Human Digestive System: Stomach Anatomy

• The human digestive system breaks down food, absorbs nutrients, and eliminates waste.
• It consists of the gastrointestinal tract (GI tract) and accessory organs.
• The GI tract includes the mouth, esophagus, stomach, small intestine, large intestine, rectum, and anus.
• Accessory organs include the liver, pancreas, and gallbladder.

Stomach

• The stomach is a J-shaped organ in the upper abdomen.
• It receives food from the esophagus and starts digestion.
• The four main regions are the cardia, fundus, body, and pylorus.
• The cardia connects the esophagus to the stomach.
• The fundus is dome-shaped and located above the cardia.
• The body is the stomach's main central region.
• The pylorus connects the stomach to the small intestine.
• The stomach wall layers are the mucosa, submucosa, muscularis externa, and serosa.
• The mucosa contains gastric pits and glands and secretes gastric juice, including hydrochloric acid and pepsin.
• Hydrochloric acid denatures proteins and kills bacteria.
• Pepsin breaks down proteins into smaller peptides.
• The stomach mixes food with gastric juice to form chyme.
• The pyloric sphincter controls chyme release into the small intestine.
• The stomach can expand to hold a large food volume.
• Gastric emptying is regulated hormonally and neurally.

Small Intestine

• The small intestine is a long, coiled tube and the primary site of nutrient absorption.
• It extends from the stomach's pylorus to the ileocecal valve.
• The small intestine has three segments: the duodenum, jejunum, and ileum.
• The duodenum is the shortest segment and receives chyme from the stomach.
• The jejunum is the middle segment and the main nutrient absorption site.
• The ileum is the longest segment and connects to the large intestine.
• The inner surface is highly folded, with circular folds, villi, and microvilli, increasing the surface area for absorption.
• Villi are finger-like projections containing blood capillaries and lacteals for nutrient absorption.
• Microvilli are tiny projections on the villi's surface that further increase the surface area.
• The small intestine secretes enzymes and hormones to aid digestion and absorption.
• Pancreatic juices and bile from the liver enter the small intestine to further digest the chyme.
• Peristalsis moves the chyme through the small intestine.
• Most nutrients, including carbohydrates, proteins, and fats, are absorbed there.

Large Intestine

• The large intestine is wider and shorter than the small intestine.
• It extends from the ileocecal valve to the anus.
• The large intestine includes the cecum, colon, rectum, and anal canal.
• The cecum is a pouch that receives undigested material from the small intestine.
• The appendix is a small projection extending from the cecum.
• The colon is the longest part, divided into the ascending, transverse, descending, and sigmoid colon.
• The ascending colon travels up the right side of the abdomen.
• The transverse colon crosses the abdomen from right to left.
• The descending colon travels down the left side of the abdomen.
• The sigmoid colon is S-shaped and connects to the rectum.
• The main functions include water and electrolyte absorption, feces formation and storage, and housing beneficial bacteria.
• Gut flora ferments indigestible material, producing vitamins and gases.
• Peristaltic movements propel feces towards the rectum.

Rectum

• The rectum is a short, straight segment between the sigmoid colon and the anus.
• It stores feces until defecation.
• The rectal wall has stretch receptors that trigger the urge to defecate.

Liver

• The liver is the largest internal organ, located in the upper right quadrant of the abdomen.
• It produces bile, metabolizes nutrients, detoxifies harmful substances, and stores glycogen.
• Bile emulsifies fats in the small intestine, aiding digestion and absorption.
• The liver receives blood from the hepatic artery and the hepatic portal vein.
• The hepatic artery carries oxygenated blood.
• The hepatic portal vein carries nutrient-rich blood from the digestive organs.
• The liver consists of hepatic lobules, containing hepatocytes.
• Hepatocytes perform the liver's metabolic functions.
• The liver can regenerate if damaged.

Pancreas

• The pancreas is a gland located behind the stomach with exocrine and endocrine functions.
• The exocrine function produces pancreatic juice with enzymes that digest carbohydrates, proteins, and fats in the small intestine.
• Pancreatic juice is secreted into the duodenum through the pancreatic duct.
• The endocrine function produces hormones like insulin and glucagon, which regulate blood sugar levels.
• Insulin lowers blood sugar levels by promoting glucose uptake by cells.
• Glucagon raises blood sugar levels by stimulating glycogen breakdown in the liver.
• It is essential for digestion and glucose homeostasis.