Circulatory System Flashcards
what is the primary function of the circulatory system?
transport of O2/CO2, nutrients and metabolic waste
what are the secondary functions of the circulatory system? (2)
thermoregulation
transport of immune cells/hormones
what does the vascular system consist of? (2)
heart and blood vessels
what are the heart and blood vessels collectively referred as
blood vascular system
what are the two components to the circulatory system?
pulmonary circulation
systemic circulation
what is the flow of the pulmonary circulation?
right atrium and ventricle pulmonary aa lungs pulmonary veins left atrium
what is the flow of the systemic circulation?
left atrium and ventricle
aorta
rest of body
passive drainage system for returning extravascular fluid (lymph) to blood and vascular system
lymph vascular system
what does the circulatory system lack?
intrinsic pump
what does the circulatory system rely on? (2)
muscle contraction
body movement
Blood vessels of circulatory system have common basic structure with three
tunics
tunics
concentric layers
innermost layer of simple squamous endothelial cells lining lumen
tunica intima
thickness of tunica intima
very thin, 1-2 cells thick
what does the tunica intima form?
a semi-permeable barrier, supported by a basement membrane
fascia occludens
specialized discontinuous tight junctions between endothelial cells
what kind of connective tissue does tunica intima contain?
variable amounts of sub endothelial connect tissue
Internal elastic lamina, if present, separates
tunica intima & media
what is the internal elastic lamina composed of?
elastic fibers
tunica media
highly variable middle layer
what is contained in the tunica media? (2)
smooth muscle cells and fibroblasts connective tissue
in arteries, the tunica media may also contain (2)
reticulin (type 3 collagen)
elastic fibers
where is external elastic lamina located?
between tunica media and adventitia
external elastic lamina compared to the internal elastic lamina
also composed of elastic fibers but less organized
outermost layer
tunica adventitia
what kind of connective tissue is found in the tunica adventitia?
loose fibroblastic connective tissue
what types of structures are found in the tunica adventitia? (4)
fibroblasts
collagen
elastic fibers
smooth muscle cells
is the tunica adventia thick or thin in arteries?
thinner
what is the thickest of the layers in venuoles?
tunica adventitia
what does the tunica adventitia contain in larger vessels?
vasa vasorum
what is contained in both large Aa and Vv?
small blood vessels that supply the tunica media and adventitia
tunica adventitia also contains autonomic nerves, called
nervi vasculares
what do Nervi vascular control?
smooth muscle contraction in vessel walls (vasoconstriction and vasodilation)
Vasoconstrictionof blood vessels due to action of
sympathetic, post-ganglionic nerve fibers
what does vasoconstriction on smooth Mm of tunica media to cause
a decrease in lumen diameter
what does it mean that vasoconstriction is passive?
occurs in the absence of inhibition of sympathetic stimulation
vasodilation is accomplished via
indirect parasympathetic innervation
how does acetylcholine act on edothelial cells?
causes the cells to release NO
what does NO cause
smooth muscle cells to relax
in response to low O2 tension, smooth muscle in the walls of arterioles
relax
relaxation of smooth muscle arterioles results in (2)
vasodilation
increase blood flow
two types of specialized sensory receptors located in walls of blood vessels
baroreceptors
chemoreceptors
baroreceptors detect
blood pressure
where are baroreceptors located? (2)
carotid sinus
aortic arch
chemoreceptors detect changes in (3)
CO2, CO2 tension
pH
where are chemoreceptors located? (2)
at bifurcation of carotid Aa
in aortic bodies of aortic arch
where does the arterial system conduct blood?
away from the heart, to the capillary bed
the venous system returns blood from
capillaries to the heart
cyclical pumping of heart
pulsatile blood blow
systole
contraction of ventricles
pressure wave
diastole
relaxation
decrease pressure
normal blood pressure
120/80 mm Hg
expansion and recoil of elastic arteries maintains
blood pressure
Regulation of bp accompanied by changes in
diameter of blood vessels
Regulation of bp accompanied by changes in diameter of blood vessels occurs via
sympathetic control of smooth Mm in vessel walls
Arteries contain large amounts of (2)
elastin & smooth Mm
arterial vessel wall diameter compared to lumen diameter
vessel wall thick relative to lumen diameter
elastic aa diameter
> 1 cm in diameter
elastic aa
large conducting vessels, receive blood directly from heart
elastic aa have sheets of elastic tissue in
tunica media
elastic tissue helps maintain bp between
systole and diastole
what do elastic aeries contain (2)
internal and external elastic laminae
diameter of muscular aa
~2-10 mm in diameter—medium-sized distributing Aa
muscular arteries have more — and less — than tunica media than elastic arteries
more smooth muscle
less elastin
what is the thickest later in muscular arteries?
the tunica media
muscular arteries have distinct
internal elastic lamina
larger muscular arteries may contain
external elastic lamina
diameter of arterioles
~10-100 um in diameter
arterioles contain relatively little
smooth Mm (tunica media only ~2-3 cells thick)
in arterioles, what is absent?
elastin laminae
arterioles are the terminal branches of the
arteriole system
what do arterioles supply?
capillary beds
what are arterioles a major site of? (2)
vasoconstriction
vasodilation
arterioles regulate distribution of blood to capillaries via
pre-capillary sphincters
pre-capillary sphincters
intermittent rings of smooth M within walls of arterioles
Metarterioles
small diameter arterioles; intermediate in size between arterioles & capillaries
what are metaarterioles characterized by
discontinuous layer of smooth Mm in tunica media
In general, amount of smooth Mm increase with
an increase in diameter of vessel (& relative amount of connective tissue decrease)
what is microcirculation is concerned with the exchange of? (5)
gases fluids nutrients metabolites waste products
where does microcirculation primarily occur within?
capillaries, also includes arterioles and venues
diameter of capillaries?
8-10 um, thin walled vessels
what are capillaries lined by?
a single layer of endothelial cells
what are capillaries supported by? (2)
basal lamina
small number of pericytes
Pericytes derived from same precursor cell as
endothelial cells
capillaries can differentiate into (2) following injury
endothelial cells or smooth Mm cells
what do capillaries lack? (2)
outer connective tissue layer (no tunica adventitia) smooth Mm (no tunica media)
what layer do capillaries contain?
tunica intima
do capillaries exhibit vasomotor activity?
Do not exhibit vasomotor activity themselves
Vasodilation & vasoconstriction accomplished via smooth Mm contraction in arterioles & pre-capillary sphincters, resulting in a
passive change in capillary diameter
continuous capillaries
endothelium forms continuous lining; most common (e.g., Mm, lung, CNS)
fenestrated capillaries
endothelial cells possess pores, or fenestraewithincells(e.g., endocrine glands, GI tract)
discontinuous
basal lamina not continuous; endothelial cells separated by large gaps between cells
(e.g., liver, spleen, bone marrow, lnn)
Discontinuous capillaries may form
sinusoids (large diameter capillaries ~ 30-40 um)
Transport across capillaries may occur via (3)
fenestrae, transcytosis, or diapedesis
