Digestive system
Monday, 25 October 2021 8:30 AM
Organization of the gastrointestinal tract
- Alimentary tract
○ Mouth, pharynx, esophagus, stomach, small intestines and
large intestines
- Sphincters
○ Muscular structures that separate different regions of the
GI tract
○ Upper / lower esophageal, pyloric, sphincter of Oddi,
ileocecal, external and internal anal sphincters
○ Contract in response to nerve / hormone signals
- Accessory organs
○ Salivary glands
○ Liver / gallbladder
○ Pancreas
Layered-structure of gastrointestinal tract
- Mucosa
○ Consists of
§ Epithelium
□ Different functions / arrangements in different
areas of GI tract
® Villus in small intestines to increase SA
® Arrangement dictated by functional
needs
® Esophagus
◊ Epithelium is smooth for passage
of food
□ Secretions
® Exocrine
◊ For digestion
} Acids / digestive enzymes
® Mucous
◊ Protecting the epithelium
® Endocrine
◊ Hormones into the blood
} Regulating GI function
§ lamina propria
§ muscularis mucosa
, ◊ Protecting the epithelium
® Endocrine
◊ Hormones into the blood
} Regulating GI function
§ lamina propria
§ muscularis mucosa
○ Endocrine cells, mucous cells, exocrine glands, enterocytes
- Submucosa
○ Major blood and lymphatic vessels
○ Submucosal (Meissners) plexus
- Muscularis externa
○ Inner circular muscle layer
§ Narrowing of the lumen when contracts
○ Outer longitudinal muscle layer
§ Shortening of tube when contracts
○ Myenteric (Auerbachs) plexus
○ Brings about motility of the GI tract
- Serosa
- Enteric nervous system
○ Submucosal and myenteric plexuses
○ Located wholly in GI tract
§ Independent nervous system
§ Works on its own or with the autonomic nervous
system
○ ENS forms local reflex arcs to coordinate GI activity
○ Submucosal controls secretory activity
○ Myenteric controls smooth muscle activity
Major processes of GI tract
- Digestion
○ Breaking down / dissolving of ingested food
- Secretion
○ Release of acid / enzymes / hormones / mucus
- Absorption
○ Movement of nutrients and water from lumen of GI tract
to blood and lymph
- Motility
○ Muscle contractions / peristalsis
- Elimination
○ Cholesterol / steroids / drug metabolites / feces
§ But most elimination is from kidneys
Regulation of GI tract
- Chemical regulation
○ Endocrine
§ Long distance
Monday, 25 October 2021 8:30 AM
Organization of the gastrointestinal tract
- Alimentary tract
○ Mouth, pharynx, esophagus, stomach, small intestines and
large intestines
- Sphincters
○ Muscular structures that separate different regions of the
GI tract
○ Upper / lower esophageal, pyloric, sphincter of Oddi,
ileocecal, external and internal anal sphincters
○ Contract in response to nerve / hormone signals
- Accessory organs
○ Salivary glands
○ Liver / gallbladder
○ Pancreas
Layered-structure of gastrointestinal tract
- Mucosa
○ Consists of
§ Epithelium
□ Different functions / arrangements in different
areas of GI tract
® Villus in small intestines to increase SA
® Arrangement dictated by functional
needs
® Esophagus
◊ Epithelium is smooth for passage
of food
□ Secretions
® Exocrine
◊ For digestion
} Acids / digestive enzymes
® Mucous
◊ Protecting the epithelium
® Endocrine
◊ Hormones into the blood
} Regulating GI function
§ lamina propria
§ muscularis mucosa
, ◊ Protecting the epithelium
® Endocrine
◊ Hormones into the blood
} Regulating GI function
§ lamina propria
§ muscularis mucosa
○ Endocrine cells, mucous cells, exocrine glands, enterocytes
- Submucosa
○ Major blood and lymphatic vessels
○ Submucosal (Meissners) plexus
- Muscularis externa
○ Inner circular muscle layer
§ Narrowing of the lumen when contracts
○ Outer longitudinal muscle layer
§ Shortening of tube when contracts
○ Myenteric (Auerbachs) plexus
○ Brings about motility of the GI tract
- Serosa
- Enteric nervous system
○ Submucosal and myenteric plexuses
○ Located wholly in GI tract
§ Independent nervous system
§ Works on its own or with the autonomic nervous
system
○ ENS forms local reflex arcs to coordinate GI activity
○ Submucosal controls secretory activity
○ Myenteric controls smooth muscle activity
Major processes of GI tract
- Digestion
○ Breaking down / dissolving of ingested food
- Secretion
○ Release of acid / enzymes / hormones / mucus
- Absorption
○ Movement of nutrients and water from lumen of GI tract
to blood and lymph
- Motility
○ Muscle contractions / peristalsis
- Elimination
○ Cholesterol / steroids / drug metabolites / feces
§ But most elimination is from kidneys
Regulation of GI tract
- Chemical regulation
○ Endocrine
§ Long distance
