GI tract Flashcards
main role of the gastrointestinal tract
transfer nutrients and water from food into the body
what environment is the lumen a part of
external
name the order of organs in GI tract
oral cavity
esophagus
stomach
small intestine
large intestine
rectum
order of the accessory glands
salivary glands
liver
gall bladder
pancreas
liver
makes vile for digestion
gall bladder
stores and concentrates vile
pancreas
enzymes, dumps them into small intestine
chemical digestion
oral cavity
mechanical and chemical digestion
esophagus
passage to the stomach
transport tube, perystalsis
stomach
continued digestion,
mechanical (muscular contractions of wall)
chemical
small intestine
duodenumm(bulk of chemical digestion and reabsorption), jejunum, ileum
where most digestion and reabsorption happens
large intestine
final balance of salt and water
colon absorbs water and electrolytes; production of feces
rectum holds feces until defecation throguh anus
supports an environment that facilitate colonization by healthy bacteria
digests bacteria
order of sphincters of GI tract
- upper espophageal sphincter
- lower esophageal
- pyloric
- ileocecal
- internal anal (no control, smooth muscle), external anal (voluntary, skeletal muscle)
sphincters
seperate compartments
rings of smooth muscle
tonically contracted, relaxations allows food to pass
serve as one way valves
Name the order of walls of the GI tract tissue
- mucosa
- submucosa
- muscularis externa (circular muscle, longitudinal muscle)
- serosa
epithelium of mucosa
epithelium:
lines the lumen of the GI tract
single layer of epithelial cells
transporting cells (will have transporters and channels. water, ions, digestive products)
secretory cells (enzymes, mucus, hormones)
stem cells (undifferentiated epithelial cells that can replace the cells face the external environment that are short lived)
mucosa
brings nutrients into the body, innermost layer
epithelium
lamina propria
muscularis mucosae
lamina propria of mucosa
loose connective tissue
contains glands, lymph vessels, blood supply, nerve fibers
muscularis mucosae of mucosa
does not contribute to gastro contraction
adjuster or SA
thin layer of smooth muscle separates muscosa from submucosa
can contract to alter the SA of the mucosa for absorption
submucosa
made of loose connective tissue
has nerve trunks, blood supply (larger blood vessels) and lymph vessels
intestine has submucosal plexus (network of neurons regulating gut function)
muscularis externa
2 layers of smooth muscle cells
inner circular layers (constrict lumen)
outer longitudinal layers (shorten tract)
stomach has additional oblique layer just below submucosa
the myentric plexus ( another part of the enteric nervous system) located between the two muscle layers
serosa
suspends abdominal organs
outer covering of the entire GI tract and is continuous with peritoneal membrane that lines the abdominal cavity
made of secretory epithelium and connective tissue layers. lubricates, protects, suspends
secretion
movement of material from cells into lumen or ecf
digestion
chemical ad mechanical breakdown of food into absorbable units
absorption
movement of material from GI lumen to ECF
ree fatty acids, ions, water
motility
perastilus, segmental
movement of material through the GI ract as a result of muscle contraction
perstalic contractions
propel content forwards
circular muscles contract just behind the bolus to push it forwards
segmental contractions
mixing contents to break up food and increase exposure to enzymes
short segments of intestine alternately contract and relax
back and forth
bolus
once we have swallowed food
chyme
just come from stomach
soupy mixture of partially digested food
what does the GI secrete
sodium
potassium
cloride
bicarbonate
H+
water
digestive enzymes
mucus
short reflexes
integrated in the enteric nervous system and occurs entirely in the gut wall
- sensory recepters send information to enteric nervous system via interneurons
long reflexes
integrated within CNS
may originate in or outside of the GI tract
feedforward and emotional reflexes are initiated and integrated entirely outside the GI tract. Called cephalic reflexes
GI peptides
may be secreted in both short and long reflexes, or independently
signaling molecules that alter GI secretion and motility and eating related behaviours
SNS response
inhibits GI motility and secretions
PNS response
stimulates GI motility and secretions
what are the 3 pairs of salivary glands
parotid
sublingual
submandibular
salivary secretions
under automatic control (mostly parsympathetic)
lubrication and moistening of food
solubilization of material for taste
initial digestion of starches (salivary amylase)
lingual lipase contributes minorly to lipid hydrolysis
antibacterial actions (lysozyme, immunoglobulins)
lysozyme
antibacterial enzyme
immunoglobulins
antibodies
swallowing reflex
- tongue pushes against soft palate and back of mouth, triggering the swallowing reflex (we stop breathing momentarily (do not want bolus in trachea, automatic)
- breathing inhibited as the bolus passes through the airway. Upper esophageal sphincter relaxes
- food moves downward into the esophagus, propelled by peristaltic waves and aided by gravity. Gravity helps but is not essential
epiglottis
shuts over top of trachea so food does not go down there
gastric phase
digestion (mechanical and chemical)
- gastric contractions continue to break food up and help mix it with gastric acid and secretions for chemical digestions
- produces chyme
protection
- acidic environment destroys pathogens
- mucus and bicarbonate to protect itself - from gastric juice
storage
release of chyme into small intestine is regulated.
until its ready to be released to the next compartment
longer for proteins and fats, shorter for pure carbs
gastric mucous cells
mucous and bicarbonate
bicarbonate is chemical barrier which fills mucous droplets
mucous is the physical barrier that form wall on inside of the stomach
pepsinogen
is an inactive protease secreted by chief cells of the gastric glands
pepsin
starts as pepsinogen then activated by H+ becomes pepsin
optimally active between between 1.8 - 3.5
chops up peptide bonds (protein needs to be denatured) then pepsin begins protein digestion by cleaving specific peptide bonds of polypeptides
- protein product entering small intestine is a mixture of intact protein, polypeptides and some free amino acids
fats in gastric chemical digestion
minor 10% digested in stomach
gastric motility
gastric lipase
gastric motility
forms an emulsion of lipids and gastric lipase
gastric lipase
hydrolyzes triglycerides into monoglycerides and FFAs
triglyceride
how we consume and store fats
gastric chemical digestion of carbohydrase
none
salivary amylase is inactivated at low pH
where are free fatty acids absorbed
duodenum (small intestine)
what do mucous surface and neck cells secrete
mucus and bicarbonate
what is the stimulus for mucus and bicarbonate release
mucus: tonic secretion (always happening, with irritation of mucosa
bicarbonate: secreted with mucus
what is the function of mucus and bicarbonate secretion
mucus: physical barrier between lumen and epithelium
bicarbonate: buffers gastric acid to prevent damage to epithelium
what do parietal cells secrete
gastric acid (HCl) pH 2
what is the stimulus for parietal cell release
acetylcholine (PNS)
function of gastric acid secretion
activates pepsin, denatures dietary protein so pepsin can chop it up, kills bacteria
what do chief cells secrete
pepsin(ogen)
gastric lipase (10%)
what is the stimulus for chief cell release
acetylcholine, acid secretion
what is the function of pepsin and gastric lipase secretion
pepsin: digests proteins
gastic lipase: digests fats
The main functions of the small intestinal phase
regulation of gastric emptying
secretions
digestion
absorption
how does the small intestine regulate gastric emptying
chyme in the SI triggers feedback to regulate further release from the stomach
what does the SI secrete
epithelial cells (all over GI tract): mucus, digestive (brush border made within SI), enzymes
pancreas: bicarbonate: buffer to neutralize acid; digestive enzymes (work at a higher pH)
liver and gall bladder: bile
what does the SI digest
fats, carbs, proteins/peptides
what does the SI absorb
nutrients, vitamins, ions, minerals, water
enterocytes/transporting epithelium
in wall of SI
microvilli increase SA and create brush border
digestive enzymes on the brush border
nutrient reabsorption occurs along villi
crypt epithelial cells
secretion of ions water and hormones
safe space, stem cells
goblet cells
secrete mucus for protection and lubrication
capillaries
transport absorbed nutrients
lacteals
transports absorbed fats via lymphatic system
projection of lymphatic system
exocrine pancreas
proteases, amylases and llipases
exocrine secretions travel into main pancreatic duct (dumps bicarbonate into it), then into common bile duct. release into the duodenum is controlled by the sphincter of oddi
biliary secretions
triggered by lipids in small intestine
non-enzymatic solution of bile salts (amphipathic), bile pigments and cholesterol
bile is made in liver
between meals bile is diverted into gallbladded where is is concentrated and stored
bile salts help with digestion and absorption of fats
what can carbs be absorbed as
monosaccharides (absorbable bits, individual sugar bits)
glucose, fructose, galactose - end product of carb digestion
absorbed by transporters (uniport or symport)
oral phase of carb digestion
mechanical digestion by chewing
chemical digestion begins with salivary amylase
gastric phase of carb digestion
mechanical digestion due to peristaltic contractions (mixing churning)
chemical digestion paused in stomach (too acidic) salivary amylase cannot work in acidic environment
intestinal phase of carb digestion
most digestion occurs in SI
continued mechanical digestion (segmental contractions)
pancreatic amylase secreted into lumen of the duodenum (to make it smaller and smaller)
brush border enzymes on apical surface of epithelial cells in duodenum and jejunum - fine clipping (sucrase, maltase and lactase are brush border enzymes)
oral phase of protein digestion
mechanical digestion only
gastric phase of protein digestion
chemical protein digestion initiated in the stomach : HCl denatures protein; pepsin cleaves peptide bonds
mechanical digestion by peristaltic mixing/churning
results in a mixture of intact protein, large polypeptides and some free amino acids
intestinal phase of protein digestion
mechanical digestion by segmental contractions
chemical cleavage by peptidases
pancreatic enzymes: endo- and exopeptidases (trypsin,chymotrypsin,carboxypeptidases)
brush border enzymes: exopeptidase (aminopeptidase
products of protein digestion
di and tri peptides and free amino acides and some small peptides
endopeptidases
cleave internal peptide bonds
exopeptidases
cleave terminal peptide bonds
dietary lipids
triglycerides, cholesterol, phospholipids, fatty acids
provide both an energy source and reserve
form hormones, parts of cell membranes, insulation and shock absorption, transport fat soluble vitamins and other compounds
oral phase of fat digestion
mechanical digestion only, ligual lipase
gastric phase of fat digestion
begin chemical digestion by gastric lipase, course emulsification bigger droplets become smaller
intestinal phase of fat digestion
major chemical digestion by pancreatic lipase, bile salts, colipase
what is the solution to lipids being hydrophobic
course emulsification - in the stomach by mixing (large fat droplets suspended in chyme)
associated with bile salts in small intestine. fine emulsification increases SA for digestion and eventually forms micellar solution
what do bile salts do to lipids
first create a stable emulsion of lipid droplets in solution
- pancreatic lipase digest triglycerides with the help of colipase
eventually small discs called micelles are formed and brought close to enterocytes for absorption
explain fat absorption
- bile salts from gall bladder coat fat droplets
- pancretic lipase and colipase break down fats (dependent on each other) into monogylcerides and fatty acids stored in micelles
3a) monoglycerides and fatty acids move out of miclles and enter cells by diffusion
3b)cholesterol is transported in cells - absorbed fats combine with cholesterol and proteins in the intestinal cells to form chylomicrons
- chylomicrons are removed by the lymphatic system
chylomiron
goes into lymph before circulation
large fat droplet, must be packed into secretory vesicles by golgi for exocytosis
colonic microflora
bacterial ecosystem
could exten to brain health
helps with digesting dietary fiber
produces vitamin K (50% of total need)
limits growth and invasion of pathogenic microorganisms
defecation
feces do not normally contain useful nutrient
- presence of nutrient in feces is a marker of intestinal dysfunction
made of undigestible material, dead bacteria and epithelial cells, biliary metabolites, H2O
steatorrhea
undigested fat in feces
