Flashcards in Vascular System Histology Deck (81):
blood vessels arise from coalescence of hemangioblasts, which arise from blood islands
vessel formation via branches arising from existing vessels
How do major vessels form?
Why is it important to understand the processes of angiogenesis and vasculogenesis?
An understanding of these processes is relevant to developing therapeutic strategies to produce revascularization of ischemic tissues or inhibit angiogenesis in cancer and other disorders
When and where does early vasculogenesis begin?
In week 3 in extraembryonic splanchnic mesoderm surrounding the yolk sac: formation then moves into lateral plate mesoderm
What is the first site of formation of blood islands
Islands arise from mesoderm cells that are induced to form hemangioblasts, a common precursor for vessel and blood cell formation
Hemangioblasts differentiate into what two populations of cells
angioblasts and hematapoetic stem cells
vascular precursors - form endothelial cells. coalesce into cords and form a lumen
Define hematapoietic stem cells
differentiate into all types of blood cells
mesenchymal cells to hemangioblasts is regulated by
What factor elicits regional change in blood islands
VEGF (vascular endothelial growth factor)
signal to express VEG F may invlove HOXB5 which upregulates VEGF receptor FLK1
Factors involved in angiogenesis
VEGF, Ang1, Ang2
Role of Ang1
in angiogenesis, recruits pericytes to sm muscle cells in large vessels to organize mature blood vessels
Role of Ang 2
works where you might want to punch a hole and have something grow out. works on endothelial cells and stops interactions btwn them - either absence of growth OR cell death.
Vein specific genes controlling venous development
master gene for lymphatic vessel differentiation
Specification of vessel type happens when?
Soon after angioblast induction
What factors specify arterial development?
SHH from notochord induces expression of VEG-F in mesoderm
VEG-F induces Notch pathway which specifies arterial development
through expression of EphrinB2 (ligand)
AGM stands for?
Aorta - gonad - mesonephros region.
What is found in the AGM
Definitive hematopoietic stem cells. These cells will eventually colonize the liver, which becomes major hematopoietic organ of the embryo (2-7 months). Hematopoiesis moves form liver to bone marrow at 7 months.
Progression of hematopoeisis
Blood islands - FGF@ tells them to become hemangioblasts - difinitive hematopoeitic stem cells then seen in AGM - liver - bone marrow.
What is a Hemangioma
Abnormally dense collection of capillary vessels. common tumors of infancy. focal or diffuse, look for other secondary complications
What is a Port Wine Stain?
superficial and dilated capillaries in the skin.
When some of the tumor cells switch to an angiogenic phenotype, the local equilibrium between positive and negative angiogenic refulators changes. allows the tumor to grow.
Folded endothelial tube whose wall is thickened to act as a regulated pump
consisting of an endothelial lining and sub endothelial CT
Functional syncytium of striated cardiac muscle fibers foming 3 major types of cardiac muscle
3 major types of cardiac muscle
specialized excitatory and conductive muscle fibers.
Visceral layer of the pericardium
is a low friction surface
lined by a mesothelium in contact with the parietal pericardial space.
Cardiomyocytes (3 kinds)
Contract to move blood
produce atrial natriuretic factor that stimulates diuresis and excretion of Na in urine by +glomerular filtration rate, -blood volume
Specialized to regulate contraction of the heart
SA and AV node
Characteristics of cardiac muscle
striated, branched, uninucleate cells connected to e/o by intercalated discs
Intercalated disc junction types (3)
anchoring sites for actin. connect to closest sarcomere
macula adherins (desmosomes)
stop separation during contraction by binding intermediate filaments, joining cells together.
allow potentials to spread between cardiac cells by permitting the passage of ions btwn cells, producing depolarization of heart muscle
Electrical conduction system pathway of Heart
SA node --> AV node --> bundle of his (sends out)--> L and R bundle branches --> purkinje fibers
Specialized muscle cells that conduct electrical impulses
How can purkinje fibers be distinguised from myocardium?
by size (much larger) and by their staining (lighter, full of glycogen)
but they do have some of the other features of cardiac myocytes, including centrally located nubleus and intercalated disc.
Vessel that ensures continued flow through capillaries during cardiac diastole
3 major organizational levels or tunics of arteries
Tunica externa/adventitia (location, composition function)
outermost layer of blood vessel wall
composed of loose CT, elastic and collagen fibers
helps anchor vessel to other tissues
external elastic lamina that separates the tunica media from tunica externa
Tunica media (location composition fxn)
middle layer of vessel wall
composed of circularly arranged layers of sm m cells.
responds to autonomic innervation (vasoconstriction/vasodilation)
Tunica intima/ interna (location, composition function)
innermost layer of blood vessel wall
composed of an endothelium and subendothelial layer, external layer of elastic fibers, the internal elastic lamina
Three major groups of arteries
large elastic arteries
medium sized muscular arteries
small arteries and arterioles
Type of artery that 1. receives blood from heart under high pressure and 2. keeps blood circulating continuously while the heart is pumping intermittently
Large elastic (conducting) arteries
distend during systole and recoli during diastole
Examples of large elastic arteries
the aorta, and its largest branches (brachicephalic, common carotid, subclavian, common iliac)
Large amounts fo fenestrated elastic sheaths are found in the tunica media with bundles of smooth muscle cells permeating the narrow gaps between elastic lamella in this type of artery...
large elastic artery
Blood vessels, nerves and lymphatics can be recognized in the tunica adventitia of what type of artery
large elastic arteries.
What does vasa vasorum and nervi vasorum mean?
The blood vessels and nerves to the vasculature.
What type or artery allows a selective distribution of blood to different organs in response to functional needs?
Muscular distributing arteries
note that we see significant reduction in elastic components and an + in sm m fibers compared to large elastic arteries
examples of muscular (distributing) arteries
radial, tibial, popliteal, axillary, splenic, mesenteric, intercostal
What are the layers of the tunica intima of muscular arteries
internal elastic lamina
The final branches of the arterial system, which regulate the distribution of blood to different capillary beds by vasoconstriction/ vasodilation are called?
Arterioles are regarded as
resistance vessels and are the major determinants of systemic BP
partial contraction of vascular sm m. exists (TONE)
What is the microcirculation composed of
Terminal arteriole, capillary bed, adn postcapillary venules.
What is the functional unit of the cardiovascular system
smallest blood vessels. connect arterioles to venules.
contain only the tunica intima; vasment membrane and endothelium only.
lined by endothelium with tight junctions and a basal lamina with pericytes
have pores or fenestrate (GI, Kidney)
sinusoids, or discontinuous capillaries
characterized by an incomplete endothelial lining and basla lamina, with gaps or holes between and within endothelial cells
What type of vessel is the capacitance (reservoir) vessel
preferred site of migration of blood cells into the tissues(diapedesis)?
post capillary venules.
Characteristics of veins.
thin walled. High capacitance attibutable to distensibility of their wall (compliance vessels)
contain large amount of the blood volume.
also contain tunics, not as defined
VALVES, to prevent reflux of blood
Vessels responsible for transport of chylomicrons, (lipid containing particles), remove excess fluid from intersitital spaces, and conduct immune cells...
Two types of Lymphatic drainage
Intrinsic contraction (when vessle become expanded by lymph)
Extrinsic contraction (external factors such as contraction of muscle compresses the lymph vessel)
both lead to pumping of lymph.
result when lymph drainage impaired
caused by a defect in the transport of lymph bc of abnormal vessel development or damaged lymphatic vessels
parasitic infection of lymph vessels by worms
transmitted by mosquito bites
causes damage to lymphativ vessels --> chronic lymphedema of legs and genitals
Chylothroax or Chylous ascitis
accumulation of high fat containing fluid (chyle) in abodmen or thorax
result of trauma, obstuction, abnormal development of lymphatic vessels.
Endothelial cells produce what to regulate blood flow
vasoactive substances (NO, prostacyclin, endothelin 1)
NO and Prostacyclin functions
Relaxation of Sm m.
IN BLOOD VESSELS.
produced by endothelial cells.
(prostacyclin also prevents platelet adhesion and clumping leading to blood clotting)
Function of endothelin 1
potent vasoconstrictor peptide
Aside from vasoconstriction/vasodilation, endothelial cells also play a role in what two processes?
Homing and inflammation
How does the permeability of capillary endothelial cells vary?
It is tissue specific.
also topographic - endothelial cells at venous end are more permeable than those at arterial end.
In atherosclerosis, what layer do plaques deposit in?
what types of vessels do we see atherosclerosis in?
arteries sustaining High BP.
Atherosclerosis is no recognized as a chronic __________ disease. also correlates with serum levels of what
high levels of cholesterol or LDL