midterm one Flashcards
Page 4
What is nutrition?
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
Page 4
What does nutrition encompass?
It encompasses:
* Food composition
* Ingestion
* Digestion
* Absorption
* Transport of nutrients
* Functions of nutrients
* Disposal of by-products of metabolism
Page 4 - Body Diagram
Human Nutrition
- Supports brain function
- Growth and development
- Homeostatic regulation
- Repair and regeneration
- Provides energy
- Immune function regulation
Page 4 - Composition of the Human Body
What are the most abdundant atoms?
- O2 (oxygen)
- C (carbon)
- H (hydrogen)
- N (nitrogen)
Page 4 - Composition of the Human Body
How much do the abdundant atoms account for?
- Oxygen = 63%
- Carbon = 18%
- Hydrogen = 9%
- Nitrogen = 3%
Page 4
Contribution to body mass
- Water = 55% to 65%
- Proteins + lipids = 30% to 40%
- Nucleic acids, carbohydrates, other organic molecules = about 1%
- Minerals = 5%
Page 5 - Classes of Nutrients in Foods
Classes of nutrients found in foods, which are:
- carbohydrates
- lipids
- proteins
- vitamins
- minerals
- water
Page 5 - Classes of Nutrients in Foods
Macronutrients
- Body needs large amounts of them
- Carbohydrates, proteins, fats
Page 5 - Classes of Nutrients in Foods
Micronutrients
- Required in relatively small amounts
- Vitamins and minerals
Page 5 - Classes of Nutrients in Foods
Classes of Nutrients
- Macronutrients
- Micronutrients
- Essential nutrients
- Non-essential nutrients
Page 5 - Classes of Nutrients in Foods
What are essential nutrients?
Must be obtained through diet
Page 5 - Classes of Nutrients in Foods
What are non-essential nutrients?
Fully provided by endogenous synthesis if not obtained from dietary sources
Page 5 - Carbohydrates
What are carbohydrates made of?
- Carbon
- Hydrogen
- Oxygen
Page 5 - Carbohydrates
What is the ratio of carbon to water?
Typically 1:1
Page 5 - Carbohydrates
Carbohydrate “meaning”?
“Carbon with water”
Page 5 - Carbohydrates
Carbohydrate function
Major source of fuel for the body
Page 5 - Carbohydrates
Carbohydrate types
Starches and sugars
Page 5 - Carbohydrates
Carbohydrate sources
Source:
* Grains
* Vegetables
* Legumes
* Fruits
Other sources:
* Dairy products (some), meat (very little)
Page 5 - Carbohydrates
Dietary fibre
What is it? What is it important for?
- Also a carbohydrate, but it does not provide energy for cells
- Important for normal function of the GI tract
Page 5
Carbohydrates & energy
- Most dietary carbohydrates -> glucose
- Glucose is taken in by cells and used either for energy production or storage as glycogen
Page 5
Glucose in the body
Liver, skeletal muscle, brain
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
Page 6 - Lipids
Definition of lipids
By definition, lipids are compounds soluble in organic solvents such as acetone, ether, and chloroform
Page 6 - Lipids
What do lipids refer to?
Refers to fats, oils, and other fatlike substances such as cholesterol and phospholipids that are found in food
Page 6 - Lipids
(TG)
Triacylglycerols (TG) make up by far the largest proprotion of lipids consumed by humans
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
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)
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
Page 6 - Essential Fatty Acids
True essential fatty acids for humans:
- Linoleic acid (18:2 ω-6)
- Linolenic acid (18:3 ω-3)
Page 6 - Proteins
What are proteins?
Are organic compounds made of smaller building blocks called amino acids (aa)
Page 6 - Proteins
What do proteins contain?
- Carbon, oxygen, hydrogen
- Protein also contains nitrogen (N) and sulfur (S)
Page 6 - Proteins
Cell’s weight
About half (50%) of the dry weight of a typical human cell is attributable to protein
Page 6 - Proteins
Things made of proteins:
- Structural components and contractile filaments
- Antibodies
- Transporters
- Neurotransmitters and hormones
- Enzymes
Page 7
Amino acids in nature
- ~140 aa exist in nature
- Only 20 are genetically coded via mRNA and used in proteins
Page 7
Post-Translation Modification
- Human proteins can contain modified amino acids
- These modification occur after protein synthesis - “post-translation modification”
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
Page 7
What are the essential amino acids?
- Lysine
- Tryptophan
- Methionine
- Valine
- Phenylalanine
- Leucine
- Isoleucine
- Threonine
- And for infants, histidine
Page 7 - Minerals
What are minerals?
Inorganic substances that are essential to health
Page 7 - Minerals
Macrominerals
Definition and examples
- Needed in relatively large amounts
- Calcium, sodium, chloride, potassium, phosphorus, magnesium
Page 7 - Minerals
Micro or trace minerals
- Needed in small amounts
- Iron, zinc, copper, selenium, iodine, fluoride
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
Page 8 - Vitamins
Types of vitamins:
- Water-soluble vitamins
- Fat-soluble vitamins
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
Page 8 - Vitamins
Vitamins - substance and required in?
Vitamins are non-caloric and are required in very small amounts
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
Page 8 - Vitamins
Exceptions - vitamins produced in the body
Examples
- Vitamin D
- Vitamin K and biotin (made by bacteria in the large intestine)
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
Page 9
Estimated body fluid compartments
- Intracellular volume (localized inside cell) - 60%
- Extracellular volume (localized outside cell) - 40%
Page 9
Estimated body fluid compartments - extracellular compartment divisions
- Interstitial volume - 28% of total
- Plasma volume - 8% of total
- Transcellular volume - 4% of total
Page 9 - The Digestive System
Overview
- Mouth
- Oesophagus
- Stomach
- Small intestine
- Large intestine
Page 9 - The Digestive System
Overview - mouth
Contents?
Mouth:
* Tongue / salivary glands (parotid, submandibular, sublingual)
Page 9 - The Digestive System
Overview - Oesophagus
Length?
25 cm
Page 9 - The Digestive System
Overview - Stomach
Contents? Length?
- Fundus/body/antrum (25 cm)
- Oxyntic glands (HCl secretion)
Page 9 - The Digestive System
Overview - small intestine
Parts and lengths?
- Duodenum (30 cm)
- Jejunum and ileum (2.75 m)
Page 9 - The Digestive System
Overview - large intestine
Parts and length?
- Cecum/colon/rectum/anal canal
- 1.5-1.8 m
Page 9 - The Digestive System
Accessory organs
What are they?
- Liver
- Gallbladder
- Pancreas
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
Page 10 - Stomach
What does the stomach grind food into?
Grinds food -> chyme
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
Page 10 - Stomach
What is acidification of the stomach important for?
- Enzyme activation (pepsin and lipase)
- Destruction of potentially harmful bacteria
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
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
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
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
Page 11
When is maximal acid production achieved?
Maximal acid production is only achieved when all three signals are present
Page 11
What is the pH of the stomach?
pH of the stomach: ranges between 1.5-2.5
Page 11
What is acetylcholine released by?
Acetylcholine is released by the parasympathetic nervous system (vagus nerve)
Page 11
What does stomach distension lead to?
Stomach distension - stretch receptors - brain - vagus nerve - enhance acid secretion
Page 11
What do stomach enteroendocrine cells release?
Stomach enteroendocrine cells release
Page 11
How does histamine act?
Histamine acts locally through H2-receptors, on nearby cells (paracrine manner)
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
Page 11
Gastric acids
Reduce? Important for?
- Gastric acids reduce ferric to ferrous salts
- Is important for the absorption of non-heme iron
Page 11
What do oxyntic cells produce?
Oxyntic cells of the stomach produce intrinsic factor - a mucoprotein important for the absorption of vitamin B12
Page 12
Gastric acid secretion
In fasting versus in presence of food?
In between meals or fasting, gastric acid is secreted
Page 12
Gastric secretion phases:
Gastric secretion occurs in three phases:
* Cephalic
* Gastric
* Intestinal
Page 12
Gastric secretion - cephalic
Triggered by? Accounts for?
- Triggered by smell, taste, and/or thought of food
- Accounts for 30% of acid secretion
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
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
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
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
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
Page 13 - Enterocytes
Enterocytes
How often are they renewed?
Layer of cells that is renewed every 3 to 5 days
Page 13 - Enterocytes
crypts of Lieberkuhn
- Epithelial cells located between the villi
- Continuously udnergo mitosis
Page 13 - Enterocytes
Functions of enterocytes
- Nutrient absorption
- Provide a barrier that prevents bacteria from entering the bloodstream or the lymphatic system
Page 13 - Enterocytes
Brush border enzymes
- Enterocytes contain a brush border
- Where digestive enzymes are mostly found
Page 14 - Accessory Organs
Liver
What does it produce?
Liver - produces bile
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)
Page 14
What makes up 80% of the body’s total bile acids?
Chenodeoxycholic and cholic acids
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
Page 14
Bile salts
Sodium and potassium salts of these conjugated bile acids are called bile salts
Page 15 - Bile Acids/Salts
Bile Acids/Salts
What are they?
Detergents that emulsify large fat globules by fractioning them into small lipid droplets
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
Page 15 - Gallbladder
Gallbladder functions
- Concentrates bile during inter-digestive periods
- Releases bile into the small intestine in response to CCK
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
Page 15 - Gallstones
When are gallstones formed?
Formed when bile becomes supersaturated with cholesterol
Page 15 - Gallstones
Gallstone formation
- Cholesterol precipitates and provides a cystalline-like structure
- Calcium, bilirubin, phospholipids, and other compounds deposit to form a “stone”
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
Page 16 - Pancreas
Pancreas
Function? What does it contain?
- Releases pancreatic juice
- Containing bicarbonate, electrolytes, and digestive enzymes
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
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
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
Page 17 - Large Intestine
What does this structure lack?
Lack villi
Page 17 - Large Intestine
Primary function?
Primary function:
* To absorb water and electrolytes (5 to 7 L of fluid per day)
* Store fecal matter
Page 17 - Large Intestine
Essentially …
Dries and stores the undigested material present in the chyme
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
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
Page 17
How much bacteria does the large intestine house?
More than 400 different species
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)
Page 17
Probiotics
- “For life”
- Bacteria that promote health
Page 17
Probiotics
Available in what?
Available in foods such as dairy, soy, yogurt, and dietary supplements
Page 17
Prebiotics
Food components that support the growth and activity of bacteria
Page 17
Prebiotics
Available in what?
Fiber
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)
Page 18
Not hydrolyzed by human digestive enzymes
- Stachyose
- Raffinose
- Verbacose
Page 19
Rich in both amylose and amylopectin
Cereal grains, potatoes, legumes, and other vegetables
Page 19
Contribution of amylopectin and amylose to the total starch content
80 to 85% and 15 to 20% respectively
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
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
Page 20 - Digestion of Carbohydrates
What enzymes hydrolyse carbohydrates
Enzymes named glycosidases or carbohydrases hydrolyse carbohydrates
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
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
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)
α(1-6)-glucosidase
Location? Hydrolyzes?
- Located in the brush border
- Hydrolyzes α(1-6) bonds
Disaccharides
Split into?
- Lactase, sucrase, isomaltase, and trehalase located within the microvilli
- Hydrolyzes disaccharides
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)
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
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
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
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
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
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
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
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
Page 22
How does the brain adapt under prolonged starvation?
Adapts to use ketones
Page 22
Glucose transport in the brain
- GLUT3 (neurons) and GLUT1 (BBB) transport glucose into brain
- Insulin is not required for these transporters
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.
Page 23 - Glycemic Index (GI)
Represents?
The degree and duration that a particular food increases glycemia
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
Page 23 - Glycemic Load (GL)
What is it?
GI normalized to serving standards
Page 24 - The Gut Microbata
Microbiota
Definition?
The assemblage of microbes living in a habitat is referred to as microbiota
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
Page 24 - The Gut Microbata
Ratio of bacterial cells to human cells
Estimated to be around 1.3 to 1
Page 24
Site of breakdown of materials that escape digestion (dietary fiber, resistant starches, and non-carbohydrate substrates)
Colon
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
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
Page 24
Bacterial vitamin production
- Bacteria in the colon also produce B vitamins (thiamine, riboflavin, niacin, biotin, pantothenic acid, and folate) and vitamin K
Page 24
Vitamin absorption
- Vitamins originating from the diet are absorbed in the small intestine
- Microbe-produced vitamins are absorbed in the colon
Page 24 - Dietary Fiber
Dietary fiber
Definition
Dietary fiber - non-digestible carbohydrates and lignin that are intrinsic and intact in plants
Page 24 - Dietary Fiber
Functional fiber
Definition
Isolated, non-digestable carbohydrates, extracted, or manufactured that have beneficial effects to humans
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
Page 25
Soluble fiber
- Pectin
- Gums
- Mucilages
- (Fruits, legumes, oats, and some vegetables)
Page 25
Insoluble fiber
- Cellulose
- Hemicellulose
- Lignin
- (Cereals, grains, nuts, seeds, corn bran, and some vegetables and fruits)
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
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
