Gastrointestinal system

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  • Created by: Xena_H
  • Created on: 01-11-20 13:52
What is the Alimentary tract?
A tube from the mouth to the anus that is specialised in different regions for the digestion and absorption of nutrients.
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What are the 4 basic digestive processes
Motility - synchronised contraction and stretching of muscles of the GI tract
Secretion
Digestion
Absorption
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What are the 4 layers of the digestive tract? p1
Mucosa-innermost layer, lining of epithelium, provides vascular support for the GI tract.
Submucosa-loose connective tissue layer, has large blood vessels+lymphatics+nerves
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What are the 4 layers of the digestive tract? p2
Muscularis externa-smooth muscle, allow peristalsis
Serosa - layer of loose connective tissue covered by blood vessels +lympatic/nervous system
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What does the mouth do?
Mastication - slicing, tearing, grinding and mixing of food by teeth.
After mixing with saliva, the substance is called a Bolus
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What does the saliva do?
Produced by neural reflexes (PNS)from 3 glands:
Parotid-25%, only serous cells
Submandibular-70%, mainly serous cells, enzymes, mucous
Sublingual-5%, mainly mucous cells
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What are serous cells and mucous cells?
Serous - contain zymogen granules which are precursors of salivary amylase
Mucous - similar to goblet cells, secrete mucus
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What are the 3 stages of Swallowing/ Oesophageal Peristalsis
1. Oral phase-chewing food to create bolus.
2. Pharyngeal phase-medulla innervates muscles, vocal chord close, larynx rises and epiglottis moves to cover it.
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What are the 3 stages of Swallowing/ Oesophageal Peristalsis p2
3. Oesophageal phase- bolus moves down the oesophagus which contracts to move it towards the stomach, lower sphincter opens and food passes into stomach.
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What happens in the stomach?
Mechanical and chemical breakdown of bolus which produces a chyme. Has 3 specific regions: Fundus, Body, Antrum
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What mechanism happens in the stomach? p1
Signal is sent to brain denoting how much chyme is produced, so brain sends a signal saying how much chyme to secrete.
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Mechanism continued p2
Peristaltic contraction originates from the fundus and sweeps to the pyloric sphincter propelling the chyme forward.
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Mechanism continued p3
Small portion of chyme os pushed through the partially opened sphincter into the duodenum. When contraction meets sphincter, it tightly closes so no more food leaves
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Mechanism continued p4
Chyme still in the stomach is tossed back into antrum and undergoes gastric mixing through a process called Retropulsion
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Gastric secretions, give the 3 exocrine cells that secrete substances and what the secretions do.
Mucous cells-alkaline mucus, protect against mechanical/acidic injury+pepsin
Chief cells-pepsinogen, protein digestion.
Parietal cells-HCL/intrinsic factor, denatures proteins, facilitates absorption of vitamin B12
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Gastric secretions, give the 3 endocrine cells that secrete substances and what the secretions do.
Enterochromaffin-like cells (ECL), Histamine, stimulates parietal cells.
G-cells, Gastrin, stimulates parietal, chief and ECL cells.
D-cells, somatostatin, inhibits parietal, G and ECL cells.
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What happens in the small intestine?
Gapped contractions slowly mix and propel chyme, this is initiated by the BER from pacemaker cells.
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What is the BER and what does it do?
Basal Electrical Rhythm, modulates electrical neural control, spontaneous de/polarisation of pacemaker cells in the smooth muscle of the stomach and small intestine. Allow the GI tract to contract and relax.
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Card 2

Front

What are the 4 basic digestive processes

Back

Motility - synchronised contraction and stretching of muscles of the GI tract
Secretion
Digestion
Absorption

Card 3

Front

What are the 4 layers of the digestive tract? p1

Back

Preview of the front of card 3

Card 4

Front

What are the 4 layers of the digestive tract? p2

Back

Preview of the front of card 4

Card 5

Front

What does the mouth do?

Back

Preview of the front of card 5
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