Where does Food go? The Digestive System

Where does Food Go?

• The cells of the human body cannot use food directly for energy

• Food must be transformed in the digestive system before it can be put to use

• The role of the digestive system is to break down ingested food into molecules that are small enough to be absorbed by the body’s cells

• It eliminates undigested food in the form of solid waste

Transformation and Selection

• The food and air (oxygen) that enter your body are known as INTAKE.

• The INTAKE is not utilized by the body in the form in which it enters: it undergoes transformation or change and then a selection process.

• Your DIGESTIVE SYSTEM breaks down and sorts that intake.

• It transforms the food by mechanical and chemical transformations.

Mechanical Transformation

• Changes the appearance and movement of food from one place to another

• The composition (what its made of) of the resulting food remains unchanged

• Examples

– Ingestion in the mouth: INCREASES the surface area of the food in order to aid in chemical digestion

– peristalsis series of involuntary wave-like muscle contractions which move food along the digestive tract

– Churning : produced by muscle contractions, which mix food with digestive secretions

Peristalsis

Chemical Transformations

• Breaks down complex molecules into simpler molecules

• Occurs with the help of secretions from the digestive glands

• Is carried out by the digestive ENZYMES

The Digestive System • Can be broken into 2 parts:

– Digestive tract

– Digestive glands

• The digestive tract is composed of:

– The mouth

– The pharynx

– The esophagus

– The stomach

– The small intestine

– The large intestine (which ends with the rectum and anus)

Diagram of the Digestive System

1. teeth

2. epiglottis

3. liver

4. Gall bladder

5. Common bile

duct

6. Large

intestine

7. appendix

8. Salivary

glands

9. tongue

10. esophagus

11. stomach

12. duodenum

13. pancreas

14. Small

intestine

15. Rectum/

anus

• Digestion is a complicated process that involves

1. Ingestion - process of taking food into the digestive system so that it may be digested.

2. propulsion – movement of food along the digestive tract

3. digestion- the breakdown of food (either chemically or mechanically) in order to utilize nutrients

4. Absorption of nutrients

5. Elimination of fecal matter

Oral Cavity/Mouth • Includes both mechanical and chemical

transformations

• The tongue and teeth work together, breaking food apart and pushing it around.

• The resulting mixture is called the bolus

• Saliva pours into the mouth from salivary glands to begin digesting food, softening and lubricating it on its way.

• The tongue pushes against the roof of the mouth as you swallow, helping push food down the food tube (esophagus).

Teeth

• Incisors – CUT food

• Canines – TEAR & SHRED food

• Premolars & Molars – CRUSH & GRIND food

Esophagus • is about 10 inches long in an

adult. • It lies behind your windpipe

(trachea) and is flattened when empty.

• As you swallow, you stop breathing for a moment. • A trapdoor called the epiglottis automatically closes the

opening to your airway and lungs, and the soft palate at the back of the roof of your mouth swings up to shut off the passage to your nose.

• If you swallow too fast, the epiglottis may not have time to close, causing you to cough to clear out any food that might enter the trachea.

• The muscles in the esophagus ripple to push the food into the stomach using a movement called peristaltism.

Stomach

• Normally, these acids are not manufactured until food is in

the stomach and a protective mucus coats the stomach. • Like a balloon, the stomach expands with food. The

muscles which surround it begin to churn the food back and forth.

• Contains gastric juices made of hydrochloric acid and the enzyme pepsin are released to break down protein in your food.

• These acids are strong enough to eat through the wall of the stomach.

• Carbohydrates move out first and then

proteins. Fats are the last to leave the stomach. Some food may remain in the stomach for two to five hours.

• The food is now called chyme; it is a thick liquid. The chyme squeezes into the Duodenum (1st part of the small intestine).

Small Intestine • Duodenum, the first 10 inches of the small intestine

where the digestive process will be completed by other juices.

• The following organs are found around the intestine and release digestive substances to aid digestion: – The pancreas -- pancreatic juice – The liver – bile

• Pancreatic juices and bile flow into the duodenum through the bile duct and mix with the intestinal juice to complete digestion

• Small Intestine now has the completely digested food and it has been changed to nutrients which can now be absorbed through tiny fingers (villi) that line the walls of the small intestine.

• Tiny blood vessels are inside the villi. They take in the vitamins, minerals, and other nutrients and carry them to all parts of the body through the blood systems.

• The journey through the small intestine may take four to eight hours.

• What remains undigested passes into the large intestine.

Large Intestine • Large Intestine where food

spends 10 to 12 hours losing large quantities of water and nutrients.

• At the end, the solution is fed on by a colony of bacteria which decay the remains (feces).

• The feces are brown because they contain dead blood cells. • What is left of your meal passes to the rectum, ready to leave the body through the opening called the anus. • The entire journey lasts about 15 to 48 hours.

The Liver

• An organ in the upper abdomen that aids in digestion and removes waste products and worn-out cells from the blood.

• Bile is made by the liver and stored in the gall bladder. Bile works like a detergent to emulsify (soften) fats so they can be dissolved in water and absorbed into the body. – Also neutralizes acids in partly digested food.

• The liver is the largest solid organ in the body.

• The liver has many functions. Some are:

1. to produce substances that helps to break down fats

2. convert glucose to glycogen

3. produce urea (the main substance of urine),

4. make certain amino acids (the building blocks of proteins)

5. filter harmful substances from the blood (such as alcohol & drugs)

6. storage of vitamins and minerals

7. maintain a proper level or glucose in the blood

8. producing cholesterol.

The Pancreas

• The pancreas is a glandular organ that secretes (releases) digestive enzymes and hormones. In humans, the pancreas is a yellowish organ.

• the pancreas produces pancreatic juice to digest carbohydrates, proteins, and fats.

• The pancreas lies beneath the stomach and is connected to the small intestine at the duodenum.

• The pancreas produces the body's most important enzymes. The enzymes are designed to digest foods and break down starches.

• also produces the hormone insulin and secretes it into the bloodstream in order to regulate the body's glucose or sugar level.

• The pancreas also helps neutralize chyme and helps break down proteins, fats and starch.

• If the pancreas is not working properly to neutralize chyme and break down proteins, fats and starch, starvation may occur.

The Gall Bladder

• The gallbladder is a small pear-shaped organ.

• The gallbladder is connected to the liver by a duct.

• The function of the gallbladder is to store bile.

• A muscular valve in the common bile duct opens, and the bile flows from the gallbladder into the duodenum (part of the small intestine).

Chemical Transformations

Digestive glands

• A gland is an organ or group of cells that produces secretions

• Secretions are chemical substances (such as hormones) or liquids (such as sweat or maternal milk) that have different functions in the body

• Digestive glands secrete substances that aid in the digestion of food

Digestive Glands and Secretions

Digestive Glands

Secretions Location Targets

Salivary glands Saliva Mouth

Gastric glands Gastric juice Stomach

Intestinal Glands

Intestinal juice Small intestine

Pancreas Pancreatic juice

Small intestine

Liver Bile Small Intestine

Starch (complex carbs)

proteins

Proteins, carbs,fats

Proteins, carbs,fats

fats

Chemical Transformations

• In a chemical transformation, the bonds of complex molecules are broken, which gives new more simple substances

Type of Nutrient Complex Molecules (example) Simple Molecules (example)

Carbohydrate Startch

glucose

Fats triglyceride Glycerol and fatty acids

Proteins Enzymes Amino acids