Lecture 16 Flashcards
What does GI stand for
The GI (Gastro-intestinal) Tract
What are the 6 components of the GI tract and the sphincters/valces between them
- Oral cavity
— Upper esophageal sphincter - Esophagus
—- Lower esophageal sphincter - Stomach
— Pyloric sphincter - Small intestine
—- Ileocecal valve - Colon (large intestine)
— Anal sphincter - Rectum
What is the purpose of muscle Sphincters and valves
Muscle Sphincters and valves particularly segregate functions within the tube
What does the GI tract represent
Represents a vast body surface area that is exposed to external environment
The GI tract has unique mechanisms to deal with …
Can sense or expel noxious substances
– Through vomit or diarrhea
Specialized populations of T cells localized to the intestinal mucosa
– Eg. peyer’s patches
How long is the GI tract
About 28 feet long, folded extensively to fit in abdominal cavity
How large is the luminal surface in the human body
Large luminal surface of about 200 to 400 square meters due to lots of villi and microvilli
What is the luminal surface
Lumin = space within tubes, tracts, cavities and cells in body
How long does it take meals to go through the GI tract
Highly variable transit time for ingested meal (total of 30-80 hours)
What does the gut contain
microbiome (bacteria, ext)
–protects against pathogenic microbes that enter/reside in tract
What coordinates the opening and closing of sphincters
Intrinsic (AKA enteric) nervous system
What are the 4 processes of the GI tract
- Mobility
- Secretion
- Digestion
- Absorption
What does the GI tract move
Ability of organisms and fluid to move and get around
What does the GI tract secrete
Saliva
Antibodies
Digestive enzymes
Bile
Bicarbonate
What does the GI tract absorb
Water nutrients
What is the first phase of the GI tract
The Cephalic Phase of Digestion and Absorption
What is involved in the Cephalic Phase of Digestion and Absorption
Chewing and mechanical absorption
Where does the the Cephalic Phase of Digestion and Absorption begin
In the mouth
What is masticiation
Chewing
What controls salivary secretions
Salivary secretion is under autonomic control (stimulated by sympathetic and parasympathetic nervous system)
What is the purpose of salivary secretions
Softens and lubricates food
Provides enzymes: amylase and some lipase (but no protein digestion)
What are salivary secretions in response to
Sensory stimuli (sight, smell, taste)
What does salivary secretion prepare the GI tract for
Prepares the GI tract for food processing
What is the second phase of the GI tract
The Gastric Phase of Digestion and Absorption
What occurs in The Gastric Phase of Digestion and Absorption
Sensory cells of the gastric mucosa increases intestinal and gland activity and relaxes sphincters in the GI Tract
What nervous system influences the gastric phase of digestion and absorption
The parasympathetic nervous system (“rest and digest”)
What is absorbed in the stomach
Protein and fat but not carbs
Pepsin: what is the release stimulant and role
Release Stimulant: acetylcholine acid
Role: Digestions protein
Gastric lipase: what is the release stimulant and role
Release Stimulant: acetylcholine acid
Role: Digestions fats
What are the 4 things acetlycholine stimulates for release
- Gastric acid
- Pepsin
- Gastric lipase
- Gastrin
Where does lipid digestion start
Started with lingo lipase in mouth - breaks down large fats such as triglycerides
When are gastric lipases secreted
Gastric lipases secreted as fat moves to stomach
When do bile salts and pancreatic lipase interact with fats
Once in duodenum on SI
What is the effect of bile salts on fat
Bile salts cote fat droplets and causes globules to disperse, making them hydrophilic
What is the effect of pancreatic lipase on fats
Pancreatic lipase present hydrolyze triglycerides into smaller components (free fatty acids and monoglycerides)
What happens to fatty acids and monoglycerides
Free fatty acids and monoglycerides absorbed my SI for further processing
What is the main contributor of digestive enzymes
Pancrease
Are enzymes released from the pancreas in active or inactive form
Inactive - activated in select regions
What does the gallbladder store
Stores bile produced in liver
What is the importance of the small intestinal mucosa
Filled with villi which increase surface area to promote nutrient absorption
What 3 things are secreted into the lumen of the SI upon the opening of the pyloric sphincter
- Bicarbonate - from cells in the internal epithelium and in pancreatic secretions
- Digestive enzymes - from the pancreas
- Bile acids - from the liver/gallbladder
What 2 digestive enzymes are anchored onto the luminal surface of the SI
Disaccharidases
Amino peptidases
