Download Functions of the Blood Vessels/Chapter 19

Functions of the Blood
Vessels/Chapter 19
Joe Pistack MS/ED
Blood Vessels
Functions:
 Act as a delivery system
 Regulate blood pressure
 Engage in the exchange of nutrients and waste
between the capillaries and cells
 Redistribute blood in response to changing body
needs
 Help regulate body temperature
Blood Vessels
• All cells require oxygen
• Without oxygen the cells will die
• Adequate blood flow to all organs is vital
• Ischemia-impaired blood flow to the tissues
▫ Ex. of ischemia is a blockage or occlusion of an
artery
“5 Cool P’s” of occlusive arterial
disease
1. Pain. Diminished oxygen supply stimulates
pain receptors.
2. Pulselessness. The blocked artery decreases
the flow of blood to the extremity; the pulse
distal to the occlusion is diminished or absent.
3. Pallor. Due to lack of blood the extremity is
pale, especially when elevated.
“5 P’s”
4. Paresthesia. Diminished blood flow decreases
the supply of oxygen to the nerves of the leg,
causing numbness and tingling.
5. Paralysis. Persistent oxygen deficit causes
permanent nerve damage and paralysis (late
sign).
6. Coolness. Blood flow carries heat, decreased
blood flow results in a decrease in temperature
of the affected extremity.
Blood Pressure
• The force blood exerts against the walls of the
blood vessels.
• Blood pressure is determined by the pumping
action of the heart and the size (lumen diameter)
of the blood vessels.
Measuring Blood Pressure
• Blood pressure in the arteries is caused by the
heart’s pumping activity,
• When the ventricles contract, a volume of blood
(stroke volume) is pumped out of the ventricle
into the artery, thereby increasing pressure.
Measurement of Blood Pressure
 Systolic pressure - pressure in the arteries at the
peak of the ventricular contraction.
( Top number)
 Diastolic pressure - pressure in the large arteries
when the ventricles of the heart are relaxing.
(Bottom number)
 Pulse pressure - difference between the systolic and
diastolic pressure. Ex. BP 120/80, 120 -80 =40
Blood Pressure
Blood pressure readings vary according to:
 Age
 Gender
 Size
Blood pressure that is too low:
 Decrease in blood flow to vital organs
 Shock may occur
 Immediate treatment necessary
Blood Pressure
Blood pressure too high:
 Blood vessels may burst or rupture
 Major cause of stroke
Hypertension-long-term or chronic elevation in blood
pressure.
Chronic hypertension is a major cause of heart
disease.
Blood Pressure
Complications of hypertension:
 Added strain on the heart
 Damage to the blood vessels of the kidney
 Damage to the retina
Measurement of blood pressure provides valuable
information regarding a person’s general health.
Blood Pressure
Sphygmomanometer-device with a dial and an
inflatable cuff.
Cuff is placed around patient’s upper arm and inflated
with air until the brachial artery is compressed, and
flow of blood through the artery is stopped.
Stethescope is placed over brachial artery, distal to or
below the cuff, examiner listens for Korotkoff
sounds.
Blood Pressure
 Blood pressure is highest in the aorta because it
is closest to the left ventricle.
 Left ventricle pumps blood with great force.
 Blood pressure declines as blood flows from the
large arteries down to the smaller ones.
Venous Blood
 Blood pressure is high in the arterial circulation.
 Blood pressure decreases in the veins, it cannot
return blood back to the heart without help.
 Three mechanisms assist in the return of venous
blood: 1. skeletal muscle action
2. respiratory movements
3. constriction of the veins
Skeletal Muscle Action
 Large veins in the legs are
surrounded by skeletal
muscles.
 As skeletal muscles
contract, they squeeze the
large veins, squirting
blood back to the heart.
 This mechanism is called
the skeletal muscle
pump.
 Explains how exercise is
beneficial to improve
blood flow.
Respiratory Movements
 Breathing is performed by the contraction and
relaxation of the skeletal muscles of the chest.
 Respiratory movements cause the pressures in
the chest cavity to change.
Respiratory Movements
 During inhalation-diameter of the chest
increases.
 Increase in the thoracic size decreases pressure
within the thorax and increases pressure within
the abdominal cavity.
 Increase in abdominal pressure squeezes the
vena cava and pushes more blood toward the
heart. This effect is called the respiratory pump.
Constriction of the Veins
 Most of the blood is located in the venous side of
the circulation.
 Constriction of the veins pushes additional blood
out of the veins toward the heart.
 Vasoconstriction occurs by sympathetic nervous
system stimulation and hormones that cause
vasoconstriction and increasing venous return.
The Heart and Blood Vessels
 Water flows from an area
of high pressure to an area
of low pressure.
 Blood pressure is caused by
the contraction of the heart
muscle.
 The stronger the force of
contraction, the higher the
blood pressure.
 No myocardial contraction,
no blood pressure—death!
Blood Vessels
 Arterioles are composed largely of smooth
muscle.
 Contraction and relaxation of the smooth muscle
allow the arterioles to change the size of their
diameter.
Vasodilation
 Vasodilation occurs when the
muscle relaxes and the
opening of the arteriole
increases.
 Vasodilation decreases the
resistance in the blood vessels.
 Vasoconstriction occurs when
the smooth muscle contracts
and the opening of the
arteriole becomes smaller.
 Vasoconstriction increases the
resistance in the blood vessels.
Blood Pressure
 When vascular resistance decreases, blood
pressure decreases.
 When vascular resistance increases, blood
pressure increases.
 Blood pressure is affected by the ability of the
arterioles to dilate and constrict.
Cardiac Output
 Cardiac output- is the amount of blood
pumped by the heart each minute.
 Increase in heart rate or stroke volume can
increase cardiac output and increase blood
pressure.
 Decrease in heart rate or stroke volume can
decrease cardiac output and decrease blood
pressure.
Blood Pressure
 Vascular resistance-caused by the
relaxation and contraction of the
arterioles.
 Factors affecting vascular resistance:
 sympathetic nerve activity
 various hormones
 pharmacologic agents
Sympathetic Nerve Activity
 Arterioles are supplied by fibers from the
sympathetic nervous system.
 When sympathetic nerves fire, vascular smooth
muscle contracts.
 Vasoconstriction results.
 Vasoconstriction increases vascular resistance
and elevates blood pressure.
Hormones
 Epinephrine and angiotensin II cause
vasoconstriction and elevate blood pressure.
 Called vasopressors because they elevate blood
pressure.
 Some hormones may induce vasodilation ,
decreasing vascular resistance.
Pharmacologic Agents
 Many pharmacologic agents affect vascular
resistance.
 Drugs that cause vasoconstriction elevate blood
pressure, often used to treat shock. Ex.
vasopressin, epinephrine, nor-epinephrine.
 Antihypertensive agents induce vasodilation,
lower vascular resistance, lower blood pressure.
Ex. Amlodipine (Norvasc), enalapril (vasotec).
Blood Pressure
 Under normal conditions, blood pressure
remains relatively constant.
 Regulation of blood pressure involves both
rapidly acting and slowly acting mechanisms.
Blood Pressure
 Baroreceptor reflex:
 most important rapidly active mechanism.
 consists of receptors, sensory nerves, medulla
oblongata, and motor nerves.
 baroreceptors are special receptors or pressure
receptors located in the walls of the aortic arch
and carotid sinus.
Baroreceptors sense changes in blood pressure
and activate the sensory nerves, then medulla
oblongata, then motor nerves which will carry
information to the heart and blood vessels.
Baroreceptors
 Stimuli to the carotid sinus may cause syncope.
 Syncope means fainting
 Some causes:
 tight collars
Shaving over the neck
Showering with spurts of water
Shoulder-strap seat belts
Slower-Acting Mechanisms
 Several mechanisms act slowly to control blood
pressure.
 More concerned with long-term relationship of
blood pressure.
 Renin-angiotensin-aldostrone mechanism is the
most important.
Slower-Acting Mechanisms
 Activation of the renin-angiotensin-aldosterone
mechanism increases blood volume and causes
vasoconstriction.
 Both of these effects increase blood pressure.
 Other hormones that affect blood pressure
include: antidiuretic hormone (ADH), atrial
natriuretic peptide (ANP), and brain natriuretic
peptide (BNP).
Exchange Vessels
 Exchange vessels, exchange or swap
substances.
 As blood flows through the
capillaries, substances move out of
the capillary into surrounding tissue
spaces.
 Substances include: oxygen, water,
electrolytes, and nutrients needed to
live.
 The oxygen and nutrients are taken
in by the cells and the waste is taken
from the capillaries to the kidneys
and lungs for excretion.
Exchange Vessels
 Characteristics of capillaries for good exchange:
 thin capillary walls
 large number of capillaries
 slow blood flow through the capillaries
Capillary Forces
 Certain forces push and pull nutrients and waste
in and out of the capillaries:
 Diffusion-primary process causing substances to
move across the capillary wall.
(movement from an area of high concentration
to an area of lower concentration)
 Filtration-Osmosis-holes or pores in the
capillaries allow water and small substances to
squirt into the interstitium.
Edema
 Edema occurs when there is a disruption in the
forces that push and pull water across the
capillary walls.
 Diseases that may cause disruptions:
 Heart failure
 severe burn
 kidney disease
 blocked lymphatic drainage
Blood Flow
• Vasodilation and
vasoconstriction also participate
in the distribution of blood flow.
• Resting state, skeletal muscles
receive 20% of total blood flow,
kidneys and abdomen receive
19% and 24%.
• During exercise, blood is
redirected and the % of blood
flow to the skeletal muscles is
greatly increased.
Sum It Up!
 Functions of the circulatory system:
 acts as a delivery system
 regulates blood pressure
 engages in exchange of nutrients and waste
within the cells
 distributes blood in response to changing body
needs
 helps in the regulation of body temperature
As We Age
 Walls of the arteries thicken and become less
elastic and thicker.
 Blood flow to vital organs decreases.
 Blood pressure increases.
 Elderly are more prone to varicose veins.
 More prone to thrombus.
 Cardiovascular adjustment to changes in
position are slowed, may cause dizziness,
increase in falls.