Blood ocular barrier - Week 3 Flashcards
What 3 layers of tissue make up the walls of blood vessels?
- Tunica intima - single layer of flattened squamous endothelial cells + underlying conn. tissue
- Tunica media - circumferential SMCs + external elastic lamina
- Tunica adventitia - fibroelastic tissue
What cells line the blood vessel lumen?
Endothelial cells
How are endothelial cells connected
via tight junctions
What is the effect of nicotine and other toxic substances on endothelial cells?
they break the tight junctions causing leaky blood vessels
Describe the role of pinocytotic vesicles.
- allows passage of fluid across cells from the blood
Where are pinocytotic vesicles found?
In Endothelial cells
How are endothelial cells involved with blood vessel autoregulation?
They release peptides for vasoconstriction or vasodilation
How does noradrenaline affect blood vessels?
Causes them to constrict, lowering size of blood vessel lumen (is sympathetic)
What is the general term that describes the layers of tissue forming the walls of a blood vessel?
Tunics
Define Elastic Artery, what does it contain? And what does this achieve?
An artery with a large number of collagen and elastin filaments in the tunica media, giving it the ability to stretch with each pulse
Describe the location of elastic arteries (compared to other arteries)
They are the arteries closest to the heart
List all elastic arteries that are close to the heart
- aorta + branches originating from aortic arch (common carotid, subclavian)
- common iliac arteries
- pulmonary trunk
Describe the general structure of elastic arteries, what do their tunica media consist of? How is their blood supply?
- their tunica media consists of many fenestrated lamallae of elastin
- extensive vasa vasorum (network of small blood vessels supplying large blood vessels)
That’s right, elastic arteries are so THICC, that they need their own blood supply
What is another name for muscular arteries?
Distributing arteries
What are Muscular arteries? Where do they draw blood from? Where do they branch?
medium sized arteries that draw blood from elastic arteries and branch into “resistance vessels” incl. small arteries and arterioles
List the branches of the ophthalmic artery
- Central retinal artery
- Lacrimal artery
- Posterior ciliary arteries (long posterior and short)
- Muscle branches
- Supraorbital artery
- Ethmoidal arteries
- Medial palpebral arteries
- Terminal branches
Where does the ophthalmic artery arise from?
It is the first branch of the Internal carotid artery distal to the cavernous sinus
What are the distinguishing features of muscular arteries?
- internal elastic lamina = prominent + undulates (moves with smooth wave-like motion)
- THICC tunica media composed of mostly SMCs (40 layers)
- sparse vasa vasorum in tunica adventitia
Define vasa vasorum
network of small blood vessels supplying large blood vessels
Describe sympathetic blood vessel fibres involved with vasoconstriction
- they are unmyelinated and post-ganglionic
How large are arterioles
- less than 0.1mm diagmeter
In relation to the size of the lumen, how wide are the walls of arterioles?
equal to size of lumen
Describe the general features of arterioles , in terms of their tunic content
- tunica intima: no internal elastic lamina, except in larger arterioles
- tunica media: 1-3 SMCs
- no external elastic lamina
- tunica adventitia: very little
Where do capillaries arise?
From the terminal end of an arteriole
Define capillaries
basically a single layer of endothelial cells
How do pericytes interact with capillaries
They provide much needed structural support to the capillaries
What do capillaries form a network between?
arteriole and venule
Describe the general features of capillaries
- single layer of squamous endothelial cells
- only tunica intima (with no IEL)
- one endothelial cell forms the “tube” - usually 10cm
- pericytes are located on the outside of capillaries + venules
List the 3 types of capillaries. What is the key difference between them?
- Continuous
- Fenestrated (2 types)
- Non-continuous/Sinusoidal
Key difference = endo. walls. Fenestrated has holes in them, continuous has no holes.
Describe the features of fenestrated capillaries
- thin wals
- fenestrations covered by basal lamina
- large fluid movement
- found in choroid and ciliary body
Describe the features of continuous capilaries
- have endothelial cell tight junctions
- big molecules: active transport
- small molecules: diffusion
- found in retina and iris
Describe the features of dis-continuous capillaries
- large and tortuous
- fenestrated incomplete basal lamina
- not found in eye (are found elsewhere in body)
What is the role of veins?
transport blood back to the heart
What are more numerous, veins or arteries?
Veins outnumber arteries
T/F Veins have small luminal diameters
False. Veins have large luminal diameters because they carry 70% of total blood
Describe the general structure of veins
- thin walls (thinner than arteries)
- layering within walls is indistinct
- can be small, medium and large veins
- contain up to 3 tunics like arteries (muscular + elastic layers are not well developed)
Which has thinner walls, veins or arteries? What does this suggest?
Veins have thinner walls. This means the veins more easily burst open with higher IOP (still way higher than normal)
Explain how veins react to the following IOP levels: 35mmHg, 50mmHg
35: veins try to widen
50: veins can’t widen anymore, they then burst open
What happens when IOP is greater than MAP
you start to lost perfusion pressure
Where does blood from capillaries go to?
is discharged into post-capillary venules
What size are venules in diameter?
They are small, ~0.02-0.2mm in diameter
Are venule walls similar to capillaries?
yes
Describe venule walls
Thin endothelium surrounded by reticular fibres + pericytes
In venules, what happens to pericytes as diameter increases
They are replaced by SMCs (smooth muscle cells)
