digestive system

• The digestive system includes the mouth, pharynx, esophagus, stomach, small intestine, large intestine, rectum, and anus, as well as accessory structures like the salivary glands, pancreas, and liver

  
• Nutrients broken down during digestion

  • Water
  • Carbohydrates
  • Fats
  • Proteins
  • Vitamins
  • Minerals
• Human nutrition


  1. Ingestion

  2. Digestion

  3. Absorption

  4. Assimilation

  5. Egestion
• Energy available in food is measured by burning food
• Calorie


  Amount of heat needed to raise the temperature of 1 gram of water by 1 degree Celsius
• Dietary calories


  1000 calories or 1 kilocalorie
• Average teen needs


  • 2200 Calories/day for females
  • 2800 Calories/day for males
• Water is the most important nutrient
• Every cell in the human body needs water
• Water makes up the bulk of blood, lymph and other bodily fluids
• Drink at least 1-2 liters of water each day (6-8 cups)
• Not drinking enough water can lead to dehydration, which causes problems in the circulatory, respiratory, and nervous systems
• Carbohydrates


  Nutrients that are the main source of energy for the body
• Proteins


  Nutrients that are the main source of building blocks for the body
• Fats/Lipids


  Used for cellular components, such as cell membranes, also used for storage of energy
• Saturated fats


  Solid at room temperature (butter and animal fat)
• Unsaturated fats


  Liquid at room temperature (vegetable oils)
• Saturated fats are the "bad" fats, and unsaturated are the "good" fats
• Essential amino acids


  8 amino acids the body cannot make, must be obtained from food
• Vitamins


  Organic molecules that help regulate body processes (work with enzymes)
• Most vitamins are obtained from food, but vitamin K is synthesized by bacteria in the digestive tract and vitamin D is synthesized by the skin when exposed to sunlight
• Types of vitamins


  • Fat-soluble (A, D, E, K)
  • Water-soluble (C, B)
• Minerals


  Inorganic nutrients that the body needs in small amounts, also called micronutrients
• Digestion


  1. Ingestion

  2. Digestion

  3. Absorption

  4. Assimilation

  5. Egestion
• The function of the digestive system is to convert large food molecules into simpler molecules (monomers) that can be absorbed and used by the cells of the body
• Mouth


  • Teeth mechanically digest food by cutting, tearing, and crushing
  • Saliva begins chemical digestion by breaking down starches with the enzyme amylase
• Pharynx


  The back of the throat, where the larynx (passage for air) is located
• Esophagus


  Long tube of smooth muscle that connects the pharynx with the stomach, transports the chewed food (bolus) to the stomach
• Peristalsis


  Contractions of smooth muscles that squeeze food through the esophagus into the stomach
• Cardiac sphincter


  Thick ring of muscle that closes to prevent stomach contents from moving back up the esophagus
• Stomach


  • Large sac of smooth muscle that performs chemical digestion with gastric glands and mechanical digestion with smooth muscle contractions
  • Mixes food into a substance called chyme
• Pyloric valve


  Opens to allow chyme to flow from the stomach into the small intestine
• Accessory organs


  Pancreas, gallbladder, and liver
• Gallbladder


  Pouch structure that concentrates and stores bile
• Bile duct


  Tube that carries bile from the liver to the small intestine
• Bile


  Bitter, greenish-yellow alkaline fluid that emulsifies lipids (breaks apart fats)
• Pancreas


  • Organ that secretes digestive enzymes and hormones
  • Pancreatic juice digests all major nutrient types

  
• Liver


  Produces bile, which acts as a detergent to dissolve fat droplets
• Small intestine


  • Most chemical digestion takes place here
  • Simple sugars and proteins are absorbed into the inner lining
  • Fatty acids and glycerol go to the lymphatic system

  
• Villi


  Finger-like projections that cover the surface of the small intestine, increasing the surface area for absorption