L10

Question 1

example of unidirectional transcellular transport

Answer 1

secretion by the salivary gland
Primary secretion - Acinar cells. Ions from blood to lumen INTO cells. H2O too.
Secondary modification - Duct cells. reabsorb Na+ and Cl- but not H2O.

Question 2

Epithelial cells - what links them together?

Answer 2

Linked together by junctional complexes
Claudins determine tightness and selectivity of junctions between cells, mediate paracellular transport
Transcellular requires polarity, is in or out of the epithelial cells

Question 3

Blood-brain-barrier

Answer 3

endothelial cells of brain capillaries
- formed by cerebral endothelial cells, highly specialised
- phenotypically unique, tight apical junction more closely resembles epithelium than endothelium
- transporters that control what nutrients enter via AT
- Can inactivate toxic substances and remove from blood

Question 4

Circumventricular organs

Answer 4

BBB is not active here. CVO is fenestrated (leaky).
Barrier for CVO are tancytes and ependymal, allow diffusion into CVO but not blood.

Question 5

blood - CSF barrier

Answer 5

Chloride plexuses
2nd most important interface
- CSF formed in 3rd & 4th ventricles, mainly by chloride plexuses & cerebral capillaries.
- same composition as ISF & mixes freely together across pial surfaces
- tight junctions of the ependymal cells of chloride plexuses form blood-CSF barrier

Question 6

Ependymal cells of Chloride plexuses

Answer 6

epithelial-like
CSF formation facilitated by V high blood flow to chloride plexuses
600ml/day

Question 7

Astrocytes (BBB)

Answer 7

upregulate tight junction proteins
2-way, cerebral endothelium signals astrocytes
maintenance of BBB properties relies on CROSS-TALK
Buffer K+ in perivascular space