Chapter 21:Blood Vessels and

CirculationBiol141 A & P

R.L. Brashear-Kaulfers

5 Classes of Blood Vessels1. Arteries:

– carry blood away from heart

2. Arterioles:– Are smallest branches of arteries

3. Capillaries:– are smallest blood vessels– location of exchange between blood and

interstitial fluid

4. Venules:– collect blood from capillaries

5. Veins:– return blood to heart

The Largest Blood Vessels

• Attach to heart• Pulmonary trunk:

– carries blood from right ventricle– to pulmonary circulation

• Aorta:– carries blood from left ventricle– to systemic circulation

The Smallest Blood Vessels

• Capillaries• Have small diameter and thin walls • Chemicals and gases diffuse across

walls

Structure of Vessel Walls

Figure 21-1

Tunica ExternaIn arteries:

contain collagenelastic fibers

In veins:contain elastic fibers

smooth muscle

cells

Arteries vs. Veins• Arteries and veins run side-by-side• Arteries have thicker walls and higher

blood pressure• Collapsed artery has small, round lumen• Vein has a large, flat lumen• Vein lining contracts, artery lining does not• Artery lining folds • Arteries more elastic • Veins have valves

Arteries and Pressure

• Elasticity allows arteries to absorb pressure waves that come with each heartbeat

• Contractility -Arteries change diameter

• Controlled by sympathetic division of ANS

Vasoconstriction and Vasodilation

• Vasoconstriction -The contraction of arterial smooth muscle by the ANS

• Vasodilatation- The relaxation of arterial smooth muscle

Enlarging the lumen • Both Affect:

– afterload on heart– peripheral blood pressure– capillary blood flow

Structure of Blood Vessels

Figure 21-2

Artery CharacteristicsFrom heart to

capillaries, arteries change:

from elastic arteries to muscular arteries

to arterioles

Arterioles

• Are small• Have little or no tunica externa• Have thin or incomplete tunica

media

Artery Diameter

• Small muscular arteries and arterioles:– changes with sympathetic or

endocrine stimulation– constricted arteries oppose blood flow

• Resistance (R) -The force opposing blood flow

• Resistance vessels:– arterioles

Aneurysm

• A bulge in an arterial wall • Is caused by weak spot in elastic

fibers• Pressure may rupture vessel

Capillaries

• Are smallest vessels with thin walls• Microscopic capillary networks

permeate all active tissues Capillary Function• Location of all exchange functions of

cardiovascular system• Materials diffuse between blood and

interstitial fluid

Capillary Structure

Figure 21-4

2 Types of Capillaries1. Continuous capillaries-Have complete

endothelial lining Are found in all tissues except epithelia and

cartilage• Permit diffusion of:

– Water, small solutes, Lipid-soluble materials• Block:

– blood cells, plasma proteins• Are in CNS and thymus, Have very

restricted permeability e.g., the blood–brain barrier

2. Fenestrated capillaries-Have complete endothelial lining

Are found in all tissues except epithelia and cartilage, in choroid plexus, endocrine organs, kidneys,intestinal tract

Capillary Networks

Figure 21-5

Capillary bed or capillary

plexusConnect 1

arteriole and 1 venule

Capillary Sphincter

• Guards entrance to each capillary • Opens and closes, causing capillary

blood to flow in pulses• Vasomotion -Contraction and

relaxation cycle of capillary sphincters

• Causes blood flow in capillary beds to constantly change routes

Veins• Collect blood from capillaries in

tissues and organs• Return blood to heart Veins vs. Arteries• Are larger in diameter • Have thinner walls • Carry lower blood pressure

3 Vein Categories1. Venules:

– very small veins– collect blood from capillaries

2. Medium-sized veins:– thin tunica media and few smooth muscle

cells– tunica externa with longitudinal bundles of

elastic fibers

3. Large veins:– have all 3 tunica layers– thick tunica externa– thin tunica media

Valves in the Venous System

Figure 21-6

Vein ValvesFolds of tunica intima

Prevent blood from flowing backward

Compression pushes blood toward heart

Figure 21-7

Blood Distribution

Heart, arteries, and capillaries:

30–35% of blood volume

Venous system:60–65%

Venous Blood Distribution

• 1/3 of venous blood is in the large venous networks of the liver, bone marrow, and skin

Cardiovascular Physiology

Figure 21-8

Cardiovascular Regulation

• Maintains capillary blood flow in peripheral tissues and organs

Capillary Blood Flow

• Equals cardiac output• Is determined by:

– pressure and resistance in the cardiovascular system

InterActive Physiology: Cardiovascular System: Measuring Blood PressurePLAYPLAY

Measuring Pressure

• Blood pressure (BP):– arterial pressure (mm Hg)

• Capillary hydrostatic pressure (CHP):– pressure within the capillary beds

• Venous pressure:– pressure in the venous system

Viscosity

• R caused by molecules and suspended materials in a liquid

• Whole blood viscosity is about 4 times that of water

Turbulence

• Swirling action that disturbs smooth flow of liquid

• Occurs in heart chambers and great vessels

• Atherosclerotic plaques cause abnormal turbulence

Pressures in the Systemic Circuit

• Systolic pressure:– peak arterial pressure during ventricular

systole

• Diastolic pressure:– minimum arterial pressure during diastole

• Pulse pressure: – difference between systolic pressure and

diastolic pressure

• Mean arterial pressure (MAP):MAP = diastolic pressure + 1/3 pulse pressure

Abnormal Blood Pressure

• Hypertension:– abnormally high blood pressure:

• greater than 140/90

• Hypotension: – abnormally low blood pressure

Venous Return• Amount of blood arriving at right atrium

each minute• Determined by venous pressure • Low effective pressure in venous system• Low venous resistance Is assisted by:

– muscular compression of peripheral veins– the respiratory pump

• Compression of skeletal muscles:– pushes blood toward heart (one-way valves)

Capillary Exchange

• Vital to homeostasis• Moves materials across capillary

walls by:– diffusion, filtration, and reabsorption

5 Diffusion Routes1. Water, ions, and small molecules such as

glucose:– diffuse between adjacent endothelial cells– or through fenestrated capillaries

2. Some ions ( Na+, K+, Ca2+, Cl—):– diffuse through channels in cell membranes

3. Large, water-soluble compounds:– pass through fenestrated capillaries

4. Lipids and lipid-soluble materials such as O2 and CO2:

– diffuse through endothelial cell membranes5. Plasma proteins:

– cross endothelial lining in sinusoids

Figure 21-11

Capillary Filtration

Capillary Exchange

• At arterial end of capillary:– fluid moves out of capillary– into interstitial fluid

• At venous end of capillary:– fluid moves into capillary– out of interstitial fluid

The Transition Point

• Between filtration and reabsorption– is closer to venous end than arterial

end

• Capillaries filter more than reabsorb

• Excess fluid enters lymphatic vessels

4 Functions of Blood and Lymph Cycle

1. Ensures constant plasma and interstitial fluid communication

2. Accelerates distribution of nutrients, hormones, and dissolves gases through tissues

Transports insoluble lipids and tissue proteins that can’t cross capillary walls

4. Flushes bacterial toxins and chemicals to immune system tissues

Capillary Dynamics

• Hemorrhaging:– reduces CHP and NFP– increases reabsorption of interstitial fluid

(recall of fluids)

• Dehydration:– increases BCOP– accelerates reabsorption

• Increase in CHP or BCOP:– fluid moves out of blood– builds up in peripheral tissues (edema)

KEY CONCEPT• Blood flow is the goal• Total peripheral blood flow equals cardiac

output• Blood pressure overcomes friction and

elastic forces to sustain blood flow• If blood pressure is too low:

– vessels collapse, blood flow stops– tissues die

• If blood pressure is too high:– vessel walls stiffen, capillary beds may rupture

How do central and local control mechanisms interact to regulate blood

flow and pressure in tissues?

Tissue Perfusion

• Blood flow through the tissues• Carries O2 and nutrients to tissues

and organs• Carries CO2 and wastes away• Is affected by:

– cardiac output– peripheral resistance– blood pressure

3 Regulatory Mechanisms

• Control cardiac output and blood pressure:1. Autoregulation:

• causes immediate, localized homeostatic adjustments

Neural mechanisms:• respond quickly to changes at specific

sites

3. Endocrine mechanisms:• direct long-term changes

Vasodilators

• Dilate precapillary sphincters• Local vasodilators:

– accelerate blood flow at tissue level

1. Low O2 or high CO2 levels

2. Low pH (acids),Nitric oxide (NO)3. High K+ or H+ concentrations4. Chemicals released by inflammation

(histamine)5. Elevated local temperature

Patterns of Cardiovascular Response

• Blood, heart, and cardiovascular system:– work together as unit– respond to physical and physiological

changes (e.g., exercise, blood loss) – to maintain homeostasis

Table 21-2

Blood Distribution during Exercise

3 Effects of Light Exercise

1. Extensive vasodilation occurs:– increasing circulation

2. Venous return increases:– with muscle contractions

3. Cardiac output rises:– due to rise in venous return (Frank–

Starling principle) and atrial stretching

5 Effects of Heavy Exercise

1. Activates sympathetic nervous system 2. Cardiac output increases to maximum:

– about 4 times resting level

3. Restricts blood flow to “nonessential” organs (e.g., digestive system)

4. Redirects blood flow to skeletal muscles, lungs, and heart

5. Blood supply to brain is unaffected

Table 21-3

Training and Cardiovascular Performance

Effects of ExerciseRegular moderate exercise:

lowers total blood cholesterol levelsIntense exercise:

can cause severe physiological stress

Figure 21-17

Responses to Blood Loss

Responses to Severe Blood Loss

• Also called hemorrhaging• Entire cardiovascular system adjusts to:

– maintain blood pressure – restore blood volume

• To prevent drop in blood pressure:1. carotid and aortic reflexes:

• increase cardiac output (increasing heart rate)• cause peripheral vasoconstriction

Sympathetic nervous system:• triggers hypothalamus• further constricts arterioles• venoconstriction improves venous return

3 Short-Term Responses to Hemorrhage

• To prevent drop in blood pressure:1. carotid and aortic reflexes:

• increase cardiac output (increasing heart rate)• cause peripheral vasoconstriction

2. Sympathetic nervous system:• triggers hypothalamus• further constricts arterioles• venoconstriction improves venous return

3. Hormonal effects:• increase cardiac output• increase peripheral vasoconstriction (E, NE,

ADH, angiotensin II)

Shock

• Short-term responses compensate up to 20% loss of blood volume

• Failure to restore blood pressure results in shock

Circulatory ShockPLAYPLAY

4 Long-Term Responses to Hemorrhage

• Restoration of blood volume can take several days:

1. Recall of fluids from interstitial spaces

2. Aldosterone and ADH promote fluid retention and reabsorption

3. Thirst increases4. Erythropoietin stimulates red blood

cell production

What are the principle blood vessels and

functional characteristics of the

special circulation to the brain, heart, and lungs?

Blood Flow to the Brain

• Is top priority• Brain has high oxygen demand• When peripheral vessel constrict,

cerebral vessels dilate, normalizing blood flow

Stroke

• Also called cerebrovascular accident (CVA)

• Blockage or rupture in a cerebral artery

• Stops blood flow

Blood Flow to the Heart• Through coronary arteries • Oxygen demand increases with

activity• Lactic acid and low O2 levels:

– dilate coronary vessels– increase coronary blood flow

• Epinephrine:– dilates coronary vessels– increases heart rate– strengthens contractions

Heart Attack

• A blockage of coronary blood flow• Can cause:

– angina– tissue damage– heart failure– death

Blood Flow to the Lungs

• Regulated by O2 levels in alveoli• High O2 content:

– vessels dilate

• Low O2 content:– vessels constrict

Pulmonary Blood Pressure :• In pulmonary capillaries:

– is low to encourage reabsorption• If capillary pressure rises:

– pulmonary edema occurs

Figure 21-18

Circulation Patterns3 Distribution Patterns:

1. Peripheral artery and vein distribution:

is the same on right and left, except near the heart

2. The same vessel: may have different names in different

locations3. Tissues and organs usually have

multiple arteries and veins:vessels may be interconnected

by anastomoses

Figure 21-19

The Pulmonary Circuit

The Pulmonary Circuit1. Deoxygenated blood arrives at heart

from systemic circuit:– passes through right atrium and ventricle– enters pulmonary trunk

2. At the lungs:– CO2 is removed

– O2 is added

3. Oxygenated blood:– returns to the heart – is distributed to systemic circuit

Pulmonary Vessels

• Pulmonary arteries:– carry deoxygenated blood

• Pulmonary veins:– carry oxygenated blood

Pulmonary Arteries

• Pulmonary trunk:– branches to left and right pulmonary

arteries • Pulmonary arteries:

– branch into pulmonary arterioles• Pulmonary arterioles:

– branch into capillary networks that surround alveoli

Pulmonary Veins

• Capillary networks around alveoli:– join to form venules

• Venules:– join to form 4 pulmonary veins

• Pulmonary veins:– empty into left atrium

Figure 21-20

Major Systemic Arteries

The Systemic CircuitContains 84% of

blood volumeSupplies entire body:

except for pulmonary circuit

3D Peel-Away of Arteries of the Upper LimbsPLAYPLAY

Figure 21-21a, b

Arteries of the Chest and Upper Limbs

Systemic Arteries

• Blood moves from left ventricle:– into ascending aorta

• Coronary arteries:– branch from aortic sinus

The Aorta• The ascending aorta:

– rises from the left ventricle– curves to form aortic arch– turns downward to become descending aorta

• Branches of the Aortic Arch deliver blood to head and neck:– brachiocephalic trunk– left common carotid artery– left subclavian artery

• The Brachiocephalic Trunk Branches to form:– right subclavian artery – right common carotid artery

• The Subclavian Arteries Branches within thoracic cavity:– internal thoracic artery– vertebral artery– thyrocervical trunk

The Subclavian Arteries • The Subclavian Arteries Branches

within thoracic cavity:– internal thoracic artery– vertebral artery– thyrocervical trunk

• Leaving the thoracic cavity:– become axillary artery in arm– and brachial artery distally- Divides at

coronoid fossa of humerus:– into radial artery and ulnar artery

Arteries of the Neck and Head

3D Peel-Away of Arteries of the Head and NeckPLAYPLAY

Figure 21-22

The Common Carotid Arteries

• Carry blood to head and neck• Each common carotid divides into:

– external carotid artery-Supplies structures of: Neck, lower jaw, face

– internal carotid artery-Enters skull and divides into: opthalmic artery, anterior cerebral artery, middle cerebral artery

Figure 21-23

Arteries of the Brain

The Vertebral Arteries

• Also supply brain with blood supply• Left and right vertebral arteries:

– arise from subclavian arteries– enter cranium through foramen

magnum– fuse to form basilar artery

Figure 21-24a

Arteries of the Trunk

Descending Aorta - is divided by

diaphragm into:thoracic aorta

abdominal aorta

Figure 21-24b

Arteries of the Trunk

3D Peel-Away of Arteries of the TrunkPLAYPLAY

Thoracic Aorta branches are anatomically grouped into:

visceral parietal

4 Visceral Branches

• Supply organs of the chest:– bronchial arteries– pericardial arteries– esophogeal arteries– mediastinal arteries

The Abdominal Aorta

• Divides at terminal segment of the aorta into:– left common iliac artery– right common iliac artery

Branches of the Abdominal Aorta

• Unpaired branches:– major branches to visceral organs

• Paired branches:– to body wall– kidneys– urinary bladder– structures outside abdominopelvic

cavity

Figure 21-25

Arteries of the Abdominopelvic Organs

3 Unpaired Branches of the Abdominal Aorta

• Celiac trunk, divides into:– left gastric artery– splenic artery– common hepatic artery

• Superior mesenteric artery• Left mesenteric artery

5 Paired Branches of the Abdominal Aorta

1. Inferior phrenic arteries2. Suprarenal arteries3. Renal arteries4. Gonadal arteries5. Lumbar arteries

The Abdominal Aorta

• Divides to form:– right and left common iliac arteries –

Divide to form: internal iliac artery, external iliac artery

– middle sacral artery-

3D Peel-Away of Arteries of the Lower LimbsPLAYPLAY

Figure 21-26

Arteries of the Lower Limbs

Figure 21-27

Major Systemic Veins

All Systemic VeinsDrain into either:

superior vena cava (SVC)

or inferior vena cava (IVC)

Complementary Arteries and Veins

• Run side by side• Branching patterns of peripheral

veins are more variable

Differences in Artery and Vein Distribution

• In neck and limbs:– 1 set of arteries (deep)– 2 sets of veins (1 deep, 1 superficial)

• Venous system controls body temperature

Figure 21-28

Veins of the Head, Neck, and Brain

The Superior Vena Cava (SVC)

• Receives blood from:– head– neck– chest– shoulders– upper limbs

Veins of the Neck

• Temporal and maxillary veins:– drain to external jugular vein

• Facial vein:– drains to internal jugular vein

Figure 21-29

Veins of the Abdomen and Chest

Deep Veins of the Forearm

• Deep palmar veins drain into:– radial and ulnar veins– which fuse above elbow to form

brachial vein

• Veins of the Upper Arm Cephalic vein joins axillary vein:– to form subclavian vein

The Subclavian Vein

• Merges with external and internal jugular veins: – to form brachiocephalic vein– which enters thoracic cavity

Veins of the Thoracic Cavity

• Brachiocephalic vein receives blood from:

vertebral vein – internal thoracic vein

• Merge to form the superior vena cava (SVC)

Figure 21-30a

Tributaries of the Superior Vena Cava

Figure 21-30b

Tributaries of the Inferior Vena Cava

•Inferior Vena Cava collects blood from

organs inferior to the diaphragm

Figure 21-31

Veins of the Lower Limbs

The Femoral Vein • Before entering abdominal wall,

receives blood from:– great saphenous vein– deep femoral vein– femoral circumflex vein

• Inside the pelvic cavity:– becomes the external iliac vein

• The Right and Left Common Iliac Veins Merge to form the inferior vena cava

Figure 21-29

Veins of the Abdomen 6 Major Tributaries

of the Abdominal

Inferior Vena Cava:

Lumbar veinsGonadal veinsHepatic veinsRenal veins

Suprarenal veinsPhrenic veins

Figure 21-32

The Hepatic Portal System

The Hepatic Portal System

• Connects 2 capillary beds• Delivers nutrient-laden blood:

– from capillaries of digestive organs– to liver sinusoids for processing

5 Tributaries of the Hepatic Portal Vein

1. Inferior mesenteric vein:– drains part of large intestine

2. Splenic vein:– drains spleen, part of stomach, and

pancreas3. Superior mesenteric vein:

– drains part of stomach, small intestine, and part of large intestine

4. Left and right gastric veins:– drains part of stomach

5. Cystic vein:– drains gallbladder

Blood Processed in Liver

• After processing in liver sinusoids, blood collects in hepatic veins and empties into inferior vena cava

Fetal Circulation

• Embryonic lungs and digestive tract nonfunctional

• Respiratory functions and nutrition provided by placenta

Figure 21-33a

Placental Blood SupplyBlood flows to the placenta:

through a pair of umbilical arteries

which arise from internal iliac arteries

and enter umbilical cordBlood returns from placenta:

in a single umbilical veinwhich drains into ductus

venosusDuctus venosus:

empties into inferior vena cava

Figure 21-33b

The Neonatal Heart

Before Birth -Fetal lungs are collapsed

O2 provided by placental circulation

At Birth -Newborn breathes air

Lungs expandPulmonary circulation

provides O2

2 Fetal Pulmonary Circulation Bypasses

1. Foramen ovale: – interatrial opening – covered by valve-like flap– directs blood from right to left

atrium

2. Ductus arteriosus: – short vessel – connects pulmonary and aortic

trunks

Cardiovascular Changes at Birth

• Pulmonary vessels expand• Reduced resistance allows blood

flow

• Rising O2 causes ductus arteriosus constriction

• Rising left atrium pressure closes foramen ovale

Figure 21-34

Congenital Cardiovascular Problems

Develop if proper circulatory changes do not occur at birth

Aging and the Cardiovascular System

• Cardiovascular capabilities decline with age

• Age-related changes occur in:– blood– heart – blood vessels

3 Age-Related Changes in Blood

1. Decreased hematocrit2. Blood clots (thrombus)3. Blood-pooling in legs

– due to venous valve deterioration

5 Age-Related Changes in the Heart

1. Reduced maximum cardiac output2. Changes in nodal and conducting

cells3. Reduced elasticity of fibrous

skeleton4. Progressive atherosclerosis5. Replacement of damaged cardiac

muscle cells by scar tissue

3 Age-Related Changes in Blood Vessels

1. Arteries become less elastic:– pressure change can cause

aneurysm

2. Calcium deposits on vessel walls:– can cause stroke or infarction

3. Thrombi can form:– at atherosclerotic plaques

Figure 21-35

Integration with Other Systems

Clinical Patterns

• There are many categories of cardiovascular disorders

• Disorders may:– affect all cells and systems– be structural or functional– result from disease or trauma

SUMMARY (1)• 3 types of blood vessels:

– arteries– veins– Capillaries

• Structure of vessel walls• Differences between arteries and veins• Atherosclerosis, arteriosclerosis, and

plaques• Structures of:

– elastic arteries– muscular arteries– arterioles

SUMMARY (2)• Structures of capillary walls:

– continuous– Fenestrated

• Structures of capillary beds:– precapillary sphincters– vasomotion– arteriovenous anastomoses

• Functions of the venous system and valves

• Distribution of blood and venous reserves

SUMMARY (3)• Circulatory pressures:

– blood pressure– capillary hydrostatic pressure– venous pressure

• Resistance in blood vessels:– viscosity– turbulence– Vasoconstriction

• The respiratory pump • Capillary pressure and capillary exchange:

– osmotic pressure– net filtration pressure

SUMMARY (4)• Physiological controls of cardiovascular system:

– Autoregulation, neural controls– hormonal controls

• Cardiovascular responses to exercise and blood loss

• Special circulation to brain, heart, and lungs• Distribution of arteries in pulmonary and

systemic circuits• Distribution of veins in pulmonary and systemic

circuits• Fetal circulation and changes at birth• Effects of aging on the cardiovascular system