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Discuss the medical importance of digestion and absorption of the major food groups (carbohydrates, lipids, proteins)
Carbohydrates - Carbohydrates are a major component for energy metabolism. They provide also sugars that can be eventually stored as glycogen mainly in liver and muscle. A high carbohydrate diet, however, can lead to increased fatty acid de-novo synthesis in the liver and eventually can lead to an increase of fat depots of the human bodyProteins - Dietary protein digestion is important, as it does not only provide amino acids in general, but it also delivers the dietary essential amino acids which cannot be synthesized in humans. Milk, eggs, soybeans have a perfect score regarding dietary essential amino acids, followed by meats. The mixture of different plant food improves the score when eaten at the same time. (e.g. beans and wheat)Lipids - Dietary important for energy metabolism and storage in human fat cells. Dietary essential fatty acids are required for membrane fluidity and synthesis of eicosanoids. Oleic acid and the dietary essential fatty acids are protective against CHD. Cold water fish are rich in ω-3 fatty acids.Vitamins and minerals - Most vitamins are found in plants, exception is vitamin B12. The intrinsic factor formed in the parietal cells of the stomach is needed for eventual uptake of B12 into the intestinal mucosal cell (ileum). Lipid-soluble vitamins reach the liver inside of chylomicron remnants.
Describe the digestion in the mouth and in the stomach (role of salivary amylase and gastric lipase)
Salivary α-amylase - A digestive enzyme released by salivary glands into the mouth. Salivary a-amylase cleaves α(1 ,4) glycosidic bonds of starch and glycogen to branched oligosaccharides. (It cannot cleave the α(1, 6) glycosidic bonds at branch points. Cellulose is not digested as it contains β(1, 4) glycosidic bonds. Lingual lipase - A digestive acidic enzyme that originates in the mouth. It is mostly swallowed and will be active in the stomach. This is important for milk digestion in newborns.Digestion in the Stomach - When stimulated by the ingestion of food, G-cells in the antrum of the stomach release gastrin which stimulates the parietal cells to release of gastric acid (HCl) and intrinsic factors. Mucus will be released by mucus cells. Chief cells will release pepsinogen and gastric lipase.Gastric Acid - The functional component of gastric acid is the hydrochloric acid. It functions to denature proteins and nucleotides, including the salivary α-amylase. It also destroys most bacteria, viruses, and parasites.Gastric Lipase - An acidic digestive enzyme which, along with the swallowed lingual lipase, begins digestion of lipids by cleaving TAGs with medium-chain fatty acids found in milk without the presence of bile acids. These medium-chain fatty acids are later taken up into intestinal mucosal cell and released into the portal vein. These are the only types of digest lipids that reach directly to the liver.Pepsinogen and Pepsin - Pepsinogen is the non-enzymatic precursor to pepsin and released by chief cells. It is auto-catalytically activated to pepsin at high proton concentration in the lumen of the stomach. The generated pepsin can then cleave pepsinogen and generates by enzymatic proteolysis more pepsin. Pepsin is an endopeptidase that is stable at low pH.
Salivary α-amylase
A digestive enzyme released by salivary glands into the mouth. Salivary a-amylase cleaves α(1 ,4) glycosidic bonds of starch and glycogen to branched oligosaccharides. (It cannot cleave the α(1, 6) glycosidic bonds at branch points. Cellulose is not digested as it contains β(1, 4) glycosidic bonds.
Lingual lipase
A digestive acidic enzyme that originates in the mouth. It is mostly swallowed and will be active in the stomach. This is important for milk digestion in newborns.
Gastric Acid
The functional component of gastric acid is the hydrochloric acid. It functions to denature proteins and nucleotides, including the salivary α-amylase. It also destroys most bacteria, viruses, and parasites.
Gastric Lipase
n acidic digestive enzyme which, along with the swallowed lingual lipase, begins digestion of lipids by cleaving TAGs with medium-chain fatty acids found in milk without the presence of bile acids. These medium-chain fatty acids are later taken up into intestinal mucosal cell and released into the portal vein. These are the only types of digest lipids that reach directly to the liver.
Pepsinogen and Pepsin
Pepsinogen is the non-enzymatic precursor to pepsin and released by chief cells. It is auto-catalytically activated to pepsin at high proton concentration in the lumen of the stomach. The generated pepsin can then cleave pepsinogen and generates by enzymatic proteolysis more pepsin. Pepsin is an endopeptidase that is stable at low pH.
Discuss the biochemical and clinical consequences of insufficient acid production in the stomach and the effect of antacids
Gastric acid (HCL) is a strong acid needed for optimal food digestion. The acid denatures proteins and nucleic acids for better digestion and it also destroys bacteria and fungi found in food. It also provides the acidic environment necessary for functional pepsin, gastric lipase, and lingual lipase. With insufficient acid production (such as in the elderly) or excessive neutralization with antacids, pH will be increased resulting in lower ability to denature proteins and nucleic acids, weaken the ability to destroy bacteria and other pathogens, and cause your digestive enzymes to not function in their optimal environment.
Discuss the digestion of lipids found in breast milk
Breast milk is especially high in medium chain fatty acids (8-12). These are fatty acids along with TAGs are targeted by lingual and gastric lipase and are digested in the stomach. Afterwards, they are taken up into intestinal mucosal cell and released into the portal vein. These are the only types of digest lipids that reach directly to the liver. This is especially important in infants such that they have an immediate energy source available to them at an early age.
Describe the role of gastrin and the activation of pepsinogen in the stomach.
Gastrin - A peptide hormone released by G-cells in the antrum of the stomach and stimulates parietal cells to secrete gastric acid.Chief Cells - Secretory cells that release pepsinogen and gastric lipase. It is stimulated by a variety of factors including the vagus nerve and the acidic environment generated by released gastric acid.Pepsinogen is auto-catalytically activated by the low pH environment of the stomach generated by gastric acid. The pepsin it converts to also activates other pepsinogen via enzymatic proteolysis, causing an exponential activation of functional pepsin.
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