Lesson 5 - Process of Digestion (Part 1) Flashcards
How are carbohydrates digested?
• Starch -> Maltose by amylase
• Maltose -> Alpha glucose by maltase
• Lactose -> glucose+galactose by lactase
• Sucrose -> glucose+fructose by sucrase
How are proteins digested?
• Polypeptides -> dipeptides -> amino acids
• Endopeptidases (trypsin and pepsin) hydrolyse bonds in the middle of polypeptide chains
• Exopeptidases hydrolyse terminal peptide bonds
How are fats digested?
• Broken down by lipase into glycerol and fatty acids
How is the mouth specialised for digestion?
• Mechanical digestion from teeth chewing food, creating bigger SA
• Food is also mixed with saliva which is chemical digestion
What makes up saliva?
• Amylase (breaks down starch)
• Bicarbonate ions which is alkaline and creates optimum pH for amylase
• Mucus which lubricates food
What is the function of the stomach?
• Stomach walls contract rhythmically to churn bolus with gastric juice
• Sphincter muscles keep bolus of food in the stomach
What is gastric juice?
• Secreted from gastric glands in mucosa of stomach walls
• Contains mucus to protect stomach lining from enzymes
and acids, also lubricate food
• HCl acid to kill bacteria and optimum temp. for enzymes
• Pepsin for digestion of proteins
What are the regions of the small intestine?
Ileum and duodenum
How is food released into the duodenum?
Relaxation of the sphincter muscles causes bits of food (chyme) to be dropped into the duodenum, a little at a time
What occurs at duodenum?
• Receives bile and pancreatic juices
• Secretion of NaHCO3 which neutralises HCl acid
• Mucus lubricates food
What is bile and where is it found?
• Made in liver
•Stored in gall bladder
• Has bile salts which are hydrophobic and hydrophilic so it can emulsify lipids
• This turns larger globules into droplets so more SA for lipase
• Also alkaline so neutralises HCl
What are pancreatic juices?
Describe some features of the ileum
• 6 meters long
• Very folded
• Villi cover folds
• Epithelium of villi covered in projections called microvilli
What is function of goblet cells?
Secrete mucus to provide lubrication and protection to the intestine
Describe the function of columnar epithelial cells in duodenum
• Have many microvilli for large SA for faster rate of absorption
• Have many mitochondria for ATP production for active transport
What enzymes in pancreatic juices
Endopeptidase, trypsinogen, amylase and lipase
What are the crypts of Lieberkuhn?
Valleys in the duodenum between villi which contain Brunner’s glands which secrete NaHCO3 and enterokinase
What is enterokinase?
Enzyme which converts trypsinogen to trypsinogen
Why are enzymes secreted in an inactive form?
So they don’t digest tissue lining
How are molecules transported from lumen to the epithelial cells?
• Fatty acids, glycerol - Diffusion
• Glucose - co-transport with Na+
• Amino acids - hydrolysed by tri- and dipeptides and then AT
How are molecules transported from epithelial cells to the blood?
• Fatty acids and glycerol - Diffusion into lacteal then carried to blood in lymphatic system
• Glucose and galactose - FD into capillary
• Na+ - FD
• Amino acids - FD
