Vascular Structure/Function, Vascular Anomalies, and Vascular Response to Injury Flashcards
There are 3 concentric layers to a blood vessel. What are they?
Intima
Media
Adventitia
Describe the 3 layers of blood vessels (intima, media, and adventitia). Make sure to mention differences in arteries vs. veins.
Intima = single layer of endothelial cells
Media:
- arteries = well organized concentric layers of smooth muscle
- veins = haphazard
Adventitia = external to media, often separated from media by wide external elastic lamina
What layer separates intimate from media?
Internal elastic lamina
What are the 3 types of arteries?
Elastic arteries
Muscular arteries
Arterioles
Describe elastic arteries. What are they predominantly made up of and how does this affect its function?
They have a high elastin content which allows expansion during systole and recoil during diastole
Propels blood toward organs
How are elastic arteries affected by age?
Increasing age leads to less compliance leading to increased blood pressure
Describe muscular arteries.
Circumferentially oriented smooth muscle
Arteriolar smooth muscle contraction = vasoconstriction
relaxation = vasodilation
Describe arterioles.
Principal point of physiologic RESISTANCE to blood flow
How do you calculate resistance?
Resistance to fluid flow is INVERSELY proportional to 4th power of diameter
R ~ nL/r^4
What is vasa vasorum?
“vessels of the vessels”, small arterioles supply O2 to outer media of large arteries
Where might you see Large Elastic Arteries?
Aorta and its major branches (common carotid, iliac, pulm art)
Where might you see Medium Sized Muscular Arteries?
Smaller branches of the aorta (coronary and renal)
Where might you see Arterioles?
Within tissues and organs
Describe capillaries.
Diameter of an RBC, no media, pericytes (resemble smooth muscle cells)
Describe veins. How are they structured compared to arteries?
Most inflammatory reactions, vascular leakage, and leukocyte exudation
Larger lumens, thinner and less organized walls; contains about 2/3 of total blood volume
Less rigid = susceptible to dilation and compression, as well as infiltration by tumors and inflamm. processes
What are venous valves?
Valves in the extremities to prevent venous reverse flow due to gravity
Describe lymphatics. How are they structures? What is their function?
Thin walled, lined by specialized endothelium
Return intestinal tissue fluid and inflammatory cells to bloodstream
Transport bacteria and other materials
Tumor cells = pathway for disease dissemination
What are the pressure differences between arteries and veins?
Arteries have a HIGH pressure system
Veins have a LOW pressure system
What are the 3 vascular anomalies?
Aneurysms
Arteriovenous malformation (AVM)
Fibromuscular dysplasia
What are aneurysms? When do they occur?
Localized abnormal dilation of blood vessel or the heart
Not present at birth, but develop over time due to underlying defect in the media of vessel
What are arteriovenous malformations (AVMs)?
Tangle, worm-like vascular channels with prominent PULSATILE arteriovenous shunting with high blood flow
Arteriovenous shunting = arteries –> veins WITHOUT intervening capillaries
What can AVMs ultimately lead to?
Large or multiple AVMs may shunt blood from arterial to venous circulation, forces heart to pump additional volume leading to high-output cardiac failure
What is fibromuscular dysplasia? When does this occur?
Focal irregular thickening in medium and large muscular arteries (renal, carotid, splanchnic, and vertebral vessels)
Usually developmental defect, but can arise form trauma, etc.
What is HTN a consequence of?
Increase tone in small muscular arteries and arterioles
What is the defining characteristic of a berry aneurysm?
“The WORST headache I’ve ever had”
Where do Berry aneurysms typically occur, what part of this area is the most common site? What disease could they be characteristic of?
Circle of Willis
90% of berry aneurysms found near major branch points of the ANTERIOR circulation
AD polycystic kidney disease
What is most clinically significant of berry aneurysms?
It is the most frequency cause of subarachnoid hemorrhage
1/3 of ruptures associated with acute increases in intracranial pressure
How can mycotic aneurysms arise? Can you give me an example of when you may get a mycotic aneurysm?
Embolization of a septic embolus, usually complication of infective endocarditis
Extension of adjacent suppurative process
Circulating organisms directly infecting the arterial wall
EX: Pts with cardiac disease may get these aneurysms
What are fusiform and giant aneurysms?
Fusiform aneurysms bulge from all sides of an artery and do not have a neck (unlike berry)
Giant aneurysms will involve more than one artery and be over 2.5 cm wide
How can AVMs form?
Result from rupture of an arterial aneurysm into adjacent vein
Penetrating injuries that pierce arteries and veins
Inflammatory necrosis of adjacent vessels
When is an AV fistula useful?
Surgically generated AV fistulas provide vascular access for chronic hemodialysis.
Joining the artery and vein together makes the vein stronger by thickening it due to the high pressure system of the artery. It also provides better access to the blood as it will get taken from the vein, cleaned, and put directly back into the artery.
What is fibromuscular dysplasia?
Focal IRREGULAR thickening in medium and large muscular arteries (renal, carotid, splanchnic, and vertebral vessels)
Can develop aneurysms that may rupture
What is the cause of fibromuscular dysplasia? In who is it most likely seen?
Unknown, probably developmental
Young women
First degree relatives have increased incidence
What conditions may arise form fibromuscular dysplasia?
Medial and intimal hyperplasia leading to luminal stenosis
Renovascular HTN due to fibromuscular dysplasia of renal arteries
What is the marked appearance of fibromuscular dysplasia? What imaging is needed to confirm dx?
String of beads
Seen in Angiography - needed
Describe the normal expression of vascular endothelial cells.
Non-thrombogenic surface = maintains blood in fluid state
Modulate medial smooth muscle tone = influence vascular resistance
Metabolize hormones (angiotensin) Regulate inflammation Affect growth of other cell types (esp smooth muscle cells)
What is endothelial activation? Explain in detail.
When an injury (turbulent flow, HTN, cigarette smoke, lipid products, etc) leads to change in expression of endothelial cells.
Increased expression of procoagulants, adhesion molecules, and pro inflammatory factors
Altered expression of chemokine, cytokines, and growth factors
What is the initial event following vascular injury?
Endothelial activation
What is endothelial dysfunction?
Alteration in phenotype of endothelial cells leading to pro inflammatory and prothrombogenic states
Initiation of thrombus formation, atherosclerosis, and vascular lesion of HTN
Describe the conditions that vascular smooth muscle cells are responsible for.
Vascular Repair and atherosclerosis
What is the function of vascular smooth muscle cells?
Ability to proliferate
Synthesize collagen, elastin, and proteoglycans
Elaborate growth factors and cytokines
Vasoconstriction/vasodilation
What is intimal thickening?
Stereotypical response of vessel wall to any insult/injury
Describe the process of intimal thickening.
Associated with endothelial cell dysfunction or loss
Stimulates smooth muscle cell recruitment and proliferation and associated matrix synthesis
Neointimal smooth muscle cells are motile, undergo cell division, acquire new biosynthetic capabilities
They can return to nonproliferative state with normalization of endothelial layer
The healing response results in intimal thickening that may impede blood flow
In a step wise fashion, describe the response to vascular injury.
- Recruitment of smooth muscle cells or smooth muscle precursor cells to intimal
- Smooth muscle cell mitosis
- Elaboration of extracellular matrix
