Digestive System (3)

Question 1

Where does large intestine extend from?

Answer 1

• from ileocecal valve to the anus

Question 2

Major digestive function of large intestine

Answer 2

• “absorb” most remaining water from indigestible food residues
• “store” the residues temporarily
• “eliminate” them from body as feces

Question 3

Subdivisions of the large intestine

Answer 3

CACRA
- cecum
- appendix
- colon
- rectum
- anal canal

Question 4

What is ileocecal valve?

Answer 4

• sphincter muscle located at the junction of ileum and colon

Question 5

What is cecum?

Answer 5

• saclike first subdivision of large intestine
• lies below ileocecal valve

Question 6

Function of the appendix

Answer 6

• contains masses of lymphoid tissue
• plays important role in immunity (part of MALT: mucosa associated lymphoid tissue)
• bacteria storehouse

Question 7

Shortcoming of appendix

Answer 7

• its twisted structure provides ideal condition for enteric bacteria to accumulate and multiply

Question 8

Distinct regions of the colon

Answer 8

• ascending colon
• transverse colon
• descending colon
• sigmoid colon

Question 9

The rectum

Answer 9

• after sigmoid colon
• runs posteroinferiorly just in front of sacrum

Question 10

What is the sacrum?

Answer 10

• shield shaped bony structure at the base of lumbar vertebrae
• connected to the pelvis

Question 11

Anal canal

Answer 11

• last segment of large intestine
• lies in perineum
• opens to exterior at the anus

Question 12

2 sphincters of the anal canal

Answer 12

• involuntary internal anal sphincter (composed of smooth muscles)
• voluntary external anus sphincter (skeletal muscle)

Question 13

Bacterial Flora
- How is bacteria beneficial for us?

Answer 13

In the large intestine
- colonize the colon
- synthesize vitamin Bs and some vitamin Ks liver needs to produce several clotting proteins
- metabolize some host derived molecules (mucin, heparin, hyaluronic acid)
- ferment some indigestible carbohydrates (cellulose, xylan), releasing irritating acids and a mixture of gases

Question 14

Mechanism of digestion

Answer 14

• breakdown food to monomers smol enough to be absorbed by GI tract linings
• catabolic
• done by enzymes secreted into lumen of the GI tract by intrinsic and accessory glands
• enzymatic breakdown is hydrolysis

Question 15

3 common monosaccharides in our diet

Answer 15

• glucose, fructose, galactose

Question 16

Where does digestion of starch (carbohydrate) begin?

Answer 16

• in the mouth
• “salivary amylase” splits starch into oligosaccharides

Question 17

What are oligosaccharides?

Answer 17

• smaller fragment of 2 to 8 linked glucose molecules
• salivary amylase breakdown starch into that in the mouth

Question 18

When does salivary amylase work best?

Answer 18

• slightly acidic to neutral environment (pH 6.75-7)

Question 19

Until when does starch digestion continue?

Answer 19

• until amylase is inactivated by stomach acid and broken apart by stomach’s protein-digesting enzymes

Question 20

How are carbohydrates that escape salivary amylase broken down?

Answer 20

• by pancreatic amylase in the small intestine
• starch converted to oligosaccharides

Question 21

Which enzymes digest oligosacchiarides into monosaccharides?

Answer 21

• intestinal brush border enzymes

Question 22

most important brush border enzymes that act on oligosaccharides

Answer 22

• dextrinase and glucoamylase (act on oligosaccharides with more than 3 sugars)
• maltase, sucrase, lactase (hydrolyse maltose sucrose, lactose)

Question 23

Where does protein digestion begin?

Answer 23

• in the stomach
• pepsinogen is activated by HCl into pepsin

Question 24

Where does pepsin function optimally?

Answer 24

• in the acidic pH range found in the stomach 1.5-2.5
• cleaves bonds involving amino acids tyrosine and phenylalanine

Question 25

Protein fragments in small intestine

Answer 25

- trypsin and chemotrypsin secreted by pancreas cleave proteins into smaller peptides -> become grist for other enzymes - pancreatic and brush border enzyme "carboxypeptidase" splits of one by one amino acid from carboxyl end - "aminopeptidase" and "dipeptidase" liberate final amino acid products one by one from amine end

Question 26

Primary site of lipid digestion

Answer 26

- small intestine because pancreas is the major source of lipases (fat-digestion enzymes)

Question 27

Stable fat emulsion

Answer 27

- lipid digestion in small intestine - fatty droplets are pulled off the large fat globules (because of bile too) forming stable emulsion - aqueous suspension of fatty droplets

Question 28

pancreatic lipases catalysis of fats

Answer 28

- cleaves off two of fatty acid chains, yielding free fatty acids and monoglycerides (glycerol with one fatty acid chain attached)

Question 29

site of digestion of nucleic acids

Answer 29

- small intestine

Question 30

enzymes that digest nucleic acids

Answer 30

- pancreatic nucleases in pancreatic juice => nucleic acids to nucleotide monomers - intestinal brush border enzymes nucleosidases and phosphatases => break nucleotides to release free bases, pentose sugars and phosphate ions

Question 31

Which vitamins does small intestine absorb?

Answer 31

- dietary vitamins

Question 32

Which vitamins does large intestine absorb?

Answer 32

- K and B vitamins made by enteric bacterial guests

Question 33

How are most water-soluble vitamins absorbed?

Answer 33

- by diffusion or via specific active/passive transporters

Question 34

Absorption of vitamin B12

Answer 34

- intrinsic factor produced by the stomach binds to B12 - complex binds to specific mucosal receptor sites in terminal ileum - triggers uptake by endocytosis

Question 35

Why is the small intestine primary site of lipid digestion?

Answer 35

- pancreas is the major source of lipases (fat-digesting enzymes)

Question 36

Which structure absorbs vitamins?

Answer 36

- small intestine, large intestine - K and B vitamins made by enteric bacterial guests - large intestine - dietary vitamins - small intestine

Question 37

What is intrinsic factor?

Answer 37

- produced by stomach and binds to vitamin B12 - intrinsic-B12 complex binds to mucosal receptor sites in ileum - active uptake of B12 by endocytosis