lecture 15 Flashcards
what is the GI tract and what can it do?
- Vast body surface area exposed to
external environment - Sees food as well as potentially toxic
substances/infectious agents & has
unique mechanisms to deal with this - Muscular sphincters & valves partially
segregate function within the tube
How does the GI tract use its mechanisms to deal with potentially toxic substances.
- Sense & expel noxious substances (vomit,
diarrhea) - Specialized populations of T cells localized
to the intestinal mucosa (e.g. Peyer’s
patches)
How long is the GI tract and how is this possible?
28 ft long and it is folded extensively in the abdominal cavity
What is the luminal surface area of the GI tract and why?
approx 200-400 m^2 due to many villi/microvilli
What is the timing of ingesting meals?
Its highly variable, around 30-80 hours. approx 5-8 hours in stomach and small intestine, and the remainder of the time in the colon
What does gut microbiome do in the GI tract?
Gut microbiome (bacteria, etc.) protects against pathogenic microbes that enter/reside in the tract
What does the intrinsic nervous system do regarding the GI tract?
controls and coordinates function such as the opening and closing of sphincters.
What are the 4 basic processes of the GI tract?
- Motility
* Peristalsis - Secretion
* Saliva, mucous
* Antibodies (IgA)
* Digestive enzymes
* Bile
* Bicarbonate - Digestion
- Absorption
* Water
* Nutrients
What does the cephalic phase of digestion and absorption refer to?
processes in the mouth
Where does chemical and mechanical digestion begin?
Begins in the mouth
What is the mechanical thing that the mouth does?
Chewing (mastication)
What do secretions in the mouth do and how does this happen?
Secretions are in response to sensory stimuli (sight, smell, taste) and they prepare GI tract for food processing
What is salivary secretion under control by
Under autonomic control
What is salivary secretion stimulated by?
Stimulated by sympathetic & parasympathetic nervous systems
What does salivary secretion do?
- Softens & lubricates food
What does salivary secretion provide?
Provides enzymes: amylase & some lipase (no protein digestion)
What does the gastric phase of digestion and absorption refer to?
processes that occur in the stomach
What happens in the gastric phase of digestion and absorption.
- Secretory cells of the gastric mucosa
- Influence of parasympathetic nervous system (i.e. rest & digest)
- Increases intestinal & gland activity
- Relaxes sphincter muscles in the GI tract
- Digestion of protein & fat, but not carbohydrate in the stomach
What does the pancreas do?
Pancreas is the main contributor of digestive enzymes.
In what form are enzymes released from the pancreas?
Enzymes are released from the pancreas in inactive form. ex. trypsinogen
* Activated in small intestine by
enterokinase in brush border of
duodenum e.g. trypsin for protein
digestion
What does the gallbladder do?
Gallbladder stores bile produced by liver for fat digestion
How does small intestinal mucosa promote nutrient absorption?
Small intestinal mucosa has villi which increases surface area to
promote nutrient absorption
What happens regarding the small intestine upon opening of pyloric sphincter?
- Secretions into the lumen of the small intestine upon opening of pyloric sphincter & food (chyme) entering the upper duodenum
1. Bicarbonate – from cells in the intestinal epithelium & in pancreatic secretions
2. Digestive enzymes – from the pancreas
3. Bile acids (as bile fluid) – from the liver/gallbladder
Where are digestive enzymes anchored?
Digestive enzymes anchored on the luminal surface of small intestine epithelial cells
1. Disaccharidases
2. Amino peptidases
