Lecture 1 Digestion and Absorption Physiology Review

Question 1

What is energy in terms of physiology?

Answer 1

Energy is the capacity to do work and comes from the macromolecules, which are converted to ATP as a useful form (energy currency)

• Other carriers also capture energy-yielding nutrients such as NADPH.*
• ATP cannot be stored, but balance between ATP and ADP/AMP is highly regulated*

Question 2

How is most ATP created?

Answer 2

the oxidation of food fuels to CO₂ and H₂O; this is the exchange rate

Consists of substrate level oxidation and oxidative phosphorylation

Question 3

What is energy primarily required for?

Answer 3

• Basal metabolism
• Thermic effect of food
• Physical activity

Question 4

What else is produced with energy production?

Answer 4

The entire process of energy production also produces heat

Only a small fraction of total energy released from food is captured

Question 5

What are the sources of heat production?

Answer 5

• Obligatory (Essential)
• Regulatory

Question 6

How is ATP created?

Answer 6

In the mitochondria

Macronutrients go through separate processes but are eventually funnelled in the major reaction sequences, primarily leading to the CAC, ETC and finally ATPase.

Question 7

What is substrate level phosphorylation?

Answer 7

Transfer of a phosphate group from a substrate directly onto ADP to produce ATP

Transferring from a higher energy molecule to one of lower energy

Question 8

What is oxidative phosphorylation?

Answer 8

The process by which ATP synthesis is coupled to the movement of electrons through the mitochondrial electron transport chain and the associated consumption of oxygen.

It creates an electrochemical gradient in which 3 sites along electron transport chain transfer of H+ ions across membrane to generate ATP.

Question 9

What is the rate-limiting step of oxidative phosphorylation?

Answer 9

Availability of ADP

Question 10

What is the overall reaction of ATP synthesis?

Answer 10

Question 11

How much ATP is produced from 1 mole of glucose?

Answer 11

38 ATP

Question 12

What is the concept of ‘uncoupling’?

Answer 12

When there is a disruption to the normal functioning of the ETC mid-way which can decrease ATP production and result in more loss to heat

Question 13

What does more loss to heat cause?

Answer 13

• increase in O₂ consumption
• increase in oxidation of NADH & FADH without an increase in ATP production

Question 14

What is the general conversion of energy from foodstuff?

Answer 14

1. Total energy intake
2. digestible energy intake
3. Metabolizable energy
4. The energy available to couple to work
5. Energy actually used to accomplish work
6. External work done on the environment

Much of this is lost as heat as it progresses through the process

Question 15

What determines net ATP?

Answer 15

Efficiency of digestion, storage & metabolism processes determines net ATP

Question 16

What are the components of the digestive tract?

Answer 16

• Primary: oral cavity, pharynx, esophagus, stomach, SI, LI
• Accessory: teeth, tongue, glandular organs (salivary glands, liver, gallbladder, pancreas)

Question 17

What are the major functions of the GI tract?

Answer 17

• Digest complex molecules
• Absorb nutrients
• Barrier to entry of bacteria

Question 18

Why is the stomach so acidic?

Answer 18

Activate zymogens, denatures proteins, kills bacteria

Helps break down food for easier digestion

Question 19

How long is the SI?

Answer 19

10 ft or 3 m

Question 20

Major functions of the SI?

Answer 20

• Bulk of absorption
• movement of solute, water and nutrients

Question 21

Structure of the SI surface area

Answer 21

SI is a cylinder → circular folds of the mucosa → villi of mucosal surface → microvilli of absorptive epithelial cells of villi.

Question 22

What part of the SI is the major site of absorption?

Answer 22

jejunum

Question 23

What cells make up the epithelium of the SI?

Answer 23

Enterocyte

Very metabolically active and only 72 hour lifespan

Question 24

How are water soluble nutrients transported out of the SI?

Answer 24

enter directly into capillaries

Includes amino acids, monosaccharides, glycerol, short chain fatty acids (SCFAs), electrolytes, water- soluble vitamins - quick to absorb and transport about 15-45 min

Question 25

How are lipid soluble nutrients transported out of the SI?

Answer 25

transported via chylomicrons into lymphatics

Much slower absorption/ transportation

Question 26

Types of nutrient movement across membranes

Answer 26

• Passive movement
• Carrier/ receptor-mediated movement
  
  • facilitated, active, receptor-mediated

Question 27

Describe general lipid movement to the lymph

Answer 27

Lots of packaging and shipping steps

Question 28

What is a micelle?

Question 29

What are bile acids?

Answer 29

Synthesized by the liver and emulsify dietary fats

4g pool cycled up to 12 x / day (metabolize 10-50g/day)

Question 30

What are the primary bile acids?

Answer 30

Synthesized by the liver and emulsify dietary fats → break down larger fat globules in food into small droplets of fat.

• Smaller fat droplets are easier for the digestive enzymes from the pancreas to process and break down*.
• 4 g pool cycled up to 12 x / day (metabolize 10-50g/day)*

Question 31

Nutrient absorption in the stomach

Answer 31

Stomach

water, alcohol, some minerals

Question 32

Nutrient absorption in the SI

Answer 32

Small Intestine

most vitamins and minerals to varying degrees in the duodenum, jejunum & ileum

Question 33

Nutrient absorption in the jejunum

Answer 33

Jejunum

Lipids, monosaccharides, amino acids, small peptides

Question 34

Nutrient absorption in the ileum

Answer 34

Ileum

bile salts and acids

Question 35

Nutrient absorption in the large intestine

Answer 35

Large intestine

water, electrolytes, as well as vitamin K, biotin, SCFAs from bacteria

Question 36

What are the points of regulation in digestion and absorption?

Answer 36

• Digestion: gastric & pancreatic secretions, bile
• Absorption: surface area of the small intestine, motility, expression of transporters

Question 37

How are digestion & absorption regulated?

Answer 37

• Enteric nervous system: GI innervated by SNS (inhibitory) and PNS (stimulatory) nerve cells
• Hormones/ regulatory peptides: can be endocrine, paracrine, and/ or neurocrine; most have multiple actions (mostly either inhibitory or stimulatory)

Question 38

Hormones to know