GI and Liver Flashcards
(236 cards)
What are the functions of the stomach?
- Store and mix food
- Dissolve + continue digestion
- Regulate emptying into duodenum
- Kill microbes
- Secrete intrinsic factor
- Activate proteases
- Lubrication
- Mucosal protection
- Produces chyme

Mucous cells, parietal cells, chief cells, enterochromaffin (ECL)-like cells, G cells and D cells. What do these cells secrete? What is the function do these cells?

When gastric acid (HCl) is formed, H+ ions have to enter the lumen of the stomach. Is this passive or active?
This is an active process. H+ ions are pumped into the lumen of the stomach from parietal cells via a H+/K+ proton pump. It is important that H+ and K+ have the same charge.

Picture of mucous cells, parietal cells, chief cells and enteroendocrine cells.

What are the two phases responsible for turning gastric acid secretion on?
- Cephalic phase
- Gastric phase
- Also protein in stomach. Proteins in the lumen cause pH to rise by mopping up H+ ions. This decreases somastatin secretion, which increases parietal cell activity (as somastatin inhibits parietal cells)

What happens in the cephalic phase of turning on gastric acid secretion?
- Parasympathetic nervous system stimulated by sight, smell + taste of food
- Acetylcholine released. This acts directly on parietal cells + triggers release of gastrin + histamine. The net effect is increased acid production

What happens in the gastric phase of turning on gastric acid secretion?
- Gastric distension, presence of amino acids + peptides
- Gastrin release. This acts directly on ECF-like + triggers the release of histamine. Histamine acts directly on parietal cells. Net effect = increased acid production

What are the two phases involved with turning off gastric acid secretion?
- Gastric phase
- Intestinial phase
What happens in the gastric phase when turning gastric acid secretion off?
- Low luminal pH (high H+)
- This directly inhibits gastrin secretion from G cells. This indirectly inhibits histamine secretion (via gastrin).
- This low pH stimulates stomastatin release which inhibits parietal cell activity
What happens in the intestinial phase of turning off gastric acid secretion?
- In the duodenum there is:
- Distension
- Low luminal pH
- Hypertonic luminal contents
- Amino acids + fatty acids
- These factors all decrease HCl secretion via:
- Parasympathetic nerve inhibition (less ACh = less gastrin + histamine release)
- Triggering the release of enterogastrones, e.g. secretion + CKK. These inhibit gastrin release + promote somastatin release
As a summary of gastric acid regulation, what is it regulated by?
- Controlled by the brain, stomach + duodenum
- 1 parasympathetic neurotransmitter (ACh)
- 1 hormone (gastrin)
- 2 paracrine factors (histamine, somatostatin)
- 2 key enterogastrones (secretin, CCK)
What are the protective mechanisms of gastric mucosa?
- Alkaline mucus on luminal surface
- Tight junctions between epithelial cells
- Rapid cell replacement of damaged cells by stem cells present in base of pits
- Feedback loops for regulation of gastric acid secretion

What is the consequence of insufficient gastric mucosa defense? What are the causes of this condition?
- Consequence of insufficient defense = peptic ulcers
- Causes of peptic ulcers:
- Helicobacted pylori infection (damages gastric epithelium, can be treated by 1 proton pump inhibitor + 2 antibiotics, e.g. amoxicillin)
- NSAIDs (non-steroidal anti-inflammatory drugs, inhibit cyclo-oxygenase 1 which causes reduced mucosal defense. Treated by prostaglandin analogues, e.g. misoprotol, reduced acid secretion with proton pump inhibitors or H2-receptor antagonists
- Chemical irritants, e.g. alcohol, bile salts
- Gastrinoma (tumours of G cells, secret gastrin in an unregulated way). Worth noting that G cells are enterochromaffin-like cells

How is pepsin made? What is its role?
- Pepsinogen, an inactive zymogen is secreted by chief cells. This secretion is stimulated by ACh (parasympathetic)
- Pepsinogen’s secretion parallel HCl secretion from parietal cells
- Pepsinogen –> pepsin. Converted by HCl and pepsin (pepsin catalyses the reaction as it is a positive feedback loop)
- Most efficient conversion when pH < 2 (as HCl needed)
- Pepsin accounts for ~20% of protein digestion
- Pepsin increases surface area for later digestion

What is receptive relaxation in gastric motility? What is it mediated by?
- Empty stomach volume = 50ml, maximum volume after eating = 1.5L. This is achieved by receptive relaxation of muscles in body + fundus of stomach
- Mediated by:
- ACh (parasympathetic - Vagus nerve)
- Nitric oxide + serotonin (releases by enteric nerves)
What is peristalsis? How does it work?
- Peristalsis is a series of wave-like muscle contractions that moves food. It is produced in response to arriving food
- Ripple movement begins in body
- More powerful contraction wave in antrum
- Pyloric sphincter closes (little chyme can enter duodenum)
- Antral contents forced back to body - mixing
What is the basic electrical rhythm for peristalsis? What cells determine the frequency of the contractions?
- Frequency of peristaltic waves determined by pacemaker cells called the interstitial cells of Cajal and is constant (3x per minute)
- Depolarisation waves transmitted through gap junctions to adjacent smooth muscle cells
- The strength of peristaltic waves varies (excitatory hormones + neurotransmitters further depolarise membranes, action potential generated when threshold reached)
What increases the strength of gastric contractions?
- Gastrin
- Gastric distension (mediated by mechanoreceptors)

What decreases the strength of gastric contractions?
- Duodenal distension
- Increase in duodenal fat
- Increase in duodenal osmolarity
- Decrease in duodenal pH
- Increased sympathetic NS stimulation
- Decreased parasympathetic NS stimulation

Diagram of gastric emptying.

What is gastroparesis? What drugs can it be caused by?
- Gastroparesis = delayed gastric emptying, makes people feel nauseous etc.
- Caused by:
- Gastrointestinal agents, e.g. H2 receptor antagonists, proton pump inhibitors
- Anticholinergic medications, e.g. diphenhydramine (Benadryl)
- Miscellanous, e.g. calcium channel blockers
What are the main functions of the liver?
- Detoxification = filters + cleans blood of waste products
- Immune functions = fights infections + diseases
- Involved in synthesis of clotting factors, proteins, enzymes, glycogen + fats
- Production of bile + breakdown of bilirubin
- Energy storage (glycogen + fats)
- Regulation of fat metabolism
- Ability to regenerate
The liver maintains a continuous supply of energy for the body by controlling the metabolism of what? What is the liver regulated by?
- Carbohydrates and fats
- Regulated by endocrine glands, e.g. pancreas. Also regulated by nerves
What are lipids? What are triglycerides? Where can fat be stored?
- Lipds are esters of fatty acids + glycerol or other compounds, e.g. cholesterol. Insoluble in water and variety of structures and functions
- 90% of lipids are triglycerides, others phospholipids etc. Triglycerides = 1 glycerol molecule esterified to 3 fatty acids
- Storage areas of fat include adipocytes and hepatocytes






























































































