BLOOD VESSELS
HONORS ANATOMY & PHYSIOLOGY
CHAPTER 19
BLOOD VESSELS
 form a closed delivery system that begins & ends at
the heart
 3 types:
1. Arteries
2. Capillaries
3. Veins
Blood Vessel Walls
 arteries & veins have 3 distinct layers = tunics
 surround a central blood-containing space = lumen
 3 tunics:
tunica intima
2. tunica media
3. tunica externa
1.
Walls of Arteries & Veins
tunica intima
1.


innermost layer = endothelium
simple squamous epithelium: continuous with endocardium
2. tunica media

middle layer : circular smooth muscle with elastin
3. tunica externa

aka tunica adventitia

infiltrated with nervefibers, elastic fibers,

larger arteries & veins have their own smaller blood vessels
= vasa vasorum (vessels of the vessels)
Circulation of Blood
 left side heart  aorta  branches of aorta
(arteries)  arterioles  capillaries  venules 
veins  vena cava  right side of heart 
pulmonary circulation  left side of heart
Arterial System
 Artery: blood vessel with blood flow AWAY from
heart
 3 types:
Elastic Arteries
2. Muscular Arteries
3. Arterioles
1.
Elastic Arteries
 thick-walled arteries near the heart
 include aorta & its major branches
 largest of all arteries
 aka conducting arteries
 “pressure reservoirs” expand & recoil as heart
ejects blood  allows blood to flow continuously
instead of flow & ebb
Muscular Arteries
 distal to elastic arteries
 deliver blood to specific organs
 aka distributing arteries
 thickest tunica media: more smooth muscle & less
elastic tissue as elastic arteries
 more active in vasoconstriction than other types
Arterioles
 smallest of artery types
 lead to capillary beds
 small arteries (arterioles)have muscles that
control their diameters (precapillary sphincters):
used to control blood flow thru an organ
Capillaries
 where materials delivered to/from cells  blood
 walls 1 squamous cell thick: so diffusion very fast
 not elastic
Pericytes
 smooth muscle-like cells surround capillaries
stabilize capillaries
 help control capillary permeability

3 Types of Capillaries
Continuous (muscle, skin)
1.


most common
endothelial cells joined by tight jcts  fluids & small
solutes can cross, except in brain nothing crosses
(BBB)
Fenestrated (small intestine, endocrine organs, kidney)
2.


endothelial cells riddled with holes covered by thin
membrane of basal lamina material
more permeable to fluids
Sinusoid (liver, spleen, bone marrow, adrenal medulla)
3.


very leaky
allow large molecules & blood cells to pass
Types of Capillaries
Microcirculation
 capillaries don’t function solo
 form “beds”
 arteriole flow  thru capillary bed  venule =
microcirculation
Veins
 any blood vessel with blood flowing toward the heart
 low pressure vessels
 can expand to accommodate differing volumes of
blood flow
 contain valves to stop backflow of blood
Venules
 capillaries unite to form venules
 Postcapillary Venules: not much larger than
capillary and almost as porous
 larger venules have thin layer of smooth muscle
Veins
 venules join to form veins
 3 distinct tunics
larger lumens than corresponding arteries
 little smooth muscle or elastin in tunica media
 tunica externa thickest layer

 Veins called blood reservoirs because they can hold
up to 65% of blood supply
Venous Valves
 formed from folds of tunica intima
 most abundant in veins of limbs where gravity
opposes flow of blood
 Varicose Veins: tortuous, dilated veins due to
incompetent valves

superficial veins more susceptible because of
little support , deeper veins have support from
surrounding muscle
cross-section of vein with valve
Comparing Arteries & Veins
Venous Sinuses
 example:
coronary sinus in heart
 dural venous sinuses of brain (CSF drains into)

 highly specialized, flat, veins with very thin walls
only endothelial cells
Vascular Anastomoses
 special interconnections between blood vessels
 arteries supplying same territory often merge =
anastomosis
 provide alternate pathways = collateral channels for
blood to reach a given organ or region of body
 common in:
joints
 abdominal organs
 heart
 brain

Blood Flow
 volume of blood flowing through a vessel or organ, or
entire circulation in a given time (mL/min)
 blood flow = CO at rest if considering entire vascular
system

is relatively constant
 @ any given moment blood flow through individual
organs may vary widely
 directly proportional to BP & inversely proportional
to resistance
Blood Pressure (BP)
 force per unit area exerted on a vessel wall by the
blood within it
 expressed in mm Hg
 BP means systemic arterial blood pressure in largest
vessels
 *difference in BP w/in vascular system provides
driving force that keeps blood flowing

high  low pressure
Resistance
 opposition to flow
 *major determinant: small-diameter arterioles
 a measure of the amount of friction blood encounters
flowing through vessels
 blood viscosity: related to thickness or stickiness of
the blood
fairly constant
 *longer the vessel the greater the resistance
 blood vessel diameter changes

Systemic BP
 highest in aorta/ lowest in venae cavae
 steepest drop in BP occurs in arterioles (resistance is






the greatest)
Systole: peak of BP
Diasole: lowest pressure
Pulse Pressure: difference between systole & diastole
normal BP in adult: 120/80 mm Hg
Hypotension: < 90/60 (rarely a problem)
chronic HTN: 140/90 or higher

indicates increased peripheral resistance
HTN Risk Factors
1.
2.
3.
4.
5.
6.
7.
8.
high-fat, high-salt diet
obesity
Diabetes mellitus
advanced age
smoking
stress
Black race > than others
family hx of HTN
HTN
 can lead to:
1.
2.
3.
MI
CVA
Renal disease
Pulmonary Circulation
 transports O2-low, CO2-laden blood from right
ventricle  lungs  releases CO2 & fills with O2 
left atrium
Systemic Circulation
 transports O2-rich blood from left ventricle  all
body tissues
Blood Flow Through Organs
 regulated by nerves & chemical agents
 both cardiac output & blood vessel diameter controlled by
hormones & nerves
 controlled by ANS
 increasing blood pressure can increase blood flow
increasing blood
pressure  increases
cardiac output 
constricts many
arterioles  more blood
volume to other
organs
Arteries & Veins
 all arteries deep
 veins: both deep & superficial
superficial veins tend to have many
interconnections
 Hepatic Portal Circulation: unique venous
drainage of liver

Aorta
Ascending Aorta
 begins @ aortic semilunar valve
 rt & lt coronary arteries
 supply rt & lt sides of heart
 Aortic Arch
 3 important branches: brachiocephalic trunk, lt
common carotid, lt subclavian
 Descending Aorta
 travels posterior to heart
 portion in thorax called thoracic aorta
 portion in abdominal cavity called abdominal
aorta

Common Carotids
 branch into:
 External Carotid arteries
 supply blood to neck, esophagus, pharynx, larynx, lower
jaw, face
 Internal Carotid arteries
 supply blood to the brain (with the rt & lt vertebral
arteries: branches of subclavian arteries)
Arteries of Upper Extremities
 Axillary artery:
branch of subclavian
artery
 becomes Brachial artery
in the arm
 branches into Radial
(pulse)& Ulnar
arteries in lower arm

Branches of the Abdominal Aorta
 descends slightly to the left of the vertebral
column
 retroperitoneal
 Branches:
1. Celiac Trunk (3 branches)



Lt gastric artery: stomach
Splenic artery: spleen: stomach, & pancreas
Common Hepatic Artery: liver, stomach, gallbladder, &
duodenum
Branches of the Abdominal Aorta
2. Superior Mesenteric Artery:

pancreas, duodenum, small intestines, most
of large intestines
3. Inferior mesenteric Artery:

terminal portion of the colon, sigmoid
& rectum
colon,
Branches of the Abdominal Aorta
5 Paired Arteries from Abdominal Aorta
1. Inferior phrenic arteries

inferior surface of diaphragm
2. Suprarenal arteries

Adrenal glands
3. Renal arteries

kidneys
4. Gonadal arteries

Testicular or Ovarian
5. Lumbar arteries

vertebrae, spinal cord, abdominal wall
Iliac Arteries
 Abdominal Aorta branches into rt & lt Common
Iliac Arteries @ L4 level
 each branches  internal & external iliac arteries
@ level of lumbosacral joint
 Internal Iliac Arteries:

bladder, external genitalia, uterus, vagina
 External Iliac Arteries:
 blood to lower extremities
External Iliac Arteries
 when cross over to medial surface of thigh become
Femoral Arteries

branches to deep femoral & superficial femoral
 when reaches knee becomes Popliteal Artery
 where it branches  posterior & anterior Tibial
arteries
 Posterior Tibial Artery divides  Medial &
Plantar Arteries
Arteries of the Lower Extremities
Systemic Veins
 most veins run parallel to arteries of same name
Superior & Inferior Vena Cava
 SVC: large vein that receives blood from upper
body (head, neck, upper limbs)
 IVC: large vein that receives blood from the lower
body (lower limbs, pelvis, abdomen)
 both return blood to right atrium
Systemic Veins
 Internal Jugular descends parallel to common
carotid arteries  brachiocephalic veins(just as
they merge with the subclavian veins)
Veins of the Upper Extremity
 Radial & Ulnar veins
parallel arteries of
same name then
merge to become
Brachial vein 
axillary vein 
subclavian vein
 Vein draw blood
from: median cubital
Veins of the Abdomen & Pelvis
 External Iliac veins
receive blood from
the lower extremities
--> join with Internal
Iliac veins to form
the rt & lt Common
Iliac Veins  fuses
with the IVC
Veins of Abdomen & Pelvis
Hepatic Portal System
 Blood leaving the digestive organs by veins is
rich in nutrients….instead of returning directly
to IVC  heart this blood is shunted to liver
first
 This way liver can store, convert, detoxify, or
excrete materials as necessary
 Hepatic Portal vein enters liver with nutrient
rich blood