Physiology 1 - CSF and Aqueous Humor Flashcards
What is CSF mainly composed of?
Water
What produces CSF?
Secretory epithelium of the choroid plexus
Approx. how much CSF is produced a day?
500-600ml
How often is the CSF in the CNS replaced?
3-4 times daily
What is the path of CSF from being produced to being absorbed?
Formed in the ventricles and then circulates in the subarachnoid space then absorbed into venous circulation
What 3 things does the CSF supply?
Water
Amino acids
Ions
What does the CSF remove?
Metabolites
What are the 3 major general functions of CSF?
Mechanical protection (shock-absorbing medium that protects brain tissue -> brain "floats" inside the cranial cavity) Homeostatic function Circulation
What does the pH of CSF affect? (2)
Pulmonary ventilation
Cerebral blood flow
How much protein, immunoglobulins and cells does normal CSF contain?
Little protein
Little immunoglobulins
Only 1-5 cells/ ml
What 2 general things can cause CSF accumulation?
Overproduction
Obstruction
What are the ventricles of the brain?
A communicating network of cavities filled with CSF located within the brain parenchyma
What does the developing nervous system consist of at 3 weeks?
A tube - the neural canal
What does the cavity of the neural canal give rise to?
The adult brain’s ventricules and the spinal cord’s central canal
What does the choroid plexus develop from?
Cells in the walls of the ventricules -> developing arteries invaginate the roof of the ventricle to form the choroid fissure
The involuted ependymal cells along with the vessels enlarge into villi and form the choroid plexus
Where in the adult brain is the choroid plexus found?
In the 3rd, 4th and lateral ventricles
What is the choroid plexus?
Network of capillaries in the walls of the ventricles which produce CSF
What ions are transported across the epithelium from the blood to CSF in CSF production?
Na+, Cl- and HCO3- (and water)
How can secretion of ions across the epithelium from blood to CSF occur for production of CSF?
Because of the polarised distribution of specific ion transporters in the apical or basolateral membrane of the epithelial cells
What does the secretion of fluid by the choroid plexus depend on?
How does this work?
Active Na+ transport across cells into the CSF
Electrical gradient pulls along Cl- and both ions drag water by osmosis
How does the concentration of K+, glucose and protein of CSF compare to blood?
much lower
How does the concentration of Na+ and Cl- in CSF compare to blood?
Higher
What are the 3 main parts of the ventricular system of the brain?
Lateral ventricles
Third Ventricle
Fourth ventricle
What connects the lateral ventricles to the third ventricle?
Intraventricular foramina of Monroe
What connects the third and fourth ventricle?
Cerebral Aqueduct (of Sylvius)
What connects the fourth ventricle to the subarachnoid space?
Foramen of Magendie (median aperture)
Foramina of Luschka (lateral apertures)
What is the route of CSF -> Fourth ventricle?
Formed in choroid plexuses of each lateral ventricle
Flows to third ventricle through 2 opening called the inter ventricular foramina
More CSF added by choroid plexuses in roof of third ventricle
Then flows through aqueduct of midbrain (cerebral aqueduct)
And into the fourth ventricle
Another choroid plexus in fourth ventricle adds more CSF
Where does CSF pass after the 4th ventricle?
Enters the subarachnoid space through 3 openings in the room of the fourth ventricle (median aperture and lateral apertures)
Then circulates in the central canal of the spinal cord
What creates the blood-CSF barrier?
Choroid plexus
Where does CSF return to venous blood?
Through the archechnoid granulations into the superior sagittal sinus
How is the blood supply to the majority of the brain restricted?
By the blood-brain barrier
Where is the site of the blood brain barrier?
Endothelial cells in brain capillaries
What does the blood brain barrier consist of?
The capillary endothelium, its basal membrane and perivascular astrocytes
What is present between brain endothelial cells which prevents paracellular movement of molecules?
Tight junctions
What parts of the brain do not have a blood brain barrier?
Circumventricular organs or pineal gland
What is the purpose of the blood brain barrier?
Protects the brain from many common bacterial infections and toxins
What is the main obstacle for drug delivery to the CNS?
Blood brain barrier
What is the name of a tumour often found a the inter ventricular foramen?
Colloid cyst
What is the name of the tumour which arises from the ependymal cells lining the ventricles?
Ependymomas
Name of tumour which arises from the choroid plexus?
Choroid plexus tumours
What is the name for the accumulation of blood in the ventricles?
Ventricular haemorrhage
Name for an arterial bleed between the skull and dura?
Epidural haematoma
Name for a venous bleed between dura and arachnoid?
Subdural haematoma
What is hydrocephalus?
The accumulation of CSF in the ventricular system or around the brain (either due to obstruction or overproduction)
What does hydrocephalus typically cause?
Enlargement of one or more ventricles and an increase in CSF pressure
What is idiopathic intracranial hypertension?
Increased intracranial pressure in the absence of a tumour or other disease
What is another name for idiopathic intracranial hypertension?
Pseudotumour cerebri
What is papilloaedema?
Optic disc swelling due to increased intracranial pressure transmitted to the subarachnoid space surrounding the optic nerve
What is visual symptoms of papilloedema?
Enlarged blind spot, blurring of vision, visual obscurations and loss of vision
What does aqueous humor provide?
Oxygen and metabolites (also contains bicarbonate)
What does aqueous humour provide to the structures within the eye?
Oxygen and metabolites (also contains bicarbonate)
What is the purpose of the bicarbonate within the aqueous humor of the eye?
Buffers the H+ produced in the cornea and lens by anaerobic glycolysis
How is aqueous humour produced by the ciliary body?
By an energy dependent process in the epithelial layer of the ciliary body
What 2 layers cover the ciliary body and posterior surface of the iris?
A forward continuation of the pigment epithelium of the retina
Inner non pigmented epithelial layer
In terms of aqueous humour production, how are bicarbonate and H+ formed?
From hydration of CO2 catalysed by carbonic anhydrase these are then transported across the membrane of pigmented epithelial cells into the interstitial fluid in exchange for Cl- and nA+)
In the production of aqueous humour, the Na+ and Cl- ions diffuse from PE cells into NPE cells. How are they transported out of the NPE cells into the aqueous humour?
Via the Na+/K+/2Cl- co-trasnporter
What ions move from interstitial fluid to aqueous humour in the production of aqueous humour?
Cl- and Na+ (accompanied by water)
What type of drugs can be used when there is too much aqueous fluid produced/ not enough drained?
CA inhibitors (blocks carbonic anhydrase = reduced entry of Na+ and Cl- into the pigmented epithelial cell)
What causes the raised intra-ocular pressure in glaucoma?
An imbalance between the rates of secretion and removal of aqueous humor
What type of drug can be used to treat glaucoma?
CA inhibitor
What is an example of a CA inhibitor that is administered as eye drops?
Dorzolamide
Example of a CA inhibitor that is administered orally?
Acetazolomide
Side effect of Acetazolomide?
Acidosis (as also targets the kidney)
