Function of Digestive System:
Break down carbohydrates, lipids, and
proteins (polymers) into small molecules.
Allows absorption of nutrients (ions and
molecules) into bloodstream.
Alimentary canal
Accessory glands
Mouth
Mechanical digestion: teeth!
pH: 7.0
Chemical digestion: saliva
• amylase (salivary glands)
• mucin (mucins + H2O = mucous)
Saliva also regulates pH in mouth.
Esophagus
• Peristalsis: wave of muscular
contractions (reflex)
Stomach
• Mechanical & chemical: reduce food to
uniform consistency and osmolarity.
• Gastric juice = HCl (parietal cells) + pepsin
(chief cells)
• Mucus (goblet cells) protects stomach from
HCl
pH: 2.0
Small intestine
Functions:
• Digestion of lipids and carbohydrates
• Protein processing
• Absorption of nutrients and water.
pH: 7.8
Carbohydrate digestion
• Starts in oral cavity with salivary
amylase (ptyalin).
• Continues in small intestine with
pancreatic amylases.
• Polysaccharides / disaccharides >>
monosaccharides.
• Types of carbs?
Plants >> starch, cellulose
Animals >> glycogen
Protein digestion
• Starts in stomach:
– Chief cells secrete pepsinogen
– Pepsinogen + HCl = pepsin
– Proteins denatured by HCl; broken down by pepsin
• Then small intestine:
– digested by trypsin and other pancreatic enzymes
• Proteins >> peptide chains >> amino acids
Lipid digestion
Small intestine:
– bile salts from gall bladder emulsify lipids.
– pancreatic lipase digests smaller droplets.
– NaHCO3 from pancreas increases pH.
Lipids >> glycerol, fatty acids,
& glycerides.
Hormones
Molecules (e.g. peptide or steroid)
produced in one part of an
organism that trigger a specific
cellular reaction in target tissues.
Exocrine glands: secrete enzymes
that are transported through ducts.
(e.g. sweat glands, salivary glands)
Endocrine glands: secrete
hormones into circulatory system (no
ducts). (e.g. pituitary gland, adrenal gland)
Pancreas: “mixed” gland
Exocrine products:
• sodium bicarbonate (NaHCO3)
• digestive enzymes (acinar cells)
– lipase – lipids
– trypsin – proteins
– amylase – starches
Pancreas: “Islets of Langerhans”
vascularized clusters of endocrine cells.
Regulate carbohydrate metabolism
(glucose levels in blood).
Islets of Langerhans:
alpha cells = glucagon
beta cells = insulin
Glucagon:
• Promotes the release of glucose from glycogen
stores.
• This causes blood glucose levels to increase
(hyperglycemia).
• Typically released during fasting.
Insulin:
• Glucose is stored in liver (hepatic tissue) and
fat (adipose tissue) as glycogen.
• When insulin is released, these tissues uptake
glucose from the bloodstream.
• This causes blood glucose levels to decrease
(hypoglycemia).
• Typically released after feeding.
Diabetes mellitus
• characterized by hyperglycemia.
• 20.8 million people, or 7% of US
population
Type I Diabetes
•
•
•
•
•
Insulin deficiency
Autoimmune disorder
Islet cells destroyed by immune system
Treat by injection
Not hereditary
Type II Diabetes
•
•
•
•
•
•
Insulin resistance
“adult-onset” diabetes
Over 90% of diabetes
Gradual onset
Hereditary
Associated with age, obesity, physical , ethnic
background and inactivity
• Treated by diet
Mouth
Esophagus
Carbohydrates
Lipids
Amylase
Lipase
Stomach
Lumen
of small
Proteins
Pepsin
(Polypeptides)
Amylase
(Monosaccharides)
(Disaccharides,
Trisaccharides)
Bile salts &
lipase
(Monoglycerides
& Fatty acids)
Trypsin, et al.!
(Short peptides
& amino acids)
intestine
Monoglycerides
& Fatty Acids
Epithelium
of small
intestine
Monosaccharides
Triglycerides
Chylomicrons
Amino acids
Mouth
Esophagus
Carbohydrates
Lipids
Amylase
Lipase
Stomach
Lumen
of small
Proteins
Pepsin
(Polypeptides)
Amylase
(Monosaccharides)
(Disaccharides,
Trisaccharides)
Bile salts &
lipase
(Monoglycerides
& Fatty acids)
Trypsin, et al.!
(Short peptides
& amino acids)
intestine
Monoglycerides
& Fatty Acids
Epithelium
of small
intestine
Monosaccharides
Triglycerides
Chylomicrons
Amino acids
Mouth
Esophagus
Carbohydrates
Lipids
Amylase
Lipase
Stomach
Lumen
of small
Proteins
Pepsin
(Polypeptides)
Amylase
(Monosaccharides)
(Disaccharides,
Trisaccharides)
Bile salts &
lipase
(Monoglycerides
& Fatty acids)
Trypsin, et al.!
(Short peptides
& amino acids)
intestine
Monoglycerides
& Fatty Acids
Epithelium
of small
intestine
Monosaccharides
Triglycerides
Chylomicrons
Amino acids
Mouth
Esophagus
Carbohydrates
Lipids
Amylase
Lipase
Stomach
Lumen
of small
Proteins
Pepsin
(Polypeptides)
Amylase
(Monosaccharides)
(Disaccharides,
Trisaccharides)
Bile salts &
lipase
(Monoglycerides
& Fatty acids)
Trypsin, et al.!
(Short peptides
& amino acids)
intestine
FACILITATED DIFFUSION & TRANSPORT
Monoglycerides
& Fatty Acids
Epithelium
of small
intestine
Monosaccharides
Triglycerides
Chylomicrons
Amino acids
Mouth
Esophagus
Carbohydrates
Lipids
Amylase
Lipase
Stomach
Lumen
of small
Proteins
Pepsin
(Polypeptides)
Amylase
(Monosaccharides)
(Disaccharides,
Trisaccharides)
Bile salts &
lipase
(Monoglycerides
& Fatty acids)
Trypsin, et al.!
(Short peptides
& amino acids)
intestine
Monoglycerides
& Fatty Acids
Epithelium
of small
intestine
Monosaccharides
Triglycerides
Chylomicrons
Amino acids
Mouth
Esophagus
Carbohydrates
Lipids
Amylase
Lipase
Stomach
Lumen
of small
Proteins
Pepsin
(Polypeptides)
Amylase
(Monosaccharides)
(Disaccharides,
Trisaccharides)
Bile salts &
lipase
(Monoglycerides
& Fatty acids)
Trypsin, et al.!
(Short peptides
& amino acids)
intestine
Monoglycerides
& Fatty Acids
Epithelium
of small
intestine
Monosaccharides
Triglycerides
Chylomicrons
BLOODSTREAM
Amino acids