Human Digestive System (Hope you don’t find this too hard to digest)

Objectives Look at the 4 components of the digestive system. Examine the pathway of digestion. Compare physical (mechanical) and chemical digestion. Look at the importance of enzymes in the process of digestion.

The 4 Components of Digestion 1.Ingestion:taking in nutrients. 2.Digestion:breaking down (processing) nutrients. 3.Absorption:transporting these broken down nutrients to body tissues. 4.Egestion:removing waste products.

5 Main Nutrients 1.Carbohydrates 2.Proteins 3.Lipids 4.Vitamins 5.Minerals

Carbohydrates Sugars and starches. Found in bread, cereal, fruit, & vegetables. Come from plant products. Carbohydrates will be broken down into molecules of Glucose.

Proteins Meat, eggs, nuts, beans, etc. Mainly come from animal products. Break down into Amino Acids.

Lipids (Fats) Oils, butter, margarine, shortening, lard, etc. Either plant or animal based products. Breaks down into molecules of Fatty Acids & Glycerol.

Vitamins Organic molecules (carbon based) that help regulate body processes, often working with enzymes.

Fat-Soluble Vitamins

Water-Soluble Vitamins

Minerals Inorganic nutrients that the body needs, usually in small amounts.

Minerals

Consumed but not considered nutrients Cellulose (Fibre): We are incapable of digesting it as we lack the enzymes needed to break it down. It is necessary in our diet as it creates bulk in the large intestine giving the muscles something to work against. Also helps to remove dead cells lining the Small Intestine. Water: It has no real nutritional value but necessary for all chemical and enzymatic reactions that take place in your body.

Components of the Alimentary Canal (Any part that food passes through) 1.Mouth 2.Pharynx 3.Esophagus 4.Stomach 5.Small Intestine 6.Large Intestine 7.Rectum & Anus

Accessory Organs (Play a role in digestion but food never enters them) 1.Salivary Glands 2.Liver 3.Gall Bladder 4.Pancreas

Handout Diagram of the Human Digestive System 1.Salivary Gland 2.Tongue 3.Esophagus 4.Epiglottis 5.Trachea (wind pipe) 6.Liver 7.Gall Bladder 8.Stomach 9.Common Bile Duct 10. Pancreas 11. Duodenum 12. Pancreatic Duct 13. Jejunum 14. Large Intestine 15. Ileum 16. Appendix 17. Rectum 18. Anus Note: Duodenum, Jejunum, & Ileum together make up the Small Intestine.

Video Clip

The Mouth Physical digestion involves the chewing of food. Chemical digestion involves the secretion of the enzyme Amylase from the salivary glands which partially breaks down carbohydrates. Amylase works best at a pH of 7 which is the pH of your mouth. Saliva helps to lubricate the Food Bolus. When you swallow, the Food Bolus travels through the Esophagus to the stomach. The Epiglottis closes off the Trachea allowing the food to go down the esophagus and NOT down the trachea and into your lungs!

Contraction of smooth muscle down the esophagus is called Peristalsis. This is how the food bolus moves down towards the stomach. If someone vomits it is referred to as Reverse Peristalsis. Once the food bolus enters the stomach a thick ring of muscles called the Cardiac Sphincter closes and prevents the contents of the stomach coming back up the esophagus.

The Stomach The site of food storage and initial Protein breakdown. Sphincter muscles regulate food movement to and from the stomach. Two Sphincters: 1. Cardiac Sphincter – esophagus & stomach. 2. Pyloric Sphincter – stomach & small intestine. Physical digestion – muscles of the stomach contract (churn) to further break down the food into Chyme.

Mucous Cells secrete mucous layers which protects the cells inside the stomach from the acidic environment. Oxyntic Cells secrete the hydrochloric acid (HCl) into the stomach. Chief Cells secrete the inactive enzyme Pepsinogen into the stomach.

The HCl maintains an acidic pH between 1 & 3. One function of the HCl is that it kills some of the bacteria which may otherwise make you sick. The HCl also changes the inactive enzyme Pepsinogen to the active form called Pepsin. Gastric Juice consists of pepsin, HCl, & water. If the gastric juice enters the esophagus then it results in acid reflux or heart burn. Chemical digestion – pepsin partially digests proteins. This enzyme works best at a pH between 1 & 3

Small Intestine The chyme entering the small intestine is covered with HCl from the stomach. Small Intestine lacks a thick mucous layer for protection against HCl. Therefore the Pancreas secretes Bicarbonate which travels through the Pancreatic duct to the small intestine to neutralize any HCl present therefore raising the pH level up to 8 – 9.

Physical digestion – Bile emulsifies fat (breaks fat globs down into smaller fat globules). Bile is made in the Liver, stored in the Gall Bladder and secreted into the Small Intestine by the Common Bile Duct. By breaking the fat into smaller globules the surface area is increased so that the fat digesting enzymes will work more efficiently. Chemical digestion – Amylase (same enzyme in Saliva) secreted by the pancreas to complete the break down of carbohydrates to Glucose molecules. The pancreas secretes the enzyme Lipase which completely breaks down fats into Fatty Acids & Glycerol molecules. The pancreas secretes two more enzymes Trypsin & Erepsin to complete the break down of proteins into Amino Acids. All pancreatic enzymes travel down the Pancreatic Duct to the Small Intestine.

The Pancreas Song

The end products of digestion are absorbed by the Small Intestine, which is lined with finger like projections called Villi that increase the surface area and rate of absorption. Each Villi is covered with Microvilli to further increase surface area and rate of absorption. Glucose & Amino Acids are directly absorbed into the Tiny Blood Vessels inside the Villi. Fatty Acids & Glycerol are absorbed into the Lacteals which are tiny Lymph vessels inside the Villi. The Lymph system empties into the Vena Cava where the Fatty Acids & Glycerol can now enter the blood stream.

Large Intestine (Colon) Where the small & large intestine join, there is a small projection called the Appendix. It contains a sample of all of your beneficial digestive bacteria. No digestion takes place in the Colon. Water is absorbed from the food waste back into the body along with vitamins and minerals. Too much water absorption – Constipation! Not enough water absorption – Diarrhea! Bacteria are present such as E. Coli cause the pH level to drop to 7 which is neutral. Some bacteria also produce vitamin K.

Rectum & Anus Food waste is passed into the Rectum and then excreted through the Anus out of the body. Food waste is called Feces or Fecal Matter.