Digestion Power Point

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Chapter 21
Nutrition and Digestion
PowerPoint Lectures for
Campbell Biology: Concepts & Connections, Seventh Edition
Reece, Taylor, Simon, and Dickey
© 2012 Pearson Education, Inc.
Lecture by Edward J. Zalisko
Figure 21.0_2
Introduction
 All animals must eat to provide
– energy and
– the building blocks used to assemble new molecules.
 Animals also need essential
– vitamins and
– minerals.
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THE HUMAN DIGESTIVE
SYSTEM
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Food processing occurs in four stages
 Food is processed in four stages.
1. Ingestion is the act of eating.
2. Digestion is the breaking down of food into molecules
small enough for the body to absorb.
•
Remember: biomolecule  subunits by hydrolysis
3. Absorption is the take-up of the products of digestion,
usually by the cells lining the digestive tract.
4. Elimination is the removal of undigested materials out of
the digestive tract.
© 2012 Pearson Education, Inc.
Mechanical digestion = mechanical breakdown of large  small food
particles
•Just a physical change in material!!
•Increases surface area of food particles for chemical digestion
Pieces
of food
Small
molecules
Mechanical
digestion
1
Ingestion
2
Digestion
Undigested
material
Nutrient
molecules
enter body
cells
Chemical
digestion
(hydrolysis)
3
Absorption
4
Elimination
Components
Food Molecules
Proteindigesting
enzymes
Chemical digestion
•Hydrolysis of covalent
bonds within molecules
•Requires enzyme to
catalyze these events
Amino acids
Protein
Polysaccharide
Carbohydratedigesting
enzymes
Disaccharide
Monosaccharides
Nucleic-aciddigesting
enzymes
Nucleotides
Nucleic acid
Fat-digesting
enzymes
Fat
Glycerol Fatty acids
Figure 21.4
Nasal cavity
A schematic diagram of the
human digestive system
Oral cavity
(mouth)
Tongue
Oral
cavity
Salivary
glands
Salivary
glands
Pharynx
Esophagus
Esophagus
Liver
Gallbladder
Liver
Pancreas
Esophagus
Stomach
Small
intestine
Sphincters
Gallbladder
Large
intestine
Pancreas
Rectum
Anus
Small
intestine
Large
intestine
Key
Alimentary canal
Accessory digestive
glands
Rectum
Anus
Stomach
Small intestine
Mouth
 pH = 7
 Mechanical digestion
– Chewing cuts, smashes, and grinds food, making it
easier to swallow.
 Chemical digestion
– Saliva releases salivary amylase
– Polysaccharides + H2O  mono and disaccharides
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Esophageal sphincter
(contracted)
Bolus of
food
Bolus of
food
Muscles contract,
squeezing the bolus
through the esophagus.
Muscles relax,
allowing the
passageway
to open.
Stomach
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Peristalsis:
Smooth muscle
contractions that
move food
through digestive
tract
Stomach
 pH = 2
 Mechanical digestion
– Churning of stomach
– Low pH denatures proteins
 Chemical digestion
– Pepsin
– Proteins + H2O  amino acids
 Secretes gastric juice, made up of
–
Mucus (protects stomach lining from HCl)
–
Pepsinogen (inactive form of pepsin)
–
–
Gastric juice secreted
by gastric glands in
response to GASTRIN
hormone.
Pepsinogen (inactive)  pepsin (active) in presence of acid
HCl
–
kills ingested bacteria,
–
breaks apart cells in food, and
–
denatures proteins.
© 2012 Pearson Education, Inc.
Figure 21.8
Esophagus
Sphincter
Lumen (cavity)
of stomach
Stomach
Gastrin
Release of gastric juice
(mucus, HCl, and pepsinogen)
Pits
Sphincter
Epithelium
Small
intestine
Interior
surface
of the
stomach
Gastric juice
secreted by gastric
glands in response
to GASTRIN
hormone.
3
Pepsinogen
2
Mucous
cells
HCl
1
H
Gastric
gland
Cl
Chief cells
Parietal cells
Pepsin
(active
enzyme)
Pancreas
 Produces and secretes:

Pancreatic juice to small intenstine
Liver
 Trypsinogen (inactive form of
trypsin)
 Lipase
 Pancreatic juice released to small
instestine in response to SECRETIN
hormone
 Insulin and glucagon (regulate blood
sugar)
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Stomach
Gallbladder
 Na-bicarbonate (neutralize pH
of incoming stomach
secretions)
 Pancreatic amylase
Bile
Chyme
Intestinal
enzymes
Duodenum of
small intestine
Pancreatic juice
Pancreas
Liver
 Produces bile
 converts glucose in blood to glycogen,
 stores glycogen and releases sugars back into the
blood as needed,
 Detoxifies substances absorbed from digestive
tract
 Processes amino acids and produces urea
Liver
Bile
Stomach
Gallbladder
Chyme
Intestinal
enzymes
Duodenum of
small intestine
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Pancreatic juice
Pancreas
Gallbladder
 Stores bile produced by liver
– Bile released to small intestine in response to hormone
SECRETIN
 Bile
– Synthesized from cholesterol, aids in physical digestion
of lipids
Liver
Bile
– Emulsify – disperse oil
Stomach
Gallbladder
into water
– Increases efficiency of
chemical digestion of
lipids by lipase
© 2012 Pearson Education, Inc.
Chyme
Intestinal
enzymes
Duodenum of
small intestine
Pancreatic juice
Pancreas
Small Intestine
 Major organ of chemical digestion and nutrient absorption
 pH = 8 due to Na-bicarb released by pancreas
 Releases the hormone SECRETIN in response to food entering small
intestine
 Final chemical digestion of macromolecules:
– Pancreatic amylase
– Poly and disaccrharides + H2O  monosaccharides
– Trypsinogen  trypsin (active) at basic pH
– Proteins + H2O  amino acids
– Chymotrypsinogen  chymotrypsin (active) at basic pH
– Proteins + H2O  amino acids
– Lipase (with assistance of bile)
– Triglycerides + H2O  glycerol + fatty acids
© 2012 Pearson Education, Inc.
Small intestine is site of absorption!!
Villi and Microvilli increase surface area for absorption
Lumen of intestine
Nutrient absorption
Vein carrying
blood to the liver
Microvilli
Amino
acids
and
sugars
Epithelial
cells
Muscle
layers
Lumen
Fats
Blood
capillaries
Large
circular folds
Blood
Lymph
vessel
VILLI
Lymph
Nutrient
absorption
VILLI
Intestinal wall
© 2012 Pearson Education, Inc.
Fatty
acids
and
glycerol
Epithelial cells of
a villus
• Nutrients pass into epithelial cells
by facilitated or active transport
Small intestine is site of absorption!!
Lumen of intestine
Nutrient absorption
Microvilli
Amino
acids
and
sugars
Epithelial
cells
Fatty
acids
and
glycerol
Fats
Blood
capillaries
 Amino acids
and sugars
pass
•
out of the
intestinal
into blood
Blood
Lymph
vessel
Lymph
Epithelial cells of
a villus
VILLI
 Fatty acids and glycerol are
•
•
•
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recombined into fats,
coated with proteins, and
transported into lymph vessels.
 Blood from the
digestive tract
drains
– into the hepatic
portal vein
Heart
– to the LIVER.
Liver
Hepatic
portal
vein
Intestines
Large Intestine
 Excretes solid wastes
 Reabsorption of
water
 Synthesis of several Large
vitamins, like Vitamin intestine
(colon)
K, with help of
End of
bacteria
small
intestine
Unabsorbed
food material
Appendix
Cecum
Small
intestine
Rectum
Anus
Figure 21.UN02
a.
g.
b.
h.
c.
d.
e.
i.
j.
f.
k.
l.
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