Ch 20 The Cardiovascular System: Blood Vessels and Circulation

Ch 20

The Cardiovascular System:

Blood Vessels and Circulation

20-1 Structure and Function of Blood

VesselsThe 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

Vena Cava

Carries systemic blood to right atrium.

The Smallest Blood Vessels

Capillaries - small diameter and thin walls – fluids, chemicals

and gases move across walls

Types of Blood Vessels

Arteries -Carry blood away from heart Collaterals -Multiple arteries

that contribute to one capillary bed (Allow circulation if one artery is

blocked)

Arterioles - smallest branches of arteries

- most numerous

- exert most influence on BP

Capillaries

Are smallest blood vessels

Location of exchange between blood and interstitial fluid

Venules

Collect blood from capillaries

Veins

Return blood to heart

Structure of Blood Vessels

Walls (except capillaries) have three layers call tunics:

Tunica intima – innermost layer- endothelium (epithelial layer –

simple squamous)

Tunica media – middle layer- smooth muscle

Tunica externa – outside layer- connective tissue

Blood Vessels

Tunica Intima -innermost layer

The endothelial lining- simple squamous

Internal elastic membrane:

– in arteries-layer of elastic fibers in outer margin of tunica intima

Tunica Media -middle layer

Contains concentric sheets of smooth muscle in loose

connective tissue

–

Blood Vessels

Tunica Externa -outer layer

Contains connective tissue sheath

Anchors vessel to adjacent tissues in arteries Contain collagen

Elastic fibers

In veins Contains elastic fibers

Smooth muscle cells

Vasa vasorum (“vessels of vessels”) =Small arteries and veins

In walls of large arteries and veins

Supply cells of tunica media and tunica externa

Blood Vessels

Comparisons of a Typical Artery and a Typical Vein.

Differences Between Arteries and Veins

Arteries and veins run side by side

Arteries have thicker walls and higher blood pressure

Collapsed artery has small, round lumen (internal

space)

Vein has a large, flat lumen

Vein lining contracts, artery lining does not

Artery lining folds

Arteries more elastic

Veins have valves

Structure and Function of Arteries

Arteries and Pressure

Elasticity allows arteries to absorb pressure waves

that come with each heartbeat - Compliance

Contractility –smooth muscles

Arteries change diameter

Controlled by sympathetic division of ANS

Vasoconstriction:

– the contraction of arterial smooth muscle by the ANS

Vasodilatation:

– the relaxation of arterial smooth muscle

– enlarging the lumen


Vasoconstriction and Vasodilation

Affects: Afterload on heart, Peripheral blood pressure

Capillary blood flow

Arteries -From heart to capillaries, arteries change

From elastic arteries

To muscular arteries

To arterioles


Elastic Arteries -Also called conducting arteries

Large vessels (e.g., pulmonary trunk and aorta)

Tunica media has many elastic fibers and few muscle

cells

Elasticity evens out pulse force

Muscular Arteries - Also called distribution arteries

Are medium sized (most arteries- femoral, radial, etc)

Tunica media has many muscle cells


Arterioles

Are small

Have little or no tunica externa

Have thin or incomplete tunica media

Small muscular arteries and arterioles

Change with sympathetic or endocrine stimulation

Constricted arteries oppose blood flow (Resistance

= R)

– resistance (R):

» resistance vessels: arterioles

Histological Structure of Blood Vessels

Disorders in Arteries

Aneurysm -A bulge in an arterial wall

Is caused by weak spot in elastic fibers

Pressure may rupture vessel

Atherosclerosis

Plaque within an Artery

• Disease affecting vessel wall.

• It leads to the narrowing of arteries

or complete blockage.

• Lipid deposition and inflammation

in tunic intima. (Plaque)

Structure and Function of Capillaries

Capillaries - are smallest vessels with thin walls

Function

Location of all exchange functions of cardiovascular system

Materials diffuse between blood and interstitial fluid

Structure

Endothelial tube, inside thin

basal lamina/basement membrane

No tunica media No tunica externa

Diameter is similar to red blood cell

Continuous Capillaries

Types of Capillaries

Three Types

1. Continuous Capillaries -Have complete endothelial lining -

found in all tissues except epithelia and cartilage

Functions of continuous capillaries

Permit diffusion of water, small solutes, and lipid-soluble

materials

Blood cells and plasma proteins cannot leave capillaries

Specialized Continuous Capillaries - are in CNS and thymus

Have very restricted permeability

Ex, the blood–brain barrier


2. Fenestrated Capillaries

Have incomplete endothelial lining with pores.

Permit rapid exchange of water and larger solutes

between plasma and interstitial fluid

Are found in

Choroid plexus

Endocrine organs

Kidneys

Intestinal tract


3. Sinusoids (sinusoidal capillaries) Have gaps between adjacent endothelial cells

Liver

Spleen

Bone marrow

Endocrine organs

Permit free exchange

Of water and large plasma proteins

Between blood and interstitial fluid

Phagocytic cells monitor blood at sinusoids

Capillary Beds (capillary plexus)

Connect one arteriole and one venule

Thoroughfare channels

Direct capillary connections between arterioles and venules

Controlled by smooth muscle segments (metarterioles) and

sphincters

Contraction and relaxation cycle of capillary

sphincters -Causes blood flow in capillary

beds to constantly change routes

Capillary Beds

Pre-Capillary Sphincters

Guards entrance to each capillary

Opens and closes, causing capillary blood to flow in

pulses

Vasomotion

Structure and Function of Veins

Veins- act as capitance vessels

Collect blood from capillaries in tissues and organs and returns blood

to heartarger in diameter than arteries

Have thinner walls than arteries that can expand/distend (capitance)

Have lower blood pressure

Compression by skeletal muscle pushes blood toward heart

=Skeletal Muscle Pump

Respiratory Pump – Breathing acts like a straw to draw blood to

heart.

Venous Valves - folds of tunica intima

Prevent blood from flowing backward

Function of Vein Valves

Structure and Function of Veins

Vein Categories

Venules

Very small veins

Collect blood from capillaries

Medium-sized veins

Thin tunica media and few smooth muscle cells

Tunica externa with longitudinal bundles of elastic fibers

Large veins

Have all three tunica layers

Thick tunica externa

Thin tunica media

Distribution of Blood

Heart, arteries, and capillaries

30–35% of blood volume

Venous system

60–65%:

– 1/3 of venous blood is in

large venous networks of

liver, bone marrow, and skin

= Venous Reserve

20-2 Blood Flow, Pressure, and

Resistance

Characteristic of a Blood Vessel

The ability to stretch- compliance

Relationship between blood volume and blood pressure

Veins stretch more than arteries

Venous Response to Blood Loss

Vasomotor centers stimulate sympathetic nerves

Systemic veins constrict (venoconstriction)

Veins in liver, skin, and lungs redistribute venous reserve

Blood Pressure

Systolic pressure

Peak arterial pressure during ventricular contraction =

systole (120 mm Hg)

Diastolic pressure

Minimum arterial pressure during ventricular relaxation =

diastole (80 mm Hg)

Pulse pressure

Difference between systolic pressure and diastolic pressure- at

least 25% of systolic pressure

Mean arterial pressure (MAP)

MAP = diastolic pressure + 1/3 pulse pressure

Blood Pressure

Pressures within the Systemic Circuit

Pressure and Resistance

Force (F) = hydrostatic pressure

- Is proportional to the pressure difference (P)

divided by Resistance (R)

F= P/R

Resistance = characteristic that slows the flow of

blood – examples = viscosity of blood, turbulent

flow, vessel diameter

Resistance

Viscosity

R caused by molecules and suspended materials in a

liquid

Whole blood viscosity is about four 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

Resistance (R) =Vascular R

Depends on vessel length and vessel diameter:- as

vessel length lengthens- R increases

– adult vessel length is constant

– vessel diameter varies by vasodilation and

vasoconstriction:

» R increases exponentially with

vasoconstriction; R= 1/r4

» so- if vessel reduces diameter by ½; R

increases 16x

» Vessel dilates to 2x diameter- blood flow

increases 16x

Circulatory Pressure

Pressure (P)

The heart generates P to overcome resistance (R)

Absolute pressure is less important than pressure

gradient

The Pressure Gradient (P) = Circulatory pressure =

pressure gradient

-The difference between

Pressure at the heart

And pressure at peripheral capillary beds

Circulatory Pressure and Resistance


∆P across the systemic circuit (about 100 mm

Hg)

Circulatory pressure must overcome total

peripheral resistance

R of entire cardiovascular system


Overview of Cardiovascular Physiology

Measuring Pressure

Blood pressure (BP) –measured with sphygmomanometer

Arterial pressure (mm Hg) -Measured as systole/ diastole

Force exerted by blood in a vessel against air in ca closed

cuff

Normal = 120/80

Hypertension -Abnormally high blood pressure:

– greater than 140/90

Hypotension -Abnormally low blood pressure

Pulse Rate

Heart rate (HR) = heart beats/ min

Pulse rate = HR

because the increases in

blood pressure in the arteries that

lead to a noticeable pulse.

Taking the pulse is, therefore, a direct

measure of heart rate.

Pressure in Small Arteries and

ArteriolesElastic Rebound

Arterial walls -Stretch during systole

Rebound (recoil to original shape) during diastole

Keep blood moving during diastole

Pressure and distance

MAP and pulse pressure decrease with distance

from heart

Blood pressure decreases with friction

Pulse pressure decreases due to elastic rebound

Venous Pressure and Return

Determines the amount of blood arriving at right atrium each minute

Low effective pressure in venous system

Low venous resistance is assisted by Muscular compression of peripheral veins:

– compression of skeletal muscles pushes blood toward heart (one-way valves)

The respiratory pump:– thoracic cavity action

– inhaling decreases thoracic pressure

– exhaling raises thoracic pressure

20-3 Capillary Pressures and Exchange

Bulk flow- mass movement of liquids (with solutes) in

and out of capillaries by pressure.

Filtration- movement out

Reabsorption – movement in

Moves materials across capillary walls by

Diffusion- Movement of ions or molecules from high

concentration to lower concentration along the

concentration gradient

Capillary Exchange

Filtration - Driven by Capillary Hydrostatic

Pressure (CHP)

Water and small solutes

forced out through capillary

wall

Leaves larger solutes

(proteins) in bloodstream

IFHP rises only slightly-

Some fluid moves in lymph vessels

Net Hydrostatic Pressure (NHP)

The difference between Net

Hydrostatic Pressure

and Net Colloidal Osmotic Pressure

NFP = NHP – NCOP

Difference between Capillary Hydrostatic

Pressure (CHP) and Interstitial Fluid

Hydrostatic Pressure (IFHP) -

Pushes water and solutes -out of

Capillary Reabsorption

Reabsorption - result of osmotic pressure

differences (less water in capillaries now)

Blood colloid osmotic pressure (BCOP)

High Pressure caused by suspended blood

proteins (colloids) too large to cross capillary

walls (more concentrated with solutes)

Interstitial colloid osmotic pressure (IFCOP)

Low Pressure because fluid low in proteins

Net Colloid Osmotic Pressure (NCOP)

The difference between

Blood Colloid Osmotic Pressure

(BCOP) and Interstitial Fluid Colloid

Osmotic Pressure (IFCOP)

NCOP = BCOP-IFCOP

*Pulls water and solutes out of IF and

into a capillary (Osmosis here!)

Capillary Diffusion

Water, ions, and small molecules such as glucose

Diffuse between adjacent endothelial cells

Some ions (Na+, K+, Ca2+, Cl-)

Diffuse through channels in plasma membranes

Lipids and lipid-soluble materials such as O2 and CO2

Diffuse through endothelial plasma membranes

Other more porous capillaries-

Large, water-soluble compounds

Pass through fenestrated capillaries and sinusoids

Plasma proteins – large

Cross endothelial lining in sinusoids

Net Filtration Pressure (NFP)

The difference between Net Hydrostatic Pressure

and Net Colloidal Osmotic Pressure

NFP = NHP – NCOP

Results:

Filtration = 24L/day

Reabsorption= 20.4L/day

Lymph – picks up excess

IF and returns to blood

after filtering

Lymphatic Vessels and Capillary Beds

Lymph Vessels and Fluid Recycling

Excess IF (from filtration) returns back into

bloodstream via the lymphoid system

Lymphatic system:

Ensure constant plasma and interstitial fluid

levels

Moves bacterial toxins and chemicals to

immune system tissues

20-4 Homeostatic Regulation

Cardiovascular regulation changes blood

flow to a specific area

At an appropriate time- in the right area

Without changing blood pressure and blood

flow to vital organs

Tissue Perfusion

-Blood flow through the tissues

Carries O2 and nutrients to tissues and organs

Carries CO2 and wastes away

Affected by: Blood Pressure

Blood pressure = CO x R

CO=cardiac output

R= peripheral resistance

Regulation

Autoregulation

Causes immediate, localized homeostatic

adjustments by changes in blood flow

Neural mechanisms

Respond quickly to changes at specific sites

And

Endocrine mechanisms

Direct long-term changes

Autoregulation of Perfusion

Adjusted by peripheral resistance while CO stays the same.

Local vasodilators:– accelerate blood flow at tissue level

» low O2 or high CO2 levels, pH (acids)

» nitric oxide (NO), high K+ or H+ concentrations

» chemicals released by inflammation (histamine)

» elevated local temperature

Local vasoconstrictors: released by damaged tissues

– examples include prostaglandins and thromboxanes

– constrict precapillary sphincters -affect a single capillary bed

Myogenic Responses: stretching of smooth muscles in

response to blood pressure

Autoregulation

1. Neural Mechanisms -Medulla Oblongata

Cardiovascular (CV) centers

Blood Pressure Changes

– cardioacceleratory center: increases CO, blood flow

– cardioinhibitory center: reduces CO, blood flow

2. Reflex Control of Cardiovascular Function

Baroreceptor reflexes: aortic & carotid sinuses

– Stretch when blood pressure high- signals medulla oblongata

cardioinhibitory center- parasympathetic stimulation

Chemoreceptor reflexes: (located near baroreceptors)

– respond to changes in pH and dissolved gases

Baroreceptor Reflexes

Stretch receptors in walls of

Carotid sinuses: maintain blood flow to brain

Aortic sinuses: monitor start of systemic circuit

Right atrium: monitors end of systemic circuit

-When blood pressure rises, CV centers trigger

parasympathetic stimulation at SA node

Decrease CO

Cause peripheral vasodilation

-When blood pressure falls, CV centers sympathetic

stimulation at SA node

Increase CO

Cause peripheral vasoconstriction

Cardiovascular Regulation

Baroreceptor Reflexes of the Carotid and Aortic Sinuses

Chemoreceptor Reflexes

Peripheral chemoreceptors in carotid bodies and

aortic bodies monitor blood for changes in:

pH, O2, and CO2 concentrations

Produced by coordinating cardiovascular and

respiratory activities

Central chemoreceptors below medulla oblongata

Monitor cerebrospinal fluid

Control respiratory function

Control blood flow to brain

Cardiovascular Regulation

The Chemoreceptor Reflexes

Endocrine Regulation

3. Endocrine Regulation

Hormones

Hormones have short-term and long-term

effects on cardiovascular regulation

E and NE:

from adrenal medulla stimulate CO and

peripheral vasoconstriction

Hormones – kidney functions

Antidiuretic Hormone (ADH) ( affects kidneys)

Released by neurohypophysis (posterior lobe of

pituitary)

Elevates blood pressure

Reduces water loss at kidneys

ADH responds to

Low blood volume

High plasma osmotic concentration

Circulating angiotensin II

Hormones

Renin-Angiotensin-Aldosterone

-cells in kidney respond to fall in renal blood pressure and

release renin (protein) into blood.

Renin-converts angiotensinogen (liver) to angiotensin I -

Angiotensin II (lungs)

Stimulates

ADH (pituitary) release, Aldosterone (adrenal cortex)

Thirst, increase Cardiac Output (CO)

Peripheral vasoconstriction

Hormones

Erythropoietin (EPO)

Released at kidneys

Responds to low blood pressure, low O2

content in blood

Stimulates red blood cell production in red

bone marrow

Hormones

Natriuretic Peptides-responds to high BP

Atrial natriuretic (ANP) factor (peptide)

Produced by cells in right atrium and similar peptide

(B-type) in ventricles

Respond to excessive diastolic stretching

Lowers blood volume and blood pressure

Reduces stress on heart

Cardiovascular Adaptation to ExerciseLight exercise -Extensive vasodilation occurs:

– increasing circulation

Venous return increases -with muscle contractions

Cardiac output rises-

rise in venous return and atrial stretching

Heavy exercise - Activates sympathetic nervous system

Cardiac output increases to maximum:

– about four times resting level

Restricts blood flow to “nonessential” organs

(e.g., digestive system)

Redirects blood flow to skeletal muscles,

lungs, and heart

Cardiovascular Adaptation to

Hemorrhaging

Entire cardiovascular system adjusts to

Maintain blood pressure

Restore blood volume

Shock

Short-term responses compensate after blood losses

of up to 20% of total blood volume

Failure to restore blood pressure results in shock

Long-Term Restoration of Blood

Volume

Recall of fluids from interstitial spaces

Aldosterone and ADH at kidneys promote fluid

retention and reabsorption

Thirst increases

Erythropoietin stimulates red blood cell

production

Cardiovascular Responses to

Hemorrhaging and Blood Loss

20-5 Circulatory Pathways

Vascular Supply to Special Regions

Through organs with separate mechanisms to

control blood flow

Brain

Heart

Lungs

Circulatory Pathways

Blood Flow to the Brain

Is top priority

Brain has high oxygen demand

When peripheral vessels constrict, cerebral vessels

dilate, normalizing blood flow

Stroke -Also called cerebrovascular accident (CVA)

Blockage (arteriosclerosis) or rupture in a cerebral

artery

Stops blood flow

The Systemic Circuit

Circulatory Pathways

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 (myocardial infaction)- A blockage of

coronary blood flow

Pulmonary and Systemic Patterns

Three General Functional Patterns

Peripheral artery and vein distribution is the same on

right and left, except near the heart

The same vessel may have different names in

different locations

Tissues and organs usually have multiple arteries and

veins

Vessels may be interconnected with anastomoses

The Pulmonary Circuit

1. Deoxygenated blood arrives at heart from

systemic circuit:

Passes through right atrium and right 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 trunk:

– branches to left and right pulmonary arteries

Pulmonary arteries:

– branch into pulmonary arterioles

Pulmonary arterioles:

– branch into capillary networks that surround alveoli


Pulmonary Vessels

Pulmonary veins

Carry oxygenated blood

Capillary networks around alveoli:

– join to form venules

Venules:

– join to form four pulmonary veins

Pulmonary veins:

– empty into left atrium


Contains 84% of blood volume

Supplies entire body

Except for pulmonary circuit

Systemic Arteries

Blood moves from left ventricle

Into ascending aorta

Coronary arteries

Branch from aortic sinus

The Systemic Veins

Complementary Arteries and Veins

Run side by side

Branching patterns of peripheral veins are more variable

In neck and limbs

One set of arteries (deep)

Two sets of veins (one deep, one superficial)

Venous system controls body temperature

The Systemic Veins

Cerebral Veins – most veins go deep into cerebral

sinuses- ultimately through jugular foramen to

internal jugular vein (parallel to carotid)

internal jugular -Empties into brachiocephalic veins

of chest

brachiocephalic to superior vena cava


.

Blood Processed in Liver

After processing in liver sinusoids (exchange

vessels), blood collects in hepatic veins and

empties into inferior vena cava

20-6 Development and Fetal/ Maternal

Circulation Embryonic lungs and digestive tract nonfunctional

Respiratory functions and nutrition provided by placenta

Placental Blood Supply

Blood flows to the placenta

Through a pair of umbilical arteries

Which arise from internal iliac arteries

And enter umbilical cord

Blood returns from placenta

In a single umbilical vein

Fetal and Maternal Circulation

Aging and the Cardiovascular System

Cardiovascular capabilities decline with age

Age-related changes occur in

Blood

Heart

Blood vessels

Three Age-Related Changes in Blood

Decreased hematocrit

Peripheral blockage by blood clot (thrombus)

Pooling of blood in legs - due to venous valve deterioration

Aging and the Cardiovascular System

Three Age-Related Changes in Blood Vessels

Arteries become less elastic

Pressure change can cause aneurysm

Calcium deposits on vessel walls

Can cause stroke or infarction

Thrombi can form

As atherosclerotic plaques

Ch 20 The Cardiovascular System: Blood Vessels and Circulation

Documents

Transcript of Ch 20 The Cardiovascular System: Blood Vessels and Circulation