Label the following components of the digestive system:
Identify the 8 functions of the gut
- Port of entry for food into the body
- Mechanically disrupt the food
- Temporarily store the food
- Chemically digest the food
- Kill pathogens in the food
- Move the food along the tract
- Absorb nutrients from the resultant solution
- Eliminate residual waste material
Which areas of the GI tract mechanically disrupt food?
- Stomach (vigorous contractions cause the food to be liquefied – chyme)
Describe how the upper and lower areas of the stomach mechanically disrupt food
- Upper area creates basal tone (slow/sustained contractions)
- Lower area has powerful peristaltic contractions that effectively grind food (thicker muscle layer distally)
Why must the GI tract temporarily store food?
We eat faster than we digest
How does the stomach act as a storage facility?
- Distension – accommodates entry of food
- Receptive relaxation – maintains intraluminal pressures
Explain how the colon also acts as a temporary store
Contents are only evacuated several times a day from the colon (mass movements)
In which areas does chemical digestion occur?
- Oral cavity (saliva)
Which substances are used for digestion by saliva?
- Amylase (starch)
- Lipase (fats)
Which substances are used for digestion by the stomach?
- Pepsin (protein)
Which substances/structures are used for digestion by the duodenum/jejunum?
- Exocrine pancreas secretions
What are the challenges to the GI's ability to kill pathogens?
- Thin epithelia
- Large surface area
What are the defences of the GI tract to pathogens?
- Liver (kupffer cells)
- Peyers patches (immune surveillance)
I. Lymphoid follicles
II. Submucosa/mucosa (terminal ileum)
Different regions in the GI tract used different types of movement to move food along.
- Haustral shuttling
- Mass movements
What type of muscle is found in the bowel?
- Small amounts of skeletal muscle
- Mainly smooth muscle
What does the gut absorb?
- Digested food + secretions
- Fluids (fluid balance of the gut)
Which structural features of the gut aid absorption?
- Length of gut
Describe, briefly, how residual waste is eliminated from the colon by mass movement
- Colon acts as temporary storage site, so the rectum is normally empty
- Internal/external anal sphincter open and residual waste is egested via the gastrocolic reflex
What is the broad function of the mouth?
- Physical breakdown of food
- Initial digestive enzymes released
- Infection control
Identify 3 functions of the oesophagus
- Rapid transport of bolus to stomach through thorax
- Upper oesophageal sphincter prevents air from entering GI tract
- Lower oesophageal sphincter prevents reflux into oesophagus
Identify 4 functions of the stomach
- Storage facility
- Produces chyme (physical and chemical digestion)
- Infection control (HCl)
- Secretes intrinsic factor (Vit B12)
Identify 2 functions of the duodenum
- Neutralisation/osmotic stabilisation of chyme (HCO3 rich secretions)
- Concluding digestion: pancreatic secretions and bile
Identify 2 functions of the jejunum
- Final point of digestion
- Nutrient absorption
Identify 3 functions of the ileum
- Water/electrolyte absorption
- Bile recirculation
- B12 absorption (terminal ileum)
Identify 2 functions of the colon
- Final water absorption
- Final electrolyte absorption
What is the main function of the rectum/anus?