Stomach & Stomach Acid Secretions Flashcards by Sean Con

Name the 5 Functions of the Stomach

Receiving & storing food & liquids
Secretion of acid, pepsinogen, gastric lipase
Mixing of food & liquid with gastric juice
Grinding to reduce particle size (into chyme)
Regulating the exit of chyme into the duodenum

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Name the 5 Regions of the Stomach

Cardia
Fundus
Body (corpus)
Antrum
Pylorus

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What is the surface area of the stomach important for?

Secretion
Absorption
Access

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What are the secreting cells of the stomach

Mucous cell
Parietal cells
Chief cells
Enteroendocrine cells
- ECL - (Enterochromaffin - like cells)
- G cells
- D cells

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Describe Mucous neck cells and their function

Secrete mucins - viscous glycoproteins
Secrete bicarbonate - HCO₃-

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What is the function of Parietal cells?

Produce HCl
Secrete intrinsic factor - req for B12 absorption

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What is the function of Chief cells, and their secretions?

Secrete gastric lipase
Secrete pepsinogens
- Pepsinogens → pepsins at pH < 3
- Initiate protein digestion by hydrolysis

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How do Parietal cells make HCl?

CO₂from bloodstream enters parietal cell
- CO₂+H₂O → H₂CO₃ (carbonic acid)
Carbonic acid deprotonates
- H₂CO₃ → H⁺+ HCO₃^-
H⁺/K⁺ ATPase pump exchanges H+ into lumen in exchange for K+
HCO₃^-diffuses back into blood
Cl^-diffuses from blood, across parietal cell into lumen following gradient

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Key secretions from pyloric region of the stomach

Gastrin
Mucus

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What are the 3 Enteroendocrine cells and their secretions?

ECL / Enterochromaffin like cells
- Histamine - stimulates gastric acid secretion
- Ghrellin - hunger, energy homeostasis
G cells
- Gastrin - ↑ - acid secretion
D cells
- Somatostatin - ↓ stomach acid secretion

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Key secretions from the body of the stomach

HCl
Intrinsic Factor (IF)
Pepsinogens
Mucus

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Name some causes of impairments to the gastric mucosal barrier

Alcohol
NSAIDs (Ibuprofen)
Salicylates (Aspirin)
Bile acids
Infection

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3 main stimulating factors that act directly on parietal cells to increase acid production

Acetylcholine → vagus nerve → M3 muscarinic receptors
Gastrin → Antral G cells → CCK receptors
Histamine → Enterocromaffin like (ECF) cells → H2 histamine receptors

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2 factors causing indirect stimulation of gastric acid

Stimulation of ECL cells to release histamine via:

ACH
Gastrin

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3 phases of gastric acid secretion

Cephalic
Gastric
Intestinal

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Explain the cephalic phase of gastric acid secretion

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~30% acid response to meal
Occurs before food reaches stomach - smell, taste, chewing, conditioning
Mediated by branches of Vagus nerve
- Vagus → ACh → direct stimulation parietal cells
- Vagus → GRP (gastrin releasing peptide) → gastrin

Explain gastric phase of gastric acid secretion

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~60% acid prod
Food reaches stomach - distention, presence of amino acids & small peptides in stomach
Vagal stimulation
- ACh → parietal cells
- ACh → G cells → gastrin
Amino acids → G cells → gastrin
High pH → G cells → gastrin

Explain intestinal phase of gastric acid secretion

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~10% acid response
Chyme in duodenum stimulates neural & hormonal mechanisms
First stimulate, then inhibit acid production

Stimuli for gastric acid inhibition

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pH <1.5
Acidic solutions in duodenum
Chyme in duodenum
Hyper-osmotic solutions in duodenum

Stop signals to inhibit gastric acid secretion

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Somatostatin from D cells
- Inhibit parietal cells - stop HCl release
- Inhibit G cell - stop gastrin release
- Inhibit ECL cell - histamine release

Also:

Secretin → S cells
Gastric Inhibitory Polypeptide → K cells

Damage to gastric mucosa can occur from:

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↑ HCl production
↑ Pepsin production
↓ Thickness mucus layer
↓ Mucosal blood flow
↓ Bicarbonate secretion
Mucosal erosion (aspirin, NSAID’s)
Helicobacter pylori infection

How does H-pylori survive the acidic environment

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Produces large amounts of urease
Breaks down UREA → AMMONIA (NH3) + BICARBONATE (HCO3-)
Bicarbonate neutralises stomach acid → basic cloud
Ammonia is toxic to cells - increases damage to gastric epithelia

Urea + Water Urease Ammonia and Carbon dioxide

(NH₂)₂CO + H₂O → 2NH₃+ CO₂

3 drugs for “triple therapy” of H. Pylori

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Amoxycillin - antibiotic → inhibits cell wall synthesis
Clarithromycin - antibiotic → inhibits protein synthesis
Omeprazole - proton pump inhibitor

How does H-pylori contribute gastritis?

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H-pylori excrete urease enzyme to break down urea to form basic cloud to help neutralise stomach acid to survive in the harsh stomach environment
Excretion of urease causes abundance of ammonia and bicarb
Ammonia is toxic to gastric epithelial cells

Name the stimuli for Gastrointestinal Endocrine Hormones, and where they come from: Gastrin

G cells, Stomach ⇑Proteins. amino acids ⇑ Neuronal stimulation → vagus ⇑ Stretch ⇓ Acid

Name the stimuli for Gastrointestinal Endocrine Hormones, and where they come from: CCK (CholyCystoKinin)

I cells, Duodenum ⇑ Proteins/amino acids ⇑ Fatty acids

Secretin is a gastrointestinal Endocrine Hormone. Where does it come from? What promotes secretion? What does it do?

S Cells, Duodenum and small amounts of Jejunum Released due to low duodenal pH ie, when chyme is released from pyloric sphincter Targets pancreas to secrete bicarbonate rich fluid. It also reduces acid secretion of gastric parietal cells

Name the stimuli for Gastrointestinal Endocrine Hormones, and where they come from: GIP (Glucose-dependent-Insulinotrophic-Peptide AKA Gastric-Inhibitory-Polypeptide)

K cells, Duodenum ⇑ Proteins/amino acids ⇑ Fatty acids ⇑ Glucose

Describe the pathological features of erosion of the gastric mucosa

Erosion indicates an ulcer formed with death of gastric epithelial cells is shallow, and does. not penetrate beyond the mucosa

One long term complication of untreated H-pylori infection

Gastric Adenocarcinoma Gastric Lymphoma

Carcinoma Vs Adenocarcinoma

Carcinoma is the most common form of cancer. It starts in the epithelial tissue of your skin or internal organs. **Adenocarcinoma is a subtype of carcinoma**. Starts in “glandular cells” that secrete mucus and other fluids

What tumour suppressor gene is mutated in about 75% of colorectal cancers that is crucial or initiating apoptosis in cells with irreparable genetic damage in Go of the cell cycle?

p53

A 28-year-old man complains of nausea, vomiting, diarrhoea and abdominal discomfort. His symptoms have developed over night following a social BBQ. He tells you that a number of his friends have developed similar symptoms. What organism is the most-like responsible for his symptoms?

Campylobacter spp.

How does secretin reduce gastric parietal cell acid secretion?

When released from duodenal S- cells, secretin: - Stimulates somatostatin release from D-cells (pyloric antrum, duodenum, pancreatic islets) - inhibit gastrin release from pyloric antrum G-cells - Directly down regulates parietal cells

Stomach & Stomach Acid Secretions Flashcards

(34 cards)