6.1. Digestion

Question 1

What is the main purpose of digestion?

Answer 1

To break down molecules into smaller subunits, as large molecules are chemically inert and insoluble and need to be broken down and reassembled into usable products

Question 2

Role of salivary glands

Answer 2

An accessory organ. Moistens food into a bolus and begins polysaccharide digestion.

Question 3

Role of oesophagus

Answer 3

Part of alimentary canal. Transports food to the stomach.

Question 4

Role of liver

Answer 4

An accessory organ. Detoxifies certain molecules. Stores vitamins, iron, glycogen. Synthesis bile. Breaks down haemoglobin.

Question 5

Role of stomach

Answer 5

Part of alimentary canal. A temporary storage tank where food is churned and protein digestion begins. Lined by gastric pits that release digestive juices, creating an acidic environment.

Question 6

Role of gall bladder.

Answer 6

An accessory organ. Stores bile produced in the liver and releases bile into the small intestine via the common bile duct.

Question 7

Role of pancreas.

Answer 7

Accessory organ. Releases digestive enzymes into the small intestine via the duodenum. Secretes hormones like insulin and glucagon which regulate sugar concentration.

Question 8

Role of small intestine.

Answer 8

Part of alimentary canal. A long highly folded tube where usable food substances (nutrients) are absorbed. Consists of the duodenum, jejunum and ileum.

Question 9

Role of large intestine

Answer 9

Final section of alimentary canal, where water and dissolved minerals (ions) are absorbed. Consists of the ascending / transverse / descending / sigmodial colon, as well as rectum

Question 10

What are the processes of mechanical digestion:

Answer 10

1. Chewing. Food broken down in the mouth by grinding of teeth. Tongue pushes food to back of throat, where it travels down the oesophagus as a bolus.
2. Peristalsis. Movement in the oesophagus. Continuous segments of longitudinal smooth muscle rhythmically contract and relax to move food along the alimentary canal.
3. Segmentation. Involves the contraction and relaxation of non-adjacent segments of circular smooth muscle in the intestines. Contractions move chyme in both directions, allowing for a mixing of food with digestive juices. Whilst this helps to physically digest food particles, it’s bidirectional propulsion of chyme can slow overall movement.

Question 11

Role of stomach acid in chemical digestion

Answer 11

Gastric glands release digestive acids to create a low pH environment. This denatures proteins and other macromolecules. The stomach epithelium contains a mucous membrane, preventing acids from damaging the gastric lining. The pancreas releases alkaline compounds, which neutralize acids as they enter the intestine.

Question 12

Role of bile in chemical digestion

Answer 12

The liver produces bile which is stored and concentrated in the gall bladder prior to release into the intestine. Contains bile salts which interact with fat globules and divide into smaller droplets (emulsification). This increases total surface area able for enzyme activity (lipase).

Question 13

Role of enzymes in chemical digestion

Answer 13

Biological catalysts which speed up the rate of a chemical reaction by lowering activation energy. They allow digestive processes to occur at body temperaturesnand at sufficient speeds for survival. Specific for a substrate.

Protease / endopeptidase - digest proteins into polypeptides
Amylase - digest starch into maltose
Nuclease - digest DNA / RNA into nucleosides
Lipase - digest triglycerides into fatty acids

Digested enzymes are secreted by the pancreas

Question 14

How are carbohydrates digested chemically?

Answer 14

Digestion begins in the mouth with the release of amylase from salivary glands. Amylase is also secreted by the pancreas to continue carbohydrate digestion within the small intestine. Enzymes for disaccharide hydrolysis are immobilized on the epithelial lining of the small intestine, near channel proteins.

Question 15

How are proteins digested chemically?

Answer 15

Protein digestion begins in the stomach with the release of Protease that function optimally in an acidic pH. Smaller polypeptide chains enter the small intestine where they are broken down by endopeptidase released in the pancreas. These endopeptidase work optimally in neutral environments as the pancreas neutralizes the acids in the intestine.

Question 16

How are lipids digested chemically?

Answer 16

Lipid breakdown occurs in the intestines, beginning with the emulsification of fat globules by bile released from the gall bladder. Smaller fat droplets are digested by lipase released from the pancreas.

Question 17

How are nucleic acids (DNA / RNA) chemically digested?

Answer 17

The pancreas releases nucleases which digest nucleic acids into smaller nucleosides

Question 18

What are the four layers of the small intestine?

Answer 18

Serosa - a protective outer covering composed of a layer of cells reinforced by fibrous connective tissue.
Muscle layer - outer layer of longitudinal muscle (peristalsis) and an inner layer of circular muscle (segmentation)
Submucosa - composed of connective tissue separating the muscle layer from the innermost mucosa.
Mucosa - a highly folded inner layer which absorbs material through its surface epithelium from the intestinal lumen.

Question 19

What do villi do?

Answer 19

They increase the surface area of epithelium over which absorption is carried out. They absorb monomers formed by digestion as well as mineral ions and vitamins.

Question 20

Features of villi

Answer 20

Microvilli - ruffling of epithelial membrane further increases surface area
Rich blood supply - dense capillary network rapidly transports absorbed products.
Single layer epithelium - minimizes diffusion distance between lumen and blood.
Lacteals - absorbs lipids from the intestine into the lymphatic system.
Intestinal glands - exocrine pits release digestive juices.
Membrane proteins - facilitate transport of digested materials into epithelial cells.

Question 21

What is secondary active transport?

Answer 21

FOR GLUCOSE AND AMINO ACIDS.

a transport protein couples the active translocation of one molecule to the passive movement of another. Glucose and amino acids are co-transported across the epithelial membrane by the active translocation of sodium ions.

Question 22

What is facilitated diffusion?

Answer 22

FOR MONOSACCHARIDES.

Channel proteins help hydrophilic food molecules to pass through the hydrophobic portion of the plasma membrane. Channel proteins are often situated near specific membrane-bound enzymes. Certain monosaccharides, vitamins and some minerals are transported by facilitated diffusion.

Question 23

What is osmosis?

Answer 23

FOR WATER.

Water molecules will diffuse across the membrane in response to the movement of ions and hydrophilic monomers (solutes).

Question 24

What is simple diffusion?

Answer 24

FOR TRIGLYCERIDES.

Hydrophobic materials may freely pass through the hydrophobic portion of the plasma membrane. Once absorbed, lipids will pass first into the lacteals rather than being transported via the blood.

Question 25

Discuss dialysis tubing.

Answer 25

Dialysis tubing can be used to model size-specific permeability of cell membranes. They contain small pores and are semi-permeable according to molecular size. Large molecules such as starch cannot pass through the tubing, but small molecules such as maltose can cross. However, dialysis tubing is not selectively permeable based on charge like the membranes of living cells.