midterm one Flashcards
(153 cards)
1
Q
Page 4
What is nutrition?
A
How the body can use nutrients to obtain energy, to promote tissue growth, and/or to regulate function at the cell, tissue, and whole-body levels
2
Q
Page 4
What does nutrition encompass?
A
It encompasses:
* Food composition
* Ingestion
* Digestion
* Absorption
* Transport of nutrients
* Functions of nutrients
* Disposal of by-products of metabolism
3
Q
Page 4 - Body Diagram
Human Nutrition
A
- Supports brain function
- Growth and development
- Homeostatic regulation
- Repair and regeneration
- Provides energy
- Immune function regulation
4
Q
Page 4 - Composition of the Human Body
What are the most abdundant atoms?
A
- O2 (oxygen)
- C (carbon)
- H (hydrogen)
- N (nitrogen)
5
Q
Page 4 - Composition of the Human Body
How much do the abdundant atoms account for?
A
- Oxygen = 63%
- Carbon = 18%
- Hydrogen = 9%
- Nitrogen = 3%
6
Q
Page 4
Contribution to body mass
A
- Water = 55% to 65%
- Proteins + lipids = 30% to 40%
- Nucleic acids, carbohydrates, other organic molecules = about 1%
- Minerals = 5%
7
Q
Page 5 - Classes of Nutrients in Foods
Classes of nutrients found in foods, which are:
A
- carbohydrates
- lipids
- proteins
- vitamins
- minerals
- water
8
Q
Page 5 - Classes of Nutrients in Foods
Macronutrients
A
- Body needs large amounts of them
- Carbohydrates, proteins, fats
9
Q
Page 5 - Classes of Nutrients in Foods
Micronutrients
A
- Required in relatively small amounts
- Vitamins and minerals
10
Q
Page 5 - Classes of Nutrients in Foods
Classes of Nutrients
A
- Macronutrients
- Micronutrients
- Essential nutrients
- Non-essential nutrients
11
Q
Page 5 - Classes of Nutrients in Foods
What are essential nutrients?
A
Must be obtained through diet
12
Q
Page 5 - Classes of Nutrients in Foods
What are non-essential nutrients?
A
Fully provided by endogenous synthesis if not obtained from dietary sources
13
Q
Page 5 - Carbohydrates
What are carbohydrates made of?
A
- Carbon
- Hydrogen
- Oxygen
14
Q
Page 5 - Carbohydrates
What is the ratio of carbon to water?
A
Typically 1:1
15
Q
Page 5 - Carbohydrates
Carbohydrate “meaning”?
A
“Carbon with water”
16
Q
Page 5 - Carbohydrates
Carbohydrate function
A
Major source of fuel for the body
17
Q
Page 5 - Carbohydrates
Carbohydrate types
A
Starches and sugars
18
Q
Page 5 - Carbohydrates
Carbohydrate sources
A
Source:
* Grains
* Vegetables
* Legumes
* Fruits
Other sources:
* Dairy products (some), meat (very little)
19
Q
Page 5 - Carbohydrates
Dietary fibre
What is it? What is it important for?
A
- Also a carbohydrate, but it does not provide energy for cells
- Important for normal function of the GI tract
20
Q
Page 5
Carbohydrates & energy
A
- Most dietary carbohydrates -> glucose
- Glucose is taken in by cells and used either for energy production or storage as glycogen
21
Q
Page 5
Glucose in the body
Liver, skeletal muscle, brain
A
Skeletal muscle + liver:
* metabolize glucose to generate energy
* also store large amount of glucose as glycogen
Brain:
* relies on glucose for its energy needs
* depends on a steady supply from the circulation to function properly
22
Q
Page 6 - Lipids
Definition of lipids
A
By definition, lipids are compounds soluble in organic solvents such as acetone, ether, and chloroform
23
Q
Page 6 - Lipids
What do lipids refer to?
A
Refers to fats, oils, and other fatlike substances such as cholesterol and phospholipids that are found in food
24
Q
Page 6 - Lipids
(TG)
A
Triacylglycerols (TG) make up by far the largest proprotion of lipids consumed by humans
25
# Page 6 - Lipids
Specialized processing
* The non-water miscibility of lipids require these compounds to undergo specialized processing
* During: digestion, absorption, transport, storage, and utilization
26
# Page 6 - Lipids
Functions of lipids:
* Energy storage (adipose tissue) and release
* Insulation and padding of internal organs
* Cell signalling
* Cell membrane formation
* Synthesis of hormones
* Carriers of soluble vitamins (A,D,E,K)
27
# Page 6 - Essential Fatty Acids
What do humans not have?
Humans do not have ∆-12 and ∆-15 desaturases; therefore, 18-carbon ω-3 and ω-6 PUFAs are by nature essential fatty acids
28
# Page 6 - Essential Fatty Acids
True essential fatty acids for humans:
* Linoleic acid (18:2 ω-6)
* Linolenic acid (18:3 ω-3)
29
# Page 6 - Proteins
What are proteins?
Are organic compounds made of smaller building blocks called amino acids (aa)
30
# Page 6 - Proteins
What do proteins contain?
* Carbon, oxygen, hydrogen
* Protein also contains nitrogen (N) and sulfur (S)
31
# Page 6 - Proteins
Cell's weight
About half (50%) of the dry weight of a typical human cell is attributable to protein
32
# Page 6 - Proteins
Things made of proteins:
* Structural components and contractile filaments
* Antibodies
* Transporters
* Neurotransmitters and hormones
* Enzymes
33
# Page 7
Amino acids in nature
* ~140 aa exist in nature
* Only 20 are genetically coded via mRNA and used in proteins
34
# Page 7
Post-Translation Modification
* Human proteins can contain modified amino acids
* These modification occur after protein synthesis - "post-translation modification"
35
# Page 7
Essential amino acids
* Humans cannot synthesize 8-9 aa (at all or adequate amounts)
* Needed for body's need for growth and maintenance of tissues and organs
36
# Page 7
What are the essential amino acids?
* Lysine
* Tryptophan
* Methionine
* Valine
* Phenylalanine
* Leucine
* Isoleucine
* Threonine
* And for infants, histidine
37
# Page 7 - Minerals
What are minerals?
Inorganic substances that are essential to health
38
# Page 7 - Minerals
Macrominerals
| Definition and examples
* Needed in relatively large amounts
* Calcium, sodium, chloride, potassium, phosphorus, magnesium
39
# Page 7 - Minerals
Micro or trace minerals
* Needed in small amounts
* Iron, zinc, copper, selenium, iodine, fluoride
40
# Page 8 - Vitamins
Vitamins
| Definition and history
* Organic compounds that contain carbon, hydrogen, and perhaps nitrogen, oxygen, phosphorus, sulfur, and other elements
* Originally called vital amines (nitrogen containing), but later changed to vitamins as not all contain nitrogen
41
# Page 8 - Vitamins
Types of vitamins:
* Water-soluble vitamins
* Fat-soluble vitamins
42
# Page 8 - Vitamins
How does a substance gain the status of a vitamin?
It must be organic and play an essential role in at least one necessary chemical reaction of process in the human body
43
# Page 8 - Vitamins
Vitamins - substance and required in?
Vitamins are non-caloric and are required in very small amounts
44
# Page 8 - Vitamins
Vitamin production
* A vitamin cannot be made in the human body, either at all or in sufficient quantities to meet the body's needs
* Exceptions to this rule exist
45
# Page 8 - Vitamins
Exceptions - vitamins produced in the body
| Examples
* Vitamin D
* Vitamin K and biotin (made by bacteria in the large intestine)
46
# Page 8 - H2O
Water
* Chemically, water is the simplest nutrient
* Argued most important nutrient
* Essential for survival -> can survive far longer with other nutrients than without water
47
# Page 9
Estimated body fluid compartments
* Intracellular volume (localized inside cell) - 60%
* Extracellular volume (localized outside cell) - 40%
48
# Page 9
Estimated body fluid compartments - extracellular compartment divisions
* Interstitial volume - 28% of total
* Plasma volume - 8% of total
* Transcellular volume - 4% of total
49
# Page 9 - The Digestive System
Overview
* Mouth
* Oesophagus
* Stomach
* Small intestine
* Large intestine
50
# Page 9 - The Digestive System
Overview - mouth
| Contents?
Mouth:
* Tongue / salivary glands (parotid, submandibular, sublingual)
51
# Page 9 - The Digestive System
Overview - Oesophagus
| Length?
25 cm
52
# Page 9 - The Digestive System
Overview - Stomach
| Contents? Length?
* Fundus/body/antrum (25 cm)
* Oxyntic glands (HCl secretion)
53
# Page 9 - The Digestive System
Overview - small intestine
| Parts and lengths?
* Duodenum (30 cm)
* Jejunum and ileum (2.75 m)
54
# Page 9 - The Digestive System
Overview - large intestine
| Parts and length?
* Cecum/colon/rectum/anal canal
* 1.5-1.8 m
55
# Page 9 - The Digestive System
Accessory organs
| What are they?
* Liver
* Gallbladder
* Pancreas
56
# Page 9 - Mouth
Mouth - functions in digestion
* Mechanical breakdown of food and action of amylase and lingual lipase
* Limited amount of time little digestion occurs
* Lubricates and mixes food bolus
* Sets the conditions for digestion in the stomach and intestine
57
# Page 10 - Stomach
What does the stomach grind food into?
Grinds food -> chyme
58
# Page 10 - Stomach
What does the stomach release in response to gastrin?
In response to gastrin, the stomach releases gastric juice containing HCl and pepsins
59
# Page 10 - Stomach
What is acidification of the stomach important for?
* Enzyme activation (pepsin and lipase)
* Destruction of potentially harmful bacteria
60
# Page 10 - Stomach
What is the stomach protected by?
The stomach is protected by a highly alkaline mucus that resists the actions of enzymes and acids
61
# Page 10 - Stomach
What allows the stomach to hold food?
The distensibility of the stomach allows it to hold a maximum of 4 L of food
62
# Page 10 - Stomach
Stomach - releases into, how, and how much?
* The stomach progressively releases small portion of chyme through the pyloric sphincter that opens into the duodenum
* This occurs through peristaltic waves
* Each of these waves pumps 1 to 3 mL of chyme into the duodenum
63
# Page 11
What is secretion of HCl stimulated by?
| Where do these receptors act at?
Secretion of HCl is stimulated by three factors:
* Acetylcholine
* Histamine
* Gastrin
Acting at specific receptors on the oxyntic cells
64
# Page 11
When is maximal acid production achieved?
Maximal acid production is only achieved when all three signals are present
65
# Page 11
What is the pH of the stomach?
pH of the stomach: ranges between 1.5-2.5
66
# Page 11
What is acetylcholine released by?
Acetylcholine is released by the parasympathetic nervous system (vagus nerve)
67
# Page 11
What does stomach distension lead to?
Stomach distension - stretch receptors - brain - vagus nerve - **enhance** acid secretion
68
# Page 11
What do stomach enteroendocrine cells release?
Stomach enteroendocrine cells release
69
# Page 11
How does histamine act?
Histamine acts locally through H2-receptors, on nearby cells (paracrine manner)
70
# Page 11
Gastrin
| Released by? Acts on?
* Gastrin is released by enteroendorcine cells (gastric pits of pyloric region)
* Acts directly on oxyntic cells to stimulate acid secretion
71
# Page 11
Gastric acids
| Reduce? Important for?
* Gastric acids reduce ferric to ferrous salts
* Is important for the absorption of non-heme iron
72
# Page 11
What do oxyntic cells produce?
Oxyntic cells of the stomach produce **intrinsic factor** - a mucoprotein important for the absorption of vitamin B12
73
# Page 12
Gastric acid secretion
| In fasting versus in presence of food?
In between meals or fasting, gastric acid is secreted
74
# Page 12
Gastric secretion phases:
Gastric secretion occurs in three phases:
* Cephalic
* Gastric
* Intestinal
75
# Page 12
Gastric secretion - cephalic
| Triggered by? Accounts for?
* Triggered by smell, taste, and/or thought of food
* Accounts for 30% of acid secretion
76
# Page 12
Gastric secretion - gastric
| Triggered by? Accounts for?
* Triggered by stomach distension and by amino acids and peptides activating chemoreceptors
* Accounts for 60% of acid secretion
77
# Page 12
Gastric secretion - intestinal
| Triggered by? Accounts for?
* Triggered by distension of the small intestine and by the presence of proteins and products of protein digestion
* Accounts for 10% of acid secretion
78
# Page 12 - Small Intestine
Small intestine
| Primary functions
* Location where most digestion and absorption of nutrients occur
* Chyme from the stomach is mixed with pancreatic secretions
* More than 90% of the ingested carbohydrate, fat, and protein are absorbed in the small intestine
79
# Page 12 - Small Intestine
What do goblet cells produce?
| What is the function of this?
Goblet cells produce a glycoprotein-rich fluid (mucous) that protects the small intestine from the acidic chyme
80
# Page 12 - Small Intestine
Surface area adaptions
* Encompasses the area the size of a tennis court
* Folded (wrinkled) interior surface = triple the surface area
* Villi (finger-like projections) = increase surface area by 10x
* Microvilli = increase surface area by 20x
81
# Page 13 - Enterocytes
Enterocytes
| How often are they renewed?
Layer of cells that is renewed every 3 to 5 days
82
# Page 13 - Enterocytes
crypts of Lieberkuhn
* Epithelial cells located between the villi
* Continuously udnergo mitosis
83
# Page 13 - Enterocytes
Functions of enterocytes
* Nutrient absorption
* Provide a barrier that prevents bacteria from entering the bloodstream or the lymphatic system
84
# Page 13 - Enterocytes
Brush border enzymes
* Enterocytes contain a brush border
* Where digestive enzymes are mostly found
85
# Page 14 - Accessory Organs
Liver
| What does it produce?
Liver - produces bile
86
# Page 14 - Accessory Organs
Bile
| What is it? What is it composed of?
* A greenish-yellowish alkaline (pH ~7.6 to 8.6)
* Composed essentially of bile acids, salts, cholesterol, phospholipids, and pigments (bilirubin and biliverdin, which are waste products of hemoglobin degradation)
87
# Page 14
What makes up 80% of the body's total bile acids?
Chenodeoxycholic and cholic acids
88
# Page 14
Bile acid conjugation
| Bile acids conjugate with amino acids to form different bile acids
* Bile acids conjugate with either the amino acid glycine to produce glycocheno-deoxycholic and glycocholic acids
* Or with taurine to form taurocholic, taurodeoxycholic and taurochenodeoxycholic acids
89
# Page 14
Bile salts
Sodium and potassium salts of these conjugated bile acids are called bile salts
90
# Page 15 - Bile Acids/Salts
Bile Acids/Salts
| What are they?
Detergents that emulsify large fat globules by fractioning them into small lipid droplets
91
# Page 15 - Bile Acids/Salts
Bile Acids/Salts
| Also serve to?
* Also serves to eliminate substances that cannot be excreted through the urine
* Example: bilirubin - it binds to albumin in the circulation, but it is excreted in the feces when released into the duodenum
92
# Page 15 - Gallbladder
Gallbladder functions
* Concentrates bile during inter-digestive periods
* Releases bile into the small intestine in response to CCK
93
# Page 15 - Gallbladder
Release of CCK
| Released by? Stimulated when?
* Released by enteroendocrine cells (I-cells) in the duodenum
* Stimulated when acidic chyme enters the duodenum
94
# Page 15 - Gallstones
When are gallstones formed?
Formed when bile becomes supersaturated with cholesterol
95
# Page 15 - Gallstones
Gallstone formation
* Cholesterol precipitates and provides a cystalline-like structure
* Calcium, bilirubin, phospholipids, and other compounds deposit to form a "stone"
96
# Page 15 - Gallstones
Gallstone complications
* Causes inflammation in the gallbladder
* May also block flow of bile (choledocholithiasis) into the duodenum
* Clog the pancreatic duct, and cause pancreatitis
97
# Page 16 - Pancreas
Pancreas
| Function? What does it contain?
* Releases pancreatic juice
* Containing bicarbonate, electrolytes, and digestive enzymes
98
# Page 16 - Pancreas
Pancreatic secretion regulation
* Secretin, CCK, neuropeptide substance P and vasoactive intestinal polypeptide (VIP) stimulate pancreatic exocrine secretions
* These are present in neurons within the gut
99
# Page 16 - Enzymes in the pancreatic juice
Enzymes in the pancreatic juice
* Trypsinogen, chymotrypsinogen, prolastase, and collagenase (proteases)
* α-amylase (for CHO digestion)
* Pancreatic lipase (the main fat-digesting enzyme) and co-lipase
100
# Page 16 - Enzymes in the pancreatic juice
What do these enzymes digest?
| Percentages
Together, these enzymes digest:
* ~50% of all CHO and protein
* 80 to 90% of the fat ingested
101
# Page 17 - Large Intestine
What does this structure lack?
Lack villi
102
# Page 17 - Large Intestine
Primary function?
Primary function:
* To absorb water and electrolytes (5 to 7 L of fluid per day)
* Store fecal matter
103
# Page 17 - Large Intestine
Essentially ...
Dries and stores the undigested material present in the chyme
104
# Page 17 - Composition of the feces
Composition of the feces
* 30% bacteria
* 10 to 20% fat
* 10% inorganic matter
* 2 to 3% protein
* 30% undigested fibers and dried components of digested juices
105
# Page 17
Bacteria in the digestive tract
| Number? Live in?
* There are trillions of bacteria living in the digestive tract
* Most of them in the colon
106
# Page 17
How much bacteria does the large intestine house?
More than 400 different species
107
# Page 17
What can the bacteria in the large intestine produce
* Vitamin K (anti hemorrhagic)
* Biotin (co-enzyme for carboylase reactions)
* Short-chain fatty acids (acetic, propionic, butyric acids)
108
# Page 17
Probiotics
* "For life"
* Bacteria that promote health
109
# Page 17
Probiotics
| Available in what?
Available in foods such as dairy, soy, yogurt, and dietary supplements
110
# Page 17
Prebiotics
Food components that support the growth and activity of bacteria
111
# Page 17
Prebiotics
| Available in what?
Fiber
112
# Page 18 - Carbohydrate digestion and absorption
The term carbohydrate encompasses:
* Monosaccharides (simple sugars)
* Disaccharides (2 monosaccharide units)
* Oligosaccharides (3-10 monosaccharide units)
* Polysaccharides (>10 monosaccharide units)
113
# Page 18
Not hydrolyzed by human digestive enzymes
* Stachyose
* Raffinose
* Verbacose
114
# Page 19
Rich in both amylose and amylopectin
Cereal grains, potatoes, legumes, and other vegetables
115
# Page 19
Contribution of amylopectin and amylose to the total starch content
80 to 85% and 15 to 20% respectively
116
# Page 20
Cellulose
| What is it? Found in?
* Cellulose is also a polysaccharide of glucose
* Found as a major component of cell walls in plants
117
# Page 20
What is cellulose resistant to? Why?
* This molecule is resistant to human digestive enzymes
* The glycosidic bonds that link the glucose are β(1-4) instead of the α(1-4) found in starch
118
# Page 20 - Digestion of Carbohydrates
What enzymes hydrolyse carbohydrates
Enzymes named **glycosidases** or **carbohydrases** hydrolyse carbohydrates
119
# Page 20 - Digestion of Carbohydrates
Where does most digestion of polysaccharides takes place?
Most digestion of polysaccharides takes place later on as chyme reaches the small intestine
120
# Page 20 - Digestion of Carbohydrates
In the duodenum, pH is elevated by? Why?
* pH is elevated by bicarbonate
* To a level that optimizes pancreatic α-amylase activity allowing polysaccharides in the chyme to be digested in a stepwise fashion
121
α-limit dextrinase (glucoamylase)
| Removes? Produces?
Removes a single glucose unit from the ends of linear α(1-4)-glucosyl chains of dextrins and produces isomaltose (dissacharide with one unit attached by a α(1-6) glycosydic bond)
122
α(1-6)-glucosidase
| Location? Hydrolyzes?
* Located in the brush border
* Hydrolyzes α(1-6) bonds
123
Disaccharides
| Split into?
* Lactase, sucrase, isomaltase, and trehalase located within the microvilli
* Hydrolyzes disaccharides
124
# Textbook (or page 21 diagram)
Main monosaccharide transporters in small intestine:
* Sodium glucose transporter 1 (SGLT 1)
* Glucose transporter 2 (GLUT2)
* Glucose transporter 5 (GLUT5)
125
# Textbook (or page 21 diagram)
SGLT1
| Located? Binding sites? Transports?
* Active transporter in the apical membrane
* Has two binding sites (one for Na and another for glucose and galactose)
* Simultenously transports Na and either glucose or galactose in same direction
* Called a symporter
126
# Textbook (or page 21 diagram)
GLUT2 (a facilitated transporter)
| Moves?
* Moves glucose from the intestinal lumen into enterocytes
* Glucose, galactose, and fructose from the enterocyte into the blood stream
127
# Textbook (or page 21 diagram)
GLUT5
| Type of transporter? Location? Affinity for?
* Facilitated transporter
* Located on the apical membrane of enterocytes
* High affinity for fructose
128
# Page 21 - brain metabolism
Adult human brain
| Weight? Cell make up?
* The adult human brain weighs ~1.5 kg
* Estimated that ~100 billion neurons and 900 billion glial cells make up the organ
129
# Page 21 - brain metabolism
Blood supply to brain versus skeletal muscle
* Blood supply to the brain ~750 ml/min or 50 ml of blood/min/100g
* 2-5 ml/min/100g or 50 ml/min/100g for skeletal muscle under resting and vigorous exercise conditions, respectively
130
# Page 21 - brain metabolism
How does the brain maintain its high metabolic rate?
The brain oxidizes 120g of glucose/day or 20% of whole-body energy consumption in a typical day
131
# Page 22
Blood-brain barrier (BBB)
| Prevents? Relies on?
* Prevents the access of lipid soluble molecules to the brain
* Essentially relies on glucose for its energy supply
132
# Page 22
Glucose metabolism in the brain
* Glucose is mostly oxidized, with only small portion of lactate released
* Brain has a high rate of oxygen consumption and CO2 production
133
# Page 22
How does the brain adapt under prolonged starvation?
Adapts to use ketones
134
# Page 22
Glucose transport in the brain
* GLUT3 (neurons) and GLUT1 (BBB) transport glucose into brain
* Insulin is not required for these transporters
135
# Page 22
Glucose uptake and glycemia
* GLUT3 & GLUT1 are saturated at normal blood glucose levels
* Wide variations in glycemia have little effect on brain glucose uptake
* Mental function is impaired if blood glucose drops below ~2 mmol/L.
136
# Page 23 - Glycemic Index (GI)
Represents?
The degree and duration that a particular food increases glycemia
137
# Page 23 - Glycemic Index (GI)
Determined by calculating?
The area under the curve for blood glucose during the 2 hour period subsequent to the ingestion of a particular type of food that provides 50 g of digestible (available) carbohydrate
138
# Page 23 - Glycemic Load (GL)
What is it?
GI normalized to serving standards
139
# Page 24 - The Gut Microbata
Microbiota
| Definition?
The assemblage of microbes living in a habitat is referred to as microbiota
140
# Page 24 - The Gut Microbata
Microbes in and on human body comprise?
The microbes in and on the average adult human body comprise 1-3% of body mass
141
# Page 24 - The Gut Microbata
Ratio of bacterial cells to human cells
Estimated to be around 1.3 to 1
142
# Page 24
Site of breakdown of materials that escape digestion (dietary fiber, resistant starches, and non-carbohydrate substrates)
Colon
143
# Page 24
Short-Chain Fatty Acids
* Products of fermentation: acetate, propionate, butyrate
* 95% of SCFAs are used by colonic cells as energy
* Provide ~10% of total daily calories for the host
144
# Page 24
SCFAs and immune function
* Serve as messengers between the microbiota and the immune system
* Play a role in the development and function of intestinal epithelial cells and leukocytes
145
# Page 24
Bacterial vitamin production
* Bacteria in the colon also produce B vitamins (thiamine, riboflavin, niacin, biotin, pantothenic acid, and folate) and vitamin K
146
# Page 24
Vitamin absorption
* Vitamins originating from the diet are absorbed in the small intestine
* Microbe-produced vitamins are absorbed in the colon
147
# Page 24 - Dietary Fiber
Dietary fiber
| Definition
Dietary fiber - non-digestible carbohydrates and lignin that are intrinsic and intact in plants
148
# Page 24 - Dietary Fiber
Functional fiber
| Definition
Isolated, non-digestable carbohydrates, extracted, or manufactured that have beneficial effects to humans
149
# Page 24 - Dietary Fiber
The sum of dietary and functional fibers encompass?
The sum of dietary and functional fibers encompasses the total amount of fiber consumed by an individual
150
# Page 25
Soluble fiber
* Pectin
* Gums
* Mucilages
* (Fruits, legumes, oats, and some vegetables)
151
# Page 25
Insoluble fiber
* Cellulose
* Hemicellulose
* Lignin
* (Cereals, grains, nuts, seeds, corn bran, and some vegetables and fruits)
152
# Page 25
Effects of fiber on nutrient digestion and absorption
* Delays stomach emptying and alters small intestine transit time
* ↓ mixing of GI contents with digestive enzymes
* ↓ digestive enzyme function
* ↓ nutrient diffusion
* ↓ glycemic response to food
* ↓ absorption of lipids
* ↑ bile acid excretion and ↓ cholesterolemia
153
# Page 25
Effects of SCFAs on the GI tract
* Stimulate H2O and Na absorption into the mucosal cells of the colon
* Promote differentiation and proliferation of mucosal cells of the colon
* ↓ pH that reduce bile solubility and increase Ca+ binding to bile and fatty acids. May exert a protective effect against colon cancer
* Provide energy for colonic cells
* Inhibit hepatic cholesterol synthesis
* Enhance colonic blood dlow
* Enhance immune function and prevent the growth of potentially harmful cells
