gastric digestion Flashcards
(31 cards)
Salvia production
-stimulated by
-inhibted by
Stimulated by sight, smell of food (autonomic control)
Inhibited during sleep, exercise, dehydration
Contents of saliva:
Electrolytes (hypotonic); high HCO3-
Mucin: lubricating of bolus and enhancing chewing action
Salivary amylase initiates digestion
Lactoferrin: lysozyme with anti-bacterial action
Loss of saliva effects?
Causes of lack of salvia
Dry mouth
Oral infections
Dental decay
Loss of taste
Causes: Sjogrens
Anti-cholingeric drugs
MAJOR ROLES OF THE STOMACH
- Mechanical
- Reservoir: Initial digestion, food passes thorugh in controlled amounts of semi-liquid paste (chyme)
- Adjusts osmolatity
- prior to entry into the small intestine (duodenum)
- Antrum: Grinding mill
- Pylorus: regulates size of particles than can pass to duodenum
What does the stomach in general secrete?
intrinsic factor, pepsinogen, mucus, prostaglandins, gastric acid
What is DUMPING syndrome
-osmolarity effect
“Dumping” syndrome – nausea, vomiting, cramping, diarrhoea
- Food moves too quickly from stomach into duodenum and so are not completely digested
- Undigested food particles result in a hyperosmolar chyme in small bowel
- Rapid fluid shift into gut causing intestinal distension = pain
- Diarrhoea due to osmotic effect
Causes of Delayed gastric emptying
Gastroparesis (delayed gastric empyting)
- Diabetes
- Autonomic neuropathy
- variable rate of glucose absorption
- Abdominal discomfort
Function of gastric acid
- Sterilise the stomach (minimal bacteria load)
- Limited role in digestion
- Helps abs B12 and iron
Condition with low or no gastric acid and the effects of this
Achlorhydria (absent or low gastric acid)
* bacterial overgrowth
- increased risk of gastric cancer
- absorption of iron slightly decreased
Cell types of stomach and what they secerete
Goblet: Mucusu (protect stomach lining)
Pareital (Gastric acid)
Cheif cells (Pepsinogen)
D cells (Somatostatin)
G cells (gastrin)
Parietal cell function: Diagram showing flow of bicarb and HCl relationship
Co2 and water enter cell forming H+ and Bicarbonate
Acid goes to lumen thorugh ATP’ase
Bicarb goes to blood through Cl channel
LEcture Slide
How is the gastric mucosa from acid protected from acid
Lecture Slide
Mucus layer with bicarbonate secretions protect the gastric epithelium
4 Controls of gastric acidity
- Neurotransmitter
- Molecule that transmits a signal from a neuron - Autocrine
- Molecule released by a cell that targets itself - Paracrine
- Molecule released by a cell that targets adjacent cells - Endocrine
- Molecule (known as hormone) released by endocrine cells into circulation to target distant cell
LEcture Slide
Acetylcholine
- what nerve releaed by
-stimulate?
Released by vagus nerve and enteric neurons
Stimulates:
– Parietal cells to release
HCl
– ECL cells to release
histamine –> stimulates
parietal cells
– G cells to release gastrin –
> stimulates ECL and
parietal cells
Enterochromaffin-like (ECL) cells
-located?
-secretes?
-Stimulates?
- Located in body of stomach
- Secrete histamine
- Histamine is a molecule with paracrine activity
- Stimulates acid secretion directly by acting on adjacent
parietal cells
G cells
-located?
-secretes?
-Stimulates? How?
- Located in antrum of stomach
- Secrete gastrin
- Stimulates acid secretion indirectly via ECL and parietal cells
– Enters blood circulation
– Binds to ECL cells stimulating histamine release
– Histamine stimulates parietal cells to secrete HCl
– Binds to parietal cells
D cells
-located?
-secretes?
-Stimulates? Inhibits?
- Located in antrum of stomach
- Secrete somatostatin
- Somatostatin is a hormone with endocrine and paracrine
activity - Inhibits acid secretion by acting on adjacent G cells and
inhibiting gastrin release
PHASES OF DIGESTION
and description
- Cephalic phase
- Initiated by thought, sight, smell of food
- Mediated via vagus nerve through acetylcholine - Gastric phase
- Distension of both body and antrum causes acid
secretion mediated largely by the vagus nerve
- Protein in the antrum (mainly breakdown products –
amino acids and peptides) stimulates G cells – gastrin
release - Intestinal phase –
inhibition of acid secretion
- HCl in antrum causes release of somatostatin from D
cells, which inhibits gastrin – main mechanism
- HCl in duodenum stimulates secretin, which inhibits
gastric acid and gastric emptying and stimulates
pancreatic HCO3 secretion
- Partially digested fats and proteins in duodenum
stimulate cholecystokinin, which inhibits gastric acid and
gastric emptying (hunger suppressant)
- Cholecystokinin also stimulates release of pancreatic
enzymes and gallbladder contraction to release bile
What does gastric acid stimulate
What does gastric acid inhibit?
Stimulates release
* ECL cells – histamine
* G cells – gastrin
* Vagus and enteric nerves -
acetylcholine
Inhibits release
* D cells - somatostatin
Examples of Abnormal gastric acid secretion:
Increased
Decreased
Increased
- H. pylori gastritis
- Tumours that produce gastrin (gastrinoma)
Decreased
- Loss of parietal cells e.g. pernicious anaemia (covered later)
- Vagotomy: loss of vagus nerve – reduced acetylcholine
- Drugs e.g. proton pump inhibitors and histamine 2 receptor antagonists
- Gastric surgery: removal of parts of stomach that contain cells involved in HCl
secretion
Pepsinogen
- secreted by
- function
-Purpose
– Secreted from gastric chief cells
– Pepsin degrades/hydrolyses proteins
– Role in early digestion: hydrolysed proteins m ore active
stim ulus for gastrin
– If pH >4, pepsin not active
DISEASES OF THE STOMACH AND DUODENUM
- Peptic ulcer disease
- what is it
-presentation findings
Break in the mucosa
- Erosion = Partial loss
- Ulcer = Full thickness loss
* Presentation
- Pain - “burning” epigastric pain
-Gastric ulcers - worse with food (during and after the meal)
- Duodenal ulcers - worse without food (empty stomach, night)
* Bleeding
* Perforation
* Obstruction (in pylorus or duodenum) from:
– Swelling
– Scarring causing stricture
treatment for peptic ulcer disease
Medical:
- proton pump inhibitors
Omeprazole, Pantoprazole, Lansoprazole
- H2R antagonists
Surgery to reduce acid secretion (Historical)
- Gastrectomy: removes antrum, removes gastrin
- Vagotomy: divide vagus nerve, reduces acetylcholine
Cause of peptic ulcer disease
Helicobacter pylori (most common)
* Other causes:
– Aspirin
– NSAIDs (non-steroidal anti-inflammatory drugs)
