DigestionDigestion

Bio 112Bio 112

The Digestive System must The Digestive System must accomplish the following tasks accomplish the following tasks

IngestionIngestion

Mechanical breakdown Mechanical breakdown

Chemical breakdown Chemical breakdown

Absorption Absorption

EliminationElimination

MouthMouthTeeth bite off and chew Teeth bite off and chew food into a soft pulp that food into a soft pulp that is easy to swallow. is easy to swallow.

Chewing mixes the food Chewing mixes the food with watery saliva, from 6 with watery saliva, from 6 salivary glands around salivary glands around the mouth and face, to the mouth and face, to make it moist and make it moist and slippery. slippery.

AmylaseAmylase is an is an enzyme that enzyme that breaks down breaks down starch into sugars starch into sugars

PharynxPharynx - a cavity that connects the mouth - a cavity that connects the mouth to the esophagus, it also connects the nose to the esophagus, it also connects the nose and mouth (via the larynx) with the tracheaand mouth (via the larynx) with the trachea

Esophagus Esophagus The The esophagus, esophagus, or gullet, is a or gullet, is a muscular muscular tube. tube.

•It takes food from the throat and pushes it It takes food from the throat and pushes it down through the neck, and into the down through the neck, and into the stomach. stomach. •It moves food by waves of muscle It moves food by waves of muscle contraction called contraction called peristalsisperistalsis..

StomachStomach

The stomach has thick muscles The stomach has thick muscles in its wall. These contract to in its wall. These contract to mash the food into a sloppy mash the food into a sloppy soup. soup. Also the stomach lining Also the stomach lining produces strong digestive produces strong digestive juices. juices. These attack the food in a These attack the food in a chemical way, breaking down chemical way, breaking down and dissolving its nutrients. and dissolving its nutrients.

Two valves control the entrances of Two valves control the entrances of food into and out of the stomach food into and out of the stomach

Pyloric Sphincter - Pyloric Sphincter - opening to the small opening to the small intestineintestine

Esophageal Esophageal Sphincter (cardiac)- Sphincter (cardiac)- opening between opening between esophagus and esophagus and stomach.stomach.

Esophageal Esophageal (cardiac)Sphincter(cardiac)Sphincter

It stops the acid in the stomach from flowing It stops the acid in the stomach from flowing back up (reflux) into the esophagus. back up (reflux) into the esophagus.

If there is damage or weakness to this valve, If there is damage or weakness to this valve, stomach contents, including stomach contents, including hydrochloric hydrochloric acidacid, flow up into the esophagus and cause , flow up into the esophagus and cause injury to the lining of the esophagus. injury to the lining of the esophagus.

This causes pain, commonly called This causes pain, commonly called "heartburn" or "acid reflux". "heartburn" or "acid reflux".

A layer of mucus prevents the A layer of mucus prevents the stomach from digesting itself. stomach from digesting itself.

Food in the stomach is Food in the stomach is converted into a thick acidic converted into a thick acidic liquid called liquid called chymechyme, which then , which then moves into the small intestine moves into the small intestine (via peristaltic contractions)(via peristaltic contractions)

Some substances are absorbed Some substances are absorbed directly into the blood stream directly into the blood stream from the stomach - alcohol and from the stomach - alcohol and water. water.

UlcersUlcers

When the mucus barrier of the stomach breaks When the mucus barrier of the stomach breaks down, the acids in the stomach erode a hole in the down, the acids in the stomach erode a hole in the stomach, causing an ulcer. stomach, causing an ulcer.

Causes of this problem vary, smoking and stress Causes of this problem vary, smoking and stress may be related to the development of ulcers. may be related to the development of ulcers.

Recently it was discovered that a bacteria Recently it was discovered that a bacteria (Heliobacter pylori) was present in many people (Heliobacter pylori) was present in many people with ulcers. with ulcers.

Treatment with antibiotics has eliminated the Treatment with antibiotics has eliminated the occurrence of ulcers in many people. occurrence of ulcers in many people.

Small IntestinesSmall Intestines

This part of the tract is narrow, but very long - This part of the tract is narrow, but very long - about 20 feet. about 20 feet.

Here, more enzymes continue the chemical Here, more enzymes continue the chemical attack on the food. attack on the food.

Finally the nutrients are small enough to pass Finally the nutrients are small enough to pass through the lining of the small intestine, and through the lining of the small intestine, and into the blood. They are carried away to the into the blood. They are carried away to the liver and other body parts to be processed, liver and other body parts to be processed, stored and distributed. stored and distributed.

The small intestine The small intestine consists of minute consists of minute fingerlike projects called fingerlike projects called villivilli, which increase the , which increase the surface area of the small surface area of the small intestines. intestines.

Nutrients are absorbed Nutrients are absorbed across the villi and into the across the villi and into the blood stream (via blood stream (via capillaries) as chyme capillaries) as chyme travels down the small travels down the small intestine. intestine.

Pancreas Pancreas The pancreas, like the The pancreas, like the stomach, makes powerful stomach, makes powerful digestive juices called digestive juices called enzymes which help to enzymes which help to digest food further as it digest food further as it enters the small intestines. enters the small intestines. It is involved in blood sugar It is involved in blood sugar regulation, as it secretes the regulation, as it secretes the hormone insulin which is hormone insulin which is involved in the breakdown of involved in the breakdown of sugarssugars

Gall BladderGall Bladder

This small baglike part is tucked This small baglike part is tucked under the liver. under the liver.

It stores a fluid called bile, which It stores a fluid called bile, which is made in the liver. is made in the liver.

As food from a meal arrives in As food from a meal arrives in the small intestine, bile flows the small intestine, bile flows from the gall bladder along the from the gall bladder along the bile duct into the intestine. bile duct into the intestine.

It helps to digest fatty foods and It helps to digest fatty foods and also contains wastes for also contains wastes for removal. removal.

Liver Liver The liver secretes a The liver secretes a substance called bile, substance called bile, which is essential for which is essential for digestion. Bile is digestion. Bile is stored in the gall stored in the gall bladder and released bladder and released into the small intestine into the small intestine via the common bile via the common bile duct. duct.

Also, blood from the intestines flows to the Also, blood from the intestines flows to the liver, carrying nutrients, vitamins and liver, carrying nutrients, vitamins and minerals, and other products from digestion. minerals, and other products from digestion.

The liver is like a food-processing factory The liver is like a food-processing factory with more than 200 different jobs. with more than 200 different jobs.

It stores some nutrients, changes them from It stores some nutrients, changes them from one form to another, and releases them into one form to another, and releases them into the blood according to the activities and the blood according to the activities and needs of the body. needs of the body.

It also serves to detoxify blood of harmful It also serves to detoxify blood of harmful substances like alcohol and nicotine.substances like alcohol and nicotine.

Large IntestineLarge Intestine

Any useful substances Any useful substances in the leftovers, such as in the leftovers, such as spare water and body spare water and body minerals, are absorbed minerals, are absorbed through the walls of the through the walls of the large intestine, back into large intestine, back into the blood. The remains the blood. The remains are formed into brown, are formed into brown, semi-solid feces, ready semi-solid feces, ready to be removed from the to be removed from the body. body.

The large intestine has The large intestine has two parts: the two parts: the coloncolon and the and the rectumrectum (the (the final last 15cm). The final last 15cm). The large intestine is home large intestine is home to bacteria that live on to bacteria that live on unabsorbed nutrients, unabsorbed nutrients, these bacteria do not these bacteria do not harm us, and in fact harm us, and in fact help us by synthesizing help us by synthesizing important vitamins. important vitamins.

Waste is transported to the rectum, Waste is transported to the rectum, expansion of this chamber induces the expansion of this chamber induces the urge to defecate. urge to defecate.