General Principles Of GI Flashcards
Key sphincters in the GI tract
1) Upper esophageal sphincter (UES)
- separates the mouth from the esophagus
2) Lower esophageal sphincter (LES)
- separates the esophagus from the stomach
3) pyloric sphincter
- separates the stomach from the duodenum
4) illocecal sphincter
- separates the terminal ileum from the cecum (beginning of large intestine)
5) internal and external anal sphincters
- both function to separate anus from terminal colon
Esophagus primary function
Conduit from the mouth to the stomach
Stomach broad functions
Temporarily stores food and also initiates digestion by churning and secreting proteases and acids
Small vs large intestine functions
Small
- serves for absorption of nutrients from food
- aids in digestion with stomach
Large
- serves as fluid and electrolyte absorption
- aids in producing and storing fecal matter
Accessory organs in the GI tract
Salivary glands
Pancreas
Liver
Pancreas broad function
Secretes digestive enzymes into the duodenum to aid in further break down and nutrient absorption
Secretes HCO3- into the duodenum to neutralize remnant gastric acid from the stomach
Liver broad function
Secretes bile which the gallbladder stores for delivery to duodenum when needed in the presence of fatty foods
General theme of GI wall anatomy
Layers (external -> internal)
1) Serosa
2) Muscularis Externa
- outer longitudinal layer
- inner circular layer
3) Submucosa
4) Muscularis Mucosae
5) Mucosa
- Lamina propria
Serosa layer
Most superficial layer of the Gut
- Enveloping layer of connective tissue that is made up of squamous epithelial cells
Muscularis externa layer
Consists of two layers and is just deep to the mucosa layer
- outer externa = outer longitudinal layer
- inner externa = inner circular layer
Also contains enteric neurons sandwiched between the two muscle layers
- also called “myenteric (Auerbach)plexus”
- responsible for peristalsis of the GI tract
Submucosa layer
Layer of GI tract that is deep to the muscularis externa
- consists of loose CT and blood vessels
- also contains glands that secrete material into the GI lumen
Contains the submucosal (Meissener) plexus
Inner Mucosa layer
Consists of epithelium and loose CT called the lamina propria
- contains capillaries enteric neurons and immune cells
- also contains microvilli/villi and “crypts/glands”
Also conditions the muscularis mucosae
- thin layer of smooth muscle
What are crypts in the inner mucosa layer of the GI?
Invaginated folds of mucosa in the GI tract to increase surface area for digestion and absorption of nutrients/minerals
Enzymes that are found in the mouth and the macronutrients that are digested
Salivary amylase
- (a-amylase/ptyallin)
Lingual lipase
Both are used to initiate the breakdown of lipids and carbohydrates for the GI tract
Gastric enzymes and types of macronutrients it breaks down
Contains gastric proteases and gastric lipases
- initiates protein digestion
- continues fat digestion
does NOT do any carbohydrate digestion
Pancreatic enzymes include that?
Lipase
- essential for final fat metabolism
Chymotrypsin
- essential for final protein metabolism
Amylase
- essential for final carbohydrate metabolism
Small intestine enzymes
Disaccharidases
- completes carbohydrate digestion
Dipeptidases
- completes protein digestion
both are found in the brush border of the small intestine and is referred to as “membrane digestion”
Two plexus of the enteric nervous system
Submucosal plexus
- found in the proximal small intestines -> terminal large intestines
Myenteric plexus
- located between circular and longitudinal muscle layers of the muscularis externa
- found from the proximal esophagus-> the rectum
Sensory/Afferent neuron function in the enteric nervous system
Monitor changes in luminal activity such as
- distention
- smooth muscle tension
- chemistry (pH/osmolality)
- levels of specific nutrients
- levels of mechanical stimulation
Is parasympathetics of sympathetics more in control of the GI system?
Parasympathetic
What induces acinar cells in the pancreas to release bicarbonate and lipase/amylase?
Vagus nerve (parasympathetics)
- vagus stimulation is initiated via*
- conditioned stimuli
- chewing
- swallowing
- hypoglycemia
ANS physiological overview on the GI system
Sympathetics/parasympathetics leave via the spinal cord and bind to N2 receptors on the GI tract
- uses ACh as the main neurotransmitter
Sympathetics releases NE and induces GI muscle movements
Parasympathetics binds to muscarinic receptors on the GI system and increases secretion and motility
Vasovagal reflex
A loop with parasympathetic afferent fibers and the medulla
- stimulation from chemoreceptors/osmoreceptors and mechanoreceptors in the mucosa go to the medulla and are processed
- medulla sends stimulation via the vagus nerve back to these receptors and changes things as needed
What cells help signal to the pancreas the release of its enzymes via a vasovagal reflex
I cells
- sense FA’s/AA’s and peptides in the duodenum
- once sensed by I cells, releases CCK to the vagus nerve which in turn stimulates acinar cells in the pancreas to release enzymes and bicarbonate
