MEH Session 11 Flashcards
Which fuel molecules are normally available in the blood?
Glucose
Fatty acids
Which fuel molecules are only available under special conditions?
Amino acids
Ketone bodies
Lactate
What is the difference between muscle and liver glycogen use?
Muscle glycogen - used to release glucose in muscle during exercise
Liver glycogen - used to release glucose into the bloodstream when blood glucose concentration is low
What determines the availability of fuel molecules in the blood?
Hormones
Changing activity of enzymes in metabolic pathways:
- intracellular signals
- metabolites
- signals from hormone action
Why is using amino acids as a fuel not ideal?
Amino acid metabolism can form ammonia.
Ammonia is toxic
How much glucose do we have in our bodies and for how long would this last?
3-6mmol/L g plasma glucose = 12g
Supports CNS for approximately 2 hours
Which cells can use fatty acids as their fuel?
Most cells except those with an absolute requirement for glucose
Which intermediate in the keys cycle can be used for fatty acid synthesis?
Citrate
Which intermediates of the krebs cycle can be used for amino acid synthesis?
Alpha-ketoglutarate
Succinate
Fumarole
Oxaloacetate
Which intermediate of the krebs cycle can be used in both the synthesis of haem and amino acids?
Succinate
Which intermediate of th e krebs cycle can be used for glucose synthesis?
Oxaloacetate
What are the symptoms of hypoglycaemia?
CNS function impaired Confusion Slurred speech Staggering Loss of consciousness Death
What happens to insulin concentration after you eat?
Increases in concentration
What are the effects of increased insulin concentration after feeding?
- increases glucose uptake and utilisation by muscle and adipose tissue
- promotes storage of glucose as glycogen in liver and muscle
- promotes amino acid uptake and protein synthesis in liver and muscle
- promotes lipogenesis and storage of fatty acids as triacylglycerols in adipose tissue
How does hormone concentration change when you are fasting?
As blood glucose concentration falls, insulin secretion is depressed. The falling of blood glucose concentration stimulates glucagon secretion (insulin/anti-insulin hormone ratio decreases)
What are the effects of increased glucagon when fasting?
-glycogenolysis in the liver to maintain blood glucose for the brain and other glucose dependent tissues
(Activates glycogen phosphorylase)
- lipolysis in adipose tissue to provide fatty acids for use by tissues (hormone sensitive lipase)
- gluconeogenesis to maintain supplies of glucose for the brain (PEPCK and fructose, 1,6 bisphosphatase)
When do changes associated with starvation begin?
10 hours
After feeding, for how long is glucose and fat available from the gut?
2 hours
After how long is glucose and fats no longer being absorbed?
2-10 hours after feeding
How does metabolism change 2-10 hours after feeding?
Maintain blood glucose by drawing on glycogen stores
Support other metabolic activity with fatty acids released from stores
Preserve blood glucose for the brain
How long after feeding are glycogen stores depleted?
8-10 hours
How does metabolism change 8-10 hours after feeding?
- need to make more glucose for brain from amino acids, glycerol and lactate
- continue to support other metabolism with fatty acids
What are the metabolic changes that occur after 10 hours after feeding?
Gluconeogenesis - breakdown of protein and fat
Glycerol from fat provides important substrate for reducing the need for breakdown of proteins
Ketone bodies - liver starts to produce ketone bodies and brain utilises these sparing glucose requirement
Kidneys begin to contribute to gluconeogenesis
Which hormones are released in response to starvation?
Cortisol from adrenal cortex
Glucagon from pancreas
What does the metabolic response to exercise ensure?
Increased energy demands met by mobilisation of energy stores
Minimal disturbances to metabolic homeostasis by keeping rate of mobilisation equal to equal to rate of utilisation
Glucose supply to brain is maintained
End products of metabolism are removed as quickly as possible
What does the magnitude and nature of the response to exercise depend on?
Type of exercise
Intensity and duration of exercise
Physical condition and nutritional state of individual
How long can creatine phosphate give you energy for during a 100m sprint?
Approximately 5 seconds
If you continue intensive exercise for up to 2 minutes, how can it be sustained?
Breakdown of muscle glycogen
What is the cori cycle?
Liver recycles lactate produced by anaerobic metabolism
Does anaerobic respiration usually occur with an hour of low intensity exercise?
No
How is glucose uptake adapted in exercising muscle?
Usually muscle takes up blood glucose via GLUT4 transporter (insulin promotes translocation to plasma membrane) and GLUT1 (constitutively active)
Exercising muscle also has insulin independent process of glucose uptake (increase in AMP stimulates AMPK resulting in a signalling cascade which increases GLUT4 translocation)
How long could fatty acids theoretically provide energy for in low intensity exercise?
48 hours
Can fatty acids be used as a fuel in anaerobic conditions?
No
What are the limitations of using fatty acid as a fuel?
Can only be used in aerobic conditions
Slow release from adipose tissue
Limiting carrying capacity in blood
Capacity limited by uptake across mitochondrial membrane (carnitine shuttle)
Low rate of ATP production (but high capacity for sustained production)
Which fuel stores are used in a 100m sprint?
Creatine phosphate
Glucose
Muscle glycogen
Describe the metabolic processes that occur during a 100m sprint.
Anaerobic respiration - lactate production and build up in H+
Which fuel stores are used in a 1500m race?
Initial start - creatine phosphate, anaerobic muscle glycogen
Long middle phase - aerobic muscle glycogen
Final finishing sprint - anaerobic muscle glycogen
Which fuel molecules are used when running a marathon?
Muscle glycogen - depleted within a few minutes
Liver glycogen - glucose from liver glycogen peaks at 1 hour and then declines steadily
Fatty acids - rises steadily from 20-30 minutes
Describe the hormonal response to running a marathon.
Insulin falls slowly (inhibition of secretion by adrenaline)
Glucagon rises
Adrenaline and growth hormone rise rapidly
Cortisol rises slowly
What are the effects of increases glucagon when running a marathon?
-glycogenolysis in the liver to maintain blood glucose for the brain and other glucose dependent tissues
(Activates glycogen phosphorylase)
- lipolysis in adipose tissue to provide fatty acids for use by tissues (hormone sensitive lipase)
- gluconeogenesis to maintain supplies of glucose for the brain (PEPCK and fructose, 1,6 bisphosphatase)
What are the effects of increases adrenaline and growth hormone when running a marathon?
- adrenaline stimulates glycogenolysis and lipolysis
- growth hormone mobilises fatty acids (lipolysis)
What are the effects of increased cortisol when running a marathon?
Gluconeogenesis
Lipolysis
What are the benefits of exercise?
- body composition changes (decreased adipose and increased muscle)
- glucose tolerance improves (increased muscle glycogenesis)
- insulin sensitivity of tissues increases
- blood triglycerides decrease (decreases VLDL LDL, increases HDL)
- blood pressure falls
Give five cellular functions of calcium.
Neuromuscular excitability Coagulation - it is factor IV Synaptic transmission Second messenger for hormones and growth factors Regulation of gene transcription Bone formation
What is EDTA and what is it used for?
Calcium chelator - used to prevent blood from clotting when taking blood samples for a full blood count
Why do you have to give intravenous calcium to patients who have received >5 units of blood?
Citrate is a calcium chelation which is put into bags of blood obtained from donors to prevent the blood from clotting.
Therefore, the recipient will be hypocalcaemic if they are transfused with large quantities of blood.
What is normal plasma calcium concentration?
2.2-2.6mmol/L
What is normal biologically active free ionised plasma concentration of Ca2+?
1.0-1.3mmol/L
Give 5 cellular roles of phospate.
- part of ATP (energy carrier)
- activation and deactivation of enzymes
- part of membrane phospholipids
- part of DNA/RNA
- bone formation
Is plasma phosphate concentration well regulated?
No - levels fluctuate throughout the day, particularly after meals