Upper GI Tract Flashcards by Zunaira Khan

What is digestion?

-the process of breaking down macromolecules to allow absorption

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What is absorption?

-the process of moving nutrients and water across a membrane

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What are the layers of the gut wall?

(Oesophagus side)

Mucosa:

epithelium
lamina propria (loose connective tissue)
muscularis mucosae

Submucosa:
-connective tissue (contains nerve plexus)

Muscularis:
-smooth muscle (contain nerve plexus)

Serosa/Adventitia:
-connective tissue +/- epithelium

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How many teeth do adults have and what are they?

32 in total

8 incisors
4 canines
8 premolars
12 molars

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What muscles are involved in the oral cavity chewing?

masseter muscle- largest jaw muscle, responsible for biting
several other muscles control the position of the mandible

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What does saliva contain?

-digestive enzymes and aqueous secretion

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What are the 3 salivary glands?

parotid glands
sublingual glands
submaxillary gland

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What are the muscles in the tongue and their function?

Intrinsic muscles:
-fine motor control & moving food

Extrinsic muscles:

gross movement of tongue (in, out, up, down)
assists mechanical digestion

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At which C & T points does the oesophagus start and end?

-C5 and T10

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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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What is the structure and function of the epithelium of the oesophagus?

non-keratinising
‘wear & tear’ lining (extreme temp & texture)
lubrication- mucus secreting glands (&saliva)
nucleated superficial squamous cells
basal cell
basal lamina

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What is the structure and function of the muscles in the oesophagus?

tonically active
swallowing centre
upper oesophageal sphincter- skeletal muscle
lower oesophageal sphincter- skeletal & smooth muscle
peristalsis
inner circular muscle
longitudinal muscle

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What happens at the gastro-oesophageal junction?

reflux- prevented by diaphragm hiatus
epithelial transition
gastric folds- rugae

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GORD

-gastro-oesophageal reflux disease

-lining changes from stratified squamous epithelium to simple columnae epithelium which secretes the mucus

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What is hiatus hernia?

when the hiatus of diaphragm large and so can’t constrict the oesophagus anymore
part of the stomach starts migrating into the chest
keep the gastro-oesophageal junction open, acid goes up and acid reflux

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What is the purpose of the epithelial transition?

secretion in stomach by simple columnar

- protective function of stratified squamous

Why are gastric folds present?

absorbative and secretory function

- increased SA

What are the 4 stages of swallowing?

Stage 0- oral phase:

chewing and alive prepare bolus
both oesophageal sphincters constricted

Stage 1- Pharyngeal phase:

pharyngeal musculature guides food bolus towards oesophagus
both oesophageal sphincter open

Stage 2- upper oesophageal phase:

upper sphincter closes
superior circular muscle rings contract & inferior rings dilate
sequential contractions of longitudinal muscle

Stage 3- lower oesophageal phase:
-lower sphincter closes as food passes through

What are the functions of the stomach?

breaks food into smaller particles (acid & pepsin)
holds food, releasing it in controlled steady rate into duodenum
kills parasites and bacteria

What is the function of the cardia and pyloric region of the stomach?

-mucus only

What is the function of the body and fundus of the stomach?

-mucus, HCL, pepsinogen

What is the function of the antrum?

-gastrin

How much acid does the stomach produce in a day?

-2L

What are mucins?

gel coating

- HCO3- trapped in mucus gel

What is the optimal pH at the epithelial surface and lumen of the stomach?

Epithelial surface = 6-7 | Lumen = 1-2

Contrast peristalsis and segmentation in the stomach.

Peristalsis (longitudinal muscle): - 20% of stomach contractions - propels chyme towards colon - more powerful as moves from LOD to pyloric sphincter - ANS essential Segmentation (circular muscle): - 80% of stomach contractions - weaker - fluid chyme towards pyloric sphincter - solid chyme pushed back to body - stretches activate enteric NS

What do the chief cells of the stomach do?

Gastric chief cell: - protein-secreting epithelial cell - secretes pepsinogen - pepsinogen converted to pepsin to break down proteins - abundant RER - golgi packaging and modifying for export - masses of apical secretion granules

What are parietal cells?

- important in creating HCL - many mitochondria - cytoplasmic tubulovesicles (contain H+/K+ ATPase pump) - internal canaliculi (extend to apical surface) - tubulovesicles fuse with membrane - microvili project into canaliculi

How parietal cells work?

1. CO2 comes into parietal cells and mixes with water via carbonic anhydrase, broken down into H+ and HCO3- 2. K+ enters cell via Na/K pump from capillaries 3. K+ secreted into gastric lumen 4. HCO3- enters capillaries and Cl- enters cell 5. H+ into gastric lumen via H/K+ ATPase pump 6. H+ combines with Cl- to make HCL

How would inhibition of carbonic anhydrase influence acid secretion in the stomach?

-decreased HCL

What role does HCL play?

-converts pepsinogen to pepsin

What is gastrin in the stomach?

- local peptide hormone secreted by the G-cells - pyloric antrum - stimulates histamine release from chromatin cells (lamina propia)

What are the phases of gastric secretion?

Cephalic Phase: - stomach stimulated via vagus nerve (thought, sight, smell, taste of food) - controls pyloric and cardiac sphincter contraction - local stimulus via gastrin, going via bloodstream to stimulate the parietal cells Gastric Phase: - food in stomach- stretch & chemo-receptors - gastric distension stimulates local reflexes - control local reflexes - HCL & pepsin also self-stimulate the stomach - excess acidity (pH<2) causes less gastrin release, so inhibits stomach secretory activity Intestinal Phase: - sends signals to the stomach via enterohormones - Gastric inhibitory peptides, cholecystokinin, secretin produced which are enterogastrones, play a role in entergogastric reflex and inhibit/promote HCL & pepsin ``` REMEMBER- nervous stimulus hormonal stimulus local stimulus -all together control stomach function ```

What is the excitatory intestinal phase?

-protein concentration in duodenum stimulates gastrin secretion

What affect does distension of the duodenum have?

-inhibits stomach secretory activity

How might you produce a useful drug to decrease acid secretion?

- suppress H/K+ ATPase - Omeprazole - Ranitidine -somatostatin suppresses G-cell receptors

What effect will chyme fatty acid content have on acid secretion in the stomach?

- M2 receptor for ACh for parasympathetic stimulation via the vagus nerve - histamine secreted by cells in stomach wall acts on H2 receptor, causes HCL secretion - Gastrin stimulates G-cells