week 1 physiology 1 Flashcards
what is CSF?
Cerebrospinal Fluid - clear colourless liquid composed mostly of water.
contains little protein (15-45mg/dl), little immunoglobulins and only 1-5 cells/ml
where is CSF produced?
by the secretory epithelium of the choroid plexus in the ventricles - in(replaced fully 3/4 times daily)
what does the CSF do?
Supplies water, amino acids, ions
Removes metabolites
what happens after CSF is formed in the ventricles
circulates in the subarachnoid space then absorbed into venous circulation
CSF has 3 major functions what are they?
- Mechanical protection: shock-absorbing medium that protects brain tissue. Brain “floats” inside the cranial cavity
- Homeostatic function: pH of CSF affects pulmonary ventilation and cerebral blood flow. Transports hormones.
- Circulation: medium for minor exchange of nutrients and waste products between blood and brain tissue
how is CSF analysis obtained, what does it show?
obtained via a lumbar puncture, aids the diagnosis of the brain, meninges and spinal cord
what does any condition that causes CSF accumulation [overproduction or obstruction] cause? give an example
serious neurological deficits (for example hydrocephalus as seen in a fetus or newborn)
where does the nervous system develop from?(embryology)
At 3 weeks, the developing nervous system consists of a tube – neural canal
what structures arise from the cavity of the neural tube?
the adult brain’s ventricules and the spinal cord’s central canal
what structures arise from the walls of the ventricules?
The choroid plexus (specialized secreting cells that produce cerebrospinal fluid CSF)
Choroid plexus develops how?
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, responsible for CSF production
where is the choroid plexus found in adult brain?
the 3rd, 4th and lateral ventricles
what is the choroid plexus?
networks of capillaries in walls of ventricles
how is CSF produced/secreted?
CSF secretion involves the transport of ions ( Na+, Cl¯ and HCO3¯) across the epithelium from blood to CSF
occurs due to secretive distribution of transports/channels/pumps. (basolateral to apical).
the movement of ions drives osmosis
how are the ventricles connected (2 lateral, 3rd and 4th?)
Intraventricular Foramina (of Monroe): Lateral Ventricles to Third Ventricle
Cerebral Aqueduct (of Sylvius): Third Ventricle to Fourth
Foramen of Magendie: Median aperture – Fourth ventricle to subarachnoid space
Foramina of Luschka: Lateral apertures – Fourth ventricle to subarachnoid space
what connects the Lateral Ventricles to Third Ventricle
Intraventricular Foramina (of Monroe):
what connects the Third Ventricle to Fourth
Cerebral Aqueduct (of Sylvius)
what connects the Fourth ventricle to subarachnoid space (medial aperture)
Foramen of Magendie
what connects the Fourth ventricle to subarachnoid space (lateral aperture)
Foramina of Luschka
what does the Blood brain barrier aim to do?
reduce ‘raw’ circulatory system to the brain.
protects the brain from many common bacterial infections and toxins
[BBB is the determining factor for clinical CSF analysis + BBB is the main obstacle for drug delivery to the CNS]
how does CSF flow/circulate?
CSF formed in choroid plexuses of each lateral ventricle→Flows to third ventricle through two narrow openings called the interventricular foramina→
More CSF added by choroid plexus 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
how does the CSF enter the subarachnoid space ?
through 3 openings in roof of fourth ventricle
Single median aperture
Paired lateral apertures
what happens to the CSF after it enters the subarachnoid space
it circulates in the central canal of spinal cord
what cells in brain capillaries are the site of the BBB?
endothelial cells
what parts of the brain do not have a BBB?
circumventricular organs
pineal gland
name the structural elements of the BBB
BBB consists of the capillary endothelium, its basal membrane and perivascular astrocytes
Tight junctions between brain endothelial cells prevent paracellular movement of molecules
[generally] name pathologies that can affect the ventricles, choroid plexus and CSF.
tumours
Ventricular haemorrhage (accummulation of blood in the ventricles)
hydrocephalus
Idiopathic intracranial hypertension / pseudotumor cerebri
name some tumours that can affect the ventricles, choroid plexus and CSF
Tumours:
=Colloid cyst (often found at the interventricular foramen)
=Ependymomas (arising from the ependymal cells lining the ventricles)
=Choroid plexus tumours
name some types of Ventricular haemorrhage that can affect the ventricles, choroid plexus and CSF
Ventricular haemorrhage (accummulation of blood in the ventricles):
=Epidural hematoma, arterial bleed between skull and dura
=Subdural hematoma, venous bleed between dura and arachnoid
=Subarachnoid hemorrhage
what is hydrocephalus?
- accumulation of CSF in the ventricular system or around the brain (either due to obstruction or overproduction)
- subsequent enlargement of one or more ventricles and increase in CSF pressure
what is Idiopathic intracranial hypertension / pseudotumor cerebri?
- Enigmatic condition
- Symptoms include headache and visual disturbances (visual field disturbances to blindness) due to papilloaedema
- Despite increased CSF pressure no imaging features of hydrocephalus
what is Papilloedema?
optic disc swelling due to increased intracranial pressure transmitted to the subarachnoid space surrounding the optic nerve
visual symptoms of Papilloedema?
enlarged blind spot, blurring of vision, visual obscurations and loss of vision
-fundoscopy = bulging optic disc
what is aqueous humour?
a specialized fluid that bathes the structures within the eye.
what do aqueous humour contain/do?
- It provides oxygen and metabolites and contains bicarbonate (HCO3).
- Bicarbonate buffers the the H+ produced in the cornea and lens by anaerobic glycolysis.
- Ascorbate is a powerful antioxidant
how is aqueous humour produced?
It is produced by an energy dependent process in the epithelilal layer of the ciliary body into the posterior chamber of the eye.
how is aqueous circulated?
It is produced by an energy dependent process in the epithelilal layer of the ciliary body into the posterior chamber of the eye. It then flows into the anterior chamber and then drains to the scleral venous sinus through a trabecular meshwork and the canal of Schlemm, situated in the angle between the iris and cornea iridocorneal angle.
how is aqueous absorbed?
it drains to the scleral venous sinus through a trabecular meshwork and the canal of Schlemm, situated in the angle between the iris and cornea iridocorneal angle. A small amount diffuses through the vitreous being absorbed across the retinal pigment epithelium.
how is the ciliary epithelium organised?
The ciliary body and posterior surface of the iris are covered by two juxtaposed layers of epithelial cells, a forward continuation of the pigment epithelium of the retina (PE) overlain by an inner nonpigmented epithelial (NPE) layer
how is HCO3-and H+ formed in the epithelial cells
from hydration of CO2 catalysed by Carbonic Anhydrase
why does HCO3-and H+ need to be formed?
so it can be exchanged for Cl- and NA+ respectively (across basolateral membrane)
what drug decrease production of aqueous?
CA inhibitors
how do the Cl- and Na+ ions enter and leave the cell?
Enter=diffuse through the gap junctions between the PE and NPE cells
leave=out of the NPE cells into the aqueous humor via the Na+/K+/2Cl- cotransporter
net outcome of aqueous production?
net movement of Cl- and Na+ through the cells from interstitial fluid to aqueous humor is accompanied by water moving through ciliary epithelial cell water channels, aquaporins (AQP1 of the NPE cells) and through the paracellular pathway down the osmotic gradient created by solute movement.
what is the disease process in glaucoma?
raised intra-ocular pressure is caused by an imbalance between the rates of secretion and removal of aqueous humor
drugs acting on glaucoma?
Carbonic anhydrase inhibitors will reduce production of aqueous humor….. used to reduce ocular pressure in glaucoma:
Dorzolamide - is administered as eye drops- avoiding systemic side effects
Acetazolomide - oral administration ……. also targets kidney……. acidosis.
