4.1: The Human Digestive System

• Digestion - is the process of breaking down food by mechanical and enzymatic action in the alimentary canal into substances that can be used by the body.
• Digestive System - breaks food down to tiny molecules that can be absorbed into the bloodstream and distributed to cells.
• What are the two parts of the Digestive System?

  Alimentary Canal, Accessory Organs
• Alimentary Canal - is a muscular tube, which extends from the mouth to the anus.
• The Human Digestive System comprises:

  • Mouth
  • Pharynx
  • Esophagus
  • Stomach
  • Small Intestine
  • Large Intestine
  • Anus
• Mouth is also known as oral cavity
• Mouth - serves as the starting point of digestion.
• Mouth breaks food and turns into bolus
• Mechanical Digestion - with the aid of Teeth bite off and chew bite off and chew food into a soft pulp that is food into a soft pulp that is easy to swallow.
• Teeth - bite off and chew food into a soft pulp that is food into a soft pulp that is easy to swallow.
• Chemical Digestion - with the help of saliva.
• Pharynx is also known as throat
• Pharynx - It acts as a passageway for food on its way to the stomach.
• Esophagus is also known as the gullet
• Esophagus - Is a muscular tube, that takes food from the throat and pushes it down through the neck, and into the stomach.
• The esophagus moves food by waves of muscle contraction called Peristalsis
• Stomach - where protein digestion starts.
• The stomach has thick muscles in its wall. These contract to mash the food into a water soup called Chyme
• The stomach lining produces strong gastric juices.
• Gastric Juices is made up of

  • Water
  • Hydrochloric Acid
  • Enzymes
  • Mucus
• Sphincter - a gateway; prevents backflow of food.
• Small Intestine - where the final digestion of food is taking place.
• The nutrients are broken down small enough to pass through the lining of the small intestine through the help of what?

  Villi, Microvilli
• Nutrients - are carried away to the liver and other body parts to be processed, stored and distributed with the help of blood.
• Large Intestine is also known as colon.
• Feces - The remains are formed into brown, semi-solid, ready to be removed from the body.
• What are absorbed in the Large Intestine?

  Water, Mineral Salts
• Rectum - receives stool from the colon.
• Rectum temporarily stores feces until defecation.
• Anus - the last part of the digestive tract
• Anus - It is the opening at the end of the digestive tract which stool leaves the body.
• They control the release of stool:

  • Internal Sphincters
  • External Sphincters
• Salivary Glands, Liver, Gallbladder, Pancreas - are not part of the digestive tract, but they have a role in digestive activities and are considered accessory organs.
• Salivary Glands, Liver, Gallbladder, and Pancreas are considered as accessory organs.
• Salivary Glands - tissue in the mouth that expel saliva.
• Humans have three pairs of salivary glands:

  • Parotid
  • Sublingual
  • Submandibular
• Liver secretes bile
• Liver - It stores some nutrients, and releases them into the blood according to the activities and needs of the body.
• Liver helps the body maintain homeostasis
• Gallbladder - stores bile produced by the liver,