DIGESTIVE SYSTEM

• The digestive system contributes to homeostasis through the process of breaking down food into forms that can be absorbed and used by cells and eliminates wastes from the body.
• The digestive system consists of organ groups that break down food: the gastrointestinal (GI) tract which extends from the esophagus to the anus, and includes the esophagus, stomach, small intestine, large intestine and anal canal.
• Accessory organs such as teeth, tongue, pharynx, liver, gallbladder and pancreas aid in the physical and chemical breakdown of food.
• The digestive canal includes the mouth, teeth, salivary glands, pharynx, liver, gallbladder and pancreas.
• Ingestion is the process of taking food and liquids into the mouth, and secretion is the secretion of 7L of digestive chemicals into the lumen of the digestive tract.
• The liver is involved in detoxification and drug excretion into bile.
• Protein metabolism in hepatocytes involves deaminating amino acids for ATP production or converting them into carbohydrates and fats.
• Hepatocytes synthesize blood plasma proteins.
• The liver can chemically alter or excrete thyroid and steroid hormones.
• Stellate reticuloendothelial cells phagocytize aged RBC, WBC and some bacteria.
• Bilirubin is secreted into bile and is metabolized by the small intestine and eliminated in feces.
• The liver synthesizes the active form of Vitamin D.
• The resulting toxic ammonia is converted into toxic urea and excreted via urine.
• The liver is the prime storage area for glycogen, vitamins and minerals.
• Bile salts aid in emulsification and absorption of lipids.
• The liver is responsible for the excretion of bilirubin.
• The liver processes drugs and hormones.
• Motility refers to alternating contractions and relaxation that mix food and secretion and move this mixture further into the digestive system.
• Partially broken down carbohydrates are broken down by pancreatic amylase.
• Sucrase breaks down sucrose into glucose and fructose.
• Nucleotides that result from pancreatic juice nucleases are further broken down by microvillous-border enzymes nucleosidases and phosphatases.
• Byproducts (pentoses, phosphates & nitrogenous bases) are absorbed via active transport.
• Triglycerides are broken down by pancreatic lipase into fatty acids and monoglycerides.
• Lipases are enzymes that split triglycerides and phospholipids.
• The hydrophobic region of bile salts interacts with the lipid globule and the hydrophilic region interacts with the chyme.
• Large lipid globules are broken down by bile salts which are described to be amphipathic, containing a hydrophobic and hydrophilic portion.
• Protein digestion is completed by two peptidases in the brush border: Aminopeptidase cleaves amino acid at the end of the peptide and Dipeptidase splits dipeptides into single amino acids.
• Maltase breaks down maltose and maltotriose into two to three glucose molecules.
• After carbohydrates have been broken down into smaller pieces, a-dextrinase acts on resulting a-dextrins, clipping off one glucose unit at a time.
• Lactase breaks lactose into glucose and galactose.
• End with monosaccharides which can be absorbed.
• Digestion is the process of breaking down food into small molecules that can be processed by the body, which can be classified into mechanical digestion and chemical digestion.
• Parasympathetic fibers, provided by the Vagus Nerve (CN X) to most parts of the digestive canal, stimulate the Enteric Nervous System (motility and secretions).
• The visceral peritoneum forms a portion of the peritoneum.
• Major types of sensory receptors in the Enteric Nervous System include Chemoreceptors that detect certain chemicals in food and Mechanoreceptors that detect distention done by food.
• The esophagus lacks a serosa and instead has adventitia.
• The Myenteric neural plexus controls motility (frequency and strength of contractions) and is located between the longitudinal and circular smooth muscular layers.
• The brain of the gut is made up of 100 million neurons and contains motor, interneurons and sensory neurons; and is arranged into: Myenteric neural plexus and Plexus of Auerbach.
• Sympathetic fibers, provided by the thoracic and upper lumbar regions of the spinal cord, inhibit the Enteric Nervous System (motility and secretions).
• The Enteric Nervous System provides regulation of the ENS.