Human alimentary tract
Biology,  Human anatomy

Human Digestive Enzymes

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Human digestive enzymes are mainly synthesized in the salivary glands and in the pancreas As we’ve discussed, enzymes are made up of amino acids found in proteins so a ready supply of these building blocks is required to ensure there are optimal levels of digestive enzymes at all times.

Digestive enzymes are mixed in the saliva and pancreatic juices and are released into the mouth and small intestines, respectively, to support digestion of proteins, fats, and carbohydrates. Their synthesis and release occur via carefully orchestrated and tightly controlled hormone systems that are activated not just when food hits our taste buds but also by the sight, smell and sound of the food. This is why it’s important to consider not just what you eat but also how you eat to help support optimal digestion.

The pancreas plays a central role in the production of the majority of our digestive enzymes. It is a very important organ, as the endocrine Islet of Langerhans cells are responsible for the production of hormones such as insulin and glucagon, whilst the exocrine cells produce digestive enzymes and bicarbonate ions, which are released into the small intestine via the bile duct. This means within the biliary tract, the digestive enzymes and bicarbonate ions released in the pancreatic juices mix with bile. The bile and bicarbonate ions help regulate the pH within the small intestines to optimize conditions for digestive enzyme function. Bile is also essential for fat digestion

Classes of Human Salivary Digestive Enzymes

Saliva consists of alkaline juice of pH 7.5 with water, salts, digestive enzymes, and other glycoproteins, like lactoferrin to support iron absorption. Salivary enzymes start digestion in the mouth of certain food groups such as carbohydrates. Pancreatic digestive enzymes released into the small intestines do the majority of digestive work. Salivary digestive enzymes include:

Carbohydrases – break down dietary carbohydrates

  • Amylase – breaks down starch, glycogen and other carbohydrate polysaccharides into disaccharides
  • Maltase – breaks down maltose

Lipases – break down a minority of dietary fats

  • Lipase – hydrolyses a very small percentage of triglycerides into fatty acids and monoglycerides

Classes of Human Pancreatic Digestive Enzymes

Digestive enzymes are divided according to the groups of foods they breakdown. These include:

Lipases – break down the majority of dietary fats at optimum pH 8.0

  • Lipase – hydrolyses triglycerides into fatty acids and monoglycerides
  • Phospholipase – splits the fatty acids of phospholipids
  • Esterase – hydrolyses cholesterol esters

Proteases – break down proteins at optimum pH 7.9-9.7

  • Trypsin and chymotrypsin – breaks down protein polypeptides in dipeptides
  • Carboxypolypeptidase – splits peptides into individual amino acids

Carbohydrases – break down carbohydrates at optimum pH 6.7-7.2

  • Amylase – breaks down starch, glycogen and other carbohydrates polysaccharides into disaccharides

Classes of Digestive Enzymes

Lipases

Lipase breaks down lipids (fats and oils) into free fatty acids in the stomach and duodenum, ready for absorption across the gut barrier into the lacteal system. Pancreatic lipase is by far the most active of all the lipase enzymes through the pancreas also secretes phospholipases to break down phospholipids such as phosphatidylcholine. Digestion of many fats is a lengthy process requiring the presence of bile to help emulsify the fat so that it can bind to lipase enzymes to be broken down. Consequently, fat digestion is heavily dependent on optimal liver, gallbladder and pancreatic health. Phospholipid types of fats do not require emulsification by bile and are absorbed directly into the bloodstream rather than the lacteal system. This means phospholipids are more easily digested and absorbed across the gut barrier. Interestingly, Krill oil omega 3 essential fatty acids are in phospholipid form so have better bioavailability compared to fish oil and flaxseed oil omega 3 essential fatty acids, which are in triglyceride form.

Benefits of Lipases : Pancreatic lipase is the most important digestive enzyme, as it is not adequately produced outside of the pancreas. Poor digestion of triglycerides leads to excessive fat in the stools (steatorrhea) and impaired absorption of fat-soluble nutrients such as essential fatty acids and vitamins A, D, E, K., In fact, human studies have shown that supplementing with a microbial-derived lipase reduced fat in stools and improved fat digestion in patients with cystic fibrosis.

Proteases

This class of enzymes breaks down proteins in foods such as meats, dairy, eggs and plants into smaller fragments known as peptides. Dietary protein digestion begins in the stomach with the acid-stable protease pepsin, which is stable in acid, breaking down the large protein polypeptide chains. Proteases in the pancreatic juices and intestine then break the peptide bonds down further so that only small peptide units and individual amino acids remain ready for absorption and utilisation in the cells. Proteases that breakdown amino acids from the ends of the polypeptide protein chains are called exopeptidases, whereas those that cleave internal bonds within the peptide chain are termed endopeptidases. Proteases can function across a wide pH range as demonstrated by their action in the stomach and small intestines.

Benefits of Proteases: Proteolytic enzymes (i.e. proteases) taken with a meal can help in the breakdown of dietary protein. This enhances not only protein digestion but also may increase digestion of fibrous plant material by degrading proteins in plant cells walls, allowing for increased exposure to fibrolytic enzymes found in plants and some types of microbe.8 Proteases also help break down protein chains in foods that may trigger allergies in sensitive individuals. To support digestion, protease supplements should be taken with food. When taken between meals then proteases can be absorbed through the intestinal barrier and are capable of modulating a number of biochemical reactions throughout the body including reducing inflammatory.

Carbohydrases

These enzymes facilitate the breakdown of dietary carbohydrates such as starches, fibres and sugar. Carbohydrate digestion begins in the mouth with salivary amylase breaking down starch. The process slows down in the acidic conditions of the stomach but resumes again in the optimal pH levels of the duodenum where carbohydrases in the pancreatic juice break down the smaller chains of sugars (i.e. poly and
disaccharide chains) into their corresponding sugar units (i.e. monosaccharides) such as glucose. Many plant fibres are indigestible, as we do not possess specific digestive enzymes to break them down. There are many other different types of plant and microbe digestive enzymes that we will discuss later on in this newsletter.

Benefits of Carbohydrases

These enzymes facilitate the breakdown of Digestion of carbohydrates is crucial for us to absorb sugars and starches. Certain digested carbohydrates also serve as sources of food for the growth of beneficial gut bacteria, which act to support our health in many ways including production of certain vitamins, regulation of immune system activity and further digestion and absorption of nutrients. Incomplete digestion of sugars and starches from the diet can lead to fermentation by gut bacteria. This, in turn, may contribute to many symptoms including Irritable Bowel Syndrome (IBS), diarrhoea, bloating and flatulence so optimal levels of carbohydrases found in saliva and pancreatic juices are essential to health. However we do not synthesise digestive enzymes for many of our dietary carbohydrates, which is why to plant, and microbial carbohydrases are so important.

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