GI module 3 Flashcards
What is the total length of the small intestine?
5-6 meters
Where does the small intestine begin and end?
begins at pyloric sphincter, and ends at ileocecal valve
What are the 3 regions of the SI and their respective lengths?
Duodenum (25-30cm) Jejunum (2.5m), and ileum (3.5m)
What region begins at the duodenal bulb and ends at the ligament of Trietz?
Duodenum
What structure allow bile and pancreatic enzyme secretions?
Hepatopancreatic ampula (sphincter of Oddi)
What structure is located in proximal duodenum and secretes “bicarbonate rich mucus to protect against acid chyme entering the duodenum and lubricate intestinal wall?
Brunner’s glands
Describe the 2 major functions o the duodenum?
Digestion- stimulates release of enzymes from pancreas and gallbladder
Gastric feedback-provides feedback to regulate the rate of gastric emptying.
What is the initial signal for feedback pathways in the duodenum?
Acidic chyme entering the duodenum
What do the Long loop reflexes in the duodenum stimulate?
CNS increase sympathetic and decrease parasympathetic to stomach-
What do the short loop reflexes in the duodenum stimulate?
enteric neurons in stomach to decrease stomach motility
What hormones messengers work in the duodenum to inhibit motility/acid production?
Secretin, VIP, CCK
What is the major role of secretin in the duodenum?
Regulates the pH, inhibitory gastric activity and facilitates digestion
What stimulates the secretion of the hormone secretin in the duodenum?
Acidic (pH less than 4-5) chyme containing fats, partially digested protein, and hyper/hypotonic fluids
What are the target organs of the hormone secretin?
Stomach
Pancreas
Liver
Brunner’s glands
What is the driving force for Secretin?
pH
What is the driving force for CCK?
Fat content
What is the primary function of CCK?
Promotes bile/pancreatic enzyme release and inhibitory gastric activity
What is the stimulus for CCK?
Fatty chyme entering duodenum
What are the target tissues for CCK?
Stomach
Pancreas
Liver
Gallbladder
What is the action of CCK at the stomach?
Inhibitory gastric motility/secretions
What is the action of CCK at the Pancreas?
Stimulates release of pancreatic enzymes
What is the action of CCK at the Liver
Stimulates bile output (promotes fat digestion)
What is the action of CCK at the gallbladder?
Contraction to release stored bile
What is the action of Secretin at the stomach?
Inhibits gastric secretion and motility
What is the action of secretin at the pancreas?
stimulates pancreas to secrete bicarbonate solution (neutralizes)
What is the action of secretin at the liver?
Stimulates bile output (fat digestion)
What is the action of Brunner’s glands of the duodenum?
Stimulates secretion of “alkaline rich mucus”
What is GIP said to be a relative of?
Secretin
What is the stimulus for GIP?
Chyme entering the duodenum
What is the action of GIP at the stomach?
inhibitor to gastric motility/secretions
What major action does GIP have at the pancreas?
in stimulating insulin release
What is the stimulus for the release of VIP?
Chyme entering the duodenum
What is the acition of VIP at the stomach?
Inhibits gastric acid secretion
What is the major role of VIP at the intestine?
Vasodilates BV, promotes intestinal motility
What is the role of intestinal gastrin
similar as gastrin released in antrum of stomach-(promotes acid secretion/motility and gastric mucosa growth)
What is the stimulus for intestinal gastrin?
chyme entering the duodenum
t/f there is no major action of intestinal gastrin
T-not specific to any condition other than presence of chyme-sties motility and secretion
What is motilin also known as?
“housekeeper of intestinal tract”
What is the stimulus for motilin?
Fasting or periodic release (every few hours)
What is the major action of motilin at the intestine?
Initiates MMC (migrating motor complex)
Anatomically where are the Jejunum and the Ileum located in the GI system
From the ligament of Treitz and ends at ileocecal valve
What is the general function of the jejunum and ileum as a whole?
Continued digestion
absorption of water!!!
secretion of brush border enzymes to assist with digestion/absorption
What are the major functions of the jejunum?
Digested fat
carbohydrate, protein, water and electrolyte absorption
What are the major functions of the ileum?
absorption of B12, bile salts and remaining digested nutrients and water not absorbed by the jejunum
What are the 3 primary anatomical features that optimize absorption in the jejunum and ileum?
Mucosal folds
Villi (and microvilli)
Lamina propria layer
Crypts of Lieburkuhn
What is the purpose of the mucosal folds in the jejunum and ileum?
Physically slows the passage of food
Where are the Villi located?
Covering the mucosal folds
What makes the villi a functional unit of the small intestine?
Site of both secretion and absorption
What are the villi composed of?
Goblet cells (mucus secreting cells) Absorptive columnar cells (site of absorption)
What structure is located at the end of each columnar cell and forms the “brush border” of the mucosal surface?
Microvilli
What is the function of the “brush border fluid layer”
absorption of all substances except water/electrolytes
Where is the Lamina Propria layer found?
Extending into each villi
What are the two structures that are part of the lamina propria?
Central arteriole
Lacteal
What is the function of the central arteriole in the Lamina propria?
Capillary transport of substances directly to liver via hepatic portal vein
What is the function of the lacteal in the lamina propria layer?
Transports fats molecules/substances to systemic system via the thoracic duct
Where is the Crypts of Lieburkuhn found?
At the base of the villi
What are the crypts of lieburkuhn composed of?
Precursor cells (stem cells)
Paneth cells
Secretory cells
What is the function of the precursor cells of the crypts of lieburkuhn
Turnover of intestinal epithelial cells
How long does it take for Precursor cells to stimulate a complete turnover of intestinal epithelial cells?
4-7 days
What is the function of Paneth cells?
Immune function-produce/secrete antibiotic peptides
What is the function of secretory cells?
Secrete brush border digestive enzymes
What is the average motility time in the small intestine?
1-3 hours
What stimulates small intestine motility?
Secretin
CCK
Gastrin
Motilin
What three motility patterns occur in the SI?
Segmentation
Peristalsis
Migrating motor complex
When does the segmentation motility pattern occur in the small intestine?
During feeding
t/f Segmentation motility pattern occurs less frequently than peristalsis?
F - occurs MORE frequently than peristalsis
What is the function of the segmentation motility pattern?
Mixes chyme to allow contact with brush border which then facilitates absorption of all substances except water/electrolytes
What is characteristic of the contractions that occur during the segmentation motility pattern?
Frequent small rhythmic contraction of circular muscle (8-12/min)
Peristalsis motility pattern of the SI occurs when?
during feeding
What is the characteristics of the contractions of peristalsis of the SI?
Coordinated waves of contraction/relaxation of longitudinal muscles-short segments 10cm
Wave of contraction moves slowly (1-2 cm/sec) to allow for digestion/absorption
What is the major function of peristalsis in the SI?
Moves chyme toward the large intestine
When does MMC (migrating motor complex) occur?
Fasting
What are the characteristics of contractions during MMC?
Slow periodic waves of peristalsis that occurs every 1-2 hours, originating in the stomach and passing through the SI.
What is the primary function of MMC?
"house cleaning" sweeps out the stomach/SI. Pushes along residual chyme Bacteria homeostasis -transport bateria to LI -prevents reflux of bacteria from LI
What reflex inhibits gastric motility and results in a slowing down of motility and adding more chyme to SI to allow terminal ileum to empty contents into LI?
Ileogastric reflex
What stimulates the ileogastric reflex?
distended ileum
What reflex relaxes the distal small intestine resulting in the ability to move chyme toward the LI?
Intestinointestinal reflex (inhibitory-protective reflex)
What stimulates the inestinointestinal reflex?
Section of small intestine becomes distended
What reflex promotes terminal ileum motility/ileocelcal valve relaxation and results in emptying of the SI so it can receive more chyme from the stomach?
Gastroilieal reflex
What stimulates the Gastroileal reflex?
Increased stomach (gastric) motility/secretion
T/F the ileocecal valve is intrinsicaly regulated and normally closed?
TRUE
What regulatory system occurs to open the ileocecal valve?
approaching peristalsis in the ileum-results in a relaxed ileocecal sphincter
What regulatory system occurs to close the ileocecal valve?
Distention of the cecum/ascending large intestine-results in constriction of the ileocecal valve.
Which movement pattern provides 90% of motility in the LI?
Haustral segment contractions
When do austral segment contractions occur?
During FASTING
Other than Haustral segment contractions what other movement pattern works to contract the LI? (only occurs 10% of time)
Multihaustral segmentation
When does multihaustral segmentation occur?
during FASTING
What are the 4 movement patterns of the LI?
Haustral segment contraction
Multihaustaral segmentation
Mass movement peristalsis
Intestinal reflexes (orthocolic, and gastrocolic)
When does the orthocolic reflex occur?
in the morning upon standing up
what stimulates the gastrocolic reflex?
Ingestion of food (during or immediately after eating)
Which of the 4 Motility patterns of the LI occurs while eating?
Intestinal reflex-gastrocolic
What motility pattern is considered a “continuation” of the gastroileal reflex?
gastrocolic
What is the stimulus for the rectal reflex (defecation)
Stretch of the rectum wall-obviously this reflex can be overcome by voluntary control
What clinical application can result in loss of bowel control?
Cauda equina syndrome
Explain the pathway of carbohydrate digestion in the GI system
Mouth-salivary amylase breaks down
SI-Pancreatic amylase further breaks down
Brush border enzymes secreted from base of Villi breakdown further into galactose, glucose, fructose
Explain the pathway of Carbohydrate absorption in the GI system
occurs in the brush border of villi
monosaccharides (galactose, glucose, fructose) are absorbed by villi capillaries and transported directly to liver.
Explain the pathway of protein digestion in the GI system
Stomach-pepsinogen released from chief cells converts into pepsin when combined with acid, breaks down protein into smaller protein molecules
SI-Pancreatic enzyme secret by pancreas into duodenum breakdown protein into smaller molecules
Brush border-Enzymes secreted from base of villi breakdown into AA and polypeptides
What is the primary site of protein digestion in the body? A- SI B-Stomach C-Mouth D-brush border
SI
Explain the pathway of protein absorption in the body
occurs in the villi in SI
AA are absorbed by villi capillaries and transported directly to the liver
Which of the following completes absorption step by being absorbed by villi capillaries and transported directly to the liver? Choose all that apply.
a. Carbohydrates
b. Proteins
C. Fat
A. Carbohydrates
B. Protein
What needs to occur to allow fat digestion to occur?
Emulsification
What emulsifying agents exist in the GI tract?
Major players- Lecithin, bile salts
also-Fatty acids, monoglycerides, cholesterol, protein
Explain the pathway of Fat digestion in the GI tract?
Stomach-gastric lipase initiates breakdown
SI-Emulsifies fat droplets into smaller fat droplets
Lypolysis-occurs via molecules that are released from the pancreas
Explain the pathway of fat absorption in the GI tract
Micelle formation
Transport of fats into columnar epithelial cells of SI
Transport of fats into lacteals-which then form chylomicrons which exit the cell via exocytosis
How much fluid is reabsorbed through the SI back into the bloodstream?
85-90%
Where does vitamin B12 absorption occur?
in the terminal ileum
Lack of B12 causes what?
Pernicious anemia
