Digestive System Overview

• The digestive system's functions include ingestion, digestion, absorption, compaction, and defecation.
• General digestion starts in the mouth.
• The digestive tract includes the mouth, pharynx, esophagus, stomach, small intestine, and large intestine.
• The path of food: Mouth → Pharynx → Esophagus → cardiac region → body of stomach → duodenum → jejunum → ileum → cecum → ascending colon → transverse colon → descending colon → internal sphincter → external sphincter.
• The accessory organs are the teeth, salivary glands, liver, gallbladder, and pancreas.
• The four layers of the digestive system histology are the mucosa, submucosa, muscularis externa, and serosa.
• Lingual papillae contain taste buds.
• Peristalsis is the movement of food down the esophagus, controlled by smooth muscle.
• The four cells of the stomach are mucus cells, stem cells, chief cells, and parietal cells.
• Mucus cells produce mucus.
• Stem cells produce new cells.
• Parietal cells produce stomach acid and ghrelin.
• Chief cells produce gastric lipase and pepsinogen and secrete HCl.
• Hydrochloric acid activates pepsinogen into pepsin.
• Gastric lipase digests small amounts of fat in the stomach.
• Pepsin breaks down proteins into amino acids.
• The hepatic portal vein brings toxins, drug/alcohol metabolites, and hormones back into the liver to keep the body close to homeostasis.
• The gallbladder holds bile, while the liver produces it.
• Bile emulsifies fats.
• Bile release process: Liver produces bile → bile sent through the bile duct into the gallbladder for storage → food enters the duodenum, which sends a signal to the brain → parasympathetic nervous system signals gallbladder for bile release → bile emulsifies fats in the duodenum.
• The three parts of the small intestine are the duodenum, jejunum, and ileum.
• The three structures that deal with absorption of nutrients in the small intestine are villi, microvilli, and capillaries.

Hormones

• Ghrelin: A hunger hormone secreted by gastric parietal cells that signals hunger to the hypothalamus.
• Peptide YY: A hunger suppression hormone secreted by the ileum and colon to signal fullness.
• Cholecystokinin: An appetite suppressant that causes the gallbladder to release bile.
• Amylin: A hunger-suppressing hormone released by beta cells in the pancreas that stimulates fullness.
• Leptin: Signals the body to eat more based on the body's fat content, secreted by adipocytes while eating.
• Insulin is not the strongest hunger hormone in the body.

Enzymes

• Salivary amylase: Begins the breakdown of carbohydrates in the mouth into glucose.
• Carbohydrates go into the bloodstream by the capillaries after the brush border cells.
• Salivary amylase is released in the mouth.
• Pancreatic amylase is released in the stomach.
• Pepsin and trypsin break down proteins.
• Pepsin is released in the stomach.
• Trypsin is released in the duodenum.
• All macromolecules are broken down into Acetyl CoA for aerobic respiration.
• The electron transport chain makes the most ATP.
• NAD+ and FAD+ are energy carriers.
• Hydrogen protons pumped through transport proteins into the intermitochondrial space allow for ATP to be made in the electron transport chain.