3.3 Absorption and assimilation

Absorption

A process by which the products of digestion move from the digestive system into the bloodstream, so that they can be transported around the body.

Where absorption mainly takes place

Small intestine

What the small intestine is specially adapted to

To absorb as many nutrients as possible from digested food.

Adaptations of the small intestine

• Long length

• Highly folded inner lining

• Containing villi

• Containing microvilli

• Thin villus walls

How the long length of the small intestine helps it adapt to its function

It gives a large surface area for absorption to occur.

How the highly folded inner lining of the small intestine helps it adapt to its function

It further increases its surface area to absorb nutrients.

How the small intestine walls containing villi, help it adapt to its function

Each villus sticks out from the lining of the intestine and greatly increases its surface area for absorption.

How the microvilli help the small intestine adapt to its function

These tiny structures increase the surface area even further, allowing nutrients to move easily into the blood or lymphatic system.

How the thin villus walls of the small intestine help it adapt to its function

It allows nutrients to move easily into the blood or lymphatic system.

Villi

Millions of tiny projections that contain a network of blood capillaries and a vessel called lacteal.

Location of the villi

They are located in the walls of the small intestine.

Villus

The singular form of villi

Microvilli

Smaller microscopic projections on the surface of the villi.

Microvillus

The singular form of microvilli

How the blood capillaries help the villus with absorption

They absorb nutrients that dissolve easily in water like glucose and amino acids.

How the blood capillaries absorb nutrients

The nutrients diffuse from the inside of the small intestine where their concentration is high, into the blood capillaries where their concentration is low.

What nutrients do blood capillaries absorb

Nutrients that dissolve easily in water

How the lacteals help the villus with absorption

They absorb nutrients that do not dissolve easily in water like fatty acids and glycerol.

How the lacteals absorb nutrients

The nutrients enter the lacteals and are transported through the lymphatic system before entering the bloodstream.

The system lacteals are part of

The lymphatic system

What nutrients do lacteals absorb

Nutrients that do not dissolve easily in water

Blood plasma

It carries dissolved nutrients to body cells where they can be used.

Does the blood plasma transport absorbed nutrients around the body

Yes

Tissue fluid

The liquid that surrounds the cells.

How the tissue fluid is formed

• The blood reaches the body tissues

• The plasma which makes 55% of the blood, then moves out of the capillaries

• It moves out through small gaps in the capillary walls and becomes tissue fluid

Functions of the tissue fluid

• It allows nutrients such as glucose, amino acids and fats to diffuse from the fluid into the cells

• It allows cellular waste products (like carbon dioxide and urea) to diffuse out of the cells into the fluid and return to the blood

Assimilation

A process by which absorbed nutrients are used by body cells.

What the cells use absorbed nutrients for

1. Energy

2. Growth and repair

Importance of assimilation

It allows the body to use the nutrients obtained from food to maintain normal body functions.

The nutrients used by the body

1. Glucose

2. Amino acids

3. Fats

4. Vitamins

How glucose is used by the body

It is mainly used during cellular respiration to release energy

What happens when there is more glucose than the body needs

• It can be converted into a storage molecule called glycogen

• Glycogen is stored in the liver and muscles and can be broken down into glucose when more energy is required

How amino acids are used by the body

They are the building blocks of proteins, which are needed for many important functions;

1. To make enzymes which speed up chemical reactions in the body

2. To make hormones which regulate body processes

3. For growth and repair of body tissues

What fatty acids and glycerol are rebuilt into

Fats

How fats are used by the body

1. They can be stored in the body and used as an important energy reserve

2. They help insulate the body, protecting it from temperature changes

3. They help protect internal organs

4. They are important components of cell membranes

5. They are used to produce certain hormones

Vitamins

They are organic molecules that are needed by the body in small amounts to maintain good health

How vitamins are used by the body

1. Vitamin A helps maintain healthy skin, teeth and vision

2. Vitamin B supports metabolism and helps the nervous system function properly

3. Vitamin C helps keep teeth and gums healthy and supports the immune system

4. Vitamin D helps the body absorb calcium which is important for strong bones and teeth