Digestive System

Question 1

What is the basic function of the digestive system?

Answer 1

Provide body with nutrients, water & electrolytes from ingested food & fluid
This happens by food moving through gastrointestinal (GI) tract, until it’s broken down into small units that can be absorbed

Question 2

Define peristalsis

Answer 2

Rhythmic contraction of food which propels food from mouth to top of oesophagus to propel food down to stomach

Question 3

Outline the steps of digestion

Answer 3

1. Ingestion (consume food)
2. Digestion (mechanical & chemical breakdown of food into nutrients molecules - carbs & fat broken down by enzymes in saliva)
3. Absorption of nutrients (then enters bloodstream/circulation)
4. Elimination of indigestible materials

Question 4

Outline the Gastrointestinal Tract

Answer 4

The Gastrointestinal tract is a long (6-8m) continuous tubular structure running from:
* Mouth
* Oesophagus
* Stomach
* Small intestine
* Large intestine
* Rectum
* Anus

Question 5

Outline the key sites of the Digestive System

Answer 5

Mouth
Oesophagus
Stomach
Small Intestine
Large Intestine

Question 6

Outline the mouth’s role in the digestive system

Answer 6

Chewing (masticating) of food - first step of mechanical digestion Breaking it down reduces size of food particles > easier to swallow > aids rate of gastric emptying and micronutrients to be absorbed (food leaving stomach)
Increases surface area of food > increases contact area for digestive enzymes > increases rate of digestion
Mixes food particles with saliva (lubrication), making it easier to swallow

Question 7

Outline the Oesophagus’s role in the digestive system

Answer 7

Moves food into stomach (peristalsis), reoccurring squeezing actions strong enough to work in zero gravity
Oesophageal sphincter controls food entry

Question 8

Outline the Stomach’s role in the digestive system

Answer 8

Approx 1.5L but 6L when full
Approx 20-25cm long made of 3 parts: Main body, atrium & fundus
1. Stores large volumes of food (before entering small intestine)
2. Mixes food with gastric liquids to form chyme (soup-like liquid)
3. Regulates emptying of chyme into duodenum > small intestine (for digestion)
After meal it takes 1-4 hours to empty (depending on volume and composition)

Question 9

Outline the Small Intestine’s role in the digestive system

Answer 9

• Approx 6-7m long in 3 parts:
  ○ Duodenum (25-30cm approx), jejunum (2.5m) & ilium (3m)
  
  • 95% of absorption occurs in duodenum & jejunum
    ○ These have multiple folds to increase surface area (3x)
    ○ Multiple folds have finger-like strcutres (villi) to increase surface area again (10x)
    ○ These folds (villi) are covered by brush boarder with approx 600 microvilli (20x)

Food particles broken down into smaller pieces so there’s more opportunities for it to touch villi and microvilli. More opportunity to touch these allows for micronutrients to transfer across cell and into cell. Smaller food particles broken down = easier it is to engage with brush border on microvilli

Question 10

Outline the Large Intestine’s role in the digestive system

Answer 10

1.5m long 3 parts: Colon, rectum & anal canal
From small intestine, chyme moves into large via ileocecal valve (preventing back flow)
Chyme now becomes faceces after absorption of water and electrolytes

Dietary fibre excreted at end as faeces
Dietary fibre very difficult to be digested and absorbed but we need it to help maintain structure & function of GI system

Question 11

Outline the conclusions for absorption of nutrients by the Digestive System

Answer 11

In stomach, food is mixed with gastric secretions (hydrochloric acid & digestive enzymes)
Pancreatic juices & bile are added to chyme in duodenum to digest macronutrients
Specialized enzymes split these macronutrients into the smallest subunits for absorption
90 – 95% of all absorption takes place in the duodenum & jejunum (first parts of
the small intestine)
Large intestine = storage place for undigested food residues, with the final water and electrolyte absorption occurring here