Terms in this set (184)
serous membrane which surrounds abdominal organs
Layers of Peritoneum
parietal (attaches to abdomen wall)
visceral (attaches to organs)
accumulation of fluid in peritoneal cavity
acute inflammation of peritoneum
Folds of peritoneum
bonds organs to each other and to the walls of the abdominal cavity
Layers of GI Tract
Mucosa (GI tract layer)
areolar connective tissue containing blood and lymph vessels which are the routes by which nutrients absorbed into the GI tract reach other tissues of the body; contains mucosa associated lymphatic tissue
Mucosa associated lymphatic tissue
contains immune cells (lymphocytes and macrophages) which protect against microbes that may penetrate epithelium
thin layer of smooth muscle
areolaor connective tissue that binds mucosa to muscularis; contains blood vessels, lymph vessels, nerve plexus (submucousal plexus of the enteric nervous system) and glands
depending on region of GI tract, consists of either skeletal muscle or smooth muscle; 2-3 layers of muscle with fibers organized in different directions (circular, longitudinal, oblique); innervated by the myenteric plexus of the enteric nervous system
serous membrane; superficial layer of those portions of GI tract that are suspended in the abdominopelvic cavity; AKA visceral peritoneum
Salivary glands of the mouth
located inferior and anterior to the ears; between skin and masseter muscle
located beneath base of tongue in posterior floor of mouth
located superior to submandibular glands
collapsible muscular tube
Upper Esophageal Sphincter
controls passage of food into esophagus
Lower Esophageal Sphincter
controls passage of food into stomach
Regions of stomach
Rugae of mucosa
large folds that are present when stomach is empty
surrounds the superior opening of stomach
rounded region superior and to the left of the cardia
region that connects to the duodenum
controls passage of chyme into duodenum
Regions of small intestine
controls passage of chyme into the large intestine
Regions of large intesine
Internal sphincter of anal canal
smooth muscle (involuntary control)
External sphincter of anal canal
skeletal muscle (voluntary control)
thickened portion of longitudinal muscles forming bands
tonic contractions of teniae coli that cause "pouching"
opening of common bile duct merges with pancreatic duct; opens into duodenum
covered by visceral peritoneum with underlying dense irregular tissue
Nervous innervation of GI tract
PNS (vagus nerve) stimulates enteric nervous sytem, which increases GI motility; SNS inhibits GI activity, mostly inhibiting enteric nervous system
Enteric Nervous System
GI tract's own nervous system; although neurons of the ENS function independently, they are subject to regulation by ANS
innervates structures in the submucosa; controls secretion of glands; controls vasoconstriction of blood vessels
Path of food
Which 3 organs secrete substances that aid in digestion and absorption into the duodenum?
Solutes in saliva
digestive enzyme that acts on triglycerides; activated in stomach
digestive enzyme that acts on starches
secreted type of antibody that prevents attachment of microbes so they cannot penetrate epithelium
Salivation control by ANS
Digestion in mouth
food reduced to soft, flexible, easily swallowed mass called a bolus; salivary amylase digests starch; lingual lipase becomes activated once in acidic environment of stomach
Digestion of food in esophagus
peristalsis pushes food downward by coordinated contractions of circular and longitudinal muscles; no further digestion or absorption takes place here
prevents stomach contents from moving into esophagus
Digestion in stomach
bolus is reduced to chyme; digestion of fat and protein begin; activation of pepsinogen to pepsin via HCl -> digestion of protein; activation of lingual lipase and secretion of gastric lipase -> digestion of fats
How much absorption occurs in the stomach?
only a relatively SMALL amount; water, ions, short chain fatty acids, certain drugs, and alcohol
Epithelial cells of the stomach are ____ to must materials.
Mucosa of stomach
layer of simple columnar epithelium cells called surface mucous cells, lamina propria, and muscularis mucosae; epithelial cells form columns of secretory cells called gastric glands that line narrow channels called gastric pits
Muscularis of stomach
3 layers- oblique, circular, longitudinal; contraction causes peristaltic movements which macerates food, mixes it with gastric juices, and reduces it to chyme
Serosa of stomach
aka visceral peritoneum
secrete mucus; mucus forms a protective coating that prevents digestion of stomach wall by HCl
secrete HCl and intrinsic factor
HCl function in stomach
kills microbes in food; partially denatures proteins exposing peptide bonds; activates pepsinogen; stimulates secretion of hormones that promote flow of bile and pancreatic juice; acidic pH required for absorption of various drugs
Stimulation of HCl secretion
Inhibition of HCl secretion
H/K antiporter (pumps protons into stomach) -> this is where PPIs act
What is the most structurally complicated and largest vitamin?
Functions of B12
coenzyme in AA metabolism
normal fxning of nervous system
Absorption of B12
gastric acid releases B12 from food and R proteins then bind; in duodenum the pancreatic enzymes degrade R proteins and intrinsic factor binds; intrinsic factor/B12 complex is absorbed in distal ileum via receptor-mediated endocytosis
Intrinsic factor protects B12 from _____.
catabolism by intestinal bacteria
Can B12 be absorbed in the mouth?
yes, a small amount, but most is absorbed in distal ileum by intrinsic factor mechanism
secrete pepsinogen and gastric lipase
How is pepsinogen activated?
when it comes into contact with other active pepsin molecules or HCl
proteolytic enzyme that breaks peptide bonds; effective in acidic environment (pH 2) of stomach; becomes inactive at higher pH
breaks down triglycerides in milk; limited role in adult stomach
secrete gastrin into blood stream
Function of gastrin
stimulates parietal cells, chief cells, and ECL cells; increases motility of stomach; relaxes pyloric sphincter; IN GENERAL: increases activity of stomach
inhibits H+ secretion by parietal cells
stimulates H+ secretion by parietal cells
Regulation of gastric secretion and motility (3 phases)
smelling, tasting, thinking about food initiates response: PURPOSE: prepare GI tract for reception of food; reflexes initiated by sensory receptors in head; submucosal plexus stimulates gastric glands and myenteric plexus stimulates motility in stomach; pepsinogen, HCl, and mucus secreted into stomach + gastrin secreted into blood stream which enhances gastric secretion and motility even further
stimulates gastric glands during cephalic phase
stimulates motility in stomach during cephalic phase
initiated as soon as food enters stomach; food in stomach stimulates stretch and chemoreceptors initiating neural and hormonal mechanisms--> peristalsis, stimulation of gastric glands, and secretion of gastrin into blood
initiated when chyme enters duodenum; response inhibits/slows gastric digestion and motility and increases activity in the duodenum (secretion of pancreatic enzymes and bile); response is due to activation of reflexes initiated in duodenum and secretion of secretin, CCK, and GLP-1 into blood
What do secretin, CCK, and GLP-1 do?
decrease gastric secretion; slows emptying of stomach into duodenum to prevent overloading of chyme; stimulates secretions of pancreatic enzymes and bile
Where does most digestion and absorption take place?
The digestion that takes place in the small intestine is due to what substances?
enzymes on the intestinal wall (brush border), pancreatic juice, bile
Mucosa of small intestine
have features that facilitate digestion and absorption; mucosa form villi (increase surface area)
each villus contains capillary network and lacteal; the absorptive cells lining the villus have microvilli which form the "brush border"; crevices between villi form intestinal glands; crypts of Lieberkuhn which secrete digestive juices
Submucosa of small intestine
submucosa of duodenum contain Brunner's glands
secrete alkaline mucus with NaHCO3 that helps to neutralize gastric acid in the chyme
Muscularis of small intestine
two layers (oblique and longitudinal)
Serosa of small intestine
Cell types of mucosa of small intestine
contain brush border enzymes
Brush border enzymes
digests maltose into glucose and glucose
digests sucrose into glucose and fructose
digests lactose into glucose and galactose
breaks down dextrins into glucose
digests depeptides into amino acids
digests nucleic acids
activates trypsinogen into tyrpsin which digests proteins
***located in deepest part of intestinal glands; secretes hormones in blood
secrete secretin; decrease activity of stomach but increase activity of small intestine (duodenum and pancrease/bile)
secrete CCK; decrease activity of stomach but increase activity of small intestine (duodenum and pancrease/bile)
secrete GIP (glucose-dependent insulintrophic peptide) which induces insulin secretion
increases insulin secretion
decreases glucagon secretion
increases beta cell mass
inhibits acid secretion
inhibits gastric emptying
decreases food intake (+ satiety)
promotes insulin sensitivity
Regulation of GLP-1
nutrients from duodenum (+)
found in deepest part of intestinal glands; secrete lysozyme and a bactericidal enzyme; phagocytic properties
small clusters of glandular epithelial cells; endocrine- 99% clusters of acini, secretes pancreatic juice; endocrine- 1% organized into islets of langerhans, secretes glucagon, insulin, and somatostatin
1500 mL secreted QD
contain H20, salts, NaHCO3, and digestive enzymes
NaHCO3 in pancreatic juice
buffers acidic gastric juice in chyme; inactivates pepsin; creates proper pH for action of digestive enzymes in duodenum
Digestive enzymes in pancreatic juice
trypsin, chymotrypsin, carboxypeptidase, elastase
How is trypsinogen activated?
in duodenum, enterokinase from brush border cleaves it into active form trypsin
How are chymotrypsinogen, procarboxypeptidase, and proelastase activated?
trypsin activates them
What gland secretes trypsin inhibitor that inhibits trypsin that is "accidentally" activated?
regulation of pancreatic secretions
during cephalic and gastric phases of gastric secretion, activation of PNS stimulates secretion of pancreatic juice; during intestinal phase, acid chyme in the duodenum stimulates secretion of CCK and secretin which stimulates secretion of pancreatic juice
What is the only solid organ that can regenerate itself?
What can impair liver regeneration?
pear shaped sac located in depression of posterior surface of liver
What produces bile? Stores bile?
functional unit of liver
lobules (hexagon structure made up of hepatocytes)
Does the liver contain capillaries?
no, sinusoids (blood flows through them)
What are Kupffer cells?
cells in liver which phagocytose worn-out RBCs, WBCs and other foreign matter
Where does all blood coming from GI tract go through first?
liver to be detoxified before it goes through rest of circulation
liver blood supply
hepatic artery- oxygenated blood
hepatic portal vein-deoxygenated blood from GI tract
branches of hepatic portal vein, hepatic artery, and bile duct
blood flow through liver
1. oxygenated blood from hepatic artery AND deoxygenated blood from hepatic portal vein
2. liver sinusoids
3. central vein
4. hepatic vein
5. inferior vena cava
6. right atrium
What is the only way for the GI tract to get to general circulation?
bile pigments (bilirubin breakdown product of Hb)
conjugated forms of bile acids
Bile acids can be conjugated with ___ or ___.
What is the purpose of conjugation of bile acids?
decrease pK making them more water soluble in aqueous solution of intestinal lumen
Function of bile
excretion of excess cholesterol, Ca2+, bilirubin, drugs
breakdown of large lipid globules into smaller droplets; increases surface area for pancreatic lipase to act
ferry lipids to wall of GI tract for absorption
Bile flow through liver
1. secreted in hepatocytes
2. bile caniliculi
3. bile ductules
4. bile ducts
5. R and L hepatic ducts
6. common hepatic duct (exit)
sphincter of liver
sphincter of Oddi; if , bile enters cystic duct and bile is stored in gallbladder
regulation of bile secretion
liver continuously produces bile which empties into duodenum or enters gallbladder for storage; chyme in duodenum initiates several neural and hormonal stimuli promoting production and release of bile; CCK and secretin ENHANCE SECRETION of bile from liver and gallbladder; PNS STIMULATES PRODUCTION of bile by liver
Where are most salts that enter the duodenum reabsorbed?
What are bile salts synthesized from and is also excreted in bile?
What percent of bile salt pool excreted daily must be replaced?
Where is the remaining 75% of bile salts going?
returned to liver and recycled
Once reabsorbed in the ileum, bile enters portal blood flowing to the liver. How will it enter the liver?
via hepatic portal vein
Large intestine mucosa
no villi or circular folds
simple columnar epithelium
long, straight tubular intestinal glands
What is special about the submucosa in the duodenum?
brunner's glands (secrete bicarb to nuetralize chyme coming from stomach acid)
Large intestine digestion
epithelium does not have enzymes that digest macromolecules; final stage of digestion occurs in colon due to activity of bacteria; contents become solidified of solid mass called feces due to water reabsorption; large intestine absorbs water, ions, and various vitamins
What happens to any remaining carbohydrates after digestion?
ferment and release CO2 and methane gas
What happens in the final stage of digestion in the colon?
breakdown amino acids
synthesis of short chain fatty acids
fermentation of any CHOs
strong peristaltic waves that begin at middle of transverse colon and quickly drives contents into rectum; food in stomach initiates this reflex (gastrocolic reflex) and therefore takes place 3-4x/day after meals
What initiates defecation reflex?
distention in rectum (due to presence of feces)
Distension in rectum process
stretch receptors -> sacral spinal cord -> PNS (motor) -> sigmoid colon, rectum, anus -> contraction of longitudinal rectal muscles -> increase pressure -> opening of internal anal sphincter -> defecation (if external sphincter relaxed)
CHO digestion in mouth
salivary amylase converts polysaccharides to tri/disaccharides (sucrose, lactose, maltose)
CHO digestion in stomach
salivary amylase destroyed
very little CHO digestion
CHO digestion in small intestine
pancreatic amylase (polysaccharides to tri/disaccharides)
brush border enzymes (tri/disaccharides to monosaccharides)
What is the only way CHOs can be absorbed in small intestine?
CHO absorption: luminal membrane
fructose- faciliated diffusion
glucose/galactaose- secondary active transport with Na+
CHO absorption: basolateral membrane
fructose, glucose, galactose- cross membrane via facilitated diffusion
Where do monosaccharides enter once they cross the basolateral membrane?
into capillary of villus
Protein digestion: stomach
pepsin (proteins -> tri/dipeptides)
Protein digestion: small intestine
pancreatic juice (trypsin, chymotrypsin, carboxypeptidase, elastase)
brush border enzymes (aminopeptidase, dipeptidase); all of these digest proteins into tri/dipeptides or amino acids
Protein absorption: luminal membrane
tri/dipeptides and amino acids- primary or secondary active transport with Na+ or H+; once inside the cell, tri/dipeptides converted to amino acids
Protein absorption: basolateral membrane
amino acid cross membrane via diffusion
Lipid digestion: stomach
lingual and gastric lipase (triglycerides to monoglycerides and fatty acids)
Lipid digestion: small intestine
bile (emulsifies lipids and forms micelles)
pancreatic lipase (triglycerides to monoglycerides and fatty acids)
Lipid absorption: luminal membrane
short chain fatty acids cross luminal membrane via simple diffusion; long chain fatty acids and monoglycerides are ferried to epithelial membrane by micelles then diffuse across membrane leaving micelle behind
Lipid absorption: basolateral membrane
inside cell: triglycerides resynthesized and packaged into chylomicrons which then cross basolateral membrane via exocytosis (requires Apo-B for exocytosis)
Where do chylomicrons enter after crossing basolateral membrane via exocytosis?
lacteal of the villas (they are too big to cross capillary wall)
lipoprotein; spherical particles with outer shell of apoproteins, phospholipids, and cholesterol molecules surrounding inner core of triglycerides
transport triglycerides from small intestine to various tissues
What happens to chylomicrons once enters blood circulation via lymphatic vessels?
taken into adipose tissue and liver; as they pass through capillaries in adipose tissue Apo-C activates endothelial LPL which removes fatty acids from triglycerides in chylomicron; hapatocytes then take up other chylomicrons and remnants of chylomicrons that passed through adipose tissue
on chylomicrons are required for exocytosis
activates endothelial LPL
on chylomicrons; docking protein recognizing receptor on hepatocyte
Absorption of vitamins in small intestine: fat soluble
(A,D,E,K) absorbed with lipids in micelles via simple diffusion and then incorporated into chylomicrons
Absorption of vitamins in small intestine: water soluble
most absorbed via secondary active transport with Na+