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Entrance Biology > Digestive System (3) > Flashcards

Digestive System (3) Flashcards

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1
Q

Where does large intestine extend from?

A
  • from ileocecal valve to the anus
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2
Q

Major digestive function of large intestine

A
  • “absorb” most remaining water from indigestible food residues
  • “store” the residues temporarily
  • “eliminate” them from body as feces
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3
Q

Subdivisions of the large intestine

A

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

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4
Q

What is ileocecal valve?

A
  • sphincter muscle located at the junction of ileum and colon
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5
Q

What is cecum?

A
  • saclike first subdivision of large intestine
  • lies below ileocecal valve
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6
Q

Function of the appendix

A
  • contains masses of lymphoid tissue
  • plays important role in immunity (part of MALT: mucosa associated lymphoid tissue)
  • bacteria storehouse
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7
Q

Shortcoming of appendix

A
  • its twisted structure provides ideal condition for enteric bacteria to accumulate and multiply
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8
Q

Distinct regions of the colon

A
  • ascending colon
  • transverse colon
  • descending colon
  • sigmoid colon
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9
Q

The rectum

A
  • after sigmoid colon
  • runs posteroinferiorly just in front of sacrum
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10
Q

What is the sacrum?

A
  • shield shaped bony structure at the base of lumbar vertebrae
  • connected to the pelvis
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11
Q

Anal canal

A
  • last segment of large intestine
  • lies in perineum
  • opens to exterior at the anus
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12
Q

2 sphincters of the anal canal

A
  • involuntary internal anal sphincter (composed of smooth muscles)
  • voluntary external anus sphincter (skeletal muscle)
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13
Q

Bacterial Flora
- How is bacteria beneficial for us?

A

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

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14
Q

Mechanism of digestion

A
  • 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
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15
Q

3 common monosaccharides in our diet

A
  • glucose, fructose, galactose
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16
Q

Where does digestion of starch (carbohydrate) begin?

A
  • in the mouth
  • “salivary amylase” splits starch into oligosaccharides
17
Q

What are oligosaccharides?

A
  • smaller fragment of 2 to 8 linked glucose molecules
  • salivary amylase breakdown starch into that in the mouth
18
Q

When does salivary amylase work best?

A
  • slightly acidic to neutral environment (pH 6.75-7)
19
Q

Until when does starch digestion continue?

A
  • until amylase is inactivated by stomach acid and broken apart by stomach’s protein-digesting enzymes
20
Q

How are carbohydrates that escape salivary amylase broken down?

A
  • by pancreatic amylase in the small intestine
  • starch converted to oligosaccharides
21
Q

Which enzymes digest oligosacchiarides into monosaccharides?

A
  • intestinal brush border enzymes
22
Q

most important brush border enzymes that act on oligosaccharides

A
  • dextrinase and glucoamylase (act on oligosaccharides with more than 3 sugars)
  • maltase, sucrase, lactase (hydrolyse maltose sucrose, lactose)
23
Q

Where does protein digestion begin?

A
  • in the stomach
  • pepsinogen is activated by HCl into pepsin
24
Q

Where does pepsin function optimally?

A
  • in the acidic pH range found in the stomach 1.5-2.5
  • cleaves bonds involving amino acids tyrosine and phenylalanine
25
Q

Protein fragments in small intestine

A
  • 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
26
Q

Primary site of lipid digestion

A
  • small intestine because pancreas is the major source of lipases (fat-digestion enzymes)
27
Q

Stable fat emulsion

A
  • 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
28
Q

pancreatic lipases catalysis of fats

A
  • cleaves off two of fatty acid chains, yielding free fatty acids and monoglycerides (glycerol with one fatty acid chain attached)
29
Q

site of digestion of nucleic acids

A
  • small intestine
30
Q

enzymes that digest nucleic acids

A
  • 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
31
Q

Which vitamins does small intestine absorb?

A
  • dietary vitamins
32
Q

Which vitamins does large intestine absorb?

A
  • K and B vitamins made by enteric bacterial guests
33
Q

How are most water-soluble vitamins absorbed?

A
  • by diffusion or via specific active/passive transporters
34
Q

Absorption of vitamin B12

A
  • intrinsic factor produced by the stomach binds to B12
  • complex binds to specific mucosal receptor sites in terminal ileum
  • triggers uptake by endocytosis
35
Q

Why is the small intestine primary site of lipid digestion?

A
  • pancreas is the major source of lipases (fat-digesting enzymes)
36
Q

Which structure absorbs vitamins?

A
  • small intestine, large intestine
  • K and B vitamins made by enteric bacterial guests - large intestine
  • dietary vitamins - small intestine
37
Q

What is intrinsic factor?

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

Entrance Biology (23 decks)

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