GastroIntestinal

• The digestive system consists of the gastrointestinal (GI) tract or alimentary canal, which is a continuous tube from the mouth to the anus, and the accessory digestive organs such as teeth, tongue, salivary glands, liver, gallbladder, pancreas.
• The organs of the digestive system include the mouth, most of the pharynx, esophagus, stomach, small intestine, and large intestine, which together form a length of 5-7m when in a state of tonus.
• The accessory digestive organs produce or store secretions that flow in the GIT through ducts, aiding in the chemical breakdown of food.
• The muscle contraction in the digestive system breaks down food and propels food along the tract.
• The digestive system helps dissolve food by mixing them with secreted fluids.
• Ingestion is the process of taking foods and liquids into the mouth.
• Secretion is a process performed by cells within the GIT walls and the accessory digestive organs.
• Mixing and propulsion in the digestive system involves alternating contractions and relaxations of the smooth muscles in the GIT.
• Motility is the capability of the GIT to mix and move material along its length.
• Digestion is a process that involves mechanical and chemical processes that breakdown food into smaller molecules.
• Mechanical digestion in the digestive system involves teeth cutting and grinding food, which is then swallowed and churned.
• Distension of stomach walls or increase in pH can activate stretch receptors and chemoreceptors, leading to neural negative feedback loop stimulation and nerve impulse propagation in the submucoal plexus.
• The cerebral cortex, hypothalamus, and brain stem are activated when the sense of smell, sight, thought, or initial taste of food is detected, preparing the mouth and stomach for food that is about to be eaten.
• Gastric emptying is inhibited by gastric juice pH <2.0 and stimulated by pH increase.
• The Gastric Phase begins when the food reaches the stomach, where neural regulation is monitored by chemoreceptors that measure the pH of the stomach chyme.
• The purpose of the Cephalic Phase is to prepare the mouth and stomach for food that is about to be eaten.
• Constipation is characterized by decreased motility of the intestines, leading to infrequent or difficult defecation, with feces remaining in the colon for prolonged periods.
• Diarrhea is characterized by increased motility and decreased absorption of the intestines, leading to an increase in the frequency, volume, and fluid content of feces.
• Defecation reflex is voluntarily controlled and involves the voluntary relaxation of the external anal sphincter, which results in the expulsion of feces.
• Activation of parasympathetic and enteric neurons can result in waves of peristalsis and stimulation of the flow of gastric juice.
• Gastrin inhibits the stomach LES, prevents reflux of acid chyme, increases stomach motility, and relaxes the pyloric sphincter, promoting gastric emptying.
• Excessive motility can be caused by lactose intolerance, stress, and microbes.
• Gastrin is released from G cells and regulates gastric secretion, with gastric distension, partially digested protein in chyme, high pH of chyme, caffeine in gastric chyme, and Ach stimulating gastrin release.
• Chemical digestion in the digestive system involves carbohydrate, lipid, protein, and nucleic acid molecules breaking down into smaller molecules (hydrolysis).
• Absorption is the entrance of ingested and secreted fluids, ions, and products of digestion into epithelial cells lining the lumen of the GIT.
• Defecation is the process of eliminating wastes, indigestible substances, bacteria, and cells sloughed off.
• The layers of the GIT include the mucosa, epithelium, submucosa, muscularis, and serosa.
• The mucosa is the inner lining of the GIT and is protected by the epithelium.
• Motor neurons of myenteric plexus supply longitudinal and circular muscle layers of the GIT, control GIT motility, and determine the frequency and strength of contraction.
• Lymph nodes contribute macrophages and antibody-producing plasma cells to combat and contain infection.
• Retroperitoneal refers to the posterior abdominal wall not covered by peritoneum.
• The five major peritoneal folds are the greater omentum, falcifrom ligament, lesser omentum, mesentery, and mesocolon.
• The peritoneum is the largest serous membrane of the body and a layer of mesothelium with underlying areolar connective tissue.
• Sensory receptors in the GIT are initial components known as chemoreceptors and stretch receptors.
• The parietal peritoneum lines the wall of the abdominal cavity.
• The visceral peritoneum covers organs and serosa.
• The greater omentum is the largest peritoneal fold, drapes over the transverse colon and coils of the SI, is a double sheet that folds back on itself with four layers, and contains adipose tissue that expands with weight gain.
• Vagus (X) nerves supply parasympathetic fibers except for the last half of the large intestine.
• Parasympathetic preganglionic neurons of the vagus or pelvic splanchnic nerves synapse with parasympathetic postganglionic neurons located in the myenteric and submucosal plexus.
• Sympathetic nerves arise from the thoracic and upper lumbar regions of the spinal cord and decrease GI secretion and motility when stimulated.