digestive system

What is starch?

Starch is a complex carbohydrate (polysaccharide) composed of many glucose units linked together, serving as a primary energy source in plant-based foods for humans.

Where does the digestion of starch begin and what enzyme is involved?

Starch digestion begins in the mouth with the enzyme salivary amylase (ptyalin), which hydrolyses starch into smaller polysaccharides and disaccharides (e.g., maltose).

What happens to starch and salivary amylase in the stomach?

In the acidic environment of the stomach, salivary amylase is denatured due to the low pH, thus no significant starch digestion occurs here.

Where does the majority of starch digestion take place and what enzyme is essential?

The majority of starch digestion occurs in the small intestine. Here, pancreatic amylase (secreted from the pancreas into the duodenum) further breaks down starch and dextrins into maltose and other disaccharides.

What enzymes are responsible for the final breakdown of disaccharides (like maltose) in the small intestine, and where are they located?

Enzymes located in the brush border of the small intestine are responsible for the final breakdown. For starch digestion, maltase hydrolyses maltose into two glucose molecules.

What is the final absorbable product of starch digestion?

The final absorbable product of starch digestion is glucose, which is then transported across the intestinal wall into the bloodstream.

What are proteins?

Proteins are complex macromolecules composed of amino acid chains linked by peptide bonds, essential for various structural and functional roles in the body, and serving as a dietary source of amino acids.

Where does the digestion of proteins begin and what enzyme is involved?

Protein digestion begins in the stomach. The enzyme pepsin, secreted as inactive pepsinogen by chief cells and activated by hydrochloric acid (HCl), initiates protein breakdown into smaller polypeptides.

What role does hydrochloric acid (HCl) play in protein digestion in the stomach?

Hydrochloric acid (HCl), secreted by parietal cells in the stomach, denatures proteins, unfolding their complex 3D structure and making them more accessible to pepsin. It also activates pepsinogen to pepsin.

Where does the majority of protein digestion take place after the stomach?

The majority of protein digestion occurs in the small intestine.

What pancreatic enzymes are involved in protein digestion in the small intestine?

The pancreas secretes several inactive proteases (zymogens) into the duodenum, including trypsinogen, chymotrypsinogen, and procarboxypeptidases. These are activated by enteropeptidase (formerly enterokinase) and trypsin to become trypsin, chymotrypsin, and carboxypeptidases, respectively, which further break down polypeptides into smaller peptides and amino acids.

What enzymes are responsible for the final breakdown of peptides in the small intestine, and where are they located?

Enzymes located in the brush border of the small intestine are responsible for the final breakdown. These include aminopeptidases (cleave amino acids from the amino end of peptides) and dipeptidases/tripeptidases (hydrolyse dipeptides and tripeptides into single amino acids).

What are the final absorbable products of protein digestion?

The final absorbable products of protein digestion are amino acids, dipeptides, and tripeptides, which are then transported across the intestinal wall into the bloodstream or further broken down into amino acids within enterocytes before entering the bloodstream.