The Digestive System

The Digestive System

The Digestive System Introduction The digestive system is used for breaking down food into nutrients which then pass into the circulatory system and are taken to where they are needed in

the body. Introduction There are four stages to food processing: 1. Ingestion: taking in food 2. Digestion: breaking down food into nutrients 3. Absorption: taking in nutrients by cells 4. Elimination: removing

any leftover wastes The Human Digestive System Begins when food enters the mouth. It is physically (mechanically) broken down by the teeth. It is begun to be chemically broken down by amylase, an enzyme in saliva that breaks

down carbohydrates. The Human Digestive System The tongue moves the food around until it forms a ball called a bolus. The bolus is passed to the pharynx (throat) and the epiglottis makes sure the bolus passes into the esophagus and not down the

windpipe! The Human Digestive System The bolus passes down the esophagus by peristalsis. Peristalsis is a wave of muscular contractions that push the bolus down towards the

stomach. PERISTALSIS The Human Digestive System To enter the stomach, the bolus must pass through the lower esophageal sphincter, a tight muscle that keeps

stomach acid out of the esophagus. The Human Digestive System The stomach has folds and is a big muscular pouch which churns the bolus (Physical Digestion) and mixes it with gastric juice, a mixture of stomach

acid, mucus and enzymes. The Human Digestive System The acid kills off any invading bacteria or viruses. The enzymes help break down proteins Chemical Digestion. The mucus protects the lining of the

stomach from being eaten away by the acid. The Human Digestive System The stomach does do some absorption too. Some medicines (i.e. aspirin), water and alcohol are all absorbed through the stomach.

The digested bolus is now called chyme and it leaves the stomach by passing through the pyloric sphincter. The Human Digestive System

Chyme is now in the small intestine. The majority of absorption occurs here. The liver and pancreas help the small intestine to maximize absorption. The small intestine is broken down into three parts: The Human Digestive System

In first part of the Small Intestine: Bile, produced in the liver and stored in the gall bladder, enters through the bile duct. It breaks down fats. The pancreas

secretes pancreatic juice to reduce the acidity of the chyme. The Human Digestive System 2. In the middle portion of the small intestine:

The jejunum is where the majority of absorption takes place. It has tiny fingerlike projections called villi lining it, which increase the surface area for absorbing nutrients. The Human Digestive System Each villi itself has tiny fingerlike projections called microvilli, which further increase the

surface area for absorption. The Human Digestive System In the last portion of the small intestine: 3. There are fewer villi and basically compacts the leftovers to pass through into the large

intestine. The Human Digestive System The large intestine (or colon) is used to absorb water from the waste material leftover and to produce vitamin K

and some B vitamins using the helpful bacteria that live here. The Human Digestive System All leftover waste is compacted and stored at the end of the large intestine called the rectum. When full, the anal

sphincter loosens and the waste, called feces, passes out of the body through the anus. Digestion and Homeostasis The endocrine, nervous, digestive and circulatory systems all work together to

control digestion. Before we eat, smelling food releases saliva in our mouths and gastrin in our stomachs which prepares the body for a snack. The Hormone Gastrin Digestion and Homeostasis A large meal activates receptors that churn the

stomach and empty it faster. If the meal was high in fat, digestion is slowed, allowing time for the fat to be broken down. Hence why we feel fuller after eating a high fat meal.

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