Lesson 59 - Digestive system

Question 1

What are the stages of digestion?

Answer 1

Ingestion - Food is taken into the body through the mouth
Digestion - Breakdown of large (insoluble) molecules (in the food) into small, simple (soluble) molecules (by mechanical and chemical means)
Absorption - The small (soluble) molecules can be absorbed through the lining of the small intestine (the ileum) into the blood
Egestion - Any food that can’t be digested is eliminated from the body (e.g. cellulose in plant cell walls)

Question 2

What is the difference between physical and chemical breakdown of large insoluble molecules?

Answer 2

Physical/mechanical breakdown - large food is broken down into smaller pieces by chewing with teeth in the mouth (mastication) and churning of the stomach muscles
Chemical digestion - Digestive enzymes hydrolyse large insoluble molecules into smaller soluble ones which can then be absorbed and used in the body

Question 3

How are starch molecules broken down?

Answer 3

1. Amylase catalyses the break down of starch to maltose. (By catalysing hydrolysis reactions that break the glycosidic bonds in starch)
2. Maltase (in the small intestine) breaks down maltose to glucose units

Question 4

Where is amylase produced?

Answer 4

• By the salivary glands, which release amylase into the mouth
• By the pancreas, which releases amylase into the small intestine

Question 5

What are membrane bound disaccharides?

Answer 5

They are enzymes attached to the cell membranes of epithelial cells lining the ilium (final part of small intestine). They help to break down disaccharides into monosaccharides, hydrolysis of glycosidic bonds.

Question 6

Which disaccharidase hydrolyses the 3 disaccharides?

Answer 6

Sucrose: Hydrolysed by sucrase into glucose and fructose
Maltose: Hydrolysed by maltase into glucose and glucose
Lactose: Hydrolysed by lactase into glucose and galactose

Question 7

How are monosaccharides transported across the epithelial cell membranes into the ileum?

Answer 7

Via specific transporter proteins

Question 8

How are lipids digested?

Answer 8

• Lipase enzymes catalyse the hydrolysis of ester bonds in lipids, to form monoglycerides and fatty acids

Question 9

Where are lipase enzymes found?

Answer 9

They are made in the pancreas, and then secreted into the small intestine

Question 10

What is the role of bile salts?

Answer 10

• They emulsify lipids, transforming the lipids into smaller droplets.
• This increases the surface area of the of the lipids, making their hydrolysis by lipase much faster
• Once hydrolysed, the monoglycerides and fatty acids stick to the bile salts forming micelles
• Micelles help the products of lipid digestion to be absorbed

Question 11

Where are bile salts made?

Answer 11

Liver

Question 12

How are proteins digested?

Answer 12

• They are broken down by a range of different peptidases (Enzymes that catalyse the conversion of proteins into amino acids by hydrolysing the peptide bonds between amino acids.

Question 13

What are the 3 enzymes that catalyse the hydrolysis of of proteins?

Answer 13

• Endopeptidases hydrolyse peptide bonds within a protein.
• Exopeptidases hydrolyse peptide bonds at the ends of protein molecules, they remove single amino acids from proteins.
• Dipeptidases are exopeptidases that work specifically on dipeptides. Often located in the cell surface membrane of epithelial cells (membrane bound dipeptidases) in the small intestine.

Question 14

What are some examples of endopeptidases and where are they produced/secreted?

Answer 14

• Trypsin and chymotrypsin: They’re synthesised in the pancreas and secreted into the small intestine.
• Pepsin: Released into the stomach by cells in the stomach lining. Only works in acidic conditions - provided by HCl in stomach.

Question 15

How are monosaccharides absorbed into the bloodstream across the ileum epithelium?

Answer 15

• Glucose and galactose are absorbed by active transport with sodium ions via a co-transporter protein.
• Fructose is absorbed via facilitated diffusion through a different transporter protein.

Question 16

How are monoglycerides and fatty acids absorbed into the bloodstream across the ileum epithelium?

Answer 16

• Micelles help to move monoglycerides and fatty acids towards the epithelium.
• Due to micelles constantly breaking up and reforming, they can release monoglycerides and fatty acids, allowing them to be absorbed.
• Monoglycerides and fatty acids are lipid soluble, so can diffuse directly across the epithelial cell membrane.

Question 17

How are amino acids absorbed into the bloodstream across the ileum epithelium?

Answer 17

• They are absorbed via co-transport similarly to glucose and galactose.
• Sodium ions are actively transported out of the ileum epithelial cells into the blood. This creates a sodium ion conc. gradient. Sodium ions can then diffuse from the lumen of the ileum into the epithelial cell through sodium dependent transporter proteins, carrying the amino acids with them.

Question 18

What is peristalsis?

Answer 18

The contractions/waves of the oesophagus

Question 19

What is the order that food travels from the mouth? Nd what are they for?

Answer 19

Mouth (food is ingested, teeth physically digest the food) and Salivary glands (produce amylase, starting the chemical digestion of starch)
Oesophagus (tube connecting mouth to stomach)
Stomach (Muscular bag that churns food (mechanical/physical digestion), adds acid and pepsin to start protein digestion)
Ileum (Long tube with villi, site of final stages of digestion and absorption of monomers)
Liver (Produces bile (for emulsification of fats) that is stored in the gall bladder)
Pancreas (Produces many digestive enzymes, released into the duodenum)
Large intestine (Where water and ions are absorbed)
Rectum (Storage of faeces before being expelled from the anus)