Chapter 3 – Digestion and Absorption
The body’s machinery to process food and turn it into nutrients unfolds in the digestive tract
in two stages:
Digestion: the process of transforming the foods we eat into units for absorption, and
Absorption: the movement of substances into or across tissues; in particular, the
passage of nutrients and other substances into the walls of the gastrointestinal tract and
then into the bloodstream of lymphatic system for circulation
Unless you have a specific medical condition, your digestive system is ready, willing, and
able to digest and absorb the foods you eat, in whatever combination you eat them.
Chemosenses: the chemical sensing system in the body, including taste and smell. The
complex process begins when tiny molecules released by the substances around us bind to
receptors in special cells in the nose, mouth or throat. These sensory cells transmit messages
through nerves to the brain, where specific smells or tastes are identified. Three types:
Olfactory cells (smell): are nerve cells in a small patch of tissue high in the nose
connected directly to the brain to transmit messages about specific smells. Also called
smell cells.
Gustatory cells (taste): surface cells in the throat and on the taste buds in the mouth
that transmit taste information. Also called taste cells.
The common chemical sense: is a chemosensory mechanism that contributes to our
senses of smell and taste. It comprises thousands of nerve endings, especially on the
moist [=wet] surfaces of your eyes, nose, mouth and throat.
Cephalic phase responses: the responses of the parasympathetic nervous system to the sight,
smell, thought, and sound of food. Also called preabsorptive phase responses.
STIMULUS RESPONSE
Heat production system (thermogenesis): increased heat production
Cognition (thinking
(in brains)
about food)
Salivary glands: increased flow of saliva [=speeksel], changes in
saliva composition
Sound (hearing a
description of food)
Cardiovascular system: increased heart rate and blood flow,
decreased cardiac output and stroke volume
Appearance (seeing
food)
Gastrointestinal tract: increased acid and digestive enzyme
secretion, motility, gut [=bowel] hormone release (e.g.
Odour (smelling cholecystokinin)
food)
Pancreas: increased digestive enzyme secretions and hormone (e.g.
insulin) release
Taste/tactile (tasting
food, mouth feel) Renal [=kidney] system : alterations in urine volume and osmolarity
The body’s machinery to process food and turn it into nutrients unfolds in the digestive tract
in two stages:
Digestion: the process of transforming the foods we eat into units for absorption, and
Absorption: the movement of substances into or across tissues; in particular, the
passage of nutrients and other substances into the walls of the gastrointestinal tract and
then into the bloodstream of lymphatic system for circulation
Unless you have a specific medical condition, your digestive system is ready, willing, and
able to digest and absorb the foods you eat, in whatever combination you eat them.
Chemosenses: the chemical sensing system in the body, including taste and smell. The
complex process begins when tiny molecules released by the substances around us bind to
receptors in special cells in the nose, mouth or throat. These sensory cells transmit messages
through nerves to the brain, where specific smells or tastes are identified. Three types:
Olfactory cells (smell): are nerve cells in a small patch of tissue high in the nose
connected directly to the brain to transmit messages about specific smells. Also called
smell cells.
Gustatory cells (taste): surface cells in the throat and on the taste buds in the mouth
that transmit taste information. Also called taste cells.
The common chemical sense: is a chemosensory mechanism that contributes to our
senses of smell and taste. It comprises thousands of nerve endings, especially on the
moist [=wet] surfaces of your eyes, nose, mouth and throat.
Cephalic phase responses: the responses of the parasympathetic nervous system to the sight,
smell, thought, and sound of food. Also called preabsorptive phase responses.
STIMULUS RESPONSE
Heat production system (thermogenesis): increased heat production
Cognition (thinking
(in brains)
about food)
Salivary glands: increased flow of saliva [=speeksel], changes in
saliva composition
Sound (hearing a
description of food)
Cardiovascular system: increased heart rate and blood flow,
decreased cardiac output and stroke volume
Appearance (seeing
food)
Gastrointestinal tract: increased acid and digestive enzyme
secretion, motility, gut [=bowel] hormone release (e.g.
Odour (smelling cholecystokinin)
food)
Pancreas: increased digestive enzyme secretions and hormone (e.g.
insulin) release
Taste/tactile (tasting
food, mouth feel) Renal [=kidney] system : alterations in urine volume and osmolarity
