Macronutrients (L10)

Question 1

What are the three macronutrients in the human diet?

Answer 1

• Carbohydrates
• Fats
• Proteins

Question 2

What protein mediates the entry of triglycerides into cells?

Answer 2

Lipoprotein lipase

Question 3

What effect does insulin have on lipoprotein lipase

Answer 3

Upregulates it

Question 4

What digests fats in the mouth?

Answer 4

Lingual lipase, which is released by lingual glands

Question 5

What digests fats in the stomach?

Answer 5

Gastric lipase, which is released by gastric cells in the proximal stomach.

Question 6

What percentage of lipid digestion is by lingual lipase and gastric lipase?

Answer 6

• In neonates, it makes up for 50% of lipolysis

- In adults, it makes up for 30% of lipolysis

Question 7

What are the main components of bile?

Answer 7

• Bile acids
• Phospholipids
• Cholesterol
• Inorganic salts

Question 8

What digests fats in the small intestine?

Answer 8

• Pancreatic lipase

Question 9

What is the role of pancreatic lipase and colipase in fat digestion in the small intestine?

Answer 9

• Pancreatic lipase gets secrete from the pancreas alongside the co-factor pro-colipase
• Pro-colipase gets activated in the intestinal lumen by tyrosine to form colipase
• Colipase then stabilises pancreatic lipase, increasing its efficiency

Question 10

What does pancreatic lipase digest triglycerides into?

Answer 10

• Monoglyceride
• Fatty acids
• Glycerol

Question 11

How do monoglycerides and fatty acids get absorbed through the small intestine?

Answer 11

They cross the apical membrane of microvilli via lipid transporter proteins

Question 12

What happens to excess dietary carbohydrates?

Answer 12

They are stored as glycogen or fat

Question 13

Describe the digestion of starch

Answer 13

Alpha-amylase gets secreted by the salivary glands and pancreas and it digests starch into maltose, maltotriose (3x glucose) and alpha-dextrine

Question 14

What are the only three carbohydrates that can be absorbed in the small intestine?

Answer 14

• Glucose
• Fructose (limited)
• Galactose

Question 15

What happens to fibre from the diet?

Answer 15

Gets fermented by bacteria in the colon, producing short chain fatty acids (acetate, propionate and butyrate) which enhance bacterial growth

Question 16

What is the process of protein digestion in the stomach?

Answer 16

• Pepsinogen gets released by chief cells
• HCl gets released by the parietal cells
• Both are released in response to gastrin and the Vagus nerve
• The lowered pH (<5) converts pepsinogen into pepsin, which then breeks down protein

Question 17

What are the two primary pancreatic proteases?

Answer 17

• Trypsin
• Chymotrypsin
• Both are secreted in their inactive form (trypsinogen and chymotrypsinogen)
• Enterokinase, an enteropeptidase, is secreted by the mucosal membrane of the duodenum (Brunner glands) and it activates the enzymes

Question 18

Apart from breaking down proteins, what else does trypsin do?

Answer 18

Activates inactive proteases (e.g. chymotrypsinogen and proelastase

Question 19

How are amino acids absorbed in the small intestine?

Answer 19

• After binding to Na+, transporters then bind to amino acids
• The transporter then becomes fully loaded and undergoes a conformational change that causes the amino acid and Na+ to be released into the cytoplasm
• The transporter then changes back into its original shape