The Digestive System Ms. Marcos Moving into human body systems!

What does your digestive system look like? The tube starts here: And although there are a few twists and turns along the way… Anything that goes in the top hole (mouth) does not become part of the body until it is broken down then absorbed though a series of specialized structures. It comes out here:

What does the digestive system do? DIGESTION: Mechanical vs. Chemical ABSORPTION: Food molecules enter the blood or lymph Helps you make… ATP! ELIMINATION: Wastes / undigested food leave Large pieces of food to smaller pieces Enzymes break apart a molecule of food

The parts of the digestive system… Mouth Tongue Salivary glands Oral cavity Pharynx Esophagus Stomach Pyloric sphincter Liver Gall-bladder Pancreas Small intestine Large intestine Anus Rectum

Many parts work together and are coordinated by hormones.

A Tour of the Digestive System Mouth Tongue, teeth, salivary glands, pharynx Enzymes Esophagus Epiglottis and choking Peristalsis Stomach Cardiac and pyloric sphincters and stomach cell types Enzymes and gastric secretions Pancreas Digestion enzymes, pH balance and maintenance of blood sugar Liver / Gall bladder Roles in digestion and other body processes Small intestine Specialization – structure and function three sections and of the villi Enzyme action Large intestine Functions and anaerobic bacteria within Rectum and Anus Expulsion of wastes

A Tour of the Digestive System

The Mouth – Where digestion begins Hard palate Soft palate uvula Stops liquid or food from coming out your nose when you swallow Tongue moves around the food forms a bolus (a ball of food)

Types of teeth There are different types of teeth for different functions: Cutting and tearing food Grinding and mashing food Crushing and grinding food Cutting and chopping food

What’s in saliva and what does it do? Water Makes food soft Mucus Helps food slide down the esophagus Bicarbonate ions neutralize acid produced by bacteria (helps prevent tooth decay) Salivary amylase breaks down starch in the presence of water Starch  maltose (a disaccharide of glucose) How much saliva do you produce in a day? About 1-2 litres!

A Tour of the Digestive System

A Tour of the Digestive System Mouth Tongue, teeth, salivary glands, pharynx Enzymes Esophagus Epiglottis and choking Peristalsis Stomach Cardiac and pyloric sphincters and stomach cell types Enzymes and gastric secretions Pancreas Digestion enzymes, pH balance and maintenance of blood sugar Liver / Gall bladder Roles in digestion and other body processes Small intestine Specialization – structure and function three sections and of the villi Enzyme action Large intestine Functions and anaerobic bacteria within Rectum and Anus Expulsion of wastes

Traveling to the stomach… Esophagus Tube from pharynx to stomach Mucus membranes Helps the food slide down Muscle Pushes the food down the tube Food moves down by peristalsis

Peristalsis (and reverse peristalsis) How long does peristalsis take? About 9 seconds from pharynx to stomach (rate of 2-4cm/s) Swallowing Animation

Swallowing… Uvula moves back to cover openings to nose Trachea moves up Epiglottis covers the trachea Food goes down by peristalsis

Reaching the stomach… Cardiac sphincter Closes the top of the stomach Made of muscle What is heartburn and what causes it? Opening of the cardiac sphincter allowing food (soaked in stomach acid) to enter the esophagus. http://www.youtube.com/watch?v=1ZIK6Ua20JA

A Tour of the Digestive System

The Stomach How big is your stomach? About 1.5 to 2L in an adult human (300L in a cow!) This is a rabbit stomach

The Stomach PEPSIN J-shaped organ Three layers of muscle Mix up and break up the food Gastric glands make gastric juice Gastric juice has: Pepsinogen + Hydrochloric acid  Pepsin PEPSIN an enzyme: proteins  peptides (small protein sections)

Within the walls of the stomach… Pepsinogen Pepsin (Activates more Pepsinogen) HCl Gastric gland Mucus cell (shown in red) Parietal Cell Peptic cell

3 types of cells in the stomach: Mucus cells Mucus protects the stomach Parietal cells Secrete acid (HCl at pH 3) kills bacteria and helps break food down Peptic cells Secrete pepsinogen to make pepsin

Why doesn’t the stomach digest itself? HCl could eat through the stomach Stopped by the mucus layer Pepsin could digest protein in the stomach cells Pepsin is only made when pepsinogen mixes with HCl

When things go wrong… Bacterial infections Cells can’t make mucus Can cause ulcers and stomach cancer http://www.youtube.com/watch?v=1ZIK6Ua20JA&feature=channel_page

How long does food stay in your stomach? 2 - 6 hours Chyme = liquid food that leaves your stomach Enters the small intestine controlled by the Pyloric Sphincter muscle at the bottom of the stomach

Digestion Questions #1: Explain the step by step process that occurs when someone chokes on a piece of food. What goes wrong? (1) you are drinking water and accidentally laugh, causing the water to come out of your nose. What goes wrong? (1) Explain all the types of digestion that occur in the mouth. (2) What possible problem could lead to an esophageal ulcer? Explain what would happen to cause this. (2) Explain all the types of digestion that occur in the stomach. (2) If someone had a severe ulcer, would it be possible to remove his or her stomach and replace it with a bag? What properties would this bag need to have in order to function? How would that person’s diet need to change? (3)