The path of food from mouth to anus, the juices that break it down and where nutrients are absorbed.
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The alimentary canal runs from mouth → pharynx → oesophagus → stomach → small intestine (duodenum, jejunum, ileum) → large intestine → rectum → anus. Teeth cut, tear and grind food: incisors cut, canines tear, premolars and molars grind. Humans have two sets: 20 milk teeth and 32 permanent teeth. The dental formula for an adult is I 2/2, C 1/1, PM 2/2, M 3/3 for one half of each jaw.
Use the adult dental formula (I 2/2, C 1/1, PM 2/2, M 3/3) to find the total number of teeth.
One side: 2 + 1 + 2 + 3 = 8 in the upper jaw and 8 in the lower; two sides give (8 + 8) × 2 = 32 teeth.
A child's milk teeth have I 2/2, C 1/1, PM 0, M 2/2. How many are there?
(2 + 1 + 0 + 2) × 2 jaws × 2 sides = 20 teeth.
Which teeth are used for tearing flesh? Which for grinding?
Canines tear; premolars and molars grind.
Salivary glands make saliva with salivary amylase (ptyalin), which starts digesting starch to maltose. The stomach makes gastric juice: hydrochloric acid (kills germs, gives an acid medium), pepsin (proteins → peptones) and mucus. The liver makes bile, stored in the gall bladder; bile has no enzyme but emulsifies fats. The pancreas makes pancreatic juice with trypsin (proteins), amylase (starch) and lipase (fats). The intestinal juice completes digestion.
Name the enzyme in saliva and the food it acts on.
Salivary amylase (ptyalin); it acts on starch.
What is the role of bile if it has no enzyme?
It emulsifies fats, breaking them into tiny droplets so lipase can act on them. It also makes the food alkaline.
Why does the stomach need hydrochloric acid?
It kills germs in food and gives the acidic medium in which pepsin works.
Digestion is finished in the small intestine: starch → glucose, proteins → amino acids, fats → fatty acids and glycerol. The inner wall has villi, finger-like folds that give a huge surface for absorbing digested food into the blood and lymph. The large intestine absorbs water and minerals; the undigested rest (faeces) is stored in the rectum and passed out through the anus by egestion. Absorbed food is assimilated, used by cells for energy and growth.
State the final products of digestion of (a) carbohydrates, (b) proteins, (c) fats.
(a) Glucose. (b) Amino acids. (c) Fatty acids and glycerol.
How are villi adapted for absorption?
They are very numerous and finger-shaped, giving a large surface area, and each has a rich network of blood capillaries and a lymph vessel.
What is the main function of the large intestine?
To absorb water (and minerals) from undigested food and form faeces.
1. Name the parts of the alimentary canal in order.
2. Name the four kinds of teeth.
3. How many teeth does an adult human have?
4. Which gland makes bile? Where is it stored?
5. Name three enzymes in pancreatic juice.
6. Where does digestion of protein begin?
7. What are villi? Where are they found?
8. What is peristalsis?
9. Distinguish ingestion and egestion.
10. Why is chewing food well important?