The Digestive System

What is Digestion?

-The mechanical and chemical breakdown of organic molecules into units small enough for the body to absorb. These molecules provide the nutrients and energy we need to function.

There are 2 types of digestion: mechanical and chemical

Mechanical Digestion

• Mechanical digestion means the food is getting smaller 
• Examples: chewing and grinding

Chemical Digestion

• Chemical digestion is breaking down chemical bonds
• Stomach acid, bile, and enzymes are used in chemical digestion 

Digestive System

• The digestive system is the organ system that takes in food, digests it, and excretes the remaining waste. 
• The digestive system is made up of the digestive tract and accessory organs.

Stages of Food Processing

1. Ingestion: the act of eating/ingesting.

• The mouth is involved in this process

2. Digestion: the process of breaking food into small enough molecules for the body to absorb

• The mouth and stomach are involved in this process

3. Absorption

• The small and large intestines are involved in this process

4. Elimination

• The large intestine and rectum are involved in this process

The Steps of Digestion

1. The mouth is the first part of the digestion process
2. Food in the mouth is mechanically broken down by the tongue and teeth. At the same time, saliva provides water and enzymes to chemically break down the food.  
3. Once the food is pulverized and softened, it passes through the esophagus to the stomach. 
4. Smooth muscle tissue contracts to mix the food with digestive enzymes and acids produced by the stomach lining.

Digestive Tract

• The digestive tract is very complex in humans. It consists of the mouth, esophagus, stomach, small intestine,  large intestine and anus. The accessory organs are the liver, gallbladder, and pancreas. 
• It takes in, breaks up, and digests the food and later excretes the waste. 

• Digestive tube is made up of layers of muscle, tissue and nerves

• If you end up eating spoiled food, your body will recognize the toxins which are produced by bacteria. The digestive tract will respond by removing the bacteria quickly. When this happens, you will experience vomiting or diarrhea. 

• This can also occur as a result of the consumption of too much alcohol or other poisonous substances. 

Mouth

• Helps break down foods mechanically and chemically

• The teeth and saliva (from the tongue) in the mouth break down foods mechanically 
• Enzymes (a type of chemical) help break down the molecules of foods chemically

• Saliva is a mixture of water and enzymes. Saliva is added to the food in your mouth
• Saliva is produced by cells from the epithelial tissue lining in the mouth
• After foods break apart and become softened by saliva, it is swallowed and goes down the esophagus

Pharynx

• The throat
• Epiglottis - this is a flap that makes sure the food goes down our pharynx and not into the lungs 

Esophagus 

• The esophagus is a muscular tube that connects your mouth to the stomach
• The muscles are called smooth muscle tissue

• They can contract and relax without conscious thoughts

• This is called peristalsis

• These movements are controlled by nerve tissue
• The contractions aid in the movement of food

Stomach 

• Its function is to hold and breakdown food, to continue the process of digestion
• It mixes food and releases hydrochloric acid (HCl) to further breakdown food.
• The stomach lining contains cells that produce digestive enzymes and acids.
• smooth muscle tissue contracts to mix the contents in your stomach
• It contains nerves that signal when we had enough food has been eaten

• The stomach has a pH of 2

Intestine

• In mammals, it is located between the stomach and the anus and the intestine
• The intestine’s lining produces mucus. It has many fine blood vessels which are interlaced through the other tissues
• They contain smooth muscles that contract and relax without conscious thought

Small Intestine

• Approximately 6 metres long
• Narrow
• The small intestine is where most of the digestion occurs
• Goblet cells release mucus and nutrients diffuse through the wall of the small intestine and enter the bloodstream

Large Intestine

• Also called the colon

• Approximately 1.5 metres long
• Larger in diameter compared to the small intestine
• It’s lining absorbs water and nutrient that come from indigestible foods into the bloodstream
• It passes undigested material to the rectum.
• The remaining solid matter comes out from the anus as feces

Rectum

• It stores feces until it is ready to be released through the anus

Epithelial Tissue

• The whole length of the digestive tract is lined with epithelial tissue. 

• Epithelial tissue is made up of goblet cells 

• Goblet cells excrete mucus. The purpose of the mucus is to:

• Protect the digestive tube from digestive enzymes
• Allows materials to pass through the tube smoothly

Accessory Organs

• The accessory organs are the liver, gallbladder, and pancreas. 
• They help in the digestion of foods by providing enzymes and other fluids

• Liver: produces bile to help breakdown fat by making the fat mix with water 
• Pancreas:  produces enzymes called insulin 

• Insulin regulates the concentration of glucose (sugar) in the blood. 
• secretes enzymes which break down our food 

• Gallbladder: stores the bile made by the liver

Disorders/Diseases

Diabetes

• Diabetes is a disease in the pancreas
• It is when the pancreas produces too much or too little insulin
• Symptoms include:

• Weakness
• Dizziness

• Caused by too high/low glucose levels

• Certain types of diabetes can be controlled by diet

Plants

• Plants are autotrophs which mean they can produce their own food

• They do this through photosynthesis
• Carbon dioxide + water = glucose + oxygen
• The leaf of a plant is an organ that performs photosynthesis

How does it work?

• Guard cells in the lower epidermis (dermal tissue) open up to allow carbon dioxide into the leaf  
• Xylem (vascular tissue) brings water from the roots into the leaf.  
• Chloroplasts in mesophyll cells (ground tissue) use carbon dioxide and water to make sugar and oxygen.  
• Sugar made in the leaves is transported by phloem (vascular tissue) to other plant parts