Lab Notes On GI Tract Flashcards
What are the methods for speeding up hydrolysis?
- Mechanical breakdown
- Solubilisation
- Enzymes
4 basic processes of the digestive system
- Digestion
- Absorption
- Motility
- Secretion
Memorise the table of digestive enzymes and there substrates on pg 118
Ye
pH. What should it be and why?
What are the pH changes in the digestive tract
Mouth, stomach, duodenum and lower intestine
Hydrochloride acid production in stomach accelerates hydrolysis
- makes lumen of stomach acidic which is necessary to activate the enzyme pepsinogen into its active form pepsin
- acidity is also helpful in denaturing ingested proteins
- acts as protection against the ingested bacteria
Changes in pH:
Mouth: pH 7➡ saliva is buffered around 7; can become acidic due to bacterial action
Stomach: pH 1-2➡ HCL is secreted by parietal cells
Duodenum: pH 7➡ partially digested food neutralised by bicarbonate ions and in bile fluid
Lower intestine: pH 5-7➡ pH varies, can become acidic due to bacterial action
Temperature: an elevated body temp accelerates hydrolysis (faster than at room temp which is colder) why your bodies at 37degress
Tell me about gastric acid secretion and its regulation?
Gastric acid secretion is stimulated by 3 main mediators
1. Gastrin (CCK-2/ gastric receptor)
2. Histamine (H2 receptor)
3. Acetylcholine (muscarinic receptor)
Stimulation of all 3 receptors necessary for maximal secretion
-selective blocking of any one of these receptors reduces secretory response of other 2 heaps
Inhibition of gastric acid secretion:
- somatostatin released from natural D cells in response to low gastric pH
- acts a paracrine, inhibiting gastrin release from antral G cells- thus inhibiting acid secretion
- negative effect on ECL cells which stop histamine being produced which stops stimulation of acid production
So there is a proton pump which is the thing being stimulated Tito release acid. When stimulated it pumps H+ ions out of the parietal cell in exchange for K+ ions into the cells.
Learn the shit out of the table on slide 29 of lecture 35
Sketch and clearly label a parietal cell, illustrating the transporters and ion channels that are involved in the secretion of HCL
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Explain the source of the bicarbonate ions that protect the gastric mucosa from gastric acid
Protection of gastric mucosa from acid and pepsin damage: bicarbonate
- produced by oxyntic cells during acid secretion and enters mucosal capillaries in exchange for Cl-
- reaches mucosal epithelial cells via local circulation
- secreted into mucus layer, producing neutral pH next to epithelial cells
- neutralise H+ ions that penetrate mucus layer
Explain how ranitidine and omeprazole inhibit gastric acid secretion, and explain why one might be more effective than the other
Ranitidine: is a histamine H2- receptor antagonist which inhibits stomach acid production. Used in treatment for peptic ulcers
Omeprazole is a proton pump inhibitor used in the treatment of peptic ulcers
Omeprazole is better
Explain the main functions and processes of the digestive system
4 main processes
- Digestion
- Absorption
- Motility
- Secretion
Function
The gastrointestinal tract together with accessory glands such as the pancreas and liver allows nutrients, water and electrolytes to be absorbed from the external to the internal environment
Explain the specificity of enzyme action and why this is important (consider the effects of pH on digestion)
Is it because each enzyme works at a specific pH, and there are different pHs throughout the GI tract. For example salivary amylase would work best at pH of 7 but stomach enzymes would work best at a pH of 1-2.
List the three main categories of food molecules
Carbohydrate
Fats
Proteins?
Explain how enzyme activity can be assessed with enzyme assays
By knowing what the by products are of the enzymatic reaction it is doable to see how active the enzymes are by looking at the amount of product formed.
List the main enzymes, substrates and products of carbohydrates, proteins and fat digestion
Pg 118
Explain the main actions of pepsin, lipase and bile and their functions
Lipase:
- pancreatic lipase important for fat digestion but bile salts are also required
- in presence of bile salts, hydrolysis of fats by lipase allows formation of water-soluble micelles.
- lipase secretion stimulated by diets high in fat or high in protein
Pepsin:
- pepsin is a digestive enzyme that is released in the stomach as pepsinogen. The release of hydrochloride acid stimulates the activation of pepsin.
- degrades some dietary protein to peptides, the majority of degradation takes place in small intestine by action of pancreatic proteases.
Bile:
- acts as a surfactant, helping to emulsify the fats in food.
- bile salts are hydrophilic on one side and hydrophobic on the other and they aggregate around droplets of fat to form micelles with hydrophobic towards fat etc
- this greatly increases their surface area so the enzyme pancreatic lipase can act
Protein digestion by pepsin
Chief cells of the stomach glands secrete the enzyme pepsinogen which is converted to active pepsin by gastric hydrochloride acid.
Pepsin hydrolyses proteins into polypeptides and amino acid fragments
