Blood and Blood Vessels Flashcards
Revision
What is the basic 3 layer structure to the blood vessels?
Inner layer/Tunica Intima
Middle layer/Tunica media
Outer layer/Tunica adventitia
What is the Inner layer/Tunica intima comprised of?
A single layer of squamous epithelial (a surface epithelium and the thinnest form of epithelium) cells termed endothelial cells supported by a basal lamina and a thin layer of connective tissue.
What is the middle layer/Tunica media comprised of?
It is made up predominately of smooth muscle. Thickness of this layer varies tremendously.
What is the outer layer/Tunica adventitia comprised of?
It is made up of supporting connective tissue.
How is the tunica intima separated from the tunica media?
It is separated by a layer of elastic tissue called the internal elastic membrane.
How is the tunica media separated from the tunica adventitia?
They are separated by a layer of elastic tissue called the external elastic membrane.
How are the elastic fibres stained so that they can be seen under a microscope?
Elastic fibres are not stained using most common stains (including H&E) but can be visualized with special stains like the one shown - the elastic fibres are stained black.
Is the structure of blood vessels the same in all?
There are variations in the general architecture of blood vessels. For example, in the largest arteries (e.g. the aorta) a significant amount of the smooth muscle in the tunica media is replaced by sheets of elastic fibres. These are called “elastic arteries”.
Why are the largest arteries (e.g. aorta) called elastic arteries?
They have many sheets of elastic fibres in their tunica media to provide elastic recoil.
What colour does Verhoeff’s/Masson trichrome stain elastic fibres, Collagen and smooth muscle cells?
Elastic fibres are stained black, collagen green and smooth muscle cells red.
What is the vasa vasorum?
In large arteries, only the inner part of the wall can obtain nutrients from the lumen, therefore these vessels will have their own vascular supply: the vasa vasorum.
(If the blood vessel is of a decent size, the wall has to be provided with blood).
What happens as arteries become smaller until they become arterioles?
As arteries become smaller they lose smooth muscle from the t.media, until arterioles have only one or two layers of smooth muscle in their tunica media and almost no adventitia. These are particularly important in controlling blood flow in a tissue.
What are capillaries essentially composed of?
Endothelial cells and a basal lamina.
It has no smooth muscle associated with it and still has epithelial cells.
Because of how small capillaries are, What do red blood cells have to do to pass through them and why does this cause problems for people with sickle cell anemia?
Because capillaries are so small, red blood cells must deform to pass through them.
In people with sickle cell anemia, because the red blood cells are not shaped normally, they cannot deform to pass through capillaries.
what are the 3 types of capillaries?
Continuous capillary
Fenestrated capillary
Discontinuous / Sinusodal capillary
Where would continuous capillaries be found?
Muscle, nerve, lungs and skin
Where would Fenestrated capillaries be found and what is an identifiable feature of them?
Gut mucosa, endocrine glands, kidney
They have small pores (50nm).
Where would you find discontinuous or Sinusoidal capillaries and what is an identifying feature?
Liver, spleen, bone marrow.
They have large gaps.
In these types of capillaries, blood has a very intimate relationship with the tissue.
What structure do capillaries form and what diameter do they have?
Capillaries form networks and have a diameter of 4-8µm.
What is microvasculature?
Small arteriole connected to a postcapillary venule (PCV) thorugh a network mad up of metarterioles (MT), thoroughfare channels (TC) and capillaries (C). Precapillary Sphincters (PS), composed of smooth muscle, at the beginning of the capillary help control flow through the network.
It is more of a network. The sphincter can contract or relax to allow blood to pass through.
What are post-capillary venules and what are they lined with?
Capillary networks drain into post-capillary venules (10-30µm diameter), which are endothelial cell-lined and contain a thin layer of connective tissue. These are important sites for exchange, e.g. cells moving into the tissue in inflammation.
Once the vessel begins to acquire intermittent smooth muscle cells in a tunica media layer, they are referred to as venules (generally >50µm).
What layers do veins have?
Veins, in addition to tunica intima, have a thin but continuous tunica media, typically consisting of a few layers of smooth muscle cells. There is an obvious tunica adventitia.
What is the difference in large veins compared to average veins?
The largest veins (e.g. vena cava) have a thick tunic adventitia which incorporates bundles of longitudinally orientate smooth muscle.
(Even in a large vein the Tunica media will remain relatively small compared to an artery of the same size).
What is the difference in small veins compared to average veins?
Many small veins have valves (inward extensions of the T.I.) to prevent backflow of blood.
What is the lymph vascular system and what is it’s role?
It is a system of relatively thin walled vessels that drain excess tissue fluid (lymph) into the blood stream.
It transports lymph to lymph nodes for immunological surveillance. No central pump, but smooth muscle in walls, hydrostatic pressure in the tissue and compression of the vessels by voluntary muscle, combined with valves in the vessels, produces flow.
