Human Digestion (lesson three)

Question 1

Human Digestion

Answer 1

Humans have a complete digestive system

Question 2

what is the gastrointestinal tract?

Answer 2

The tube our food is digested through is called the gastrointestinal tract, or GI tract for short
- It is approximately 7-9 meters long
- Its purpose is to ingest, digest, absorb, and egest our food

Question 3

where does chemical and physical digestion start?

Answer 3

Both chemical and physical digestion of your food starts in the mouth

Question 4

how does the mouth digest physically?

Answer 4

It is broken down physically by your teeth by tearing and cutting with your incisors and canines and by grinding and crushing with your molars

Question 5

how does the mouth digest chemically?

Answer 5

It is broken down chemically with your saliva which contains enzymes

Question 6

what helps digest food in many ways?

Answer 6

your saliva helps digest your food in many ways

Question 7

Amylase

Answer 7

Amylase is an enzyme which breaks down complex carbohydrates into smaller disaccharides
- It also contains mucus which is a protective lubricant which helps you swallow

Question 8

bolus

Answer 8

When the food is ready to be swallowed as a moist ball of food it is called a bolus

Question 9

ingestion (Swallowing Food)

Answer 9

• your tongue pushes the food to the back of your mouth
• It is then pushed into the pharynx and your soft palate is raised to prevent food from entering your nasal passage
• At the same time the epiglottis covers the entrance to your trachea, called the glottis
• This process of taking food into the body by swallowing is called ingestion

Question 10

Esophagus

Answer 10

Once food is swallowed, it moves into the stomach through the esophagus
- This is a long muscular tube
- As it is stretched by the food, wave-like muscle contractions called peristalsis push the food downwards
- This process takes about 8 seconds

Question 11

The Stomach

Answer 11

• The food enters the stomach through a circular piece of muscle called the gastroesophageal sphincter
• When this muscle relaxes, food can enter the organ called the stomach
• The stomach can accommodate 2L of food
• Food mixed with gastric juices, now called chyme, exits the stomach through the pyloric sphincter

Question 12

Digestion in the Stomach

Answer 12

The stomach is also involved in both chemical and physical digestion of your food
- The muscle in the stomach churns and physically breaks down your food
- Digestive enzymes, like pepsin which breaks down proteins, chemically digest your food

Question 13

where does most of the digestion happen

Answer 13

Most of your digestion happens in the small intestines

Question 14

The Small Intestine

Answer 14

• ## This is a 7m tube about 2.5 cm in diameter that digests lipids, carbohydrates, and proteins

Question 15

how many sectors of there of a small intestine?

Answer 15

There are three sections
1. The duodenum
2. The jejunum
3. The ileum

Question 16

The duodenum

Answer 16

The duodenum, where most enzymes are added

Question 17

The jejunum

Answer 17

The jejunum, where digestion continues and some nutrients are absorbed

Question 18

The ileum

Answer 18

The ileum, where most of the nutrients are absorbed

Question 19

Absorption in the Small Intestine

Answer 19

• The inner surface of the small intestine is folded into many finger-like projections
• These are called villi and microvilli and function to maximize the surface area and absorption by a factor of 500
• The nutrients enter the bloodstream (i.e. are absorbed) through capillary beds in the villi
• This involves absorption in more than one way
• Simple diffusion that follows the concentration gradient (including osmosis)
• Facilitated diffusion through the use of a transport protein
• Active transport (goes against the concentration gradient) that uses transport proteins and ATP (energy molecule)

Question 20

The Large Intestine

Answer 20

• The large intestine is 1.5 m in length and 7.6 cm in diameter
• It is joined to the small intestines through the cecum where the appendix is also attached
• The colon is the longest part of the large intestine and is made up of the ascending, transverse, descending and sigmoid colon
• The last 20 cm is called the rectum which holds the feces until it can be eliminated, or egested, through the anus

Question 21

what important role does the large intestine play in?

Answer 21

The large intestine plays an important role in the absorption of:
- Water
- Ions
- Vitamins

Question 22

Egestion

Answer 22

• Egestion is the removal of waste food materials from the body
• These would include materials like cellulose and fibre (i.e. indigestible materials), which are important as they give us a full feeling for a longer time and reduce overeating
• Nerves in the large intestine detect the movement of food in the rectum and tell us to eject the food by a bowel movement