Gastrointestinal Module #2a Flashcards
Where does the duodenum span from?
Duodenal Bulb –> Ligament of Treitz
What does the hepatopancreatic ampula (Sphincter of Oddi) do?
Allows bile/pancreatic enzyme secretions
Where are Brunner’s Glands (submucosal glands) found?
Proximal duodenum
What do Brunner’s Glands (submucosal glands) do?
Secrete bicarbonate rich mucous:
- protect against acidic chyme entering
duodenum
- lubricate intestinal wall
What is the function of the duodenum?
Enzymatic digestion/breakdown of food
Provide feedback to regulate rate of gastric emptying
How does the duodenum function in the digestion/breakdown of food?
Stimulate release of digestive enzymes from pancreas/gall bladder
How does the duodenum provide feedback to regulate the rate of gastric emptying?
Long loop reflexes
Short loop reflexes
Release hormone messengers to inhibit stomach motility/acid production
How do long loop reflexes work?
mechanoreceptors/chemoreceptrs stimulate CNS to increase sympathetic and decrease parasympathetic to stomach
How do short loop reflexes work?
Mechanoreceptors/chemoreceptors in DUODENUM stimulate ENTERIC NEURONS in stomach to decrease stomach motility
What are the hormones that are released in the duodenum and inhibit stomach motility/acid production?
Secretin
VIP
CCK
What does secretin do?
Regulate pH in duodenum
Inhibit gastric activity
Facilitates digestion
What stimulates secretin?
Acidic chyme (pH < 4 - 5) containing fats, partially digested protein, hyper/hypotonic fluids
What does secretin do to the stomach?
Inhibit gastric secretions (inhibit gastrin)
Inhibits motility
What does secretin do to the pancreas?
Stimulate pancreas to secrete watery bicarbonate solution
What does secretin do to the liver?
Stimulate bile output –> fat digestion
What does secretin do to the Brunner’s Glands of the duodenum?
Stimulate secretion of “alkaline rich mucous”
What does CCK (cholecystokinin) do?
Promote bile/pancreatic enzyme release
Inhibits gastric activity
What are the stimuli of CCK?
Fatty chyme entering duodenum
What does CCK do to the stomach?
Inhibits gastric motility/secretions
What does CCK do to the pancreas?
Stimulate release of pancreatic enzymes
What does CCK do to the liver?
Stimulates bile output (promote fat digestion)
What does CCK do to the gallbladder?
Stimulates contraction to release stored bile
What is GIP (gastric inhibitory peptide) related to?
Secretin
What is the stimulus of GIP?
Chyme entering duodenum
What does GIP do to the stomach?
Inhibit gastric motility/secretions
What does GIP do to the pancreas?
Stimulates insulin release
What is the stimulus of VIP (vasoactive intestinal peptide)?
Chyme entering the duodenum
What does VIP do to the stomach?
Inhibit gastric acid secretion
What does VIP do to the intestine?
Vasodilate BV
Promote intestinal motility
What is the stimulus of intestinal gastrin?
Chyme entering the duodenum
What does intestinal gastrin do to the stomach?
Stimulate gastric motility and secretions
What does intstinal gastrin do to the intestines?
Stimulate motility
What is the stimulus of motilin?
Fasting or periodic release (every few hours)
What does motilin do?
“Housekeeper of intestinal tract”
Empties gastrointestinal tract of residual stuff
What is the effect of motilin on the intestines?
Initiates MMC (migrating motor complex)
Where does the jejunum/ileum span?
Begins @ ligament of Treitz
Ends @ ileocecal valve
What is the function of the jejunum?
Major site of digested fat, carbohydrate, protein, water and electrolyte absorption
What is the function of the ileum?
Absorb Vitamine B12, bile salts and remaining digested nutrients and water not absorbed in jejunum
What are the anatomical features that optimize absorption in the jejunum and ileum?
Mucosal Folds
Villi
Lamina Propria Layer
Crypts of Lieburkuhn
What do the mucosal folds of the jejunum and ileum do?
Physically slow the passage of food
What do villi do in the jejunum and ileum do?
Cover the mucosal folds
Considered the functional unit of the small intestine –> site of both secretion and absorption
What makes up the villi?
Goblet cells = mucus secreting
Absorptive columnar cells = site of absorption
Where are microvilli found?
Columnar cells –> form the brush border of the mucosal surface
What is found along the surface of the brush border and what does it do?
Thin layer of fluid –> facilitates absorption of all substances except water/electrolytes
What is the lamina propria layer made of?
Lacteal
Central Arteriole
What is the function of the central arteriole?
Capillary = transport of carbs, proteins and (very litle) fats (free fatty acids and glycerol) directly to liver via hepatic portal vein
What is the function of the lacteal?
Transport fat molecules (monoglycerides and fatty acids)/substances to systemic circulation via thoracic duct
Where are the crypts of lieburkuhn found?
@ base of villi
What are the crypts of lieburkuhn composed of?
Precursor Cells of SI Epithelium (goblet and columnar cells)
Paneth Cells
Secretory Cells
What is the function of the precursor cells in the crypts of lieburkuhn?
Act as a production factory of epithelial cells –> turnover of intestinal epithelial cells
Describe how cells are turned over in the Villi of the small intestine
Precursor cells migrate to tip of villi from crypts of lieburkuhn
Mature SI epithelial cells slough off into intestine and serve as source of (endogenous) protein
**Complete turnover of SI ~ 4 - 7 days
What is the function of paneth cells in the crypts of lieburkuhn?
Immune function –> produce/secrete antibotic peptides
What is the function of the secretory cells in the crypts of lieburkuhn?
Secrete brush border digestive enzymes
What is the average transit time of food in the small intestine?
1 - 3 hours
What are the stimuli of small intestine motility?
Small Intestine Hormones: Secretin, CCK, gastrin
Intestinal Reflexes
What are the 3 motility patterns seen in the small intestine?
Segmentation
Peristalsis
Migrating Motor Complex (MMC)
When does segmentation motility occur?
During feeding
Describe segmentation motility
Frequent rhythmic contractions of circular muscle
What is the function of segmentation motility?
Mixes chyme to allow contact w/ brush border
When does peristalsis motility occur?
During feeding
Describe peristalsis motility
Coordinated waves of contraction/relaxation of longitudinal muscles
Describe HOW peristalsis moves
Short segments –> 10 cm
Moves slowly –> 1 -2 cm/sec to allow for digestion/absorption
What is the function of peristalsis motility?
Moves chyme toward large intestine
When does migrating motor complex (MMC) motility occur?
During fasting
Describe migrating motor complex motility (MMC)
Slow periodic waves of peristalsis
**occurs ever 1 - 2 hours; originates in stomach –> intestines
What is the stimulus of migrating motor complex motility?
Motilin
What is the function of the migrating motor complex (MMC) motility?
“House cleaning” –> sweeps out stomach/small intestine
Pushes along residual chyme, non-digested substances (fiber, bones, etc)
What are the intestinal motility reflexs?
Ileogastric Reflex
Intestinointestinal Reflex
Gastroileal Reflex
What is the stimulus of the ileogastric reflex?
Distended Ileum
What is the action of the ileogastric reflex?
Inhibits gastric motility
What is the result of the ileogastric reflex?
Slows down adding more chyme to small intestine –> allow terminal ileum to empty contents into large intestine
What is the stimulus of the intestinointestinal reflex?
Section of small intestine becomes distended
What is the action of the intestinointestinal reflex?
Relaxes distal small intestine
What is the result of the intestinointestinal reflex?
Allows chyme to be moved toward large intestine
What is the stimulus of the gastroileal reflex?
Increased stomach (gastric) motility/secretion
What is the action of the gastroileal reflex?
Promotes terminal ileum motility/ileocecal valve relaxation
What is the reult of the gastroileal reflex?
Empty small intestine so it can receive more chyme from stomach
How does the ileocecal valve open?
Similar to LES and pyloric valve in stomach
What is the stimulus to open the ileocecal valve?
Approaching peristaltic wave in the ileum
What is the action to open the ileocecal valve?
Relaxation of the ileocecal sphincter
What is the stimulus that closes the ileocecal valve?
Distention of the cecum/ascending large intestine
What is the action that closes the ileocecal valve?
Constriction of the ileocecal valve
Where does the large intestine span from?
Ileocecal valve –> anus
What are the unique arrangements of the circular/longitudinal muscles of the large intestine?
Teniae coli
Haustra
O’Bierne Sphincter
What is the teniae coli?
3 longitudinal bands of muscles that span the length of the colon
What are haustra?
Pouches formed from circular muscle layer of intestine
What does the O’Bierne sphincter do?
Controls passage of chyme from sigmoid colon into rectum
What are the motility movement patterns in the large intestine?
Segmental
Peristalsis
When do haustral segment contractions occur?
During fasting
Describe the haustral segment contractions
Individual haustra segments push contents (fecal mass) back and forth
What is the function of haustral segment contractions?
Maximize absorption of water and electrolytes
**occurs 90% of the time
When does multihaustral segmentation contractions occur?
During fasting
Describe multihaustral segmentation contractions?
Several haustral segments contract/relax as single unit
What is the function of the multihaustral segmentation contractions?
Push contents (fecal mass) short distance forward
**occurs 10% of the time
What is the function of mass movement peristalsis?
Promote emptying of the intestine into the sigmoid colon and rectum
What are the intestinal reflexes of the colon?
Orthocolic reflex
Gastrocolic reflex
What is the stimulus of the orthocolic reflex?
Upon awakening –> standing first thing in the morning = peristalsis of LI
What is the action of the orthocolic reflex?
Peristalsis propels fecal mass into sigmoid colon/rectum
What is the stimulus of the gastrocolic reflex?
Ingestion of food (during or immediately after eating)
What is the action of the gastrocolic reflex?
Peristalsis propels fecal mass into sigmoid colon and rectum
**continuation of gastroileal reflex
What is the stimulus of the rectal reflex?
Stretch of the rectum wall
What is the action of the rectal reflex?
Relaxation of internal anal sphincter –> urge to have BM
Can the rectal reflex be voluntarily inhibited?
Yes –> cerebral cortex input/motor pathways in spinal cord = contract the external anal sphincter
What happens during cauda equina syndrome?
Damage to nerve roots of lower spine –> loss of bowel control
Where does digestion of carbohydrates begin?
Mouth
What is the enzyme(s) found in the mouth and what do they do?
Salivary amylase –> starches break down into smaller molecules (dextrin/oligosaccharides)
What does the pancreas release that is involved in the digestion of carbohydrates?
Pancreatic amylase
What does pancreatic amylase do?
Furthur breakdown starches into major oligosaccharides (lactose, maltose, sucrose)
What are the brush border enzymes involved in carbohydrate digestion?
Lactase
Maltase
Sucrase
Where are the brush border enzymes involved in carbohydrate digestion secreted from?
Secretory cells of base of villi (Cyrpts of Lieburkuhn)
What is the action of the brush border enzymes in the digestion of carbohydrates?
Breakdown oligosaccharides (lactose, maltose, sucrose) into monosaccharides (galactose, glucose, fructose)
Where are carbohydrates absorbed in the small intestine?
Brush Border of Villi
After being absorbed by the brush border villi where do monosaccharides go?
Directly to liver via hepatic portal vein
**insulin NOT required for absorption here
Where does protein digestion begin?
Stomach
What is the enzyme released in the stomach that is responsible for beginning digestion of proteins?
Pepsin
**pepsinogen is released from cheif cells and converted into pepsin when exposed to HCl
What is the action of pepsin?
Breaks down proteins into smaller protein molecules (proteoses, peptones)
What are the pancreatic enzymes that are responsible for digesting proteins?
Trypsin
Chymotrypsin
Carboxypepsidase
What is the action of pancreatic protein digesting enzymes?
Breakdown proteins into smaller peptides (polypeptides and dipeptides)
What are the brush border enzymes involved in protein digestion?
Aminopeptidases
Dipeptidase
Where are the brush border enzymes involved in protein digestion secreted from?
Secretory cells of base of villi (Crypts of Lieburkuhn)
What is the action of brush border protein digesting enzymes?
Breakdown smaller peptides (polypeptides and dipeptides) into amino acids
