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Questions and Answers
What triggers the production of gastrin in the stomach?
What triggers the production of gastrin in the stomach?
Gastrin is produced in response to food in the stomach, especially protein, caffeine, alcohol, and spices.
Describe the role of the large intestine in nutrient absorption.
Describe the role of the large intestine in nutrient absorption.
The large intestine acts as a storage organ and is responsible for absorbing about 5% of nutrients, while most water (85%) is absorbed in the ileum.
What is the function of secretin in the digestive system?
What is the function of secretin in the digestive system?
Secretin stimulates the secretion of alkaline pancreatic fluid in response to acid chyme and peptides.
How do amino acids enter the bloodstream after digestion?
How do amino acids enter the bloodstream after digestion?
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What condition is caused by an allergic reaction to wheat proteins and what are its main symptoms?
What condition is caused by an allergic reaction to wheat proteins and what are its main symptoms?
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What is the main function of the small intestine in digestion?
What is the main function of the small intestine in digestion?
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Name two enzymes found in intestinal juice and their functions.
Name two enzymes found in intestinal juice and their functions.
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Describe the active uptake mechanism of glucose and galactose in the gut.
Describe the active uptake mechanism of glucose and galactose in the gut.
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What causes lactose intolerance and its effects on the digestive system?
What causes lactose intolerance and its effects on the digestive system?
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How does cholera affect the digestive system?
How does cholera affect the digestive system?
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What role do phosphatases play in nutrient absorption?
What role do phosphatases play in nutrient absorption?
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Identify a traditional treatment for cholera and its outcome.
Identify a traditional treatment for cholera and its outcome.
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What are the two main types of degradation involved in digestion?
What are the two main types of degradation involved in digestion?
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What is the role of saliva in the mouth?
What is the role of saliva in the mouth?
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How does the stomach contribute to digestion?
How does the stomach contribute to digestion?
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What is pepsin and how is it activated?
What is pepsin and how is it activated?
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What is the function of bile in digestion?
What is the function of bile in digestion?
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What enzymes are secreted by the pancreas in the duodenum?
What enzymes are secreted by the pancreas in the duodenum?
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What is the approximate length of the small intestine?
What is the approximate length of the small intestine?
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What is the role of renin in digestion?
What is the role of renin in digestion?
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Why is gastric lipase important?
Why is gastric lipase important?
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What is the significance of sodium taurocholate in bile?
What is the significance of sodium taurocholate in bile?
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Study Notes
Digestion Overview
- Digestion involves mechanical and chemical degradation, absorption, and distribution of food.
The Mouth
- Mastication: Physical breakdown of food, increasing surface area for digestion and enabling swallowing.
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Saliva: Lubricant for mastication and swallowing. Contains lingual lipase and salivary amylase.
- Lingual lipase: Breaks down fats. Usually not significant in the oral cavity, but can contribute.
- Salivary amylase: Breaks down starch to maltose. Usually not sufficient to significantly breakdown starch, as it's inactivated at pH 4.0 and not lasting long in the oral cavity. Absent in most animals
Stomach
- Structure: Large, muscular sac; site of continued mechanical breakdown of food, and useful for temporary storage.
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Functions:
- Emulsifies fats.
- Acid secretion: Gastric juice containing HCl. Parietal cells in the gastric pits produce HCl at 2L per day. pH 1.0; essential for microbial control/sterilization and to denature proteins.
- Pepsin: Endopeptidase that breaks down proteins into smaller polypeptides; cleaves at Phe, Leu, and Glu, not at Val, Ala, or Gly. Produced as pepsinogen and activated by stomach acid.
- Rennin: Acts to coagulate casein in milk in kids; aiding its digestion. Only present in children.
- Gastric Lipase: Digests 30% of dietary fat.
The Duodenum
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Bile Secretion: Produced by the liver and stored in the gallbladder. Slightly alkaline (pH 7.5-8), helps neutralize stomach acid. Bile salts emulsify fats by lowering surface tension
- Excretion: especially of cholesterol; excess can lead to gallstones.
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Pancreatic Secretion: Contains numerous enzymes (Proteases, Amylase, Lipase, Ribonuclease etc) that degrade proteins, starch, fats and nucleic acids.
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Enzymes:
- Proteases degrade proteins
- Endopeptidases (Trypsin, Chymotrypsin, Elastase)
- Exopeptidase (carboxypeptidase)
- Amylase degrades starch
- Lipase degrades fat
- Ribonuclease and DNAase degrade RNA and DNA
- Contains bicarbonate for neutralization of stomach acid
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Enzymes:
Small Intestine (Ileum)
- Function: Primary site of nutrient absorption.
- Structure: Extremely large surface area (~300 m2) due to folds, villi, microvilli, and brush border cells.
- Capacity: Handles up to 9 liters of food and water daily.
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Absorption: Various mechanisms of uptake into the blood stream
- active transport (e.g glucose and amino acids); aided by carrier protein and sodium pump(transmembrane Na-ATPase)
- passive diffusion (e.g water) going down the concentration gradient
- facilitated diffusion (e.g fructose), using carrier proteins
- Intestinal Juice: Contains enzymes (aminopeptidases, disaccharidases, phosphatases, nucleosidases) that complete digestion of various nutrients to basic components (free amino acids, free sugars etc).
Carbohydrate Uptake
- Glucose and Galactose are actively absorbed (using sodium hexose symport).
- Fructose is absorbed via facilitated diffusion.
- Disaccharides must be digested (e.g. sucrose and lactose by respectively sucrase and lactase, and maltose by maltase ) into monosaccharides before absorption.
Lactose Intolerance
- Low lactase enzyme activity (low production or activity).
- Effects: Accumulation of lactose in gut, osmotic activity retaining water in gut, fermentation by intestinal bacteria, excessive gas production and abdominal cramps, diarrhoea, and flatulence.
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Types:
- Inherited
- Secondary
- Primary
Cholera
- Cause: Bacterial infection by Vibrio cholerae.
- Symptoms: Severe diarrhea, significant fluid loss (potentially over 30L per day), wasted appearance, pale skin, cold extremities, slow/undetectable pulse, thick dark blood and can lead to rapid death in several hours.
- Pandemic History: Endemic in South Asia, recorded in 18th-century India, spread to Russia, and had a notable pandemic in 1829. Recorded first death in UK in 1830 in Sunderland.
- Traditional treatments: Ineffective attempts to treat the blood, and using purgatives.
- New treatments: Rehydration therapy (oral or IV); reintroducing water and electrolytes (especially sodium or glucose)
Coeliac Disease
- Cause: Allergic reaction to wheat proteins (gluten).
- Symptoms: Weight loss, diarrhea, lethargy, anaemia, antibodies against gluten.
- Mechanism: Malabsorption; gluten (peptides) enter the brush border cells, causing an immune response in the intestinal mucosa.
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Treatment: Gluten-free diet.
- Impacts microvilli and intestinal villi/brush borders, causing reduced surface area for absorption.
Amino Acid Absorption
- Amino acids are actively absorbed via specific carriers (neutral, phenylalanine/methionine, proline, lipophilic, cationic).
- Absorbed via enter portal vein
Lipid Absorption
- Tiny lipid droplets (liposomes/micelles) form in the presence of bile salts
- Intestinal Lipase degrades triglycerides to fatty acids and monoglycerides
- Uptake of separate components
- Resynthesis of triglycerides in the intestinal cells
- Formation of chylomicrons in the Golgi apparatus
- Chyle (milky fluid containing chylomicrons) enters the lymphatic system
Large Intestine (Colon)
- Function: Absorbs remaining water and salts; stores faeces and contains many bacteria.
- Absorbs: Remaining water and electrolytes
- Bacteria: Important for nutrient and vitamin production; fermentation of remaining materials. Can cause gas, ammonia, and certain toxins
Regulation of Digestion by Peptide Hormones
- Gastrin: Produced in the stomach, responding to food (especially proteins, caffeine, alcohol and spices), nerve stimulation; promotes stomach acid and enzyme secretion as well as contraction of oesophageal sphincter.
- Gastric Inhibitory Peptide (GIP): Produced in the duodenum, responding to fats and proteins; inhibits stomach acid and enzyme secretion and stomach muscle action.
- Cholecystokinin (CCK): Produced in the duodenum, responding to food (especially protein and fat); primarily promotes pancreatic fluid and enzyme secretion, and contraction of gallbladder (promoting bile release).
- Secretin: Produced in the duodenum; responding to acid chyme and peptides, promotes alkaline pancreatic fluid secretion and reduces stomach muscle action.
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Description
Explore the intricate processes involved in digestion, focusing on the roles of the mouth and stomach. Understand the mechanics of mastication, saliva's components, and the stomach's function in breaking down food. This quiz covers essential concepts about how our bodies process and utilize nutrients.
