digestive system

What is the definition of digestion?

The physical and chemical breakdown of food.

• Physical: Teeth / Churning
• Chemical: Enzymes / Acid

Why is digestion necessary? (3 Reasons)

1. To make food soluble.
2. So food is easily absorbed.
3. So food is easily transported.

Name the 5 stages of nutrition in order.

1. Ingestion: Taking food into the alimentary canal.
2. Digestion: Breaking down food.
3. Absorption: Nutrients moving from the ileum into the bloodstream/lymph via diffusion.
4. Assimilation: Nutrients carried from blood to body cells to be used.
5. Egestion: Removal of unabsorbed waste.

What are the components and functions of saliva?

Saliva has a neutral pH (7) and contains:

• Water & Mucus: Lubricates food.
• Amylase: Enzyme that breaks down starch into maltose.
• Lysozymes: Destroys bacterial cell walls.

What is the human Dental Formula, and what does each letter stand for?

• I = Incisors (Slice & cut)
• C = Canines (Grip & tear)
• P/M = Pre/Molars (Crush & grind)

What is a bolus, and how does it safely travel past the windpipe?

A bolus is chewed food rolled into a ball. When pushed into the pharynx, a flap of tissue called the epiglottis closes over the trachea (windpipe) so food safely enters the oesophagus.

What is peristalsis?

An involuntary wave of muscular contraction that moves food along the alimentary canal.

What is the pH environment of the stomach, and what enzyme works there?

pH 2 (highly acidic due to hydrochloric acid). The active enzyme is pepsin, which breaks down proteins into peptides.

What are 6 major functions of the Liver?

1. Produces bile.
2. Deamination (breaks down excess amino acids into urea).
3. Breaks down old red blood cells.
4. Stores glucose as glycogen (and stores iron/vitamins).
5. Converts excess carbohydrates into fats.
6. Detoxifies the body.

Where is bile produced, where is it stored, and what are its 2 functions?

Produced in the liver, stored in the gallbladder. It travels through the bile duct to the duodenum to:

1. Neutralise chyme coming from the stomach.
2. Emulsify lipids (break large fat droplets into tiny droplets to increase surface area for lipase).

What 3 substances are produced by the Pancreas for digestion?

1. Sodium hydrogen carbonate (neutralises stomach acid).
2. Amylase (Starch \rightarrow Maltose).
3. Lipase (Lipids \rightarrow Fatty Acids + Glycerol). _(Note: It also produces Trypsin for protein digestion).

What is the true biological role of the Appendix?

In humans, it is a vestigial organ (largely lost its original function). In herbivores, it is large and houses symbiotic bacteria that produce enzymes to digest cellulose.

What are the primary functions of the Colon and the Rectum?

• Colon: Reabsorbs water from unabsorbed waste.
• Rectum: Stores faeces before egestion via the anus.