3.2 Histology of Blood Vessels Flashcards
What is contained within the wall of large blood vessels?
Lumen
Describe the thickness of the tunica intima
Thin
Describe the thickness of the tunica media
Thickest, particularly in arteries
What does the tunica adventitia merge with?
Surrounding connective tissue (anchors vessel)
How many layers of cells in the endothelium? What kind of cells?
1 layer of epithelial cells
What are the layers of the tunica intima?
Endothelium, basement membrane, connective tissue (which has fine elastic and collagen fibres)
Describe the composition of the tunica media, both in elastic and muscular arteries
- Middle layer, thickest in arteries
- In elastic arteries, mostly composed of elastic tissue
- In muscular arteries, mostly composed of smooth muscle
How do you work out how much smooth muscle is in a magnified image of the tunica media?
Count the nuclei
What is the purpose of fenestrations in elastic laminae?
Diffusion/transport of substances
True or false: smooth muscle can be present in the tunica adventitia of veins
True. This is not the case for arteries
What are vasa vasorum?
Small blood vessels supplying oxygen and nutrients to outer wall of blood vessels.
Which type of artery is closest to the heart (i.e. elastic or muscular)?
Elastic (Think: windkessel effect)
Which type of artery has a prominent internal elastic lamina?
Muscular
How do you distinguish between arterioles and arteries?
- Arterioles have thicker walls relative to their lumen
- Arterioles have fewer layers of smooth muscle cells (count the nuclei)
Which is the most prominent layer an arteriole?
The tunica media
Why do smooth muscles in arterioles contract and relax? Why does this make sense?
To regulate blood distribution and reduce blood pressure through the capillaries.
This makes sense because the blood needs to be moving through slowly in order for substances to be exchanged.
Describe the tunica intima of venules
Just the endothelium (simple squamous epithelia sitting on its basement membrane)
What are pericytes and where can they be found?
- Contractile cells that control blood flow through microvasculature
- Can be found surrounding small venules and capillaries
Describe the smooth muscle and connective tissue present in small and large venules
Small: very small amount (almost none)
Large: still small, but a bit more substantial
Could the lumen of veins be considered regular or irregular in shape?
Irregular
What layer of the wall of veins do valves exist in? What are they made of?
- Exist in tunica intima
- Make of subendothelial connective tissue, and coated in endothilium
Does the tunica media of medium veins have high or low muscle content? How does this explain their tendency to distend?
Low. because of this, they can change in shape (i.e. distend) more readily
Do large veins have valves?
No
Do large veins have internal or external elastic laminae?
No
Why can’t large veins distend too much?
They have a high collagen content, which gives them some rigidity
What percentage of full blood capacity do veins tend to exist at? Why?
30-70%
This gives leeway for blood to be redistributed
Describe the distribution of smooth muscle in veins
Patchy
What are the three kinds of capillaries?
- Continuous
- Fenestrated
- Sinusoidal/Discontinuous
Why does it make sense that capillaries have reduced wall structure compared to larger blood vessels?
Capillaries are the site of substance exchange from the blood, meaning substances must be able to enter and exit them quickly. Therefore, the wall structure must be as simple as possible to facilitate this.
Describe the wall structure of capillaries
- Endothelium (pinocytotic vesicles, sometimes fenestrations and tight junctions)
- Basal Lamina (external to endothelial cell)
- Pericytes (not paracytes), which are contractile cells
Which type of blood vessels have the smallest diameter?
Capillaries
How do you distinguish between the lining of a blood vessel and the lining of a duct of a gland? Why does this make sense?
The lining of a vessel will always be simple squamous. The lining of a duct will be cuboidal or maybe even columnar, which makes sense since these cells are known for their excretory capabilities.
What does it mean that endothelial cells are “attenuated”
This means they are thin, which allows optimal exchange of substances across the membrane.
What does anti-thrombogenic mean?
Preventing the formation of a blood clot
What junctions exist between endothelial cells? Why?
Tight junctions. Prevents substances from moving between, hence prompting selective diffusion
What determines the speed of larger molecules across the endothelium of continuous capillaries?
Number of pinocytotic vesicles
What defines continuous capillaries?
- Tight junctions
- Many pinocytotic vesicles for exchange
- No gaps between endothelial cells
(The name says it all)
What characterises fenestrated capillaries?
Interruptions (i.e. fenestrations) in a capillary
What types of exchange do the pores of fenestrated capillaries allow for?
More extensive exchange, but limited by particle size (i.e. must be small enough to fit through)
Are capillary fenestrations with diaphragms more or less selective than those without?
More
What traits characterise a sinusoidal capillary?
- Larger diameter
- Irregular pathway
- Incomplete endothelial lining/basal lamina
- Numerous large fenestrations
