56. GI Physiology Part 2 Flashcards
How is almost all fat ingested?
Triacylglycerol (glycerol and 3 stearic acids)
Explain the first process of fat digestion?
Bile salts and phospholipids combine into emulsified droplets. This prevents re-aggregigation.
Explain the second part of the digestion of fat?
Micelles are formed by lipase. These are small moelcules that allow the fatty acids and monoglycerides to travel to the intestine.
A proton breaks down the micelles allowing them to release the fatty acids and monoglycerides
What happens to the FA and monoglycerides once they enter the intestine?
Reformed into triacylglycerols by the smooth endoplasmic reticulum.
What happens to these droplets of triacylglycerol?
They are released into chylomicrons (lacteals that transfer the fat for storage)
How are vitamins digested?
Fat soluble- A,D,E,K
Water soluble- B group, C and folic acid
Vit B12 is different
How is vitamin B12 digested?
As it is a large charged molecule it has to be bound to intrinsic factor in the stomach to form complex which is absorbed via the distal ileum.
How is iron absorbed?
Transported in the intestine by DMT1
Incorporated into ferritin
Iron in blood binds to transferrin
How is chewing controlled?
What are the digestive glands of the face?
Somatic nerves–> skeletal muscle of the mouth/jaw
Reflex
Parotid, submandibular and sublingual (all pairs)
What is in saliva
Water Mucins- lubricant A-amylase- catalyst of polysacharide digestion Electrolytes (pH) Lysozyme- bacteriocidal
Explain the direct nervous inputs to swallowing?
Parasympathetic- Cranial nerves VII and IX
Sympathetic- a1 adrenoceptor
B2 adrenoceptors
Why do you have glands in your oesophagus?
For swallowing
Explain the process of swallowing
Control centre in the medulla
oral phase (voluntary, tongue pushes bolus back)
Pharyngeal phase-(soft palate backward and upward)
Pre-oesophageal (UOS relaxes, epiglottis covers larynx)
Oesophageal phase- UOS contracts
What are the functions of the stomach?
Temporary store of ingested material
Dissolves food particles nad initiates the digestive process
Controls delivery of contents to the small intestine
Sterilises ingested material
Produces intrinsic factor (Vit B12)
Describe the passage of food from the oesophagus to the pyloric sphicnter
Oesophagus–> cardiac opening–> cardiac region–> fundus–> body–pylorus–> pyloric sphincter
What does each region of the stomach do?
Fundus- Storage
body- Storage, mucus, HCl,pepsinogen, intrinsic factor
Antrum- mixing and grinding- gastrin
Explain the structure of the gastric glands
Mucous neck cells- mucous secreting
Parietal cells- HCl, intrinsic factor (middle)
Chief cells- pepsinogens
How is hydrochloric acid produced by the stomach?
Carbonic acid is formed by CO2 and H20
Hydrogen comes from the carbonic acid and bicarbonate is exchanged for chloride
What receptors control the secretion of gastric digestions?
Gastrin
Histamine
Acetylcholine
Prostaglandins (inhibits)
What is the cephalic (pre- digestive) phase of digestion?
The sight smell and taste of food stimulates the vagus nerve. This causes acetylcholine and gastrin to act on the parietal cells
Gastrin and acetylcholine also cause enterocromin like cells found in the fundus to release histamine that acts on parietal cells
Explain the gastric phase of digestion?
Distension of stomach–>ach
Peptides in luem–> g cell–> gastrin
Gastrin/Ach–> ecl–> histamine
All these cause increased action on parietal cells
How is gastric acid secretion inhibited?
Cephalic phase (stop eating)
Gastric phase (lower pH, lower gastrin, neg feedback)
Acid/ fat.carbs in duodenum–> secretin and gastric inhbitng polypetide released
What are the enterogastrones
What is their fucntion?
Secretin, cholecystokinin and Gastric inhibitory polypeptide.
Released in response to acid, hypertonic solutions fatty acids or monoglycerides in duodenum
INHIBIT GASTRIC ACID
REDUCE GASTRIC MOTILITY
What is the main zymogen in the stomach?
Inactive precursor. Prevents cellular digestion
Pepsingoen is released in response to pH lower than 3. This becomes pepsin through already released pepsin.
Pepsin digests protein
What is the role of gastric mucous?
Protects mucosal surface from mechanical surface
Bicarb sits there to stop cells from exploding
HCL does not have it pH lowered by passing through the gastric mucous
