Transcript Digestive_System_and_Body_Metabolism__Ch

The Digestive System and
Body Metabolism
Chapter 14
1
Outline
•
•
•
•
The Functions of the Digestive Tract
The Digestive Tract
– Mouth
– Pharynx
– Esophagus
– Stomach
– Small Intestine
– Large Intestine
– Accessory Organs
Metabolism
Homeostatic Considerations
2
Functions of the Digestive Tract
•
•
•
•
•
Ingest food.
Digest food into nutrients that can cross
plasma membranes.
Absorb nutrients.
Eliminate indigestible remains.
Critically involved in homeostasis.
3
Figure 14.1 The human digestive system: Alimentary canal and accessory organs.
The Digestive Tract
Mouth (oral cavity)
Tongue
Parotid gland
Sublingual gland
Submandibular
gland
Salivary glands
Pharynx
Esophagus
Stomach
Pancreas
(Spleen)
Liver
Gallbladder
Small
intestine
Duodenum
Jejunum
Ileum
Anus
© 2015 Pearson Education, Inc.
Transverse colon
Descending colon
Ascending colon
Cecum
Sigmoid colon
Rectum
Appendix
Anal canal
Large intestine
Figure 14.2a Anatomy of the mouth (oral cavity).
The Digestive Tract: Mouth
Nasopharynx
Hard
palate
Oral
cavity
Soft palate
Lips (labia)
Palatine tonsil
Vestibule
Lingual tonsil
Lingual
frenulum
Tongue
Hyoid bone
Trachea
(a)
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Uvula
Oropharynx
Epiglottis
Laryngopharynx
Esophagus
The Digestive Tract: Mouth
•
Mouth
– Ceiling: anterior-hard palate (bone); posteriorsoft palate (cartilage).
– Floor: tongue; contains taste buds; composed of
skeletal muscle; mixes chewed food with saliva
and forms a bolus in preparation for swallowing.
– Tonsils help protect against infection.
– Teeth used to chew food into pieces small
enough to swallow.
– Three pairs of salivary glands send juices
through ducts to the mouth.
 Saliva contains bicarbonate and salivary
amylase (some carbohydrate breakdown).
6
Figure 14.2a Anatomy of the mouth (oral cavity).
The Digestive Tract: Mouth
Nasopharynx
Hard
palate
Oral
cavity
Soft palate
Lips (labia)
Palatine tonsil
Vestibule
Lingual tonsil
Lingual
frenulum
Tongue
Hyoid bone
Trachea
(a)
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Uvula
Oropharynx
Epiglottis
Laryngopharynx
Esophagus
The Digestive Tract: Mouth and Teeth
(Gingiva)
8
The Digestive Tract: The Pharynx
•
Pharynx
– Receives air from the nasal cavities and
food from the mouth. Paths of air and
food cross.
– Swallowing
 A reflex action that occurs in the
pharynx.
 Soft palate moves to close off
nasopharynx, and the trachea moves
under the epiglottis to cover the glottis.
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The Digestive Tract: The Pharynx; Swallowing
10
Wall of the Digestive Tract
11
Figure 14.3 Basic structure of the alimentary canal wall.
Visceral peritoneum
Intrinsic nerve plexuses
• Myenteric nerve plexus
• Submucosal nerve plexus
Submucosal glands
Mucosa
• Surface epithelium
• Lamina propria
• Muscle layer
Submucosa
Muscularis externa
• Longitudinal muscle
layer
• Circular muscle layer
Serosa
(visceral peritoneum)
Mesentery
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Nerve
Artery
Vein
Gland in
mucosa
Lumen
Duct of gland
outside alimentary
canal
Lymphoid tissue
The Digestive Tract: The Esophagus
•
Esophagus
– A muscular tube that conducts food bolus from
the pharynx through the thoracic cavity and
diaphragm into the stomach in the abdominal
cavity.
– Motility of GI Tract
Peristalsis: Rhythmic smooth muscle movements
push food along the digestive tract.
 Segmentation: Smooth muscle contractions
result in back-and-forth mixing of lumen
contents.

–
Sphincters encircle tubes and act as valves.
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Motility of the
Gastrointestinal
Tract
Esophagus
Bolus of food
Stomach
a) Peristalsis.
b) Segmentation.
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Figure 14.3
The Digestive Tract: The Stomach
•
Stomach
– Stores food and aids in digestion.
– Columnar epithelial lining contains gastric pits leading
into gastric glands.
 Produce gastric juice containing enzyme pepsin
(some protein breakdown), hydrochloric acid (HCl),
mucus.
 pH in stomach from HCl is 1-2; kills bacteria.
– Walls of stomach have folds which help churn and mix
food and gastric juices.
 Chyme leaves the stomach and enters the small
intestine.
– A bacterium, Helicobacter pylori, lives in the mucus and
is the cause of gastric ulcers.
15
Anatomy of the Stomach
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esophagus
lower gastroesophageal
sphincter
pyloric
sphincter
muscularis layer
has three layers
of muscle.
mucosa layer
has rugae.
c. Gastric pits in mucosa
gastric pit
SEM 3,260x
lower gastroesophageal
sphincter
a. Stomach
gastric pit
gastric gland
cells that secrete
gastric juice
b. Gastric glands
pyloric
sphincter
d. How the stomach empties
c: © Dr. Fred Hossler/Visuals Unlimited
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Figure 14.15 Peristaltic waves in the stomach.
Pyloric
valve
closed
Pyloric
valve
slightly
opened
1 Propulsion: Peristaltic
waves move from the
fundus toward the pylorus.
2 Grinding: The most
vigorous peristalsis and
mixing action occur close to
the pylorus. The pyloric end
of the stomach acts as a
pump that delivers small
amounts of chyme into the
duodenum.
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Pyloric
valve
closed
3 Retropulsion: The
peristaltic wave closes the
pyloric valve, forcing most of
the contents of the pylorus
backward into the stomach.
The Digestive Tract: The Small Intestine
•
The Small Intestine: Duodenum, Jejunum, Ileum
– The primary site for digestion. (duodenum,
jejunum)
Receives digestive enzymes from pancreas;
pancreatic amylase, trypsin, lipase; also sodium
bicarbonate to neutralize stomach acid.
 Produces peptidases and maltase.
 Receives bile from liver to emulsify fat.

–
The primary site for nutrient absorption.
(jejunum, ileum)
Walls contain villi which increase surface area and
thus absorptive capability.
 Nutrients (amino acids, glucose) move into blood
capillaries and fats move into the lacteals headed for
the lymphatic system.

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Figure 14.1 The human digestive system: Alimentary canal and accessory organs.
The Digestive Tract
Mouth (oral cavity)
Tongue
Parotid gland
Sublingual gland
Submandibular
gland
Salivary glands
Pharynx
Esophagus
Stomach
Pancreas
(Spleen)
Liver
Gallbladder
Small
intestine
Duodenum
Jejunum
Ileum
Anus
© 2015 Pearson Education, Inc.
Transverse colon
Descending colon
Ascending colon
Cecum
Sigmoid colon
Rectum
Appendix
Anal canal
Large intestine
Figure 14.6 The duodenum of the small intestine and related organs.
Right and left
hepatic ducts
from liver
Cystic duct
Common hepatic duct
Bile duct and sphincter
Accessory pancreatic duct
Pancreas
Gallbladder
Jejunum
Duodenal
papilla
Hepatopancreatic
ampulla and sphincter
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Main pancreatic duct and sphincter
Duodenum
Digestion and Absorption of Nutrients
21
Figure 14.7 Structural modifications of the small intestine.
Blood vessels
serving the small
intestine
Muscle
layers
Villi
Small Intestine Anatomy
Microvilli
(brush border)
Lumen
Circular folds
(plicae circulares)
Absorptive
cells
Lacteal
(a) Small intestine
(c) Absorptive
cells
Villus
Blood
capillaries
Lymphoid
tissue
Intestinal
crypt
Muscularis
mucosae
Venule
Lymphatic vessel
Submucosa
(b) Villi
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Left subclavian
vein
Villus (greatly enlarged)
Chylomicron
Heart
Liver
Hepatic
portal
vein
Thoracic duct
Small
shortchain
fatty
acid
Blood
capillary
Amino acid
Lacteal
Monosaccharide
Arteriole
Venule
Blood
Lymphatic vessel
Lymph
(b) Movement of absorbed nutrients into blood and lymph
Inferior vena cava
Accessory
Organs: LiverHepatic Portal
System
Hepatic veins
Liver
Spleen
Hepatic
portal vein
Stomach
Pancreas
Small intestine
Large
intestine
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Figure 14.11
Accessory Organs: Liver (Con’t)
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Accessory Organs: Liver (Cont.)
•
Liver: Acts as gate keeper for blood
– Hepatic portal system
All blood from digestive tract goes to liver first before
entering the body
 Fats entering lacteals do not go to liver first

–
Main biochemical processing plant for body.







Detoxifies blood; excretes drugs and chemically alters them.
Stores iron & copper and fat-soluble vitamins (A, B12, D, E, K).
Makes plasma proteins (albumins, fibrinogen, prothrombin)
Stores glucose as glycogen, breaks down glycogen to glucose
to maintain blood glucose levels.
Converts amino acids & lactic acid to glucose or fats
Phagocytizes old red & white blood cells, put waste into bile;
phagocytizes some bacteria
Produces & regulates cholesterol levels, converts some to bile
salts
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Accessory Organs: Liver (Cont.)
•
Liver: Acts as gate keeper for blood (Cont.)
– Main biochemical processing plant for body
(Cont.)
Stores some triglycerides
 Produces lipoproteins that transport fatty acids,
triglycerides & cholesterol throughout the body
 Involved in activation of vitamin D with skin & kidneys
 Protein metabolism- deamination of amino acids so
they can be converted to glucose or fats- ammonia
converted to urea

27
•
Accessory Organs: Pancreas
Pancreas
– Endocrine Function: Secretes insulin and
glucagon that regulate blood glucose
levels.
– Exocrine Function: Secretes digestive
enzymes (pancreatic amylase, trypsin,
lipase) and sodium bicarbonate.
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The Digestive Tract: The Large Intestine
•
•
The large intestine absorbs water, salts, and some
vitamins, and stores fecal material.
Contains bacteria that produce Vitamin K
(symbiosis)
– Cecum is blind end of large intestine.
– Colon.
 Ascending.
 Transverse.
 Descending.
 Sigmoid.
– Rectum.
– Anus.
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Figure 14.1 The human digestive system: Alimentary canal and accessory organs.
The Digestive Tract
Mouth (oral cavity)
Tongue
Parotid gland
Sublingual gland
Submandibular
gland
Salivary glands
Pharynx
Esophagus
Stomach
Pancreas
(Spleen)
Liver
Gallbladder
Small
intestine
Duodenum
Jejunum
Ileum
Anus
© 2015 Pearson Education, Inc.
Transverse colon
Descending colon
Ascending colon
Cecum
Sigmoid colon
Rectum
Appendix
Anal canal
Large intestine
Figure 14.8 The large intestine.
The Digestive Tract: The Large Intestine
Left colic
(splenic) flexure
Transverse
mesocolon
Right colic
(hepatic) flexure
Transverse
colon
Haustrum
Descending
colon
Ascending colon
Cut edge of
mesentery
Ileum (cut)
Ileocecal valve
Teniae coli
Sigmoid
colon
Cecum
Appendix
Rectum
Anal canal
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External anal sphincter
The Digestive Tract: Regulation of Digestive
Secretions
• Secretion of digestive juices is promoted by
the nervous system and by hormones.
– Hormones are produced by one set of
cells and affect a different set of cells.
Gastrin: from stomach; increases gastric
glands secretion.
 Gastric inhibitory peptide (GIP): from
duodenum; decrease gastric gland secretion.
 Secretin: from duodenum; increase
pancreatic and liver secretions.
 Cholecystokinin (CCK): from duodenum;
increase pancreatic secretions & gallbladder
contraction (bile delivery increased).

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Hormonal Control of Digestive Secretions
33
Basic Chemical Reactions Underlying Metabolism
•
Metabolism
– Collection of all the controlled biochemical
reactions that take place within the body
– Enzymes are responsible for controlling all of
the reactions
– Two types of processes involved:
 Catabolism
 Anabolism
Basic Chemical Reactions Underlying Metabolism
•
Catabolism and Anabolism
– Two major classes of metabolic reactions
– Catabolic pathways
 Break larger molecules into smaller
products

–
Exergonic (release energy)
Anabolic pathways
 Synthesize large molecules from the
smaller products of catabolism

Endergonic (require more energy than they
release)
Exergonic & Endergonic: Differences
36
Potential energy
Activation Energy
Activation
energy
Energy
absorbed
to start
reaction
Energy
released
as new
bonds
form
Energy of
reactants
Energy of
products
Progress of the reaction
Activation Energy: Effect of Catalyst
Activation energy
needed without catalyst
Potential energy
Activation energy
needed with catalyst
Energy of
reactants
Energy of
products
Progress of the reaction
The effect of enzymes on chemical reactions
Figure 5.4
Metabolism composed of catabolic and anabolic
reactions
Figure 5.1
ATP as “Energy Currency” of cell
Heat
released
Catabolic reactions
transfer energy from
complex molecules to
ATP
Simple molecules such as
glucose, amino acids, glycerol,
and fatty acids
ATP
ADP +
P
Complex molecules such as
glycogen, proteins, and
triglycerides
Anabolic reactions
transfer energy from
ATP to complex
molecules
Heat
released
•
•
Glucose Metabolism
Glucose breakdown requires three subpathways.
– Glycolysis.
– Citric Acid Cycle (Krebs cycle).
– Electron Transport System.
Altogether, the breakdown of one glucose
molecule results in 36 ATP molecules.
42
Glucose Metabolism (Cont.)
43
Figure 14.20 During cellular respiration, ATP is formed in the cytosol and in the mitochondria.
Chemical energy (high-energy electrons)
Chemical energy
CO2
CO2
Glycolysis
Cytosol
of cell
Krebs
cycle
Pyruvic
acid
Glucose
1 During glycolysis,
each glucose molecule
is broken down into two
molecules of pyruvic
acid as hydrogen atoms
containing high-energy
electrons are removed.
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H2O
Mitochondrion
Mitochondrial
cristae
Via substrate-level
phosphorylation
2
ATP
Electron transport
chain and oxidative
phosphorylation
Via oxidative
phosphorylation
2
ATP
2 The pyruvic acid enters
the mitochondrion, where
Krebs cycle enzymes
remove more hydrogen
atoms and decompose it
to CO2. During glycolysis
and the Krebs cycle, small
amounts of ATP are formed.
28
ATP
3 Energy-rich electrons picked up by
coenzymes are transferred to the electron
transport chain, built into the cristae
membrane. The electron transport chain
carries out oxidative phosphorylation,
which accounts for most of the ATP
generated by cellular respiration, and
finally unites the removed hydrogen with
oxygen to form water.
Summary of Glucose Metabolism
1 Glucose
1
2
GLYCOLYSIS
ATP
+
2 NADH + 2 H
2 Pyruvic acid
2
FORMATION
OF ACETYL
COENZYME A
2 CO2
4
2 NADH + 2 H+
2 Acetyl
coenzyme A
ELECTRON
TRANSPORT
CHAIN
32 or 34
3
KREBS
CYCLE
2
ATP
4
CO2
6
NADH + 6 H+
2
FADH2
Electrons
ATP
e–
e–
e–
6
O2
6
H2O
Summary of Electron Transport Chain
Outer membrane
Matrix
Inner membrane
H+
channel
High H+ concentration
between inner and
outer mitochondrial
membranes
2
H+
H+
Electron
transport chain
(includes proton
pumps)
Inner
mitochondrial
membrane
1
3
Energy from
NADH + H+
Low H+ concentration in
matrix of mitochondrion
ADP + P
ATP synthase
ATP
Summary of Electron Transport Chain
Space between outer and
inner mitochondrial
H+
membranes
H+ channel
H+
Cyt c
e–
Inner
mitochondrial
membrane
e–
e–
Q
e–
e–
Mitochondrial
matrix
NADH + H+
NAD+
H+
3
2H+ + 1/2 O2
ADP + P
H2O
1
NADH dehydrogenase
complex: FMN and five
Fe-S centers
2
H+
Cytochrome b–c1
complex: cyt b,–cyt c1,
and an Fe-S center
3
ATP synthase
Cytochrome oxidase
complex: cyt a, cyt a3,
and two Cu
ATP
Possible arrangement of an electron transport chain
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Figure 5.18
Lipid Metabolism
•
Transport of Lipids
– Very insoluble in water
– Liver and intestine make proteins to make lipids
water-soluble
 Lipoproteins- spherical combinations of
proteins, phospholipids & cholesterol
 Proteins are called apoproteinsdesignated A, B, C, D & E- each have
different function in uptake
 Four classes of lipoproteins
1.
Chylomicrons
2.
Very-low-density lipoprotein
3.
Low-density lipoprotein
4.
High-density lipoprotein
Apo C-2
Nonpolar lipids:
Cholesterol ester
Triglyceride
Apo E
Amphipathic lipids:
Phospholipid
Cholesterol
Apo B100
Lipid Metabolism
•
Transport of Lipids (Cont.)
1.
2.
3.
Chylomicrons (85% triglycerides)
 Made by intestinal cells- transport of dietary lipids
to adipose tissue- in plasma only a few minutes;
liver takes up chylomicron remnants after adipose
passage
Very-low-density lipoprotein (VLDL) (50%
triglycerides)
 Made by hepatocytes- endogenous lipids from liver
to adipose tissue for storage- converted to LDL
Low-density lipoprotein (LDL) (50% cholesterol)
 Made by hepatocytes- deliver cholesterol to all
body cells for cell membrane repair, making steroid
hormones, bile salts- involved with fatty plaque
build up in atherosclerosis
Lipid Metabolism
•
Transport of Lipids (Cont.)
4.
High-density lipoprotein (HDL) (40-45% protein)
– Made by hepatocytes- remove excess cholesterol
from body cells for transport to liver for elimination;
prevent accumulation of cholesterol in blood- help
prevent fatty plaque build up & thus atherosclerosis
•
Essential Fatty Acids
–
Two essential fatty acids the body can’t synthesizemust be ingested
1. Linoleic acid
2. Linolenic acid
Lipid Catabolism: Lipolysis catalyzed by
lipases
Up to 129 ATP from 16 carbon FA
Figure 5.23
1 Glucose
1
2
GLYCOLYSIS
ATP
+
2 NADH + 2 H
2 Pyruvic acid
2
FORMATION
OF ACETYL
COENZYME A
2 CO2
4
2 NADH + 2 H+
2 Acetyl
coenzyme A
ELECTRON
TRANSPORT
CHAIN
32 or 34
3
KREBS
CYCLE
2
ATP
4
CO2
6
NADH + 6 H+
2
FADH2
Electrons
ATP
e–
e–
e–
6
O2
6
H2O
Protein Metabolism
•
No Storage of Protein
– Amino acids (dietary)
 Oxidized to produce ATP
 Used to synthesis new proteins
 Excess amino acids converted to glucose
(gluconeogenesis) or triglycerides
(lipogenesis)
 Uptake into cells stimulated by: Insulin
Protein Catabolism
•
Certain amount of protein catabolism each day
– Stimulated by cortisol
 Proteins from worn-out cells; amino acids transformed to
other amino acids, recycled for use in other proteins
 Transamination- exchange of amino groups between
molecules
 Small amount of amino acids oxidized to produce ATP by
all cells of the body
 Deamination- amino group needs to be removed
before molecule can enter Krebs cycle
 Occurs in liver, produces ammonia (NH3)- highly
toxic, converted to urea by liver
Amination and Transamination
Figure 5.31
Protein catabolism
NH3
Figure 5.24
Alanine
Cysteine
Glycine
Serine
Threonine
Phenylalanine
Pyruvic acid
Tyrosine
Leucine
Lysine
Tryptophan
Aspartic acid
Asparagine
Phenylalanine
Tyrosine
Acetoacetyl
CoA
Acetyl CoA
Oxaloacetic acid
Isoleucine
Leucine
Tryptophan
Citric acid
Malic acid
Isocitric acid
Fumaric acid
Alpha-ketoglutaric
acid
Succinic acid
Succinyl CoA
Isoleucine
Methionine
Valine
Glutamic
acid
Arginine
Histidine
Glutamine
Proline
1 Glucose
1
2
GLYCOLYSIS
ATP
+
2 NADH + 2 H
2 Pyruvic acid
2
FORMATION
OF ACETYL
COENZYME A
2 CO2
4
2 NADH + 2 H+
2 Acetyl
coenzyme A
ELECTRON
TRANSPORT
CHAIN
32 or 34
3
KREBS
CYCLE
2
ATP
4
CO2
6
NADH + 6 H+
2
FADH2
Electrons
ATP
e–
e–
e–
6
O2
6
H2O
Protein Anabolism
•
•
•
•
Protein synthesized on ribosomes
Stimulated by insulin-like growth factor, thyroid hormones,
insulin, estrogen, testosterone
Adequate intake of protein is critical to life
Essential Amino Acids
– Of the 20 amino acids, 10 are essential- 10 essential
amino acids can’t be made by the body, 10 nonessential
can be made
Essential Amino Acids
62
Homeostatic Considerations
•
•
•
•
The digestive system brings in nutrients so that all
the cells of the body can survive.
Digestive system is part of the endocrine system
as it produces hormones to help regulate itself.
The pancreas is part of the digestive and
endocrine systems as it produces the main
digestive enzymes and secretes the main glucose
regulatory hormones insulin and glucagon.
The liver is part of the digestive system, the
endocrine system, the defense system, and
regulates all aspects of the blood. As the main
biochemical processing plant, it can be considered
the most important organ in the body.
63
Need to Know
1.
Small Intestine
A.
Most digestion occurs here
B.
Most absorption occurs here
C.
Digestive enzymes come from pancreas such
as pancreatic amylase, trypsin, and lipase
D.
Liver provides bile to help digest fats
E.
Absorption surface high due to villi and
microvilli
F.
Amino acids and glucose go into capillaries
while fat goes into the lacteals
G.
Digestion under nervous and significant local
hormonal control
H.
Sodium bicarbonate from pancreas
neutralizes all of the acid from the stomach
64
Need to Know (Cont.)
2.
Liver
A.
Main biochemical processing plant
B.
Hepatic portal system: all blood from
digestive tract must flow through the
liver first before going to the rest of the
body
C.
Regulates the composition of the blood
65
Need to Know (Cont.)
3.
4.
Stomach
A.
Low pH for killing bacteria not for digestion
B.
Very little digestion occurs in the stomach
C.
It’s function is to help break up the food so
that it can move down the rest of the tube
easily
Large Intestine
A.
Principal area where water, salt, and vitamins
are absorbed
B.
Indigestible waste is eliminated
66
Need to Know (Cont.)
5.
6.
Mouth
A.
Teeth mash food for passage down
esophagus
B.
Salivary glands produce juices to add to the
food to make it into a swallowable material
C.
Tongue: area of taste buds; forms food bolus
for swallowing
Pancreas
A.
Besides producing digestive enzymes, the
organ produces insulin and glucagon for
glucose regulation
67