Download OVERVIEW OF HEALTHY EATING HABITS

THE ALIMENTARY CANAL:
DIGESTION AND ABSORPTION
CHAPTER 3
Copyright © 2015, 2010, 2005, 1998 by Saunders, an imprint of Elsevier Inc.
Components of the
Alimentary Tract
 Oral cavity
 Pharynx
 Esophagus
 Stomach
 Small intestine
 Duodenum
 Jejunum
 Ileum
 Large intestine
 Cecum
 Colon
 Rectum
 Accessory organs:
 Salivary glands
 Liver
 Gallbladder
 Pancreas
Copyright © 2015, 2010, 2005, 1998 by Saunders, an imprint of Elsevier Inc.
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Digestion of Food
 Chemical actions
 Reduce foodstuffs to absorbable
molecules

Enzymes
 Mechanical actions
 Break up and mix foods,
permitting better blending with
the chemicals


Chewing
Peristalsis
Copyright © 2015, 2010, 2005, 1998 by Saunders, an imprint of Elsevier Inc.
3
Process of Nutrition: Oral Cavity
 Food choices influenced by
the three sensory perceptions:
 Sight
 Smell
 Taste
 The oral cavity is the “port of
entry” where receptors for the
sense of taste or taste buds
are located
 Taste bud consists of 30 to 100
cells
Copyright © 2015, 2010, 2005, 1998 by Saunders, an imprint of Elsevier Inc.
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Process of Nutrition: Oral Cavity
 Mechanical digestion
 Begins w/biting and
chewing food

Smaller food pieces
provide more surface
area for digestive
enzymes to function
 Chemical digestion
 Salivary amylase
 Allows large molecule
carbohydrates, which are not
fermentable by plaque acids,
to be hydrolyzed into shorter
chains that are fermentable
 Saliva containing
mucus causes food to
stick together into a
bolus; lubricates the
mass for swallowing
From Patton KT, Thibodeau GA: Anatomy & Physiology, ed
8. St. Louis: Mosby, 2013.
Copyright © 2015, 2010, 2005, 1998 by Saunders, an imprint of Elsevier Inc.
5
Process of Nutrition: Esophagus
 No digestion occurs
 The bolus passes
back to the pharynx
under voluntary
control
 The process then
becomes involuntary
 Peristalsis moves the
food rapidly to the
stomach
From Patton KT, Thibodeau GA: Anatomy & Physiology, ed
8. St. Louis: Mosby, 2013.
Copyright © 2015, 2010, 2005, 1998 by Saunders, an imprint of Elsevier Inc.
6
Process of Nutrition: Stomach
 Stomach secretions
 Chief cells produce pepsinogen
 Parietal cells release HCl to make gastric
contents acidic (1.5 to 3 pH)




Halts the action of salivary amylase
Aids in absorption of minerals like calcium, iron, zinc
Kills or inhibits growth of food bacteria
Secrete intrinsic factor to aid absorption of vitamin B12
From Patton KT, Thibodeau
GA: Anatomy & Physiology, ed
8. St. Louis: Mosby, 2013.
 Pepsinogen and HCl work together to begin hydrolysis
of protein
 Gastric lipase to digest short- and medium-chain fatty
acids (FAs)
 Stomach empties in 1 to 4 hrs depending on
amount and types of food eaten
Copyright © 2015, 2010, 2005, 1998 by Saunders, an imprint of Elsevier Inc.
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Process of Nutrition:
Small Intestine
 Digestion
 Acidic chyme from the stomach stimulates the
release of pancreatic enzymes



CHOs: pancreatic amylase
Protein: trypsin, chymotrypsin, carboxypeptidase
Fat: lipase
 Microvilli in intestinal wall produce:
 Lactase, sucrase, and maltase: CHOs
 Aminopeptidase and dipeptidase: proteins
 Lipase: fats
 Bile produced by the liver and stored in the
gallbladder aids in emulsification of fats
Copyright © 2015, 2010, 2005, 1998 by Saunders, an imprint of Elsevier Inc.
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Process of Nutrition:
Small Intestine–Absorption
 Means of transport (3 to 10 hr transit time)
 Active
 Carrier systems require energy, e.g., intrinsic factor
 Pumps require energy, e.g., absorption of glucose, Na, K,
Mg, P, I, Ca, Fe, and amino acids
 Pinocytosis: engulfing of small drops of intestinal contents

Allows for absorption of whole proteins, such as immunoglobulins
in breast milk
 Passive
 Diffusion
Copyright © 2015, 2010, 2005, 1998 by Saunders, an imprint of Elsevier Inc.
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Process of Nutrition:
Small Intestine–Absorption
 Duodenum
 Electrolytes
 Minerals (Fe, Ca, Mg, Zn)
 Jejunum
 Water-soluble vitamins (C,
thiamine, riboflavin, B6, folic
acid)
 Mono- and disaccharides
 Ileum
 Protein
 Fat-soluble vitamins
 Fat/cholesterol
 Vitamin B12
From Patton KT, Thibodeau GA: Anatomy & Physiology,
ed 8. St. Louis: Mosby, 2013.
Copyright © 2015, 2010, 2005, 1998 by Saunders, an imprint of Elsevier Inc.
10
Process of Nutrition:
Large Intestine
 Cecum (proximal portion)
 Water
 Electrolytes: Na and K
 Colon
 Additional digestion of materials occurs
 Several nutrients are formed by bacterial synthesis during the
process including vitamins K and B12, thiamine, riboflavin
 Intestinal flora ferment CHO and fiber
 Rectum
 Anal canal
Copyright © 2015, 2010, 2005, 1998 by Saunders, an imprint of Elsevier Inc.
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Dental Hygiene Considerations
 Assess nutritional status of patients with gustatory
or olfactory disorders for changes in dietary habits
 Monitor quality and quantity of food intake for
patients with difficulty chewing and swallowing food
 Heartburn: result of regurgitation (gastroesophageal
reflux) of stomach contents into the esophagus
 Over an extended time, chronic problems with vomiting or
reflux can result in sensitive teeth and superficial or deep
tooth erosion, especially on lingual and occlusal surfaces
Copyright © 2015, 2010, 2005, 1998 by Saunders, an imprint of Elsevier Inc.
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Practical Application
 A patient has had a
gastric bypass that
removes the lower
portion of the
stomach and much of
the duodenum and
jejunum
 Give a rationale for
which nutrients might
be affected
From Mahan LK, Escott-Stump S: Krause’s Food and
Nutrition Therapy, ed 13. St. Louis: Saunders, 2012.
Copyright © 2015, 2010, 2005, 1998 by Saunders, an imprint of Elsevier Inc.
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Practical Application
 A patient has
reactions to gluten
 Discuss the three main
conditions related to gluten
allergies
 Give a rationale for which
foods might best be avoided
by patients with this
sensitivity
 What nutrient absorption
might be affected for these
patients?
 How would you counsel
them regarding nutrition?
From Standring S: Gray's anatomy: the anatomical basis of
clinical practice, ed 40, London, 2009, Churchill Livingstone.
Copyright © 2015, 2010, 2005, 1998 by Saunders, an imprint of Elsevier Inc.
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