Digestive System
The digestive organs are:
- Oral cavity
- Pharynx
- Esophagus
- Gastrointestinal(GI) tract
- Stomach
- Small intestine(SI)
- Large intestine(LI)
The digestive tract/alimentary canal is a continuous tube of organs where food
travels through and is eliminated as feces.
The organs part of the gastrointestinal(GI)tract are:
- Stomach
- Small intestine(SI)
- Large intestine(LI)
The accessory digestive organs & their function:
- Teeth
- Tongue
- Salivary glands
- Liver
- Gallbladder
- Pancreas
- Fxn: All assist digestion in the GI tract
The general functions of the digestive system are:
- Ingestion: Putting solid/liquids into oral cavity.
- Digestion: breakdown food into smaller structures/molecules.
- Mechanical digestion: physical break down into smaller structures
to increase surface area for enzymes to act on food. Ex: chewing &
churning stomach.
- Segmentation: mechanical digestion by mixing of
food and digestive secretion along the intestines.
- Chemical digestion: breakdown macromolecules into monomers
by digestive enzymes.
- Propulsion: movement through alimentary canal.
- Peristalsis: muscular contraction that propels food down alimentary
canal
- Secretion: production and release of secretions from accessory and digestive
organs to help the digestion of food.
- Absorption: transport of digestive products, electrolytes, vitamins, water through
GI epithelium to blood and lymph vessels.
, - Elimination/Defecation: indigestible materials and waste products are
eliminated by defecation.
The layers of the digestive tract:
- Mucosa: inner layer of the digestive tract that faces the lumen(space where
food/bolus/chyme/feces travels through)
- Epithelium: Simple columnar epithelium(for the digestive tract)&
Stratified squamous epithelium( for the oral cavity to the esophagus
and at the end of the anal canal to protect from friction)
- Lamina propria: loose connective tissue
- Muscularis mucosae: contracts to create grooves/ridges to
increase surface area to contact with food to increase absorption
- Mucosa-associated lymphatic tissue(MALT): mucosa contains a
lot of lymphocytes and lymphatic nodules to help fight off
pathogens
- Submucosa: made of loose connective tissue with blood vessels, lymphatic
vessels, nerve plexus, and possibly glands. MALT is also found in this layer.
- Muscularis externa: typically two smooth muscles layers
- Inner circular layer: circular smooth muscle that prevents the
backflow of food/etc. Sphincters are also in this layer.
- Outer longitudinal layer: longitudinal smooth muscles that propels
food/etc forwards
- Serosa: outermost layer of the digestive tract from the lower esophagus to the
large intestine prior to the rectum and is the continuation of the visceral
peritoneum.
- Serosa is made out of Areolar Tissue.
- Mesothelium: Made of simple squamous epithelium
- Adventitia: most outer layer of the pharynx, most of the esophagus, and rectum
with their connective tissue blending into other connective tissues of other
organs.
The main difference between serosa and adventitia is that serosa covers the organs
in the body cavities whereas adventitia attaches the organ to the surrounding tissues.
Dense bodies are found on the sarcolemma of smooth muscles and are similar to Z
discs of skeletal muscles.
The different types of smooth muscles are:
- Single-unit: located in walls of hollow organs (Ex: uterus, blood vessels,
digestive viscera). Cells are connected by gap junctions so when it contracts, it
contracts as a single unit. Some are autorhythmic
- Multiunit: located within the eye and arrector pili muscles. Cells are in bundles
or single smooth muscle cells without gap junctions with each cell with a neuron
innervating it.
, The source of calcium for smooth muscles is sarcoplasmic reticulum and
extracellularly.
The Enteric Nervous System: regulates motility, secretion, and blood flow of the
esophagus, stomach, and intestines; regulated by parasympathetic system.
- The structures part of this nervous system are:
- Submucosal plexus / Meissner plexus: within the submucosa layer for the
muscularis mucosae and glandular secretion.
- Myenteric plexus / Auerbach plexus: between the muscularis externa
layers for peristalsis.
Periotoneum: serous membrane lining the viscera and abdominopelvic walls to reduce
friction between viscera and walls.
- The different parts of the peritoneum:
- Parietal peritoneum
- Peritoneal cavity
- Visceral peritoneum
The retroperitoneal organs are posterior organs behind the parietal peritoneum (Ex:
duodenum, pancreas, ascending/descending colon, rectum)
Mesentery: are peritoneum that connect visceral peritoneum of organs and the parietal
peritoneum.
- The different types of mesenteries and their locations:
- Falciform ligament: connects liver to anterior abdominal wall and
diaphragm
- Greater omentum: covers the abdominal organs from the greater
curvature of the stomach
- Lesser omentum: connects the lesser curvature of stomach to the liver
- Mesenetery / Mesentery proper : suspends most of SI from the posterior
abdominal wall
- Mesocolon: peritoneum that suspends parts of the large intestine to
posterior abdominal wall
- Transverse mesocolon: suspends the transverse colon from the
posterior wall
- Sigmoid mesocolon: suspends the sigmoid colon from the posterior
wall
The oral cavity is the “mouth” and entrance of the digestive tract lined with
nonkeratinized stratified squamous epithelium and is surrounded by the labia (lips),
buccae(cheeks), palate, and tongue.
Functions of the oral cavity:
- Ingestion of food (taking in food)
- Taste and touch sensation
- Mastication(chewing): mechanical digestion
The digestive organs are:
- Oral cavity
- Pharynx
- Esophagus
- Gastrointestinal(GI) tract
- Stomach
- Small intestine(SI)
- Large intestine(LI)
The digestive tract/alimentary canal is a continuous tube of organs where food
travels through and is eliminated as feces.
The organs part of the gastrointestinal(GI)tract are:
- Stomach
- Small intestine(SI)
- Large intestine(LI)
The accessory digestive organs & their function:
- Teeth
- Tongue
- Salivary glands
- Liver
- Gallbladder
- Pancreas
- Fxn: All assist digestion in the GI tract
The general functions of the digestive system are:
- Ingestion: Putting solid/liquids into oral cavity.
- Digestion: breakdown food into smaller structures/molecules.
- Mechanical digestion: physical break down into smaller structures
to increase surface area for enzymes to act on food. Ex: chewing &
churning stomach.
- Segmentation: mechanical digestion by mixing of
food and digestive secretion along the intestines.
- Chemical digestion: breakdown macromolecules into monomers
by digestive enzymes.
- Propulsion: movement through alimentary canal.
- Peristalsis: muscular contraction that propels food down alimentary
canal
- Secretion: production and release of secretions from accessory and digestive
organs to help the digestion of food.
- Absorption: transport of digestive products, electrolytes, vitamins, water through
GI epithelium to blood and lymph vessels.
, - Elimination/Defecation: indigestible materials and waste products are
eliminated by defecation.
The layers of the digestive tract:
- Mucosa: inner layer of the digestive tract that faces the lumen(space where
food/bolus/chyme/feces travels through)
- Epithelium: Simple columnar epithelium(for the digestive tract)&
Stratified squamous epithelium( for the oral cavity to the esophagus
and at the end of the anal canal to protect from friction)
- Lamina propria: loose connective tissue
- Muscularis mucosae: contracts to create grooves/ridges to
increase surface area to contact with food to increase absorption
- Mucosa-associated lymphatic tissue(MALT): mucosa contains a
lot of lymphocytes and lymphatic nodules to help fight off
pathogens
- Submucosa: made of loose connective tissue with blood vessels, lymphatic
vessels, nerve plexus, and possibly glands. MALT is also found in this layer.
- Muscularis externa: typically two smooth muscles layers
- Inner circular layer: circular smooth muscle that prevents the
backflow of food/etc. Sphincters are also in this layer.
- Outer longitudinal layer: longitudinal smooth muscles that propels
food/etc forwards
- Serosa: outermost layer of the digestive tract from the lower esophagus to the
large intestine prior to the rectum and is the continuation of the visceral
peritoneum.
- Serosa is made out of Areolar Tissue.
- Mesothelium: Made of simple squamous epithelium
- Adventitia: most outer layer of the pharynx, most of the esophagus, and rectum
with their connective tissue blending into other connective tissues of other
organs.
The main difference between serosa and adventitia is that serosa covers the organs
in the body cavities whereas adventitia attaches the organ to the surrounding tissues.
Dense bodies are found on the sarcolemma of smooth muscles and are similar to Z
discs of skeletal muscles.
The different types of smooth muscles are:
- Single-unit: located in walls of hollow organs (Ex: uterus, blood vessels,
digestive viscera). Cells are connected by gap junctions so when it contracts, it
contracts as a single unit. Some are autorhythmic
- Multiunit: located within the eye and arrector pili muscles. Cells are in bundles
or single smooth muscle cells without gap junctions with each cell with a neuron
innervating it.
, The source of calcium for smooth muscles is sarcoplasmic reticulum and
extracellularly.
The Enteric Nervous System: regulates motility, secretion, and blood flow of the
esophagus, stomach, and intestines; regulated by parasympathetic system.
- The structures part of this nervous system are:
- Submucosal plexus / Meissner plexus: within the submucosa layer for the
muscularis mucosae and glandular secretion.
- Myenteric plexus / Auerbach plexus: between the muscularis externa
layers for peristalsis.
Periotoneum: serous membrane lining the viscera and abdominopelvic walls to reduce
friction between viscera and walls.
- The different parts of the peritoneum:
- Parietal peritoneum
- Peritoneal cavity
- Visceral peritoneum
The retroperitoneal organs are posterior organs behind the parietal peritoneum (Ex:
duodenum, pancreas, ascending/descending colon, rectum)
Mesentery: are peritoneum that connect visceral peritoneum of organs and the parietal
peritoneum.
- The different types of mesenteries and their locations:
- Falciform ligament: connects liver to anterior abdominal wall and
diaphragm
- Greater omentum: covers the abdominal organs from the greater
curvature of the stomach
- Lesser omentum: connects the lesser curvature of stomach to the liver
- Mesenetery / Mesentery proper : suspends most of SI from the posterior
abdominal wall
- Mesocolon: peritoneum that suspends parts of the large intestine to
posterior abdominal wall
- Transverse mesocolon: suspends the transverse colon from the
posterior wall
- Sigmoid mesocolon: suspends the sigmoid colon from the posterior
wall
The oral cavity is the “mouth” and entrance of the digestive tract lined with
nonkeratinized stratified squamous epithelium and is surrounded by the labia (lips),
buccae(cheeks), palate, and tongue.
Functions of the oral cavity:
- Ingestion of food (taking in food)
- Taste and touch sensation
- Mastication(chewing): mechanical digestion
