Tissue Specific Metabolism

Question 1

Hepatocytes job

Answer 1

metabolize carbs, AA, and lipids into energy precursors for extra-hepatic tissues
maintain nutrient supply and precursor demand balance with enzymatic flexibility and sensitivity to hormones
demands depend on diet, feeding, level of activity and health

Question 2

metabolic flexibility

Answer 2

rapid turnover of enzymes to achieve metabolic requirements of other tissues

Question 3

White adipose tissue location and structure

Answer 3

Found under skin, around major blood vessels and abdomen

Squeezing nucleus and mitochondria into a thin layer against the plasma membrane, with 1 large lipid droplet

15% of body mass is white fat

Question 4

White adipose tissue metabolic capabilities

Answer 4

Energy source required: glucose, but can also oxidize pyruvate/FA

Can do fatty acid synthesis from glucose (insulin sensitive)
Stores TAGs and can hydrolyze TAGs to NEFA (epinephrine sensitive)
Cannot synthesize TAGs (lacks glycerol kinase)

Question 5

Brown adipose tissue location and structure

Answer 5

Found under skin around chest and back
Only/mostly found in babies (can differentiate from pre-adipocytes under extreme cold conditions)
Contain many mitochondria and many small lipid droplets

Question 6

Brown adipose tissue metabolic capabilities

Answer 6

Receive high blood supply/high metabolic demands
Can do fatty acid metabolize/beta oxidation for energy/heat
Unique thermogenin (uncoupling protein 1) production - non shivering thermogenesis (heat production)

Question 7

How non-shivering thermogenesis works

Answer 7

BAT cells can bypass ATP synthase with H+ gradient during oxidative phosphorylation and instead dissipate the energy as heat to protect viscera and nervous system
In babies this helps to maintain body temp during birth

Question 8

Skeletal muscle energy utilization under resting, moderate and heavy activity states

Answer 8

Uses FA and ketone bodies (yield acetyl-coA) and glucose for energy

Resting state: FA from adipocytes, and ketone bodies from liver
Moderate activity: blood glucose in addition to FA and ketone bodies

Heavy activity energy sources:
1) Glycogenolysis –> produce glucose (aerobic respiration) (3 ATP per freed glucose from glycogen)
2) Without sufficient ATP/O2, glucose to yield anaerobic lactate
Rapid response (epinephrine)
3) Phosphocreatine buffers ATP (maintain constant levels in cells) - by rapid regen of ATP from ADP - Creatine (diet or from 3 AA)

Can also do shivering thermogenesis - shivering motion helps to warm body

Question 9

Cori cycle

Answer 9

1) Glycogen broken down into lactate via anaerobic metabolism (ATP generated)
2) Lactate is brought to the liver where it is converted to glucose (requires ATP)

Lactate build up decreases pH of muscle, reduces efficiency

Question 10

Phosphocreatine/creatine system

Answer 10

During exercise: Phosphocreatine + ADP –> ATP + creatine
acts as buffer supply of ATP

During recovery: Creatine + ATP –> phosphocreatine + ADP

Question 11

Cardiac muscle metabolic needs

Answer 11

Requires constant aerobic metabolism - cells will die without O2 supply, which happens during a myocardial infarction

Cells contain abundant mitochondria
Energy source: fatty acids, but can also use ketone bodies and glucose (minimal stored glycogen)

Question 12

Cerebral metabolic needs

Answer 12

Energy source:
Neurons: glucose (130g glucose per day), but can use B-hydroxybutyrate during fasting/starvation (up to 60% energy)
Astrocytes: can metabolize fatty acids
- ATP is used to maintain Na-K-ATPase membrane requiremements
- Aerobic only, no glycogen stores

During starvation ketone bodies are produced and glucose produced via AA gluconeogenesis

Question 13

Slow twitch vs fast twitch muscle

Answer 13

Slow/red: low tension but high resistance to fatigue
Dense network of blood vessels for ATP production

Fast/white: high tension but fatigues quickly
Fewer mitochondria and blood vessels than red muscle
So fast that blood flow cannot provide oxygen fast enough

Question 14

Slow twitch muscle energy utilization in marathon case study

Answer 14

1) Until max heart/lung capacity is reached, anaerobic glycolysis occurs - takes 2 minutes to reach capacity (reliance on free ATP/phosphocreatine for 80m and then anaerobic glycolysis 2-3 ATP)
2) After 2 min, aerobic glycolysis kicks in
3) Before 45 minutes, anaerobic glycolysis peaks (uphill fight)
4) By 45 min, endorphins peak and runner’s high sets in
5) Glycogen stores are sufficient for about 30km
6) 1 hour 42 min runner’s wall - glycogen stores deplete/minimal glycolysis
7) Followed by fatty acid oxidation and slower ATP yield

Question 15

Fast twitch energy utilization sprinter case study

Answer 15

100m sprint:
1) first 20m ATP from phosphocreatine
2) 20-60m ATP from anaerobic glycolysis + phosphocreatine
3) last 40m ATP just from anaerobic glycolysis

Anaerobic glycolysis highest 2-5 seconds
Breathing still required to produce glucose via gluconeogenesis and replenish glycogen (cori cycle)