What is absorption in the context of human nutrition?

In human nutrition, absorption refers to the process by which the end products of digestion are taken up by the cells lining the small intestine and transported into the bloodstream. This allows nutrients to be distributed throughout the body to be used for energy, growth, and repair. Absorption is a crucial step in the digestive process, ensuring that the body receives the necessary nutrients from the food we consume.

How does the structure of the small intestine facilitate absorption?

The small intestine is uniquely structured to maximize absorption. It has a large surface area due to the presence of villi and microvilli, which are tiny, finger-like projections that line the intestinal walls. These structures increase the surface area available for absorption, allowing for more efficient uptake of nutrients. Additionally, the thin walls of the villi and the rich supply of blood vessels help in the rapid transfer of nutrients into the bloodstream.

What role do villi play in the absorption process?

Villi are small, finger-like projections that line the inner surface of the small intestine. They play a critical role in the absorption process by increasing the surface area available for nutrient uptake. Each villus contains a network of capillaries and a lymph vessel called a lacteal, which help transport absorbed nutrients into the bloodstream and lymphatic system. This structure ensures that nutrients such as amino acids, glucose, and fatty acids are efficiently absorbed and distributed throughout the body.

What nutrients are absorbed in the small intestine?

The small intestine is responsible for the absorption of most nutrients from digested food. This includes carbohydrates (as glucose), proteins (as amino acids), and fats (as fatty acids and glycerol). Additionally, vitamins, minerals, and water are also absorbed in the small intestine. The efficient absorption of these nutrients is essential for maintaining energy levels, supporting growth, and ensuring overall health.

How does the absorption of fats differ from that of carbohydrates and proteins?

The absorption of fats differs from carbohydrates and proteins due to their solubility. Fats are not water-soluble, so they are first emulsified by bile salts in the small intestine, forming micelles. These micelles facilitate the transport of fatty acids and monoglycerides to the intestinal lining, where they are absorbed. Inside the intestinal cells, they are reassembled into triglycerides and packaged into chylomicrons, which enter the lymphatic system before reaching the bloodstream. In contrast, carbohydrates and proteins are directly absorbed into the bloodstream as glucose and amino acids, respectively.

Why is "Saying ALL water is absorbed in the LARGE intestine." a common mistake in Absorption?

Why it happens: The large intestine's main role IS water absorption. How to avoid it: MOST water is absorbed in the SMALL intestine. The large intestine absorbs the REMAINING water from waste material (and adds firmness to faeces).

Why is "Saying fats are absorbed straight into the BLOOD." a common mistake in Absorption?

Why it happens: Sugars and amino acids do, so fats seem similar. How to avoid it: Fats (fatty acids + glycerol) enter the LACTEAL (lymph) first. Lymph eventually drains into the blood, but the initial path is different.

Why is "Saying absorbed glucose goes straight to body cells." a common mistake in Absorption?

Why it happens: Cells need glucose for respiration. How to avoid it: First stop: the LIVER (via hepatic portal vein). The liver regulates blood glucose before sending it on. Same for amino acids — liver deaminates excess.

Human NutritionCambridge IGCSE Biology (0610)

Absorption

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Absorption — Cambridge IGCSE 0610 Biology Extended (2026)

After digestion, small soluble nutrients enter the blood (and lymph) via the small intestine. The liver gets the first look at them.

What you’ll learn

Mapped to the Cambridge IGCSE 0610 syllabus (2026-2028).

7.5 — Identify the small intestine as the site of absorption of digested food.
7.5 — Identify the large intestine as the site of water absorption.
7.5 — Describe villi structure and how it adapts the small intestine for absorption.
7.5 — Outline the role of the liver in assimilation.

Where absorption happens

Small intestine = nutrient absorption. Large intestine = water absorption.

Different parts of the gut do different jobs.

Small intestine (~6 metres long).

The MAIN site of absorption.
Glucose, amino acids, fatty acids + glycerol, vitamins, minerals, MOST water → all absorbed here.
Long length + large folded surface area + millions of villi = ideal for absorption.

Large intestine (~1.5 m).

Receives indigestible material + remaining water.
Absorbs the REMAINING water from gut contents.
Bacteria here make some vitamin K.
Produces FAECES, sent on for egestion via the rectum and anus.

Worked qualitative. Why does diarrhoea cause dehydration?

Diarrhoea = food moves through the gut too fast.
The large intestine doesn't have time to absorb water → watery faeces.
Body loses water and salts → dehydration.
Treatment: oral rehydration salts (water + glucose + electrolytes).

Cambridge tip. "Absorption" without specifying which gut loses you marks. Always say "small intestine" for nutrients and "large intestine" for the last of the water.

Small intestine: nutrient absorption.
Large intestine: remaining water.
Diarrhoea bypasses water absorption → dehydration.

How the small intestine is adapted

Long + folded + villi + microvilli = enormous surface area.

Adaptations of the SMALL INTESTINE:

1. Length. ~6 m. More length = more time for digestion AND more surface area.

2. Internal folds. The wall folds inward (circular folds) — multiplies surface area.

3. Villi. Finger-like projections covering the inside surface — millions of them. Each villus is ~1 mm long. They multiply surface area MASSIVELY.

4. Microvilli. Tiny projections on EACH epithelial cell of every villus. Multiply surface area AGAIN.

Total surface area: ~250 m² — about the size of a tennis court.

Adaptations of a single VILLUS:

Feature	Why
Long, finger-shaped	Increases surface area.
Thin epithelium (1 cell thick)	Short DIFFUSION distance.
Capillary network inside	Carries absorbed nutrients away — keeps a steep gradient.
Lacteal in centre	Absorbs products of fat digestion (lymph route).
Microvilli on cells	Even more surface area + active transport.

How nutrients enter:

Glucose, amino acids: into blood capillaries by ACTIVE TRANSPORT (against the gradient) and facilitated diffusion.
Fatty acids + glycerol: into the LACTEAL by absorption through the cell.
Water + minerals: by osmosis / diffusion / active transport.

Worked qualitative. Why is the wall of the small intestine "one cell thick"?

A short diffusion path means nutrients reach the blood quickly.
Thicker walls would slow absorption.

Cambridge tip. When asked "how is the small intestine adapted", give 4 features each PAIRED with a reason. "Long" alone = 0; "long, providing a large surface area" = 1.

Long + folded + villi + microvilli.
Total surface ~250 m².
Thin wall: short diffusion path.
Capillary + lacteal: blood + lymph routes.

The liver — first stop after absorption

Hepatic portal vein delivers nutrient-rich blood to the liver. Liver controls glucose, deaminates amino acids, detoxifies, makes bile.

The route.

Blood capillaries in villi → small veins → HEPATIC PORTAL VEIN → LIVER → hepatic vein → vena cava → rest of body.

So the liver gets FIRST LOOK at everything you absorb.

Roles of the liver in assimilation:

1. Glucose regulation.

Excess glucose → stored as GLYCOGEN.
When blood glucose drops → glycogen broken back to glucose.
Hormones insulin and glucagon control this (see Coordination topic).

2. Amino acid management.

Body cells take up the amino acids they need to build proteins.
EXCESS amino acids can't be stored.
Liver REMOVES the amine group (-NH₂) — DEAMINATION.
Amine group → ammonia (toxic) → converted to UREA (less toxic).
Urea sent to KIDNEYS for excretion.
The remaining carbohydrate part can be respired or stored.

3. Detoxification.

Alcohol, drugs, food preservatives, toxins from gut bacteria — all processed here.
Heavy alcohol use damages liver cells (cirrhosis).

4. Bile production.

Liver makes BILE from cholesterol and waste pigments (bilirubin from old red blood cells).
Bile stored in gall bladder, used in fat digestion.

5. Iron storage.

Iron from worn-out red blood cells (and from food) stored in the liver.
Released when needed for new haemoglobin.

6. Stores fat-soluble vitamins (A, D).

Worked qualitative. A patient drinks heavily for years and has yellow skin (jaundice). What's happening?

Heavy drinking damages liver cells (alcoholic hepatitis / cirrhosis).
Damaged liver can't process bilirubin from worn-out red blood cells.
Bilirubin builds up in blood → yellow tint to skin and eyes (jaundice).

Cambridge tip. When asked about the role of the liver, list AT LEAST THREE: glucose, amino acids, bile. Forgetting one means losing marks.

Hepatic portal vein → liver first.
Glucose: stored as glycogen.
Amino acids: deaminated, urea formed.
Detoxifies, makes bile, stores iron + vitamins.

How it’s examined

Absorption appears every Paper 4 (5-7 marks: villus structure, role of liver, deamination). Examiner reports flag students saying 'large intestine absorbs nutrients', forgetting the lacteal for fats, and missing the hepatic portal vein.

Sources: Cambridge IGCSE Biology 0610 syllabus 2026-2028 (7.5); 0610/42 May/Jun 2024 — Q6 (absorption); 0610 Examiner Reports 2022-2024. Last reviewed 2026-05-07.

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Step-by-step worked examples — Absorption

Step-by-step solutions to past-paper-style questions on absorption, written exactly the way a tutor would explain them at the board.

1Villi adaptations for absorption
Core• villi
Question
Describe FOUR adaptations of a VILLUS that help absorption.
Step-by-step solution
1. Step 1
  Long, finger-like shape: greatly increases SURFACE AREA. (Plus tiny MICROVILLI on the cells multiply this even further.)
2. Step 2
  Thin epithelium (one cell thick): short DIFFUSION distance for nutrients to enter the blood.
3. Step 3
  Rich blood supply (capillary network): maintains a steep CONCENTRATION GRADIENT (absorbed nutrients are quickly carried away).
4. Step 4
  LACTEAL (lymph capillary inside): absorbs the products of fat digestion (fatty acids + glycerol).
Answer
Villi are long, thin-walled, well supplied with blood and lymph (lacteal). Microvilli further increase surface area.
Examiner tip
Cambridge marks each adaptation paired with its REASON. List 4 features and 4 reasons.
2Where in the gut is each absorbed?
Core• absorption sites
Question
State where each is absorbed: glucose, amino acids, fatty acids + glycerol, water.
Step-by-step solution
1. Step 1
  Glucose — small intestine, into BLOOD CAPILLARIES.
2. Step 2
  Amino acids — small intestine, into BLOOD CAPILLARIES.
3. Step 3
  Fatty acids + glycerol — small intestine, into the LACTEAL (lymph) — eventually drains into blood.
4. Step 4
  Water — most in the SMALL intestine; rest in the LARGE INTESTINE (where faeces dry out).
Answer
Sugars + amino acids: blood (SI). Fats: lacteal/lymph (SI). Water: SI + LI.
3The role of the liver after absorption
Extended• Adapted from 0610/42 May/Jun 2024 Q6• liver, assimilation
Question
Once nutrients are absorbed, why are they sent to the LIVER first? Give THREE roles of the liver.
Step-by-step solution
1. Step 1
  Absorbed nutrients in blood go via the HEPATIC PORTAL VEIN to the LIVER first.
2. Step 2
  Role 1: regulates blood GLUCOSE — excess glucose is stored as GLYCOGEN; glycogen broken back to glucose when needed.
3. Step 3
  Role 2: deals with amino acids — keeps what the body needs; DEAMINATES the rest (removes the amine group → forms UREA, which the kidneys excrete).
4. Step 4
  Role 3: processes other absorbed substances — alcohol, drugs, toxins (detoxification); makes BILE; stores iron and vitamins.
Answer
Hepatic portal vein → liver. Liver controls glucose (glycogen storage), deaminates excess amino acids (urea), detoxifies, makes bile.

Key Definitions and Keywords — Absorption

Definitions to memorise and the exact keywords mark schemes credit for absorption answers — sharpened from recent examiner reports for the 2026 0610 sitting.

Villus (plural: villi)
Examiner keyword
Finger-like projection on the inner wall of the small intestine. Increases surface area for absorption.
Microvilli
Tiny projections on the surface of villus epithelial cells. Further increase surface area.
Lacteal
Examiner keyword
Lymph capillary inside each villus. Absorbs the products of fat digestion (fatty acids + glycerol).
Hepatic portal vein
Examiner keyword
Vein carrying nutrient-rich blood from the small intestine directly to the liver.
Deamination
Examiner keyword
Removal of the amine group (-NH₂) from an excess amino acid. Done in the liver. Produces UREA, excreted via the kidneys.

Common Mistakes and Misconceptions — Absorption

The traps other students keep falling into on absorption questions — taken from recent Cambridge IGCSE 0610 examiner reports and mark schemes — and how to avoid them.

✕Saying ALL water is absorbed in the LARGE intestine.
Why it happens
The large intestine's main role IS water absorption.
How to avoid it
MOST water is absorbed in the SMALL intestine. The large intestine absorbs the REMAINING water from waste material (and adds firmness to faeces).
✕Saying fats are absorbed straight into the BLOOD.
Why it happens
Sugars and amino acids do, so fats seem similar.
How to avoid it
Fats (fatty acids + glycerol) enter the LACTEAL (lymph) first. Lymph eventually drains into the blood, but the initial path is different.
✕Saying absorbed glucose goes straight to body cells.
Why it happens
Cells need glucose for respiration.
How to avoid it
First stop: the LIVER (via hepatic portal vein). The liver regulates blood glucose before sending it on. Same for amino acids — liver deaminates excess.

Practice questions

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Past paper style quiz

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Absorption — frequently asked questions

The things students keep getting wrong in this sub-topic, answered.

Absorption

Short Study Notes in the form of Slides

Detailed Study Notes

What you’ll learn

How it’s examined

1Villi adaptations for absorption

2Where in the gut is each absorbed?

3The role of the liver after absorption

Villus (plural: villi)

Microvilli

Lacteal

Hepatic portal vein

Deamination

✕Saying ALL water is absorbed in the LARGE intestine.

✕Saying fats are absorbed straight into the BLOOD.

✕Saying absorbed glucose goes straight to body cells.

Practice questions

Past paper style quiz

Assess your understanding

Video lesson

Absorption — frequently asked questions