Download Digestive Physiology

Digestive System
Functions
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Ingestion
Secretion
Mixing and propulsion
Digestion
Absorption
Defecation
Digestive Organs
 GI tract:
 Mouth, Pharynx, Esophagus,
Stomach, Small Intestine, Large
Intestine, Anus
 Accessory organs:
 Teeth, Tongue, Salivary glands,
Liver, Gallbladder, Pancreas
GI Tract Layers
 Mucosa
 Epithelium - Strat. Squamous to Simple
Columnar
 Lamina propria
 Some smooth muscle
 Submucosa - areolar
 Muscularis - skeletal higher, smooth
lower
 Serosa - visceral peritoneum
Peritoneum
 Largest serous membrane
 Parietal and visceral
 Five major folds:
 Contain adipose tissue
 Anchor major organs
 Contain blood vessels and lymph
nodes
 Greater Omentum and Mesentary
as examples
Macromolecule Review
1. Carbohydrates - Mono- and
Polysaccharides
2. Proteins - Amino acids form
polypeptides
3. Lipids - Simple, complex, steroids
4. Nucleic Acids
 What kinds of enzymes break
down each group?
Mouth
 Ingestion
 Mastication and
moistening
 Beginning of chemical
digestion
 Movement of bolus to
oropharynx
Accessory Organs in
Mouth
 Salivary glands - parotid,
submandibular, sublingual
 Tongue - papillae and lingual
frenulum
 Teeth
 20 deciduous teeth, 32 permanent
 Incisors (4), canines (2), bicuspid
(4), molars (4-6?) per jaw
Mouth
 Mechanical Digestion
 Mastication - Tongue, teeth, saliva 
Bolus
 Chemical Digestion
 Salivary Amylase - starch  maltose, dextrins
 Lingual Lipase - Activated in stomach Triglycerides  F.A.s and Diglycerides
 Saliva also used to:
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Destroy bacteria (Lysozyme, IgA)
Lubricate food (mucus)
Remove waste
Aid gustation (water)
Esophagus
 Laryngopharynx to stomach
 Upper esophageal sphincter
(skeletal muscle)
 Lower esophageal sphincter
(cardiac)
 Passes through diaphragm at
esophageal hiatus
Esophagus
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Deglutition
(Swallowing)
Peristalsis
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Wavelike
contractions
Alternating
bands of
muscle
Stomach
Stomach
 Mechanical digestion
 Mixing waves - produce chyme and
promote gastric emptying
 Chemical digestion
 Pepsin - proteins into smaller peptides
 HCl - partial denaturation
 Absorbs some water, ions, Fas, some
drugs and alcohol
Gastric Glands
 Gastric Juice
 HCl
 kills microbes
 converts pepsinogen to pepsin
 Pepsin - protein digestion
 Gastric lipase - Triglycerides 
Fas and monoglycerides
 Mucous - protects lining
Gastric glands
Pancreas
 Endocrine and exocrine gland
 Pancreatic islets: insulin and
glucagon (and others)
 Acini: Pancreatic juice
 Sodium bicabonate
 Enzymes to digest all four
macromolecule groups
Liver
 Secretion of Bile
 Bile stored in gall bladder
 Used for:
 Excretion of Bilirubin
 Emulsification of lipids by bile
salts
 Easier absorption of lipids
 Excretion of drugs and hormones
Other Liver Functions
1. Glycogen storage and glucose
release/production
2. Lipid Metabolism
3. Protein metabolism - ease conversion of
a.a., synthesize plasma proteins
4. Detoxification
5. Storage of vitamins/minerals
6. Phagocytosis of old blood cells and
some bacteria
7. Activation of vitamin D
Small Intestine
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90% of all absorption
Aided by:
1. Length (10 ft avg)
2. Villi (1 mm)
3. Microvilli (1 um) - “Brush Border”
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Monomers absorbed into
capillaries or Lacteals
Small Intestine
 Duodenum, jejunum, ileum
 Intestinal glands
 Duodenal glands - alkaline mucus - why?
 Digestive enzymes along w/ pancreas
 Circular folds - better absorption
 Villi
 Absorptive cells
 Capillaries and lacteals
 Microvilli
Small Intestine
 Chemical Digestion
 Brush Border enzymes – all
major groups
 Intestinal Juices - water and
mucus
 Pancreatic Juice, Bile and
Intestinal juice work in
combination
Large Intestine
 Mechanical digestion
 Haustral churning - contraction
following distension
 Peristalsis
 Mass peristalsis - pushes contents into
rectum
 Chemical digestion by bacteria
 Absorption of water, ions, and some
vitamins
Defecation
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Feces formed in large intestine
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Water, Inorganic salts, Bacteria and their
products, Unabsorbed/Indigestible
material, Epithelial cells
Defecation Reflex
1. Rectum distended
2. Stretch receptors  spinal cord
3. Parasymp  contraction of colon
and rectum
4. Internal anal sphincter opens
5. External is voluntarily relaxed
pH
 Enzymes operate at optimal pH
 Saliva = 6.5
 Gastric juice = 2
 Pancreatic Juice = 7.1-8.2
 Intestinal Juice = 7.6
 pH adjusted by negative
feedback (Buffers, Hormone
release)
Hormones
 Gastrin - gastric glands gastric juice , gastric emptying
, Sphincter control
 Cholecystokinen (CCK) - s. Int Pancreatic juice , Bile release
, gastric emptying , satiation
 Secretin - S. Int - Pancreatic
Juice , Gastric Juice 