week 1 physiology 1

Question 1

what is CSF?

Answer 1

Cerebrospinal Fluid - clear colourless liquid composed mostly of water.

contains little protein (15-45mg/dl), little immunoglobulins and only 1-5 cells/ml

Question 2

where is CSF produced?

Answer 2

by the secretory epithelium of the choroid plexus in the ventricles - in(replaced fully 3/4 times daily)

Question 3

what does the CSF do?

Answer 3

Supplies water, amino acids, ions

Removes metabolites

Question 4

what happens after CSF is formed in the ventricles

Answer 4

circulates in the subarachnoid space then absorbed into venous circulation

Question 5

CSF has 3 major functions what are they?

Answer 5

• 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

Question 6

how is CSF analysis obtained, what does it show?

Answer 6

obtained via a lumbar puncture, aids the diagnosis of the brain, meninges and spinal cord

Question 7

what does any condition that causes CSF accumulation [overproduction or obstruction] cause? give an example

Answer 7

serious neurological deficits (for example hydrocephalus as seen in a fetus or newborn)

Question 8

where does the nervous system develop from?(embryology)

Answer 8

At 3 weeks, the developing nervous system consists of a tube – neural canal

Question 9

what structures arise from the cavity of the neural tube?

Answer 9

the adult brain’s ventricules and the spinal cord’s central canal

Question 10

what structures arise from the walls of the ventricules?

Answer 10

The choroid plexus (specialized secreting cells that produce cerebrospinal fluid CSF)

Question 11

Choroid plexus develops how?

Answer 11

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

Question 12

where is the choroid plexus found in adult brain?

Answer 12

the 3rd, 4th and lateral ventricles

Question 13

what is the choroid plexus?

Answer 13

networks of capillaries in walls of ventricles

Question 14

how is CSF produced/secreted?

Answer 14

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

Question 15

how are the ventricles connected (2 lateral, 3rd and 4th?)

Answer 15

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

Question 16

what connects the Lateral Ventricles to Third Ventricle

Answer 16

Intraventricular Foramina (of Monroe):

Question 17

what connects the Third Ventricle to Fourth

Answer 17

Cerebral Aqueduct (of Sylvius)

Question 18

what connects the Fourth ventricle to subarachnoid space (medial aperture)

Answer 18

Foramen of Magendie

Question 19

what connects the Fourth ventricle to subarachnoid space (lateral aperture)

Answer 19

Foramina of Luschka

Question 20

what does the Blood brain barrier aim to do?

Answer 20

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]

Question 21

how does CSF flow/circulate?

Answer 21

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

Question 22

how does the CSF enter the subarachnoid space ?

Answer 22

through 3 openings in roof of fourth ventricle
Single median aperture
Paired lateral apertures

Question 23

what happens to the CSF after it enters the subarachnoid space

Answer 23

it circulates in the central canal of spinal cord

Question 24

what cells in brain capillaries are the site of the BBB?

Answer 24

endothelial cells

Question 25

what parts of the brain do not have a BBB?

Answer 25

circumventricular organs | pineal gland

Question 26

name the structural elements of the BBB

Answer 26

BBB consists of the capillary endothelium, its basal membrane and perivascular astrocytes Tight junctions between brain endothelial cells prevent paracellular movement of molecules

Question 27

[generally] name pathologies that can affect the ventricles, choroid plexus and CSF.

Answer 27

tumours Ventricular haemorrhage (accummulation of blood in the ventricles) hydrocephalus Idiopathic intracranial hypertension / pseudotumor cerebri

Question 28

name some tumours that can affect the ventricles, choroid plexus and CSF

Answer 28

Tumours: =Colloid cyst (often found at the interventricular foramen) =Ependymomas (arising from the ependymal cells lining the ventricles) =Choroid plexus tumours

Question 29

name some types of Ventricular haemorrhage that can affect the ventricles, choroid plexus and CSF

Answer 29

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

Question 30

what is hydrocephalus?

Answer 30

- 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

Question 31

what is Idiopathic intracranial hypertension / pseudotumor cerebri?

Answer 31

- 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

Question 32

what is Papilloedema?

Answer 32

optic disc swelling due to increased intracranial pressure transmitted to the subarachnoid space surrounding the optic nerve

Question 33

visual symptoms of Papilloedema?

Answer 33

enlarged blind spot, blurring of vision, visual obscurations and loss of vision -fundoscopy = bulging optic disc

Question 34

what is aqueous humour?

Answer 34

a specialized fluid that bathes the structures within the eye.

Question 35

what do aqueous humour contain/do?

Answer 35

- 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

Question 36

how is aqueous humour produced?

Answer 36

It is produced by an energy dependent process in the epithelilal layer of the ciliary body into the posterior chamber of the eye.

Question 37

how is aqueous circulated?

Answer 37

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.

Question 38

how is aqueous absorbed?

Answer 38

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.

Question 39

how is the ciliary epithelium organised?

Answer 39

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

Question 40

how is HCO3-and H+ formed in the epithelial cells

Answer 40

from hydration of CO2 catalysed by Carbonic Anhydrase

Question 41

why does HCO3-and H+ need to be formed?

Answer 41

so it can be exchanged for Cl- and NA+ respectively (across basolateral membrane)

Question 42

what drug decrease production of aqueous?

Answer 42

CA inhibitors

Question 43

how do the Cl- and Na+ ions enter and leave the cell?

Answer 43

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

Question 44

net outcome of aqueous production?

Answer 44

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.

Question 45

what is the disease process in glaucoma?

Answer 45

raised intra-ocular pressure is caused by an imbalance between the rates of secretion and removal of aqueous humor

Question 46

drugs acting on glaucoma?

Answer 46

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.