Block 2 NotesBlock 2 Notes

Digestive SystemDigestive System

Overview of the digestive Overview of the digestive systemsystem

There are three There are three main functions of main functions of the digestive the digestive system:system:

1. it ingests (takes 1. it ingests (takes in) food in) food

2. breaks the food 2. breaks the food down so nutrients down so nutrients can be absorbedcan be absorbed

3. eliminates what 3. eliminates what cannot be digestedcannot be digested

Overview cont.Overview cont. Types of digestion:Types of digestion: 1. 1. mechanical mechanical – – involves involves

chewing food to break it down chewing food to break it down into smaller pieces into smaller pieces (also uses (also uses the smooth muscles of the the smooth muscles of the stomach to help churn the stomach to help churn the food)food)

Chemical digestion Chemical digestion – – breaks breaks down large molecules of food down large molecules of food into smaller substances using into smaller substances using enzymesenzymes ( (the smaller stuff can the smaller stuff can be absorbed into the body’s be absorbed into the body’s cells more easilycells more easily))

Remember – enzymes are Remember – enzymes are proteins (a macromolecule) proteins (a macromolecule) that speed up reactions that speed up reactions (amylase is an enzyme found in (amylase is an enzyme found in saliva that starts the process of saliva that starts the process of chemical digestion by breaking chemical digestion by breaking starches down)starches down)

Organs that are part of the Organs that are part of the digestive systemdigestive system

Tongue, Tongue, esophagus, several esophagus, several sphincters, sphincters, stomach, small stomach, small intestine, large intestine, large intestine, intestine, pancreas, liver, pancreas, liver, gall bladder, colon gall bladder, colon

The path food takes during The path food takes during digestiondigestion

Starts in the mouth with saliva Starts in the mouth with saliva (enzymes begin breaking down (enzymes begin breaking down the food)the food)

The tongue pushes chewed food The tongue pushes chewed food to the back of the mouth which to the back of the mouth which stimulates swallowing reflexesstimulates swallowing reflexes

Food is forced into the upper Food is forced into the upper part of the esophagus part of the esophagus ((which is a which is a muscular tube that connects the muscular tube that connects the pharynx – or upper throat – to pharynx – or upper throat – to the stomachthe stomach))

The wall of the esophagus is The wall of the esophagus is lined with smooth muscles that lined with smooth muscles that contract to move the food contract to move the food through the digestive system through the digestive system (this is called (this is called peristalsisperistalsis) – even ) – even if you were upside down, food if you were upside down, food would still move toward your would still move toward your stomachstomach

When you swallow, your When you swallow, your epiglottis covers the trachea to epiglottis covers the trachea to prevent chokingprevent choking

Path of food cont.Path of food cont. When food leaves the esophagus, it When food leaves the esophagus, it

passes through a round muscle called passes through a round muscle called a a sphinctersphincter, and into the stomach., and into the stomach.

The The walls of the stomach walls of the stomach are made of are made of 3 overlapping layers of smooth 3 overlapping layers of smooth muscle that muscle that help digestion by help digestion by contractingcontracting, which , which breaks down the breaks down the food and mixes it with secretions of food and mixes it with secretions of gastric glands that line the inner wall gastric glands that line the inner wall of the stomachof the stomach

The gastric glands secrete (release) The gastric glands secrete (release) an acidic solution an acidic solution (if the sphincter (if the sphincter allows any of this through, it causes allows any of this through, it causes heartburn)heartburn)

Cells in the lining of the stomach Cells in the lining of the stomach secrete mucus to help prevent secrete mucus to help prevent damage from the aciddamage from the acid

Not much is absorbed in the stomachNot much is absorbed in the stomach The muscular walls of the stomach The muscular walls of the stomach

contract and push food farther along contract and push food farther along the digestive tract the digestive tract (at this point your (at this point your food is the consistency of tomato food is the consistency of tomato soup), soup), through another sphincter to through another sphincter to the small intestinethe small intestine

Path of food cont.Path of food cont. Your small intestine is about 7 meters Your small intestine is about 7 meters long; the first part is called the long; the first part is called the duodenumduodenum

The smooth muscles in the walls of your The smooth muscles in the walls of your small intestine continue to push food small intestine continue to push food farther through the digestive tractfarther through the digestive tract

The pancreas, liver and gallbladder all The pancreas, liver and gallbladder all help with chemical digestion herehelp with chemical digestion here

The pancreas produces enzymes that The pancreas produces enzymes that digest carbohydrates, proteins, and fats. digest carbohydrates, proteins, and fats. It also releases a fluid that raises the pH It also releases a fluid that raises the pH to a little above 7 to a little above 7 (this helps the (this helps the intestine enzymes survive)intestine enzymes survive)

The liver is the largest organ of the body The liver is the largest organ of the body and makes bile, which helps break down and makes bile, which helps break down fats fats (you make about 1 L of bile each (you make about 1 L of bile each day). day).

Extra bile is stored in the gallbladderExtra bile is stored in the gallbladder Digestion is completed here and most of Digestion is completed here and most of

the nutrients are absorbed in the small the nutrients are absorbed in the small intestine, into the bloodstream through intestine, into the bloodstream through fingerlike structures called fingerlike structures called villivilli

The remaining food, now in a semi-liquid The remaining food, now in a semi-liquid form called form called chymechyme, moves to the large , moves to the large intestine intestine – this is the stuff that couldn’t – this is the stuff that couldn’t be digested or absorbedbe digested or absorbed

Path of food contPath of food cont The large intestine is the end of The large intestine is the end of

the digestive tractthe digestive tract It’s about 1.5 meters long and It’s about 1.5 meters long and

includes the colon, the rectum, includes the colon, the rectum, and the appendixand the appendix

The colon absorbs water from the The colon absorbs water from the chymechyme

The indigestible material gets The indigestible material gets more solid and becomes your more solid and becomes your feces (poop)feces (poop)

Peristalsis continues to move Peristalsis continues to move feces toward the rectumfeces toward the rectum, , causing causing the walls of the rectum to stretch. the walls of the rectum to stretch.

This initiates a reflex that causes This initiates a reflex that causes the final sphincter muscle to the final sphincter muscle to relax, and eliminate the feces relax, and eliminate the feces through the anusthrough the anus

This entire process usually takes This entire process usually takes about 12-24 hours (most of the about 12-24 hours (most of the time is spent in the large time is spent in the large intestine)intestine)

AssignmentAssignment

Love letter: Students will write a five Love letter: Students will write a five paragraph love letter to their digestive paragraph love letter to their digestive system. (20 min)system. (20 min)

IntroductionIntroduction 3 reasons why they love their digestive 3 reasons why they love their digestive

systemsystem Conclusion/summaryConclusion/summary Diagram: Students will spend the Diagram: Students will spend the

remaining time coloring and labeling a remaining time coloring and labeling a digestive system diagram hat will go into digestive system diagram hat will go into their notebooks. (20 min)their notebooks. (20 min)