GI 6 Flashcards
Where is most water absorbed
Small intestine
How is water absorbed in colon.
Na, Cl go into interstitial space and contribute to osmotic gradient which pulls water
What ions contribute to water absorption in small int
Na, Cl, AA’s, glucose, lipids
What is intestinal phase regulated by in small int
Distension, acidity, digestive products through short and long reflexes and endocrine signalling
What does regulation of intestinal phase in small int cause
Reduces motility and secretions in sotmach, increases in int
Increases secretions and motility in presence of chyme
What can cause variations in what is excreted in GI
2 different meals
What do long neural reflexes from duodenum cause
Increase sympathetic effferents and decrease parasympathetic to stomach causing decrease gastric emptying
Short reflexes from duodenum cause
Decrease gastric emptying in stomach
Distension, acidity and digestive products in duodenum also cuase
Increase secretions of enterogastrones (hormone)
Intestinal motility influenced primarily by
ENS neurons (myenteric plexus)
During fed state in sm int what type of contractions occur
Mostly segmental
Peristaltic
What are contractions stimulated by
Increased parasympathetic input (long reflexes)
During fasting state in sm int what type of contraction occurs
Migrating motor complex
What is migrating motor complex in sm int drive by
Alterations in parasympathetic input coupled with motilin from MO cells
Possibly by alkaline pH
Accessory secretions are caused by
Long reflexes
What secretes hormones
Enteroendocrine cells in crypts
Cells that secrete GI peptides (hormones) in sm int
S cells, I cells, K cells, L cells
S cell
Secretin
I cells
Cholecystokinin
K cells
Glucose dependent insulinotropic peptide (GIP)
L cellls
Glucagon-like peptide 1 (GLP-1)
What to villi do
Absorb substances and produce mucus
When do pancreatic secretions begin
Cephalic and gastric phases
What start secretions from pancreas
Sight, thought, smell of food will stimulate pancreas
What hormone and neurons cause pancreatic secretions
Gastrin from G cells and parasympathetic neurons
What type of reflex is pancreatic secretions
Enteropancreatic
As chyme enters small int what happens to pancreas
Further parasympathetic output to further secretions
Where does parasympathetic output go to in pancreas
To duct cells and acinar cells to get more HCO3 and more enzyme secretion
What is secretin stimulated by
Acid entering the duodenum from stomach
What is primary role of secretin
Regulation of pH
2 ways secretion regulates pH
- Stimulates bicarbonate secretion from pancreas (buffers stomach acid entering)
- Inhibition of gastric acid secretion
What is secondary role of secretin
Stimulates bile secretion from liver
How is secretin stimulated to be released in stomach to go and act on pancreas
H+ stimulated S cells in duodenum which then secretin acts on duct cells stimulating HCO3 secretion
What is all 4 hormones secondary role
Inhibition of gastric acid secretion and motility and this gastric emptying in sm int
What do the enterogastrones inhibit to inhibit gastric acid secretion and motility
Parietal cells, Gcells and ECL cells
What is cholecystokinin (CCK) stimulated by
Presence of fatty acids and amino acids in chyme
Primarily fat
2 roles of CCK
- Regulate pancreatic enzyme secretion
- Regulate bile secretion (secondary)
What cells does CCK stimulate
Acinir cells in pancreas which drives enzyme secretion to sm int
What does increase enzymes caused by CKK cause in sm it
Increased digestion of fats and protein
How does CCK regulate bile secretion
Contraction of gallbladder
Relaxation of sphincter of oddi
Primary endocrine function of GIP and GIP-1
Glucose homeostasis
What causes GIP and GIP-1 secretion
Carbs entering sm int
What does GIP and GLP-1 cause
Feedforward production of insulin so can take up glucose once enters bloodstream
Enterogastric reflex
Acid, enzymes, and digested food results in hyperosmotic chyme that inhibits gastric emptying
Main role of large int
Store and concentrate fecal matter
How much chyme proceeds through ileocecal valve
1.5L
How dose chyme proceed through ileocecal valve
Valve relaxes as contraction proceeds through ileum
Gastroileal reflex
Food in stomach causes contraction of ileum and relaxation of ileocecal valve
Parts of large int
Ileocecal valve, cecum, ascending colon, transverse colon, descending colon, sigmoid colon
What is site of fluid secretions in large int
Intestinal glands
Primarily mucus from goblet cells
What is absorbed and what is left in large int
Ions and water reabsorbed leaving 0.1L
What does large int lack
Villi because decreased absorption
Secretions in large int
Minimal and primarily mucus from goblet cells
Digestion in large int
Traditionally believed zero
How are indigestible complex carbs, fats and proteins broken down
By bacteria through fermentation process
What does fermentation process prodce
- Lactate and short chains FA’s
- Absorbable vitamins (k)
- Gases
What are short chain FA’s used for
By colonocytes for energy production
3 parts of motility in large int
- Slow segmental contractions
- Haustral rolling or churning
- Mass peristalsis
How long is digestion in large int
18-24 hours
Haustral rolling or churning
Thickened bands of longitudinal muscle layer Taenia coli (creates pouched called Haustra)
Rolls fecal matter through
Mass peristalsis
Forceful contraction initiated in transverse colon
2-3 times per day
What reflex causes mass peristalsis
Gastrocolic reflex, stimulated by food in stomach
Pushes everything down to make more room