7.1.14Human Nutrition
Adaptations of the Small Intestine — Cambridge IGCSE Biology 0610 Revision Notes & Topical Questions
5 min read 5 parts Lesson 9 of 9 Unit quiz
Curriculum Equation Key قوانين الرقم الهيدروجيني والاتزان الأيوني - pH & Acid-Base Equilibrium FormulasFast Exam Solution
pH = -log[H⁺] | pOH = -log[OH⁻] | pH + pOH = 14 | [H⁺][OH⁻] = 10⁻¹⁴
Word Equation & Conditions: الرقم الهيدروجيني = -لوغاريتم تركيز أيون الهيدروجين | pH + pOH = 14
Location & Specifications: الاتزان الأيوني، كيمياء 3 ثانوي، التحصيلي، و AP Chemistry.
Section 1 of 5Increasing Surface Area
A large surface area lets more nutrients be absorbed in the same time.
Length
- Length The ileum is very long, which gives digested food a long surface to be absorbed across.
Folded lining
- Folded lining The inner surface is highly folded, which increases the area available for absorption.
Villi
- Villi Millions of tiny finger-like projections called villi greatly increase the surface area of the ileum.
Microvilli
- Microvilli The cells on the surface of each villus have microvilli, which increase the surface area even further.
Section 2 of 5Structure of a Villus
Structure of a Villus
Thin wall
- Thin wall The wall of the villus is one cell thick, so substances only have a short distance to cross.
Capillaries
- Capillaries A dense network of blood capillaries removes absorbed glucose and amino acids in the blood.
Lacteal
- Lacteal A lacteal runs through the centre of each villus and transports fatty acids and glycerol away in the lymph.
Absorption methods
- Absorption methods Nutrients cross the single layer of cells by diffusion and by active transport.
| Feature | Function |
|---|---|
| Wall one cell thick | Short diffusion distance |
| Network of blood capillaries | Carries glucose and amino acids away |
| Lacteal in the centre | Carries fatty acids and glycerol in lymph |
| Microvilli | Greater surface area |
Section 3 of 5Maintaining a Steep Gradient
Absorption is faster when absorbed substances are removed quickly.
1
Digested food molecules such as glucose are present at a high concentration in the lumen of the ileum.
2
They move across the thin villus wall into the blood capillaries by diffusion or active transport.
3
The flowing blood carries the glucose and amino acids away, keeping the concentration low in the capillaries.
4
The steep concentration gradient means further absorption can continue quickly and efficiently.
Section 4 of 5Answering Exam Questions
Link structure to function
- Link structure to function Always state the feature, then explain what it does, such as thin wall giving a short diffusion distance.
Name the products
- Name the products Say that glucose and amino acids enter blood capillaries while fatty acids and glycerol enter the lacteal.
Use surface area language
- Use surface area language Villi and microvilli increase surface area so absorption takes place faster and more efficiently.
Avoid vague terms
- Avoid vague terms Write one cell thick rather than very thin, and blood supply rather than lots of blood.
Section 5 of 5Exam Checklist & Tips
7.1.14 – Key Points for the Exam
- Ileum The part of the small intestine where most absorption of digested food occurs.
- Villus A finger-like projection from the lining of the small intestine.
- Lacteal A lymph vessel in the centre of a villus that carries away fatty acids and glycerol.
- Absorption Movement of digested food molecules through the gut wall into the blood or lymph.
Common Mistakes
- Saying that the villi have a thick wall; the wall is one cell thick to give a short diffusion path.
- Stating that all nutrients enter the blood; fatty acids and glycerol enter the lacteal.
- Forgetting microvilli, which add a further increase in surface area.
- Writing that villi increase absorption because they are long, without stating that this raises surface area.
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