Digestive system

• What is peristalsis?

  The involuntary contraction and relaxation of smooth muscles to push food through the digestive tract.

  This is controlled by the autonomic nervous system.
• What are the components of the digestive system?

  • mouth
  • oesophagus
  • stomach
  • pancreas
  • liver
  • duodenum, ileum and colon, including layers of the gastrointestinal tract
  • associated glands linked to these components, including salivary glands in the mouth, gall bladder and bile duct
• How do glands know when to secrete enzymes, bile or acid?

  • The food is seen, tasted or smelt.
  • Signals are then sent to the brain via the sensory neurons.

  The brain processes the signals and the send them to the digestive glands to release their products.
• Digestion

  1. Salivary glands produce mucin and amylase to lubricate and start breakdown of carbohydrates

  2. Teeth grind food

  3. Tongue manipulates food into bolus

  4. Swallowing

  5. Pharynx muscles contract and relax to push food into oesophagus

  6. Peristalsis in oesophagus pushes bolus into stomach

  7. Stomach churns food with enzymes pepsin and lipase

  8. Chyme leaves stomach into small intestine

  9. Bile and pancreatic enzymes neutralise and continue digestion in duodenum

  10. Absorption in jejunum and ileum through villi and microvilli

  11. Large intestine reabsorbs water from undigested waste

  12. Rectum sends impulses to brain to voluntarily release waste through anus
• What is physical digestion?

  This is when food is broken down into smaller pieces to increase the efficiency of chemical digestion.
• What is the process of physical digestion?

  • Chewing the food which begins the mechanical breakdown and mixes the food with saliva. The saliva helps lubricate the chewed food and contains the enzyme salivary amylase.

  • It continues in the stomach where contraction of smooth muscle in the stomach wall causes a churning action, mixing the food with digestive enzymes and acid.
• What is chemical digestion?

  This involves digestive enzymes that catalyse (speed up) the hydrolysis reactions that break down the large molecules in food (proteins, lipids and starch) into smaller and simpler molecules.
• What is the role of the pancreas in chemical digestion?

  The pancreas is a major source of digestive enzymes.

  Pancreatic fluid is made by the pancreas and released into the duodenum via the pancreatic duct.
• What adaptions does the small intestine have in order to facilitated absorption?

  • Rich blood supply (The constant movement of blood means there will be a constant favourable concentration gradient for nutrients, which will be absorbed).
  • Villi & Micro Villi (These project into the lumen, increasing the SA).

  Epithelial cells have many mitochondria to provide ATP for active transport.
• Explain the process of absorption in the small intestine.

  • The sodium-potassium pump co-transports sodium and potassium between the epithelial cell and the blood.
  • Sodium then diffuses down its gradient through the sodium-glucose pump. It brings glucose with it via symport.
  • Glucose has now been taken into the cell.
  • The glucose then moves by facilitated diffusion into the blood.
  • The potassium is then pumped back out via the potassium pump.
  • Everything is now back as it was, and this process repeats.
• What is diffusion?

  Diffusion is the movement of particles from an area of high concentration to an area of low concentration.
• What is facilitated diffusion?

  Facilitated diffusion is the passive movement of molecules across a cell membrane with the help of transport proteins.
• What is active transport?

  Active transport is the movement of molecules or ions across a cell membrane against their concentration gradient, requiring energy in the form of ATP.
• What is co-transport?

  Transport involving more than one type of molecule
• What is Crohn’s?

  Crohn’s disease is one of a group of conditions called inflammatory bowel disease, where parts of the digestive system become inflamed.

  Therefore, this is an inflammatory bowel disease. While the immune system is involved, it is not thought to be an autoimmune disease. It is chronic, and can’t be cured.

  It affects all ages but is usually diagnosed at the ages of 15 to 40.
• What causes Crohn’s?

  The cause is unclear, but some factors are thought to play a part:

  • genes: the risk of developing Crohn’s is higher if a close family member has the disease.

  • The immune system attacking the gut: possibly targeting bacterial antigens, causing inflammation.

  • Smoking.

  • A previous gut infection.

  • An imbalance in the microbiome (population of gut bacteria).
• What are symptoms of Crohn’s?

  Crohn’s can effect any part of the gut, but mostly effects the large intestine (colon).

  • Diarrhoea

  • Stomach aches and cramps, particularly in the lower right abdomen

  • Blood in stool

  • Tiredness

  • Weight loss

  Rectal bleeding

  • Joint pain and swelling

  • Ulcers
• Steroids

  Tablets which give the pupil a higher dose of man-made steroids, those which the body makes naturally
• How steroids treat Crohn's

  1. Reduces the activity of the immune system

  2. Reducing inflammation in the gut
• Steroids

  • Can be taken orally (prednisolone), which takes 1 to 4 weeks to start working
  • Can be taken rectally which take a week of 2 to better symptoms
  • Aren't usually used for more than a couple months, as long term use can cause side effects
• Side effects of steroids

  • Weight gain
  • Indigestion
  • Insomnia
  • Increased risk of infection
  • Increased appetite
  • Acne
  • Mood swings
  • Muscle weakness
• Immunosuppressants

  Used to relieve symptoms if steroids on their own aren't effective
• How immunosuppressants treat Crohn's

  1. Keep the immune system working as it should, by stopping it from attacking healthy cells

  2. Weakens your immune system

  3. Long term treatment
• Azathioprine

  A tablet causing side effects like nausea, a fever, fatigue, arthralgias and bone marrow suppression
• Azathioprine

  Contraindicated with acenocoumarol and adalimumab
• Mercaptopurine


  A tablet causing side effects like black stool, gum bleeding, clay coloured stool, a cough, hoarseness, a fever, nausea, and a pale complect ion
• Mercaptopurine

  Contraindicated with acitretin, alcohol, alectanib and amsacrine
• Biological medications

  Medications produced via biological process where living organisms produce active substances made of proteins
• Biological medications for Crohn's

  • For moderate to severe Crohn's
  • Given when other medications are not effective or have bad side effects
• Monoclonal antibodies

  Such as adalimumab that binds to and blocks TNF-(alpha) that attacks the gut
• How biological medications work

  Block the activity of cytokines (a protein that responds to injury and that is responsible for inflammation)
• Administration of biological medications

  • Injected into the vein or as a drip every 2-8 weeks
  • May be needed for several months to years
• Side effects of biological medications

  • Headaches
  • Fatigue
  • Rashes
• How does diet treat Crohn’s?

  You would strip your diet of any possible allergens and slowly introduce them to see your reaction to them. Common Crohn’s diets are low FODMAP, high fibre, specific carb, gluten free and vegan.
• How does surgery treat Crohn’s?

  If no medications aren’t controlling their symptoms or they are having complications they may undergo surgery.

  They may have a stricture plasty or bowel resection where a part of the bowel is cut out if it is unhealthy, and join the healthy parts.

  They may also have a Colostomy where part of the bowels brought to the surface of the stomach with a stoma bag or an ileostomy.

  Surgery can relieve symptoms and prevent them from returning for a time, but they will return eventually.