DIGESTIVE SYSTEM

• Digestive system


  Complex network of organs and tissues responsible for processing food, extracting nutrients, and eliminating waste from the body
• Digestive system


  • Its primary function is to break down ingested food into smaller molecules that can be absorbed into the bloodstream and utilized by the body for energy, growth, and repair
• Main parts of the human digestive system

  • Mouth
  • Pharynx (throat)
  • Esophagus
  • Stomach
  • Small intestine
  • Large intestine (colon)
  • Rectum
  • Anus

  
• Mechanical digestion in the mouth

  1. Chewing (mastication)

  2. Mixing with saliva
• Saliva


  Contains water, electrolytes, mucus, and enzymes (e.g., amylase, lipase) that help initiate the digestion process
• Chemical digestion in the mouth

  Amylase breaks down starches into maltose
• Esophagus

  Muscular tube approximately 25-30 centimeters long that connects the throat (pharynx) to the stomach

  
• Function of the esophagus

  Transporting chewed food (bolus) from the mouth to the stomach through peristalsis

  
• Stomach


  Muscular organ located in the upper abdomen, between the esophagus and the small intestine, divided into four main regions: the cardia, fundus, body, and pylorus
• Functions of the stomach

  • Storage of ingested food
  • Mechanical digestion through muscular contractions
  • Chemical digestion through gastric juice containing hydrochloric acid and digestive enzymes (e.g., pepsin)
• Small intestine

  Long, coiled tube located between the stomach and the large intestine, consisting of three main segments: the duodenum, jejunum, and ileum
• Functions of the small intestine

  • Digestion of food through enzymes from the pancreas and bile from the liver
  • Absorption of nutrients (such as sugars, amino acids, fatty acids, and vitamins) into the bloodstream through villi and microvilli

  
• Villi and microvilli


  Tiny finger-like projections lining the small intestine that greatly increase the surface area for efficient nutrient absorption
• Nutrient absorption in the small intestine

  • Carbohydrates broken down into simple sugars (e.g., glucose)
  • Proteins broken down into amino acids
  • Fats broken down into fatty acids and glycerol, then absorbed into the lymphatic system
• Movement in the small intestine

  1. Peristalsis: Contractions of the muscular wall propel chyme and aid in mixing with digestive enzymes

  2. Segmentation: Circular muscle contractions segment and mix chyme, facilitating nutrient absorption
• Large intestine (colon)


  Final segment of the digestive tract, consisting of several regions including the cecum, colon (ascending, transverse, descending, sigmoid), rectum, and anus

  
• Functions of the large intestine

  • Absorption of water and electrolytes from undigested food, forming feces
  • Formation of feces as water is absorbed, compacting remaining undigested food, bacteria, and waste products
• Gut bacteria


  Beneficial bacteria in the large intestine that help ferment undigested carbohydrates, produce vitamins, and maintain a healthy balance in the gut microbiota
• Defecation


  Reflex action triggered when feces fill the rectum, causing the muscles in the anus to relax and allow feces to pass out of the body
• Liver


  Large organ located in the upper right abdomen, just below the diaphragm, responsible for producing bile, filtering and detoxifying blood, and playing a key role in carbohydrate, protein, and fat metabolism
• Pancreas


  Glandular organ located behind the stomach, adjacent to the small intestine, responsible for producing digestive enzymes and regulating blood sugar levels

  
• Gallbladder


  Small sac located beneath the liver, which stores and concentrates bile produced by the liver
• Coordination with the digestive system

  1. Bile production and release by the liver and gallbladder to aid in fat digestion

  2. Enzyme secretion by the pancreas into the small intestine to further break down carbohydrates, fats, and proteins
• Accessory organs of the digestive system

  Organs that work along with the gastrointestinal tract as part of the digestive system, but are not part of the gastrointestinal tract itself
• Accessory organs of the digestive system

  • Liver
  • Pancreas
  • Gallbladder
  • Salivary glands

  
• Liver


  • Largest gland in the body
  • Accessory organ of the digestive system

  
• Liver location


  • Located primarily in the right hypochondriac and epigastric regions of the abdomen, just beneath the diaphragm

  
• Liver structure


  • Divided into two major lobes and two smaller lobes
  • Functional units are lobules with sinusoids that carry blood from the periphery to the central vein of the lobule

  
• Liver size


  • Normally weighs about 1.5 kg (3.3 lb) in adults
  • Largest internal organ and largest gland in the human body

  
• Liver blood supply


  • Connected to two large blood vessels: the hepatic artery (carries oxygen-rich blood) and the portal vein (carries blood rich in digested nutrients and wastes)
• Liver functions


  • Secretion
  • Synthesis of bile salts
  • Synthesis of plasma protein
  • Storage
  • Detoxification
  • Excretion
  • Carbohydrate metabolism
  • Lipid metabolism
  • Protein metabolism
  • Filtering

  
• Bile


  Yellowish alkaline liquid produced by the liver, consisting of water, electrolytes, bile salts, cholesterol, and other substances
• Bile production and secretion

  • Synthesized by hepatocytes and secreted into small ducts that join together to form larger ducts, with one large duct carrying bile out of the liver

  
• Gallbladder


  A pear-shaped sac attached to the visceral surface of the liver by the cystic duct, serving as a storage reservoir for bile

  
• Gallbladder size and location


  • Small, hollow, pouch-like organ about 8 cm (3.1 in.) long, lying just under the right side of the liver

  
• Pancreas


  A glandular organ that is part of both the digestive system and the endocrine system, located in the abdomen behind the stomach
• Pancreas functions


  • Produces digestive enzymes and hormones like insulin and glucagon that regulate blood sugar levels
• Pancreatic digestive enzymes


  • Amylase (digests carbohydrates)
  • Trypsin and chymotrypsin (digest proteins)
  • Lipase (digests lipids)
  • Deoxyribonucleases and ribonucleases (digest nucleic acids)
• People can live without a pancreas, but surgery to remove the entire pancreas is typically not done anymore