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"Digestion and absorption of carbohydrate, Lecture notes of Zoology

Carbohydrate digestion transforms complex polysaccharides and disaccharides into absorbable monosaccharides—glucose, fructose, and galactose. This process begins in the mouth with salivary amylase breaking down starch into smaller chains and halts in the acidic stomach environment. In the small intestine, pancreatic amylase further hydrolyzes starch into oligosaccharides and disaccharides, while brush-border enzymes (maltase, sucrase, lactase, isomaltase) complete digestion into monosaccharides. Glucose and galactose enter enterocytes via secondary active transport (SGLT1), fructose via facilitated diffusion (GLUT5), and all three exit to the bloodstream through GLUT2 before delivery to the liver for metabolism or storage

Typology: Lecture notes

2024/2025

Available from 05/08/2025

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The Incredible Carbohydrate Adventure: From
Carbohydrates, commonly referred to as
"carbs," are one of the primary forms of food
They exist in many different forms, ranging
from the sugar found in your fruit to the starch
What Types of Carbs Are We Consuming?
Let's learn about our players before we
Monosaccharides (Single Sugars):
They
Glucose (your body's chief fuel!),
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The Incredible Carbohydrate Adventure: From Carbohydrates, commonly referred to as "carbs," are one of the primary forms of food They exist in many different forms, ranging from the sugar found in your fruit to the starch

What Types of Carbs Are We Consuming?

Let's learn about our players before we

Monosaccharides (Single Sugars): They

Example: Glucose (your body's chief fuel!),

These are the only ones your body can take up

Disaccharides (Double Sugars): Two single

Example: Sucrose (table sugar = glucose +

These require a single "snip" from an enzyme

Polysaccharides (Many Sugars): Very long

chains of numerous single sugars attached

Example: Starch (found in plants such as

potatoes, rice, wheat), Glycogen (the way animals, including us, store glucose), These need to be broken down extensively by enzymes. Starch, for example, has two kinds

Chemical Digestion: Your salivary glands

secrete saliva, which has a vital enzyme called salivary amylase. How it works: Salivary amylase begins breaking up long chains of starch (polysaccharides) into short chains such as

Example: Chewing a chunk of plain bread for

an extended period of time will cause it to

Step 2:

like ball known as a bolus) goes down your

What does (or doesn't) happen: The

stomach is highly acidic because of

This acid is perfect for breaking down proteins, but it prevents salivary amylase from Therefore, carbohydrate digestion effectively

Step 3:

This is where most of the carb digestion and When the partially digested food (now referred to as chyme) reaches the small intestine, two The pancreas secretes a potent enzyme called pancreatic amylase into the small

What it does: Pancreatic amylase continues

It hydrolyzes any remaining starch and dextrins into shorter oligosaccharides (short

Special one! Some individuals lack sufficient lactase. When they drink milk, the lactose is not It passes to the large intestine, where bacteria ferment it, producing gas, bloating, This is a textbook example of what occurs Now we have our basic sugars (glucose, fructose, galactose), which are small enough to be absorbed from the small intestine into These are absorbed into the cells of the intestine through secondary active transport

Imagine it as a revolving door that requires both a sodium ion and a glucose/galactose molecule to rotate and admit them into the It takes advantage of the energy of a sodium gradient (low sodium within the cell, high without) that is kept up by another pump (the This is "active" because it depends on the Fructose is taken in through facilitated diffusion with another transporter protein It is similar to a special door just for fructose. It doesn't require energy directly, but it When they are inside the intestinal cell, glucose, galactose, and fructose all leave to

Fiber also provides bulk to stool, promoting From the starchy potato to the glucose fueling your brain, carbohydrates are subject to a sophisticated and effective process of breakdown and uptake, whereby your body is