Transcript The Digestive System - Dr. Annette M. Parrott

The Digestive System
Organ groups of digestion
• Alimentary organs
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Mouth
Pharynx
Esophagus
Stomach
Small and large intestine
• Accessory digestive
organs
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Teeth and tongue
Liver
Pancreas
Salivary glands
gallbladder
The processes
of digestion
• Ingestion
• Secretion
• Mixing and
propulsion
• Mechanical and
chemical digestion
• Absorption
• Defecation
Peristalsis and segmentation
• Peristalsis
Layers of the GI tract
• Mucosa
– Layer of
epithelium
– Lamina propria
(connective
tissue)
– Thin layer of
smooth muscle
(muscularis
mucosae)
• Submucosa
• Muscularis
• Serosa
ANS input
• Vagus nerve supplies parasympathetic
input to most parts of the GI tract.
• Preganglionic parasympathetic neurons
synapse on postsynaptic neurons in the
submucosal and myenteric plexuses.
• Parasympathetic stimulation increases
motility and GI secretion.
• Sympathetic postsynaptic neurons in
the plexuses decrease GI section and
decrease motility by inhibiting neurons
of ENS
Mouth
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Buccal cavity
Oral mucosa
Vestibule
Gingivae
Hardpalate
Soft palate
Uvula
• Cleanse
mouth
• Dissolve
food
chemicals
• Moisten
food
• Enzymes
break down
carbs
Salivary glands
Teeth
• Crown, neck and
root
• Peridontal
ligament
• Enamel
• Dentin
• Root canal
Tooth varieties
Incisors
Cuspids
Bicuspids
Molars
Mastication
 Bolus
Tongue
Swallowing
• Deglutition
• 3 phases
– Buccal
– Pharyngeal
– Esophogeal
• Peristalsis
– Secondary
peristaltic
waves
Deglutition
• Fundus
• Body
• Pylorus
– Pyloric
sphincter
• Rugae
Stomach
Stomach
histology
Gastric
Glands
• Mucous cells
– Surface & neck
• G cells
• Parietal cells
• Chief cells
• Enteroendocrine
cells
Stomach and chemical digestion
Cephalic (Reflex) phase
– Triggered by sensory signals surrounding food.
– Activates vagal nerve and ANS to enhance
secretions
– Hydrochloric Acid Production in Parietal Cells
Stomach and chemical digestion
Gastric Phase
– Activation of local myeteric reflexes and
vagovagal reflexes
– Gastrin
– Release of HCl from parietal cells
Stomach and chemical
digestion
• Intestinal Phase
– Excitatory component
– Inhibitory component
Gastric Secretion: 3 Phases
Stomach and mechanical
digestion
• Stomach filling
• Contractile activity
– Peristalsis
• Gastric emptying
Small intestine and associated
organs
Small intestine histology
Small intestine histology
Liver
• Digestive function is to produce bile.
• Metabolic function is to process venous
blood from digestive tract
• Functional unit is a lobule
Liver
Liver Functions
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Carbohydrate metabolism
Lipid metabolism
Protein metabolism
Processing of drugs and hormones
Excretion of bilirubin
Synthesis of bile salts
Storage
Phagocytosis
Activation of vitamin D
Cholesterol
Accessory organs
Bile
• Alkaline solution that includes bile salts,
phospholipids and electrolytes.
– Bile salts derived from cholesterol
• Bile salts emulsify fats and solubilize
cholesterol, increasing absorption.
• Bile is recycled
• Fatty chyme and bile returning to liver
stimulates more production of bile.
Gallbladder
• The gallbladder stores and
concentrates bile.
• Bile release into duodenum
1. Fatty chyme stimulates release of CKK and
secretin.
2. CKK enters bloodstream
3. Bile salts and secretin in the blood
stimulate liver to rapidly produce bile.
4. Vagal stimulation leads to weak
contractions.
5. CKK causes gallbladder to contract and
the hepatopancreatic sphincter to relax;
Pancreatic juice
• Insulin & Glucose
Regulation
Digestion in Small intestine:
chemical
• Digestion of carbohydrates
– Pancreatic amylase
– Brush-border enzymes
• Digestion of proteins
– Enzymes from pancreatic juice
– Brush-border peptidases releases single AAs
• Digestion of lipids
– Digestion & Absorption of Fats
• Digestion of nucleic acids
Digestion in Small intestine:
mechanical
• Segmentation leads to chyme being
moved backwards and forwards.
• Parasympathetic input increases
intensity of contractions; sympathetic
input decreases intensity.
• Peristalsis occurs after nutrients are
absorbed; regulated by motilin.
– Migrating motility complex
• Movement through ileocecal sphincter is
enhanced by gastrin.
• Once meal has passed through sphincter
Water
• Water moves in
both directions
and follows flow
of electrolyhtes
Large intestine (5 ft)
• Mechanical
digestion—
haustral churning,
peristalsis, mass
peristalsis
• Chemical digestion
• Absorption
• Feces formation
• Reflexes in the
Colon
Ulcerative Colitis
Defecation reflex
• Mass peristaltic
movements
• Voluntary
contractions of
diaphragm and
abdominals
• Parasympathetic
input
• Voluntary input
Resources
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Human Digestion
Heart Burn Video
Peristalsis Animation
Digestive System