Ch21

Chapter 21

The Cardiovascular System: Blood Vessels
and Hemodynamics

Lecture Outline

Principles of Human Anatomy and Physiology, 11e 1

INTRODUCTION

• One main focus of this chapter considers hemodynamics,
the means by which blood flow is altered and distributed and
by which blood pressure is regulated.
• The histology of blood vessels and anatomy of the primary
routes of arterial and venous systems are surveyed.


Chapter 21
The Cardiovascular System: Blood Vessels and
Hemodynamics

• Structure and function of
blood vessels
• Hemodynamics
– forces involved in
circulating blood
• Major circulatory routes


STRUCTURE AND FUNCTION OF BLOOD
VESSELS
• Angiogenesis: the growth of new blood vessels
– It is an important process in the fetus and in postnatal
processes
– Malignant tumors secrete proteins called tumor
angiogenesis factors (TAFs) that stimulate blood vessel
growth to nature the tumor cells
• Scientists are looking for chemicals that inhibit angiogenesis
to stop tumor growth and to prevent the blindness
associated with diabetes.


Vessels

• Blood vessels form a closed system of tubes that carry
blood away from the heart, transport it to the tissues of the
body, and then return it to the heart.
– Arteries carry blood from the heart to the tissues.
– Arterioles are small arteries that connect to capillaries.
– Capillaries are the site of substance exchange between
the blood and body tissues.
– Venules connect capillaries to larger veins.
– Veins convey blood from the tissues back to the heart.
– Vaso vasorum are small blood vessels that supply blood
to the cells of the walls of the arteries and veins.


Arteries

• The wall of an artery consists of
three major layers (Figure 21.1).
• Tunica interna (intima)
– simple squamous epithelium
known as endothelium
– basement membrane
– internal elastic lamina
• Tunica media
– circular smooth muscle &
elastic fibers
• Tunica externa
– elastic & collagen fibers


Arteries

• Arteries carry blood away from the heart to the tissues.
• The functional properties of arteries are elasticity and
contractility.
– Elasticity, due to the elastic tissue in the tunica internal
and media, allows arteries to accept blood under great
pressure from the contraction of the ventricles and to
send it on through the system.
– Contractility, due to the smooth muscle in the tunica
media, allows arteries to increase or decrease lumen size
and to limit bleeding from wounds.


Sympathetic Innervation

• Vascular smooth muscle is innervated by sympathetic
nervous system
– increase in stimulation causes muscle contraction or
vasoconstriction
• decreases diameter of vessel
– injury to artery or arteriole causes muscle contraction
reducing blood loss (vasospasm)
– decrease in stimulation or presence of certain chemicals
causes vasodilation
• increases diameter of vessel
• nitric oxide, K+, H+ and lactic acid cause vasodilation


Elastic Arteries
• Large arteries with more elastic fibers and less smooth
muscle are called elastic arteries and are able to receive
blood under pressure and propel it onward (Figure 21.2).
• They are also called conducting arteries because they
conduct blood from the heart to medium sized muscular
arteries.
• They function as a pressure reservoir.


Muscular Arteries

• Medium-sized arteries with more muscle than elastic fibers
in tunica media
• Capable of greater vasoconstriction and vasodilation to
adjust rate of flow
– walls are relatively thick
– called distributing arteries because they direct blood flow


Arterioles

• Arterioles are very small, almost microscopic, arteries that
deliver blood to capillaries (Figure 21.3).
• Through vasoconstriction (decrease in the size of the lumen
of a blood vessel) and vasodilation (increase in the size of
the lumen of a blood vessel), arterioles assume a key role in
regulating blood flow from arteries into capillaries and in
altering arterial blood pressure.


Arterioles

• Small arteries delivering blood to
capillaries
– tunica media containing few
layers of muscle
• Metarterioles form branches into
capillary bed
– to bypass capillary bed,
precapillary sphincters close
& blood flows out of bed in
thoroughfare channel
– vasomotion is intermittent
contraction & relaxation of
sphincters that allow filling of
capillary bed 5-10
times/minute


Capillaries form Microcirculation
• Microscopic vessels that connect arterioles to venules
• Found near every cell in the body but more extensive in highly active
tissue (muscles, liver, kidneys & brain)
– entire capillary bed fills with blood when tissue is active
– lacking in epithelia, cornea and lens of eye & cartilage
• Function is exchange of nutrients & wastes between blood and tissue
fluid
• Capillary walls are composed of only a single layer of cells
(endothelium) and a basement membrane (Figure 21.1).


Types of Capillaries
• Continuous capillaries
– intercellular clefts are gaps between
neighboring cells
– skeletal & smooth, connective tissue and
lungs
• Fenestrated capillaries
– plasma membranes have many holes
– kidneys, small intestine, choroid plexuses,
ciliary process & endocrine glands
• Sinusoids
– very large fenestrations
– incomplete basement membrane
– liver, bone marrow, spleen, anterior pituitary,
& parathyroid gland


Venules

• Small veins collecting blood from capillaries
• Tunica media contains only a few smooth muscle
cells & scattered fibroblasts
– very porous endothelium allows for escape of
many phagocytic white blood cells
• Venules that approach size of veins more closely
resemble structure of vein


Veins

• Veins consist of the same three tunics as arteries but have a
thinner tunica interna and media and a thicker tunica
externa
– less elastic tissue and smooth muscle
– thinner-walled than arteries
– contain valves to prevent the backflow of blood (Figure
21.5).
• Vascular (venous) sinuses are veins with very thin walls with
no smooth muscle to alter their diameters. Examples are the
brain’s superior sagittal sinus and the coronary sinus of the
heart (Figure 21.3c).


Veins
• Proportionally thinner walls
than same diameter artery
– tunica media less muscle
– lack external & internal
elastic lamina
• Still adaptable to variations
in volume & pressure
• Valves are thin folds of
tunica interna designed to
prevent backflow


Varicose Veins

• Twisted, dilated superficial veins
– caused by leaky venous valves
• congenital or mechanically stressed from prolonged standing or
pregnancy
– allow backflow and pooling of blood
• extra pressure forces fluids into surrounding tissues
• nearby tissue is inflamed and tender
• The most common sites for varicose veins are in the esophagus,
superficial veins of the lower limbs, and veins in the anal canal
(hemorrhoids). Deeper veins not susceptible because of support of
surrounding muscles
• The treatments for varicose veins in the lower limbs include:
sclerotherapy, radiofrequency endovenous occlusion, laser occlusion,
and surgical stripping


Anastomoses
• Union of 2 or more arteries supplying the same body region
– blockage of only one pathway has no effect
• circle of willis underneath brain
• coronary circulation of heart
• Alternate route of blood flow through an anastomosis is known as
collateral circulation
– can occur in veins and venules as well
• Arteries that do not anastomose are known as end arteries. Occlusion
of an end artery interrupts the blood supply to a whole segment of an
organ, producing necrosis (death) of that segment.
• Alternate routes to a region can also be supplied by nonanastomosing
vessels
• Table 21.1 summarizes the distinguishing features of the various
types of blood vessels.


Blood Distribution (Figure 21.6).

• 60% of blood volume at rest is in systemic veins and venules
– function as blood reservoir
• veins of skin & abdominal
organs (liver and spleen)
– blood is diverted from it in
times of need
• increased muscular activity
produces venoconstriction
• hemorrhage causes
venoconstriction to help
maintain blood pressure
• 15% of blood volume in arteries & arterioles


Capillary Exchange

• Movement of materials in & out of a capillary
– diffusion (most important method)
• Substances such as O2, CO2, glucose, amino acids, hormones,
and others diffuse down their concentration gradients.
• all plasma solutes except large proteins pass freely across
– through lipid bilayer, fenestrations or intercellular clefts
– blood brain barrier does not allow diffusion of water-soluble
materials (nonfenestrated epithelium with tight junctions)
– transcytosis
• passage of material across endothelium in tiny vesicles by
endocytosis and exocytosis
– large, lipid-insoluble molecules such as insulin or maternal
antibodies passing through placental circulation to fetus
– bulk flow see next slide


Bulk Flow: Filtration & Reabsorption

• Movement of large amount of dissolved or suspended material in same
direction
– move in response to pressure
• from area of high pressure to area of low
– faster rate of movement than diffusion or osmosis
• Most important for regulation of relative volumes of blood & interstitial
fluid
– filtration is movement of material into interstitial fluid
• promoted by blood hydrostatic pressure & interstitial fluid osmotic
pressure
– reabsorption is movement from interstitial fluid into capillaries
• promoted by blood colloid osmotic pressure
– balance of these pressures is net filtration pressure


Dynamics of
Capillary
Exchange
• Starling’s law of the
10 9 capillaries is that the
volume of fluid & solutes
reabsorbed is almost as
large as the volume
filtered (Figure 21.7).


Net Filtration Pressure

• Whether fluids leave or enter capillaries depends on
net balance of pressures
– net outward pressure of 10 mm Hg at arterial end
of a capillary bed
– net inward pressure of 9 mm Hg at venous end of
a capillary bed
• About 85% of the filtered fluid is returned to the
capillary
– escaping fluid and plasma proteins are collected
by lymphatic capillaries (3 liters/day)


Edema
• An abnormal increase in interstitial fluid if filtration
exceeds reabsorption
– result of excess filtration
• increased blood pressure (hypertension)
• increased permeability of capillaries allows
plasma proteins to escape
– result of inadequate reabsorption
• decreased concentration of plasma proteins
lowers blood colloid osmotic pressure
– inadequate synthesis or loss from liver
disease, burns, malnutrition or kidney
disease blockage of lymphatic vessels
postoperatively or due to filarial worm
infection
• Often not noticeable until 30% above normal

HEMODAYNAMICS: FACTORS AFFECTING
BLOOD FLOW
• The distribution of cardiac output to various tissues depends
on the interplay of the pressure difference that drives the
blood flow and the resistance to blood flow.
• Blood pressure (BP) is the pressure exerted on the walls of
a blood vessel; in clinical use, BP refers to pressure in
arteries.
• Cardiac output (CO) equals mean aortic blood pressure
(MABP) divided by total resistance (R).


Hemodynamics - Overview

• Factors that affect blood pressure include cardiac output,
blood volume, viscosity, resistance, and elasticity of arteries.
• As blood leaves the aorta and flows through systemic
circulation, its pressure progressively falls to 0 mm Hg by
the time it reaches the right atrium (Figure 21.8).
• Resistance refers to the opposition to blood flow as a result
of friction between blood and the walls of the blood vessels.
• Vascular resistance depends on the diameter of the blood
vessel, blood viscosity, and total blood vessel length.
• Systemic vascular resistance (also known as total peripheral
resistance) refers to all of the vascular resistances offered
by systemic blood vessels; most resistance is in arterioles,
capillaries, and venules due to their small diameters.

Hemodynamics
• Factors affecting circulation
– pressure differences that drive the blood flow
• velocity of blood flow
• volume of blood flow
• blood pressure
– resistance to flow
– venous return
• An interplay of forces result in blood flow


Volume of Blood Flow

• Cardiac output = stroke volume x heart rate
• Other factors that influence cardiac output
– blood pressure
– resistance due to friction between blood cells and
blood vessel walls
• blood flows from areas of higher pressure to
areas of lower pressure


Blood Pressure
• Pressure exerted by blood on walls of a
vessel
– caused by contraction of the ventricles
– highest in aorta
• 120 mm Hg during systole & 80
during diastole
• If heart rate increases cardiac
output, BP rises
• Pressure falls steadily in
systemic circulation with distance from
left ventricle
– 35 mm Hg entering the capillaries
– 0 mm Hg entering the right atrium
• If decrease in blood volume is over 10%,
BP drops
• Water retention increases blood pressure

Velocity of Blood Flow

• The volume that flows through any tissue in a given period
of time is blood flow.
• The velocity of blood flow is inversely related to the cross-
sectional area of blood vessels; blood flows most slowly
where cross-sectional area is greatest (Figure 21.11).
• Blood flow decreases from the aorta to arteries to capillaries
and increases as it returns to the heart.


Velocity of Blood Flow
• Speed of blood flow in cm/sec is inversely related to cross-
sectional area
– blood flow is slower in the
arterial branches
• flow in aorta is 40 cm/sec while
flow in capillaries is .1 cm/sec
• slow rate in capillaries allows for
exchange
• Blood flow becomes faster when vessels merge to form veins
• Circulation time is time it takes a drop of blood to travel from
right atrium back to right atrium


Venous Return (Figure 21.9).
• Volume of blood flowing back to the heart from the systemic
veins
– depends on pressure difference from venules (16 mm
Hg) to right atrium (0 mm Hg)
– tricuspid valve leaky and
buildup of blood on venous
side of circulation
• Skeletal muscle pump
– contraction of muscles &
presence of valves
• Respiratory pump
– decreased thoracic pressure and increased abdominal
pressure during inhalation, moves blood into thoracic
veins and the right atrium


Clinical Application

• Syncope, or fainting, refers to a sudden, temporary loss of
consciousness followed by spontaneous recovery. It is most
commonly due to cerebral ischemia but it may occur for
several other reasons


CONTROL OF BLOOD PRESSURE AND BLOOD
FLOW


Factors that Increase Blood Pressure


• Friction between blood and the walls of vessels
– average blood vessel radius
• smaller vessels offer more resistance to blood flow
• cause moment to moment fluctuations in pressure
– blood viscosity (thickness)
• ratio of red blood cells to plasma volume
• increases in viscosity increase resistance
– dehydration or polycythemia
Resistance
– total blood vessel length
• the longer the vessel, the greater the resistance to
flow
• 200 miles of blood vessels for every pound of fat
– obesity causes high blood pressure
• Systemic vascular resistance is the total of above
– arterioles control BP by changing diameter

Control of Blood Pressure & Flow

• Role of cardiovascular center
– help regulate heart rate & stroke volume
– specific neurons regulate blood vessel diameter


Cardiovascular Center - Overview

• The cardiovascular center (CV) is a group of neurons in the medulla that
regulates heart rate, contractility, and blood vessel diameter.
– input from higher brain regions and sensory receptors
(baroreceptors and chemoreceptors) (Figure 21.12).
– output from the CV flows along sympathetic and parasympathetic
fibers.
– Sympathetic impulses along cardioaccelerator nerves increase heart
rate and contractility.
– Parasympathetic impulses along vagus nerves decrease heart rate.
• The sympathetic division also continually sends impulses to smooth
muscle in blood vessel walls via vasomotor nerves. The result is a
moderate state of tonic contraction or vasoconstriction, called
vasomotor tone.


Input to the Cardiovascular Center

• Higher brain centers such as cerebral cortex, limbic
system & hypothalamus
– anticipation of competition
– increase in body temperature
• Proprioceptors
– input during physical activity
• Baroreceptors
– changes in pressure within blood vessels
• Chemoreceptors
– monitor concentration of chemicals in the blood


Output from the Cardiovascular Center
• Heart
– parasympathetic (vagus nerve)
• decrease heart rate
– sympathetic (cardiac accelerator nerves)
• cause increase or decrease in contractility & rate
• Blood vessels
– sympathetic vasomotor nerves
• continual stimulation to arterioles in skin &
abdominal viscera producing vasoconstriction
(vasomotor tone)
• increased stimulation produces constriction &
increased BP

Neural Regulation of Blood Pressure

• Baroreceptors are important pressure-sensitive sensory
neurons that monitor stretching of the walls of blood vessels
and the atria.
– The cardiac sinus reflex is concerned with maintaining
normal blood pressure in the brain and is initiated by
baroreceptors in the wall of the carotid sinus (Figure
21.13).
– The aortic reflex is concerned with general systemic
blood pressure and is initiated by baroreceptors in the
wall of the arch of the aorta or attached to the arch.
• If blood pressure falls, the baroreceptor reflexes accelerate
heart rate, increase force of contraction, and promote
vasoconstriction (Figure 21.14).


Neural Regulation of
Blood Pressure
• Baroreceptor reflexes
– carotid sinus reflex
• swellings in internal carotid artery wall
• glossopharyngeal nerve to cardiovascular
center in medulla
• maintains normal BP in the brain
– aortic reflex
• receptors in wall of ascending aorta
• vagus nerve to cardiovascular center
• maintains general systemic BP
• If feedback is decreased, CV center reduces
parasympathetic & increases sympathetic
stimulation of the heart


Innervation of the Heart

• Speed up the heart with sympathetic stimulation
• Slow it down with parasympathetic stimulation (X)
• Sensory information from baroreceptors (IX)


Carotid Sinus Massage & Syncope
• Carotid sinus massage can slow heart rate in paroxysmal
superventricular tachycardia
• Stimulation (careful neck massage) over the carotid sinus
lowers heart rate
– paroxysmal superventricular tachycardia
• tachycardia originating from the atria
• Anything that puts pressure on carotid sinus
– tight collar or hyperextension of the neck
– may slow heart rate & cause carotid sinus syncope or
fainting


Syncope
• Fainting or a sudden, temporary loss of consciousness not
due to trauma
– due to cerebral ischemia or lack of blood flow to the brain
• Causes
– vasodepressor syncope = sudden emotional stress
– situational syncope = pressure stress of coughing,
defecation, or urination
– drug-induced syncope = antihypertensives, diuretics,
vasodilators and tranquilizers
– orthostatic hypotension = decrease in BP upon standing


Chemoreceptor Reflexes

• Carotid bodies and aortic bodies
– detect changes in blood levels of O2, CO2, and H+
(hypoxia, hypercapnia or acidosis )
– causes stimulation of cardiovascular center
– increases sympathetic stimulation to arterioles & veins
– vasoconstriction and increase in blood pressure
• Also changes breathing rates as well


Hormonal Regulation of Blood Pressure
• Renin-angiotensin-aldosterone system
– decrease in BP or decreased blood flow to kidney
– release of renin / results in formation angiotensin II
• systemic vasoconstriction
• causes release aldosterone (H2O & Na+ reabsorption)
• Epinephrine & norepinephrine
– increases heart rate & force of contraction
– causes vasoconstriction in skin & abdominal organs
– vasodilation in cardiac & skeletal muscle
• ADH causes vasoconstriction
• ANP (atrial natriuretic peptide) lowers BP
– causes vasodilation & loss of salt and water in the urine

• Table 21.1 summarizes the relationship between hormones and
blood pressure regulation.


Local Regulation of Blood Pressure

• The ability of a tissue to automatically adjust its own blood flow to
match its metabolic demand for supply of O2 and nutrients and removal
of wastes is called autoregulation.
• Local factors cause changes in each capillary bed
– important for tissues that have major increases in activity (brain,
cardiac & skeletal muscle)
• Local changes in response to physical changes
– warming & decrease in vascular stretching promotes vasodilation
• Vasoactive substances released from cells alter vessel diameter (K+,
H+, lactic acid, nitric oxide)
– systemic vessels dilate in response to low levels of O2
– pulmonary vessels constrict in response to low levels of O2


CHECKING CIRCULATION


Evaluating Circulation
• Pulse is a pressure wave
– alternate expansion & recoil of elastic artery after each systole of
the left ventricle
– pulse rate is normally between 70-80 beats/min
• tachycardia is rate over 100 beats/min/bradycardia under 60
• Measuring blood pressure with sphygmomanometer
– Korotkoff sounds are heard while taking pressure
– systolic blood pressure is recorded during ventricular contraction
– diastolic blood pressure is recorded during ventricular contraction
• provides information about systemic vascular resistance
– pulse pressure is difference between systolic & diastolic
– normal ratio is 3:2:1 -- systolic/diastolic/pulse pressure


Pulse Points


Evaluating Circulation


Blood Pressure

• The normal blood pressure of a young adult male is 120/80
mm Hg (8-10 mm Hg less in a young adult female). The
range of average values varies with many factors.
• Pulse pressure is the difference between systolic and
diastolic pressure. It normally is about 40 mm Hg and
provides information about the condition of the arteries.


SHOCK AND HOMEOSTASIS

• Shock is an inadequate cardiac output that results in failure
of the cardiovascular system to deliver adequate amounts of
oxygen and nutrients to meet the metabolic needs of body
cells. As a result, cellular membranes dysfunction, cellular
metabolism is abnormal, and cellular death may eventually
occur without proper treatment.
– inadequate perfusion
– cells forced to switch to anaerobic respiration
– lactic acid builds up
– cells and tissues become damaged & die


Types of Shock

• Hypovolemic shock is due to decreased blood volume.
• Cardiogenic shock is due to poor heart function.
• Vascular shock is due to inappropriate vasodilation.
• Obstructive shock is due to obstruction of blood flow.
• Homeostatic responses to shock include activation of the
renin-angiotensin-aldosterone system, secretion of ADH,
activation of the sympathetic division of the ANS, and
release of local vasodilators (Figure 21.16).
• Signs and symptoms of shock include clammy, cool, pale
skin; tachycardia; weak, rapid pulse; sweating; hypotension
(systemic pressure < 90 mm HG); altered mental status;
decreased urinary output; thirst; and acidosis.


Types of Shock
• Hypovolemic shock due to loss of blood or body fluids
(hemorrhage, sweating, diarrhea)
– venous return to heart declines & output decreases
• Cardiogenic shock caused by damage to pumping action
of the heart (MI, ischemia, valve problems or
arrhythmias)
• Vascular shock causing drop inappropriate vasodilation --
anaphylatic shock, septic shock or neurogenic shock
(head trauma)
• Obstructive shock caused by blockage of circulation
(pulmonary embolism)


Homeostatic Responses to Shock

• Mechanisms of compensation in shock attempt to return
cardiac output & BP to normal
– activation of renin-angiotensin-aldosterone
– secretion of antidiuretic hormone
– activation of sympathetic nervous system
– release of local vasodilators
• If blood volume drops by 10-20% or if BP does not rise
sufficiently, perfusion may be inadequate -- cells start to
die


Restoring BP during Hypovolemic Shock


Signs & Symptoms of Shock
• Rapid resting heart rate (sympathetic stimulation)
• Weak, rapid pulse due to reduced cardiac output & fast
heart rate
• Clammy, cool skin due to cutaneous vasoconstriction
• Sweating -- sympathetic stimulation
• Altered mental state due to cerebral ischemia
• Reduced urine formation -- vasoconstriction to kidneys
& increased aldosterone & antidiuretic hormone
• Thirst -- loss of extracellular fluid
• Acidosis -- buildup of lactic acid
• Nausea -- impaired circulation to GI tract


CIRCULATORY ROUTES


Introduction

• The blood vessels are organized into routes that deliver
blood throughout the body. Figure 21.17 shows the
circulatory routes for blood flow.
• The largest circulatory route is the systemic circulation.
• Other routes include pulmonary circulation (Figure 21.29)
and fetal circulation (Figure 21.30).


Circulatory Routes

• Systemic circulation is left side heart
to body & back to heart
• Hepatic Portal circulation is capillaries
of GI tract to capillaries in liver
• Pulmonary circulation is right-side
heart to lungs & back to heart
• Fetal circulation is from fetal heart
through umbilical cord to placenta &
back


Systemic Circulation

• The systemic circulation takes oxygenated blood from the left ventricle
through the aorta to all parts of the body, including some lung tissue (but
does not supply the air sacs of the lungs) and returns the deoxygenated
blood to the right atrium.
• The aorta is divided into the ascending aorta, arch of the aorta, and the
descending aorta.
• Each section gives off arteries that branch to supply the whole body.
• Blood returns to the heart through the systemic veins. All the veins of
the systemic circulation flow into the superior or inferior venae caveae or
the coronary sinus, which in turn empty into the right atrium.
• The principal arteries and veins of the systemic circulation are described
and illustrated in Exhibits 21.1-21.12 and Figures 21.18-21.27.
• Blood vessels are organized in the exhibits according to regions of the
body. Figure 21.18a shows the major arteries. Figure 21.23 shows the
major veins.


Arterial Branches of Systemic Circulation

• All are branches from aorta
supplying arms, head, lower limbs
and all viscera with O2 from the
lungs
• Aorta arises from left ventricle
(thickest chamber)
– 4 major divisions of aorta
• ascending aorta
• arch of aorta
• thoracic aorta
• abdominal aorta


Aorta and Its Superior Branches

• Aorta is largest artery of the body
– ascending aorta
• 2 coronary arteries supply myocardium
– arch of aorta -- branches to the arms & head
• brachiocephalic trunk branches into right common carotid and
right subclavian
• left subclavian & left carotid arise independently
– thoracic aorta supplies branches to pericardium, esophagus, bronchi,
diaphragm, intercostal & chest muscles, mammary gland, skin,
vertebrae and spinal cord


Coronary Circulation

• Right & left coronary
arteries branch to supply
heart muscle
– anterior & posterior
interventricular aa.


Subclavian Branches
• Subclavian aa. pass superior to
the 1st rib
– gives rise to vertebral a. that
supplies blood to the Circle of
Willis on the base of the brain
• Become the axillary artery in the
armpit
• Become the brachial in the arm
• Divide into radial and ulnar
branches in the forearm


Common Carotid Branches

Circle of Willis
• External carotid arteries
– supplies structures external to skull as branches of maxillary and
superficial temporal branches
• Internal carotid arteries (contribute to Circle of Willis)
– supply eyeballs and parts of brain


Abdominal Aorta and Its Branches

• Supplies abdominal & pelvic viscera & lower extremities
– celiac aa. supplies liver, stomach, spleen & pancreas
– superior & inferior mesenteric aa. supply intestines
– renal aa supply kidneys
– gonadal aa. supply ovaries
and testes
• Splits into common iliac
aa at 4th lumbar vertebrae
– external iliac aa supply
lower extremity
– internal iliac aa supply
pelvic viscera


Visceral Branches off Abdominal Aorta

• Celiac artery is first branch inferior to diaphragm
– left gastric artery, splenic artery, common hepatic artery
• Superior mesenteric artery lies in mesentery
– pancreaticoduodenal, jejunal, ileocolic, ascending & middle colic aa.
• Inferior mesenteric artery
– descending colon, sigmoid colon & rectal aa


Arteries of the Lower Extremity

• External iliac artery become femoral artery when it passes under the
inguinal ligament & into the thigh
– femoral artery becomes popliteal artery behind the knee

Veins of the Systemic Circulation

• Drain blood from entire body &
return it to right side of heart
• Deep veins parallel the arteries in
the region
• Superficial veins are found just
beneath the skin
• All venous blood drains to either
superior or inferior vena cava or
coronary sinus


Major Systemic
Veins

• All empty into the right atrium of the heart
– superior vena cava drains the head and upper extremities
– inferior vena cava drains the abdomen, pelvis & lower limbs
– coronary sinus is large vein draining the heart muscle back into the
heart

Veins of the Head and Neck

• External and Internal
jugular veins drain the
head and neck into the
superior vena cava
• Dural venous sinuses
empty into internal
jugular vein


Venipuncture

• Venipuncture is normally performed at cubital fossa, dorsum of the
hand or great saphenous vein in infants


Hepatic Portal Circulation

• A portal system carries blood between two capillary
networks, in this case from capillaries of the gastrointestinal
tract to sinusoids of the liver.
• The hepatic portal circulation collects blood from the veins of
the pancreas, spleen, stomach, intestines, and gallbladder
and directs it into the hepatic portal vein of the liver before it
returns to the heart (Figure 21.28).
– enables nutrient utilization and blood detoxification by the
liver.


Hepatic Portal System
• Subdivision of systemic
circulation
• Detours venous blood from GI
tract to liver on its way to the
heart
– liver stores or modifies
nutrients
• Formed by union of splenic,
superior mesenteric & hepatic
veins


Arterial Supply and Venous Drainage of Liver


Pulmonary Circulation

• The pulmonary circulation takes deoxygenated blood from the right
ventricle to the air sacs of the lungs and returns oxygenated blood from
the lungs to the left atrium (Figure 21.29).
• The pulmonary and systemic circulations differ from each other in
several more ways.
– Blood in the pulmonary circulation is not pumped so far as in the
systemic circulation and the pulmonary arteries have a larger
diameter, thinner walls, and less elastic tissue.
– resistance to blood flow is very low meaning that less pressure is
needed to move blood through the lungs.
– normal pulmonary capillary hydrostatic pressure is lower than
systemic capillary hydrostatic pressure which tends to prevent
pulmonary edema.


Pulmonary
Circulation


Pulmonary Circulation

• Carries deoxygenated blood from right ventricle to air sacs in the lungs
and returns it to the left atria
• Vessels include pulmonary trunk, arteries and veins
• Differences from systemic circulation
– pulmonary aa. are larger, thinner with less elastic tissue
– resistance to is low & pulmonary blood pressure is reduced


Fetal Circulation

• Oxygen from placenta reaches
heart via fetal veins in umbilical
cord.
– bypasses liver
• Heart pumps oxygenated blood
to capillaries in all fetal tissues
including lungs.
• Umbilical aa. Branch off iliac aa.
to return blood to placenta.


Lung Bypasses in Fetal Circulation

Ductus arteriosus is
shortcut from
pulmonary trunk to
aorta bypassing the
lungs.

Foramen ovale is shortcut
from right atria to left
atria bypassing the lungs.

DEVELOPMENT OF BLOOD VESSELS AND
BLOOD
• Development of blood cells and blood vessels begins at 15
– 16 days. (Figure 21.31).
• It begins in the mesoderm of the yolk sac, chorion, and body
stalk.
• A few days later vessels begin to form within the embryo
• Blood vessels and blood cells develop from hemangioblasts.
– Blood vessels develop from angioblasts which are
derived from the hemangioblasts
– Angioblasts aggregate to form blood islands
– Spaces appear and become the lumen of the vessel
– Blood cells develop from pluripotent stem cells which are
also derived from hemangioblasts.

Developmental Anatomy of Blood Vessels

• Begins at 15 days in yolk sac,
chorion & body stalk
• Masses of mesenchyme called
blood islands develop a “lumen”
• Mesenchymal cells give rise to
endothelial lining and muscle
• Growth & fusion form vascular
networks
• Plasma & cells develop from
endothelium


Aging and the Cardiovascular System

• General changes associated with aging
– decreased compliance of aorta
– reduction in cardiac muscle fiber size
– reduced cardiac output & maximum heart rate
– increase in systolic pressure
• Total cholesterol & LDL increases, HDL decreases
• Congestive heart failure, coronary artery disease and
atherosclerosis more likely


DISORDERS: HOMEOSTATIC IMBALANCES

• Hypertension, or persistently high blood pressure, is defined
as systolic blood pressure of 140 mm Hg or greater and
diastolic blood pressure of 90 mm Hg or greater.
• Primary hypertension (approximately 90-95% of all
hypertension cases) is a persistently elevated blood
pressure that cannot be attributed to any particular organic
cause.
• Secondary hypertension (the remaining 5-10% of cases)
has an identifiable underlying cause such as obstruction of
renal blood flow or disorders that damage renal tissue,
hypersecretion of aldosterone, or hypersecretion of
epinephrine and norepinephrine by pheochromocytoma, a
tumor of the adrenal gland.

DISORDERS: HOMEOSTATIC IMBALANCES

• High blood pressure can cause considerable damage to the
blood vessels, heart, brain, and kidneys before it causes
pain or other noticeable symptoms.
• Lifestyle changes that can reduce elevated blood pressure
include losing weight, limiting alcohol intake, exercising,
reducing sodium intake, maintaining recommended dietary
intake of potassium, calcium, and magnesium, not smoking,
and managing stress.
• Various drugs including diuretics, beta blockers,
vasodilators, and calcium channel blockers have been used
to successfully treat hypertension.


end


Ch21

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