question 29

What does the Jejunum absorb?

Answer 29

Most of the sugars, AA's and fatty acids

Question 30

What does the Ileum absorb?

Answer 30

Vitamin B12, bile acids and remaining nutrients

Question 31

What are the areas of the Large Intestine?

Answer 31

* Caecum * Ascending colon * Transverse colon * Descending colon * Sigmoid colon

Question 32

Dimensions of the Large Intestine:

Answer 32

1.2 m long and 6-9cm wide

Question 33

What does the epithelium of the crypts of Lieberkuhn produce?

Answer 33

Mucus and supplies cells to the surface | Surface epithelial cells absorb water and electrolytes

Question 34

Bacteria of the Large Intestine are involved in:

Answer 34

* Synthesis of vitamins K, B12, thiamine and riboflavine * Breakdown of 1' to 2' bile acids * Conversion of bilirubin to non-pigmented metabolites

Question 35

Decreased absorption or increased secretion of the gut can result in:

Answer 35

Life threatening dehydration Life threatening electrolyte imbalance

Question 36

Somatic neural control is involved in:

Answer 36

Ingestion (mouth and first third of Oesophagus) Excretion

Question 37

Autonomic nervous system controls what parts of the digestion:

Answer 37

All apart from ingestion and excretion

Question 38

Paracrine control of the gut

Answer 38

Histamine (production of acid in stomach) Vasoactive substances (affect blood flow in gut)

Question 39

Endocrine control of the gut hormones control:

Answer 39

* Secretion of stomach acid * Alkali secretion from liver and pancreas * Enzyme secretion

Question 40

What does Secretin do?

Answer 40

Promotes bicarbonate secretion from duct cells of pancreas Promotes bike production by the liver Inhibits secretion of acid by parietal cells of stomach

Question 41

What does Cholecystokinin (CCK) do?

Answer 41

Made and secreted by enteroendocrine cells of the duodenum Promotes release of digestive enzymes from the pancreas Promotes release of bike from the gall bladder Is a hunger suppressant

Question 42

What does Gastrin do?

Answer 42

Promotes HCl production (gastric acid) by the parietal cells of the stomach. Released by G cells of pyloric antrum of stomach, pancreas and duodenum.