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Flashcards in Digestive system lecture Deck (141):
1

What biomolecule is digested in the stomach?

Primarily proteins, a little bit of fat

2

Technical term for the chemical breakdown of molecules into smaller biomolecules

Digestion

3

Process of taking biomolecules (usually) in their smallest form and moving it either into the blood or the lymph?
What is taken into the lymph?

Absorption
Fat is taken into the lymph

4

Most of the digestion takes place in the?

small intestine, also where absorption takes place

5

Process of moving certain substances i.e. signal molecules, enzyme, or hydrochloric acid from a cell into the lumen of the GI tract?

Secretion

6

pH of gastric juice?
What else is in there besides hydrochloric acid?

2

7

What protects the stomach from the strong acid?

Mucus layer that contains bicarbonate which protects the cells of stomach from extreme pH of gastric juice

8

What is secreted into the stomach?

Zymogens, brush border enzymes

9

Enzymes built into the microvilli

Brush border enzymes

10

Which type of muscle activity would cause squeezing and mixing

Segmental contractions, also called segmentation

11

Which cells secrete hydrochloric acid in the stomach?

Parietal

12

Which cells secrete enzymes in the stomach?

Chief cells

13

In the stomach which cells secrete paracrines?

Enterochromaffin-like (ECL) cells secrete histamine. D-cells secrete somatostatin

14

Pepsin breaks peptide bonds but is secreted....

In its inactive form called pepsinogen

15

Breaks down fat a little bit in the stomach

gastric lipase

16

What is motility

It is more than movement of peristalsis and segmental contractions, even chewing your food, putting food in your mouth

17

Deglutition is

Swallowing, putting food into the esophagus

18

Different kinds of secretion

Exocrine
Endocrine
Paracrine

19

When you think of the muscle layer lining the GI tract there are two arrangements of the smooth muscle

1) Some muscle fibers are called longitudinal, they run the length of the tract. They shorten and lengthen
2) Others are called circular, when they contract they squeeze, these push behind the bolus & mixes the food
They coordinated together to move the bolus forward

20

Smallest component of triglyceride.
In the GI tract you end up with a?

Fatty acid
Monoglyceride & fatty acids to get it out of the GI tract then it forms chylomicron

21

We get glycogen from?

Animal products

22

We get starch from

Plants

23

We want to convert galactose & fructose into?

Glucose

24

Total fluid input into digestive system.
Total fluid removed from digestive system

9 liters into lumen
9 liters removed from lumen

25

Motility in the mouth?

Yes. Ingestion, mastication, deglutition begins here, segmentation

26

Secretions in the mouth.

Salivary amylase in saliva

27

Digestion in the mouth

Mechanically & chemically by the action of salivary amylase which acts on starch which breaks down into individual glucose molecules and that is when we can absorb it. Very little digestion actually takes place in the mouth

28

Do we absorb anything in the mouth?

Not a lot but certain substances can be absorbed under the tongue (sublingual delivery) like certain medications, even a tiny bit of glucose. The benefit of this is it doesn't have to face digestive processes further along

29

Oral cavity & esophagus: Motility

Motility- Swallowing, chewing


30

Stomach:

Motility- Peristaltic mixing and propulsion

31

Small intestine motility

Motility- Mixing & propulsion primarily by segmentation

32

Large intestine motility

Segmental mixing; mass movement for propulsion

33

Do we have motility in the esophagus?

Yes peristalsis

34

Do we have digestion in the esophagus?
Does the esophagus contribute to digestion?

Yes digestion does take place a little bit because after you swallow food it takes about 10 seconds to pass down the esophagus which gives time for salivary amylase to break it down
No the esophagus does not contribute to digestion, digestion just continues

35

Motility in the stomach

Yes lots of muscle activity there to mix the food & direct the chyme into the small intestine

36

Which branch of the nervous system is housed completely within and around the GI tract?
Another branch involved in regulating digestion.

Enteric
Parasympathetic

37

Does histamine enter the stomach?

No it acts as a signal molecule & binds to neighboring cells

38

These cells of the stomach secrete enzymes.
What is digested based on these enzymes?

Chief cells
Proteins & fats

39

This helps to unwind tertiary structures (bending and folding) which is held by ionic contractions, repulsions, hydrogen bonds, disulfide bonds

Gastric acid (hydrochloric acid)

40

What happens when you bombard proteins with hydrogen ions which is what happens in the stomach

It starts to unravel and enzymes can go in and start breaking bonds

41

What type of bond do you find between two adjacent amino acids?
What enzyme in present in the stomach to break these bonds?

A peptide bond
Pepsin

42

Why does only 10% of fat digestion take place in the stomach?

Because the fat is a giant glob and the enzymes don't have a lot of time to break it down

43

Does the stomach contribute to the breakdown of carbohydrates?
Will hydrochloric acid break down carbohydrates?

No, onces it gets to the stomach salivary amylase will not break down carbohydrates any more. Enzymes only work within its optimum pH and the pH of the stomach is too acidic for it.
Hydrochloric acids don't break covalent bonds

44

Presence of protein

Secretes hydrochloric acid

45

Proton pump inhibitor would work here

Parietal cell

46

Who takes a proton pump inhibitor?

Someone who has excess secretion of hydrogen chloride in the stomach

47

Where does the stomach get its hydrogen ions?

When carbon dioxide diffuses into the cell the enzyme carbonic anhydrase catalyzes a reaction between the carbon dioxide and water to form carbonic acid. Carbonic acid then dissociates into bicarbonate ion and hydrogen ion

48

The layer of the wall of the digestive tract that contains blood vessels, small glands, and a nerve plexus is the

Submucosa layer

49

The largest pair of salivary glands is the

Parotid glands

50

Which of these cells in the lining of the duodenum produce digestive enzymes?

Absorptive cells

51

In which phase of stomach secretion does the greatest amount of secretion take place?

Gastric

52

Gastrin secretion is stimulated by

duodenal pH greater than 3

53

The ______ secretes peptidases and disaccharidases, whereas the _______ secretes trypsin, chymotrypsin, amylase, lipase, and nuclease

small intestine, pancreas

54

Initial chemical digestion of proteins occurs in the ______ by the digestive secretion _______.

Stomach; pepsin

55

Defecation is stimulated by

parasympathetic reflexes & local reflexes

56

Carbon dioxide plus water gives you?

Carbonic acid

57

Type of transporter for the chloride shift

Channel

58

Why does chloride follow hydrogen in the parietal cell?

Chloride accumulates in the cells so it moves by diffusion out to the lumen of the stomach

59

Do our cells secrete hydrochloric acid?

No, they secrete hydrogen and chloride

60

What do proton pump inhibitors do?

They block hydrogen-potassium pump

61

Remember what H+ is...

A proton, so this is where a proton pump inhibitor would work, wherever there is a hydrogen pump

62

What is a proton pump inhibitor?

A class of drugs for example; Prilosec, Nexium, Protonix, etc.

63

Does bicarbonate mix with the gastric juice?

No it stays in/mixed with the mucus otherwise you will neutralize the acid and it won't be able to digest anything

64

Small intestine secretions come from

The pancreas & the cells of the duodenum & gallbladder

65

What is digested in the small intestine?

Biomolecules: carbohydrates, fats, & proteins

66

Function of pancreatic amylase in the small intestine does what?`

Goes after complex carbohydrates

67

Disacchridases enzymes in the small intestine do what?

Break down disaccharides; sucrose, maltose, lactose
Sucrose will be broken down to glucose & fructose
Maltose will be broken down to glucose & glucose
Lactose will be broken down to galactose & glucose
All of these can be absorbed from the GI tract into the blood, they'll go to the liver for processing

68

Explain fat digestion in the small intestine

First thing you want to do is expose it to bile, & the bile salts will cause this fat to emulsify (break apart) then lipase can get in and start breaking triglycerides down

69

Who breaks covalent bonds?

Enzymes

70

What does the small intestine absorb?

1) Amino acids
2) Monosaccharides l Fat
3) Water
4) Electrolytes

71

Chyme is entering from the stomach with a pH of 2. The enzymes in the small intestine have an optimum pH of around 7. So the chyme gets exposed to bicarbonate which?

Will neutralize it and bring it to a normal pH range. Mucus is also secreted from the intestinal goblet cells, bile produced & secreted by the liver; temporarily stored & secreted by the gallbladder

72

Pacreatic enzymes of the small intestine

Inactivated zymogens are activated once they get into the small intestine

73

Why do we have zymogens?

Because the goal of all the enzymes is to break down biomolecules into their monomers. So the reason they are inactive is because we are made up of biomolecules and if they were always activated we wouldn't be able to survive, they would destroy the cells that produce them and all the cells they come into contact with

74

When are zymogens activated?

Only when they are in a location where there are molecules that you want broken down

75

What happens when trypsinogen becomes activated?

Called trypsin & activates zymogens to their activated enzyme form

76

Must have activated trypsin present in order to activate?

All the zymogens

77

How do you activate trypsin?

It comes out as a zymogen, an inactive enzyme. enteropeptidase in brush border activates trypsin

78

Another name for enteropeptidase

Enterokinase

79

Why wouldn't you want phospholipase to come out in its active form?

Because it breaks apart phospholipids of cell membranes

80

Activates Trypsin (Trypsinogen --> Trypsin)

Enteropeptidase

81

Trypsin activates other pancreatic enzymes such as?

1) Chymotrypsin
2) Carboxypeptidase
3) Phospholipase
4) Colipase

82

Where is the last chance to take water back (reabsorption)

Large intestine

83

Absorption of electrolytes that include Vitamin B, K

Large intestine

84

Where is vitamin folic acid and vitamin k produced?

Formed by microflora in the gut

85

Breakdown of carbohydrates is going from the more complex polysaccharide to?

Monosaccharides

86

Describe the breakdown of carbohydrates in the mouth

1) Starts in the mouth by salivary amylase which breaks down starch into its smallest components
2) Action continues until amylase is exposed to extreme pH in the stomach
No more digestion of carbohydrates until you get to the small intestine

87

Describe the breakdown of carbohydrates in the small intestine

1) Once in the small intestine pancreatic amylase continues digestion of starch into di-, tri- and oligosaccharides
2) Brush border disaccharidases: Maltase breaks down maltose into 2 glucose, sucrase breaks down sucrose into fructose & glucose, lactase breaks down lactose into glucose & galactose

88

Which form of carbohydrates are absorbed?

Only monosaccharides which is the smallest unit

89

Which transporter is moving fructose out of the lumen of the GI tract? And exits on?

Facilitated diffusion
GLUT 5
Exits on GLUT 2

90

Carbohydrate absorption: Glucose & Galactose move by?

Sodium moving down its gradient
Cotransport with Na+
Secondary active transport
• Active transport of Na+ maintains concentration gradient

91

Where do monosaccharides go after the small intestine?

1) Into blood
2) Hepatic portal vein to
3) Liver

92

Describe fructose & galactose absorption

1) Converted into glucose in the liver
2) Fructose can be converted to fat by adipocytes

93

Describe glucose absorption

1) Stored as glycogen in liver or muscle (or as fat in adipocytes) OR
2) Delivered to other cells for immediate use

94

Carbohydrate absorption (brief)

1) Initially broken down by salivary amylase in the mouth
2) Continues down esophagus, gets to the stomach
3) NO MORE carbohydrate digestion in the stomach
4) Once in small intestine pancreatic amylase breaks it down
5) Then the disaccharidases
6) Then it can be absorbed

95

Who breaks the proteins quaternary & tertiary structure?

Hydrochloric acid being secreted into the GI tract in the stomach by parietal cells

96

First step of protein digestion

We want to first unravel it and then start breaking it down. HCl is responsible for unraveling it.

97

Does protein digestion take place in the mouth or esophagus?

No because there is no enzyme in the mouth or esophagus to break it down

98

Enzymes that breakdown proteins are called?

Proteases or peptidases which are not in the saliva but are in the stomach

99

Destroys tertiary structure, exposes peptide bonds

Hydrochloric acid (HCl)

100

Breaks peptide bonds, larger into smaller peptides

Pepsin activated by hydrochloric acid (low pH)

101

Pancreatic enzymes in the small intestine that digest proteins

1) Trypsin
• Internal peptide bonds (endopeptidase)
2) Chymotrypsin
• Internal peptide bonds
3) Carboxypeptidase
• Carboxyl-end amino acids (exopeptidase)

102

Can break up amino acids only from the carboxyl-end

Carboxypeptidase

103

Brush border enzymes of small intestine

1) Aminopeptidase
• Breaks down di- and tri-peptides into free amino acids
• Cleaves amino-end peptide bonds (exopeptidase)
2) Enteropeptidase
• Activates trypsin

104

Brush border enzyme that takes from the amine end of proteins

Aminopeptidase

105

Endopeptidases include

Pepsin in the stomach, trypsin and chymotrypsin in the small intestine

106

Endopeptidases digests?

Internal peptide bonds

107

Exopeptidases digest?

Terminal peptide bonds to release amino acids

108

Aminopeptidase is found

In the brush border

109

Carboxypeptidase is found

Pancreatic

110

What is a di-peptide made up of?

Two amino acids

111

For protein absorption free amino acids co-transportout of lumen with?

(Fig. 21.8d)
Na+ (symport)

112

How do the di-and tripeptides get absorbed?

(Fig. 21.8d)
1) Via transporter molecules
-secondary active transport with H + into epithelial cells
2) Once inside the epithelial cells there are di- and tri-peptidases which hydrolyzed into free AAs
3) Free amino acids leave cell via Na+ antiport
4) Remaining Di- and tri-peptides leave cell via H+ exchanger
5) AAs & di- & tri-peptides enter hepatic portal vein and then get delivered to liver

113

Enzymatic fat digestion is carried out by?

Lipases, enzymes that remove two fatty acids from each triglyceride molecule. The result is one monoglyceride & two free fatty acids

114

In the digestive tract in the gut in the presence of lipase, triglyceride is broken down into?

A monoglyceride with a glycerol and one fatty acid & the other two fatty acids are free. This is what happens to get it out of the lumen of the GI tract. The monoglyceride and the 3 fatty acids can then be taken across the cell membrane

115

Most fat digestion takes place in the?

Small intestine

116

Fat digestion

1) First has to be exposed to bile which causes emulsification where its broken into droplets
2) Now lipase can go in and start breaking the covalent bonds & getting those fatty acids off of the complex structure
3) Lipase breaks the bonds where you end up with triglyceride

117

Phospholipids into free fatty acids

Phospholipase

118

What does lipase do?

Breaks bonds between fatty acids and glycerol
• Triglyceride--->monoglyceride+2 free fatty acids

119

Intestinal hormone that regulates digestive function and may play a role in appetite

Cholecystokinin (CCK)

120

Digestive hormone cholecystokinin (CCK):
Stimulus for release:
Primary targets:
Primary effects:
Other info.:

Stimulus for release: Fatty acids and some amino acids
Primary targets: Gallbladder, pancreas, stomach
Primary effects: Stimulates gallbladder contraction & pancreatic enzyme secretion. Inhibits gastric emptying & acid secretion
Other info.: Promotes satiety (sense of being full). Some effects may be due to CCK as a neurotransmitter
Hypothalamus

121

Digestive hormone glucagon-like peptide-1 (GLP-1)
Stimulus for release:
Primary targets:
Primary effects:
Other info.:

Stimulus for release: Mixed meal that includes carbohydrates or fats in the lumen
Primary targets: Endocrine pancreas
Primary effects: Stimulates insulin release. Inhibits glucagon release & gastric function
Other info.: Promotes satiety (sense of being full)
Hypothalamus

122

5 steps for fat digestion & absorption

1) Bile salts from liver coat fat droplets
2) Pancreatic lipase & collapse break down fats into monoglycerides & fatty acids stored in micelles
3a) Monoglycerides & fatty acids move out of micelles and enter cells by diffusion
3b) Cholesterol is transported into cells
4) Absorbed fats combine with cholesterol & proteins in the intestinal cells to form chylomicrons
5) Chylomicrons are removed by the lymphatic system

123

Cephalic Phase is?

1) Stimuli & sensors in the head
-The thought of food, the smell or sight of food, food in the mouth
2) Signal processed in Medulla Oblongata
Efferent: Autonomic Nervous System: Parasympathetic
3) Effectors
-Salivary glands, stomach, intestine, glandular organs

124

Gastric Phase is?

1) Stimuli & Sensors in the Stomach
- Distension of the stomach
- Presence of peptides/proteins/amino acids in stomach
2) Signals processed by Gastric mucosal cells
- Efferent: Paracrines, hormones
3) Effectors
- Secretory cells & smooth muscle

125

Intestinal Phase is?

1) Stimuli & Sensors in the Intestines
- Entry of chyme into duodenum
2) Signals processed in Small Intestine
- Efferent: Enteric nervous system & other cells in intestine
• Feedback to stomach to slow motility & secretions
• Feed-forward to pancreas to secrete insulin when
carbohydrates are present
3) Effectors
- Gastric mucosal cells, beta cells of pancreas

126

Increased gastric activity & Increases ileum motility

Gastroileal Reflex (gastro=stomach, ileal=last segment of small intestine)

127

Ileum distension & Decreased gastric motility means slow down the emptying of the stomach, can go in the other direction

Ileogastric Reflex

128

Extreme distension of one segment & Increased relaxation of other segments

Intestino-intestinal reflexes

129

Segments of the small intestine

1) Duodenum
2) Jejunum
3) Ileum

130

Secretion in the oral cavity & esophagus

Saliva (salivary glands) (only in the oral cavity)

131

Digestion in the oral cavity & esophagus

Carbohydrates, fats (minimal)

132

Absorption in the oral cavity & esophagus

None

133

Stomach secretions

1) HCl by parietal cells
2) Pepsinogen and gastric lipase by chief cells
3) Mucus and bicarbonate by surface mucus cells
4) Gastrin by G-cells
5) Histamine by ECL cells

134

Stomach digestion

Proteins & a little bit of fat

135

Stomach absorption

Lipid soluble substances such as alcohol & aspirin

136

Small intestine secretion

1) Enzymes;
2) bicarbonate & enzymes by the pancreas
3) bile by the liver
4) mucus by goblet cells
5) hormones: CCK, secretin, GIP, & other hormones

137

Small intestine digestion

Carbohydrates, fats, polypeptides, nucleic acids

138

Small intestine absorption

Peptides by active transport; amino acids, glucose, & fructose by secondary active transport; fats by simple diffusion; water by osmosis; ions, minerals, & vitamins by active transport

139

Large intestine secretion

Mucus by goblet cells

140

Large intestine digestion

None, except by bacteria

141

Large intestine absorption

Ions, water, minerals, vitamins, & small organic molecules produced by bacteria