Brain Metabolism Flashcards
oxygen flow to the brain is regulated by
neuronal activity and cerebral blood flow
diagnostic functional imaging is done on what substrate
glucose
how much of the bodys O2 consumption is done by the brain
20%
what are the fuels of the brain?
glucose, and under prolonged fast ketone bodies
where does the brain use its energy
to power Na-K ATPase which maintains membrane potential
does the brain store glycogen?
yes very little
below what level of glucose leads to brain dysfunction
<2-2.5mM
how much energy is used by glial cells ?
17%-40%
the brain has metabolic compartmentation, what does this mean?
presence in a tissue of more than one distinct
pool of a given metabolite.
uses of compartmentation
Separate pools of a metabolite are not in rapid equilibrium with one another,
but rather maintain their own integrity and turnover rates.
• Compartmentation makes metabolism in the brain complex and continuous
interactions of neurons and glial cells essential for brain function.
what makes up the blood brain barrier
- endothelium
- basement membrane
- astrocytes
- pericytes
- vasculr smooth muscle cells
- microglia
what is the function of the blood brain barrier selectivity
To establish a stable ionic environment ensuring appropriate firing of neurons and
propagation of membrane potentials
what can pass the BBB by passive diffusion
small molecules: H2O, O2 , CO2 , NH3 , ethanol - soluble lipids: steroid hormones
what can pass through carrier mediated transport
glucose using GLUT2 (insulin independant)
amino acids
what role do astrocytes have in the BBB
- tightening of tight junctions (physical barrier)
- modulation of expression and polarized localization of transporters (transport barrier)
- controlling specialized enzyme systems (metabolic barrier)
what are the major nutrient transporters in the BBB
GLUT1, MCT1 (monocarboxylc acid transporter)
side note on MCT1
High amounts of MCT1 are present in the brain microvasculature during nursing/suckling, and decline significantly after 14 days of age (in the rat brain), with a concomitant dramatic increase in the GLUT1 content. • This phenomenon is paralleled by a metabolic switch to glucose as the predominant energy fuel of the brain.
levels of x and y increase with cerebral maturation and synaptogenesis
GLUT1 GLUT3
in a neonate what does the brain use for metabolism?
ketone bodies
what are ketone bodies?
the acetyl-CoA produced by fatty acid oxidation in liver mitochondria is
converted to acetone, acetoacetate and b-hydroxybutyrate (ketone bodies)
−These are transportable forms of fatty acids
−In starving state oxaloacetate is mainly used in gluconeogenesis, therefore acetyl
CoA produced by b-oxidation cannot enter TCA
−Source of fuel for brain, heart and muscle (major energy source for brain during
starvation)
is succinyl-coA present in the liver
no
an increase in glucose metabolism during brain maturation is accompanied by
increased oxidation of glycolytically derived pyruvate via the TCA cycle.
in the brain, what is the % of glucose and oxygen extraction?
glucose: 10%
O2: 50-70%
neurovascular coupling has 2 subsets
Cerebral autoregulation: ensures constant cerebral blood flow over a wide range of arterial
pressures (60-150 mmHg).
Functional hyperemia: ensures rapid delivery of oxygen and glucose to active neurons
net uptake of glucose is x on plasma glucose concentration
independant, it is transported by facilitated diffusion. It has a significant tissue glucose [].
is there glycogen in the brain?
- yes, very little
- glycogen granules are only present in the astrocytes of adult animals.
- glycogen phosphorylase in in astrocytes only
brain glycogen metabolism is affected by
- vasoactive intestinal peptide, noradrenaline, insulin
glycogen [] increases
s in conditions of decreased electrical activity (e.g., deep pentobarbital anesthesia)
glycogen [] and its enzymes are modulated by
sleep deprivation
glycogen is needed for
maintaining intense firing in an isolated axon
