Transcript Glucose Pyruvic acid

The Digestive System and Body
Metabolism
 Digestion
 Breakdown of ingested food
 Absorption of nutrients into the blood
 Metabolism
 Production of cellular energy (ATP)
 anabolic and catabolic cellular activities
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Organs of the Digestive System
Figure 14.1
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Layers of Alimentary Canal Organs
 Structure: 4 common layers
throughout the system
 Mucosa: innermost layer,
nutrients pass through
 Submucosa: connective tissue,
lymph and blood vessels,
nerves
 Muscularis: two or three layers
of smooth muscle, responsible
for motility in GI tract
 Serosa: outermost layer,
connective tissue sheath
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Processes of the Digestive System
Mechanical processing and
movement: chewing, mixing
Secretion: fluid, digestive
enzymes and hormones, bile, acid,
alkali, mucus
Digestion: breaking down food to
smallest absorbable units
Absorption: through mucosa, into
blood or lymph vessels
Elimination: undigested material
eliminated
Figure 14.11
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Digestive Activities of the Mouth
 Mechanical breakdown
 Food is physically broken down by
chewing
 Chemical digestion
 Food is mixed with saliva
 Breaking of starch into maltose by salivary
amylase
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Teeth
 The role is to
masticate (chew) food
 Humans have two sets
of teeth
 Deciduous (baby or
milk) teeth
 20 teeth are fully
formed by age two
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Deglutition (Swallowing)
Buccal phase
 Food is formed into a bolus
 The bolus is forced into the pharynx by the
tongue
Pharyngeal-esophageal phase
 All passageways except to the stomach are
blocked
 Mucus-secreting cells: assist passage of food
 Food motility: gravity and peristalsis
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Stomach Functions
 Acts as a storage tank for food
 Mechanical breakdown, chemical breakdown of
protein begins
 Regulates delivery of chyme to the small intestine
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Propulsion in the Stomach
 Food must first be well mixed
 Rippling peristalsis occurs in the lower
stomach
Figure 14.15
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Food Breakdown in the Stomach
 Gastric juice is regulated by neural and hormonal
factors
 Presence of food or falling pH causes the release of
gastrin
 Gastrin causes stomach glands to produce proteindigesting enzymes (pepsinogen)
 HCl makes the stomach contents very acidic
 Intrinsic Factor; for absorption of Vitamin B12
 Mucus: protects stomach lining from acid
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Chemical Digestion in the Small Intestine
 Source of enzymes: intestinal cells, pancreas,
bile (made by liver) enters from the gall bladder
Figure 14.6
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Role of the Liver in Metabolism
 Bile - bile salts, pigment, cholesterol,
phospholipids, electrolytes
 Detoxifies drugs and alcohol
 Degrades hormones
 Produce blood proteins (albumin and clotting
proteins) and lipids
 Central role in glucose metabolism
 Converts NH4+ to urea for excretion
 Destroys old RBCs
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Propulsion in the Small Intestine
 Suspended from the
posterior abdominal wall
by the mesentery
 Peristalsis is the major
means of moving food
 Segmental movements
 Mix chyme with
digestive juices
 Aid in propelling food
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Small Intestine
 Chemical breakdown to small products
amino acids, sugars, lipids
 95% of food is absorbed here
 Water is absorbed along entire length
 End products of digestion
 Most absorbed by active transport
 Lipids are absorbed by diffusion
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Wall of the Small Intestine
 Villi - fingerlike
structures formed by
the mucosa, with
capillaries
 Microvilli - small
projections of the
plasma membrane
 Found on absorptive
cells
Figure 14.7a
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Absorption of Nutrients
 Proteins and carbohydrates: active transport
 Lipids: broken down and reassembled
 Water: osmosis
 Vitamins and minerals: assorted means
PLAY
Press to play Digestion animation
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Absorption of Proteins and
Carbohydrates
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Figure 14.13
Absorption of Fats
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Figure 14.14
Food Breakdown and Absorption in the
Large Intestine
 No digestive enzymes are produced
 Resident bacteria digest remaining nutrients
 Produce some vitamin K and B
 Release gases
 Water and vitamins K and B are absorbed
 Remaining materials are eliminated via feces
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Large Intestine
Figure 14.8
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Propulsion in the Large Intestine
 Sluggish peristalsis
 Mass movements
 Slow, powerful movements
 Occur three to four times per day
 Presence of feces in the rectum causes a defecation
reflex
 Internal anal sphincter is relaxed
 Defecation occurs with relaxation of the
voluntary (external) anal sphincter
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Endocrine and Nervous Systems
Regulation of Digestion
 Regulation dependent on volume and content of food
 Nervous system: stretch receptors in stomach
 Hormones:
 Gastrin: stimulates release of gastric juice
 Secretin: stimulates pancreas to secrete water and bicarbonate
 Cholecystokinin (CCK): signals pancreas to secrete digestive
enzymes
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Dietary Sources of Major Nutrients
 Carbohydrates
 Mostly from plants
 Includes sugars, starch, cellulose,
glycogen (animals)
 Lipids
 Saturated fats from animal products
 Unsaturated fats from nuts, seeds, and vegetable
oils
 Trans fats - hydrogenated plant oils
 Cholesterol from egg yolk, meats, and milk
products
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Dietary Sources of Major Nutrients
 Proteins
 Complete proteins – contain all essential
amino acids
 Most are from animal products
 Plant tissues also have proteins, but do not
have the needed ratios of amino acids
 Vitamins
 Needed as cofactors with enzymes
 Found in all major food groups
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Dietary Sources of Major Nutrients
 Minerals
 Play many roles in the body
 Most mineral-rich foods are vegetables,
legumes, milk, and some meats
 Water
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Carbohydrate Metabolism
 The body’s preferred source to produce
cellular energy (ATP)
 Glucose (blood sugar) is the major digestive
product and serves as fuel to make ATP
Figure 14.17
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Metabolic Pathways Involved in Cellular
Respiration
Figure 14.18
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Glycolysis harvests chemical energy by
oxidizing glucose to pyruvic acid
Glucose
Figure 6.9A
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Pyruvic
acid
Pyruvic acid is chemically groomed for the
Kreb cycle
 Each pyruvic acid molecule is broken down to form CO2
and a two-carbon acetyl group, which enters the Kreb
cycle
Pyruvic
acid
Acetyl CoA
(acetyl coenzyme A)
CO2
Figure 6.10
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The Krebs cycle completes the oxidation of
organic fuel
Acetyl CoA
 enzymes convert
acetyl to CO2
and generate
many NADH
and FADH2
molecules
KREBS
CYCLE
Figure 6.11A
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2
CO2
Steps in the Electron Transport System
1. Set up H+ gradient using energy of e2. Downhill flow of H+ is used to make ATP
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Figure 3.28
cell
outer
membrane
inner
membrane
mitochondrion
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 An overview of cellular respiration
High-energy electrons
carried by NADH
GLYCOLYSIS
Glucose
Pyruvic
acid
KREBS
CYCLE
Cytoplasmic
fluid
Figure 6.8
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ELECTRON
TRANSPORT CHAIN
AND CHEMIOSMOSIS
Mitochondrion
Fermentation is an anaerobic alternative
to aerobic respiration
 Without oxygen, cells can use glycolysis alone to
produce small amounts of ATP
 But a cell must replenish NAD+
Glucose
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Pyruvic
acid
 In lactic acid fermentation, pyruvic acid is
converted to lactic acid
 NAD+ is recycled
 Contributes to muscle soreness
GLYCOLYSIS
2 Pyruvic
Glucose
acid
Figure 6.15B
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2 Lactic
acid
 Pathways of molecular breakdown
Food, such as
peanuts
Polysaccharides
Fats
Proteins
Sugars
Glycerol Fatty acids
Amino acids
Amino
groups
Glucose
G3P
Pyruvic
acid
Acetyl
CoA
GLYCOLYSIS
Figure 6.16
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KREBS
CYCLE
ELECTRON
TRANSPORT CHAIN
AND CHEMIOSMOSIS
 Biosynthesis of macromolecules from
intermediates in cellular respiration
ATP needed to
drive biosynthesis
KREBS
CYCLE
GLUCOSE SYNTHESIS
Acetyl
CoA
Pyruvic
acid
G3P
Glucose
Amino
groups
Amino acids
Fatty acids Glycerol
Sugars
Proteins
Fats
Polyscaccharides
Cells, tissues, organisms
Figure 6.17
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Body Energy Balance
 Energy intake = total energy output (heat +
work + energy storage)
 Energy intake from food oxidation
 Proteins, carbs have 4 Cal/gm
 Fats have 9 Cal/gm
 Energy output
 Heat is usually about 60%
 Storage energy is in the form of fat or
glycogen
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Regulation of Food Intake
 Body weight is usually relatively stable
 Energy intake and output remain about
equal
 Mechanisms that may regulate food intake
 Levels of nutrients in the blood
 Hormones
 Body temperature
 Psychological factors
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Metabolic Rate and Body Heat
Production
 Basic metabolic rate (BMR) reflects the amount
of energy spent per unit of time by a body at rest
 Factors that influence BMR:
 Body shape (height and weight),
gender, body composition, age,
stress, food intake, genetics
 TMR = Total Metabolic Rate
 Total energy spent, includes activity above
BMR
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Disorders of the Digestive System
 Disorders of digestive (GI) tract: lactose
intolerance, diverticulosis, colon polyps
 Disorders of accessory organs: hepatitis,
gallstones
 Malnutrition: 13% of world’s population
undernourished
 Obesity: epidemic in US
 Eating disorders: anorexia nervosa, bulimia
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