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Gastrointestinal System > Secretion, Chemical Digestion And Absorption > Flashcards

Secretion, Chemical Digestion And Absorption Flashcards

1
Q

What are the six essential nutrients?

A
  • carbohydrates
  • fats
  • water
  • proteins
  • vitamins
  • minerals
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2
Q

What are the major nutrients?

A
  • carbohydrates = sugar chains = sucrose, maltose, lactose
  • proteins = amino acid chains
  • fats = triglycerides
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3
Q

What are carbohydrates broken down into?

A
  • galactose
  • fructose
  • glucose
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4
Q

What are proteins broken down into?

A
  • dipeptides
  • tripeptides
  • amino acids
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5
Q

What are triglycerides broken down into?

A
  • monoglyceride
  • free fatty acids
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6
Q

What is chemical digestion?

A

Breaking down food with enzymes into molecules that can be absorbed

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7
Q

What is absorption?

A

Moving the digested molecules through the gastrointestinal epithelium and into the blood or lymph

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8
Q

Digestion of carbohydrates and fat in the mouth:

A
  • salivary glands secrete saliva
  • 1-2L a day
  • 99.5% water, 0.5% electrolytes, mucus or proteins
  • softens & moistens food
  • allows for taste = dissolved food chemicals
  • lubrication = via mucus
  • defence = antibacterial lysozyme & antibodies
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9
Q

Digestion of starch and fat:

A
  • salivary amylase converts starch to = maltose, maltotriose, limit dextrin
  • these are denatured by the stomach acid
  • salivary lipase converts triglycerides to = monoglycerides and free fatty acids
  • makes up 10% of lipid digestion
  • optically active in acid
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10
Q

No digestion or absorption happens in the oesophagus - why?

A
  • oesophagus secretes mucus
  • this is the only secretion in the oesophagus
  • it is secreted by mucus-secreting gland cells in the mucosa
  • this lubricates the passage of food
  • prevents damage to oesophageal wall by coarse food materials
  • protects the wall from acid & enzymes into the gastric juice, if gastric reflux occurs
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11
Q

Secreted throughout the stomach:

A

Mucus & bicarbonate = by surface mucosa & neck cells
Pepsinogen = by chief cells

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12
Q

Secreted in the fundus & body:

A

Hydrochloric acid and intrinsic factor = by parietal cells
Histamine = by enterochromaffin-like cells

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13
Q

Secreted in the fundus only:

A

Lipase = by chief cells

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14
Q

Secreted in the pyloric gland:

A

Gastrin = by g cells
Somatostatin = by d cells

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15
Q

Gastric exocrine secretions:

A
  • mucus
  • hydrochloric acid
  • digestive enzymes
  • intrinsic factor
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16
Q
  1. Mucus
A
  • protective barrier against injury to the gastric mucosa
  • lubricative function
  • protects the stomach wall from self-digestion by inhibiting pepsin
  • rich in bicarbonate ion, helps protect against acid injury by neutralising hydrochloric acid
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17
Q
  1. Hydrochloric acid
A
  • hydrogen ions are actively transported by the h+ k- at phase = proton pump
  • in the membrane of parietal cells
  • this lowers the stomach ph to 1.5-2
  • this converts pepsinogen to pepsin, provides an acid medium which is ideal for pepsin activity
  • denatures proteins = it exposes more peptide bonds, for enzymatic attack by pepsin
  • breaks down plant cell walls, connective tissue & meat fibre
  • this means it reduces large food particles into smaller ones
  • kills bacteria & microorganisms in food
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18
Q
  1. Digestive enzymes
A
  • pepsin
  • pepsinogen
  • gastric lipase
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19
Q

Pepsinogen:

A
  • constituent of gastric secretion
  • stored in the cytoplasm
  • secreted into gastric lumen by chief cells
  • it is an inactive enzyme
  • converted to active form = pepsin = by hydrochloric acid in the gastric lumen
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20
Q

Pepsin:

A
  • active enzyme
  • breaks peptide bonds between tyrosine & phenylalanine
  • produces peptide fragments & some single amino acids
  • works best in an acidic environment
  • denatured in ph of small intestine
  • acts on pepsinogen to produce even more pepsin
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21
Q

Gastric lipase:

A
  • secreted with pepsinogen by chief cells
  • breaks down triglycerides
  • best active in acidic conditions
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22
Q
  1. Intrinsic factor
A
  • essential for absorption of vitamin B12
  • important for normal functioning of red blood cells
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23
Q

Gastric endocrine & paracrine secretions:

A
  • Gastrin stimulates hydrochloric acid & histamine secretion
  • histamine acts with Gastrin to stimulate hydrochloric acid release
  • somatostatin acts locally to reduce gastric secretion
  • gastrointestinal motility & inhibiting the secretion of hormones = Gastrin & secretin’s role
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24
Q

Chemical digestion in the stomach - protein digestion:

A
  • catalysed by pepsin, helped by hydrochloric acid
  • produces peptide fragments and some amino acids
  • 10-15% of protein digestion
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25
Carbohydrate digestion in the stomach:
- continues by unexposed salivary amylase
26
Lipid digestion in the stomach:
- continues by gastric & salivary lipase
27
The stomach absorbs certain small molecules:
Water = in dehydrated body - 10-20% of ingested alcohol - aspirin = weak acidic medication - it is lipid soluble in the highly acidic environment of the stomach
28
Where does most chemical digestion & absorption happen?
The small intestine
29
Intestinal secretions - from the small intestine:
Pancreatic juice = pancreas Bile = liver
30
Small intestine absorption & digestion:
- membrane bound digestive enzymes - digestion of carbohydrates, proteins & fat are complete
31
The pancreas secretes enzymes & bicarbonate into the small intestine:
- the pancreas is a mixture of exocrine & endocrine tissue
32
Exocrine = delivered into the duodenum via the pancreatic duct, through the sphincter of oddi - they are:
Acinar cells = digestive enzymes Duct cells = NaHCO3
33
Endocrine:
Islets of Langerhans = insulin & glucagon
34
What is enzyme rich pancreatic juice stimulated by?
Cholecystokinin
35
What are the protein digestive enzymes?
- trypsinogen - chymotrypsinogen - procarboxypeptidase
36
Trypsinogen = inactive
- enteropeptidases at brush border - trypsin = active
37
Trypsinogen = inactive II
- trypsin - trypsin = active
38
Chymotrypsinogen = inactive
- trypsin - chymotrypsinogen = active
39
Procarboxypeptidase = inactive
- trypsin - carboxypeptidase = active
40
Proteins:
- small peptide chains & amino acids
41
Amylase = active
- starch - disaccharides & monosaccharides
42
Lipase = active
- fat - monoglycerides & free fatty acids
43
Nuclease = active
- dna & rna - nucleotides
44
What is bicarbonate rich pancreatic juice stimulated by?
Secretin
45
What does bicarbonate rich pancreatic juice do?
- largest component of pancreatic secretion - neutralises acid from the stomach - produces optimal ph environment for pancreatic digestive enzymes Duct
46
The secretions of the small intestine:
- 1-5 litres a day - salt & mucus - no digestive enzymes are secreted
47
Structure of villi:
- epithelial cells = outer layer - they have goblet cells - capillaries - they cover the central lacteal - brush border microvilli on the edge of epithelial cells
48
Carbohydrate digestion & absorption in the small intestine:
- pancreatic amylase digests carbohydrates in the duodenum - intestinal brush border enzymes complete digestion of carbohydrates - they are monosaccharides for absorption - once they are inside epithelial cells, the monosaccharides exit the basolateral surface of the cells - and enter blood capillaries
49
Protein digestion & absorption in the small intestine:
- pancreatic proteases = trypsin = break proteins into smaller peptides & single amino acids - brush border enzymes continue digestion of the peptides - most proteins are absorbed as dipeptides or tripeptides - which are digested by intracellular peptidases - to single amino acids inside small intestine epithelial cells - single amino acids exit epithelial cels at the basolateral side - enter the blood capillaries
50
Fats digestion and absorption in the small intestine:
- duodenum, by pancreatic lipase - bile salts form bile, aid fat digestion & absorption
51
What is bile and what does it do?
Contains organic compounds = bile salts, lecithin, cholesterol, bilirubin Bicarbonate = neutralises acidic chyme in the duodenum - continuously secreted by the liver - concentrated in the gallbladder between meals - emptied to small intestine during meals, by the sphincter of oddi Bile salts = emulsify fat, to increase surface area for digestion & absorption
52
What is emulsification?
- bile salts absorb onto small fat droplets to prevent reformation of large droplets
53
What does colipase do?
- secreted by pancreas - participates in fat digestion
54
What happens in fat digestion?
- bile salts surround glycerides & free fatty acids - this forms micelles - micelles release glycerides & free fatty acids in the luminal membrane of epithelial cells - these diffuse into the cells - short chain fatty acids are absorbed into the blood capillaries - long chain fatty acids & glycerides are made into triglycerides inside the cell - they are coated with lipoproteins, to form chylomicrons - which exit basolaterally - enter lacteal lymphatic capillaries
55
How are minor nutrients absorbed?
- salt, vitamins & minerals - small intestine mucosa - water - small intestine via osmosis
56
What does the large intestine secrete and what does it do?
- mucus and bicarbonate Mucus = lubricates faeces, protects colon from damage Bicarbonate = neutralises irritating acids produced by local bacteria - no digested enzymes - contains a large amount of beneficial bacteria
57
What does the large intestine cause?
- slow colonic movement - not all ingested bacteria are killed before entering the colon
58
Absorption in the large intestine:
Water & salts = concentrated faeces - small amounts of b complex vitamins - large quantities of vitamin k = from colonic bacteria = vital for blood clotting properties
59
What is faeces comprised of for example?
50g solid = cellulose, bilirubin, bacteria, salt 150g =water
60
Mouth & oesophagus summary:
S = secretion = water, mucus, salivary amylase, lipase, lysozyme D = digestion = carbohydrates, lipids A = absorption = vitamins, drugs
61
Stomach summary:
S = hydrochloric acid, pepsinogen, gastric lipase, mucus, bicarbonate, gastrin D = proteins, lipids A = lipid soluble substances
62
Small intestine summary:
S = bicarbonate, mucus, enzymes, bile, hormones D = carbohydrates, lipids, polypeptides, nucleic acids A = peptides, amino acids, glucose, lipids, water, minerals, vitamins, bile, salts
63
Large intestine summary:
S = mucus D = nothing A = ions, water, minerals, vitamins = produced by bacteria

Gastrointestinal System (5 decks)

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