Downing- Blood Vessel Histology Flashcards
What are the three layers of a blood vessel?
- intima
- media
- adventitia
What is the innervation for blood vessels?
Postganglionic unmyelinated sympathetic nerve fibers
Do the nerves enter the tunica media?
No
What do the sympathetic nerves do to the blood vessels?
Release NE that causes contraction. Impulses are than propagated via GAP junctions.
What are the largest arteries called and what are examples of them?
Elastic Conducting Arteries
Aorta
Common carotid and subclavian arteries
Common iliac arteries
Pulmonary trunk
What do the elastic arteries look like?
Appear yellowish in fresh specimens d/t abundance of elastin in arterial walls
What is the endothelium of the tunica intima of the elastic arteries composed of?
- Elongated simple squamous endothelial cells 2. oriented in a longitudinal plane
- connect by occluding junctions.
Why does the plasma membrane of the tunica intima of Elastic arteries contain small vesicles?
For transport of water, macromolecules and electrolytes.
What are Weibel-Palade bodies?
WPBs are membrane bound inclusions contained in arterial endothelial cells.
What do Weibel Palade bodies contain?
- vWF (facilitates coagulation of platelets during clot formation)
- P selectin
Why do the endothelial cells of the EA contain blunt processes that reach through the internal elastic lamina?
- To form gap junction w/ nearby smooth muscle cells of the tunica media
* Gap junctions metabolically couple endothelial cells w/ smooth muscle cells
What is the internal elastic lamina of the EA?
thin lamina of elastic fibers that is the boundary between the intima nad the media
What is the tunica media of the EA?
Circularly arranged smooth muscle bands alternated with elastin that contains a fenestrated membrane.
What is the dominant component of hte tunica media of hte EA?
Elastin
Extracellular matrix is produced by what cells in the tunica media?
Smooth muscle cells
How does the adventitia of EA compare to the intima and the media?
It’s relatively thin.
What is the t. adventitia of the EA composed of?
Loose fibroeleastic CT w/ fibroblasts
What does the t. adventitia of the EA contain?
vasa vasorum (blood vessels of the blood vessels) that give rise to capillary beds that nourish the tunica media
What are examples of Muscular arteries?
Pretty much most of the named arteries that we know.
What are the chief characteristics of the muscular arteries?
- Thick tunic media
2. Composed primarily of smooth muscle cells
Is the t. intima of the MA thinner or thicker than the EA?
THINNER
What is prominent in the t. intima of MA?
Internal elastic lamina (has an undulating contour which the endothelium conforms to)
What’s the role of blunt processes in the MA?
Similar to the EA endothelial cells have blunt processes that reach through the internal elastic lamina, forming gap junctions and coupling the metabolic activity of endothelial with smooth muscle cells.
What is the t. media composed of and arranged in MA?
Smooth muscle cells
circumferrentially arranged
How many layers of smooth muscle in smaller muscular arteries?
4-3 layers
How many layers of smooth muscle in large muscular arteries?
up to 40 layers
What encloses each muscle cell of the t. media in the MA?
external basal lamina
What connects adjacent muscle cells in teh t. media of the MA?
gap junctions
What produces the extracellular matrix of the t. media in MA?
Smooth muscle cells
Chondroitin sulfate, elastic fibers, type III colagen
What is present in large muscular arteries and helps define the boundary between the t. media and t. adventitia?
External elastic lamina
What produces the t. adventia of the MA?
fibroblasts produces CT containing elastic fibers, collagen and ground substance.
Unmyelinated nerve endings enters the ______ of the t. adventitia of the MA?
vaso vasorum
What is the typical diameter of arterioles?
< .1 mm
How does the diamter of the wall compare to the diameter of the lumen in an arteriole?
They’re the same
What does the t. intima look like in the arteriole?
- endothelium
- thin layer of CT
- internal elastic lamina
What does the t. media look like in small and larger arterioles?
small- one layer of smooth muscle cells
larger- 2-3 layers smooth muscle cells
Is an external elastic lamina present in an arteriole?
NO
Does an arteriole have a t. adventitia?
NO
What are metarterioles?
Smooth muscle cells that can act as sphincters and control blood flow into the capillary bed by encircling the vessel where a capillary comes from
Are smooth muscle cells in metarterioles continuous?
NO
What are the carotid sinuses?
BARORECEPTORS that perceive changes in blood pressure
Where are the carotid sinuses located?
In the walls of the internal carotid arteries just above the bifurcation of the common carotid arteries
What is unique about the adventitia in the carotid sinuses?
It’s thicker and heavily endowed w/ sensory nerve endings from CN 9 (glossopharyngeal)
What does the t. media of the carotid sinus do?
It’s thin, so it permits distention of the blood vessels w/ increasing BP which stimulates the nerve endings and leads to appropriate adjustments in vasoconstriction to maintain proper blood pressure.
What are the carotid and aortic bodies?
Chemoreceptors
Where are carotid bodies located?
At the bifurcation of the common carotid arteries
What is the function of carotid and aortic bodies?
They have special chemoreceptor nerve endings that monitor changes in oxygen, carbon dioxide, and H ions in the blood
What supplies afferent fibers to the carotid bodies?
CN 9 and 10 (glossopharyngeal and vagus)
Where are aortic bodies located?
Arch of the aorta between the r. subclavian and L. common carotid and between the l. common carotid and l. subclavian
What is the general length and diameter of capillaries?
usually short (1 mm) and 8-10 um in diameter
What type of cells makes up a capillary? What are they joined together by?
- single layer of elongated simple squamous endothelial cells
- fasciae occludentes
What is associated with the plasmalemma of hte capillary?
pinocytotic vesicles
What is hte external surface of a capillary covered by?
basal lamina
Where are pericytes found?
- Outside capillaries and small venules and they share a basal lamina of endothelial cells.
- Have primary and secondary processes that run longitudinally and circumferentially along and around the capillary
What do pericytes do?
Contractile and help regulate blood flow through capillaries
What may pericytes do if they’re injured?
Give rise to smooth muscle and endothelial cells
What are the three types of capillaries?
- continuous
- fenestrated
- sinusoidal
What are the characteristics of continuous capillaries?
- no interruptions (pores/fenestrae)
- found in muscle, nervous and CT
- joined by fascia occludentes
What are the characteristics of fenestrated capillaries?
Pores in walls of capillaries, that occur in clusters, that are covered by a thin diaphram (glycocalyx).
Where are fenestrated capillaries found?
pancreas, intestines and ENDOCRINE GLANDS
What are the characteristics of sinusoidal capillaries?
- irregularly shaped pools/channels
- LARGER diametr than otehr capillaries
- Contain many fenestrae
Where are sinusoidal capillaries found?
Bone marrow, liver, spleen, lymphoid organs, and certain glands.
Where do AVAs occur?
Where an artery joins a venous channel
What are the three segments of an AVA?
- arterial segmennt
- intermediate segment (thickened t. media)
- venous segment
Which segment is richly innervated w/ adrenergic and cholinergic fibers?
Intermediate segment
What happens in the AVA is the shunt is open?
Blood bypasses the capillary bed
What happens in the AVA if the shunt is closed?
Blood passes into the capillary bed
The AVA plays an important role in…
thermoregulation (skin)
What is the central channel composed of?
Metarterioles and a capillary bed
What is the role of the central channel?
It can bypass the capillary bed by closing the precapillary sphincters.
Where does hte capillary bed drain into?
The venule
What is transcytosis?
vesicle transport–substances are taken up by pincocytotic vessels on the adluminal side and discharged on the abluminal side of the endothelial cell
What is leukocyte adhesion?
When leukocytes bind to the endothelium and pass through the endothelium to enter the extravascular spaces
What does attachment and adhesion involve?
- selectins
2. integrins
What is the role of histamine and bradykinin?
They accumulate at the site of inflammation and increase capillary permeability—> edema
What do endothelial cells produce?
prostacyclin, plasminogen activator, IL-1, GFs, collagen types, fibronectin, laminin
What type of enzymes does a capillary have?
- ACE enzymes that convert angiotensin I to II
2. enzymes that break down lipoproteins to fatty acids and triglycerides which can be stored in a fat droplet of a cell
Are there more veins or arteries?
veins
What can hold more blood: veins or arteries?
diameter of veins is larger than arteries, so 70% of blood volume is in the vessels
What are postcapillary venules?
recieve blood from capillary bed
Describe the endothelium of postcapillary venules?
Thin endothelium surrounded by pericytes
What happens to pericytes in larger venules?
The pericytes are replaced by smooth muscle cels. As the venules get larger the smooth muscle cell layer becomes more complex.
What is HEV?
Specialized versions of the small venules in certain lymphatic organs
How is the HEV endothelium unique?
it is CUBOIDAL rather than squamous
What does the HEV do?
Ensures that specific lymphocytes migrate into the proper regions of the lymphoid parenchyma
What do the medium veins parallel and how big are they?
Muscular arteries
<1 cm in diameter
What do medium veins do?
Have valves that help prevent backflow
What is the thickest layer of the medium veins?
t. adventitia
What are examples of large veins?
vena cavae, pulmonary, portal, renal, internal jugular, iliac and azygous veins
What two layers blend together in large veins?
The t. intima and t. media
What is unique about the t. adventitai of large veins?
The inferior vena cava has an abundance of LONGITUDINALLY oriented smooth muscle bundles
What are varicose veins?
abnormally enlarged and tortuous veins
What cause varicose veins?
- loses of muscle tone
- wall degeneration
- valvular incompetence
Where else can varicose veins occur?
lower esophagus (esophageal varices) terminus of anal canal: hemorrhoids
In what veins are valves found?
In small and medium sized veins–not many in the thorax and abdomen and they’re ABSENT in the brain and spinal cord
What do valves consist of in veins?
Folds of intima: endothelium and CT core rich in elastic fibers
What do valves do?
Prevent backflow
How do lymph capillaries differ from blood capillaries?
- large diameter
- end blindly in the tissue
- have a scanty basement membrane (no barrier to entry of macromolecules)
- held together by few tight junctions
The collecting vessels of the lymphatic system have a vein like structure except:
- walls tend to be thinner than walls of veins of equal size
- valves are MORE CLOSELY SPADED than in veins
What are hte main trunks of the lymphatic system?
- thoracic and right lymphatic ducts and their tributaries
2. vein like structure
