week 5: cardiac physiology: blood vessels and hemodynamic Flashcards
functions of human vascular network
-blood flow
-supply of O2 and nutrients
-removal of metabolic byproducts
-hormonal regulation
-thermal regulation
-immune responses to infection
-fluid balance
-route for infection
-utilised in drug delivery
systemic system
oxygenated blood leaves aorta
arteries carry oxygenated blood to tissues
gas exchange occurs by diffusion in capillaries
veinous system
deoxygenated blood returned to the right atrium via vena cava
pulmonary system
pulmonary arteries carry deoxygenated blood to lungs
gas exchange occurs at capillaries surrounding alveolae
pulmonary arteries carry oxygenated blood back to left atrium
how are blood vessels arranged
parallel or series depending on location and function
variations in blood pressure occurs due to
contractions of heart, ejecting blood out into systemic circulation
systemic: left side
pulmonary: right side
pressure of systemic vs pulmonary system
systemic: higher
pulmonary: lower
relationship between total cross sectional area and velocity of flow of blood vessels
greater total cross-sectional area= lower velocity of blood flow
blood leaves via aorta to >
elastic arteries> muscular arteries > arteriole> continuous capillary
blood passes form continuous capillary back to rhs of heart through
fenestrated capillary> venules> medium sized- veins > large veins
windkessel effect
recoil of large elastic blood vessels during diastole helps maintain flow even though heart is not actively pumping
3 distinct layers of arteries and veins
tunica adventitia
tunica media
tunica intima
tunica adventitia
connective tissue- collagen fibres
tunica media
smooth muscle and elastin
tunica intima
squamous endothelium
what does capillaries only having a single endothelial layer enable
efficient bidirectional diffusion of nutrients and metabolites between blood and tissues
walls of arteries
thick, muscular and elastic
high pressure, carries blood away from heart, maintains blood flow during idastolic period
vein walls
thin and elastic
return blood to heart at low pressure
valves facilitate unidirectional blood flow
major arteries and precapillary arterioles are innervated by
sympathetic nerves
what do venules and capillaries not have
smooth muscle
are venules and capillaries directly innervated by sympathetic nerves
no
fur distinct layers of an artery
(lumen)
endothelium (inner lining)
elastic and connective tissue
muscle fibres and elastic
protective outer coat
what does elastic layer of artery allow
vessel walls to stretch without tearing in response to increase in pressure
operate at highest blood pressure (80-120mm Hg)
atherosclerosis
fat and lipid lesions in vessel wall, leads to arterial narrowing and blockage,
reduce or loss of oxygenated blood flow
causes arterial dysfunction
how can a blocked coronary artery be repaired
insertion of stent by angioplasty
restores oxygenated blood flow
what organs have more extensive capillary networks
organs with more metabolic requirements
e.g heart, liver
pressure over capaillary bed from arteriole end to venule end
pressure decreases
at any given time, capillary beds hold to ….% of total blood volume
25
capillary wall
endothelial cells surrounded by thin basement membrane
feature of continuous capillaries
porous
water filled pores
continuous capillaries being porous allows
exchange between blood and tissues
small, water-soluble substances can pass through pores
how can lipid soluble substances pass between blood and tissues
(continuous capillaries)
pass through endothelial cells
how are exchangeable proteins passed between blood and tissues (continuous capillaries)
vesicular transport
can plasma proteins cross continuous capillary wall
no
how do fenestrated capillaires increase their exchange rate
larger openings
where are fenestrated capillaries found
kidneys, small intestine and endocrine glands
why is important capillary blood pressure is low
capillaries are very fragile
0-10 mmHg
what can pulmonary hypertension in lungs lead to
damage of capillaries that surround the alveolae
layers of veins
adventitia
smooth muscle
basement membrane
endothelium
valve
lumen
why is muscular later of veins and venules thinner than aerteriole system
operate at low pressure 0-10mm Hg
venous blood flow during exercise
facilitated by intermittent compression due to skeletal muscle contraction
when muscles contract, veins squashed, pushing blood back towards the heart- skeletal muscle pump
varicose veins
veins become stretched and lose elasticity, valves weaken
blood collects in veins, become swollen and large
underlying causes unclear
action of endothelial cells
sense and respond to a number of substances and stimuli
responses regulate blood pressure
how does the endothelium regulate blood pressure
receptor-ligand complexes
activate signal transduction pathways
leads to synthesis of gaseous NO in a process involving L-arginine
NO is second messenger which regulates blood pressure and cell function
how does receptor signalling lead to NO synthesis
-substances in intravascular compartment interact with receptors on endothelial surface
- activation of receptors lead to signalling cascade, ultimatly induced activation of eNOS
- eNOS hydrolyses L-arginine producing NO and L-citrulline
eNOS
endothelial nitric oxide synthase
VEGF
vascular growth factor
PIGF
placental growth factor
Akt
serine/ threonine protein kinase
qithin pathways
Akt
Ca2+
a rise in intercellular calcium activates
eNOS
what can eNOS also be activated by
shear stress:
tangential force caused by blood flow acting on the surface of the endothelium
shear stress eNOS activation involves
Akt or PKA induced phosphorylation
how does NO regulate vascular smooth muscle relaxation
NO diffuses out of activated endothelium
NO targets soluble guanylate cyclase (sGC) in VSMCs
NO stimualtes sGC to convert GTP into cGMP
cGMP binds and activates protein kinase G (PKG)
VSMCs
vascular smooth muscle cells
what does protein kinase G cause
VSMC relaxation and reduce blood pressure
protein kinase G action
PKG phosphorylates and activates myosin light chain phosphatase (MLCP)
MLCP de-phosphorylates contractile myosin
causes relaxation of vascular smooth muscle cell
relaxation increases dilation of blood vessel, reducing blood pressure
