Today’s Outline Topic: Intro to the Digestive System Class Outline: - Finish notes and Textbook work Today’s Assigned Work: - Textbook work Upcoming Assignments: - Monday May 9 th : Lab - Tuesday May 10 th : ICA - Thursday May 12 th : Test

Anatomy & Physiology of the Human Digestive System

Digestion Digestion is the breakdown of large, complex organic molecules into smaller components that can be used by the body. Digestion is the breakdown of large, complex organic molecules into smaller components that can be used by the body. Molecules need to be small enough to diffuse across plasma membranes. Molecules need to be small enough to diffuse across plasma membranes.

Four Components of Digestion Ingestion – this is the consumption of or taking in of nutrients. Ingestion – this is the consumption of or taking in of nutrients. Digestion – the chemical breakdown of large organic molecules into smaller components by enzymes. Digestion – the chemical breakdown of large organic molecules into smaller components by enzymes. Absorption – the transport or delivery of digested nutrients to body tissues. Absorption – the transport or delivery of digested nutrients to body tissues. Egestion – the elimination of food waste materials from the body. Egestion – the elimination of food waste materials from the body.

Mechanical Digestion Physical breakdown of food begins with the teeth grinding the food and increasing its surface area allowing for easier chemical digestion. Physical breakdown of food begins with the teeth grinding the food and increasing its surface area allowing for easier chemical digestion. Smooth muscles in the stomach and small intestine also aid in mechanical digestion. Smooth muscles in the stomach and small intestine also aid in mechanical digestion.

Chemical Digestion Enzymes that are released from glands in the digestive system chemically break down foods into smaller subunits that are small enough to be absorbed. Enzymes that are released from glands in the digestive system chemically break down foods into smaller subunits that are small enough to be absorbed.

Oral Cavity Food enters the human digestive tract through the mouth or oral cavity. Food enters the human digestive tract through the mouth or oral cavity. The teeth, tongue and salivary glands work to mechanically and chemically digest food. The teeth, tongue and salivary glands work to mechanically and chemically digest food.

Oral Cavity - Taste Buds As the food particles dissolve in the saliva they penetrate the cells of the taste buds located on the tongue and cheeks. As the food particles dissolve in the saliva they penetrate the cells of the taste buds located on the tongue and cheeks. Humans can differentiate between sweet, sour, salty and bitter. Humans can differentiate between sweet, sour, salty and bitter.

Oral Cavity - Swallowing Saliva also lubricates the food and helps to form a bolus. Saliva also lubricates the food and helps to form a bolus. The tongue pushes the bolus to the back of the throat and it is swallowed. The tongue pushes the bolus to the back of the throat and it is swallowed.

Esophagus The bolus of food moves down the esophagus propelled by wave-like muscular contractions known as peristalsis. The bolus of food moves down the esophagus propelled by wave-like muscular contractions known as peristalsis. Peristalsis moves food all the way through the gastrointestinal tract. Peristalsis moves food all the way through the gastrointestinal tract.

Esophagus - Sphincters The esophagus attaches to the stomach at the esophageal sphincter (rings of muscle). The esophagus attaches to the stomach at the esophageal sphincter (rings of muscle). The sphincter controls the release of food into the stomach. The sphincter controls the release of food into the stomach.

Stomach The stomach acts as a temporary storage site for food (about 4 hours) The stomach acts as a temporary storage site for food (about 4 hours) Stores about 1.5 litres of food. Stores about 1.5 litres of food. Millions of cells lining the stomach secrete gastric fluids consisting of mucus, hydrochloric acid, pepsinogens and other substances. Millions of cells lining the stomach secrete gastric fluids consisting of mucus, hydrochloric acid, pepsinogens and other substances. Mucus coats and protects the lining of the stomach. Mucus coats and protects the lining of the stomach. pH of about pH of about Sphincter located at the bottom slowly releases partially digested food into the small intestine. The partially digested food is called chyme. Sphincter located at the bottom slowly releases partially digested food into the small intestine. The partially digested food is called chyme.

Stomach Ulcers An stomach ulcer is a lesion in the lining of the stomach. It occurs when the protective mucus lining breaks down and the cell membranes are exposed to the HCl and pepsin An stomach ulcer is a lesion in the lining of the stomach. It occurs when the protective mucus lining breaks down and the cell membranes are exposed to the HCl and pepsin Most stomach ulcers are linked to the bacterium shown on the right known as Heliobacter pylori. Most stomach ulcers are linked to the bacterium shown on the right known as Heliobacter pylori.

Endoscopy An endoscope (shown on the right) can be used to view things such as stomach ulcers or as shown below, a tumor growing in the large intestine. An endoscope (shown on the right) can be used to view things such as stomach ulcers or as shown below, a tumor growing in the large intestine. The endoscope can also extract small pieces of tissue for a biopsy. The endoscope can also extract small pieces of tissue for a biopsy.

Small Intestine The small intestine is up to 7 m in length but only 2.5 cm in diameter. The small intestine is up to 7 m in length but only 2.5 cm in diameter. Chyme from the stomach empties into the first section known as the duodenum. Most chemical digestion occurs here. Chyme from the stomach empties into the first section known as the duodenum. Most chemical digestion occurs here. It contains an opening from the bile duct and pancreatic duct through which bile and pancreatic enzymes enter the small intestine. It contains an opening from the bile duct and pancreatic duct through which bile and pancreatic enzymes enter the small intestine.

Absorption in Small Intestine Most nutrients are absorbed in the small intestine. Most nutrients are absorbed in the small intestine. The small intestine is lined with millions of small finger-like projections known as villi. The villi increase the surface area of the small intestine which increases it’s ability to absorbed digested nutrients. The small intestine is lined with millions of small finger-like projections known as villi. The villi increase the surface area of the small intestine which increases it’s ability to absorbed digested nutrients.

Large Intestine Large Intestine The large intestine is only 1.5 m in length but 7.6 cm in diameter. The large intestine is only 1.5 m in length but 7.6 cm in diameter. The large intestine (or colon) stores waste products long enough so that water can be reabsorbed from the wastes. The large intestine (or colon) stores waste products long enough so that water can be reabsorbed from the wastes. Along with the water, some inorganic salts, minerals and vitamins are absorbed. Along with the water, some inorganic salts, minerals and vitamins are absorbed.

Large Intestine The large intestine is home to several different types of bacteria. The large intestine is home to several different types of bacteria. These bacteria use waste materials to synthesize vitamins B and K. This is an example of a symbiotic relationship. These bacteria use waste materials to synthesize vitamins B and K. This is an example of a symbiotic relationship.

Interesting Fact: Small Intestine In mammals the length of the small intestine is directly related to their diet. In mammals the length of the small intestine is directly related to their diet. Due to the fact that meats are easier to digest than plant materials, carnivores (lion) will have a shorter intestine than herbivores (rabbit). The length of the digestive tract of omnivores falls somewhere in the middle. Due to the fact that meats are easier to digest than plant materials, carnivores (lion) will have a shorter intestine than herbivores (rabbit). The length of the digestive tract of omnivores falls somewhere in the middle.

Absorption of Nutrients Chemical digestion of nutrients is completed by the time it reaches the large intestine. Chemical digestion of nutrients is completed by the time it reaches the large intestine. Now that nutrients are small enough they need to be absorbed into the blood stream so they can diffuse inside cells. Now that nutrients are small enough they need to be absorbed into the blood stream so they can diffuse inside cells.

The Accessory Organs

Salivary Glands There are 3 pairs of salivary glands. There are 3 pairs of salivary glands. Saliva is released from the salivary glands and it contains the enzyme salivary amylase which breaks down carbohydrates. Saliva is released from the salivary glands and it contains the enzyme salivary amylase which breaks down carbohydrates.

Pancreas The pancreas is an accessory organ of the digestive system. It releases chemicals to aid in digestion. The pancreas is an accessory organ of the digestive system. It releases chemicals to aid in digestion. It also releases a solution containing bicarbonate ion into the small intestine where it will neutralize the acidic chyme and raise the pH from 2.5 to 9.0. It also releases a solution containing bicarbonate ion into the small intestine where it will neutralize the acidic chyme and raise the pH from 2.5 to 9.0.

Liver & Gall Bladder The liver is a large accessory organ of the digestive system that is constantly producing a fluid known as bile. The liver is a large accessory organ of the digestive system that is constantly producing a fluid known as bile. Bile is stored in the gall bladder until it is needed in the small intestine. It will be released through the bile duct. Bile is stored in the gall bladder until it is needed in the small intestine. It will be released through the bile duct.