histology of blood vessels Flashcards
what are the 3 layers of blood vessels
tunica externa (adventitia) tunica media tunica intima
in the heart, whch layers correspond with the 3 tunicas
tunica intima = endocardium tunica media (muscle layer) = myocardium tunica externa = epicardium
stucture of tunica intima
epithelium, BM, connective tissue
structure of tunica media
muscle + elastic tissue
difference between epicardium and tunica externa
epicardium - fibrous connective tissue, BM, epithelium tunica externa - fibrous connective tissue
diameter of artery vs vein
arteries are smaller diameter than accompanying vein veins tend to be floppy and expanded due to thinner TM than artieries which are more contracted
wall of artery vs vein
arteries have thicker wall than accompanying vein arteries have thin TM and thin adventitia (less need to stabilise) vein has thicker adventitia
tunica media and adventitia thickness artery vs vein
artery - thick media, thin adventitia vein - thin media, thick adventitia
individual diameters of blood vessels comparison
artery > arterioles > capillaries
total cross sectional area of blood vessels comparison
arteries < arterioles < capillaries capillary bed has huge SA
what are the 3 types of arteries
elastic muscular arterioles
elastic arteries
large conducting expand and contract to move blood around e.g. aorta, common carotid, pulmonary
muscular arteries
distributing arteries less elasticity, more of a channel for the blood e.g. coronary arteries, radial, femoral
arterioles
terminal branches which supply blood to the capillary bed
what is the function of elastic arteries
pressure reservoir
state of elastic arteries during systole and diastole
stretched during systole during diastole heart relaxes, pressure falls, artery recoils, maintaining pressure on the blood
what is the recoil and stretchability in elastic arteries due to
presence of extensive amounts of elastic fibres in tunica media in the form of layers (laminae)
what are the elastic fibres in elastic arteries secreted by
smooth muscle cells
what type of vessel is this and why?
elastic artery
very thin tunica intima
lots of layers of elastic fibres in the TM which are obscuring the muscle
elastic fibres occur in layers
what is the function of muscular arteries
controls distribution of blood to regions
describe the structure of muscular arteries
thick tunica media has smooth muscle cells
no elastic laminae between muscle cells in TM
elastic fibres are concentrated in 2 well defined sheets called the internal elastic lamina (IEL)just under the epithelium and the external/outer elastic lamina (OEL) between TM and TA
what type of blood vessel is this and why
muscular artery
smooth muscle cells
presence of OEL and IEL
streucture of arterioles
no IEL
only 1-2 layers of smooth muscle in TM
no T adventitia
round oval nuclei visible in smooth muscle
function of arterioles
smaller muscular arteries gradually change histologically to become arterioles
control blood flow to capillary beds (local)
control systemic blood pressure
nerve innervation of arterioles
rich sympathetic nerve innervation
controls diameter
what type of blood vessel is this and why
arteriole
function of capillaries
main exchange site for nutrients and gases
low BP
structure of capillaries
very thin walled
T intima only - endothelium on BM
no TM or TA
pericytes
sum of diameters of all capillaries in body > diameter of aorta
lumen only big enough for one RBC
what are pericytes
incomplete layer of cells surrounding BM
have contractile properties which help control the flow of blood in the capillaries
what type of blood vessel is this and why
capillaries
what are the 3 types of capillaries
continuous
fenestrated
discontinuous
continuous capillaries
no gaps in endothelium
complete basal lamina
found in muscles
fenestrated capillaries
fenestrated endothelial lining
complete basal lamina
allows more substance through
gaps are sometimes abridged by protein membranes but not always
found in endocrine glands
discontinuous capillaries
fenestrated endothelial lining
incomplete basal lamina
lots of stuff allowed through
found in liver sinusoids
function of continuous capillaries
can control what is exchanged
material must pass through cell or between cells
junctions can control transport - selective transport mechanisms
fenestrated capillary function
fenestrations
with or without protein diaphragms which filter molecules by MW and/or charge
e.g. endocrine glands, kidney renal corpuscle
function of discontinuous capillaries
gaps between endothelial cells and BM
allow free passage of fluid and cells
e.g. liver, spleen, bone marrow
sinusoids
large diameter discontinuous capillaries
found where large amount of exchage takes place
TI contains phagocytic cells
e.g. liver, some endocrine glands
capillary beds and arteriovenous shunts
bypasse capillary beds
e.g. in skin for thermoregulation
veins blood vessel progression
capillary bed
small venule
small-medium vein
large
structure of veins
thin TI
IEL and OEL thin or absent
TM very thin or absent
TA - collagenous tissue
valves to prevent backflow (endothelial projections into lumen)
what can the failure of valves in veins lead to
varicose veins
what type of blood vessel is this
vein
superficial vs deep veins
difference most obvious in lower limb
veins tend to have a corresponding artery that they mirror
superficial - thick walled compared to deep, no surrounding support
deep - thin walled, surrounding support from deep fascia and muscle, close to the bone
lympathic system
tends to lie next to big vessels (esp veins), nodes found alongside major veins and origins of major arteries
drains tissue fluid lost from blood capillaries
drains into the systemic venous system
valves direct flow
why is the lymphatic system clinically important
tumour cell metastases
cancerous cells can easily spread to other places in the body
lymphogenic spread - spread through the lymphatic system
describe the structure of lymph capillaries
blind ended capillaries
lined by very thin endothelium
no fenestrations
absent/rudimentary basal lamina
lumen maintained at -ve hydrostatic pressure
anchoring filaments - fine collagenous filaments link endothelial cell to surrounding tissue keeping lumen open
NO RBC in lumen
blood vessels as organs
nerve supply - sympathetic (skin), sympathetic + parasympathetic (heart)
blood supply - vasa vasorum (vessels of the vessels)
lymphatics in T adventitia
