Blood Vessels Part 2 Slides by Barbara Heard and W. Rose. figures from Marieb & Hoehn 9 th eds....

Blood VesselsPart 2

Slides by Barbara Heard and W. Rose.

figures from Marieb & Hoehn 9th eds.

Portions copyright Pearson Education

© 2013 Pearson Education, Inc.

Monitoring Circulatory Efficiency

• Vital signs: pulse and blood pressure, along with respiratory rate and body temperature

• Pulse: pressure wave caused by expansion and recoil of arteries

• Radial pulse (taken at the wrist) routinely used

• Pressure points where arteries close to body surface– Can be compressed to stop blood flow


Figure 19.12 Body sites where the pulse is most easily palpated.

Superficial temporal artery

Facial artery

Common carotid artery

Brachial artery

Radial artery

Femoral artery

Popliteal artery

Posterior tibialartery

Dorsalis pedisartery


Measuring Blood Pressure

• Systemic arterial BP– Measured indirectly by auscultatory method

using a sphygmomanometer– Pressure increased in cuff until it exceeds

systolic pressure in brachial artery– Pressure released slowly and examiner

listens for sounds of Korotkoff with a stethoscope


Measuring Blood Pressure

• Systolic pressure, normally less than 120 mm Hg, is pressure when sounds first occur as blood starts to spurt through artery

• Diastolic pressure, normally less than 80 mm Hg, is pressure when sounds disappear because artery no longer constricted; blood flowing freely


Variations in Blood Pressure

• Transient elevations occur during changes in posture, physical exertion, emotional upset, fever.

• Age, sex, weight, race, mood, and posture may cause BP to vary


Alterations in Blood Pressure

• Hypertension: high blood pressure– Sustained elevated arterial pressure of 140/90

or higher– Prehypertension if values elevated but not

yet in hypertension range• May be transient adaptations during fever, physical

exertion, and emotional upset• Often persistent in obese people


Homeostatic Imbalance: Hypertension

• Prolonged hypertension major cause of heart failure, vascular disease, renal failure, and stroke– Heart must work harder myocardium

enlarges, weakens, becomes flabby– Also accelerates atherosclerosis


Primary or Essential Hypertension

• 90% of hypertensive conditions

• No underlying cause identified– Risk factors include heredity, diet, obesity,

age, diabetes mellitus, stress, and smoking

• No cure but can be controlled– Restrict salt, fat, cholesterol intake– Increase exercise, lose weight, stop smoking– Antihypertensive drugs


Homeostatic Imbalance: Hypertension

• Secondary hypertension less common– Due to identifiable disorders including

obstructed renal arteries, kidney disease, and endocrine disorders such as hyperthyroidism and Cushing's syndrome

– Treatment focuses on correcting underlying cause


Alterations in Blood Pressure

• Hypotension: low blood pressure– Blood pressure below 90/60 mm Hg– Usually not a concern

• Only if leads to inadequate blood flow to tissues

– Often associated with long life and lack of cardiovascular illness


Homeostatic Imbalance: Hypotension

• Orthostatic hypotension: temporary low BP and dizziness when suddenly rising from sitting or reclining position

• Chronic hypotension: hint of poor nutrition and warning sign for Addison's disease or hypothyroidism

• Acute hypotension: important sign of circulatory shock; threat for surgical patients and those in ICU


Blood Flow Through Body Tissues

• Tissue perfusion involved in– Delivery of O2 and nutrients to, and removal of

wastes from, tissue cells – Gas exchange (lungs)– Absorption of nutrients (digestive tract)– Urine formation (kidneys)

• Rate of flow is precisely right amount to provide proper function


Figure 19.13 Distribution of blood flow at rest and during strenuous exercise.

Brain

Heart

Skeletalmuscles

Skin

Kidneys

Abdomen

Other

750

250

1200

500

1100

1400

600

750

750

12,500

1900

600

600

400

Total bloodflow at rest5800 ml/min

Total blood flow duringstrenuous exercise17,500 ml/min


Velocity of Blood Flow

• Changes as travels through systemic circulation

• Inversely related to total cross-sectional area

• Fastest in aorta; slowest in capillaries; increases in veins

• Slow capillary flow allows adequate time for exchange between blood and tissues


Relative cross-sectional area ofdifferent vesselsof the vascular bed

Total area(cm2) of thevascularbed

Velocity ofblood flow(cm/s)

50

Art

erio

les

40

30

20

0

10

5000

4000

3000

2000

0

1000A

orta

Art

erie

s

Vei

ns

Cap

illar

ies

Ven

ules

Ven

ae c

avae

Figure 19.14 Blood flow velocity and total cross-sectional area of vessels.

AutoregulationAutomatic adjustment of blood flow to tissues to

meet metabolic requirementsControlled intrinsically (i.e. locally) by modifying

arteriolar diameter - does not require autonomic nervous system activity

Organs regulate their own blood flows by varying resistance of their own arterioles

AutoregulationTwo types of autoregulation

• Metabolic control• Myogenic control

Combination of both determines overall response

AutoregulationKeeping flow constant when pressure gradient changes.

In a rigid pipe:Resistance (R) does not change. The equation Flow = ΔP / Rpredicts that when pressure changes, flow will change by the same percent as pressure.

In an elastic tube:A pressure change causes a diameter change, and hence a resistance change: pressure ↑ diameter ⇒ ↑ resistance⇒ ↓As a result, a pressure change will cause a larger flow change than what you’d get in a rigid pipe.

In a vascular bed with autoregulation:Flow changes little when the pressure gradient changes.Percent change in flow is smaller than percent change in pressure.

Graph shows pressure-flow relation (vertical axis=change in flow, horiz. axis=change in pressure) for rigid pipes (), elastic tubes (), “perfect” autoregulation (), and actual measurements in dogs whose neural reflexes are temporarily blocked (). We expect “passive “ blood vessels to look like . The fact that they look like shows they are not passive – they autoregulate.

Coleman, Granger, Guyton 1971

Measurements in animals with neural reflexes blocked

AutoregulationKeeping flow constant when pressure gradient changes.


Metabolic Autoregulation

Vasodilation of arterioles and relaxation of precapillary sphincters occurs in response to

– Declining tissue O2

– Substances from metabolically active tissues (H+, K+, adenosine, and prostaglandins) and inflammatory chemicals


Metabolic AutoregulationEffects

– Relaxation of vascular smooth muscle if flow is insufficient for demand

– Release of NO (powerful vasodilator) by endothelial cells

Endothelins released from endothelium are potent vasoconstrictors

NO and endothelins balanced unless blood flow inadequate, then NO wins

Inflammatory chemicals also cause vasodilation

Myogenic AutoregulationHow it seems to work:Pressure ↑ tension in vessel wall ⇒ ↑

⇒ vascular smooth muscle constricts ⇒ diameter ↓ resistance ⇒ ↑

Therefore, a pressure change causes a resistance change that prevents flow from changing as much as it would have, if resistance had just stayed the same (or worse, if resistance had changed in the way you’d expect for an elastic tube)

P.C. Johnson, Circ Res. 1986.


Figure 19.15 Intrinsic and extrinsic control of arteriolar smooth muscle in the systemic circulation.

Vasodilators

Metabolic Neuronal

Intrinsic mechanisms(autoregulation) Vasoconstrictors

Extrinsic mechanisms

Myogenic

Metabolic

Neuronal

Hormonal

Sympathetic tone

• Neuronal or hormonal controls• Maintain mean arterial pressure (MAP)• Redistribute blood during exercise and thermoregulation

• Metabolic or myogenic controls• Distribute blood flow to individual organs and tissues as needed

• Stretch

• Angiotensin II• Antidiuretic hormone• Epinephrine• Norepinephrine

• Endothelins

Hormonal

Sympathetic tone

• Atrial natriuretic peptide

O2

CO2

H+

K+

• Prostaglandins• Adenosine • Nitric oxide


Long-term Autoregulation

• Occurs when short-term autoregulation cannot meet tissue nutrient requirements

• Angiogenesis– Number of vessels to region increases and

existing vessels enlarge – Common in heart when coronary vessel

occluded, or throughout body in people in high-altitude areas


Blood Flow: Skeletal Muscles

• Varies with fiber type and activity– At rest, myogenic and general neural

mechanisms predominate - maintain ~ 1L /minute

– During muscle activity• Active or exercise hyperemia - blood flow

increases in direct proportion to metabolic activity• Local controls override sympathetic

vasoconstriction • Muscle blood flow can increase 10


Blood Flow: Brain

• Blood flow to brain constant as neurons intolerant of ischemia; averages 750 ml/min

• Metabolic controls– Decreased pH of increased carbon dioxide

cause marked vasodilation

• Myogenic controls– Decreased MAP causes cerebral vessels to

dilate – Increased MAP causes cerebral vessels to

constrict


Blood Flow: Brain

• Brain vulnerable under extreme systemic pressure changes – MAP below 60 mm Hg can cause syncope

(fainting)– MAP above 160 can result in cerebral edema


Blood Flow: Skin

• Blood flow through skin– Supplies nutrients to cells (autoregulation in

response to O2 need)

– Helps regulate body temperature (neurally controlled) – primary function

– Provides a blood reservoir (neurally controlled)


Blood Flow: Skin

• Blood flow to venous plexuses below skin surface regulates body temperature– Varies from 50 ml/min to 2500 ml/min,

depending on body temperature– Controlled by sympathetic nervous system

reflexes initiated by temperature receptors and central nervous system


Temperature Regulation

• As temperature rises (e.g., heat exposure, fever, vigorous exercise)– Hypothalamic signals reduce vasomotor

stimulation of skin vessels – Warm blood flushes into capillary beds – Heat radiates from skin


Temperature Regulation

• Sweat also causes vasodilation via bradykinin in perspiration– Bradykinin stimulates NO release

• As temperature decreases, blood is shunted to deeper, more vital organs


Blood Flow: Lungs

• Pulmonary circuit unusual– Pathway short– Arteries/arterioles more like veins/venules

(thin walled, with large lumens)– Arterial resistance and pressure are low

(24/10 mm Hg)


Blood Flow: Lungs

• Autoregulatory mechanism opposite that in most tissues– Low O2 levels cause vasoconstriction; high

levels promote vasodilation• Allows blood flow to O2-rich areas of lung


Blood Flow: Heart

• During ventricular systole– Coronary vessels are compressed

• Myocardial blood flow ceases• Stored myoglobin supplies sufficient oxygen

• During diastole high aortic pressure forces blood through coronary circulation

• At rest ~ 250 ml/min; control probably myogenic


Blood Flow: Heart

• During strenuous exercise– Coronary vessels dilate in response to local

accumulation of vasodilators– Blood flow may increase three to four times

• Important–cardiac cells use 65% of O2 delivered so increased blood flow provides more O2


Blood Flow Through Capillaries

• Vasomotion– Slow, intermittent flow– Reflects on/off opening and closing of

precapillary sphincters


Capillary Exchange of Respiratory Gases and Nutrients

• Diffusion down concentration gradients– O2 and nutrients from blood to tissues

– CO2 and metabolic wastes from tissues to blood

• Lipid-soluble molecules diffuse directly through endothelial membranes

• Water-soluble solutes pass through clefts and fenestrations

• Larger molecules, such as proteins, are actively transported in pinocytotic vesicles or caveolae


Figure 19.16 Capillary transport mechanisms. (1 of 2)

Red bloodcell in lumen

Endothelialcell

Fenestration(pore)

Intercellularcleft

Tightjunction

Endothelialcell nucleus

Pinocytoticvesicles

Basementmembrane


Figure 19.16 Capillary transport mechanisms. (2 of 2)

Pinocytoticvesicles

Caveolae

Intercellularcleft

Transportvia vesiclesor caveolae(largesubstances)

Movementthroughfenestrations (water-solublesubstances)

Basementmembrane

Movementthroughintercellularclefts (water-solublesubstances)

Diffusionthroughmembrane(lipid-solublesubstances)

Endothelialfenestration(pore)

Lumen

12

3

4


Fluid Movements: Bulk Flow

• Fluid leaves capillaries at arterial end; most returns to blood at venous end– Extremely important in determining relative

fluid volumes in blood and interstitial space

• Direction and amount of fluid flow depend on two opposing forces: hydrostatic and colloid osmotic pressures


Hydrostatic Pressures

• Capillary hydrostatic pressure (HPc) (capillary blood pressure)– Tends to force fluids through capillary walls – Greater at arterial end (35 mm Hg) of bed

than at venule end (17 mm Hg)

• Interstitial fluid hydrostatic pressure (HPif)

– Pressure that would push fluid into vessel– Usually assumed to be zero because of

lymphatic vessels


Colloid Osmotic Pressures

• Capillary colloid osmotic pressure (oncotic pressure) (OPc)

– Created by nondiffusible plasma proteins, which draw water toward themselves

– ~26 mm Hg

• Interstitial fluid osmotic pressure (OPif)

– Low (~1 mm Hg) due to low protein content


Hydrostatic-osmotic Pressure Interactions: Net Filtration Pressure (NFP)

• NFP—comprises all forces acting on capillary bed– NFP = (HPc + OPif) – (HPif + OPc)

• Net fluid flow out at arterial end

• Net fluid flow in at venous end

• More leaves than is returned– Excess fluid returned to blood via lymphatic

system


The big pictureFluid filters from capillaries at their arteriolar end and flows through the interstitial space. Most is reabsorbed at the venous end.

For all capillary beds, 20 L of fluid is filteredout per day—almost 7times the total plasmavolume!

• Due to fluid pressing against a boundary• HP “pushes” fluid across the boundary

• In blood vessels, is due to blood pressure

• Due to nondiffusible solutes that cannot cross the boundary• OP “pulls” fluid across the boundary

• In blood vessels, is due to plasma proteins

Piston

Boundary

Solutemolecules(proteins)

Boundary

“Pushes” “Pulls”

Hydrostatic pressure (HP) Osmotic pressure (OP)

17 L of fluid per day is reabsorbedinto the capillariesat the venous end.

LymphaticcapillaryVenule

About 3 L per day of fluid (and anyleaked proteins) areremoved by thelymphatic system(see Chapter 20).

Arteriole

Fluid moves through the interstitial space.

Net filtration pressure (NFP) determines thedirection of fluid movement. Two kinds of pressure drive fluid flow:

Figure 19.17 Bulk fluid flow across capillary walls causes continuous mixing of fluid between the plasma and the interstitial fluid compartments, and maintains the interstitial environment. (1 of 5)



Net filtration pressure (NFP) determines thedirection of fluid movement. Two kinds ofpressure drive fluid flow:

• Due to fluid pressing against a boundary• HP “pushes” fluid across the boundary• In blood vessels, is due to blood pressure

• Due to nondiffusible solutes that cannot cross the boundary• OP “pulls” fluid across the boundary• In blood vessels, is due to plasma proteins

Piston

Boundary

Solutemolecules(proteins)

Boundary

“Pushes” “Pulls”

Hydrostatic pressure (HP) Osmotic pressure (OP)



How do the pressures drive fluid flow across a capillary?

Net filtration occurs at the arteriolar end of a capillary.

Capillary Boundary(capillary wall)

Hydrostatic pressure in capillary “pushes” fluid out of capillary.

Osmotic pressure in capillary “pulls” fluidinto capillary.

HPc = 35 mm Hg

OPc = 26 mm Hg

OPif = 1 mm Hg

HPif = 0 mm Hg

NFP = 10 mm Hg

Interstitial fluid

Hydrostatic pressure ininterstitial fluid “pushes” fluid into capillary.

Osmotic pressure in interstitial fluid “pulls” fluid outof capillary.

To determine the pressure driving the fluid out of the capillary at any given point, we calculate the net filtration pressure (NFP)––the outward pressures (HPc and OPif) minus the inward pressures(HPif and OPc). So,

NFP

As a result, fluid moves from the capillary into the interstitial space.

= (HPc + OPif) – (HPif + OPc) = (35 + 1) – (0 + 26)= 10 mm Hg (net outward pressure)



Hydrostatic pressure in capillary“pushes” fluid out of capillary.The pressure has droppedbecause of resistance encounteredalong the capillaries.

Osmotic pressure in capillary “pulls” fluid into capillary.

HPc = 17 mm Hg

OPc = 26 mm Hg

Hydrostatic pressure in interstitial fluid “pushes” fluid into capillary.

Osmotic pressure in interstitial fluid “pulls” fluid out of capillary.

HPif = 0 mm Hg

OPif = 1 mm Hg

NFP= –8 mm Hg

Capillary Boundary(capillary wall)

Interstitial fluid

Again, we calculate the NFP:

Notice that the NFP at the venous end is a negative number. This means that reabsorption, not filtration, is occurring and so fluid moves from the interstitial space into the capillary.

= (HPc + OPif) – (HPif + OPc)

= (17 + 1) – (0 + 26)

= –8 mm Hg (net inward pressure)

NFP

Net reabsorption occurs at the venous end of a capillary.


Circulatory Shock

• Any condition in which– Blood vessels inadequately filled– Blood cannot circulate normally

• Results in inadequate blood flow to meet tissue needs


Circulatory Shock

• Hypovolemic shock: results from large-scale blood loss

• Vascular shock: results from extreme vasodilation and decreased peripheral resistance

• Cardiogenic shock results when an inefficient heart cannot sustain adequate circulation


Figure 19.18 Events and signs of hypovolemic shock.

Acute bleeding (or other events that reduceblood volume) leads to:

1. Inadequate tissue perfusion resulting in O2 and nutrients to cells

2. Anaerobic metabolism by cells, so lactic acid accumulates

3. Movement of interstitial fluid into blood, so tissues dehydrate

Initial stimulus

Physiological response

Signs and symptoms

Result

Chemoreceptors activated(by in blood pH)

Baroreceptor firing reduced(by blood volume and pressure)

Hypothalamus activated(by blood pressure)

Respiratory centersactivated

Cardioacceleratory and vasomotor centers activated

Sympathetic nervoussystem activated

ADHreleased

Neuronsdepressed

by pH

Centralnervous system

depressed

Heart rateIntense vasoconstriction

(only heart and brain spared)

Renal blood flow

Renin released

Angiotensin IIproduced in blood

Aldosteronereleased

Kidneys retainsalt and water

Waterretention

Rate anddepth of

breathing

Tachycardia;weak, thready

pulse

Skin becomescold, clammy,and cyanotic

Urine output Thirst Restlessness(early sign)

Coma(late sign)

CO2 blownoff; bloodpH rises

Blood pressure maintained;if fluid volume continues to

decrease, BP ultimatelydrops. BP is a late sign.

Major effect Minor effect

Adrenalcortex

Kidneys

Brain


Circulatory Pathways: Blood Vessels of the Body

• Two main circulations– Pulmonary circulation: short loop that runs

from heart to lungs and back to heart– Systemic circulation: long loop to all parts of

body and back to heart


Figure 19.19a Pulmonary circulation.

Pulmonarycapillariesof theR. lung

R. pulmonaryartery

L. pulmonaryartery

Pulmonarycapillariesof theL. lung

Fromsystemic circulation

R. pulmonary veins

Pulmonarytrunk

L. pulmonaryveins

RA

RV LV

LA

Schematic flowchart.

Tosystemiccirculation


Figure 19.19 Pulmonary circulation. Pulmonarycapillariesof theR. lung

R. pulmonaryartery

L. pulmonaryartery

Pulmonarycapillariesof theL. lung

Fromsystemic circulation

R. pulmonary veins

Pulmonarytrunk

L. pulmonaryveins

RA

RV LV

LA

Left pulmonaryartery

Aortic arch

Pulmonary trunk

Right pulmonaryartery

Three lobar arteriesto right lung

Rightatrium

Pulmonaryveins

Rightventricle

Leftventricle

Two lobar arteriesto left lung

Pulmonaryveins

Left atrium

Pulmonarycapillary

Air-filledalveolusof lung

Schematic flowchart.

Illustration. The pulmonary arterial system is shown in blue to indicate that the blood it carries is oxygen-poor. The pulmonary venous drainage is shown in red to indicate that the blood it transports is oxygen-rich.

Gas exchange

Tosystemiccirculation


Commoncarotid arteriesto head andsubclavianarteries toupper limbs

Capillary beds ofhead and upper limbs

Aorta

Superiorvena cava Aortic

arch

RA LA

RV LV

Azygossystem

Thoracicaorta

Venousdrainage

Arterialblood

Capillary beds ofmediastinal structuresand thorax walls

Inferiorvenacava

Diaphragm

Abdominalaorta

Capillary beds ofdigestive viscera,spleen, pancreas,kidneys

Inferiorvenacava

Capillary beds ofgonads, pelvis, andlower limbs

Figure 19.20 Schematic flowchart showing an overview of the systemic circulation.


Arteries Veins

Delivery Blood pumped into single systemic artery—the aorta

Blood returns via superior and interior venae cavae and the coronary sinus

Location Deep, and protected by tissues Both deep and superficial

Pathways Fairly distinct Numerous interconnections

Supply/drainage Predictable supply Usually similar to arteries, except dural sinuses and hepatic portal circulation

Differences Between Arteries and Veins

Greg Johnson

change "interior venae" to "inferior venae"


Developmental Aspects

• Endothelial lining arises from mesodermal cells in blood islands

• Blood islands form rudimentary vascular tubes, guided by cues

• Vascular endothelial growth factor determines whether vessel becomes artery or vein

• The heart pumps blood by the 4th week of development



• Fetal shunts (foramen ovale and ductus arteriosus) bypass nonfunctional lungs

• Ductus venosus bypasses liver

• Umbilical vein and arteries circulate blood to and from placenta

• Congenital vascular problems rare



• Vessel formation occurs– To support body growth– For wound healing– To rebuild vessels lost during menstrual

cycles

• With aging, varicose veins, atherosclerosis, and increased blood pressure may arise

Blood Vessels Part 2 Slides by Barbara Heard and W. Rose. figures from Marieb & Hoehn 9 th eds....

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Transcript of Blood Vessels Part 2 Slides by Barbara Heard and W. Rose. figures from Marieb & Hoehn 9 th eds....