Intestinal absorption of nutrients Flashcards
Outline the digestion of protein, carbohydrates and fat from mouth to colon
Mouth: Digestion begins in the mouth with the mechanical and chemical breakdown of food. Chewing breaks food into smaller pieces, and the enzyme amylase begins the breakdown of carbohydrates.
Esophagus: Food is transported to the stomach through the esophagus.
Stomach: In the stomach, food is mixed with gastric juices, which contain hydrochloric acid and pepsin. Pepsin breaks down proteins into smaller polypeptides.
Small intestine: The majority of nutrient absorption occurs in the small intestine, where the pancreas secretes enzymes that further break down food. The pancreatic enzyme trypsin breaks down proteins into smaller peptides and amino acids. Carbohydrates are broken down into glucose molecules by pancreatic amylase, and fats are broken down into fatty acids and glycerol by pancreatic lipase. The small intestine also secretes enzymes such as maltase, lactase, and sucrase to break down specific sugars.
Liver: The liver produces bile, which is stored in the gallbladder and released into the small intestine to help break down fats.
Large intestine: The large intestine absorbs water and electrolytes from the remaining indigestible food, and bacteria in the large intestine help to break down any remaining nutrients. The waste products are eliminated as feces.
Describe mechanisms involved in intestinal absorption of carbohydrates,proteins, fats: uptake sugars, amino acids, dipeptides and fats
Carbohydrate absorption: Carbohydrates are broken down into simple sugars such as glucose, fructose, and galactose in the small intestine. These sugars are then absorbed into the bloodstream through the intestinal lining via two main mechanisms:
Active transport: Glucose and galactose are transported into the intestinal cells against their concentration gradient using sodium-dependent glucose transporters (SGLT). This process requires energy and relies on the concentration gradient of sodium ions.
Facilitated diffusion: Fructose is transported into the intestinal cells down its concentration gradient using glucose transporter proteins (GLUT). This process does not require energy.
Once inside the intestinal cells, the simple sugars are transported across the basolateral membrane of the cells and into the bloodstream.
Protein absorption: Proteins are broken down into smaller peptides and amino acids in the small intestine. These molecules are then absorbed into the bloodstream through the intestinal lining via two main mechanisms:
Active transport: Some amino acids are transported into the intestinal cells against their concentration gradient using sodium-dependent amino acid transporters (SAA). This process requires energy and relies on the concentration gradient of sodium ions.
Facilitated diffusion: Other amino acids and small peptides are transported into the intestinal cells down their concentration gradient using specific transporter proteins. This process does not require energy.
Fat absorption: Fats are broken down into fatty acids and glycerol in the small intestine. These molecules are then absorbed into the bloodstream through the intestinal lining via a different mechanism:
Micelle formation: Fatty acids and glycerol are insoluble in water and must be transported across the intestinal lining with the help of bile salts and other emulsifiers. These substances form micelles, which are small droplets of fat surrounded by a layer of emulsifiers that are soluble in water. The micelles can then diffuse through the intestinal lining and into the intestinal cells.
Once inside the intestinal cells, fatty acids and glycerol are reassembled into triglycerides and packaged into chylomicrons. These chylomicrons are then transported out of the intestinal cells and into the lymphatic system, which eventually empties into the bloodstream.
explain the role of pancreas and liver in the digestion of fat
Pancreas: The pancreas secretes pancreatic lipase, which is an enzyme that breaks down triglycerides (fats) into fatty acids and glycerol. Pancreatic lipase is secreted in an inactive form called pro-lipase and is activated by a protein called colipase, which is secreted by the pancreas as well. Colipase binds to the surface of fat droplets and exposes the triglycerides to pancreatic lipase for breakdown. Additionally, the pancreas secretes bicarbonate ions, which neutralize the acidic chyme (partially digested food) from the stomach and create a slightly alkaline environment in the small intestine. This alkaline environment is important for the optimal functioning of pancreatic lipase.
Liver: The liver produces bile, which is a greenish-yellow fluid that is stored in the gallbladder and released into the small intestine when fat is present. Bile contains bile salts, which emulsify fat and break it down into smaller droplets, increasing the surface area available for pancreatic lipase to act upon. Emulsification is important because fats are hydrophobic (water-repelling) and tend to clump together, making it difficult for enzymes to access and break them down. Bile also helps neutralize the acidic chyme from the stomach, which creates a more favorable environment for the action of pancreatic lipase.
explain the possible clinical consequences of malabsorption of
nutrients
Nutritional deficiencies: Malabsorption can lead to deficiencies in essential nutrients such as vitamins, minerals, carbohydrates, proteins, and fats. These deficiencies can cause a range of symptoms, such as fatigue, weakness, anemia, osteoporosis, delayed growth and development in children, and impaired immune function.
Gastrointestinal symptoms: Malabsorption can cause a range of gastrointestinal symptoms, such as abdominal pain, bloating, diarrhea, constipation, and flatulence. These symptoms can be due to incomplete digestion and absorption of nutrients, leading to fermentation of undigested food in the gut.
Weight loss: Malabsorption can cause weight loss, as the body is unable to absorb enough calories and nutrients to meet its needs. This can lead to malnutrition and a weakened immune system, making the body more vulnerable to infections.
Malabsorption syndromes: Malabsorption can be caused by a variety of medical conditions such as celiac disease, Crohn’s disease, ulcerative colitis, lactose intolerance, pancreatic insufficiency, and bile acid malabsorption. These conditions can cause chronic malabsorption, leading to long-term health problems.
Increased risk of other diseases: Malabsorption can increase the risk of developing other diseases, such as osteoporosis, anemia, and certain cancers. For example, chronic malabsorption of calcium and vitamin D can lead to osteoporosis and an increased risk of bone fractures.
