Lipid Metabolism PDF

Lipid Digestion and Absorption Learning outcomes: 1. Elaborate the digestion and absorption of fats. 2.Explain the function of Lipid Metabolism. 3.Value the importance of the digestion and absorption of Lipids inside the human body.  Introduction Fats within the body are ingested as...

Lipid Digestion and Absorption Learning outcomes: 1. Elaborate the digestion and absorption of fats. 2.Explain the function of Lipid Metabolism. 3.Value the importance of the digestion and absorption of Lipids inside the human body.  Introduction Fats within the body are ingested as food or synthesized by adipocytes (fat cells) or hepatocytes (liver cells) from carbohydrate precursors.  Introduction Lipid metabolism entails the oxidation of fatty acids to either generate energy or synthesize new lipids from smaller constituent molecules.  Introduction Lipid metabolism is associated with carbohydrate metabolism, as products of glucose can be converted into lipids. Lipid Digestion  Lipid Digestion in mouth The major dietary lipids are triacylglycerol, cholesterol and phospholipids. Filipino consumes average of 56.56 grams per day.  Lipid Digestion in mouth Chewing mechanically breaks food into smaller particles and mixes them with saliva. An enzyme called lingual lipase is produced by cells on the tongue Lipid Digestion in mouth  Lipid Digestion in Stomach Up to 30% digestion of triglycerides occurs in stomach. Two lipases play only a minor role in fat digestion  Lipid Digestion in Stomach The lingual lipase from the mouth enters stomach along with the food. It has an optimum pH of 2.5-5). It acts on short chain triglycerides (SCT). Lipid Digestion in Stomach  Lipid Digestion in Stomach Cells in the stomach produce another lipase, called gastric lipase. Gastric lipase is acid stable, with an optimum pH around 5.4. Lipid Digestion in Stomach  Lipid Digestion in Small intestine Most of the dietary lipids are undigested and clustered in large droplets. Lipid Digestion in Small intestine  Lipid Digestion in Small intestine Bile is made in the liver and stored in the gallbladder, is released into the duodenum. Emulsification makes lipids more accessible to digestive enzymes by increasing the surface area for them to act.  Lipid Digestion in Small intestine The pancreas secretes pancreatic lipases into the small intestine to enzymatically digest triglycerides. Triglycerides are broken down to fatty acids, monoglycerides (glycerol backbone with one fatty acid still attached), and some free glycerol. Lipid Digestion in Small intestine  lipid absorption in small intestine Products of fat digestion (fatty acids, monoglycerides, glycerol, cholesterol, and fat-soluble vitamins) need to enter into the circulation so that they can be used by cells around the body. Bile salts cluster around the products of fat digestion to form structures called micelles. The products of fat digestion diffuse across the membrane of the intestinal cells, and bile salts are recycled back to do more work emulsifying fat and forming micelles. lipid absorption in small intestine  lipid absorption in small intestine Inside the intestinal cell, short- and medium-chain fatty acids and glycerol can be directly absorbed into the bloodstream.  lipid absorption in small intestine Larger lipids such as long-chain fatty acids, monoglycerides, fat-soluble vitamins, and cholesterol need help with absorption and transport to the bloodstream. Incorporated into transport vehicles called chylomicrons. lipid absorption in small intestine  lipid absorption in small intestine From the lymphatic system, the chylomicrons are transported to the circulatory system.  lipid absorption in small intestine Once in the circulation, they can either go to the liver or be stored in fat cells (adipocytes) that comprise adipose (fat) tissue found throughout the body.  SPECIAL ADAPTATION IN INFANTS Lipids are an important part of an infant’s diet. Breast milk contains about 4 percent fat, similar to whole cow’s milk. Whether breastfed or formula-fed, fat provides about half of an infant’s calories, and it serves an important role in brain development. Infants are born with low levels of bile and pancreatic enzyme secretion, which are essential contributors to lipid digestion in older children and adults.  SPECIAL ADAPTATION IN INFANTS They have plenty of lingual and gastric lipases right from birth. Breast milk actually contains lipase enzymes that are activated in the baby’s small intestine.  LIPOLYSIS A process that breaks down fat stores into energy. Takes place in the cytoplasm. The resulting fatty acids are oxidized into acetyl CoA, which is used by the Krebs cycle to obtain energy.  LIPOLYSIS One triglyceride molecule yields three fatty acid molecules with as much as 16 or more carbons in each one, fat molecules yield more energy than carbohydrates and are an important source of energy for the human body. When glucose levels are low, triglycerides can be converted into acetyl CoA molecules and used to generate ATP through aerobic respiration.  lipogenesis Creates lipids (fat) from the acetyl CoA and takes place in the cytoplasm of adipocytes (fat cells) and hepatocytes (liver cells). When you eat more glucose or carbohydrates than your body needs, your system uses acetyl CoA to turn the excess into fat.  seatwork Trace the pathway of Lipid metabolism using the table below. Event Process Organ Enzymes (Describe what happens) Digestion Absorption