The Circulatory System
Blood Vessels
Anatomy & Physiology II
Chapter 15
The Vascular System

Closed system

Blood vessels

Four heart chambers
Blood Vessels

Delivery system of dynamic structures
that begins and ends at the heart
◦ Arteries: carry blood away from the heart;
oxygenated except for pulmonary circulation
and umbilical vessels of a fetus
◦ Capillaries: contact tissue cells and directly
serve cellular needs
◦ Veins: carry blood toward the heart
Blood Vessels
Five types of blood vessels

Arteries

Arterioles

Capillaries

Venules

Veins
Blood Circuits
Two groups of blood vessels
 The pulmonary circuit
◦ Pulmonary artery and its branches
◦ Capillaries in lungs
◦ Pulmonary veins
 The systemic circuit
◦ Aorta
◦ Systemic capillaries
◦ Systemic veins
Blood flow in a closed system of vessels
Oxygen content changes
as blood flows through
the capillaries.
Zooming In •
Judging from color coding,
which vessels pick up oxygen?
Which vessels release oxygen?
Vessel Structure
Three tunics (coats) of arteries and veins

Inner (endothelium)

Middle (smooth [voluntary] muscle)
◦ Controlled by autonomic nervous system
◦ Thinner in veins

Outer (supporting connective tissue)
Sections of small blood vessels
Drawings show the
thick wall of an
artery, the thin wall
of a vein, and the
single-layered wall of
a capillary.
A venous valve also
is shown.The arrow
indicates the
direction of blood
flow.
Zooming In: Which
vessels have valves
that control blood
flow?
Systemic Arteries
The aorta

Largest artery

Receives blood from left ventricle

Branches to all organs
The Aorta and Its Parts

Ascending aorta

Aortic arch

Thoracic aorta

Abdominal aorta
The aorta and its branches
Zooming In:
How many
brachiocephalic
arteries are there?
Principal systemic arteries
Zooming In: How many brachiocephalic arteries are there?
Branches of the Ascending Aorta and
Aortic Arch

Ascending aorta
◦ Left and right coronary arteries

Aortic arch
◦ Brachiocephalic artery
 Right subclavian artery
 Right common carotid artery
◦ Left common carotid artery
◦ Left subclavian artery
Branches of the Thoracic Aorta
Branches to chest wall, esophagus, and
bronchi
 Intercostal arteries

Branches of the Abdominal Aorta

Celiac trunk
◦ Left gastric artery
◦ Splenic artery
◦ Hepatic artery
Superior mesenteric artery
 Inferior mesenteric artery
 Paired lateral branches

◦
◦
◦
◦
◦
Phrenic arteries
Suprarenal arteries
Renal arteries
Ovarian and testicular arteries
Lumbar arteries
The Iliac Arteries and Their
Subdivisions
Internal iliac arteries
 External iliac arteries

◦ Femoral artery
 Popliteal artery
 Tibial arteries
 Dorsalis pedis
Arteries That Branch to the Arm
and Head

External carotid artery

Internal carotid artery

Subclavian artery
◦ Vertebral artery
◦ Axillary artery
 Brachial artery
 Radial artery
 Ulnar artery
Anastomoses
Communication between two vessels

Circle of Willis

Superficial palmar arch

Mesenteric arches

Arterial arches
Arteries that supply the brain
The bracket at
right groups
the arteries
that make up
the circle of
Willis.
Arterioles
Smallest arteries
 Lead to capillary beds
 Control flow into capillary beds via
vasodilation and vasoconstriction

Systemic Veins

Superficial veins
◦ Cephalic, basilic, median cubital veins
◦ Saphenous veins

Deep veins
◦ Femoral and iliac vessels
◦ Brachial, axillary, subclavian vessels
◦ Jugular veins
◦ Brachiocephalic vein
The Venae Cavae and Their Tributaries

Superior vena cava
◦ Head, neck, upper extremities

Azygos vein
◦ Chest wall

Inferior vena cava
◦ Right, left veins from paired parts, organs
◦ Unpaired veins from spleen, digestive tract
Principal systemic veins
Zooming In: How many brachiocephalic veins are there?
Venous Sinuses

Coronary sinus

Cranial venous sinuses
◦ Cavernous sinuses
 Petrosal sinuses
◦ Superior sagittal sinus
 Confluence of sinuses
◦ Transverse sinuses (lateral sinuses)
Cranial venous sinuses
The inset shows
the paired
transverse
sinuses, which
carry blood from
the brain to the
jugular veins.
The Hepatic Portal System
Carries blood from abdominal organs to
liver

Superior mesenteric vein

Splenic vein

Gastric, pancreatic, inferior mesenteric
veins

Sinusoids
Hepatic portal system
Veins from the
abdominal organs
carry blood to the
hepatic portal vein
leading to the liver.
Arrows show the
direction of blood
flow.
Zooming In: What
vessel do the hepatic
veins drain into?
Circulation Physiology

Blood exchanges oxygen, carbon dioxide,
other substances generated by cells

Tissue fluid (interstitial fluid) is exchange
medium
Connection between small blood
vessels through capillaries
The blood delivers
oxygen (O2) to the
tissues and picks up
carbon dioxide
(CO2) for transport
to the lungs.
Note the lymphatic
capillaries, which aid
in tissue drainage.
Capillaries

Microscopic blood vessels

Walls of thin tunica intima, one cell thick

Pericytes help stabilize their walls and
control permeability

Size allows only a single RBC to pass at a
time
Capillaries
In all tissues except for cartilage, epithelia,
cornea and lens of eye
 Functions: exchange of gases, nutrients,
wastes, hormones, etc.

Capillaries

Three structural types
1. Continuous capillaries
2. Fenestrated capillaries
3. Sinusoidal capillaries (sinusoids)
Continuous Capillaries

Abundant in the skin and muscles
◦ Tight junctions connect endothelial cells
◦ Intercellular clefts allow the passage of fluids
and small solutes

Continuous capillaries of the brain
◦ Tight junctions are complete, forming the
blood-brain barrier
Pericyte
Red blood
cell in lumen
Intercellular
cleft
Endothelial
cell
Basement
membrane
Tight junction
Endothelial
nucleus
Pinocytotic
vesicles
Continuous capillary:
Least permeable, and most common (e.g., skin, muscle).
Fenestrated Capillaries

Some endothelial cells contain pores
(fenestrations)

More permeable than continuous
capillaries

Function in absorption or filtrate
formation (small intestines, endocrine
glands, and kidneys)
Pinocytotic
vesicles
Red blood
cell in lumen
Fenestrations
(pores)
Endothelial
nucleus
Basement membrane
Tight junction
Intercellular
cleft
Endothelial
cell
Fenestrated capillary: Large fenestrations (pores) increase
permeability. Occurs in special locations (e.g., kidney, small intestine).
Sinusoidal Capillaries

Fewer tight junctions, larger intercellular
clefts, large lumens

Usually fenestrated

Allow large molecules and blood cells to
pass between the blood and surrounding
tissues

Found in the liver, bone marrow, spleen
Endothelial
cell
Red blood
cell in lumen
Large
intercellular
cleft
Tight junction
Incomplete
basement
membrane
Nucleus of
endothelial
cell
Sinusoidal capillary: Most permeable. Occurs in special
locations (e.g., liver, bone marrow, spleen).
Blood Flow Through Capillary Beds

Precapillary sphincters regulate blood
flow into true capillaries

Regulated by local chemical conditions
and vasomotor nerves
Vascular shunt
Precapillary
sphincters
Terminal arteriole
Metarteriole
Thoroughfare channel
True capillaries
Postcapillary venule
(a) Sphincters open—blood flows through true capillaries.
Terminal arteriole
Postcapillary venule
(b) Sphincters closed—blood flows through metarteriole
thoroughfare channel and bypasses true capillaries.
Capillary Exchange
How substances move between cells and
capillary blood
 Diffusion
◦ Main process
 Blood
pressure
◦ Moves material into tissue fluid
 Osmotic
pressure
◦ Moves material into capillaries
Factors Aiding Venous Return
1. Respiratory “pump”: pressure changes
created during breathing move blood
toward the heart by squeezing abdominal
veins as thoracic veins expand
2. Muscular “pump”: contraction of skeletal
muscles “milk” blood toward the heart and
valves prevent backflow
3. Vasoconstriction of veins under sympathetic
control
The Dynamics of Blood Flow
Vasomotor center in medulla regulates
vasomotor activities

Vasodilation

Vasoconstriction

Precapillary sphincter
Return of Blood to the Heart
Mechanisms that promote blood’s return
to heart
 Contraction of skeletal muscles
 Valves
 Breathing

Role of skeletal muscles and valves
in blood return.
Role of skeletal muscles and valves in blood return. (A) Contracting skeletal muscle
compresses the vein and drives blood forward, opening the proximal valve, while the distal
valve closes to prevent backflow of blood. (B) When the muscle relaxes again, the distal valve
opens, and the proximal valve closes until blood moving in the vein forces it open again.
The Pulse




Ventricular contraction
Wave of increased pressure
Begins at heart and travels to arteries
Influenced by various factors
◦
◦
◦
◦
◦
◦
◦
Body size
Gender
Age
Muscular activity
Emotion
Body temperature
Thyroid secretion
Blood Pressure

Force exerted by blood against vessel walls

Determined by heart’s output and
resistance to blood flow
Systemic Blood Pressure

The pumping action of the heart generates
blood flow

Pressure results when flow is opposed by
resistance

Systemic pressure
◦ Is highest in the aorta
◦ Declines throughout the pathway
◦ Is 0 mm Hg in the right atrium

The steepest drop occurs in arterioles
Arterial Blood Pressure

Systolic pressure: pressure exerted
during ventricular contraction

Diastolic pressure: lowest level of
arterial pressure

Pulse pressure = difference between
systolic and diastolic pressure
Systemic Blood Pressure
Systolic pressure
Mean pressure
Diastolic
pressure
Arterial Blood Pressure

Reflects two factors of the arteries close
to the heart
◦ Elasticity (compliance or distensibility)
◦ Volume of blood forced into them at any time

Blood pressure near the heart is pulsatile
Capillary Blood Pressure

Ranges from 15 to 35 mm Hg

Low capillary pressure is desirable
◦ High BP would rupture fragile, thin-walled
capillaries
◦ Most are very permeable, so low pressure
forces filtrate into interstitial spaces
Maintaining Blood Pressure
 Requires
◦ Cooperation of the heart, blood vessels,
and kidneys
◦ Supervision by the brain
Maintaining Blood Pressure
 The
main factors influencing blood
pressure:
◦ Cardiac output (CO)
◦ Peripheral resistance (PR)
◦ Blood volume
Maintaining Blood Pressure
F = P/PR and CO = P/PR
 Blood pressure = CO x PR (and CO
depends on blood volume)
 Blood pressure varies directly with CO,
PR, and blood volume
 Changes in one variable are quickly
compensated for by changes in the other
variables

Cardiac Output (CO)
Determined by venous return and neural
and hormonal controls
 Resting heart rate is maintained by the
cardioinhibitory center via the
parasympathetic vagus nerves
 Stroke volume is controlled by venous
return (EDV)

Cardiac Output (CO)

During stress, the cardioacceleratory
center increases heart rate and stroke
volume via sympathetic stimulation
◦ ESV decreases and MAP increases
Exercise
BP activates cardiac centers in medulla
Activity of respiratory pump
(ventral body cavity pressure)
Activity of muscular pump
(skeletal muscles)
Parasympathetic
activity
Sympathetic activity
Epinephrine in blood
Sympathetic venoconstriction
Venous return
Contractility of cardiac muscle
EDV
ESV
Stroke volume (SV)
Heart rate (HR)
Initial stimulus
Physiological response
Result
Cardiac output (CO = SV x HR
Figure 19.8
Control of Blood Pressure

Short-term neural and hormonal controls
◦ Counteract fluctuations in blood pressure by
altering peripheral resistance

Long-term renal regulation
◦ Counteracts fluctuations in blood pressure by
altering blood volume
Cardiac Output

Volume of blood pumped out of each
ventricle in

one minute

Heart rate
◦ Beats per minute

Stroke volume
◦ Controlled by force of contractions
Resistance to Blood Flow
Peripheral resistance is affected by

Vasomotor changes

Baroreceptors in large arteries

Elasticity of blood vessels

Viscosity

Total blood volume
Blood Pressure Measurement
Pressure is measured in the brachial arm
artery using a sphygmomanometer
Systolic
pressure
◦ Occurs during heart contraction
◦ Normal systolic: 120 mmHg
Diastolic
pressure
◦ Occurs during heart relaxation
◦ Normal diastolic: 80 mmHg
Abnormal Blood Pressure

Hypotension
◦ Lower than normal blood pressure

Hypertension
◦ High blood pressure

Essential hypertension
◦ No apparent medical cause
Treatment of Hypertension

Stage 1
◦ 140/90 mm Hg
◦ Diet, exercise, weight loss

Stage 2
◦ 160/100 mm Hg
◦ Drugs added to treatment
Arterial Degeneration and
Other Blood Vessel Disorders
Arteriosclerosis
◦ Atherosclerosis
 Clot formation
 Leg cramps, pain, lameness
 Cerebral artery sclerosis
 Hypertension
 Coronary artery arteriosclerosis
 Renal artery damage
 Ischemia, gangrene

Treatment for Arterial Degeneration

Balloon catheterization

Bypass grafts

Stents

Endarterectomy
Aneurysm

Bulging sac in blood vessel wall

Swelling deranges other structures

Can burst, causing death

Surgery can replace damaged segment
Hemorrhage

Profuse escape of blood from vessels

Internal or external

Can be life-threatening
◦ Apply pressure to wound
◦ Elevate extremity above heart
◦ Apply pressure to pressure point
Shock
Inadequate blood flow to tissues

Classified by type
◦ Cardiogenic
◦ Septic
◦ Hypovolemic
◦ Anaphylactic

Classified by severity (cause unknown)
◦ Mild
◦ Severe
Thrombosis
Formation of blood clot in a vessel

Deep venous thrombosis (DVT)

Embolus

Pulmonary embolism

Phlebitis

Thrombophlebitis
Varicose Veins
Superficial veins that are swollen, distorted,
and ineffective

Saphenous veins of lower extremities

Rectal veins (hemorrhoids)
End of Presentation