Chapter 1. Digestion, absorption, transport and excretion of nutrients Flashcards
(126 cards)
1
Q
The gastrointestinal tract is designed to complete 3 main tasks, which? (others tasks exists as well)
A
- Digest protein, carbohydrates, and lipids from ingested foods and drink
- Absorb fluids, micronutrients, and trace elements.
- Provide a physical and immunological barrier to microorganisms, foreign material, and potential antigens from food
2
Q
Depending on the nature of the diet consumed, 90 to 97% of food is digested and absorbed, most of the unabsorbed material is of what origin?
A
Plant origin
3
Q
The Gastrointestinal tract extends from… to where?
A
The mouth to the anus
4
Q
What structures are included in the GIT?
A
Oropharyngeal structures, esophagus, stomach, liver and gallbladder, pancreas, and small and large intestine
5
Q
Which structure in the human body has the largest amount of immune cells, and is also one of the most metabolically active tissues in the body?
A
GIT
6
Q
Because of the unusually high metabolic activity and requirements of the GIT, the cells lining it are more susceptible than most tissues to….?
A
Micronutrient deficiencies; protein-energy malnutrition; and damage resulting from toxins, drugs, irradiation, or interruption of its blood supply.
7
Q
What senses can start the secretions and movements of the GIT?
A
Sight, smell, taste, even thought of food
8
Q
The movement of ingested and secreted material in the GIT is regulated primarily by…?
A
Peptide hormones, nerves, and enteric muscles
9
Q
What does the small intestine absorb?
A
Macronutrients, minerals, vitamins, trace elements, and fluid
10
Q
What does the colon absorb?
A
Electrolytes and small amount of remaining nutrients
11
Q
Most nutrients of the GIT enter the portal vein for transport to what organ?
A
The liver
12
Q
When nutrients are absorbed by the GIT and enter the liver, what does the liver do?
A
Stores it, or transforms it into another substance, or it releases it into circulation
13
Q
Some of the carbohydrate and fiber resistant to digestion in the upper GIT serve as “prebiotic” material by producing SCFAs, what does this do?
A
Decreasing the colonic pH, and increasing the mass of helpful bacteria
14
Q
Digestion of food is accomplished by?
A
Enzymatic hydrolysis
15
Q
Which cofactors facilitate the digestive and absorptive process?
A
Hydrochloric acid, bile, and sodium bicarbonate
16
Q
Digestion and absorption are essentially complated in the small intestine, except for which substances?
A
Fiber and some carbohydrates
17
Q
In people with GI disease (e.g. infections, inflammatory bowel disease, irritable bowel syndrome), the enteric nervous system may be overstimulated, resulting in…?
A
Abnormal secretion, altered blood flow, increased permability, and altered immune function
18
Q
Autonomic innervation is supplied by the symphatetic fibers that run along blood vessels and by the parasymphathetic fiber in which nerves?
A
Vagal and pelvic nerves
19
Q
In general, what activates symphatetic neurones?
A
Fear, anger and stress
20
Q
Which effect does the symphatetic neurones have on the GI contents?
A
Slows transit by Inhibiting secretions and muscle contraction
21
Q
In what way does vagal activity affect the GI tract?
A
Secretes acid from parietal cells scattered along the walls of the stomach
22
Q
Which kind of pains signals is translated by the vagal and spinal nerves from the GI tract?
A
Colicky pain, sharp pain, nausea, urgency or gastric fullness, or gastric emptiness
23
Q
What is Ghrelin?
A
A neuropeptide secreted from the stomach
24
Q
What is motilin?
A
Horomone secreted from the duodenum
25
What singal does Gherlin and motilin send to the brain?
"Hungry" message
26
Where is the site of the release of the neurotransmitter GABA?
CNS
27
Where is the site of release of the Norepinephrine?
CNS, spinal cord, symphatetic nerves
28
Where is the site of release of Acetylcholine?
CNS, autonomic system, other tissues
29
Where is the site of release of Neurotensin?
GI-tract, central nervous system
30
Where is the site of release of Serotonin?
GI-tract, spinal cord
31
Where is the site of release of Nitric oxide?
Central nervous system, GI tract
32
Where is the site of release of Substance P
Gut, CNS, GI tract
33
What is the primary function of GABA?
Relaxes lower esophagal sphincter
34
What is the primary action of Norepinephrine?
Decreases motility, increases contraction of sphincters, inhibits secretions
35
What is the primary action of Acetylcholine?
Increases motility, relaxes sphincters, stimulates secrection
36
What is the primary action of Neurotensin?
Inhibits release of gastric emptying and acid secretion
37
What is the primary action of Serotonin?
Facilitates secretion and peristalsis
38
What is the primary action of Nitric oxide?
Regulates blood flow, maintains muscle tone, maintains gastric motor activity
39
What is the primary action of Substance P
Increases sensroy awareness (Imainly pain) and peristalsis
40
What organ does Gastrin affect?
Stomach, esophagus, GIT in general
41
What organ does Secretin affect?
Pancreas, duodenum
42
What is the effect on the organs of gastrin?
Stimulates secretion of HCI and pepsinogen
Increases gastric antral motility
Increases lower esophagal sphincter tone
Weakly stimulates contraction of gallbladder
Weakly stimulates pancreatic secretion of bicarbonate
43
What organ does the hormone CCK affect?
Pancreas, Gallbladder, Stomach, Colon
44
What is the effect on the organs by CCK?
```
Stimulates secretion of pancreatic enzymes
Causes contraction of gallbladder
Slows gastric emptying
Increases motility
May mediate feeding behavior
```
45
What organ is affected by the hormone GIP?
Stomach pancreas
46
What is the effect of the GIP hormone on the organ?
Stimulates insulin release
47
What is the effect of GLP-1 hormone on the organ?
Prolongs gastric emptying.
Inhibits glucagon release.
Stimulates insulin release
48
What organ is affected by the hormone Motilin?
Stomach, small bowel, colon
49
What is the effect of Motilin on the organ?
Promotes gastric emptying and GI motility
50
What stimulates release of Gastrin?
Peptides, amino acids, caffeine
Distention of the antrum
Som alcoholic beverages
Vagus nerve
51
What stimulates the release of Secretin?
Acid in small intestine
52
What stimulates the release of CCK?
Peptides, amino acids, fats, HCI
53
What stimulates the release of GIP?
Glucose, fat
54
What stimulates the release of GLP-1
Glucose, fat
55
What stimulates the release of Motilin?
Biliary and pancreatic secretions
56
Small bowel mucosal "I" cells secrete what hormone?
Cholecystokinin (CCK)
57
Cholecystokinin is released in the prescence of which substances?
Protein and fat
58
What are the major functions of Cholecystokinin (CCK)?
1. Stimulate the pancreas to secrete enzymes, some bicarbonate, and water
2. Stimulate gallbladder contractions
3. Increase colonic and rectal motility
4. Slow gastric emptying
5. Increase satiety
59
What substances are released from the intestinal mucosa in the prescence of meals rich in glucose and fat, stimulating insulin synthesis and release?
GLP-1 and GIP
60
What are some of the functions of GLP-1?
Decreases glucagon secretion, delays gastric emptying, and may help promote satiety
61
GLP-1 and GIP are examples of of incretin hormones, which help keep....?
Blood glucose from rising excessively after a meal
62
What is the most probable reason why glucose load received enterally results in less of an increase in blood glucose than when an equal amount of glucose is received intravenously?
Because incretin hormones such as GLP-1 and GIP in the digestive tract prevents blood glucose from rising excessively after a meal
63
What hormone is released during fasting, where and why?
Motilin.
Endocrine cells in the duodenal mucosa.
To stimulate gastric emptying and intestinal motility
64
Somatostatin is released by what, and where?
D cells in the antrum and pylorus
65
What are Somatostatin's primary roles?
Inhibitory and antisecretory.
| It decreases motility of the stomach and intestine, and inhibits or regulates the release of several GI hormones
66
Somatostatin and its analog, octreotide are being used to treat certain malignant diseases, as well as numerous GI disorders such as...?
Diarrhea, Short bowel syndrome, pancreatis, dumping syndrome, and gastric hypersecretion
67
When eaten alone, which food nutrition leaves the stomach the most rapidly and which others follow?
1. Carbohydrates
2. Protein
3. Fat
4. Fiber
68
Bile salt insufficiency becomes clinically important in patients who have resections of the distal small bowel and diseases affecting the small intenstine, such as..?
Crohns disease
Radiation enteritis
Cystic fibrosis
69
Where in the digestive tract is vitamin B12 absorbed?
Distal ileum
70
Lipids are taken up and transported through the endoplasmic reticulum and Golgi apparatus where...?
Fatty acids are re-esterified to triglyceride
71
Triglycerides are packaged, along with other lipids, into chylomicrons, which are released into the?
Lymphatic circulation
72
Cholesterol absorption is facilitated by a..?
Protein transport system specific to cholesterol and not the other sterols
73
In absoprtion, nutrients pass through the intestinal mucosal cells (enterocytes or colonocytes) and make their way into the... to the...?
Venous system to the liver or into the lymphatic circulation
74
Random movment through openings in or between the membranes of the mucosal cell walls using channel proteins is known as what?
Passive diffusion
75
Random movment through openings in or between the membranes of the mucosal cell walls using carrier/transport proteins is known as what?
Facilitated diffusion
76
Some nutrients may share the same carrier and thus compete for absorption. Transport or carrier systems can also become saturated, leading to which effect?
Slowing the absorption of the nutrient
77
What is Pinocytosis?
The 'drinking in' or engulfing, by the epithelial cell membrane of small drop of intestinal content
78
What does Pinocytosis do?
Allows large particles such as whole proteins to be absorbed in small quantities
79
How can Pinocytosis cause allergic reactions?
By allowing movement of foreign proteins across the GIT into the bloodstream
80
The large intestine consists of them?
Cecum, colon, and rectum
81
What protects the intestinal wall of the large intestine from excoriation and bacterial activity and provides the medium for binding feces together?
Mucus secreted by the mucosa
82
The large intestine is 'also' the site of bacterial fermentation of remaining...?
Carbohydrates, amino acids, synthesis of small amount of vitamins, storage and excretion of fecal residues
83
Mouth-to-anus transit time may vary from?
18-72 hours
84
What organisms are the chief component of the GIT flora until an infant begins to eat solid foods?
Lactobacillus
85
Following Lactobacillus organisms being dominant during infancy what organisms becomes dominant after this in the distal ileum?
Escherichia coli and genus Bacteroides
86
Decreased gastric secretion can increase the risk of...?
Inflammation of the gastric mucosa (gastritis)
Increase the risk of bacterial overgrowth in the small intestine
Increase the numbers of microbes reaching the colon
87
Which acid-tolerant bacterium is known to infect the stomach and may cause gastritis and ulceration in the host?
Helicobacter pylori
88
Which part of the GIT is bacterial action most intense?
The large intestine
89
Colonic bacteria continue the digestion of some materials
that have resisted previous digestive activity. During the
process, several nutrients are formed by bacterial synthesis. What are some examples of these nutrients?
Vitamin K, vitamin B12, thiamin, and riboflavin
90
Increased consumption of prebiotic material may lead to what and which of the species are thought to be beneficial?
Increase in SCFAs and in the microbial mass, in particular, indigenous Bifidobacteria and Lactobacailli (both beneficial)
91
What are Prebiotics?
Oligosaccharide components of the diet that are preferred energy substrates of 'friendly' microbes in the GIT
92
What are Synbiotics?
A combination of probiotics and prebiotics
93
The disposal of residual substrates through production of SCFAs is called?
Colonic salvage
94
What is the function of SCFAs?
They serve as fuel for the coloncytes and gut microbes
Stimulates coloncyte proliferation and differentiation
Enhance the absorption of electrolytes and water
Reduce the osmotic load of malabsorbed sugars
95
The ability to salvage carbohydrates is limited in humans. Colonic fermentation normally disposes of how many grams of carbohydrates over 24 hours?
20-25 gram of carbohydrates
96
Excess amounts of carbohydrates and fermentable fiber in the colon can cause...?
```
Incerased gas production,
Abdominal distention
Bloating
Pain
Increased flatulence
Decreased colonic pH
Diarrhea
```
97
In the mouth, there is an enzyme which operates at a neutral or slightly alkaline pH and starts the digestive action by hydrolyzing a small amount of the starch molecules into smaller fragments. Which enzyme is this?
Salviary amylase (ptyalin)
98
When does Amylase deactivate?
After contact with hydrochloric acid
99
What is amylase?
An enzyme, found chiefly in saliva and pancreatic fluid, that converts starch and glycogen into simple sugars
100
Pancreatic amylase breaks the large starch molecules at 1-4 linkages to create...?
Maltose, maltotriose, and "alphalimit" dextrins
101
What are examples of monosaccharides?
Glucose, galactose, and fructose
102
The monosaccharides pass through the mucosal cells and into the bloodstream via the cappilaries of the vili, where they are carried by the potal vein to the...?
Liver
103
At low concentrations glucose and galactose are absorbed by active transport, primarily by a sodium-dependent transporter called the...?
Glucose (galactose) cotransporter
104
At high luminal concentrations of glucose or galactose which transporter becomes the primary facilitative transporter into the intestinal cell?
Glucose transporter 2 (GLUT 2)
105
Fructose is more slowly absorbed and uses which transporter from the lumen?
GLUT 5
106
What is the reason why sodium-glucose drinks are used to rehydrate infants with diarrhea or athletes who have lost too much fluid?
The sodium-dependent transport of monosaccharides
107
Glucose is transported from the liver to...?
The tissues, some of it is stored in the liver and others stored in muscles as glycogen
108
Consumption of large amounts of lactose (especially in individuals with a lactase deficiency), fructose, stachyose, raffinose, or alcohol sugars (e.g., sorbitol, mannitol, or xylitol) can result in considerable amounts of these sugars...?
Passing unabsorbed into the colon, and may cause increased gas and loose stool
109
Which sort of protein is more efficiently digested, plant proteins or animal proteins?
Animal proteins
110
Protein digestion begins in the stomach, where some of the proteins are split into...?
Proteoses, peptones, and large polypeptides
111
Inactive pepsinogen is converted into the enzyme..... when it contacts hydrochloric acid and other pepsin molecules
Pepsin
112
Unlike any of the other proteolytic enzymes, pepsin digests...?
Collagen, the major protein of connective tissue
113
Where does most of the digestion of protein take place?
Upper portion of the small intestine, but it continues throughout the GIT
114
What happens to any residual protein fractions which is not digested?
It is fermented by colonic microbes
115
Contact between chyme and the intestinal mucosa stimulates the release of?
Enterokinase
116
What is Enterokinase?
An enzyme that transforms inactive pancreatic trypsinogen into active trypsin, the major pancreatic protein-digesting enzyme. Trypsin in turn activates the other pancreatic protelytic enzymes.
117
Which enzymes break down intact protein and continue the breakdown started in the stomach until small polypeptides and amino acids are formed?
Pancreatic trypsin, chymotrypsin and carboxypeptidase
118
Proteolytic peptidase located on the brush border also act on polypeptides, breaking them down into?
Amino acids, dipeptides and tripeptides
119
The final phase of protein digestion takes place in the brush border, where some of the
dipeptides and tripeptides are hydrolyzed into their constituent amino acids by...?
Peptide hydrolase
120
End products of protein digestion are absorbed as both...?
Amino acids and small peptides
121
How much of the protein is absorbed by the time it reachs the jejunum and how many % is found in the feces?
Almost all, 1%
122
How many % of dietary lipids are in the form of Triglycerides, and phospholipids and cholesterol
97%, phospho and cholesterol remaining 3%
123
Most of the fat digestion takes place in the?
Small intestine
124
The entrance of fat and protein into the small intestine stimulates the release of? Which inhibit?
CCK and enterogastrone, which inhibit gastric secretions and motility, thus slowing the delivery of lipids
125
As a result of the release of CCK and enterogastrone, a portion of a large, fatty meal may remain in the stomach for how long?
4 hours or longer
126
Bile is a secretion from the?
Liver
