Physiology Flashcards
GIT function
Motility, digestion, absorption
Enzymes involved in chemical digestion of carbohydrates
Pancreatic amylase (main) Alpha-dextrinase, sucrase, lactase, maltase in brush border ---> all end in monosaccharides
Enzymes in the chemical digestion of proteins
- Trypsin, chymotrypsin, carbopeptidase and elastase from pancreas
- aminopeptidase and dipeptidases in brush border
Enzymes in lipid chemical digestion
- most lipase from pancreas
- pancreatic lipase most important in TGL digestion
- emulsification by bile salt to increase SA
Nucleic acid enzymes in chemical digestion
Nucleases
- ribo/deoxyribonuclease in pancreatic juice
- nucleosidases and phosphates in brush border
What is located on the apical membrane of brush border?
Brush border enzymes
What is muscle contraction stimulated by?
Calcium ions, via calmodulin –> MLCK (not troponin C)
What are the two types of waves in the phasic pacemaker of enteric smooth muscle?
- slow waves - basal rhythm, not AP/not contraction
2. spikes - when slow waves pass threshold and AP generated
Effect of ACh and Adrenaline on digestion
Ach increases
Adr decreases
What is peristalsis and what induces it?
Feeding induces it Gut wall (any part) reflex initiates retrograde circular contraction and anterograde circular relaxation
What are involuntary sphincters controlled by?
- myogenic tone (ANS/ENS/reflexes/hormones)
2. relative pressures
What are the direct and indirect effects of ACh on enteric muscle?
Direct - constriction, prevents flow
Indirect - relaxation, excites interneurons and facilitates flow
Nerve plexuses of enteric nervous system (intrinsic)
Submucosal plexus (Meissner’s): between mucosa and circular muscle layer Myenteric plexus (Auerbach’s): between circular and longitudinal muscle layer
What are the components of the extrinsic autonomic nervous system in digestion
Parasympathetic stimulation increases secretion and activity by stimulating ENS
Sympathetic stimulation decreases secretions and activity by inhibiting ENS
GIT > prevertebral SNS ganglia > GIT reflexes
Gastrocolic reflex: stomach colon evacuation
Enterogastric reflex: colon small intestine to inhibit stomach motility/secretion
Colonoileal reflex: colon ileum to inhibit ileal emptying
GIT > CNS > GIT reflexes
Control gastric motility/secretion: stomach/duod brainstem GIT
Pain reflexes general inhibition of entire GIT
Defecation reflexes: colon/rectum spinal cord powerful colon/rectum/abdominal contractions
4 phases of digestion and main control
- Interdigestive phase
- Cephalic phase (neural)
- Gastric phase (neural + hormonal)
- Intestinal phase (hormonal)
Coordination of the cephalic phase in digestion
smell/taste > reflex from taste buds > stimulate vagal centre in CNS > cranial nerves stimulate secretions (saliva, pancreas, stomach) > vagus also increases motility of stomach and intestine
Coordination of the gastric phase in digestion
Food stimulates vago-vagal reflexes and hormone release > stimulates gastric and pancreatic secretion > hormones further stimulate secretion > vagal activity stimulates gastric motility
Coordination of the intestinal phase
food > hormones released from gut mucosa > stimulate secretion of exocrine pancreas > H. stimulate gallbladder contraction > inhibitory hormones act on stomach to inhibit acid secretion (overload protection)
Interdigestive phase coordination in digestion
Stomach - small volume
Jejunum - empty
Pancreas - v little secretion
Liver and gallbladder - sphincter of oddi closed, bile diverted to gall bladder to be stored and concentrated
What are the 4 layers of the stomach and what cells do they contain?
- mucosa
- 3 types of exocrine glands: mucous neck, parietal and chief cells
- G cell
- D cell
What do mucous neck cells secrete and what is their function?
Mucus - physical barrier between lumen and epithelium
Bicarbonate - buffers gastric acid
What do parietal cells secrete and what is the function?
Gastric acid - activates pepsin and kills bacteria
Intrinsic factor - B12 absorption