5a. Digestion & Health - Digestive System Flashcards
What are the three primary functions of the digestive system?
Digestion
Absorption
Excretion
What constitutes digestion?
Mechanical - chewing, peristalsis
Chemical - gastric juices, pancreatic enzymes, bile & enterocyte enzymes
Where does most absorption occur?
Small intestine
Where are most substances absorbed into?
Blood
Lymph
How are waste materials excreted?
As faeces
Via urine
Skin
Lungs
Which elements make up the digestive tract?
Mouth Pharynx Oesophagus Stomach Small/large intestine
Which elements make up accessory organs?
Salivary glands Pancreas Liver Gall bladder Biliary tract
Which is the first location in the GI tract where digestion occurs?
Mouth/oral cavity
What is the process of digestion in the mouth?
Chewing breaks down food into smaller chunks
Triggers the salivary glands to release saliva
Why is saliva important in digestion?
Contains enzyme amylase that breaks down polysaccharides (starches found in foods)
How often should food be chewed?
Up to 20 times per bite
What happens the more you chew?
More amylase is released
The more carbs can be broken down and made available to the body
Why should you avoid drinking with meals?
Drinking dilutes saliva and gastric juices
What does diluted digestive juices result in?
Fewer nutrients being made available to the body
What is the optimal pH for salivary amylase to function?
6.8
What happens to amylase once it reaches the stomach?
Denatured by stomach acid
Becomes inactive once the bolus arrives in the stomach
What happens to carbs not broken down in the mouth?
They remain unutilised as the small intestine can only absorb single sugars
What can challenge the optimal saliva pH?
Excess acidity in body tissues which are excreted via saliva
What does the lowering of salivary pH do?
Impairs the functionality of salivary amylase
Impacts the digestion of carbs in the oral cavity
What factors can lower pH in the mouth?
Refined sugars Meat Dairy Processed foods Alcohol Coffee Chewing gum Cigarettes Chronic stress Sedentary lifestyle Heavy metal exposure e.g. fillings
How does digested food enter the stomach?
Through the lower oesophageal sphincter (cardiac sphincter)
What happens when food enters the stomach?
Food stretches the stomach
Stimulates the enteric nerves in stomach wall
And release of hormone gastrin
Both stimulate peristalsis leading to release and formation of gastric juices containing HCI and digestive enzymes
Stomach churns the bolus, mixing it with gastric juices to break down food
Which digestive enzymes are released from the stomach wall?
Pepsinogen
Gastric lipase
What is pepsinogen?
Inactive enzyme which becomes active when exposed to HCl
What does pepsinogen convert to?
Pepsin (the active form)
What does pepsin do?
Breaks down proteins into smaller protein chains
What does gastric lipase do?
Breaks down lipids
What substances can the stomach absorb?
Water
Alcohol
Iodine
Fluoride
What happens to the substances which are absorbed by the stomach?
They enter the venous circulation and escorted to the liver by the portal vein to be processed
What is the pH of HCl?
2-3
Which nutrients are needed to make HCl?
Zinc
B6
What are food sources of zinc?
Nuts Seeds (esp pumpkin) Eggs Fish Meat Oysters
What are food sources of B6?
Whole grains Sunflower seeds Legumes Walnuts Green vegetables Carrots Potatoes Avocado Fish
What function does stomach acid have?
Breaks down proteins (pepsin)
Breaks down fats (lipase)
Triggers release of pancreatic juice and bile into the duodenum
Eliminates micro-organisms - bacteria. viruses, fungi
What can low HCl production in the stomach be caused by?
Chronic stress Low B6 and zinc Medications e.g. PPIs Chronic H. pylori Ageing AI gastritis
What can low HCl lead to?
Poor protein digestion
What can poor protein digestion result in?
Protein putrefaction in SI
What does protein putrefaction create?
Compounds called polyamines
Which pathology are polyamines implicated in?
Colorectal cancer
What does undigested food in the SI do to bacteria?
Allows it to proliferate
Which pathology is caused by a proliferation of bacteria in the SI?
SIBO
What can low HCl do to the production of intrinsic factor?
Reduces production
What can low intrinsic factor compromise?
B12 absorption
How can low stomach acid present within 1-2 hrs after meals?
Bloating
Belching
Flatulence
How can low stomach acid present after eating?
Abdominal pain
Fullness
Foul smelling stools
How can you increase stomach acid?
Apple cider vinegar in a little water before meals Zinc and B6-rich foods Avoid overeating Bitter foods and herbs Eat fermented vegetables
Examples of bitter foods
Rocket
Artichoke
Watercress
Chicory
Examples of bitter herbs
Gentian
Barberry bark
Dandelion
Goldenseal
What is released as chyme is drip fed through the pyloric sphincter into the duodenum?
CCK
cholecystokinin
What is CCK?
Hormone released from the duodenal wall
What are the functions of CCK?
Triggers release of pancreatic juice
Triggers release of bile
Induces sense of satiety
What triggers the release of CCK?
Presence of proteins and/or fats in the chyme
What is the pH of chyme?
2
What neutralises chyme in the duodenum?
Bicarbonate
Where is the bicarbonate to neutralise the chyme released from?
Liver
Pancreas
What is the pH of the duodenum?
6.5
What is the main function of the SI?
Digestion
Absorption
What percentage of nutrients are absorbed in the SI?
90%
What are the three regions of the SI?
Duodenum
Jejunum
Ileum
What mainly happens in the duodenum?
Digestion
What mainly happens in the jejunum?
Absorption
What mainly happens in the illeum?
Absorption of B12
What feature does the SI have to aid absorption?
Villi
What do villi contain?
Blood capillaries
Lymphatic capillaries
What is the brush border also known as?
Microvilli
How are the nutrients absorbed in the SI?
Through the microvilli
What are attached to the microvilli to aid absorption?
Brush border enzymes
What are the names of the brush border enzymes?
Sucrase
Maltase
Lactase
Dipeptidase
What are the functions of maltase, sucrase and lactase?
Break down double-chained sugars into single sugars
e.g. glucose, fructose, galactose
What is the function of dipeptidase?
Breaks down proteins into amino acids
In what form do carbs, proteins and fats need to be in to be able to be digested?
In their simplest forms
e.g. single chains
What determines if macronutrients are able to be broken down into their simplest forms?
Optimal function of the mouth, stomach, pancreas and gallbladder
Once absorbed by the microvilli, where do carbs and proteins go?
Through blood capillaries to the liver
Once absorbed by the microvilli, where do lipids go?
Through lymphatic capillaries
What is the exocrine function of the pancreas?
To produce enzymes that digest carbs, proteins and fats
Where are the pancreatic enzymes secreted into?
SI as part of pancreatic juice
Which pancreatic enzyme digests carbs?
Pancreatic amylase
Which pancreatic enzyme digests fats?
Pancreatic lipase
Which pancreatic enzymes digest proteins?
Proteases - trypsin, chymotrypsin