Blood Lactate (S1) Flashcards
(38 cards)
How does the rate of ATP production from glycolysis compare to oxidative phosphorylation from carbohydrates and fats?
Glycolysis provides ATP at a high rate (as it’s anaerobic so doesn’t need oxygen)
- 2x rate of oxidation from carbs
- > 3x rate of oxidation from fat
Does lactate only get produced in cells during hypoxia / what is it dependent on?
No, lactate production is not independent of oxygen levels (lactate is still produced in cells with loads of oxygen)
- it’s primarily dependent on the rate of energy demand in the cells
How do H+ ions contribute to fatigue during high-intensity exercise?
H+ ions lower pH, which causes a decrease in muscle function by impairing enzyme activity and contributing to fatigue
What other substances, besides H+, are linked to fatigue during anaerobic exercise?
ADP and inorganic phosphate (Pi) concentrations rise, contributing to fatigue by disrupting muscle contraction and energy production
What does elevated lactate reflect about energy utilization during exercise?
Elevated lactate reflects increased glycogen utilization and depletion, as lactate is produced when anaerobic glycolysis is active and glycogen stores are being used
How does lactate arise?
During anaerobic glycolysis from the conversion of pyruvate (a 2 carbon molecule)
- otherwise pyruvate would go through Krebs cycle + ETC in presence of oxygen
Why do we refer to it as lactate rather than lactic acid?
Lactic acid is produced from pyruvate BUT it almost immediately dissociates into lactate and H+
- traditional view
What’s an alternative view of acidosis (lactic acid vs lactate)
From lactate dehydrogenase we don’t get lactic acid AT ALL -> pyruvate goes straight into lactate and the H+ are occurring from somewhere else
Why is it said that conversion of pyruvate to lactate actually prevents greater levels of acidosis?
The conversion of pyruvate to lactate consumes more H+ to allow more NAD+ to be produced from NADH so glycolysis can continue = exercise for longer
- so does it do this to prevent further acidosis?
Describe the relationship between lactate and pH
As blood lactate increases, blood pH decreases
- it’s the H+ causing the change in pH not the lactate, but lactate is reflective of it
- clearing lactate away consumes H+ so blood pH rises
What are the 2 determinants of blood lactate concentration?
- Rate of lactate clearance in other tissues (by type I fibres - utilised in cardiac muscle + cleared by liver - cori cycle)
- Rate of lactate production (by skeletal muscle - Type II fibres)
Is there always lactate present in the blood + when may levels elevate?
YES - resting blood lactate conc sits between 0.5-2mmol/L
- shows it’s still being produced at rest and may get elevated resting levels after eating a large meal / needing to recover
What happens to lactate production and removal during increasing exercise intensity?
At baseline, lactate is produced and removed at the same rate
- However, as exercise intensity increases, lactate production exceeds removal, leading to lactate accumulation
What are the 3 key sites of lactate removal and state the % of total lactate removed
- Most of it is oxidised by working muscles (55-75%)
- Liver + kidneys remove roughly 20-25%
- Cardiac muscle removes roughly 10%
Briefly explain how working muscles remove lactate
Lactate is primarily produced in Type II fibres, it then shuttles to adjacent Type I fibres and is utilised to help us stave off the glycogen depletion longer
- some of it is also stored as glycogen in muscle or liver (after being converted by liver)
What percentage of produced lactate appears in the vascular bed?
Only 50% of the lactate produced appears in the vascular bed, with the rest being oxidized and processed by muscles
Why does measuring blood lactate concentration (BLa) not fully reflect lactate production?
Measuring blood lactate reflects the balancing act between lactate production and removal, as some lactate is cleared before reaching the blood
How does lactate move through the vasculature to other muscles?
Lactate can shuttle through the vasculature (blood vessels), reaching other muscles demanding fuel, where it may diffuse in and be oxidised for energy
How does lactate contribute to the energy supply in active muscles?
Lactate is reperfused into active muscles and the heart, where it is used as an energy source through oxidation
Why is it important for sprinters to cool down after a maximal sprint?
Lactate will be produced in Type II fibres during the sprint and Type I fibres can utilise it by ensuring a constant blood flow via cooling down
How is lactate used to produce ATP?
Lactate is converted back to pyruvate, which then enters the Krebs cycle and electron transport chain (ETC), generating ATP
Why is lactate often considered more than just a waste product?
Lactate can be used for ATP production, showing that it’s not just a waste product but also a valuable energy source when converted to pyruvate
What role does the liver play in lactate metabolism?
Lactate can be shuttled to the liver, where it undergoes gluconeogenesis to produce glucose, which can then be used as fuel
Describe the process of the Cori Cycle from muscle -> liver
- During intense exercise, when oxygen availability is limited, muscles rely on anaerobic glycolysis to produce ATP (glucose -> pyruvate -> lactate)
- Lactate is released into the bloodstream and transported to other tissues, primarily the liver
- In the liver, lactate is converted back into pyruvate which undergoes gluconeogenesis (process that uses energy to convert pyruvate into glucose)
- Glucose can then be utilised in Krebs + ETC or stored as liver glycogen
