Lecture 5- Structure and Function of Blood Vessels Flashcards
what supply do all tissues have
arterial supply
what drainage do all tissues have
venous drainage
3 core functions of blood vessels
-resilient
-flexible
-always remain open
what is the standard blood vessel structure
tunica intima->tunica media-> tunica adventitia/ externa
what epithelium is found in the tunica intima?
simple squamous epithelium
endothelium
epithelium that lines blood vessels
what do the epithelial cells in the tunica intima have
basal lamina (extracellular matrix of epithelial cells)
what connective tissue is found in the tunica intima
subendothelial connective tissue
what is found in the loose connective tissue of the tunica media
smooth muscle fibres
which fibres may the tunica media contain
elastic fibres
structure of the tunica externa/adventia
Connective tissue
Merges with surrounding connective tissue
May contain vaso vasorum (vessles of the vessels)
why do arteries have thick walls
blood is under high pressure
what do arteries resemble and what do veins resemble
arteries- garden hoses (smaller lumen)
veins- fire hoses (larger lumen)
why do valves have thin walls
as blood travels under low pressure
which is more resilient: arteries or veins?
arteries
what are the 3 types of arteries
elastic (conducting)
muscular (distributing)
arterioles (resistance vessels)
examples of elastic (conducting) arteries
aorta, brachiocephalic and common carotid
diameter of elastic (conducting arteries )
up to 2.5 cm
function of elastic (conducting arteries)
withstand changes in pressure during the cardiac cycle and ensure continuous blood flow
structural adaptations of elastic ( conducting arteries)
thick tunica media with many elastic fibers and few smooth muscle cells
examples of muscular (distributing) arteries
brachial and femoral arteries
diameter of muscular (distributing) arteries
0.5 mm – 0.4 cm
function of muscular (distributing) arteries
-Distribute blood to muscles and organs
-Capable of vasodilation and vasoconstriction
in order to control the rate of blood flow to
suit the needs of the organ
-e.g contracting muscles during exercise- dilate blood vessels
structural adaptations of muscular (distributing) arteries
smooth muscle cells in tunica media
distinct internal (IEL) & external elastic laminae (EEL)
thick tunica externa
diameter of arterioles (resistance vessels)
</= 30 um
function of arterioles (resistance vessels)
-Capable of vasoconstriction &
vasodilation
-Control blood flow to organs
-Involved in blood pressure control
structural adaptations of arterioles (resistance) vessels
one to two layers of smooth muscle cells in tunica media
poorly defined tunica externa
functions of capillaries
Connect arterioles and venules
(microcirculation)
Site of gaseous exchange
why are there thin walls of capillaries
facilitate diffusion
why is blood flow through the capillaries slow
ensures enough time for exchange of gases
what exchange does the structure of capillaries allow
2 way exchange
diameter of capillaries
8-μm (micrometres) in diameter
what else aids the thin walls of the capillaries
endothelium and basement membrane
what are the 3 types of capillaries
continuous
fenestrated
sinusoidal
features of continuous capillaries
no gaps between cells, all next to each other
Skeletal and smooth muscle, CT, and the
lungs
features of fenestrated capillaries
- Pores penetrate the endothelial lining
- Rapid exchange of water or large solutes
(e.g. small peptides) - Absorption (kidney, choroid plexus and
endocrine glands
choroid plexus
area where we produce cerebral spinal fluid in the brain
intracellular clefts
gaps between adjacent cells of fenestrated capillaries
features of sinusoidal capillaries
- Spaces between endothelial cells
- Incomplete or absent BM
- Exchange of large solutes i.e.
plasma proteins - Specialised lining cells (e.g. in
the liver, phagocytic cells engulf
damaged RBCs) - Blood moves slowly through
sinusoids
how are capillaries organised
into groups called capillary beds
what do capillary beds allow
allow slow flow between arteriole and venule to allow exchange of gases and nutrients
what supplies a single capillary bed
metarteriole
structure of metarteriole
Each metarteriole continues as a thoroughfare channel
which leads directly to a vein and has numerous
capillaries leading off it
what can reduce flow to a whole capillary bed
constriction of the metarteriole
precapillary sphincter
guards the entrance to each capillary (controls entrance diameter)
constriction of the precapillary sphincter
narrows the entrance therefore reduces flow
relaxation of the precapillary sphincter
relaxation dilates entrance therefore increases flow
arteriovenous anastomosoes
Form direct communication between the arteriole and venule (no capillaries tunning off them)
dilated arteriovenous anastomoses
blood bypasses the capillary bed and flows directly to the venous circulation
venules
collect blood from capillary beds and deliver it to small veins
diameter of venules
varies, average 20 m
structural adaptations of venules
Small– endothelium on a basement membrane
Larger– increasing numbers of smooth
muscle cells located outside endothelium
how are veins (capacitance vessels) classified
according to size
Small < 2mm in diameter
Medium 2-9 mm in diameter
Large > 9mm in diameter e.g. superior and inferior vena cava
features of veins
low-pressure system
easily distensible (capacitance- can store/ hold more blood in the vein)
structural adaptations of veins
Thin walled
Tunica externa is predominant
Valves to aid blood flow
anatomical planes- sagittal
passes from front to back splitting body
into right and left sides
anatomical planes- coronal/frontal
passes from side to side-splitting body into front and back
anatomical planes - transverse/ horizontal
splits the body into upper and lower parts
anterior
passes from front to back splitting the body
into right and left sides
distal
a direction away from the point of attachment or origin e.g. for a limb, away from its attachment to its trunk
inferior
Below, in reference to a particular structure,
with the body in the anatomical position.
lateral
pertaining to the side
medial
towards the midline of the body
posterior (dorsal)
towards the back
superior
Above, in reference to a portion of the body
in the anatomical position
anatomical position
An anatomical reference position; the body viewed from the anterior
surface with the palms facing forward.
