Lecture 16 Flashcards
What does the GI tract represent?
a vast body surface area that is exposed to the external environment.
What does GI Tract deal with?
food and potentially toxic
substances and infectious agents
How does GI tract deal with the material it houses? What Mechanisms are used?
Sense and expel noxious substances
* vomit, diarrhea
* Specialized populations of T cells localized to
the intestinal mucosa
* E.g. Peyer’s patches
name parts of GI tract / GI tube in order
- oral cavity
- upper esophageal sphincter
- esophagus
- lower esophageal sphincter
- stomach
- pyloric sphincter
- small intestine
- ileocecal valve
- colon (large intestine)
- anal sphincter
- rectum
How is the GI tract segregated?
Muscular sphincters and valves partially
segregate function within the tube
Length and Surface Area of GI tract
~28 ft. long – has to be folded extensively in abdominal cavity
- Large luminal surface area of ~200-400 m2 due to lots of villi
/ microvilli (equivalent to a tennis court)
transit time for ingested meal
Highly variable, total of 30-80 hours, 5-8 hours in stomach and small intestine, Rest of time in the colon
Higher fiber meals
Stay in GI system for longer
Function of Gut Microbiome
protects against pathogenic microbes that enter/reside in tract. Bacteria breaks things down and has significant connection to health.
intrinsic (enteric) nervous system function
to control and
coordinate the functioning of GI tract (e.g. opening and closing of
sphincters)
GI tract Basic Processes (4)
Motility, Secretion, Digestion, Absorption
Motility
includes peristalsis. The involuntary constriction and relaxation of the muscles of the intestine or another canal, creating wave-like movements that push the contents of the canal forward
Secretion
Includes:
* Saliva, mucous
* Antibodies (IgA)
* Digestive enzymes
* Bile
* Bicarbonate
Absorption
Water (large Intest.) + Nutrients (small intest.)
The Cephalic Phase of Digestion and Absorption
- Chemical and mechanical digestion begins in the mouth
- Chewing (mastication)
- Secretions in response to sensory stimuli (sight, smell, taste), prepares the GI tract for food processing
Salivary Secretion
- under autonomic control, stimulated by Sympathetic and Parasympathetic Nervous Systems
- Softens and lubricates food
- Provides enzymes: amylase and some lipase (but no protein digestion)
Gastric Phase of Digestion and Absorption
Secretory cells of the gastric mucosa – (influence of Parasympathetic Nervous System “rest and digest”) - increases
intestinal and gland activity, and relaxes sphincter muscles in the GI tract.
bile
break glycerol into backbone + fatty acid chains
Bicarbonate
Homeostasis mechanism, maintains careful pH range
secretions in response to sensory stimuli example
smell of baking cookies will want to make you eat more even though you just ate.
Sympthetic Nerve
digest food quicker
parasympathetic nerve
inhibits GI, less food break down (eg. during excersize)
where does carb digestion begin?
in the mouth
What is digested in the stomach
protein and fat, but not carbohydrate
Acetylcholine
spikes after eating a meal to trigger release of stomach enzymes
pepsin
stomach enzyme that serves to digest proteins found in ingested food
gastric lipase
digestion of exogenous lipid. Triglycerides are digested to diglycerides then followed by fatty acids.
Patient Dietary recall: identify lipids / dietary fats
BREAKFAST:
- Black coffee
- White bread with peanut
butter and honey
LUNCH:
- Curry chicken with basmati
rice, onion, peppers, broccoli
DINNER:
- Veggie spring rolls
- Side of stir-fried veggies
EVENING SNACK:
- Plain potato chips
- Soda
White bread, peanut butter, Curry chicken (coconut milk), veggie spring rolls (pastry), stir-fried veggies (oil), potato chips
Patient Dietary recall: identify dietary proteins
BREAKFAST:
- Black coffee
- White bread with peanut
butter and honey
LUNCH:
- Curry chicken with basmati
rice, onion, peppers, broccoli
DINNER:
- Veggie spring rolls
- Side of stir-fried veggies
EVENING SNACK:
- Plain potato chips
- Soda
Peanut butter, curry chicken
Fat is:
abundant in western diet, easier to consume than protein
What happens in the pancreas
main contributor of digestive enzymes, Enzymes are released from
pancreas in inactive form
E.g. trypsinogen
enzymes in small intestineare activated by
enterokinase in the brush border of duodenum to form trypsin – for
protein digestion
what does Gallbladder do?
stores bile (produced by liver) and Fat digestion
Absorption in Small Intestine
Small intestinal mucosa – villi increase surface area to promote nutrient absorption
secretion into lumen (small intestine) happens when
pyloric sphincter opens resulting in food (chyme) entering the upper duodenum
Bicarbonate comes from
cells in the intestinal epithelium and in pancreatic secretions
digestive enzymes come from
pancreas
bile acids (fluid) come from
liver / gallbladder
digestive enzymes are anchored on…
the luminal surface of small intestine epithelial cells
digestive enzymes on small intestine include
disaccharidases and amino peptidases
