6.1 Digestion

Question 1

Why is digestion necessary?

Answer 1

Carbohydrates, lipids, proteins and nucleic acids are large, insoluble polymer molecules. They must be digested into monomers small enough to pass through the cell membrane of the cells lining the digestive tract so they can be absorbed into the bloodstream.

Minerals, vitamins and water can be absorbed directly (because of their small molecule size)

Question 2

The alimentary canal

Answer 2

Consists of organs through which food actually passes (oesophagus, stomach, small & large intestine)

Question 3

Accessory organs

Answer 3

Aid in digestion but do not actually transfer food (salivary glands, pancreas, liver, gall bladder)
- Secrete chemicals, enzymes

Question 4

Why do we need digestive enzymes?

Answer 4

Digestion involves hydrolysis of food molecules. Digestive enzymes catalyze the hydrolysis of insoluble food molecules to soluble end products.

Question 5

Digestion

Definition

Answer 5

Digestion is the break-down of large, insoluble food molecules into small, water soluble molecules using mechanical and chemical processes.

Question 6

Mechanical digestion

Answer 6

The mechanical breakdown of food into smaller pieces. It increases the surface area of the food so makes chemical digestion more efficient.
- Mechanical digestion occurs in the mouth (chewing) and in the stomach (churning).
- Some mechanical mixing of food also occurs in the oesophagus (peristalsis).

Question 7

Chemical digestion

Answer 7

The breakdown of insoluble food molecules into soluble molecules.
- This chemical change is usually carried out by enzymes, however some non-enzymatic chemicals (hydrochloric acid and bile) may also be involved.

Question 8

Six stages in the digestive process

Answer 8

1. Ingestion: the taking in of food
2. Mastication: the mechanical breakdown of food by chewing
3. Digestion: the mechanical and chemical breakdown of food in the alimentary canal
4. Absorption: the uptake of molecules through the intestine wall into the bloodstream
5. Assimilation: teh incorporation of absorbed food into various parts of the body
6. Egestion: the removal of non-absorbed molecules/waste

Question 9

Mouth

State its funtion

Answer 9

• Ingestion
• Teeth for mastication
• Tounge mixes food with salive which contains salivary amylase to digest starch into maltose

Question 10

Salivary glands

State its function

Answer 10

Produces salivary amylase which digests starch to maltose.

Question 11

Oesophagus

State its function (hint: peristalsis)

Answer 11

Takes food from mouth to stomach by peristalsis.
- Persitalsis is the process that occurs when we swallow: muscles along the oesophagus contract in waves, forcing the food through the oesophagus into the stomach.
- The smooth muscle contracts behind the bolus, forcing it forward.
- The smooth muscle relaxes in front of the bolus, allowing the bolus to move.

Question 12

Stomach

State its function

Answer 12

• Contains acid (HCl) to kill bacteria and to provide optimum pH for pepsin
• Produces pepsin to break down protein (into peptides)
• Churns food: Mechanical digestion

Question 13

Pancreas

State its function

Answer 13

• Produces a broad spectrum of enzymes that are released into the duodenum/the lumen of the small intestine: protease (trypsin - for dipeptides), amylase and lipase
• Also secretes certain hormones (insulin, glucagon), which regulate blood sugar concentrations

Question 14

Liver

State its function

Answer 14

• Produces bile, which is stored in the gall bladder: Bile is a yellow green alkaline solution.
• Stores glucose and amino acids absorbed into the body

Question 15

Gall bladder

State its function

Answer 15

• Stores bile: emulsifies fats in the duodenum and neutralises gastric juice (stomach acid) as it enters the duodenum.

Question 16

Small intestine - duodenum

State its function

Answer 16

Region where bile and pancreatic juices are released

Question 17

Small intestine - ileum

State its function

Answer 17

• Produces enzymes to complete digestion
• Absorption occurs here
• Absorb nutrients

Question 18

Large intestine - colon

State its function

Answer 18

Reabsorption of water, leaving solid waste (mostly fibre) which becomes faeces.

Question 19

Large intestine - rectum

State its function

Answer 19

Stores faeces

Question 20

Anus

State its function

Answer 20

Muscle that controls the release of faeces, location of egestion

Question 21

Where does peristalsis occur

Answer 21

Along the digestive tract: oesophagus, stomach?, and intestines

Question 22

Digestive enzymes for carbohydrates

Answer 22

• Salivary amylase produced in the salivary glands and released in the mouth
• Pancreatic amylase produced in the pancreas and released in the small intestine
• Maltase produced in the small intestine and released in the small intestine

Question 23

Digestive enzymes for protein

Answer 23

• Pepsin produced in the gastric glands and released in the stomach
• Trypepsin produced in the pancreas and released in the small intestine
• Peptidases produced in the small intestine and released in the small intestine

Question 24

Digestive enzymes for nucleic acids

Answer 24

Nuclease produced in the pancreas and released in the small intestine

Question 25

Digestive enzymes for fats

Answer 25

Lipase produced in the pancreas and released in the small intestine

Question 26

What are the processes occurring in the small intestine that result in the digestion of starch and transport of the products of digestion to the liver?

Answer 26

• When starch reaches the small intestine, it has to be broken down into smaller monomers to be absorbed
• This is done by amylase secreted from the pancreas
• Once the starch is broken down into simple sugars, those glucose molecules are absorbed and taken into the bloodstream
• If there is a large amount of sugar in the blood, the extra glucose will be stored as glycogen in the liver
• From there, it can be broken up and used as an energy source if blood sugar levels get too low

Question 27

Tissue layers in transverse sections of the small intestine

From outside to inside

Answer 27

• Longitudnal muscle
• Circular muscle
• Submucosa
• Mucosa
• Villi

Question 28

What is the main function of the small intestine and what allows it to carry out that function?

Answer 28

• To absorbe nutrients
• In order for this to happen at a high rate, the lining of the small intestine needs to have a large surface area: the small intestine has villi (and microvilli)

Question 29

Villi

Answer 29

• Finger-like projections that cover the walls of the small intestine and increase its surface area
• Villi have a large blood supply, with blood capillaries in each villus, so nutrients absorbed from the intestine can be transported away quickly.
• The villi have microvilli

Villi absorb monomers formed by digestion, mineral ions and vitamins.

Question 30

Microvilli

Answer 30

• The villi themselves have further finger-like projections called microvilli.
• Again, these increase the surface area of the small intestine, so nutrients can be absorbed more rapidly into the bloodstream.
• Increases the rate of absorption

Question 31

What can dyalisis tubing be used for?

Answer 31

To model absorption in the small intestine.
- The main reson for it being such a good model is that the tubing is designed with very tiny pores that only small molecules can pass through, just like the workings of the small intestine.

Question 31

Do different nutrients require different membrane transport methods?

Answer 31

Yes, it depends on their size and structure.
- Active transport: glucose, amino acids
- Facilitated difussion: monosaccharides
- Osmosis: water
- Simple difussion: triglycerides
- Endocytosis

Question 32

Which type of cell secretes mucus into the lumen of the small intestine to facilitate the movement of the chyme?

Answer 32

Goblet cells
Note: the chyme is the acidic fluid which passes from the stomach to the small intestine, consisting of gastric juices and partly digested food