Cole: Vascular System Histology Flashcards
Large Veins: Typical Feature, causes of varicose veins, causes of hemorrhoids, thormbosis vs embolus
Typically have valves to prevent reflux of blood
varicose veins occur when valves don’t close properly
hemorrhoids are dilations of the internal or external rectal venous plexuses.
thrombosis is an aggregate of RBCs in the veins
embolus is when the thrombosis begins sending out aggregates of RBCs
Vasculitis
inflammation of our blood vessels
causes changes in the wall of blood vessels, including thickening, weakening, narrowing and scarring
changes restrict blood flow, resulting in organ and tissue damage
Vascular development: what two ways to blood vessels form?
vasculogenesis
angiogenesis
Vasculogenesis
blood vessels arise from coalescence of hemangioblasts which arise from blood islands
Angiogensis
vessel formation via branches arising from existing vessels
major vessels form through
vasculogenesis
Early vasculogenesis
begins in what region of the fetus….
when?
then what?
begins in XE splanchnic mesoderm surrounding the yolk sac
week 3
formation THEN moves into lateral plate mesoderm
Early vasculogenesis: site of blood islands
yolk sac
first site of blood sac formation
Blood islands
arise from mesoderm cells that are induced to form hemangioblasts, common precursor for vessel and blood cell formation
Early erythropoiesis occurs in the
yolk sac
Blood islands: what are they made from, what do they develop into
in yolk sac. they contain hemangioblasts and contain two different cell populations
hemangioblasts 1: angioblasts (vascular precursors) form endothelial cells
hemangioblasts 2: hematopoietic stem cell
FGF2
binds to mesenchymal cells (mitogen) –> hemangioblasts
VEGF
may be expressed in response to HOXB5 which upregulates VEGF receptor FLK1
vascular endothelial growth factor elicits regional change in blood islands (2 receptors)
FLK1
receptor for VEGF, induced by HOXB5 to be induced
VEGFR1
induces tube formation
VEGFR2
induces hemangioblast formation
Central cells in the blood islands become
hematopoietic stem cells
Peripheral cells differentiate into
angioblasts —> endothelium of blood vessels
Angiogenesis:
Angeiopoietin 1
so once nascent vascular bed is established through VEGF signaling, angiopoietin 1 interacts with receptor Tie2
this recruits periendothelial cells (pericytes) to smooth muscle cells in large vessels to organize mature blood vessels
Ang1
Angipoietin 1 interacts with Tie1 to cause periendothelial cells (pericytes)
Ang2
Angiopoietin 2
interacts with tie2 to induce losee of contact of endothelial cells with ECM. this causes absence of growth of endothelial cells or their death
Ang2 is an increasing target for cancer treatment
What do blood islands do in vasculogenesis?
they fuse together to form primary capillary plexus
Once blood circulation is established -
primary plexi are remodelled into hierarchical network of Arterioles Arteries Capillaries Venules Veins
SHH from the Notochord induces
VEGF
VEGF induced by SHH from the notochord does what
induces NOTCH pathway, which specifies arterial development through expression of ephrin2 (ligand)
EPHB4
gene specific for controlling venous development
PROX1
Master gene for lymphatic vessel differentiation
AGM
Aorta-gonad-mesonephros region
Definitive hematopoietic stem cells develop where
AGM
site surrounding the aorta near the developing mesonephric kidney
hematopoietic stem cells eventually…
colonize the liver, which becomes the major hematopoietic organ of the embry (2-7 months)
2-7 months hematopoiesis occurs in –
7 months >, hematopoiesis occurs in the —
liver, then bone
Hemangioma
abnormally dense collection of capillary vessels
common tumors in infancy (10%)
Naevus flammeus
Port Wine Stain
superficial and deep dilated capillaries in the skin
Cardiac Wall consists of
three layers
1) Endocardium
2) Myocardium
3) Epicardium
Endocardium
the inner most layer that sits under an epithelia
Myocardium
a functional syncytium of striated cardiac muscle fibers forming three major types of cardiac muscle:
atrial muscle
ventricular muscle
specialized excitatory and conductive muscle fibers
Epicardium
visceral layer of the pericardium
low friction surface lined by a mesothelium in contact with the parietal pericardial space
Cardiocytes
contractile: contract to move blood
myoendocrine: produces atrial natriuretic factor (ANF)
Nodal: specialized to regulate contraction of the heart (SA and AV nodes)
Arteries do what two things
pump blood from the heart and store blood
3 major layers of an artery
tunica intima
tunica media
tunica externa
Tunica externa
- outermost layer: tunica Adventitia
- composed of a loose CT that contains elastic and collagen fibers
- helps anchor the vessel to other tissues
- an external elastic lamina can be seen separating the tunica media from adventitia
has vasa vasorum
tunica media
middle later
composed of circularly arranged layers of smooth muscle cells
vasoconstriction (narrowing of the blood vessel lumen)
vasodilation: widening of the blood vessel lumen
tunica intima
innermost layer of a blood vessel wall
composed of an endothelium and a subendothelial layer
external layer of elastic fibers, the internal elastic lamina
Arteries from the heart can be classified into three groups
large elastic
medium sized
small arteries and arterioles
Large Elastic (conducting) arteries: two major characteristics
- they receive blood from the heart under high pressure
2. they keep blood circulating continuously while the heart is pumping intermittently
Which arteries distend during systole and recoil during diastole?
large elastic arteries
Tunica Intima consists of the
endothelium and the subendothelial connective tissue
large fenestrated sheaths are found in the
tunica media
fenestrated sheaths with bundles of smooth muscle cells permeating the narrow gaps between the elastic lamellae
Vasa Vasorum and Nervi varosum are located in the
tunica adventitia of large elastic arteries
as well as lymphatics
what major vessels constitute large elastic arteries
the aorta and its largest branches (brachiocephalic trunk, common carotids, subclavian, common iliac arteries)
muscular/distributing arteries: the layers
tunica intima
media
externa
tunica intima consist of three
1) endothelia
2) subendothelia
3) internal elastic lamina (IEL)
junction of tunica adventitia and media there’s a fenestrated external elastic lamina
tunica media’s “transitional” character in muscular/distributing arteries can be described how?
a major reduction in the elastic component and an increase in the smooth muscle component
“medium” sized arteries =
radial, tibial, popliteal, axillary, splenic, mesenteric, intercostal arteries
arterioles are considered the
real determinants of systemic blood pressure
arterioles regulate
distribution of blood to capillary beds
arterioles can both
vasoconstrict and vasodilate, and partially constriction
arterioles possess a
internal elastic lamina and a layer of endothelial cells
microcirculation bed is composed of
Terminal arteriole (and metaarteriole), the capillary bed, and postcapillary venules
capillary bed in a microcirculation contains a number of different capillaries
1) large capillaries: called PREFERENTIAL or Thoroughfare Channels
2) Small capillaries called True capillaries
Preferential/Thoroughfare channels
here, blood is continuous
True capillaries
blood flow is intermittent
the functional unit of the cardiovascular system is called the
CAPILLARY
diameter of a capillary
5-10 micrometers
how many layers does a capillary have?
only the tunica intima, but this layer consists of the basement membrane and endothelium only
Continuous capillaries
lined by an endothelium, tight junctions, and basement lamina with pericytes
Fenestrated capillaries
have pores or fenestrae (GI & kidney)
sinusoids
discontinuous capillaries. gaps in endothelia and basal lamina.
found in liver and spleen
what kind of capillary would you find in the GI and kidney?
fenestrated
what kind of capillary would you find in the liver and spleen?
sinusoid
veins are “reservoir vessels” what is another name for this
capacitance
What is the preferred site of blood cell migration into tissues?
postcapillary venules via diapedesis
veins are “reservoir vessels” what is another name for this
capacitance
why do veins have a high capacitance
because of their high distensibility
tunics in veins
distinction between TM and TA is not clear
muscular tunica media is thinner than in arteries.
smooth muscle cells have an irregular orientation
distinct elastic lamina is not seen
MT is thinner than in arteries, and smooth muscle cells and have irregular orientation approximately circular
typical characteristic of veins is the presence of valves to prevent reflux of blood
Hemorrhoids
dilations of the internal or external rectal venous plexuses
varicose veins
occurs when valves in the veins don’t close appropriately
Vasculitis
inflammation of the blood vessels
causes thickening, weakening, scarring, narrowing
changes restrict blood flow, resulting in organ and tissue damage
varicose veins
occurs when valves in the veins don’t close appropriately
Vasculitis
inflammation of the blood vessels
causes thickening, weakening, scarring, narrowing
changes restrict blood flow, resulting in organ and tissue damage
Vasculitis of large sized vessels
chronic inflammation infiltrates arterial wall, a thrombus obliterates vascular lumen
“Takayasu’s arteries”
Vasculitis of medium sized vessels
Burger’s disease –> symptoms like Takayasu’s arteries
Polyarteries nodosa —> perivascular chronic inflammatory reaction
Fibrinoid necrosis of the tinuca intima predisposes to thrombosis
Lymphatic vessels begin as
dilated tubes with closed ends in proximity to blood capillaries and collect tissue fluid (lymph)
where are lymphatics lacking?
cartilage, bone, epithelia, CNS and placenta
Lymphatic vessels begin as
dilated tubes with closed ends in porximity to blood capillaries and collect tissue fluid (lymph)
Lymphangions
valves that divide each segment of a lymphatic vessel
this helps it behave like an automatic pump
Intrinsic and Extrinsic contraction of lymph vessels
intrinsic: when vessels expand they retract
extrinsic: outside vessel structures like muscle and vasculature helps further lymph fluid
lymphedema
caused by defect in the transport of lymph because of abnormal vessel development
chylous ascites and chylothorax
caused by the accumulation of high fat containing fluid or chyle in the abdomen or thorax as a result of trauma
obstruction
or abnormal development of lymphatic vessels
chylous ascites and chylothorax
caused by the accumulation of high fat containing fluid or chyle in the abdomen or thorax as a result of trauma
obstruction
or abnormal development of lymphatic vessels
Endothelial cell mediated regulation of blood flow
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