Review of Digestion & Metabolism

Question 1

What is digestion?

Answer 1

The process of breaking down food sufficiently to be absorbed by the body

Question 2

What is absorption?

Answer 2

The process by which the food moves into the body from the digestive tract

Question 3

What is transit time?

Answer 3

The amount of time it takes food to pass the length of the GI tract

Question 4

What is the effect of fiber on transit time and absorption?

Answer 4

• slows absorption but increases transit time

Question 5

How is gut microbiota important to health?

Answer 5

• Prevent pathogen entry via commensalism
• There is a link between types of bacteria in the gut and health
• Obesity, cancer, inflammation, cardiovascular disease, liver disease, and even some mental illnesses have all been linked with gut microbiota

Question 6

Obesity is correlated with…

Answer 6

Lower bacterial numbers and more pro-inflammatory species in the gut microbiome

Question 7

A plant-based diet has been shown to reduce symptoms of which GI disease?

Answer 7

• Crohn’s disease

Question 8

Is animal or plant protein more beneficial more gut microbiota?

Answer 8

• Plant protein; reduces inflammation and improves gut barrier

Question 9

How are carbohydrates digested and absorbed?

Answer 9

• Broken down by salivary amylase and pancreatic amylase, then further by brush border enzymes
• Absorbed into the portal vein

Question 10

How are proteins digested and absorbed?

Answer 10

• Broken down by gastric acid and pepsin, then by trypsin and other enzymes in the intestines
• Absorbed into the portal vein

Question 11

How are fats digested and absorbed?

Answer 11

• Broken down to fatty acids
• Long chain FAs (chylomicrons) must be absorbed by the lymph vessel to enter the blood as they are too large
• Short chain FAs can enter the portal vein

Question 12

Catabolism produces…

Answer 12

CO2

Question 13

What element does protein contain that the other nutrients do not?

Answer 13

NITROGEN is only present in protein – this is very important as the breakdown product is ammonia which is toxic and must be converted to urea to be excreted

Question 14

In the presence of oxygen, nutrients are broken down to form…

Answer 14

CO2, ATP, and water

Question 15

The urinary system eliminates…

Answer 15

Nitrogenous waste

Question 16

Ammonium ions from nitrogen travel to the ___ to be broken down as urea.

Answer 16

Liver

Question 17

Dietary fuels are ___ to produce energy.

Answer 17

Oxidized

Question 18

How is ATP produced in three steps?

Answer 18

1) Macronutrients are converted to acetyl-CoA
2) Acetyl-CoA enters the citric acid cycle in the presence of O2
3) Electrons are transferred to the electron transport chain, producing ATP and H2O

Question 19

What happens in the absence of oxygen?

Answer 19

• Anaerobic glycolysis (produces 2 ATP compared to 30)

- NADH is reoxidized continulously to reduce pyruvate to lactate

Question 20

Glucose levels in blood must remain almost ___.

Answer 20

Constant

Question 21

What is the fed state?

Answer 21

• Insulin is released after a meal
• Glucose used by the body for fuel and stored in the liver and muscle as glycogen
• Excess glucose stored as TGs in adipose tissue

Question 22

What is the fasted state?

Answer 22

• Glucagon released as blood sugars drop
• Results in glycogenolyisis to produce glucose until glycogen stores in liver are depleted
• Gluconeogenesis also occurs; glycerol, amino acids, and lactate are converted to glucose
• Fatty acids produce ketone bodies, which can be used for fuel

Question 23

What happens in starvation?

Answer 23

• After prolonged fasting, glycogen stores will be depleted
• Gluconeogenesis of glycerol, lactate, and amino acids decreases
• Muscle wasting can occur but decreases to preserve
• Muscle decreases use of ketones from FAs, whereas the brain increases its use
• Production of urea decreases after weeks
• RBCs and brain still need glucose to survive; cannot rely entirely on ketones

Question 24

When does death due to starvation occur?

Answer 24

• 40% of body weight is lost

- BMI of 11 for women, and 13 for men (30-50% protein lost, 70-95% fat depleted)