The components of the digestive system
●Mouth
●Oesophagus
●Stomach
●Pancreas
●Liver
●Small intestine (duodenum and ileum)
●Large intestine (colon)
The gastrointestinal tract
Consists of the oesophagus, stomach, and small and large intestine. The wall of the GI tract has four layers.
The four layers of the wall of the GI tract
☆Mucosa
☆Submucosa
☆Muscularis
☆Serosa
Mucosa
The innermost layer, surrounding the lumen, serving as the primary site for digestion, absorption, and protection.
Submucosa
Consists of a dense layer of connective tissue with blood vessels, lymphatic vessels and nerves. Provides structural support and flexibility
Muscularis
Consists of two main smooth muscle layers- the middle circular layer and an out longitudinal layer- involved in food propulsion and peristalsis. The inner oblique layer is unique to the stomach for churning.
Serosa
A thin, smooth, lubricating membrane the forms the outer layer and consists of several layers of connective tissue.
Physical digestion
Refers to the way in which food is broken up into smaller pieces.
- Chewing food (mastication) mixes food with saliva which lubricates the chewed food and contains enzyme salivary amylase.
- Smooth muscle in the stomach wall causes a churning action, continually mixing food with digestive enzymes and acid
- Peristalsis is the rhythmic movement of the wall of the gut that contracts and pushes food forward along the GI tract.
Chemical digestion
Involves digestive enzymes that catalyse the hydrolysis reactions that break down the large molecules in food, into smaller, simpler molecules.
A major source of digestive enzymes is the pancreas. Pancreatic fluid is released Into the duodenum via the Pancreatic duct.
Salivary amylase (location/source and action)
Source- saliva (in the mouth)
Action- begins the digestion of starch into maltose
Pancreatic amylase (location/source and action)
Source-Pancreatic fluid (in the pancreas)
Action- completes the digestion of starch into Maltose
Proteases (location/source and action)
Source- Pepsin is located in the stomach
Others are contained in the pancreatic fluid
Action- converts proteins into smaller fragments: peptides and eventually amino acids
Lipases (location/source and action)
Source- pancreatic fluid
Action- break down lipids into fatty acids and glycerol
Hydrolysis
The breaking down of proteins into smaller peptides and amino acids by the addition of water and the presence of enzymes
Hydrochloric acid
Secreted by glands in the stomach wall- this helps to sterilise food and provides the acidic conditions required by the stomach proteases and pepsin in chemical digestion
Bile
Produced in the the liver, stored in the the gall bladder and released in duodenum via the bile duct and pancreatic duct. Bile helps break down large fat globules into smaller droplets so that lipases can work more effectively
Digestion of the main food types
(Proteins, polysacchrides, and lipids)
Proteins —> amino acids
Polysaccharides —> monosaccharides
Lipids —> fatty acids and glycerol
Where does the absorption of the products of digestion occur
Mainly in the ileum in the epithelial cells lining the wall of the gut.
Crohn’s disease
Is a inflammatory bowel disease, where the digestive system become inflamed. It cannot be cure.
Causes of crohn’s disease
☆Genetics
☆The immune system attacking the gut, possibly targeting bacterial antigens
☆Smoking
☆a previous gut infection
☆an imbalance in the microbiome
Impact of crohn’s on systems within the body
Most commonly affects the large intestine
●diarrhoea
●stomach aches and cramps, particularly in the lower right abdomen
●blood in the faeces
●tiredness and weight loss
●higher risk of bowel cancer and other inflammatory diseases
●depression and anxiety
Treatments for crohn’s
■Steroids- reduces inflammation, not for long term use, side effects such as weight gain, indigestion, insomnia and increased risk of infection
■Immunosuppressants- If steroids do not work on their own, relive symptoms and can be used long term
■Changes to diet can help control symptoms
■biological treatments- block what is attacking the immune system, given by injection or drip every 2-8 weeks
■surgery- last case scenario. Involves resection of the bowel, carried out by key hole surgery. The inflamed section of bowel is removed and the healthy parts are stitched back together. This can relieve symptoms for a time
