Transcript Class 3 4-5 protein digestion

Chapter 4
Proteins
Square meals often make round people. Cossman
Copyright © 2009, by Mosby, Inc. an affiliate of Elsevier, Inc. All rights reserved.
1
Key Concepts
• Food proteins provide the amino acids
necessary for building and maintaining
body tissue.
• Protein balance, both within the body and in
the diet, is essential to life and health.
• The quality of a protein food and its ability
to meet the body’s needs are determined by
the composition of amino acids.
Copyright © 2009, by Mosby, Inc. an affiliate of Elsevier, Inc. All rights reserved.
2
Amino Acids: Basic Building
Material
• Each protein is composed of hundreds of amino
acids
• Amino acids form unique chain sequences to form
specific proteins; the sequencing determines the
function of the completed protein
• When protein foods are eaten, proteins are broken
down into amino acids
• Amino acids are reassembled in the body to form
a variety of proteins
Copyright © 2009, by Mosby, Inc. an affiliate of Elsevier, Inc. All rights reserved.
3
Classes of Amino Acids
• Indispensable amino acids
– Body cannot manufacture in sufficient
quantity so it is essential to eat them
• Dispensable amino acids
– Body can synthesize from
indispensable amino acids
• Conditionally indispensable amino acids
– Normally synthesized but some health
conditions may require dietary intake
Copyright © 2009, by Mosby, Inc. an affiliate of Elsevier, Inc. All rights reserved.
4
A Healthy Balance
• Protein balance
– Catabolism: breakdown
– Anabolism: synthesis
• Nitrogen balance (intake = excretion)
– Positive nitrogen balance: body stores
more than it excretes
– Negative nitrogen balance: body takes in
less than it excretes
Copyright © 2009, by Mosby, Inc. an affiliate of Elsevier, Inc. All rights reserved.
5
Functions of Protein
•
•
•
•
•
•
Tissue building & repair
Energy
Water balance
Metabolism
Body defense system
Hormones, immunoglobulins, muscles,
albumin, & antibodies are all proteins
Copyright © 2009, by Mosby, Inc. an affiliate of Elsevier, Inc. All rights reserved.
6
Tissue Building
• Fundamental structural material of every
cell
• Comprises bulk of:
– Muscles
– Internal organs
– Brain and Nerves
– Blood plasma
• Protein repairs worn-out, wasted, or
damaged tissue
Copyright © 2009, by Mosby, Inc. an affiliate of Elsevier, Inc. All rights reserved.
7
Energy
• May provide body fuel if the supply of
carbohydrate and fat is insufficient for
needs
• Body’s third choice for energy production
• Less efficient
Copyright © 2009, by Mosby, Inc. an affiliate of Elsevier, Inc. All rights reserved.
8
Water Balance
• Plasma proteins (especially albumin)
attract water, resulting in maintenance of
normal circulation volume
• Proteins have a unique structure to act as
buffering agents in pH balance
Copyright © 2009, by Mosby, Inc. an affiliate of Elsevier, Inc. All rights reserved.
9
Metabolism
• Enzymes
– Digestive enzymes: amylases, lipases,
proteases
• Transport agents
– Lipoproteins
– Hemoglobin
• Hormones
– Insulin and glucagon
– Thyroxine, calcitonin
Copyright © 2009, by Mosby, Inc. an affiliate of Elsevier, Inc. All rights reserved.
10
Body Defense
• Immune system defends against
disease and infection
– White blood cells
– Antibodies
Copyright © 2009, by Mosby, Inc. an affiliate of Elsevier, Inc. All rights reserved.
11
Key Concepts
• Food proteins provide the amino acids
necessary for building, maintaining and
repairing body tissue.
• Protein balance, both within the body and
in the diet, is essential to life and health.
• The quality of a protein food and its ability
to meet the body’s needs are determined
by the composition of amino acids.
Copyright © 2009, by Mosby, Inc. an affiliate of Elsevier, Inc. All rights reserved.
12
Food Sources of Protein
• Complete proteins
– Meat, fish, poultry, seafood
– Soy
• Incomplete proteins
– Plant-origin foods
• Grains and Legumes
• Nuts and Seeds
• Fruits and vegetables
Copyright © 2009, by Mosby, Inc. an affiliate of Elsevier, Inc. All rights reserved.
13
Vegetarian Diets
• Must combine foods to cover all amino
acid needs (makes a complete protein)
• Types of vegetarian diets
– Lacto-ovo vegetarian
– Lacto-vegetarian
– Ovo-vegetarian
– Vegan
Copyright © 2009, by Mosby, Inc. an affiliate of Elsevier, Inc. All rights reserved.
14
Lacto-Ovo Vegetarian Diet
Pyramid
Copyright © 2009, by Mosby, Inc. an affiliate of Elsevier, Inc. All rights reserved.
15
Digestion of Proteins
• Mouth – mechanical, no digestion
• Stomach: enzymatic breakdown of protein by
proenzymes
– Pepsinogen & Hydrochloric acid = Pepsin
– Rennin
• Small intestine
– Pancreatic secretions
• Trypsin, chymotrypsin, carboxypeptidase
– Intestinal secretions
• Aminopeptidase, dipeptidase
Copyright © 2009, by Mosby, Inc. an affiliate of Elsevier, Inc. All rights reserved.
16
Summary of Protein Digestion
Copyright © 2009, by Mosby, Inc. an affiliate of Elsevier, Inc. All rights reserved.
17
Body Needs for Protein
• Tissue growth and repair
• Dietary protein quality is important
• Additional needs caused by disease and skin
injury like decubiti or burns
Copyright © 2009, by Mosby, Inc. an affiliate of Elsevier, Inc. All rights reserved.
18
Dietary Deficiency or Excess
• Protein energy malnutrition
– Kwashiorkor
– Marasmus
• Excess protein
– Usually also means excess fat intake
– Protein displaces other healthy foods in diet
– Extra burden on kidneys to rid body of nitrogen
waste
Copyright © 2009, by Mosby, Inc. an affiliate of Elsevier, Inc. All rights reserved.
19
Dietary Guides
• Recommended Dietary Allowances (RDAs)
– Relate to age, sex, weight
– Highest at birth and slowly decline into
adulthood
– Men and women: 0.8 g/kg of desirable weight
– 10% to 35% of total caloric intake from protein
(children and adults)
Copyright © 2009, by Mosby, Inc. an affiliate of Elsevier, Inc. All rights reserved.
20
Calculating Protein Needs,
cont’d
• DRI:
– Assumes individual consumes 2200
kcal/day; based on recommendation of
10% to 35% of total kilocalories from
protein
– 2200 kcal x 0.1- 0.35 = 220-770
kcal/day from protein
– 220-770 kcal x 4 kcal/g = 55-192.5
g/day of protein
Copyright © 2009, by Mosby, Inc. an affiliate of Elsevier, Inc. All rights reserved.
21
Summary
• Protein provides the body with its primary
tissue-building units, amino acids
• *20 common amino acids
• Nine of the 20 amino acids are
indispensable in the diet
• Body can manufacture the remaining 11
amino acids
• Complete proteins are foods that supply
all the indispensable amino acids
Copyright © 2009, by Mosby, Inc. an affiliate of Elsevier, Inc. All rights reserved.
22
Summary, cont’d
• Complete proteins are usually of animal
origin and soy
• Plant foods are considered incomplete
proteins because they lack one or more of
the indispensable amino acids (with the
exception of soy)
• Vegetarian diets can be strict with only
plant proteins (vegan), whereas other
variations include dairy, egg, and
sometimes fish
Copyright © 2009, by Mosby, Inc. an affiliate of Elsevier, Inc. All rights reserved.
23
Summary, cont’d
• Adequate dietary protein and a reserve
“pool” of amino acids help maintain
overall protein balance
• A powerful digestive team of six proteinsplitting enzymes acts to break down the
protein into amino acids for vital tissuebuilding tasks
• Protein requirements are influenced by
growth needs and nature of diet in terms
of protein quality and energy intake
Copyright © 2009, by Mosby, Inc. an affiliate of Elsevier, Inc. All rights reserved.
24
Summary, cont’d
• Clinical influences on protein include fever, disease,
surgery, or other trauma to the body
• Protein needs are calculated based on RDA standards
related to age, sex, and weight, & is set at 0.8 g of
high quality protein per kilogram of body weight/ day
• Adjustments for protein intake are required for:
– infants and pregnant and breastfeeding women
– individuals following a vegan diet
– critical illness
Copyright © 2009, by Mosby, Inc. an affiliate of Elsevier, Inc. All rights reserved.
25
Key Concepts of Digestion,
Absorption and Metabolism
• Through a balanced system of mechanical
and chemical digestion, food is broken
down into smaller substances and the
nutrients are released for biologic use.
• Special organ structures and functions
conduct these tasks through the successive
parts of the overall system.
Copyright © 2009, by Mosby, Inc. an affiliate of Elsevier, Inc. All rights reserved.
26
Mechanical Digestion
• GI motility: Beginning in the mouth, muscles and
nerves in the tract coordinate their actions to
provide motility, an automatic response to the
presence of food.
• EX chewing, peristalsis and segmentation
Copyright © 2009, by Mosby, Inc. an affiliate of Elsevier, Inc. All rights reserved.
27
Mechanical Digestion, cont’d
• Muscles
– Muscle tone/tonic contraction: Ensures
continuous passage of the food mass and valve
control along the GI tract
– Periodic muscle contraction and relaxation:
Rhythmic waves that mix the food mass and
move it forward
Copyright © 2009, by Mosby, Inc. an affiliate of Elsevier, Inc. All rights reserved.
28
Mechanical Digestion, cont’d
• Nerves
– Specific nerves regulate muscle action along
the GI tract
– The intramural nerve plexus is the network of
nerves in the GI wall extending from the
esophagus to the anus
Copyright © 2009, by Mosby, Inc. an affiliate of Elsevier, Inc. All rights reserved.
29
Chemical Digestion
• Digestive enzymes: Break down nutrients
• Hydrochloric acid and buffer ions: Produce the correct pH
necessary for enzyme activity
• Mucus: Lubricates and protects the GI tract tissues; helps
mix the food mass
• Water : Carry and circulate the products of digestion
through the tract and into the tissues
• Electrolytes: absorbed, transported and play a role in
homeostasis
• Bile: Emulsifies fat into smaller pieces to assist fat
enzymes
Copyright © 2009, by Mosby, Inc. an affiliate of Elsevier, Inc. All rights reserved.
30
Digestion in the Mouth and
Esophagus
• Mechanical digestion
– Mastication breaks down food orally.
– Food is swallowed and passes down
esophagus.
– Muscles at tongue base facilitate the
swallowing process.
– Gastroesophageal sphincter at
stomach entrance relaxes, allowing
food to enter, then constricts to retain
food.
Copyright © 2009, by Mosby, Inc. an affiliate of Elsevier, Inc. All rights reserved.
31
Digestion in the Mouth and
Esophagus, cont’d
• Chemical digestion
– Salivary glands secrete fluid containing salivary
amylase or ptyalin.
– Salivary glands also secrete a mucous material to
lubricate and bind food particles, facilitating the
swallowing of the food bolus.
– Secretions from the mucous glands in the esophagus
help ease movement of food toward the stomach.
Copyright © 2009, by Mosby, Inc. an affiliate of Elsevier, Inc. All rights reserved.
32
Digestion in the Stomach
• Mechanical digestion
– Under sphincter control, the food enters the upper
portion of the stomach as individual bolus masses.
– Stomach muscles knead, store, mix, and propel the
food mass forward.
– By the time the food mass reaches the lower portion
of the stomach, it is a semi-liquid acid/food mix called
chyme.
– Chyme is released slowly into the first section of the
small intestine (duodenum) by the pyloric valve.
Copyright © 2009, by Mosby, Inc. an affiliate of Elsevier, Inc. All rights reserved.
33
Digestion in the Stomach,
cont’d
• Chemical digestion: three types of gastric
secretions
– Hydrochloric acid: Parietal cells in the stomach lining
secrete acid to promote gastric enzyme activity.
– Mucus: Secretions protect the stomach lining from the
erosive effect of the acid and also bind and mix the food
mass and help move it along.
– Pepsinogen is secreted by stomach cells and activated by
acid to become pepsin, a protein-splitting enzyme.
Copyright © 2009, by Mosby, Inc. an affiliate of Elsevier, Inc. All rights reserved.
34
Digestion in the Small
Intestine
• Mechanical digestion
– Peristaltic waves slowly push food
mass forward.
– Segmentation rings chop food mass
into successive soft lumps and mix
them with secretions.
– Longitudinal rotation rolls food in a
spiral motion, exposing new surfaces
for absorption.
Copyright © 2009, by Mosby, Inc. an affiliate of Elsevier, Inc. All rights reserved.
35
Digestion in Small Intestine,
cont’d
• Pancreatic enzymes
– Carbohydrate: Pancreatic amylase converts
starch to maltose and sucrose.
– Protein: Trypsin and chymotrypsin split large
protein molecules into small peptide fragments
and eventually into single amino acids.
– Fat: Pancreatic lipase converts fat to glycerides
and fatty acids.
Copyright © 2009, by Mosby, Inc. an affiliate of Elsevier, Inc. All rights reserved.
36
Digestion in the Small
Intestine, cont’d
• Small Intestine enzymes
– Carbohydrate: Disaccharid-ases convert
disaccharides into monosaccharides.
– Protein: Enterokinase activates trypsinogen
from the pancreas to become trypsin; amino
peptidase removes end amino acids from
polypeptides; dipeptidase splits dipeptides into
amino acids.
– Fat: Intestinal lipase splits fat into glycerides
and fatty acids.
Copyright © 2009, by Mosby, Inc. an affiliate of Elsevier, Inc. All rights reserved.
37
Digestion in the Small
Intestine, cont’d
• Mucus: Large quantities of mucus protect the
mucosal lining from irritation and erosion.
– Bile: Emulsifying agent produced by the liver
and stored in the gallbladder aids fat digestion
and absorption.
– Hormones
• Secretin
• Cholecystokinin
Copyright © 2009, by Mosby, Inc. an affiliate of Elsevier, Inc. All rights reserved.
38
Factors Influencing GI Tract
Secretions
•
•
•
•
Nervous control
Conditioned reflexes
Oral reflexes
Physical contact
Copyright © 2009, by Mosby, Inc. an affiliate of Elsevier, Inc. All rights reserved.
39
Bioavailability
• Bioavailability refers to:
– Amount of nutrient present in the GI tract
– Competition between nutrients for absorption
– Form in which the nutrient is present
• All nutrients present in a food are not absorbed
because of differing bioavailability.
– This is considered when determining dietary intake
standards
Copyright © 2009, by Mosby, Inc. an affiliate of Elsevier, Inc. All rights reserved.
40
Absorption in the Small
Intestine
• Three absorbing structures
– Mucosal folds: Surface of small intestine piles
into folds
– Villi: Small, finger-like projections cover the
mucosal folds, increasing the area of exposed
intestinal surface
– Microvilli: Smaller projections cover each villi
(look like bristles on a brush)
Copyright © 2009, by Mosby, Inc. an affiliate of Elsevier, Inc. All rights reserved.
41
Absorption Processes
• Simple diffusion: The force by which particles move
outward in all directions—from areas of greater to
lesser concentration.
• Facilitated diffusion: Similar to simple diffusion but
uses a protein channel to carry larger items.
• Active transport: The force by which particles move
from areas of lesser to greater concentration using a
carrier to “ferry” particles.
• Endocytosis: Penetration of larger materials by
attaching to the cell membrane and being engulfed by
the cell.
Copyright © 2009, by Mosby, Inc. an affiliate of Elsevier, Inc. All rights reserved.
42
Absorption in Large Intestine
• Bacteria helps make Vitamin K
• Water is taken up by the large intestine
– Most water in chyme is absorbed in the first
half of the colon
– Only a small amount remains to form and
eliminate feces
• Dietary fiber is not digested
– Contributes bulk to food mass
– Helps form feces
Copyright © 2009, by Mosby, Inc. an affiliate of Elsevier, Inc. All rights reserved.
43
Transport
• Nutrients must be transported to cells
• Vascular (blood circulatory) system
– Veins and arteries
– Transports waste, such as carbon dioxide and
nitrogen, to lungs and kidneys for removal
• Lymphatic system
– Route for fatty materials, which are not water
soluble
– Fat molecules pass into lymph vessels in villi
Copyright © 2009, by Mosby, Inc. an affiliate of Elsevier, Inc. All rights reserved.
44
Metabolism
• Two metabolic processes
– Catabolism: Breaking down of large substances
into smaller units (e.g., breaking down a protein
chain into amino acids)
– Anabolism: Building of larger substances from
smaller particles (e.g., building a complex
protein from single amino acids)
Copyright © 2009, by Mosby, Inc. an affiliate of Elsevier, Inc. All rights reserved.
45
Metabolism, cont’d
• Metabolic processes ensure that the body has
energy in the form of adenosine triphosphate
(ATP).
• Metabolism of glucose (4 kcal/kg) from
carbohydrates yields less energy than metabolism
of fat (9 kcal/kg). Still, glucose is the body’s
primary source of energy.
• Protein can be an energy source, but it is relatively
inefficient.
Copyright © 2009, by Mosby, Inc. an affiliate of Elsevier, Inc. All rights reserved.
46
Energy Storage:
Glycogenesis
• Glycogenesis: Anabolic process of converting
extra glucose into glycogen
• Glycogen is stored in the liver and muscles for
quick energy to be used at a later time
• Gluconeogensis: Making glucose from non
carbohydrate sources
Copyright © 2009, by Mosby, Inc. an affiliate of Elsevier, Inc. All rights reserved.
47
Energy Storage: Lipogenesis
• When glycogen reserves are full, additional excess
energy from carbohydrates, fat, or protein is stored
as fat in adipose tissue
• Lipogenesis: The building up of triglycerides for
storage in adipose tissue
Copyright © 2009, by Mosby, Inc. an affiliate of Elsevier, Inc. All rights reserved.
48
Genetic Disease
• Phenylketonuria
– Protein metabolism
• Galactosemia
– Carbohydrate metabolism
Copyright © 2009, by Mosby, Inc. an affiliate of Elsevier, Inc. All rights reserved.
49
Lactose Intolerance
• Most common disaccharidase deficiency
• Lactase is not present in sufficient amounts,
it is not absent
• Causes abdominal cramping and diarrhea
Copyright © 2009, by Mosby, Inc. an affiliate of Elsevier, Inc. All rights reserved.
50
Summary
• Nutrients from food must be changed,
released, regrouped, and rerouted into forms
the body can use.
• The activities of digestion, absorption, and
transport ensure that key nutrients are
delivered to the body’s cells so metabolic
tasks can be completed.
Copyright © 2009, by Mosby, Inc. an affiliate of Elsevier, Inc. All rights reserved.
51
Summary, cont’d
• Mechanical digestion consists of spontaneous
muscular activity responsible for initial mechanical
breakdown and the movement of the food mass
along the GI tract by the motion of peristalsis.
• Chemical digestion involves the enzymatic action
that breaks food down into smaller components and
releases nutrients for absorption.
Copyright © 2009, by Mosby, Inc. an affiliate of Elsevier, Inc. All rights reserved.
52
Summary, cont’d
• Absorption involves the passage of food nutrients
from the intestines into the mucosal lining of the
intestinal wall.
• Nutrients absorbed are transported throughout the
body by the circulatory system.
• Metabolism is the sum of the body processes that
change food energy taken in (carbohydrate,
protein, and fat) into various forms of energy
Copyright © 2009, by Mosby, Inc. an affiliate of Elsevier, Inc. All rights reserved.
53