The Digestive System

Question 1

Summarise the digestive system

Answer 1

• Enable the intake of nutrients required by the body
• Food is broken down into absorbable molecules, which can then be taken into the blood stream (absorption)
• Waste can be eliminated from the body
• The whole process occurs in the Gastro Intestinal Tract (GI tract)

Question 2

What are the 7 classes of food we need to eat?

Answer 2

• Protein
• Carbohydrates
• Nucleic acids
• Fats
• Vitamins
• Minerals
• Fibre (Roughage)

Question 3

Why do we need carbohydrates?

Answer 3

Energy

Question 4

Why do we need proteins?

Answer 4

Growth and repair

Question 5

Why do we need nucleotides?

Answer 5

To make DNA

Question 6

Why do we need fats?

Answer 6

Energy store

Question 7

Why do we need vitamins and minerals?

Answer 7

Essential to perform 100s of functions e.g. boost the immune system, support growth

Question 8

Why do we need fibre?

Answer 8

Gut motility, bowel health

Question 9

What is the main function of the gastrointestinal tract (GI tract)?

Answer 9

Take in large particles of food (polymers)
Make them smaller (digestion)
Smallest molecules (monomers are absorbed0
Waste (non-absorbable matter) is removed

Question 10

What is the structure of carbohydrates?

Answer 10

• Monosaccharides like glucose are easily absorbed
• Disaccharides and polysaccharides like starch need to be broken down into monosaccharides
  (usually glucose) before they can be absorbed
• Sucrose = disaccharide of glucose and fructose (fruit sugar)
• Fructose = monosaccharide goes to the liver to make glucose and glycogen
• Lactose becomes glucose and galactose

Question 11

Order of mechanical processes in digestive system

Answer 11

Ingestion, digestion, absorption, egestion

Question 12

Give the order of the digestive system from mouth to large intestine (including accessory structures)

Answer 12

Mouth > pharynx > oesophagus > stomach > small intestine (liver and pancreas) > large intestine

Question 13

Describe mechanical digestion

Answer 13

• Teeth (mastication)
• Churning by muscles = peristalsis (longitudinal muscles) and segmentation mixing (circular muscles)

Question 14

Describe chemical digestion

Answer 14

Enzymes and bile

Question 15

Describe key aspects of the mouth and its role in digestion

Answer 15

Saliva - contains salivary amylase (breaks down carbs) pH 6.35-7
Lubrication
Lingual lipase (breaks down fats when food reaches stomach)
Saliva is squirted from all 3 sets of glands when you eat
The uvula (dangly bit at the back of your mouth) blocks food from travelling to the nasal cavity
The epiglottis blocks food from getting into the trachea

Question 16

Describe key aspects of the tongue and its role in digestion

Answer 16

• Immunocompromised patients can have thrush
• Colour and smell indicates health
• Smells like poo indicates problem with intestines
• Smells like wee indicates liver failure
• Smells like pear drops = diabetes

Question 17

Describe key aspects of the stomach and its role in digestion

Answer 17

• Gastric = Stomach Itis = inflamation
• Production of gastric juice, stimulated by release of hormone gastrin
  Components of gastric juice:
  1 = hydrochloric acid - really acidic - kills bacteria and pathogens in food
  2 = Pepsinogen (pepsin is the thing that breaks down, the ‘ogen’ needs to be removed by HCl)
  3 = Mucus - produces big layer which protects the stomach from HCl and pepsinogen
  Stomach contents (chyme) now pass from stomach to small intestine

Question 18

Which cells secrete the components of the gastric juice?

Answer 18

Parietal cells = HCL
Chief cells = Pepsinogen
Mucuos cells = mucus

Question 19

What is GORD?

Answer 19

• Gastro-Oesophageal Reflux Disease
• Gastric juice rises back up into the oesophagus through lower oesophageal sphincter (LES - does not close completely; wanes with age)
• Symptoms include burning pain in chest on
  bending or lying (Heartburn), belching
• Complications include choking or aspiration
  of acid
• Manage with antacids

Question 20

What are ulcers?

Answer 20

If blood from lungs - bright red and frothy
If darker red the coming from the stomach which could be the result of an ulcer.
- Ulcers may form when mucosal lining is exposed to gastric acid and its resistance (i.e. mucus production), is undermined
- Main implicating factor is a bacteria -Helicobacter pylori, which causes gastritis
and damages mucus lining. NSAIDs also
break down the mucus barrier
- Increased HCl production may be involved
in some ulcers as may diet and smoking etc
- Gnawing pain experienced. Manage ulcers
with antibiotics and PPI drugs

Question 21

What are the four layers of the GI tract wall?

Answer 21

Inside > Outside
1) Mucosa
2) Sub Mucosa
3) Muscularis
4) Serosa

Question 22

When does food leave the stomach?

Answer 22

• Most liquids can leave the stomach
  after about 10 mins.
• Carbohydrates can begin to leave the
  stomach after about 30 mins.
• Proteins can stay in the stomach for
  several hours
• Fats and fibre stay for longer.
• Chyme is squirted out regularly at
  intervals into the duodenum

Question 23

Describe key aspects of the small intestine and its role in digestion

Answer 23

4.6-9.8metres in length
2.5-3 cm in diameter hence ‘small intestine’
The duodenum is a short structure (about 20–
25 cm long) continuous with the stomach
- The jejunum is the midsection of the small
intestine, connecting the duodenum to the ileum. Itis about 2.5 m long
- The ileum is the final section of the small intestine. It is about 3m long

Question 24

Describe absorption in the small intestine

Answer 24

• The jejunum contains villi that increase
  its surface area
• products of digestion (sugars, amino acids, and small fatty acids) are absorbed into the bloodstream here.
• Larger fat molecules go into the
  central lacteals of the lymphatic system
• The ileum also contains villi similar
  to the jejunum.
• But it absorbs mainly vitamin B12 and bile acids, as well as any other remaining nutrients.

Question 25

Describe key aspects of the liver (+gallbladder) and its role in digestion

Answer 25

1) WATER and electrolytes 2) BILE ACIDS (SALTS) Bile salts = (sodium glycocholate, sodium taurocholate) 3) LIPIDS - Mainly cholesterol 4) BILE PIGMENTS biliverdin bilirubin

Question 26

What is the main role of bile?

Answer 26

- Neutralise stomach acids entering duodenum (pH =8) - Emulsification of Fats

Question 27

Where do the enzymatic sources of digestion originate from?

Answer 27

Walls of small intestine The pancreas

Question 28

Describe key aspects of the pancreas and its role in digestion

Answer 28

Pancreatic amylase - carbohydrates Pancreatic lipase - fats Trypsinogen - protein Chymotrypsinogen - protein

Question 29

What is pancreatitis?

Answer 29

- Pancreas can become acutely inflamed - This can be due to obstruction, so enzymes cannot leave and begin to auto-digest pancreas - Upper abdominal (and back) pain is most severe symptom - Two major causes are alcohol abuse and gall stone obstruction.

Question 30

Explain hunger and obesity

Answer 30

1. Ghrelin – Hunger hormone (Produced by stomach - Stimulates appetite) 2. Leptin – Satiety hormone (Made by fat cells - Blocks appetite). * As more fat is stored, more leptin is made, but leptin resistance can develop * In people with obesity - brain becomes less sensitive or fails to respond to the hormone's signals, even though leptin levels in the blood are very high Why does this happen? * Leptin needs to cross the blood-brain barrier (BBB) to reach the hypothalamus in the brain, where it signals satiety (fullness). * In obesity, this transport system becomes saturated with leptin. * Transport system has a limited number of carriers to move leptin aross the barrier. * Once all the carriers are full, no matter how high the circulating leptin levels in obesity become, no more signal reaches the brain 3. Cortisol, the “stress” hormone also stimulates appetite and intake of palatable foods (high sugar and high fat) * The stress response is evolutionary- beneficial when stress was physical and required quick bursts of energy for "fight or flight" 4. GLP-1 (Glucagon-like Peptide-1) is a gut hormone that inhibits gastric emptying, and decreases food intake by increasing satiety signals in the brain

Question 31

Summarise anti-obesity drugs

Answer 31

- Wegovy/Ozempic is a brand name for a new Danish drug (semaglutide - a GLP-1 analogue - NICE issued guidelines this year recommending Wegovy be prescribed to people with a particularly high BMI and at least one weight-related health condition. - Mounjaro is a drug that mimics the effects of two gut hormones GLP-1 and GIP - GIP (glucose-dependent insulinotropic polypeptide) is a hormone produced in the duodenum after eating, especially fats. - Its role is to stimulate the pancreas to release insulin, using up glucose to make more energy. - Safety profile of Mounjaro is unknown – possible risks include pancreatitis and thyroid tumours

Question 32

What is the role of the small intestine brush border?

Answer 32

- A series of digestive enzymes are found here - These include lactase, sucrase and other intestinal lipases and peptidases - These enzymes participate in the final stages of digestion of ingested carbohydrates and proteins - Specialised for absorption

Question 33

Describe key aspects of the large intestine and its role in digestion

Answer 33

- The large intestine is about 1.5m long and 6-7cm in diameter - Harbours thousands of “good” bacteria e.g. E. coli - Stores food residues prior to elimination as faeces - Secretion of mucus - Absorption of remaining water and sodium (few small fats) (need to know anatomy)

Question 34

Describe malabsorption (D+C)

Answer 34

Diarrhoea: - If intestines cannot absorb normally, body can lose 7-9 litres of water per day. - Consequences of diarrhoea can be very severe with loss of vital electrolytes and dehydration, hypovolemic shock or cardiac events (due to fall in K+) Constipation: - Poor low fibre diet, IBS, medications or obstruction may result in constipation - If intestinal motility is too slow, hard, dehydrated faeces form and patient needs to strain to pass faeces.

Question 35

Describe the gut microbiome

Answer 35

-There are trillions of microorganisms living inside every person - Most importantly, these bacteria help to digest carbohydrates that we cannot digest ourselves - But we now believe that several diseases including cancer and autism are influenced by the gut microbiome To ensure good, useful bacteria in the gut: diet is important; - Maintaining a high fibre diet - Eating fermented foods e.g yoghurt - Help in production of short chain fatty acids - Linked to good health

Question 36

Describe defecatation

Answer 36

Abdominal pressure forces contents out of rectum, through anal canal and out of anus