HUN1201 Nutrition Lecture Notes
Digestion, Absorption, & Metabolism
Digestion, Absorption, Metabolism – Chapter 3
Role in Wellness
• Growth, maintenance, & energy needs depend on the nutrients available.
• The digestive system relies on nutrient intake for its maintenance.
• Processes of digestion, absorption, & metabolism work together to provide all body
cells with energy and nutrients.
The Human Body: Role of Nutrition- Food: Change & Transformation
Through a successive interrelated system, foods are transformed into simple substances
that can be absorbed into the body & enter the metabolic pathways in the cell.
Importance for Health & Nutrition
• Food as it occurs naturally is a mixture of chemical substances & nutrients.
• Nutrients released from food remain unavailable to the body until they cross the
intestinal wall & are transported to tissues for storage or immediate use.
• Disease & malnutrition impair absorption of nutrients
• Internal control for maintaining a constant chemical environment is called
homeostasis.
Digestion & Absorption
• Biochemically, “You are what you eat” is scientifically true!
• Food & fluid taken into the body is broken down into smaller components so it
can be used by the body
GI Tract- Long hollow tube that begins at the mouth & ends at the anus.
Component Parts
• Mouth
• Esophagus
• Stomach
• Small intestine
• Large intestine
Organs that lie outside the tract:
• Pancreas
• Gallbladder
• Liver
4 Major functions in digestion & absorption:
1. Receives food.
2. Releases nutrients from food.
3. Delivers nutrients into the blood.
4. Excretes nondigestible waste.
http://www.youtube.com/watch?v=PpzfKt-47iA
https://www.youtube.com/watch?v=_QYwscALNng
Gastrointestinal Tract - Sensory stimulation & GI function
• Physiologic & psychological factors influence digestion
• Sensory stimulation—sight, smell or proximity to food—brings about the
secretion of digestive juices & muscle motility
1
Lectures are based on the HUN1201 course textbook Essentials of Nutrition and Diet Therapy, Williams, 13th Edition, Elsevier
Publishing Company. Your exam and quiz questions are based on the book.
, HUN1201 Nutrition Lecture Notes
Digestion, Absorption, & Metabolism
• Initiate secretion of enzymes & digestive fluids and promote
gastrointestinal motility.
• Control secretion of hormones that influence appetite, food intake, &
satiety
•
Neural responses
• Initiate secretion of enzymes & digestive fluids and promote gastrointestinal
motility.
• Control secretion of hormones that influence appetite, food intake, & satiety
Principles of Digestion
Digestion: First step in preparing food for use by the body
2 Types of actions involved:
1. Muscular
2. Chemical
Gastrointestinal Secretions
• Food is digested chemically through the combined action of several secretions:
• Enzymes
• Hydrochloric Acid (HCL) & Buffer Ions
• Mucus
• Water & Electrolytes
Special cells in the mucosal lining of the gastrointestinal tract & in adjacent
accessory organs produce these secretions.
Types of Muscles-Muscle layers from the outer surface inward
• Serosa
• Longitudinal muscle layer
• Circular muscle layer
• Submucosa
• Mucosa
Esophagus - Muscular Actions in Digestion
Muscles along the GI tract produce
• Longitudinal muscles help propel food mass forward.
• Circular contractile muscles: rhythmic sweeping waves push food forward
(peristalsis).
• Rhythmic contractions propel the food mass forward along the tract.
• Mucosal muscles: local constrictive contractions to chop & mix the food
mass.
• Tonic & Periodic rhythmic contractions.
Mouth & Esophagus
Taste & Smell
• Taste buds located on the tongue, roof of the mouth, & throat contain chemical
receptors that respond to food & produce the 4 sensations of taste: Salty, Sweet,
Sour, & Bitter
• Much of what we perceive as taste of a food may actually be its odor.
2
Lectures are based on the HUN1201 course textbook Essentials of Nutrition and Diet Therapy, Williams, 13th Edition, Elsevier
Publishing Company. Your exam and quiz questions are based on the book.
Digestion, Absorption, & Metabolism
Digestion, Absorption, Metabolism – Chapter 3
Role in Wellness
• Growth, maintenance, & energy needs depend on the nutrients available.
• The digestive system relies on nutrient intake for its maintenance.
• Processes of digestion, absorption, & metabolism work together to provide all body
cells with energy and nutrients.
The Human Body: Role of Nutrition- Food: Change & Transformation
Through a successive interrelated system, foods are transformed into simple substances
that can be absorbed into the body & enter the metabolic pathways in the cell.
Importance for Health & Nutrition
• Food as it occurs naturally is a mixture of chemical substances & nutrients.
• Nutrients released from food remain unavailable to the body until they cross the
intestinal wall & are transported to tissues for storage or immediate use.
• Disease & malnutrition impair absorption of nutrients
• Internal control for maintaining a constant chemical environment is called
homeostasis.
Digestion & Absorption
• Biochemically, “You are what you eat” is scientifically true!
• Food & fluid taken into the body is broken down into smaller components so it
can be used by the body
GI Tract- Long hollow tube that begins at the mouth & ends at the anus.
Component Parts
• Mouth
• Esophagus
• Stomach
• Small intestine
• Large intestine
Organs that lie outside the tract:
• Pancreas
• Gallbladder
• Liver
4 Major functions in digestion & absorption:
1. Receives food.
2. Releases nutrients from food.
3. Delivers nutrients into the blood.
4. Excretes nondigestible waste.
http://www.youtube.com/watch?v=PpzfKt-47iA
https://www.youtube.com/watch?v=_QYwscALNng
Gastrointestinal Tract - Sensory stimulation & GI function
• Physiologic & psychological factors influence digestion
• Sensory stimulation—sight, smell or proximity to food—brings about the
secretion of digestive juices & muscle motility
1
Lectures are based on the HUN1201 course textbook Essentials of Nutrition and Diet Therapy, Williams, 13th Edition, Elsevier
Publishing Company. Your exam and quiz questions are based on the book.
, HUN1201 Nutrition Lecture Notes
Digestion, Absorption, & Metabolism
• Initiate secretion of enzymes & digestive fluids and promote
gastrointestinal motility.
• Control secretion of hormones that influence appetite, food intake, &
satiety
•
Neural responses
• Initiate secretion of enzymes & digestive fluids and promote gastrointestinal
motility.
• Control secretion of hormones that influence appetite, food intake, & satiety
Principles of Digestion
Digestion: First step in preparing food for use by the body
2 Types of actions involved:
1. Muscular
2. Chemical
Gastrointestinal Secretions
• Food is digested chemically through the combined action of several secretions:
• Enzymes
• Hydrochloric Acid (HCL) & Buffer Ions
• Mucus
• Water & Electrolytes
Special cells in the mucosal lining of the gastrointestinal tract & in adjacent
accessory organs produce these secretions.
Types of Muscles-Muscle layers from the outer surface inward
• Serosa
• Longitudinal muscle layer
• Circular muscle layer
• Submucosa
• Mucosa
Esophagus - Muscular Actions in Digestion
Muscles along the GI tract produce
• Longitudinal muscles help propel food mass forward.
• Circular contractile muscles: rhythmic sweeping waves push food forward
(peristalsis).
• Rhythmic contractions propel the food mass forward along the tract.
• Mucosal muscles: local constrictive contractions to chop & mix the food
mass.
• Tonic & Periodic rhythmic contractions.
Mouth & Esophagus
Taste & Smell
• Taste buds located on the tongue, roof of the mouth, & throat contain chemical
receptors that respond to food & produce the 4 sensations of taste: Salty, Sweet,
Sour, & Bitter
• Much of what we perceive as taste of a food may actually be its odor.
2
Lectures are based on the HUN1201 course textbook Essentials of Nutrition and Diet Therapy, Williams, 13th Edition, Elsevier
Publishing Company. Your exam and quiz questions are based on the book.
