Starvation and Exercise

Question 1

What are the 4 stages of starvation?

Answer 1

-Post absorptive
-Early
-Intermediate
-Late

Question 2

Give a brief description of what happens at each stage of starvation

Answer 2

-Post absorptive: depletion of free glucose and stored glycogen. Gluconeogenesis initiated
-Early: Protein catabolism to support increased gluconeogenesis. Lipolysis initiated
-Intermediate: carbohydrate and protein sparing effects of increased lipolysis, ketogenesis
-Late: fat and protein depletion

Question 3

What are the 4 main metabolic priorities post prandial

Answer 3

-generate energy as needed in the form of ATP
-replenish glycogen
-store excess calories as triglycerides in adipose tissue
-synthesize new protein as needed

Question 4

What does insulin stimulate in the fed state?

Answer 4

-Glucose update: GLUT4 increases
-glycogen synthesis: glycogen synthase
-fatty acid uptake and TG storage and fatty acid synthesis: LPL and acetyl CoA carboxylase
-Protein synthesis

Question 5

What does insulin inhibit in the fed state?

Answer 5

-Glycogenolysis
-fatty acid release from TG in adipose

Question 6

Why is gluconeogenesis more active in carnivores and ruminants?

Answer 6

Because they take in less dietary glucose

Question 7

What does the liver do in the post absorptive phase?

Answer 7

transitions to gluconeogenesis to maintain blood glucose levels

Question 8

What happens in adipose tissues during the post absorptive state?

Answer 8

Lipolysis initiation, HSL is activated by glucagon and catecholamines

Question 9

What happens in muscle during the post absorptive state?

Answer 9

AA exchange, not breakdown of muscle protein. Switches to fatty acid oxidation for energy

Question 10

What is the primary glucogenic amino acid in the liver?

Answer 10

alanine

Question 11

What three molecules can muscle export to the liver for gluconeogenesis during the post absorptive state?

Answer 11

Pyruvate, alanine, and lactate

Question 12

What are the main processes that occur during early starvation?

Answer 12

-hepatic gluconeogenesis
-lipolysis increases
-ketogenesis initiates in the liver

Question 13

what is providing the glucogenic AA for gluconeogenesis in early starvation?

Answer 13

muscle protein breakdown

Question 14

Why is gluconeogenesis still running in early starvation? Why doesnt the body just switch to fatty acid for energy?

Answer 14

the brain relies on glucose

Question 15

What allows the heart to take up more fatty acids from VLDL TG in preference over adipose for use as energy during starvation?

Answer 15

The cardiac LPL had a 10 fold lower Km fro TG than adipose

Question 16

What are the 4 main gluconeogenic substrates during early starvation?

Answer 16

-Lactate
-Glucogenic AA
-Glycerol
-Propionate (mainly ruminants)

Question 17

What three organs transition to ketone body usage in early starvation?

Answer 17

muscle, heart, and kidney

Question 18

Why do muscle cells inhibit pyruvate dehydrogenase in mitochondria during early starvation?

Answer 18

so that pyruvate can be converted to alanine to export to liver for gluconeogenesis instead of entering the TCA cycle in the myocite

Question 19

Why can circulating VLDLs rise during early starvation in some species?

Answer 19

When the liver reesterifies some fatty acids to TG and package them for export to other tissues

Question 20

What is hepatic lipidosis?

Answer 20

abnormal accumulation of lipid in the liver

Question 21

What is the main cause of hepatic lipidosis in cats?

Answer 21

any disease leading to inadequate dietary intake or cellular nutrition

Question 22

What is the pathophysiology of hepatic lipidosis?

Answer 22

anorexia leads to usage of fat stores, increases FFA and uptake by liver, increased accumulation in the liver outpaces the ability of the liver to esterify FA into TG and export as VLDL, this can lead to hepatocyte swelling and membrane damage.

Question 23

What stage does the body switch to mainly fat for energy?

Answer 23

intermediate phase

Question 24

What happens in the brain during intermediate stage?

Answer 24

can begin to use ketone bodies ~70%, but still needs ~30% glucose

Question 25

What is the main gluconeogenic substrate during intermediate starvation? why?

Answer 25

glycerol, due to high fatty acid oxidation rates and protein conservation begins

Question 26

What happens to the BMR during intermediate starvation?

Answer 26

it drops due to thyroid hormone levels dropping

Question 27

What characterizes end stage starvation?

Answer 27

depletion of fat reserves

Question 28

All protein will be catabolized in end stage starvation, what is the order of protein catabolized?

Answer 28

-digestive enzymes
-liver enzymes for processing food nutrients
-muscle proteins

Question 29

What is refeeding syndrome?

Answer 29

It is when there is a sudden influx of calories and glucose which leads to insulin secretion. insulin drives movement of electrolytes from blood into cells, when electrolyte store are already low, this can lead to dangerously low levels causing hemolysis, arrhythmias, seizures, decreased cardiac output, coma.

Question 30

How much does cardiac output increase during exercise?

Answer 30

2-5 fold

Question 31

What 3 areas has increased blood flow during exercise?

Answer 31

coronary, skeletal muscle, and cutaneous blood flow

Question 32

Explain what happens to the GI blood flow during exercise?

Answer 32

-initially decreased
-with increased exercise duration hypoxia can occur so there is autoregulation that can result in vasodilation when needed

Question 33

What are the energy sources to skeletal muscle during sudden bursts of exercise?

Answer 33

-preformed ATP
-Glucose
-Creatine phosphate