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Human Nutrition

Balanced diet, digestion, villi

Balanced Diet — Seven Components

1. Carbohydrates: Energy (4 kJ/g). Starches & sugars.

2. Proteins: Growth & repair (4 kJ/g). Amino acids.

3. Fats/Lipids: Energy (9 kJ/g). Insulation, membranes.

4. Vitamins: Disease prevention. Examples: C (scurvy), D (rickets).

5. Minerals: Disease prevention. Examples: iron (anaemia), calcium (weak bones).

6. Fibre: Digestion. Cellulose from plants. Prevents constipation.

7. Water: Solvent. Thermoregulation. Metabolic reactions.

Vitamin & Mineral Deficiencies

Deficiency	Cause	Effect
Vitamin C	Lack of fruit/veg	Scurvy (weak connective tissue, bleeding gums)
Vitamin D	Lack of sunlight/dairy	Rickets (weak, curved bones; poor teeth)
Iron	Lack of meat/beans	Anaemia (fatigue, pale, weak RBCs)
Calcium	Lack of dairy/leafy greens	Weak bones & teeth; poor muscle contraction

Digestive System Organs

Mouth: Mechanical & chemical digestion (amylase). Swallowing.

Stomach: Churning (mechanical). Protease (pepsin). Acid environment (pH 2).

Small intestine: Main absorption site. Villi increase surface area. Pancreatic enzymes & bile.

Large intestine: Water reabsorption. Faeces formation.

Pancreas: Produces amylase, protease, lipase. Releases into small intestine.

Liver: Produces bile (emulsifies fats). Stores glucose as glycogen.

Digestive Enzymes

Enzyme	Substrate	Product	Location
Amylase	Starch	Maltose (sugar)	Saliva, pancreas
Protease (pepsin)	Protein	Peptides	Stomach
Lipase	Fats/lipids	Fatty acids + glycerol	Pancreas
Trypsin	Protein	Peptides	Small intestine

Bile — Emulsification of Fats

Bile: Made by liver, stored in gallbladder. Contains bile salts (no enzymes).

Emulsification: Breaks large fat droplets into smaller droplets. Increases surface area for lipase to act.

Without bile → fats not properly broken down → poor absorption & diarrhoea

Villi — Absorption Adaptation

Villi: Finger-like projections lining small intestine.

Features for absorption:
• Large surface area (thousands of villi) → max nutrient uptake
• Thin walls (one cell thick) → short diffusion distance
• Rich blood supply (capillaries) → carries absorbed nutrients away

Glucose & amino acids: absorbed by active transport (needs ATP). Fatty acids & glycerol: absorbed by diffusion.

Digestion in Mouth & Stomach

Mouth: Teeth break food into smaller pieces (mechanical). Saliva amylase starts starch digestion (chemical).

Swallowing: Bolus (food ball) travels down oesophagus (peristalsis = muscle contractions)

Stomach: Churning mixes food with gastric juice (contains pepsin + HCl). Forms chyme (paste).

Note: Starch digestion starts in mouth, stops in stomach (acid denatures amylase)

Exam Tips

✓ Know 7 balanced diet components with functions

✓ Enzyme deficiency diseases: scurvy (C), rickets (D), anaemia (Fe), weak bones (Ca)

✓ Bile emulsifies fats (no enzymes)

✓ Villi: large SA, thin walls, blood supply

✓ Amylase breaks starch to maltose, lipase breaks fats to fatty acids + glycerol

Key Takeaways

✅ Balanced diet: 7 components (carbs, protein, fat, vitamins, minerals, fibre, water)

✅ Deficiencies: scurvy (C), rickets (D), anaemia (Fe)

✅ Bile emulsifies fats for lipase to work

✅ Villi: large SA, thin walls, blood supply for absorption

✅ Enzymes: amylase (starch), protease (protein), lipase (fat)

You are what you eat! 🍽️✓