Chapter 3: Digestion: From Meals to Molecules
EXCI 204 — Food for Sport · Chapter Study Notes
Chapter Overview
The human body has been compared to a car: we fill the tank with gasoline to get down the highway
and fill our body with food to get on with life; in both, combustion with oxygen releases energy. Bodies
are also virtually identical inside, like cars, because they rely on the same fundamental chemical
reactions. But there are differences: a car cannot use gasoline to heal itself or grow; gasoline travels
unchanged to the engine, whereas the digestive system must break fuel down into smaller units
before the body can use it; and cars run on one fuel, while the digestive system processes fuel from
many sources.
The chapter covers: (3.1) the organization of life from atoms to organisms and the 11 organ systems;
(3.2) the digestive system’s organs, tissue layers, and secretions; (3.3) digestion and absorption organ by
organ, including absorption mechanisms; (3.4) the GI tract’s immune function, the intestinal microbiota,
food allergies, gluten-related disorders, and other digestive problems; (3.5) delivery of nutrients by the
cardiovascular and lymphatic systems and elimination of wastes; and (3.6) an overview of metabolism.
3.1 The Organization of Life
Learning objectives: Describe the organization of living things, from atoms to organisms · Name the
organ systems that work with the digestive system to deliver nutrients and eliminate wastes.
All matter — a meal or the plate it’s on — is made of atoms. Atoms combine to form molecules, which
can have different properties from the atoms they contain. In living systems, molecules are organized
into cells, the smallest units of life. Similar cells form tissues; tissues form organs; organs usually work as
part of an organ system.
KEY DEFINITION ⭐
atom — The smallest unit of an element that retains the properties of the element.
KEY DEFINITION ⭐
molecule — A group of two or more atoms of the same or different elements bonded together.
KEY DEFINITION ⭐
cell — The basic structural and functional unit of living things.
KEY DEFINITION ⭐
tissue — (Described in text) Cells that are similar in structure and function; the human body contains
four types — muscle, nerve, epithelial, and connective.
EXCI 204 · Chapter 3 · Page 1
, KEY DEFINITION ⭐
organ — A discrete structure composed of more than one tissue that performs a specialized
function.
KEY DEFINITION ⭐
organ system — (Described in text) A group of organs that work together to perform a particular
function; the body has 11 organ systems.
From Atoms to Organisms ⭐
Level Description (Figure 3.1 — Process Diagram)
1. Atoms → molecules Atoms linked by chemical bonds form molecules
2. Molecules → cells Molecules form the structures that make up cells. Each cell is bounded
by a membrane; in multicellular organisms cells are usually specialized
for specific functions
3. Cells → tissues Groups of similar cells form tissues (e.g., muscle). Four tissue types:
muscle, nerve, epithelial, connective
4. Tissues → organs Organs (e.g., the stomach) are made of several tissue types; discrete
structures with specific functions
5. Organs → organ A group of organs working together for a particular function
systems
6. Organ systems → Organ systems work together to ensure proper functioning of the entire
organism organism
One organ, two systems. An organ may belong to more than one system — the pancreas is part of the
endocrine system (secretes hormones such as insulin) and the digestive system (secretes substances
that help break down nutrients).
KEY DEFINITION ⭐
hormone — A chemical messenger that is produced in one location in the body, is released into the
blood, and travels to other locations, where it elicits responses.
Table 3.1 — The 11 Major Organ Systems ⭐
Organ system What it includes What it does
Nervous Nerves, sense organs, brain, Responds to stimuli from external and
spinal cord internal environments; conducts
impulses to activate muscles and
glands; integrates activities of other
systems
EXCI 204 · Chapter 3 · Page 2
, Organ system What it includes What it does
Respiratory Lungs, trachea, air Supplies the blood with oxygen and
passageways removes carbon dioxide
Urinary Kidneys, bladder, associated Eliminates wastes and regulates the
structures balance of water, electrolytes, and acid
in the blood
Reproductive Testes, ovaries, associated Produces offspring
structures
Cardiovascular/circulatory Heart and blood vessels Transports blood, which carries oxygen,
nutrients, and wastes
Lymphatic/immune Lymph, lymph structures, Defends against foreign invaders; picks
white blood cells up fluid leaked from blood vessels;
transports fat-soluble nutrients
Muscular Skeletal muscles Provides movement and structure
Skeletal Bones and joints Protects and supports the body;
provides a framework for the muscles
to use for movement
Endocrine Pituitary, adrenal, thyroid, Secretes hormones that regulate
pancreas, and other ductless processes such as growth,
glands reproduction, and nutrient use
Integumentary Skin, hair, nails, sweat glands Covers and protects the body; helps
control body temperature
Digestive Mouth, esophagus, stomach, Ingests and digests food; absorbs
intestines, pancreas, liver, nutrients into the blood; eliminates
gallbladder unabsorbed food wastes
Organ systems that work with the digestive system ⭐
System How it helps the digestive system
Endocrine Secretes hormones that help regulate how much we eat and how
quickly food and nutrients travel through the digestive system
Nervous Sends nerve signals that help control the passage of food through
the digestive tract
Cardiovascular Transports nutrients to individual cells
Urinary, respiratory, Eliminate wastes generated in the body
integumentary
Concept Check (3.1):
EXCI 204 · Chapter 3 · Page 3
, 1. How are atoms, molecules, and cells related to one another?
2. How do the endocrine and nervous systems interact with the digestive system?
3.2 The Digestive System
Learning objectives: Define digestion and absorption · List the organs that make up the digestive system
· Describe the tissue layers of the GI tract wall · Explain the roles of mucus, enzymes, nerves, and
hormones in digestion.
The digestive system is primarily responsible for digestion and for the absorption of nutrients.
KEY DEFINITION ⭐
digestion — The process by which food is broken down into components small enough to be
absorbed into the body.
KEY DEFINITION ⭐
absorption — The process of taking substances from the gastrointestinal tract into the interior of the
body.
EXAM EXAMPLE
Digesting a taco
The tortilla, meat, cheese, lettuce, and tomato are broken apart, releasing nutrients and other food
components.
• Water, vitamins, and minerals are taken into the body without being broken into smaller
units.
• Proteins → amino acids; most carbohydrate → sugars; most fats → fatty acids (long carbon
chains). Sugars, amino acids, and fatty acids can then be absorbed.
• Fiber (whole grains, fruits, vegetables) cannot be digested and is not absorbed; it and other
unabsorbed substances are eliminated in feces.
KEY DEFINITION
fatty acid — (Described in text) Molecules with long carbon chains produced when most fats are
digested; they can be absorbed into the body.
KEY DEFINITION ⭐
feces — Body waste, including unabsorbed food residue, bacteria, mucus, and dead cells, which is
eliminated from the gastrointestinal tract by way of the anus.
EXCI 204 · Chapter 3 · Page 4
EXCI 204 — Food for Sport · Chapter Study Notes
Chapter Overview
The human body has been compared to a car: we fill the tank with gasoline to get down the highway
and fill our body with food to get on with life; in both, combustion with oxygen releases energy. Bodies
are also virtually identical inside, like cars, because they rely on the same fundamental chemical
reactions. But there are differences: a car cannot use gasoline to heal itself or grow; gasoline travels
unchanged to the engine, whereas the digestive system must break fuel down into smaller units
before the body can use it; and cars run on one fuel, while the digestive system processes fuel from
many sources.
The chapter covers: (3.1) the organization of life from atoms to organisms and the 11 organ systems;
(3.2) the digestive system’s organs, tissue layers, and secretions; (3.3) digestion and absorption organ by
organ, including absorption mechanisms; (3.4) the GI tract’s immune function, the intestinal microbiota,
food allergies, gluten-related disorders, and other digestive problems; (3.5) delivery of nutrients by the
cardiovascular and lymphatic systems and elimination of wastes; and (3.6) an overview of metabolism.
3.1 The Organization of Life
Learning objectives: Describe the organization of living things, from atoms to organisms · Name the
organ systems that work with the digestive system to deliver nutrients and eliminate wastes.
All matter — a meal or the plate it’s on — is made of atoms. Atoms combine to form molecules, which
can have different properties from the atoms they contain. In living systems, molecules are organized
into cells, the smallest units of life. Similar cells form tissues; tissues form organs; organs usually work as
part of an organ system.
KEY DEFINITION ⭐
atom — The smallest unit of an element that retains the properties of the element.
KEY DEFINITION ⭐
molecule — A group of two or more atoms of the same or different elements bonded together.
KEY DEFINITION ⭐
cell — The basic structural and functional unit of living things.
KEY DEFINITION ⭐
tissue — (Described in text) Cells that are similar in structure and function; the human body contains
four types — muscle, nerve, epithelial, and connective.
EXCI 204 · Chapter 3 · Page 1
, KEY DEFINITION ⭐
organ — A discrete structure composed of more than one tissue that performs a specialized
function.
KEY DEFINITION ⭐
organ system — (Described in text) A group of organs that work together to perform a particular
function; the body has 11 organ systems.
From Atoms to Organisms ⭐
Level Description (Figure 3.1 — Process Diagram)
1. Atoms → molecules Atoms linked by chemical bonds form molecules
2. Molecules → cells Molecules form the structures that make up cells. Each cell is bounded
by a membrane; in multicellular organisms cells are usually specialized
for specific functions
3. Cells → tissues Groups of similar cells form tissues (e.g., muscle). Four tissue types:
muscle, nerve, epithelial, connective
4. Tissues → organs Organs (e.g., the stomach) are made of several tissue types; discrete
structures with specific functions
5. Organs → organ A group of organs working together for a particular function
systems
6. Organ systems → Organ systems work together to ensure proper functioning of the entire
organism organism
One organ, two systems. An organ may belong to more than one system — the pancreas is part of the
endocrine system (secretes hormones such as insulin) and the digestive system (secretes substances
that help break down nutrients).
KEY DEFINITION ⭐
hormone — A chemical messenger that is produced in one location in the body, is released into the
blood, and travels to other locations, where it elicits responses.
Table 3.1 — The 11 Major Organ Systems ⭐
Organ system What it includes What it does
Nervous Nerves, sense organs, brain, Responds to stimuli from external and
spinal cord internal environments; conducts
impulses to activate muscles and
glands; integrates activities of other
systems
EXCI 204 · Chapter 3 · Page 2
, Organ system What it includes What it does
Respiratory Lungs, trachea, air Supplies the blood with oxygen and
passageways removes carbon dioxide
Urinary Kidneys, bladder, associated Eliminates wastes and regulates the
structures balance of water, electrolytes, and acid
in the blood
Reproductive Testes, ovaries, associated Produces offspring
structures
Cardiovascular/circulatory Heart and blood vessels Transports blood, which carries oxygen,
nutrients, and wastes
Lymphatic/immune Lymph, lymph structures, Defends against foreign invaders; picks
white blood cells up fluid leaked from blood vessels;
transports fat-soluble nutrients
Muscular Skeletal muscles Provides movement and structure
Skeletal Bones and joints Protects and supports the body;
provides a framework for the muscles
to use for movement
Endocrine Pituitary, adrenal, thyroid, Secretes hormones that regulate
pancreas, and other ductless processes such as growth,
glands reproduction, and nutrient use
Integumentary Skin, hair, nails, sweat glands Covers and protects the body; helps
control body temperature
Digestive Mouth, esophagus, stomach, Ingests and digests food; absorbs
intestines, pancreas, liver, nutrients into the blood; eliminates
gallbladder unabsorbed food wastes
Organ systems that work with the digestive system ⭐
System How it helps the digestive system
Endocrine Secretes hormones that help regulate how much we eat and how
quickly food and nutrients travel through the digestive system
Nervous Sends nerve signals that help control the passage of food through
the digestive tract
Cardiovascular Transports nutrients to individual cells
Urinary, respiratory, Eliminate wastes generated in the body
integumentary
Concept Check (3.1):
EXCI 204 · Chapter 3 · Page 3
, 1. How are atoms, molecules, and cells related to one another?
2. How do the endocrine and nervous systems interact with the digestive system?
3.2 The Digestive System
Learning objectives: Define digestion and absorption · List the organs that make up the digestive system
· Describe the tissue layers of the GI tract wall · Explain the roles of mucus, enzymes, nerves, and
hormones in digestion.
The digestive system is primarily responsible for digestion and for the absorption of nutrients.
KEY DEFINITION ⭐
digestion — The process by which food is broken down into components small enough to be
absorbed into the body.
KEY DEFINITION ⭐
absorption — The process of taking substances from the gastrointestinal tract into the interior of the
body.
EXAM EXAMPLE
Digesting a taco
The tortilla, meat, cheese, lettuce, and tomato are broken apart, releasing nutrients and other food
components.
• Water, vitamins, and minerals are taken into the body without being broken into smaller
units.
• Proteins → amino acids; most carbohydrate → sugars; most fats → fatty acids (long carbon
chains). Sugars, amino acids, and fatty acids can then be absorbed.
• Fiber (whole grains, fruits, vegetables) cannot be digested and is not absorbed; it and other
unabsorbed substances are eliminated in feces.
KEY DEFINITION
fatty acid — (Described in text) Molecules with long carbon chains produced when most fats are
digested; they can be absorbed into the body.
KEY DEFINITION ⭐
feces — Body waste, including unabsorbed food residue, bacteria, mucus, and dead cells, which is
eliminated from the gastrointestinal tract by way of the anus.
EXCI 204 · Chapter 3 · Page 4
