Digestive System 3

Question 1

What type of organ is the pancreas?

Answer 1

Dual-function

Question 2

How is the pancreas an exocrine gland?

Answer 2

It manufactures the precursors of digestive enzymes and secreting then as alkaline “pancreatic juice” via a duct system leading to the duodenum; enzyme precursors are converted to their active form once they arrive in the duodenum. Most food substances are digested by pancreatic enzymes (proteins, carbohydrates, lipids and nucleic acids)

Question 3

How is the pancreas an endocrine gland?

Answer 3

Islets of langerhans make up 1% of the pancreas and secrete hormones into the bloodstream. The hormones (insulin and glucagon) regulate blood glucose levels

Question 4

What is the trunk of the pancreas?

Answer 4

Main pancreatic duct

Question 5

What is the small branch of the pancreas?

Answer 5

Interlobular ducts

Question 6

What are the twigs of the pancreas?

Answer 6

Intercalated ducts

Question 7

What are the leaves of the pancreas?

Answer 7

Acini (made up of serous type secretory cells)

Question 8

Dimensions of the small intestine?

Answer 8

3 diameter, a little over 3m long

Question 9

What occurs in the small intestine?

Answer 9

Most digestion and absorption- at its upper end it receives exocrine secretions from the liver (ie bile, stored in the gallbladder) and pancreas (pancreatic juice, containing digestive enzyme precursors)

Question 10

Three regions of the small intestine?

Answer 10

Duodenum (25cm long, c shaped tube, not suspended by mesentery, receives biliary and pancreatic ducts)
Jejenum (1m)
Ileum (2m)

Question 11

Differences of the small intestine to the four layers of the gut?

Answer 11

1. The mucosa is specialised to greatly increase the surface area available for secretion and absorption
2. The submucosa just downstream of the pyloric spinchter contains mucous glands (glands of brunner)

Question 12

Orders of increasing surface area in the small intestine?

Answer 12

Gross convolutions
Plicae
Villi
Microvilli

Question 13

What are plicae?

Answer 13

Circular folds 1cm high- each plica is covered with mucosa and has a core of submucosa

Question 14

What is the villi?

Answer 14

Fingers 1mm high. Covering is epithelium, core is lamina propria

Question 15

What are microvilli?

Answer 15

Fingers 1micrometre high. They form a “brush border” on the surface of individual absorptive cells. Each microvillus is covered with cell membrane and filled with cytoplasm

Question 16

What do columnar absorptive cells (enterocytes) do?

Answer 16

Absorb the small molecules resulting from digestion

Question 17

What do goblet cells do?

Answer 17

Secrete mucus

Question 18

What do enteroendocrine cells do?

Answer 18

Secrete hormone secretin (and others) into capillaries of the lamina propria

Question 19

What do undifferentiated cells do?

Answer 19

They’re stem cells dividing to generate new epithelium

Question 20

What do paneth cells do?

Answer 20

Secrete bacterial enzyme lysozyme and are phagocytic

Question 21

What are venules in the submucosa tributaries of, and what travels through them?

Answer 21

Hepatic portal vein- transports carbohydrates (absorbed as monosaccharides), proteins (absorbed as amino acids), water and electrolytes

Question 22

What travels through lymphatic vessels of the small intestine?

Answer 22

Absorbed lipids

Question 23

What is the lifespan of the epithelium of the small intestine like?

Answer 23

Short-lived. Cell divisions occurs deep in the glands, then the entire sheet (except paneth cells) move slowly up the gland walls and up the sides of the villi. Old cells are shed from the villous tip. The entire journey lasts 5 days

Question 24

What is the lymph vessel within each villus like?

Answer 24

Lacteal

Question 25

What happens to the lymph in the small intestine?

Answer 25

It's "milked" along the lacteal by contraction of smooth muscle fibres in the lamina propria which shorten the villus- these fibres arise from the muscularis mucosae

Question 26

What stimulates the release of secretin from enteroendocrine cells?

Answer 26

The arrival of acid chyme

Question 27

What does secretin in the bloodstream do?

Answer 27

Stimulates the release of pancreatic juices (cholecystokinin similar)

Question 28

What is also secreted by the enteroendocrine cells of the small intestine and stomach and what does it do?

Answer 28

Gastrin- stimulates gastric gland to secrete acid and enzymes

Question 29

Describe the small intestine?

Answer 29

A soft muscular tube about 1.5m long with 17 parts

Question 30

Functions of the large intestine?

Answer 30

1. Absorption of salts and water (1 litre/day compared with 8litre/day absorbed in the small intestine) 2. Conversion of chyme into faeces. Bacteria ferment remaining carbohydrates 3. Bacteria produce some vitamins (B & k) which are absorbed 4. Secretion of mucous to lubricate faeces 5. Defecation

Question 31

Parts of the large intestine?

Answer 31

1. Vermiform appendix 2. Cecum 3. Ascending colon 4. Transverse colon 5. Descending colon 6. Sigmoid colon 7. Rectum/anal canal/anus

Question 32

What controls intermittent flow of chyme from ileum into caecum?

Answer 32

Ileocecal valve

Question 33

What is the caecum like?

Answer 33

A dilated pouch (much larger in herbivores), where bacteria (not enzymes) are responsible for digestion. Humans produce no enzymes capable of digesting the cellulose of plants

Question 34

What is the appendix?

Answer 34

A vestigial worm-like appendage of the caecum

Question 35

What do faeces contain?

Answer 35

Bacteria (30%), undigested dietary fibre (30%), cells shed from the intestinal lining and mucus. Their colour is from pigments derived from bacterial decomposition of bilirubin

Question 36

What is the mucosa of the large intestine like?

Answer 36

No villi but many intestinal glands (also called crypts of lieberkuhn) Surface epithelial cells are enterocytes (absorptive) similar to small intestine Intestinal glands contain mostly goblet (mucous), no paneth cells Cell renewal same as small intestine (entirely renewed every 4-5 days) Many clusters of lymphocytes (lymphoid nodules) in the lamina propria, reflecting large bacterial content of colon

Question 37

What's the external muscle of the large intestine like?

Answer 37

Outer longitudinal muscle is thickened in three strips. The strips (teniae coli) contract to pull the intestinal tube into sac like pockets (haustra coli). Haustra change shape and position

Question 38

What do columnar absorptive cells (enterocytes) do in the large intestine?

Answer 38

Absorb water

Question 39

What do goblet cells do in the large intestine?

Answer 39

Secrete mucus to lubricate the passage of faeces

Question 40

What do undifferentiated cells do in the large intestine?

Answer 40

Stem cells which divide to generate new epithelium

Question 41

What do white blood cells do in the large intestine?

Answer 41

Mostly lymphocytes which provide defence against bacteria invading from the lumen of the colon

Question 42

Describe the rectum?

Answer 42

Makes up final 20cm of the gut tube (last 2cm are the anal canal), the canal is closed by two sphincters

Question 43

What are the two sphincters of the rectum like?

Answer 43

``` Internal= involuntary smooth muscle Outer= voluntary skeletal muscle ```

Question 44

When is there an urge to defecate?

Answer 44

When the rectum fills to 25% capacity

Question 45

What does stretching of the rectal wall do?

Answer 45

Initiates a reflex contraction of teniae coli in the descending colon and rectum. Shortening of this part if the gut tube further increases pressure in the rectum. The internal anal sphincter relaxes (opens) as part of the reflex

Question 46

What happens in regards to time and the external sphincter?

Answer 46

If convenient, it's relaxed voluntarily, if not; maintained in contact reacted state and defecation reflex subsides (children take time to learn to control external spinchter)