Vascular System Flashcards
vasculogenesis
-blood vessels arise from the coalescence of hemangioblasts which arise from blood islands
what type of vessels does vasculogenesis form?
major vessels
steps of vasculogenesis
- begins XE splanchnic mesoderm surrounding the yolk sac (week 3) after which the formation moves into the lateral plate mesoderm
- yolk sac is first site of formation of blood islands
- islands arise from mesoderm cells which are induced to form hemangioblasts, a common precursor for vessel and blood cell formation
- islands contain cells, hemangioblasts, which are capable of differentiating into 2 populations of cells
a. vascular precursors (angioblasts)–form endothelial cells
b. remaining hemangioblasts are hematopoietic stem cells
angiogenesis
vessel formation via branches arising from existing vessels
blood islands
- contain cells (hemangioblasts) which are capable of differentiating into 2 populations of cells
- vascular precursors (angioblasts)–form endothelial cells
- angioblasts coalesce into cords and form a lumen
- remaining hemangioblasts are hematopoietic stem cells
FGF2
binds to mesenchymal cells and induces them to form hemangioblasts
VEGF
- vascular endothelial growth factor
- elicits regional change in blood islands using VEGF-R2/R1 (Flk1 and Flt1)
- regulates formation of additional vasculature via angiogenesis once vascular bed is established
what is involved in the signal to express VEGF?
HOXB5–upreguates the VEGF receptor FLK1
with VEGF, what do central cells and peripheral cells become?
- central cells become hematopoietic stem cells
- peripheral cells differentiate into angioblasts–>endothelium of blood vessels
besides VEGF, platelet derived growth factor (PDGF) and TGF-beta do what?
regulation of maturation and remodeling of vasculature
what are the three pathways involved in angiogenesis?
- VEGF-R pathway
- Notch receptor pathway
- Tie receptor-angiopoietin pathway
VEGF-R pathway and Tie R pathway of angiogenesis
- both receptors have an intracellular tyrosine kinase domain
- ligand binding to either R will lead to dimerization and autophosphorylation
- phosphorylated R interacts with a variety of cytoplasmic signaling mcs leading to angiogenesis involving proliferation and differentiation of endothelial cells
Notch receptor pathway of angiogenesis
-activation of Notch receptor by ligand binding results in release of Notch intracellular cell domain (NICD) that translocates into the cell nucleus to regulate gene expression in angiogenesis
tumors and angiogenesis
- progressive tumor growth is dependent on angiogenesis
- an understanding of angiogenesis is relevant to developing therapeutic strategies to produce revascularization of ischemic tissues or inhibit angiogenesis of tumors
SHH from notochord induces…
expression of VEGF (mesoderm)
what is vein specific genes controlling venous development?
EPHB4
What is the master gene for lymphatic vessel differentiation?
PROX1
aorta gonad mesonephros region (AGM)
- in the fetus are derived from mesoderm surrounding aorta in site near the developing mesonephric kidney
- cells eventually colonize the liver, which becomes the major hematopoietic organ of embryo (2-7 months)
when does hematopoiesis move from the liver to the bone marrow?
month 7
hemangioma
- abnormally dense collection of capillary vessels
- common tumors of infancy (10%)
- focal or diffuse, more secondary complications
port wine stain
- naevus flammeus
- superficial and deep dilated capillaries in the skin
heart
folded endothelial tube whose wall in thickened to act as regulated pump
endocardium
consisting of an endothelial lining and sub endothelial CT
myocardium
functional synctium of striated cardiac muscle fibers forming 3 major types of cardiac muscle
3 major types of cardiac muscle myocardium
- 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
what are 3 types of cardiomyocytes?
- contractile
- myoendocrine
- nodal
contractile
- type of cardiomyocyte
- contract to move blood
myoendocrine
- type of cardiomyocyte
- produce atrial natriuretic factor that stimulates both diuresis and excretion of sodium in urine by increasing the glomerular filtration rate, reduces blood volume and blood pressure
nodal
- type of cardiomyocyte
- specialized to regulate contraction of the heart (SA node and AV node)
what do arteries do?
- conduct blood from the heart to the capillaries
- carry oxygenated blood except in pulmonary arteries
- they store some of the pumped blood during each cardiac systole to ensure continued flow through the capillaries during cardiac diastole
three layers of arteries
- tunica intima
- tunica media
- tunica externa
tunica intima
- innermost layer of blood vessel wall
- composed of an endothelium and sub endothelial layer
- external layer of elastic fibers–internal elastic lamina
tunica media
- middle layer of vessel wall
- composed of circularly arranged layers of SM cells
- vasoconstriction (narrowing of vessels)
- vasodilation (widening of blood vessel lumen)
tunica externa/adventitia
- outermost layer of blood vessel wall
- composed of loose CT that contains elastic and collagen fibers
- helps anchor the vessel to other tissues
- external elastic lamina separates media from adventitia
- vaso vasorum (adventitia of large vessels contains small vessels)
SA Node
-which generates impulses to cause rhythmic contractions of cardiac muscle
internal pathway
-conducts impulse from SA node to AV node in which atrial impulse is delayed before reaching the ventricles, AV bundle, left and right bundles of Purkinje fibers
atrioventricular bundle
conducts impulse from atria to ventricles
left and right bundles of Purkinje fibers
conduct impulse to all parts of ventricles
large elastic arteries
- receive blood from heart under high pressure
- keep blood circulating continuously while heart is pumping intermittently
- disten during systole and recoil during diastole
- tunica intima is endothelium and sub endothelial CT
- large amounts of fenestrated elastic sheaths in tunica media with bundles of SM cells permeating gaps b/w elastic lamellae
- blood vessels, nerves, and lymphatics in tunica adventitia
- includes: aorta and largest branches
muscular or distributing arteries
- allow selective distribution of blood to different organs in response to functional needs
- 3 layers to tunica intima
- endothelium
- sub endothelium
- internal elastic lamina
- in larger vessels, fenestrated external elastic lamina can be seen at junction of tunica media and adventitia
- tunica media shows significant reduction in elastic components and an increase in SM fibers
- examples: radial, tibial, popliteal, axillary, scenic, mesenteric, and intercostal arteries
arterioles or resistance vessels
- final branches of arterial system
- regulate distribution of blood to different capillary beds by vasocontriction/dilation
- structural adaption is was with circularly arranged SM
- partial conduction (tone) of vascular SM exists here
- arterioles are regarded as resistance vessels and are major determinants of capillary blood pressure
microvascular bed
- site of microcirculation
- composed of terminal arteriole, the capillary bed, and post capillary venules
capillary bed
- consists of slightly large capillaries (called preferential or thoroughfare channels), where blood flow is continuous and small capillaries (called true capillaries) where blood flow is intermittent
- provide for exchange of gases and solutes b/w blood and tissue
3 types of capillaries
- continuous
- fenestrated capillaries
- sinusoids
continuous capillaries
-lined by endothelium with tight junctions and a basal lamina with pericytes (which are modified SM cells that keep everything in and everything else out of vessel)
fenestrated capillaries
- have pores or fenestra
- in GI and kidney
- allow some things and and keep others out based on size or charge
sinusoid capillaries
- discontinuous capillaries
- characterized by an incomplete endothelial lining and basal lamina, with gaps or holes b/w and within endothelial cells (liver or spleen)
veins
- reservoir so collect blood from capillaries and take blood back to heart
- thinner wall compared to artery
- has distensibility in wall so content of blood is large
- have tunica layers but tunica media and adventitia can not often be distinguished
- muscular tunica media is thinner than in arteries and SM cells have an irregular orientation
- have valves to prevent back flow
post capillary venules
preferred site of migration of blood cells into tissue (diapedesis)
vasculitis
- inflammation of blood vessels which causes changes in blood vessels, including thickening, weakening, narrowing, and scarring
- changes restrict blood flow, resulting in organ and tissue damage
- can be caused by infectious and immunologic pathogens
lymphatic vascular system
- conduct immune cells and lymph to lymph nodes
- remove excess fluid accumulated in interstitial spaces, and transport chylomicrons, lipid containing particles, through lacteal lymphatic vessels inside intestinal villi
lymphatic drainage by intrinsic contraction
- when vessels become expanded by lymph, the SM of wall contracts
- each segment of lymphatic vessel b/w successive valves, called lymphangions, behaves like an automatic pump
lymphatic drainage by extrinsic contraction
- external factors such as contraction of surrounding muscles during exercise, arterial pulsations, and compression of tissues by forces outside the body compress the lymph vessel and cause pumping
- when lymph drainage is impaired, excess fluid accumulates in tissue spaces (edema)
lymphedema
-cause by a defect in transport of lymph b/c of abnormal vessel development or damaged lymphatic vessels
filariasis (elephantiasis)
- parasitic infection of lymphatic vessels by Wuchereria bancrofti or Brugia malayi worms, transmitted by mosquito bites
- causes damage to lymphatic vessels with chronic lymphedema of legs and genitals
- occurs in tropical countries
chylous ascites and chylothorax
-caused by accumulation of high fat containing fluid, or chyle, in abdomen or thorax as a result of trauma, obstruction, or abnormal development of lymphatic vessels
major functions of endothelial cells
- mediate regulation of blood flow and produce vasoactive substances that can induce contraction and relaxation of SM vascular wall
- NO and prostacyclin–relaxation of SM
- prostacyclin prevents platelet adhesion and clumping
- endothelin 1 is potent vasoconstrictor peptide