objective 4 pt 1 Flashcards
the delivery system that begins and ends at heart
works with lymphatic system to circulate fluids
blood vessels
carry blood away from heart; carry oxygenated blood except for pulmonary artery and umbilical vessels of fetus
arteries
site of gas exchange; directly serve cellular needs; connect arteries and veins
capillaries
carry blood toward heart; carry deoxygenated except for pulmonary veins and umbilical vessels of fetus
veins
central blood-containing space, surrounded by a wall
lumen
what are the 3 layers of tunics of a vessel?
tunica intima
tunica media
tunica externa
Innermost layer that is in “intimate” contact with blood
Contains endothelium which is found in lumen of all
vessels
Endothelium is continuous with endocardium
Its slick surface reduces friction
tunica intima
Middle layer
mostly smooth muscle and sheets of elastin
Innervated by Sympathetic nervous system, controlling:
Bulkiest layer responsible for maintaining blood flow
and blood pressure
tunica media
Outermost layer
Also called
tunica adventitia
Composed mostly of loose collagen fibers that protect
and reinforce vessel wall and anchor it to surrounding
structures
Infiltrated with nerve fibers & lymphatic vessels
Large veins also contain elastic fibers in this layer
tunica externa
decreased lumen diameter
vasoconstriction
increased lumen diameter
vasodilation
system of tiny blood vessels found in
larger vessels
Function to nourish outermost external layer
vasa vasorum
what are the 3 groups of arteries?
elastic arteries
muscular arteries
arterioles
large arteries close to heart
◦ Aorta and its major branches
◦ conducting arteries because they conduct blood from
heart to medium sized vessels
} Contains elastin
} Contains smooth muscle, but inactive in
vasoconstriction
} Act as pressure reservoirs that expand and recoil
as blood is ejected from heart
◦ Allows for continuous blood flow downstream even
between heartbeats
elastic arteries
Elastic arteries give rise to muscular arteries
}
distributing arteries because they deliver blood to
body organs
} Account for most of named arteries
} Have thickest tunica media with more smooth
muscle
} less elastic tissue
◦ Tunica media sandwiched between
elastic
membranes
} Active in vasoconstriction
muscular arteries
smallest of all arteries
◦ Various sizes
◦ Regulate flow into capillary beds via vasodilation
and vasoconstriction of smooth muscle
◦ resistance arteries because changing diameters of
lumens changes resistance to blood flow
◦ Lead to capillary beds
arterioles
Smallest of 3 types of blood vessels
} Microscopic; diameters so small only single
RBC can pass through at a time
} Strategically placed pericytes
} Walls have only a thin tunica intima
} Supply almost every cell, except for cartilage,
epithelia, cornea, and lens of eye
capillaries
what is the function of capillaries?
exchange of gases, nutrients,
wastes, hormones, etc., between blood and
interstitial fluid
what are the 3 types of capillaries?
continuous capillaries
fenestrated capillary
sinusoidal capillaries
Abundant in skin, muscles, lungs, and CNS
Continuous capillaries of brain are unique
Form blood brain barrier
Least permeable as they lack pores
Often have pericytes
continuous capillaries
Found in areas involved in active filtration (kidneys),
absorption (intestines), or endocrine hormone
secretion
Endothelial cells contain Swiss cheese–like pores called
(
fenestrations) to promote permeability
Moderate permeability
fenestrated capillary
Most permeable of the capillaries
Fenestrated with larger clefts; incomplete basement
membrane
Found only in the liver, bone marrow, spleen, and
adrenal medulla
Blood flow is sluggish—allows time for modification of large
molecules and blood cells that pass between blood and tissue
Contain macrophages in lining to capture and destroy
foreign invaders
sinusoidal capillaries
interwoven network of capillaries between arterioles and venules
capillary bed
smallest form of artery
arteriole
smallest form of vein
venule
flow of blood through capillary bed
microcirculation
carry blood from capillary bed
toward the heart
} Contains valves
} Formation begins when capillary beds unite in venules
and merge into larger and larger ______
veins
Smallest form of a vein
– Very porous; allow fluids and WBCs into tissues
– Large venules have one or two layers of smooth
muscle cells
venules
Have all 3 tunics, but thinner walls with large
lumens compared to arteries
} Tunica media is thin, contains little smooth muscle
or elastin
} Tunica externa is thick, contains collagen fibers
and elastic networks
} Large lumen and thin walls make veins good
storage vessels (contain upto 65% of blood supply)
veins
prevent backflow of blood
most abundent in veins of limbs
venous valves
Flattened veins with extremely thin walls
Composed only of endothelium
venous sinuses
diameter lumens offer little resistance so this ensures blood
returns to heart at same rate it was pumped into circulation
large
interconnections between
blood vessels the provide alternate channels for
blood flow
vascular anastomoses
provide alternate pathways
even if one artery is blocked
◦ Common in joints, abdominal organs, brain, and
heart; none in retina, kidneys, spleen
arterial anatomoses
shunts in
capillaries
arteriovenous anastomoses
so abundant that
occluded veins rarely block blood flow
venous anastomoses
volume of blood flowing through
vessel, organ, or entire circulation in given
period
◦ Measured in ml/min, it is equivalent to cardiac output
(CO)
◦ relatively constant when at rest, but at any given
moment, varies at individual organ level, based on
needs
blood flow
force per unit area
exerted on wall of blood vessel by blood
◦ Expressed in mm Hg
◦ Pressure gradient provides driving force that keeps
blood moving from higher- to lower-pressure areas
blood pressure
opposition
to flow
◦ Measurement of amount of friction blood
encounters within vessel walls, generally in
systemic circulation
resistance (peripheral resistance)
what are the 3 most important sources of resistance?
Blood viscosity
Blood vessel length
Blood vessel diameter
The thickness or “stickiness” of blood due to formed
elements and plasma proteins
The greater the viscosity, the less easily molecules are
able to slide past each other
Increased viscosity equals increased resistance
blood viscosity
The longer the vessel, the greater the resistance
encountered
total blood vessel legnth
Has greatest influence on resistance
Frequent changes alter resistance
Viscosity and blood vessel length are generally constant
Resistance varies inversely with vessel diameter
If diameter of a vessel increases, resistance decreases, and
vice-versa
blood vessel diameter
diameter arterioles are major determinants of
resistance as diameter changes frequently, in contrast
to larger arteries that do not change often
small
Pumping action of heart generates blood flow
} Pressure results when flow is opposed by
resistance
} Systemic pressure is highest in aorta and
declines throughout pathway
◦ Steepest drop occurs in arterioles, where resistance
is greatest
systemic blood pressure
what is arterial blood pressure determined by?
Elasticity (
compliance or
distensibility) of arteries
close to heart
2. Volume of blood forced into them at any time
rises and falls with each heartbeat
pulsatile
pressure exerted in aorta
during ventricular contraction
◦ Left ventricle pumps blood into aorta, that stretches
aorta
◦ Averages 120 mm Hg in normal adult
systolic pressure
when heart is at rest
diastolic pressure
difference between systolic and
diastolic pressure (systolic – diastolic)
pulse pressure
throbbing of arteries due to difference in
pulse pressures, which can be felt under skin
pulse
pressure that
keeps blood moving throughout the cardiac cycle
mean arterial pressure
pulse and blood pressure, along with
respiratory rate and body temperature
vital signs
most common
radial pulse
areas where arteries are close to body surface
pulse points
less than 120mmHg
Pressure when sounds first occur as blood starts to
spurt through artery
systolic pressure
less than 80 mmHg
Pressure when sounds disappear because artery is no
longer constricted, blood is flowing freely
diastolic pressure
Changes little during cardiac cycle
} Important for return flow to heart and CO
} Small pressure gradient, only about 15 mm Hg
◦ If vein is cut, low pressure of venous system
causes blood to flow out smoothly
◦ If artery cut, blood spurts out because pressure is
higher
} Low pressure is due to resistance
} Non-pulsatile
} Low pressure of venous side requires
adaptations to help with venous return
venous blood pressure
what are the factors that aid venous return?
muscular
respiratory
sympathetic venoconstriction
contraction of skeletal
muscles “milks” blood back toward heart;
valves prevent backflow
muscular
pressure changes during
breathing move blood toward heart by
squeezing abdominal veins as thoracic veins
expand
respiratoru
under
sympathetic control, smooth muscles constrict,
pushing blood back toward heart
sympathetic venoconstrictionn
what are the 3 main factors regulating BP?
cardiac output
peripheral resistance
blood volume
what can factors of BP be affected by?
neural controls
hormonal controls
renal controls
