Week 2 - Chapter 2 Flashcards
Main structures of the digestive tract (top to bottom)
Oral cavity (Pharynx) Esophagus Stomach Small intestine Large intestine
Upper GI tract =
oral cavity, esophagus
Lower GI tract =
stomach, intestines
Digestive tract accessory organs
pancreas, liver, gallbladder
4 layers of lumen of digestive tract (inner to outer)
mucosa, submucosa, muscularis externa, serosa (adventitia)
Mucosa - 3 sublayers
epithelium, lamina propria (lymphoid tissue), muscularis mucosa (smooth muscle)
Mucosa - epithelium contains
contains endocrine and exocrine cells
Submucosa - 3 sublayers
connective tissue, lymphoid tissue, submucosal plexus
Submucosa generally gives the lumen
flexibility
Muscularis externa - 3 components
circular/longitudinal smooth muscle, myenteric plexus
Serosa/adventitia
connective tissue, visceral peritoneum
3 salivary glands
Above tongue - parotid
Below tongue - submandibular, sublingual
Oral cavity moves food through ___ to ___ by ____
through pharynx to esophagus by swallowing
Bolus =
in esophagus, = food + salivary juices
3 stages of swallowing
voluntary, pharyngeal, esophageal
Peristalsis
wave-like motion from muscle fibers contracting and relaxing
Gastroesophageal sphincter
between esophagus and stomach, aka lower esophageal sphincter
GERD aggravated by
smoking, chocolate, high-fat foods, alcohol, and carminatives (peppermint/spearmint) promote relaxation of the esophageal sphincter and increase the likelihood of acid reflux
4 main regions of the stomach
Cardia - top
Fundus
Body - main
Antrum or distal pyloric region - bottom with pyloric sphincter
Food in the stomach =
chyme, = food + gastric juices
Rugae in stomach (folds) purpose
increase SA
Stomach is ______ but small intestine is ______
Stomach - acidic
Small intestine - alkaline
Stomach pH approx
2
Barrier between stomach and small intestine
pyloric sphincter
Gastric (stomach) glands (3)
cardiac, oxyntic, pyloric
Cells in gastric glands (4)
Neck (mucus)
Parietal (oxyntic)
Chief (peptic or zymogenic)
Enteroendocrine
Neck (mucus) cells
secrete bicarbonate and mucus
Parietal (oxyntic)
secrete HCl and intrinsic factor
Chief (peptic/zymogenic) cells
secrete enzymes that break down proteins (pepsinogens)
Enteroendocrine cells
produce hormones like gastrin that stimulates other cells to secrete
Gastric juice components
HCl, enzymes (pepsin, amylase, lipase), mucus, intrinsic factor
HCl function in stomach (4)
Converts pepsinogen to pepsin
Denatures proteins
Releases nutrients from organic complexes
Acts as bacteriocide
Enzymes in stomach mostly
pepsin - mostly protein digestion occurs in the stomach
Pepsin is an
endopeptidase; hydrolyzes interior peptide bones within proteins; optimal activity at about 3.5 pH
alpha amylase in stomach
originates from salivary glands; retains some activity until inactivated by low pH of gastric juice
Gastric lipase
made by chief cells
Mucus in stomach stimulated by
prostaglandins and nitric oxide
Intrinsic factor is necessary to
absorb B12
What’s absorbed in the stomach
water, alcohol, a few drugs and a few minerals
HCl important for _____, IF important for ______
HCl - iron
IF - B12
HCl release stimulated by
gastrin, acetylcholine (NT released by neurons in myenteric plexus), histamine
Zollinger-Ellison syndrome
usually caused by a tumor, extremely high levels of gastrin into the blood (–>hypergastrinemia) –> formation of multiple ulcers
Peptic ulcers result when
normal defense and repair systems that protect the GI tract are disrupted
Most common cause of peptic ulcers
H. pylori
Can disrupt barriers and –> peptic ulcers
aspririn, alcohol, and NSAIDs
Migrating motility complex/myoelectric complex
sweeps out the GI contents and prevents bacterial overgrowth in the intestine
Gastric emptying following a meal usually take between
2 to 6 hours
Zooming in on small intestine
folds of kerkring –> villi/crypts of lieberkuhn –> microvilli
_________ in the small intestine is where nutrients are absorbed
capillary network in the villi
Each cell within a villus has
a brush border with microvilli
Microvilli
hair-like extensions of the cells’ plasma membranes
Crypts of lieberkuhn
cells in the crypts will migrate up to eventually become absorptive cells in the tips of the villus
Enterocyte (small intestine cell) turnover occurs every
3-5 days
Factors that increase intestinal secretions and motility (4)
1) VIP (vasoactive intestinal polypeptide) in myenteric plexus
2) Neuropeptide substance P
3) Motilin
4) CCK
Factors that decrease secretions and motility in the small intestine (3)
1) Peptide YY
2) Secretin
3) Glucagon-like peptides
Hormone definition
act at a distant location; can be protein or not
3 ways nutrients cross cell membrane to be absorbed
simple diffusion, facilitated diffusion, active transport
2 ways nutrients are absorbed that depends on a concentration gradient
Simple and facilitated diffusion
Simple diffusion
water and small lipids cross into intestinal cells freely
Facilitated diffusion
water-soluble nutrients (etc.) diffuse using a transporter protein
Active transport
Some nutrients (like glucose and AA) move against a concentration gradient using ATP
Immune cells and tissues are found throughout the GI tract but especially high concentrations in the
small intestine
Immune system protection of the GI tract (2 types of tissue)
Mucosa-associated lymphoid tissue (MALT)
Gut-associated lymphoid tissue (GALT) - non-mucosal layer
Pancreas is located
right below stomach
2 types of active cells in the pancreas
1) ductless endocrine
2) acinar exocrine
Pancreatic ductless endocrine cells secrete
hormones (insulin, glucagon etc.) into the blood
Pancreatic acinar exocrine cells secrete
digestive enzymes (produce pancreatic juice)
Pancreatic juice contains
bicarbonate, electrolytes, digestive enzymes
Pancreatic juice bicarbonate purpose
neutralizes the acidic chyme
Secretions from the pancreas go into the
small intestine
3 parts of small intestine
duodenum (1st), jejunum (longest), ileum (last)
Islets of langerhans
ductless endocrine portion of pancreas that secretes hormones
Pancreatic enzymes work on
fat and carb mostly
Factors that promote pancreatic secretion
Secretin, CCK, neuropeptide substance P, VIP
Liver consists of
2 lobes made of lobules
Owing to the alkaline pH of bile, the conjugated bile acids combine with _______ to form bile salts
sodium, potassium, or calcium
Bile is made in the
liver
Bile is composed of
bile acids, salts, cholesterol, phospholipids, and bile pigments (bilirubin and biliverdin) in an alkaline solution
About 90% of the bile acids and salts secreted into the duodenum are
reabsorbed in the ileum
Bile goes to
small intestine
Cholecystokinin (CCK) is secreted by ___ and does what?
small intestine, stimulates gallbladder to contract and release bile
________ inhibits gallbladder contraction
somatostatin
Gallstones form when
bile becomes supersaturated with cholesterol
Some medication enhance (cholesterol meds)
fecal excretion of bile to reduce cholesterol
After aiding in lipid digestion, the bile constituents are reabsorbed from the ileum and returned to ___ via
the liver via the hepatic portal vein
Gallbladder contracts to release bile into the ____ which combines with the ______ to form the _________ which goes to small intestine
Gallbladder contracts to release bile into the cystic duct which combines with the hepatic duct to form the common bile duct which goes to small intestine
Carb –>
Protein –>
Fats/lipids –>
Carb –> monosaccharides
Protein –> AA
Fats/lipids –> triglycerides and FAs
Mechanism of absorption depends on
solubility (fat vs water), concentration of electrical gradient, size of molecule
Unabsorbed molecules continue to
colon (large intestine)
Colon contracts to
mix materials
Proximal colonic epithelia absorb
Na, Cl, H2O
Materials in the colon are
dehydrated
Passage of material through the colon takes
12-70 hours
Ileocecal sphincter is where
the ileum connects to the large intestine
Lots of bacteria in
large intestine
Presence of SCFAs from bacteria effectively
lowers pH of colon to effect nutrient absorption
SCFAs including butyric acid stimulate…
GI cell proliferation and maintain integrity of intestinal epithelial cells
Probiotics are thought to (5)
1) Enhance immunity
2) Prevent colonization by pathogens
3) Lower pH of colon
4) Transform/promote excretion of toxic substances
5) Enhance fecal bulk (may decrease transit time)
Myenteric plexus - 2 main functions
peristalsis, motility
Submucosal plexus - 2 main functions
secretions, local blood flow
Paracrines
have a local action, diffuse through extracellular spaces to target tissue rather than being secreted into the blood
Enteric nervous system = nervous system of the GI tract subdivided into 2 networks
myenteric plexus and submucosal plexus
NPY in hypothalamus
stimulation –> hunger
Ghrelin (hunger regulation)
from stomach, stimulates NPY
PYY (hunger regulation)
From large and small intestines, inhibits NPY
CCK (hunger regulation)
From small intestine, inhibits NPY
Insulin (hunger regulation)
From pancreas, inhibits NPY
MCS (melanocortin secreting hormones) in hypothalamus
stimulation –> satiety
Leptin (hunger regulation)
From adipose tissue, stimulates MCS
PYY prevents
stomach from emptying too quickly
Short term appetite regulators
ghrelin, PYY, CCK
Long term appetite regulators
Leptin, insulin
Human obesity is linked to unresponsiveness to
leptin
Leptin inhibits secretion of
appetite stimulants
GERD can result in
esophagitis
Symptoms of GERD
heartburn, sometimes excessive belching or coughing
IBD characterized by
acute, relapsing or chronic inflammation of the GI tract, especially the intestines
How does IBD impair nutrient absorption?
Diminishes brush border activity
Reduces transit time
Causes direct damage to enterocytes
Symptoms of IBD
diarrhea and steatorrhea
General recs for IBD
low fat diet bc fat digestion is impaired
inc. vit./nutrients/pritein because lost or not well absorbed
In Celiac disease, gluten consumption –>
inflammation of small intestine and attack of mucosa by immune cells, villi damaged
Chronic pancreatitis can result from
long-term excessive use of alcohol, gallstones, liver disease, viral infections, and certain medications
With chronic pancreatiti, pancreas can ultimately fail to
produce sufficient digestive enzymes and juices
Chronic pancreatitis symptoms
pain (esp. with eating), nausea, vomiting, diarrhea
Chronic pancreatitis diet
needs to be low-fat because not enough pancreatic lipase