Upper GI tract

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What are the 6 major functions of the GI tract?
Ingestion, secretion, mixing and movement, digestion, absorption and excretion
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Why do herbivores utilise microbial fermentation?
Structural carbohydrates can't be digested by mammalian enzymes (eg cellulose)
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What factors into the energy balance?
Energy in food, activity, growth and repair and cellular metabolism
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Describe short term regulation of energy balance
If the stomach is stretched ghrelin decreases which feeds back to the nucleus tractus solitaries and then to the hypothalmus. If small bowel has products of digestion CCK and GLP-1 increase which feeds back to the NTS and then the hypothalmus
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Describe long term regulation of energy balance
As white adipose tissue increases, leptin increases which feeds back to the hypothalmus to decrease the desire to eat
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What does the musculature mucosa in the GIT do?
It agitates the mucosa to cause movement
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The network of nerve cells in the wall of the GIT is part of?
The enteric nervous system
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What increases the surface area of the GIT?
Folding of mucosa, villi and microvilli
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Where does absorption occur in small intestine?
In the villus epithelium
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Where does secretion occur in the small intestine?
In the crypt epithelium
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How is GIT function co-ordinated?
Nervous system, paracrine substances and hormones
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What do the fundus and corpus secrete?
Acid
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What does the pylorus secrete?
Gastrin
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What phases makes up gastrin secretion?
Cephalic phase, gastric phase and intestinal phase
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What is the cephalic phase?
It is mental and uses the autonomic nervous system (vagus)
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What is the gastric phase?
Stretch receptors in the stomach directly stimulate gastrin release which stimulates the reflex and products of digestion (especially proteins) stimulate gastrin release
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How are parietal cells stimulated?
All three receptors are necessary these include: ACh from vagus nerve, Gastrin from G cells and Histamine from ECL cells (stimulated by gastrin)
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How are parietal cells inhibited (physiologically)?
Somatostatin receptors signal through Gi which inhibits adenylyl cyclase which has the opposite effect of histamine. A low pH also inhibits release of gastrin.
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How are parietal cells inhibited (pharmacological)?
Histamine receptor blocker and proton pump inhibitors
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In the small intestine, why are mucus and bicarbonate secreted?
Mucus is a glycoprotein resistant to enzymes and serves to protect the epithelium. Bicarbonate gets trapped in the mucus and raises the pH to pH7 therefore protecting the epithelium.
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How is GIT motor activity regulated?
It is regulated and coordinated by the enteric nervous system
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What can cause vomiting?
Physiological factors via cerebral cortex, opiates via the chemical trigger zone in the brain, bacterial/viral toxins via vagus and motion/infection via vestibular apparatus. All these triggers then go to the vomiting centre in the brain.
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What normal physiology causes vomiting?
normal voiding of indigestible items from the stomach and over distension of the stomach
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What chemical causes are there for vomiting?
Commonly used drugs, enteric pathogens, bacterial/viral toxins that act from within the lumen or centrally after absorption
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What pathological causes are there for vomiting?
Inflammation/ulceration of stomach, elevated blood urea/ammonia, infections of GIT and blockade of the small or large bowel
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Which species can't vomit?
Rodents, horses, rabbits and potentially foxes
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Why can't rodents vomit?
They lack connections between feeling nauseous and mechanical
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What are the key receptors for emesis?
Serotonin type 3, dopamine type 2, neurokinin type 1 and alpha adrenergic type 2
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During vomiting, what generates the required pressure?
The abdomen with a low pressure in the thorax to open the oesophagus to allow vomit to pass
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What physiological consequences are there from chronic vomiting?
Significant loss of fluids causing dehydration and cardiovascular impairment. Loss of acid makes the body increasingly alkaline causing metabolic alkosis.
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What behavioural consequences are there from chronic vomiting?
Avoidance of foods consumed prior to vomiting
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How can chronic vomiting cause pancreatitis?
High pressure in abdomen forcing pancreatic juices into pancreas therefore digesting the pancreas
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Other cards in this set

Card 2

Front

Why do herbivores utilise microbial fermentation?

Back

Structural carbohydrates can't be digested by mammalian enzymes (eg cellulose)

Card 3

Front

What factors into the energy balance?

Back

Preview of the front of card 3

Card 4

Front

Describe short term regulation of energy balance

Back

Preview of the front of card 4

Card 5

Front

Describe long term regulation of energy balance

Back

Preview of the front of card 5
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