Module B-07 Flashcards
Which are the 3 extracellular fluid compartments and the volume of each?
1) Plasma
2) Interstitial fluid
3) CSF
Where is majority of fluid of body found ?
Intracellular 60%
Where is CSF found?
1) Intraventricular (23ml)
2) Subarachnoid space (67-117 ml)
volume of CSF
90-140ml
4 functions of CSF
1) Maintains Extracellular environment
2) Removes metabolites from CNS
3) regulated cerebral blood flow and pulomonary ventilation
4) Cushions brain
How does CSF influence cerebral blood flow and pulmonary ventilation?
Owing to changes in its pH
What is present in high levels in CSF compared to plasma?
Cl-, Mg++ and Na+ (only slightly higher)
What is present in low levels in CSF compared to palsma
protein, glucose, K+ ,Ca++
At what levels is lumbar puncture done
L3/L4 or L4/L5
What is relevance of a lumbar puncture?
1) analysis of CSF
2) measurement of intracranial pressure
4 adverse effects of Elevated intracranial pressure (ICP)
1) Nausea
2) Bradycardia
3) Systemic hypertension
4) Papilledema
What does the Monroe-Kellie Doctrine state?
An increase in volume of one component (e.g., brain, blood, or cerebrospinal fluid) will elevate pressure (ICP) or decrease the volume of one of the other elements.
What are the 3 components of the Blood Brain Barrier
1) Endothelial cells,
2) Astrocytic endfeet
3) Capillary basement membranes
What are 2 characteristics of capillaries of the brain
lack fenestrations and have tight junctions to prevent paracellular flow (only Transcellular flow takes place)
What can pass through the BBB?
Small hydrophobic molecules, blood gases, small uncharged polar molecules,urea and glycerol
The higher the Oil/water partition coefficient the ____ (less/more) effective the transfer of the solute across the BBB
more
What are 2 substances moved by facilitated diffusion across the BBB
L-DOPA and Glucose
Ratio of solubility in oil versus water predicts
transcellular transfer of solutes into CNS
What transporter is used in BBB endothelial cells for glucose transport?
GLUT-1
What transporter is used in BBB endothelial cells for L-DOPA transport?
Neutral amino acid carrier
How does glycine cross the BBB (brain to blood)
Na+-dependent cotransporter ( secondary active transport)
What can cause the tight junctions of BBB to become leaky?
1) Hypertension (high blood pressure)
2) Hyperosmolality
3) Trauma, ischemia, inflammation or pressure
4) Infection
How does hyperosmolarity cause leaky endothelium
hypertonic infusions shrink endothelial cells and disable tight junction but this is reversible
Clinical use of hyperosmolarity with BBB
may permit delivery of lipid-insoluble drugs to
the CNS
What differs circumventricular organs from rest of CNS
lack tight junctions in capillaries and thus lack
the BBB
Name the Circumventricular organs
1) Area postrema
2) Median eminence
3) Neurohypophysis
4) Organum vasculosum
5) Pineal body
6) Subcommissural organ
7) Subfornical organ
What cells line the ventricles
Ependymal cells (group1)
What cells form the choroid plexuses?
Secretory Ependymal cells (group 2 )
where does CSF circulate?
the ventricles, the spinal canal and the entire
subarachnoid space
Where does CSF come from?
1) Choroid plexus (70%)
2) specialized secretory ependymal cells of the subcommisural organ (30%)
How is CSF transported by choroid plexus?
- co-transporters for Na+ , K+ and Cl in the basolateral membrane
- co-transporters for K+ and Cl ions in the microvilli
of the apical membrane. - The membranes also have ion channels for Na+, K+
and Cl in addition to Na/K pumps. - net transport of Na+, K+ and Cl into ventricles, with water following by local osmosis.
- transport of water also involves specific water
channels (aquaporins) of which AQP1 is expressed in the choroid plexus.
How much CSF is produced per day?
500ml per day
CSF accumulation leads to________
Hydrocephalus
Where does CSF drain into
Subarachnoid space=> Arachnoid villi(granulations) =>Superior Sagittal SInus => venous system
CSF composition: Increased protein, normal glucose, RBCs present
Subarachnoid hemmorhage
CSF composition: Very high protein, normal glucose, few WBCs present
Guillian-Barre syndrome
CSF composition: increased protein, normal to decreased glucose, Increased number of WBC Tumor cells
Metastatic cancer in the meninges
CSF composition: Increased protein, normal glucose, excessive WBCs (lymphocytes)
Viral meningitis
CSF composition: Increased protein, Decreased glucose, increased WBCs (lymphocytes)
Tubercular meningitis
CSF composition: Increased protein, decreased glucose, increased number of WBCs (polymorphonuclear leukocytes)
Bacterial Meningitis
Where are changes in CSF composition detected in the CNS
CSF osmolality are sensed by mechanosensitive, nonselective cation channels expressed in the supraoptic and paraventricular nuclei.
These nuclei also bear osmolarity sensing volume regulated anion channels in glial cells
2 types of hydrocephalus
noncommunicating( obstructive)
communicating
Common feature of both types of hydrocephalus
increased ventricular volume
What causes Obstructive hydrocephalus
obstruction (conegnital or cellular debris)of
- interventricular foramina,
- cerebral aqueduct
- or foramina of fourth ventricle
What causes Communicating hydrocephalus
• Overproduction – Choroid tumor
• Insufficient drainage – Malfunction of arachnoid villi
• Ex vacuo – Enlargement secondary to tissue
loss
What happens in Hydrocephalus ex vacuo
ventricular enlargement arises as spatial compensation for neurodegenerative losses of brain mass without increasing
intracranial pressure
what happens in Normal pressure hydorcephalus
Transient increases in ICP ( not seen in older patients)
What forms blood CSF barrier
Choroid plexus
what is brain edema?
localized or generalized excess accumulation of water in the intracellular and/or extracellular spaces of both the grey and white matter
Two types of Brain edema
1) Vasogenic
2) Cytotoxic
What causes Vasogenic edema?
disruption of the BBB => increase in capillary permeability
What causes cytotoxic edema
- tissue damage or by an inadequate blood supply to neurons and glia.
- When the Na/K pump eventually fails in the ATP-starved cells, ionic gradients dissipate, leading to cellular
swelling
Treatment fro Brain edema
Osmotherapy
Why arent astrocytes damaged during brain edema
capable of regulating their cellular volume
after the initial swelling
