GI Flashcards
What % of Gi system receives CO?
33
Splanchnic circulation is organized into what?
Series & parallel components
Series components
Venous drainage empties into portal v. & perfuses liver
What 3 aa make up parallel circulation?
- Celiac a.
- SMA
- IMA
Secretions stimulated by cephalic phase
- Saliva (large volume)
- Gastric acid (small)
- Pepsin (small)
- Pancreatic enzymes (small)
What reinforces the cephalic phase?
Chewing!
Cephalic phase characteristics
- Activates enteric neurons via PNS traveling in vagus n.
- Releases Ach
- Stimulates secretions in salivary glands, parietal cells, & enzyme secreting cells.
Where is initial fluid (saliva) formation?
In acinar cells
- via Cl- pump
- isotonic solution
Where is NaCl reabsorbed during salivary secretion?
In ductal cells
Composition of salivary secretion
- Low Na+, Cl-
- High K+, HCO3-
- Amylase, lipase (digestion)
- Lysozyme, lactoferrin (antimicrobial)
- Mucus (lubrication)
Factors that influence salivary flow
- Hydration status (most important!)
- Circadian rhythm (peaks at end of afternoon, 0 during sleep)
- Medications
Which gland contributes the most during “stimulated” salivary flow?
Parotid
- Aqueous saliva
Which gland contributes the most during “unstimulated” salivary flow?
Submandibular
- Viscous, mucin glycoproteins
What is a good indicator of properly functioning salivary glands?
alpha-amylase
Muscular composition in upper vs lower esophagus
- Upper 1/3 = skeletal
- Middle 1/3 = skeletal & smooth
- Lower 1/3 = smooth
Deglutition
Swallowing reflex
- Oral
- Pharyngeal
- Esophageal
Deglutition events
- Nasopharynx closes –> breathing inhibited
- Laryngeal mm contract to close glottis & elevate larynx
- Peristalsis begins in pharynx –> propels food toward esophagus
- Esophageal sphincter relaxes –> food enters
Oral phase
- Tongue pushes bolus toward pharynx
- Somatosensory receptors activated
- Signal travels to afferents
- Involuntary swallowing reflex initiated (info sent via glossopharyngeal, vagus, & hypoglossal)
Pharyngeal phase
- Begins when receptors are stimulated
- Block nasopharynx & trachea
- UES opens
- Respiration inhibited
- CN IX & X
Esophageal phase
- Begins when food enters esophagus
- UES closes
- Primary peristaltic wave
- Secondary peristalsis (enteric NS): initiated by esophageal distention
Gastric phase
- Food stretches wall of stomach, neural reflex stimulates acid secretion
- Peptides & aa stimulate G cells to release gastrin
- Food acts as buffer –> ph increases –> removal of stimulus for somatostatin secretion from D cells
- When acid secretion sufficient to lower ph, somatostatin can inhibit gastrin release & digestion completed
What forms H2CO3?
Aerobic metabolism combines w/ H2O
- catalyzed by carbonic anhydrase
HCl secretion
- H2CO3 –> H+ & HCO3
- H+ secreted via H+-K+ATPase
- Cl- follows via Cl- channels
- HCO3 absorbed into blood via Cl-HCO3 exchanger = “alkaline tide”
When do S cells release secretin?
When pH is 4.5 or less –> HCO3- secretion
3 layers of smooth muscle in GI
- outer longitude
- inner circular
- muscular mucosa
Smooth muscle cells are connected by what?
Gap jxns that form electrical syncytium
In smooth muscle, interaction of actin & myosin is controlled by what?
Binding of Ca2+ to calmodulin
Migrating motility complex: Type I
No contractions
MMC: Type II
- Intermittent peristaltic contractions
- Variable amplitude
MMC: Type III
Strong peristaltic contractions
MMC characteristics
- Initiated during fasting
- Begins in stomach
- Moves undigested material to colon
- Repeats every 90-120 mins
Myogenic contractility
Gut has some contractility w/out any nervous input
Importance of tonic inhibitory tone
Constant inhibitory tone of VIP & NO –> prevents, slows down contractility
Major carbs
- Complex starches
(amylopectin, amylose) *Digestion begins at mouth - Disaccharides (sucrose, maltose, lactose, trehalose) *Digestion begins at intestine
Digestion, absorption of carbs
- Enzyme active in mouth until stomach inactivates it
- Salivary & pancreatic amylase produce products
- Enzymes hydrolyze starch to glucose
Alpha-amylase breaks down starch into what?
- Alpha-dextrins
- Maltose
- Maltotriose
What breaks maltose into glucose?
Maltase
What breaks down alpha dextrins into glucose?
Alpha-dextrinase
What breaks down maltotriose into glucose?
Sucrase
Carb absorption: apical
- Na+-glucose cotransporter
- Na+-galactose cotransporter
- Fructose facilitated diffusion
Carb absorption: basolateral
Facilitated diffusion w/ GLUT 2 transporter
Fxn of incretins
Hormones that help insulin
Incretin hormones
- GLP1
- GIP
What produces GLP 1?
Intestinal cells
GLP1 fxn
- Stimulates insulin biosynthesis & secretion
- Inhibits glucagon secretion
- Protective effects in heart/brain
- Improves insulin signaling –> insulin sensitivity increased, gluconeogenesis reduced
Protein absorption: apical
- Na+-aa cotransport
- H+-di/tripeptide cotransport
Protein absorption: basolateral
- Further breakdown to aa
- Facilitated diffusion
What are the final digestive products of lipids?
- Monoglycerides
- Cholesterol
- Lysolecithin
- Free fatty acids
What are the final digestive products of proteins?
- AA
- Dipeptides
- Tripeptides
How does absorption of lipids occur?
Via micelles & chylomicrons
Cl- secretion from crypts
Requires activation by Ca2+ or cAMP
