1 Flashcards
Chemical Composition of the Brain:
-About 80% of the brain tissue is water.
-Most of the brain dry weight is lipids; (cholesterol, glycerophospholipids, sphingomyelin, & glycolipids).
- The remainder of brain dry weight is proteins.
Chemical Composition of Myelin
Myelin is a lipid-rich structure formed of lipids & proteins.
Proteins:
Two major myelin proteins are found in CNS:
1.Proteo-lipid proteins (PLP).
2.Myelin basic proteins (MBP).
Lipid : 1 Cholesterol. 2 Phospholipids 3 Galactolipids
Myelin contains very high levels of cholesterol &
cerebrosides, especially galacto-cerebrosides.
The major fatty acid associated with these complex lipids is “oleic acid” which is a mono- unsaturated FA.
Myelin is a …………. packed structure. Diaw
The layers of myelin are held to gether by ………………..
Any disruption can lead to demyelination of the membrane.
tightly
protein/lipid &protein/protein interactions.
Demyelinating Diseases:
1. Demylination of CNS:…………..
2. Demyelination of PNS:……………
3. Other relatively rare demyelinating
diseases.
Demylination of CNS:
e.g. multiple sclerosis (MS)
2. Demyelination of PNS:
e.g. Guillain-Barre syndrome (GBS)
In young children, dietary FAs are important for the development of the nervous system.
Children are better when served by fatty sources
of foods like…….,………..
milk and fish.
Multiple sclerosis (MS)?
demyelinating disease which can lead to inability to walk
I diet rich in essential FAs can help
Reduce symptoms as well as relapses of MS according to the national MS society
Although the brain contributes only …….of the
adult weight, the brain consumes about ……. of
the basal oxygen consumption of the body at rest
2%
20%
Blood Brain Barrier Selectivity:
Blood Brain Barrier Selectivity:
1. Free permeability (passive diffusion):
Small molecules: H2O, O2, CO2 & NH3, ethanol.
Lipid soluble molecules: steroid hormones.
2. Carriermediatedtransport:
Glucose: GLUT-1 & 3, (insulin-independent).
Amino acids.
3. Pinocytosis.
Inter-tissue Relationship
In Absorptive State:
In the well-fed state, brain
uses
glucose exclusively
as a source of energy,
oxidizing about 120-140
normal fasting blood glucose
If blood glucose levels fall <40 mg/100 ml, cerebral
function is impaired (normal fasting blood glucose
=70–100 mg/dl).
Brain Metabolism In Fasting & Starvation:
This results in an exchange of substrates between
liver, adipose tissue, muscles & brain that is guided
by two priorities:
1) To maintain adequate plasma glucose levels to
sustain energy metabolism of the brain and other
glucose-requiring tissues,
2) To mobilize fatty acids from adipose tissue & the
synthesis and release of ketone bodies from the
liver, to supply energy to all other tissues.
Brain Metabolism In Fasting & Starvation:
During the first days of fasting, the brain continues to use glucose exclusively as a fuel.
Blood glucose is maintained by hepatic gluconeogenesis from glucogenic precursors, such as amino acids provided by the rapid degradation of muscle protein and glycerol.
In prolonged fasting (>2-3 ws), plasma ketone bodies reach significant high levels and the brain acquires the ability to use ketone bodies in addition to glucose to form ATP.
one factor that has been suggested to
cause central fatigue.
Changes in the brain 5-hydroxytryptamine (5-
HT)
The rate-limiting step in the synthesis of “5-HT”
is the
is the transport of tryptophan across the BBB
Ingestion of BCAAs causes delay of fatigue
increase their plasma concentration è decrease tryptophan uptake of by the brain 5-HT synthesis, causing delay of
fatigue.
-In some situations the intake of BCAAs also
improves physical performance.
branched chain amino acids (BCAAs), which are
leucine, isoleucine & valine. They are transported by the same carrier system
