Flashcards in Histology of the CVS Deck (134)
What are the most common type of capillaries?
Where are continuous capillaries located?
Nervous, muscle and connective tissues, exocrine glands, and the lungs
What do continuous capillaries consist of?
Continuous endothelial layer, with the cells joined by tight or occluding junctions
Where are fenestrated capillaries found?
In parts of the gut, endocrine glands and the renal glomerulus
What exists in fenestrated capillaries?
‘Little windows’, or interruptions, across thing parts of the endothelium, which are bridged by a thin diaphragm (except in the renal glomerulus)
What are the possible routes of transport across the endothelial wall of a fenestrated capillary?
Diffusion through intercellular cleft
Diffusion through fenestration
Through pinocytic vesicles
How do sinusoids differ from other capillaries?
They have a larger diameter and a slower blood flow
What is the diameter of sinusoids?
Where are sinusoids found?
In the liver, spleen and bone marrow
What do sinusoids have?
Gaps in the wall
What is the purpose of the gaps in the walls of sinusoids?
Allows whole cells to move between blood and tissue
What do pericytes form?
A branching network on the outer surface of the endothelium
What are pericytes capable of?
Dividing into muscle cells or fibroblasts, during angiogenesis, tumour growth and wound healing
How are postcapillary venules similar to capillaries?
The wall is similar, in that it has an endothelial lining with associated pericytes
What is the diameter of postcapillary venules?
What is more permeable, capillaries or post-capillary venules?
What tends to drain into post-capillary venules?
Why does fluid tend to drain into post-capillary venules?
Because their pressure is lower than that of capillaries or the surrounding tissues
When does fluid not drain into the postcapillary venules?
When an inflammatory response is operating, in which case fluid and leukocytes emigrate
What are the post-capillary venules the preferred location for?
Emigration of leukocytes from the blood
At what point do smooth muscle fibres begin to be associated with the endothelium of venules?
As the diameter of merging venules begin to increase to more than 50µm
What is happening as smooth muscle fibres begin to appear in venules?
A tunica media is beginning to appear
What is the diameter of venules?
Up to 1mm
What is the endothelium of venules associated with?
What can venules have?
What do venules valves consist of?
Thin, intimal extensions
What do venules valves do?
By pressing together, they restrict retrograde transport of blood, stopping blood flow in the opposite direction
What is the general rule regarding veins?
They have a larger diameter than any accompanying artery, and a thinner wall that has more connective tissue and fewer elastic and muscle fibres
What do small and medium sized veins have?
A well developed adventitia