Essentials of Digestion

An enzyme in saliva that helps digest fats, especially in infants.

The process of breaking down fats into smaller molecules for absorption.

An enzyme produced by the pancreas, essential for fat digestion.

An enzyme in the stomach that assists in fat digestion.

Liver-produced substance crucial for emulsification of fats.

Breaking down large fat globules into smaller droplets.

Stores bile produced in the liver, releasing it for fat digestion.

Physical breakdown of food, not involving enzymes.

In the small intestine, fats go through three main steps: 1. Emulsification by bile, breaking down large fat droplets into smaller ones. 2. Enzymatic digestion by pancreatic lipase, breaking down triglycerides into monoglycerides and fatty acids. 3. Absorption, where short- and medium-chain fatty acids and glycerol go directly into the bloodstream, while long-chain fatty acids and monoglycerides are packaged into chylomicrons for transport.

Chylomicrons are transport vehicles that carry digested fats (triglycerides), cholesterol, and fat-soluble vitamins from the small intestine to the bloodstream.

Short- and medium-chain fatty acids are small enough to be directly absorbed into the bloodstream from the intestinal cell, bypassing the chylomicron route.

Long-chain fatty acids are too big to directly enter the blood. They need to be packaged into chylomicrons along with monoglycerides, cholesterol, and fat-soluble vitamins.

Chylomicrons are large structures with a core of triglycerides and cholesterol surrounded by a membrane of phospholipids, proteins (apolipoproteins), and cholesterol.

Chylomicrons transport digested fats (triglycerides) from the intestines through the lymphatic system and into the bloodstream.

Short and medium-chain fatty acids are small enough to be absorbed directly into the bloodstream through capillaries in the intestinal wall.

Long-chain fatty acids are too large for direct absorption. They are packaged into chylomicrons and transported through the lymphatic system.

Chylomicrons are formed in the intestinal epithelial cells, enter the lacteals (lymphatic capillaries), travel through the lymphatic system, and finally enter the bloodstream via the jugular vein.

The stomach is divided into three major zones: the cardiac zone, the body, and the pyloric zone, each with its specific functions.

The pyloric zone includes the antrum, pyloric canal, and pyloric sphincter, each playing a role in controlling the passage of food into the small intestine.

Chyme is the semi-liquid mixture of partially digested food that exits the stomach and enters the small intestine.

Parietal cells secrete hydrochloric acid (HCl) for food breakdown, kill bacteria, and intrinsic factor for Vitamin B12 absorption.

GIP is a hormone released in the small intestine that inhibits HCl production by parietal cells in the stomach, slowing down digestion.

Factors triggering stomach secretions include neurogenic stimuli (e.g., vagus nerve), stomach distension, and secretagogues (substances like gastrin).

Chief cells are specialized cells in the stomach that produce pepsinogen, an inactive form of the digestive enzyme pepsin.

Pepsinogen is converted into active pepsin by the acidic environment of the stomach, specifically by HCl.

Gastrin is a hormone produced by G-cells in the stomach that stimulates the release of histamine from ECL cells.

Histamine, released by ECL cells, acts on parietal cells to increase the production of HCl in the stomach.

The duodenum is the first part of the small intestine where the final stage of chemical digestion occurs. It receives enzymes from the pancreas and bile from the gallbladder.

The jejunum is a major site of nutrient absorption in the small intestine, absorbing carbohydrates, proteins, fats, minerals, and vitamins.

The ileum is the last part of the small intestine that primarily absorbs bile acids, fluids, and vitamin B12.

The breakdown of glycogen (a stored form of glucose) into glucose. This process occurs primarily in the liver and muscles, releasing glucose into the bloodstream for energy.

Metabolic processes that involve breaking down large molecules into smaller ones, releasing energy in the process. Often involve oxidation.

A hormone produced by the beta cells of the pancreas that helps regulate blood glucose levels by promoting the uptake and storage of glucose by cells.

A hormone produced by the alpha cells of the pancreas that raises blood glucose levels by stimulating glycogenolysis in the liver.

Metabolic processes that break down large molecules into smaller ones, releasing energy. Example: Glycogenolysis.

Digestion involves 2 major parts: mechanical digestion, the physical breakdown of food, and chemical digestion, the breakdown of food molecules by enzymes.

A hormone secreted by the stomach that stimulates the release of gastric juice.

Trypsin, chymotrypsin, and elastase are the key pancreatic enzymes involved in protein breakdown.

Lactase is a brush border enzyme that breaks down lactose, a sugar found in milk.

Sucrase, maltase, and lactase are the key brush border enzymes involved in carbohydrate breakdown.

Pancreatic enzymes, like trypsin and chymotrypsin, break down proteins into smaller peptides and amino acids.

Bile, produced by the liver and stored in the gallbladder, emulsifies fats, breaking large fat globules into smaller droplets, allowing for better digestion by lipases.

Lipase enzymes break down fats (triglycerides) into smaller molecules like fatty acids and glycerol.

Lactose intolerance arises due to a deficiency or absence of lactase, an enzyme responsible for digesting lactose in milk.

In the small intestine, brush border enzymes, like sucrase and maltase, break down carbohydrates (starch) into simple sugars like glucose and fructose.

Endopeptidases break peptide bonds within the protein chain, while exopeptidases cleave amino acids from the ends of the chain.

Protein digestion starts in the stomach with the help of pepsin, which breaks down proteins into smaller polypeptides.

Nucleic acids are digested by enzymes like ribonuclease (RNAse) and deoxyribonuclease (DNAse), breaking down nucleic acids into nucleotides.

Metabolism involves three main stages: anabolism (building up complex molecules), catabolism (breaking down complex molecules), and energy production.

Undigested lactose in lactose intolerance ferments in the intestines by bacteria, producing acids and gas, leading to bloating, diarrhea, and intestinal discomfort.