Science

• Digestive system


  Mechanism that allows organisms to get nutrients from their environment
• The food that we eat travels through the digestive tube or alimentary canal where it gets digested
• Digestion


  Process of converting food into usable, organic compounds and nutrients that provide energy
• Different digestive organs process the food along the gastrointestinal (GI) tract and excrete the waste materials through the anus
• Metabolism


  The process of how cells use the energy obtained from food during digestion
• Digestion is a complex process that begins with breaking the food into smaller pieces, which later on are converted into smaller substances that cells absorb and use to produce energy
• Mouth (Oral Cavity)


  • Entry point of food
  • Site of first stage of digestion: ingestion
• Ingestion


  1. Mastication (chewing)

  2. Saliva mixing with food
• Saliva


  Liquid containing water, electrolytes, enzymes, proteins, and nitrogenous products that lubricates and begins chemical digestion of food
• Saliva contains an enzyme called ptyalin or salivary amylase that partially digests the starch content of the food
• pH of saliva


  Normal range is 6.2 to 7.6, can be affected by food, drinks, and age
• Proper pH balance of saliva helps maintain a healthy mouth and protects the teeth
• Teeth


  • Located in different positions and perform different functions (tearing, biting, chewing)
  • Children have 20 primary teeth, adults have 32 teeth
• Tongue


  Assists in mixing food with saliva, contains taste buds that detect different tastes
• Pharynx


  Connects the mouth to the esophagus, serves as passageway for food and air
• Esophagus


  Muscular tube that pushes food down to the stomach through peristalsis
• Stomach


  • Muscular, expandable organ that receives food from the esophagus
  • Contains glands that secrete acid and enzymes to continue digestion
  • Stomach muscles contract to mix and churn the food
• Pepsin


  Digestive enzyme in gastric juice that breaks down proteins
• Small Intestine


  • About 6-7 meters long, where 90% of chemical digestion and absorption of nutrients occurs
  • Has three segments: duodenum, jejunum, ileum
• Villi and microvilli


  Folded, finger-like projections that increase the surface area for nutrient absorption
• Lymph vessels


  Thin-walled tubes that absorb undigested fats and fatty acids and transport them to the circulatory system
• Accessory Organs


  • Pancreas, liver, gallbladder
  • Secrete substances needed for chemical digestion but food does not pass through them
• Pancreatic juice


  Mixture of water, digestive enzymes, bicarbonates, and electrolytes that breaks down proteins, fats, and carbohydrates
• Pancreatic enzymes


  Amylase, trypsin, lipase
• Accessory organs


  The pancreas, the liver, and the gallbladder
• Pancreas


  • A long, narrow gland that stretches from the spleen to about halfway through the duodenum
  • Secretes pancreatic juice, a mixture of water, digestive enzymes, bicarbonates, and electrolytes
  • Pancreatic juice breaks down proteins, fats, and carbohydrates
  • Passes through the main pancreatic duct to the common bile duct, and then to the duodenum
  • Contains bicarbonate salts that neutralize the acidity of the chyme from the stomach to maintain the proper pH balance and aid digestion
• Pancreatic amylase


  Changes starch and glycogen into maltose, a disaccharide
• Trypsin or proteolytic enzyme


  Digests proteins from food
• Lipase


  Helps the body absorb fats by breaking down dietary fats and converting triglycerides into fatty acids and monoglycerides
• Liver


  Continuously produces bile, a yellowish-brown fluid that aids chemical digestion by helping the small intestine with the emulsification and digestion of lipids (fats)
• Gallbladder


  A green, pear-shaped sac that stores and concentrates excess bile
• These nutrients - glucose, amino acids, fatty acids, and glycerol with some water, vitamins, and minerals - are the end products of digestion
• These substances are absorbed by the capillaries of the circulatory system so they can be distributed by the blood throughout the entire body
• Large intestine or colon


  • Shorter than but wider than the small intestine
  • Approximately 1.5 m long and 7 cm wide
  • Has four parts: ascending colon, transverse colon, descending colon, and sigmoid colon
• Digestion does not happen in the large intestine
• Appendix


  A small, thin tube that sits at the lower right abdomen, about 10 cm long, attached to the large intestine and connected to the cecum
• The function of the appendix is unknown and it does not have any participation in the digestion process of humans
• Stages of digestion


  • Ingestion
  • Digestion
  • Absorption/Assimilation
  • Elimination/Excretion
• Ingestion


  The process of taking food into the mouth and breaking it down by chewing and grinding, lubricated by saliva, and swallowing
• Digestion


  The process of further breaking down food into a more usable form that the tissues of the body can absorb and assimilate, including mechanical digestion and chemical digestion