Cerebrospinal fluid and blood brain barrier Flashcards
The brain and the spinal cord are enveloped by 3 sheets of connective tissue called …
meninges
What are the 3 meninges?
- Dura mater
- Arachnoid mater
- Pia mater
Dura mater
- thick layers of fibroblast
- it fuses with the bone inner surface of the skull bone
Arachnoid mater
- Spiderweb-like
- thin layer of fibroblast that trap CSF between it and Pia mater
Pia mater
single layer of fibroblasts
What is the cerebrospinal fluid?
is a clear fluid present in the:
- ventricles of the brain
- central canal of the spinal cord
- subarachnoid space (brain and spinal cord)
What are the functions of the cerebrospinal fluid (CSF) ?
- to cushion the brain (buffering blows to the head)
- maintaining a consistent extracellular microenvironment for the neurons and glia cells
- waste control system for the removal of potentially harmful cellular metabolites
- Distribution medium for the peptide hormones and the growth factors that are secreted into the CSF
Where is CSF produced?
in specialized ependymal cells in the choroid plexus located in each of the 4 ventricles (floor or roof) at a constant rate
Where are the lateral ventricles located ?
respectively located in the two cerebral hemispheres
Location of the third ventricle
found at the midline of the diencephalon.
Location of the fourth ventricle
located between the cerebellum and the dorsal surface of the hindbrain (pons and medulla)
The __________ consist of tufts of capillaries covered by _______________ that form a selective, tight-juction barrier to the secretions of the leaky capillaries and to other surrounding fluids (e.g. CSF, extracellular fluids)
plexus, ependymal cells
relevant processes in regards to the plexus and what it does:
- active transport of sodium ions (Na+) and chloride (Cl-) into the ventricles
- water flows the NaCl passively into the ventricles
- Metabolization of some potentially harmful waste products
CSF flows down a pressure gradient from its site of formation at the _____________ through the ventricular system and the subarachnoid space into the venous system.
Explain the order of that flow
- Choroid plexus
- lateral ventricles
- into the third ventricle through the interventricular foramina (foramina of monro)
- through the cerebral aqueduct (aqueduct of Sylvius) of the midbrain
- into the fourth ventricle
- into the subarachnoid space through the foramina of Luschka
CSF can be sample by placing a stilettoed spinal needle where ?
into the subarachnoid space.
- in most veterinary species between the skull and the first cervical vertebra (atlas) in anesthetized animals.
How is normal CSF suppose to be?
clear and translucent
- turbidity indicates increased cellularity
- pink tint suggest the presence of blood
Where does the absorption of the CSF into the venous system take place ?
in the dura-lined venous sinuses within the skull
Most of the fluid is absorb from the subarachnoid space into the _______________ through _______________.
dural sinuses, arachnoid villi
What are arachnoid villi?
small, fingerlike projections of the arachnoid membrane that poke through the walls of the sinus.
Absorption appear to be _________ dependent and is ______________.
pressure, unidirectional
The entire volume of CSF is replaced ____________ times a day.
several
Hydrocephalus
Increased CSF volume in the skull, often associated with an increased ventricular volume and increased intracranial pressure
Non-communicating hydrocephalus
Normally caused by an obstruction to CSF flow ( narrow cerebral aqueduct or blocked exits from the fourth ventricle.
- this causes the ventricular regions inside the brain to expand at the expense of the surrounding brain tissue, and intracranial pressure rises
Communicating hydrocephalus
Impairment of absorption (can be secondary to meningitis or hemorrhage)
- this can increase CSF volume in the subarachnoid space, which increases pressure on the outside surface of the brain and increases intracranial pressure.
The blood brain barrier consist of specialized capillary endothelial cells that are lined by the:
- basal lamina
- astrocytic endfeet
- pericytes
-microglial cells
In ___________, passage through ______________ is blocked by tight junctions, and exchange of blood solutes is highly selective.
brain capillaries, intercellular clefts
Blood brain barrier histological characteristics
- few or no fenestrations
- pinocytes very uncommon to observe at the BBB
- tight junctions
- luminal and abluminal side of the endothelium (polarized)
- specific carrier systems for the uptake of solutes
- Endothelium is surrounded by pericytes and astrocytes
BBB functional characteristics
- Molecules that are small, uncharged, lipid soluble, and unbound to plasma proteins (O2, CO2, ethanol, nicotine) can easily pass across the capillary endothelium of the BBB
- Molecules that don’t fit this profile (glucose, some amino acids) are able to pass through the BBB by specific, carrier-mediated transport mechanisms
- Many antibiotics, anti parasitic drugs, as well as various potentially harmful substances will be “repelled” by the BBB (carrier-mediated process) and will never reach the nervous system
Pgp: MDRs (Multidrug Resistance Protein) is an example of what ?
One of many transport systems in the BBB.
