Blood Vessels - BradyGreatPath

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Blood Vessels
Blood Vessels: The Vascular System
 Transport blood to the tissues and
back
 Carry blood away from the heart
 Arteries
 Arterioles
Arterioles
 Exchanges between tissues and blood
 Capillary beds
 Return blood toward the heart
 Venules
 Veins
Venules
Cross-section of Artery & Vein
Assume you are viewing a blood vessel under the microscope. It has a lopsided lumen, relatively thick
externa, and a relatively thin media. Which kind of blood vessel is this?
Figure 11.9a
Name and describe from the inside out the three tunics making up the walls of
arteries, and veins, and give the most important function of each
Tunic
Description
Function
Tunica intima
A single layer of squamous
epithelium
provides a smooth, friction-reducing
lining for the vessel.
Tunica media
A middle layer, consisting of
smooth muscle
The smooth muscle is activated by the
sympathetic nervous system when
vasoconstriction (and increases in
blood pressure) is desired.
and
Tunica externa
connective tissue
(primarily elastic fibers)
The elastic fibers provide for stretching
and then passive recoil of vessels close
to the heart, which are subjected to
pressure fluctuations
The outermost layer, made of
fibrous connective tissue
basically a protective and supporting
layer
Blood Vessels: The Vascular System
Figure 11.9b
Why are artery walls so much thicker than those of
corresponding veins?
Arteries are much closer to the
pumping action of the heart and must
be able to withstand the pressure
fluctuations at such locations. Veins, on
the distal side of the capillary beds of
the tissues, are essentially low-pressure
vessels that need less
strength/support/ elasticity than do
arteries.
Figure 11.9a
Skeletal Muscles and Valves
Name three factors that are important in promoting
venous return.
1. The presence of valves,
2. the milking action of skeletal muscles against the
veins as the muscles contract,
3. the respiratory pump (pressure changes in the
thorax during breathing)
Figure 11.10
Breathing in pulls blood into right
atrium from vena cava
 the “thoracic pump” which generates negative pressure in the
lungs during inhalation causing blood to rush through the
vena cava and right heart filling the dense
The thoracic pump draws blood
from the extremities on inhalation
and sends blood throughout the
body on exhalation
Arteries are often described as vessels that carry oxygen-rich blood, and veins are
said to carry oxygen –poor (carbon dioxide-rich) blood. Name two sets of
exceptions to this rule that were discussed in this chapter.
 Pulmonary arteries carry oxygen-poor blood and pulmonary
veins carry oxygen-rich blood.
 Umbilical arteries carry oxygen-poor blood from the fetus
and the umbilical vein carries the most oxygen-rich blood to
the fetus.
Arteries lack valves, but veins have them. How is the
structural difference related to blood pressure?
Blood pressure in veins is much lower
in arteries because veins are farther
along in the circulation pathway. Veins
need extra measures to force blood
back to the heart.
Describe the structure of capillary walls
Capillary walls are essentially just
the tunica intima (endothelium
plus the basement membrane);
thus, they are exceedingly thin.
Capillary Beds
 Capillary beds consist of two types of vessels
 Vascular shunt—vessel directly connecting an arteriole to a
venule
 True capillaries—exchange vessels
 Oxygen and nutrients cross to cells
 Carbon dioxide and metabolic waste products cross into blood
How is the structure of capillaries related to
their function in the body?
 Capillary walls consist only of the
innermost intima layer which is very
thin. Capillaries are the exchange
vessels between the and tissue, thus,
thin walls are desirable
Left ventricle to ascending aorta  aortic arch  brachiocephalic artery  subclavian artery  axillary
artery  brachial artery  radial (or ulnar) artery
 capillary network of wrist 
radial (or ulnar) vein  brachial vein  axillary vein  subclavian vein  right brachiocephalic vein 
superior vena cava  right atrium of the heart.
Figure 11.12
Left ventricle  ascending aorta  aortic arch  descending aorta  right common iliac
artery  external iliac artery  femoral artery  popliteal artery  anterior tibial artery 
dorsalis pedis artery
capillary network 
anterior tibial vein  popliteal vein  femoral vein  external iliac vein  common iliac
vein  inferior vena cava  right atrium of the heart.
Figure 11.12
In what part of the body are the femoral, popliteal, and arcuate
arteries found?
Lower Limb
In what part of the body are the axillary, cephalic,
and basilic arteries found?
Upper Limb
What is the function of the hepatic portal circulation?
In what way is a portal circulation a “strange” circulation?
The hepatic portal circulation carries nutrient-rich
blood from the digestive viscera to the liver for
processing before the blood enters the systemic
circulation.
A portal circulation involves a capillary bed that is
both fed and drained by veins; the usual circulation
has a capillary bed that is fed by arteries and drained
by veins.
Figure 11.16
Which vessel – the hepatic portal vein, hepatic vein, or hepatic
artery- has the highest content of nutrients after a meal?
 The hepatic portal vein carries nutrient-rich
blood from the digestive viscera to the liver for
processing before the blood enters the systemic
circulation. The liver removes nutrients (and
toxins) from blood.
Comparison of Blood Pressures
in Different Vessels
Figure 11.19
Capillary Exchange
 Substances exchanged due to concentration gradients
 Oxygen and nutrients leave the blood
 Carbon dioxide and other wastes leave the cells
Capillary Exchange:
 Direct diffusion across plasma membranes
 Endocytosis or exocytosis
 Some capillaries have gaps (intercellular clefts)
 Fenestrations (pores) of some capillaries
What is the different about the capillary exchanges seen in a capillary
with fenestrations and intracellular clefts and the exchanges seen in a
capillary lacking those modifications?
 Intercellular clefts allow limited
passage of solutes and fluid.
 Fenestrated capillaries allow
very free passage of small
solutes and fluids.
 Capillaries lacking these
modifications are relatively
impermeable.
Figure 11.22
Capillary Types

Continuous basement membrane is
continuous and intercellular clefts are
tight; these capillaries have the
lowest permeability.;

Fenestrated perforations (fenestrae)
in endothelium result in relatively
high permeability.

Discontinuous − large intercellular
gaps and gaps in basement membrane
result in extremely high
permeability
Fluid Movements at Capillary Beds
 Blood pressure forces fluid and solutes out of capillaries
 Osmotic pressure draws fluid into capillaries
 Blood pressure is higher than osmotic pressure at the arterial
end of the capillary bed
 Blood pressure is lower than osmotic pressure at the venous
end of the capillary bed
Would you expect fluid to be entering or leaving
the capillaries at the venous end of a capillary bed?
Arterial end of
capillary bed:
Fluid leaving
capillary
Venous end of capillary bed:
Fluid entering capillary
Figure 11.23
Explain why blood flow in arteries is
pulsatile* and blood flow in veins is not.
 Blood flow in arteries is pulsatile because it is under a greater
amount of pressure compared to veins.
 Arteries are located closer to the ventricles, so their walls
must be capable of expanding and contracting under the
changes in pressure when the ventricles contract.
 When blood reaches the veins, the pressure is very low, and
so instead of veins having a pulsatile ability to maintain
pressure, they instead have valves to prevent backflow
*beating rhythmically; pulsating or throbbing
What is the relationship between cross-sectional area of a blood
vessel and velocity (speed) of blood flow in that vessel?
 The greater the cross-sectional area in a blood vessel, the
faster that blood can flow through that vessel.
 Smaller vessels, like capillaries, are only one cell thick in
diameter, which slows down blood flow and allows nutrient
and gas exchange to occur.
Which type of blood vessel is most important in regulating vascular
resistance*, and how does it achieve this?
Arterioles are the blood vessels that are most important in regulating
vascular resistance.
These vessels can constrict as a result of activity from the sympathetic
nervous system, which alters blood pressure.
(Arterioles are enervated by the sympathetic nervous system. Sympathetic
nerve fibers secrete norepinephrine to receptors on the smooth muscles of
arterioles causing contraction and thus leads to vasoconstriction.)
Atherosclerosis in these vessels also causes narrowing due to plaque
deposits, which also affects blood pressure
*Resistance of blood flow through blood vessels
In a fetus, the liver and lungs are almost entirely bypassed by blood.
Why is this? Name the vessel that bypasses the liver. Name two lung
bypasses. Three vessels travel in the umbilical cord; which of these
carries oxygen and nutrient rich blood.
 In a fetus, both liver and lungs are nonfunctional (the liver
relatively so).
 The ductus venosus bypasses the liver.
 The ductus
arteriosus and the foramen ovale
bypass the lungs.
 The umbilical vein carries nutrient-rich and oxygenrich blood to the fetus through the umbilical cord.
Ductus venosus BYPASS LIVER
What is the ductus venosus,
and what is its function?
The ductus venosus is the liver
bypass in the fetus.
Since the mother’s liver is working
for the fetus as well, the entire
fetal liver need not be
continuously suffused with blood.
Liver
Foramen ovale & Ductus arteriosus
BYPASS LUNGS
Umbilical Cord- contains three blood vessels:
two arteries and one vein.
Umbilical vein- bright red = high
oxygenation
Umbilical arteries – pink = low
oxygenation
Define pulse.
 Pulse: The alternate expansion and recoil of an artery that
occur with each heartbeat.
Which artery is palpated at the wrist? A
At the groin? B
At the side of the neck? C
At the front of the ear? D
At the back of the knee? E
D
C
A
B
E
Define systolic and diastolic pressure.
 Systolic pressure—pressure in the arteries at the peak of
ventricular contraction
 Diastolic pressure—pressure in the arteries when ventricles
relax
Two elements define blood pressure – the cardiac output of the heart
and the peripheral resistance, or friction, in the blood vessels.
Name two factors that increase cardiac output.
Name two factors that increase peripheral resistance.
Cardiac output is increased by
• increased venous return
• increased heart rate.
Peripheral resistance is increased by
• decreased diameter of the blood vessels
• increased blood viscosity.
Increased
blood
viscosity
Increased
venous
return
How does blood pressure change throughout the systemic
circulatory pathway?
It decreases from heart to
vena cavae
What is the effect of hemorrhage on blood
pressure? Why?
 Hemorrhage reduces blood pressure initially
because blood volume drops.
..Then the heart begins to beat more rapidly as it tries to compensate.
However because blood loss reduces venous return, the heart beats weakly and
inefficiently. In such cases, the sympathetic nervous system causes vasoconstriction to
increase blood pressure so venous return increases and circulation can continue.
In which position – sitting, lying down, or standing- is the
blood pressure normally highest? Lowest?
 Blood pressure is normally highest in the recumbent
position and lowest immediately after standing up;
however, the sympathetic nervous system quickly
compensates in a healthy individual.
 Very often an individual can become hypotensive after
remaining still in the sitting position for an extended
period.
When you stand, gravity causes
Both systolic BP and diastolic BP were significantly
higher in the supine than in the sitting position.
blood to pool in your leg veins,
reducing the amount of blood
that returns to your heart. This
causes your blood pressure to
drop
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