GI Physiology Flashcards
Describe motility of the mouth
mastication
- skeletal muscle
- under voluntary control
Describe mouth secretions and the functions of saliva
salivary glands secrete saliva (99% is water)
functions:
• Lubrication for swallowing (and speech)
• Antibacterial – (lysozyme, thiocyanate)
• Amylase (carbohydrate digestion)
Describe the digestion that occurs in the mouth
Salivary Amylase – Begins carbohydrate (polysaccharide) digestion: Starch (plants) and Glycogen (animals)
- Breaks alpha 1,4 linkage: Hydrolyses into mixture of maltose and glucose
- No effect on other disaccharides (lactose, sucrose) or monosaccharides (glucose, galactose, fructose)
- Cellulose cannot be broken down in humans due to lack of cellulase to break beta 1,4 linkage)
Describe absorption in the mouth
no absorption
Describe the 2 types of saliva reflexes which enhance saliva secretion
- Simple / Unconditioned Salivary reflex:
Chemo and pressure receptors in oral cavity, info sent from afferent nerves fibres to salivary centre in medulla - Acquired / Conditioned Salivary reflex
Thinking about food etc.
describe motility of the oesophagus
- propels bolus from pharynx to stomach
- Swallowing initiated voluntarily (pharyngeal phase 1 sec), then completed involuntarily (oesophageal phase 5-9 secs)
- Primary Peristaltic wave: innervated by vagus nerve (parasympathetic), controlled by swallowing centre in medulla
- Secondary Peristaltic wave: if food stuck – pressure receptors in oesophagus – more forceful contractions
describe secretion of the oesophagus
mucous for lubrication and protection
describe digestion and absorption of the oesophagus
no digestion and absorption
Describe motility of the stomach
- Storage through receptive relaxation (fundus dilates when food passes down the OE) – BER for the body
- Mixing food and gastric secretions into chyme – strong antral peristalsis propels chyme against closed pyloric sphincter
Describe secretion of the stomach
- Vagal stimulation (Ach) causes G cells to release gastrin
- vagal stimulation and gastrin causes parietal cells to release HCl
- gastrin acts on enterochromaffin cells to release histamine which acts on parietal cells to produce HCl
- Vagal stimulation and Gastrin Acts on Chief cells to promote secretion of Pepsinogen which is converted to Pepsin by presence of acid
- Increased acid causes D cells to release somatostatin which inhibits Gastrin -> inhibits acid secretion
- parietal cells also secrete intrinsic factor which combines with B12 to facilitate absorption in ileum
what are the functions of HCl
- Pepsinogen to Pepsin
- Connective tissue and muscle fibre break down
- Denatures Protein
- Barrier Immunity
describe protein digestion in the stomach
Pepsin initiates protein digestion by breaking down splitting amino acid linkages to yield polypeptides, peptide fragments which are further broken down by pancreatic secretions
Absorption of which two things occurs in the stomach
alcohol
aspirin
Describe the triggers of the cephalic and gastric phase of gastric secretion (stimulation)
- Cephalic Phase – smelling, tasting chewing food = increased Ach release Vagus Nerve (parasympathetic)
- Gastric phase – Presence of proteins in stomach, distention (enlargement)- food entering stomach
Describe the factors that inhibit gastric secretion (inhibitory)
- Removal of proteins and distention as stomach empties
- Accumulation of acid – D cells release Somatostatin (inhibits Parietal, G and ECL cells)
- Intestinal phase – Enterogastric reflex, enterogastrones released (CCK and secretin). Inhibit parietal and chief cells as well as smooth muscle contractions