Upper GI Flashcards by Iihan Ali

What is digestion?

Process of breaking down macromolecules to allow absorption.

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What is absorption?

Process of moving nutrients and water across a membrane.

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Outline the basic plan of the gut wall

Mucosa: Epithelium, Lamina propria (loose connective tissue), Muscularis mucosae
Submucosa: Connective tissue containing nerve plexus
Muscularis: Smooth muscle containing nerve plexus
Serosa/adventitia: Connective tissue +/- epithelium

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What do the upper, mid and hind gut consist of respectively?

Upper - Oesophagus + stomach, which arise from the foregut. Liver, pancreas, GB and a portion of duodenum.

Mid - SI and portion of LI including transverse colon.

Hind - Lower GI tract, entire colon, rectum + anus

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What 2 layers make up the muscularis?

Inner circular and outer longitudinal muscle layer

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List all teeth in the oral cavity.

8 incisors
4 canines
8 premolars
12 molars

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What is the largest muscle in the oral cavity?

Masseter muscle - responsible for biting.

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What are the salivary glands?

Parotid, sublingual and submandibular.

(Food mixed with saliva (aqueous secretion and digestive enzymes)).

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What do the intrinsic and extrinsic muscles of the tongue control?

Intrinsic - Fine motor control and moving food.

Extrinsic - Gross movement of tongue (in, out, up and down) + assists mechanical digestion.

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What is the function of the oesophagus?

Conduit for food, drink and swallowed secretions from pharynx to stomach.

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Describe the epithelium of the oesophagus.

Non-keratinising squamous epithelium preventing wear and tear of lining → protects from acid reflux (Extremes of temperature and texture).

Lubrication - mucus secreting glands and saliva

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What separates the oesophagus from the stomach?

Zigzag (Z) line

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What are rugae?

Gastric folds

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Why are gastric folds present?

Increase SA of epithelia of GI tract so that more digestion and absorption can occur.

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Outline the 4 phases of swallowing.

Stage 0 - Oral phase:
Chewing and saliva prepare bolus. Both oesophageal sphincters constricted.

Stage 1 - Pharyngeal phase
Pharyngeal musculature moves bolus towards oesophagus.

Stage 2 - Upper oesophageal phase
Upper sphincter closes. Superior circular muscle rings contract and inferior rings dilate. Sequential contractions of longitudinal muscle.

Stage 3 - Lower oesophageal phase.
Lower sphincter closes as food passes through.

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What are the functions of the stomach?

Breaks food into smaller particles (acid and pepsin)
Holds food, releasing it in a controlled steady rate into duodenum.
Kills parasites and certain bacteria.

What are the 3 main parts of the stomach and what do they secrete?

Cardiac and pyloric region - Mucus only.

Body and fundus - Mucus, HCl and pepsinogen.

Antrum - Gastrin

Purpose of acid?

Activates pepsinogen into pepsin → Food digestion.

How much acid does the stomach secrete daily?

2L/day; 150 mM H+ (3 mill x that in blood)

What do mucin (gel coating of stomach) trap?

Bicarbonate ions

Outline the pH of the stomach.

Epithelial surface - pH 6-7

Lumen - pH 1-2

Stomach contractions: What are they?

Peristalsis: 20% contractions
Propels chyme towards colon. More powerful as moves from LOS to pyloric sphincter. ANS essential.

Segmentation: 80% contractions. Weaker. Fluid chyme towards pyloric sphincter. Solid chyme pushed back to body. Stretching activates ENS.

What are gastric chief cells?

Protein-secreting epithelial cells abundant in ER
Golgi packaging and modifying for export.
Masses of apical secretion granules.

What do gastric chief cells secrete?

Pepsinogen (HCL → Pepsin)

Describe the intracellular structure of parietal cell (resting) in the stomach (gastric).

``` Many mitochondria (requires lots of ATP) Cytoplasmic tubulovesicles (contain H+/K+ ATPase) Internal canaliculi (extend to apical surface) ```

What is the difference between a secreting and resting parietal cell?

Tubulovesicles fuse with membrane | Microvilli project into canaliculi

Explain how the parietal cells secrete HCl?

Na+/K+ pump, transports Na+ into interstitial fluid from the parietal cell and K+ transported from interstitial fluid into the parietal cell and then into the canaliculi that have fused with the tubulovesicles. CO2 taken up by parietal cells and reacts with H20 using carbonnic anhydrase, forming H+ and HCO3-. HCO3- transported out by AE1 antiporter and Cl- transported into the parietal cell and then into canaliculi. H+/K+ ATPase transports H+ into the canaliculi and moves K+ from the canaliculi back into the parietal cell.

How is this HCl secretion triggered?

H2 receptors which are found on the surface of the parietal cells. When histamine gets released form different triggers, this is detected by the H2 receptors which starts the process of HCl secretion.

What is the function of Gastrin?

Stimulates release of histamine from chromaffin cells (lamina propria).

What part of the stomach secretes gastrin?

Pyloric antrum

Describe the cephalic phase of gastric secretion.

Thought, sight, smell and taste of food stimulates gastric secretion. Vagus nerve activates parietal cells through ACh to trigger the whole cascade.

Describe the gastric phase of gastric secretion.

Food in stomach activates the stretch- and chemo-receptors. Signals sent to and from the brain via vagus nerve to activate the secretion of acid.

Describe the intestinal phase of gastric secretion.

Once the chyme with pH less than 2 reaches the duodenum. Signal is transmitted by the vagus nerve and this causes secretion of hormones that inhibit the secretion of gastric HCL and pepsin too. These hormones are Gastric inhibtory peptide, Cholecystokinin and Secretin

What is the mechanism of action of Omeprazole?

Blocks the protein pumps (H+/K+ ATPase) → prevent acid formation.

What is the mechanism of action of Ranitidine?

Blocks the H2 receptors to prevent the triggering of the whole cascade by Histamine which leads to acid secretion.

Would chyme fatty acid content and protein content increase or decrease acid secretion in the stomach?

Decrease