25 - Vascular biology I Flashcards
1
Q
Overview of blood vascular system
A
Peripheral tissues
- Arteries deliver blood to peripheral tissues
- Microcirculation is where nutrient exchange occurs
- The vena cava returns peripheral circulation to the heart
Pulmonary circulation
- Consists of microcirculation in the lungs
2
Q
Lymphatic vascular system - What is the most important protein in the blood? Is there a net loss or net gain of fluid from the tissues during circulation?
A
Works in concert with the blood vascular system
- Albumin is an important plasma protein because it exerts colloid osmotic pressure
- As blood moves through microcirculation, various pressures cause blood to move in and out
- There will ALWAYS be a net LOSS of fluid into the tissues
- To prevent excess blood accumulation in the tissues, the lymphatic system picks up the extra fluid and returns lymph to venous circulation
3
Q
What is the general structure of a blood vessel?
A
3 layers:
- Intima: creates the lumen of the blood vessel - innermost layer
- Media: middle layer
- Adventitia: outermost layer, AKA externa
4
Q
How many layers are in the tunica intima? What are they?
A
4 layers
- Endothelium of tunica intima (innermost)
- Basal lamina
- Subendothelial connective tissue
- Internal elastic membrane (outer most layer)
5
Q
Endothelium of tunica intima
A
Endothelium of tunica intima = Innermost layer of tunica intima
- Has DIRECT contact with blood
- Contains an epithelial layer of simple squamous cells
- These are called endothelial cells when they are associated with the vascular system
- The endothelium is connected to the basal lamina
6
Q
Basal lamina of the tunica intima
A
Connected to the innermost layer, the endothelium of the tunica intima, and is therefore the second innermost layer
7
Q
Subendothelial connective tissue of the tunica intima
A
Subendothelial connective tissue of the tunica intima
- External to the basal lamina
- Contains the extracellular matrix plus the cells that synthesize that matrix
- Occasionally smooth muscle cells are found here, but this is generally a precursor to atherosclerosis
8
Q
Internal elastic membrane of the tunica intima
A
Internal elastic membrane of the tunica intima
- Outer most layer of the tunica intima
- This layer is fenestrated, meaning that there are tiny openings within this layer
- The purpose of this is to move gas and nutrients
- Blood will mvoe externally out
9
Q
What is the tunica media comprised of?
A
Tunica media
- The bulk of the tunica media is smooth muscle cells
- There are also variable amounts of elastin - this depends on the type of vessel
- The outermost component of the tunica media is an external elastic lamina (this will appear as a bluish line at the microscopic level)
10
Q
What is the tunica adventitia (externa) comprised of?
A
Tunica adventitia (externa)
-
Blood vessels and nerve fibers are transmitted in this layer
- The vasculature sends branches through fenestrations of external elastic membrane to the outer layer of tunica media
- The walls of the vessels are supplied by blood in the lumen
- Externally, they are supplied by vasa vasorum (“vessels of the vessels”)
11
Q
When are vasa vasorum required?
A
Required for vessels greater than 1 mm
12
Q
How can you differentiate between arteries and viens by looking at only the vasa vasorum?
A
There is a difference between the depth of penetration of vasa vasorum toward the tunica intima
- Vasa vasorum in veins will penetrate much deeper, and closer to the tunica intima than in arteries
- This is because the veins are carrying deoxygenated blood
- Oxygenated blood carried by the arteries is able to “feed” the tunica intima in arteries
13
Q
What is the relationship between vasa vasorum and inflammation? What are some examples of this?
A
Inflammation
- The vasa vasorum contributes to inflammation
- Examples
- Angiogenesis is seen in atherosclerosis
- Syphylis also shows changes in teh vasa vasorum
14
Q
What are the effects of syphilis on the vasa vasorum of the ascending aorta?
A
Endarteritis and periarteritis
- Degeneration of elastic tissue and smooth muscle
- Inflammatory cells are observed around the vasa vasorum
- Dark specs will show up - these are inflammatory cells
- Syphilis will lead to inflammation of the ascending aorta and eventually, the wall of the aorta will begin to degenerate
15
Q
What is nervi vasorum (vascularis)?
A
Nerves that supply the walls of blood vessels
- Nervi vasorum translates to the “nerves of the vessels”
- These are found in the tunica aventitia (external)
- Can also be called “nervi vascularis”
- Most of these nerves are soley sympathetic
- Some also have parasympathetics
16
Q
What is meant by the “light halo” of the nervi vasorum?
A
The light halo = sympathetic nerve endings external to the tunica media, forms a “halo” around the tunica adventitia
- These nerve endings do NOT penetrate the tunica media
- They innervate the OUTER part of smooth muscle
- Once acitvated by sympathetic activation, they can communicate through gap junctions to smooth muscle cells
- They release norepinephrine
17
Q
Describe endothelial cells
A
Endothelial cells are flattened cells
- Oriented in the direction of blood flow
- Elongated in the direction of blood flow
Junctional complexes connect two endothelial cells
- Lumen is above, where the blood flow is
- Microvili will, on occasion, be found in the apical domain of endothelial cells
18
Q
How are nutrients absorbed from the circulation into the tissues?
A
Numerous pinocytotic vesicles
- Important transport process of enothelial cells of the vascular system
- Transport from the lumen of the blood vessel across the cytoplasm and into the subendothelial tissue compartment of the tunica intima
19
Q
What is a myoendothelial junction? What is the result?
A
Myoendothelial junction
- The myendothelial junction is the junction between the endothelium and the smooth muscles
- The shear stress that is exerted by the blood flow produces endothelial cell hyperpolarization
- Increased flow through the vascular system increases the level of stress on the endothelial cells
- Hyperpolarization communicates through gap junctions to the smooth muscles, causing hyperpolarization of smooth muscles as well
- This results in vasodilation - an increase in the diameter of the vessel
20
Q
What are Weibel-Palade (WP) granules?
A
Weibel-Palade (WP) granules
- The storage granules of endothelial cells, the cells that form the inner lining of the blood vessels and heart
- They store and release two principal molecules, von Willebrand factor and P-selectin, and thus play a dual role in hemostasis and inflammation
21
Q
What is von Willebran factor important for?
A
Coagulation!
- A deficiency in von Willebrand factor will result in a hemorrhagic disease
22
Q
What is P-selectin important for?
A
P-selectin
- Important for allowing leukocytes to connect to endothelial cell membranes and facilitate migration through the wall of vasculature
23
Q
What are the 6 main functions of endothelial cells?
A
-
Produce prostacyclin
- Prostacyclin is a vasodilator, so it increases blood flow
- Also inhibits blood clotting
-
Act as a chemical mediator
- Functions in both vasodilation and vasoconstriction
- Nitrate oxide is a potent vasodilator
-
Produce endothelin I
- Potent vasoconstrictor of the walls of the vessels
-
Control vascular growth
- Angiogenesis
-
Inhibit or promote blood clot formation
- Important to prevent excessive blood loss
-
Regulate movement of inflammatory cells from the lumen into the tissues
- Selectin is an important adhesion molecule to allow inflammatory cells to recognize the membrane
24
Q
What are the segmental characteristics of blood vessels?
A
When looking at different vessesls, there are segmental differences in hwo the tunics are arranged
- High pressure vessels
- Arterial circulation
- Walls are thick and the tunica media is prominent
- Low pressure
- Thinner walls
25
Why do we see segmental characteristics?
Segmental characteristics are due to form-fuction relationships
\*\*\*VERY IMPORTANT\*\*\*
26
What are the segmental characteristcs of high pressure environments?
High pressure environments
* A lot of smooth muscle and elastic elements
* The wall of the aorta is elastic, so it can stretch with ejection of blood and will recoil with diastoel to maintain driving pressure
* You will see diminishing amounts of smooth muscle and elastic materials in smaller arteries
* Less elastic elements in arterioles
27
What are the segmental characteristcs of the microcirculation?
Microcirculation is where there are capillaries and pericytic venules
* Endothelium and basal lamina ONLY
* No extra tunics are present _because they would interrupt the exchange of gas and nutrients_
* This is a very thin component
* Metabolic factors determine the framework/structure of the wall
28
What are the segmental characteristcs of venous components?
Venous components
* A lot of connective tissue
* Not a lot of change in the amount of smooth muscle from large vessels to small vessels
* Pick up elastic components again
29
Architecture of an artery vs. vein
Signature features of **Arteries:**
* Prominent elastic membrane
* Internal or external elastic membrane indicates arterial side
* Thick muscular tunica media
Signature features of **Veins:**
* Do NOT hae a prominent internal or external lamina
* Thin tunica media compared to arteries
* Tunica adventitia has a lot of connective tissue and is therefore the thickest layer of the vein
* The wall of the vein does not have as much connective tissue
30
What are some examples of elastic arteries?
Aorta, brachiocephalic trunk
31
Describe the tunica media of an elastic artery
Tunica media of an elastic artery
* Alternating smooth muscle and elastic lamellae that are fenestrated
* Soley elastin in elastic lamellae (no elastin)
32
Describe the tunica adventitia of an elastic artery
Tunica adventitia of an elastic artery
* Mylinated nerve fiber
* Connective tissue cells
* Fibroblasts
33
Describe Marfan syndrome
Marfan syndrome
* A genetic disorder of human connective tissue
* It has various expressions ranging from mild to severe effects... The most serious complications are defects of the heart valves and aorta, which often lead to early death
* In the tunica media, elastic lamellae are connected and supported by _true elastic fibers_
* This is what's dysfunctional in Marfan's
* There is a "state of disarray" because the elastic fibers have microfibrils
* There is a loss of structural integrity of the aorta due to the loss of interconnections in teh elastic fibers
34
How does the aorta change over a lifetime?
From birth to adulthood
* M lamellae increase with age, as needed
* Adipose tissue is seen in newborns
* Tunica media is much thicker in adults
35
Effects of aging on the aorta
Age changes features of the aorta
* The _subendothelial compartment_ is more robust/thicker than normal
* Moderal intimal _fibrosis_ occurs, which is a normal effect of aging
* The _tunica media_ undergoes minor fragmentation of the elastic lamellae, which is also a normal change with age
36
Age-related changes in muscular arteries
Young muscular artery
* Internal elastic membrane appears scalloped
* A huge vasa vasorum is visible
Elderly, less-muscular artery
* Some fragmentation and intimal hyperplasia
* Duplication of the internal elastic membrane
37
What is meant by the ratio of unity in arterioles?
Arterioles
* The wall-to-lumen ratio is 1, meaning that the opening of the lumen is the same size as the wall of the arteriole
* The wall will contain one or two smooth muscle layers
* Arterioles are the main resistance vessels
38
What is microcirculation?
Microcirculation is the circulation between arterioles and venules
* _Arteriole_: a small diameter blood vessel in the microcirculation that extends and branches out from an artery and leads to capillaries
* _Venule_: a very small blood vessel in the microcirculation that allows blood to return from the capillary beds to drain into the larger blood vessels, the veins
39
What mechanism is utilized by the microcirculation to control volumes of blood flow?
Sphincter mechanism
* The sphinters are located on metarterioles (branches of arterioles)
* They control the volume of blood flow from arterioles to the microcirculation
* **Relaxes** sphinters allow for **more** blood flow into the microcirculation
* Sphinters are _controlled by tissue metabolism_
* _Active tissues_ will have relaxes sphincters
* Relaxed sphincters allow for more blood flow into the microcirculation
* **Contracted** sphinters **limit** the amount of blood flow through the microcirculation
* This occurs in _less active tissues_
40
What type of tissues will have relaxed sphincters of the microcirculation? What type of tissues will have contracted sphincters?
**Active tissues**
* _Relaxed_ sphincters
* More blood flow
* More delivery of oxygen and nutrients
**Less active tissues**
* _Contracted_ sphincters
* Less blood flow
* Lower need for oxygen and nutrient delivery
41
What are the 3 classes of capillaries?
1. Continuous
2. Fenestrated (two subclasses)
* With diaphragms in fenestration openings
* Without diaphragms in fenestration openings
3. Sinusoid
42
What is a pericyte?
Pericyte
* Undifferentiated mesenchymal cells that are contractile in nature that can differentiate into smooth muscle cells or fibroblasts under the appropriate stimuli
* Help control the diameter of the microcirculation
* Associated with capillaries and pericytic venules
43
Describe a the cause of a cerebral aneurysm
Cerebral aneurysm
* Bifurcation and branching points in circle of Willis are points of weakness and have the potential for aneurysms
* Aneurysms in the cerebral cortex are found at the _anterior communicating artery_ 30% of time
* Aneurysms of the circle of Willis differ in etiology of that in, for example, the abdominal aorta
44
Why are branching points prone to aneurysms?
Lack of smooth muslce
* At points of bifurcation, there is a gap in smooth muscle because the smooth muscle that developed along the main artery didn't fill in the gap
* Lack of smooth muscle degreases the structural integrity at the point of bifurcation
* A breakdown of the wall of the artery at the point of bifurcation will lead to an aneurysm
45
How can you tell if someone is living with an aneurysm?
You can't!
* Aneurysms are silent
* People can live with them until they rupture, at which point it may be too late to save their life
