DIGESTIVE SYSTEM

• The Digestive System

  Breaks down ingested food into simple nutrients such as carbohydrates, fats, and proteins, which can be absorbed and assimilated through the bloodstream so the body can use them for energy, growth and cell repair. Waste products that the body cannot use exits the body through bowel movements.
• Digestion Process

  1. Ingestion

  2. Digestion

  3. Absorption

  4. Assimilation

  5. Elimination
• Ingestion


  Intake of food into the body
• Digestion


  Breakdown of food, whereas large food molecules are broken down into simpler molecules
• Absorption


  Digested food materials are absorbed by the body cells
• Assimilation


  Transport and use of absorbed nutrients by the cells such as the food conversion into new protoplasm to provide energy
• Elimination


  Passing of undigested material out of the digestive tract
• 2 Processes of Digestion

  • Mechanical Digestion
  • Chemical Digestion
• Mechanical Digestion


  Begins in the mouth and involves physical movement to make the food smaller (e.g. chewing)
• Chemical Digestion


  Breakdown of the complex molecules such as carbohydrates, proteins, and fats into smaller molecules so that it could be absorbed into the bloodstream. There are certain enzymes that help in the process of breaking the food.
• Mouth


  The ingestion (intake) of food starts with mouth which leads to the mouth cavity. Around the sides and front of the mouth cavity are the upper and lower jaws. Physical digestion occurs.
• Four Types of Teeth

  • Incisors
  • Canines
  • Premolar
  • Molar
• Tongue


  It is used to taste the food that we eat. It has special sense cells or the taste buds. There are 5 basic tastes: bitter, salty, sweet, sour, umami (savory taste that blends with other taste)
• Salivary Glands


  Secretes saliva and other senses can increase the secretion of saliva. About 1L saliva secreted a day.
• Functions of Saliva


  • Musin - Helps to soften the food, while chewing helps to break down the food into smaller pieces
  • Ptyalin (salivary amylase) - the enzyme that chemically digests cooked starch into the disaccharide maltose
  • Boli (Bolus) - The term for food after it has been ingested, chewed and mixed with saliva in one's mouth. The function of bolus is to provide a more compact package of food that can be better swallowed.
• Pharynx


  It is the common passage for food and air. The pharynx permits the passage of swallowed solids and liquids into the esophagus, or gullet, and conducts air to and from the trachea, or windpipe, during respiration. Epiglottis covers the larynx when swallowing to avoid food particles from entering the trachea.
• Esophagus


  It is a narrow, muscular tube that after swallowing, the smooth muscles force the food into it. Peristalsis - wavelike muscle movement of food in the alimentary canal (passage of food from mouth to anus).
• How Peristalsis Works

  1. The muscle contracts and the other muscle relaxes

  2. Each bolus of food passes down the esophagus into the stomach partly with the help of gravity and partly by peristalsic movement of esophageal walls. It takes 7 seconds.
• Stomach


  Stomach is a J-Shaped organ which lies beneath the diaphragm and partly covered by a liver. It has thick muscle in its wall. While food is in the stomach it undergoes physical and chemical digestion. Bolus mixes food with gastric juices. Gastric juice or the dilute solution of Hydrochloric acid (HCl) kills germs and any potential parasites. The enzymes help breaks down proteins and lipids.
• Enzymes in Stomach

  The enzymes are released in the pancreas. The enzyme Amylase is responsible for breaking down of complex carbohydrates, Lipase is for breaking down of fats and Protease is for breaking down of protein. The mucus protects the lining of the stomach from being eaten away by the acid.
• Food in Stomach

  The food normally remains in the stomach for about 2-6 hours but can stay longer up to 24 hours depending on the food you eat (calorie). Food found in the stomach is called Chyme.
• Esophageal Sphincter


  To enter the stomach, the bolus must pass through the esophageal sphincter, a tight muscle that keeps stomach acid out of the esophagus.
• Parts of Small Intestine

  • Duodenum
  • Jejunum
  • Ileum
• Mucosal Fold


  This not only increases the surface area, but helps regulate the flow of digested food through your intestine.
• Villi


  Tiny projections which stick out into the open space inside your small intestine (or lumen), and are covered with cells that help absorb nutrients from the food that passes through.
• Microvilli


  The cells on the villi are packed full of tiny hairlike structures called microvilli. This helps increase the surface area of each individual cell, meaning that each cell can absorb more nutrients.
• Absorption in Small Intestine

  The nutrients from the food pass into the bloodstream through the small intestine walls. Absorbs: 80% ingested water, Vitamins, Minerals, Carbohydrates, Proteins, Lipids.
• Liver and Gallbladder

  Liver is the largest organ in the body. It is responsible for bile production. Bile emulsifies fats and neutralizes the acidity of the partly digested food (chyme) that comes from the stomach. Bile is concentrated and stored in the gallbladder. About 500 to 1,000 mL of bile is stored and concentrated in the liver daily.
• Pancreas


  It is an organ of the digestive system and of the endocrine system. The exocrine pancreas produces enzymes that help to digest food, particularly protein. Amylase - Carbohydrates, Lipase - Fats, Protease - Protein. The endocrine pancreas makes the hormone insulin, which helps to control blood sugar levels.
• Large Intestine


  The undigested food that leaves the small intestine passes through it which is much shorter and broader compared to the small intestine. Connects small intestine to anus. There are three regions: (1) Cecum, (2) Colon, (3) Rectum.

  
• Functions of Large Intestine

  Absorb water and mineral salt from the undigested food material. Does not participate in the digestion of food. After the nutrients are absorbed by the cells, they provide fuel for energy. The process of transport and use of absorbed nutrients is known as assimilation. Eliminates indigestible food from the body as feces. The process of removing undigested matter from the body is called egistion, defecation or bowel movement.
• Rectum and Anus

  Rectum is the warehouse of the undigested residues or feces. Anus is the exit point for fecal materials.
• Digestion begins with chewing food to break it down into smaller pieces.
• Saliva contains enzymes that begin breaking down carbohydrates.
• The digestive system is responsible for the breakdown, absorption, and transportation of nutrients.
• Incisors


  Bite food and cut it into smaller pieces
• Canines


  Help cut and tear food into bite sized pieces
• Premolar


  Help you tear, crush and grind food into smaller pieces
• Molar


  Good for crushing and grinding your food
• Esophagus


  from greek word oisen meaning "to carry" and phagein "to eat" or simply "carry what is eaten