CIE iGCSE Biology-7.5 Absorption- Study Notes- New Syllabus
CIE iGCSE Biology-7.5 Absorption- Study Notes – New syllabus
CIE iGCSE Biology-7.5 Absorption- Study Notes -CIE iGCSE Biology – per latest Syllabus.
Key Concepts:
Core
- State that the small intestine is the region where nutrients are absorbed
- State that most water is absorbed from the small intestine but that some is also absorbed from the colon
Supplement
- Explain the significance of villi and microvilli in increasing the internal surface area of the small intestine
- Describe the structure of a villus
- Describe the roles of capillaries and lacteals in villi
Absorption of Nutrients in the Small Intestine
What Is Absorption?
Absorption is the process by which digested food molecules (small, soluble substances) pass through the wall of the intestine into the bloodstream or lymphatic system, so they can be delivered to cells around the body.
Where Does Absorption Take Place?
Most absorption takes place in the small intestine, specifically in the ileum, the longest part of the small intestine.
Why the Small Intestine Is Ideal for Absorption:
| Feature | Function |
|---|---|
| Very long (up to 6 meters) | Provides a large surface area and time for absorption |
| Lined with villi | Finger-like projections that increase surface area |
| Villi have microvilli | Even more surface area for maximum absorption |
| Thin wall (one cell thick) | Short diffusion distance for nutrients |
| Rich blood supply | Maintains concentration gradient for rapid absorption |
| Lacteals in villi | Absorb fatty acids and glycerol into lymphatic system |
What Nutrients Are Absorbed and Where?
| Nutrient | Absorbed into | Where It Goes |
|---|---|---|
| Glucose | Blood capillaries | Delivered to cells for respiration |
| Amino acids | Blood capillaries | Used to build proteins in body cells |
| Fatty acids + Glycerol | Lacteal (lymphatic system) | Used for energy storage and membranes |
🔹 Specialized Structures – The Villi
Each villus contains:
- Capillary network: absorbs glucose and amino acids into blood
- Lacteal: absorbs fatty acids and glycerol into lymph
- Thin epithelium: allows rapid diffusion
- Microvilli: further increases surface area
Summary:
The small intestine is the main site of nutrient absorption. It has several adaptations such as villi, thin walls, and rich blood supply to ensure efficient nutrient uptake. Absorbed nutrients are transported to body cells for assimilation and energy use.Water Absorption in the Digestive System
Where Is Water Absorbed?
- Most water is absorbed in the small intestine, especially in the ileum.
- Some water is also absorbed in the colon (part of the large intestine).
Why Is Water Absorption Important?
- Maintains the body’s water balance
- Keeps the contents of the intestine in a semi-solid state
- Prevents dehydration
- Allows proper transport of nutrients and waste
🔹 Functions of Different Parts:
| Part of Digestive System | Role in Water Absorption |
|---|---|
| Small Intestine (Ileum) | Absorbs most of the water from digested food |
| Large Intestine (Colon) | Absorbs remaining water and forms solid faces |
Most water is absorbed in the small intestine, but some absorption also occurs in the colon to help form faces and prevent water loss.
Villi and Microvilli – Increasing Surface Area in the Small Intestine
What Are Villi?
- Villi are tiny, finger-like projections that line the inner surface of the small intestine.
- Each villus (singular) is covered in epithelial cells.
What Are Microvilli?
- Microvilli are even smaller folds found on the surface of epithelial cells that line each villus.
- They form a brush border and greatly multiply the surface area.
Why Is Surface Area Important?
- A larger surface area = faster absorption of nutrients.
- Nutrients like glucose, amino acids, fatty acids, vitamins, and minerals can pass more efficiently into the blood or lymph.
Structure & Function Table:
| Structure | Description | How It Helps |
|---|---|---|
| Villi | Tiny finger-like projections lining the inner wall of the small intestine | Increase surface area and contain blood capillaries + lacteals for absorption |
| Microvilli | Microscopic folds on the surface of epithelial cells of the villi | Further increase surface area for rapid and efficient nutrient absorption |
Additional Adaptations of Villi:
- Thin walls: One cell thick for faster diffusion
- Rich blood supply: Quick transport of absorbed nutrients
- Lacteals: Absorb fatty acids and glycerol into the lymphatic system
Summary:
Villi and microvilli massively increase the internal surface area of the small intestine, enabling rapid and efficient absorption of digested food into the blood and lymph.
Structure of a Villus
What is a Villus?
A villus (plural: villi) is a tiny finger-like projection that lines the inner wall of the small intestine. Villi are specially adapted to increase the surface area for the absorption of nutrients from digested food.
Key Structural Features of a Villus:
| Part | Description | Function |
|---|---|---|
| Epithelial (surface) layer | A single layer of thin cells on the outer surface | Short diffusion path for nutrients to pass through easily |
| Microvilli | Microscopic folds on the epithelial cells | Further increase surface area for faster absorption |
| Capillary network | A dense supply of blood capillaries inside each villus | Absorbs glucose, amino acids, and other small soluble molecules |
| Lacteal (lymph vessel) | A small central lymphatic vessel in the villus | Absorbs fatty acids and glycerol into the lymph system |
| Goblet cells | Special cells in the lining that secrete mucus | Protects and lubricates the intestinal surface |
| Muscle fibers | Smooth muscle at the base of the villus | Helps maintain movement to improve contact with food |
Summary:
The villus is perfectly adapted for nutrient absorption with its large surface area, thin surface layer, and rich supply of blood vessels and lymphatic tissue.
Roles of Capillaries and Lacteals in Villi
Role of Capillaries in Villi
Structure: Each villus contains a network of blood capillaries near its surface.
Function: Absorb water-soluble nutrients like:
- Glucose (from carbohydrate digestion)
- Amino acids (from protein digestion)
- Some vitamins and minerals
These nutrients are carried into the bloodstream.
Blood transports them to the liver via the hepatic portal vein for processing.
Role of Lacteals in Villi
Structure: A lacteal is a tiny lymphatic vessel found in the center of each villus.
Function: Absorb fatty acids and glycerol (from fat digestion).
- These molecules enter the lymphatic system, not the blood at first.
- They are eventually transported to the bloodstream near the heart.
🔍 Summary Table
| Structure | Nutrients Absorbed | Transport System |
|---|---|---|
| Capillaries | Glucose, amino acids, minerals | Blood (circulatory system) |
| Lacteals | Fatty acids and glycerol | Lymph (lymphatic system) |
Key Point:
Capillaries and lacteals work together in each villus to absorb all types of nutrients from digested food and transport them to where the body can use them.