unit 5 blood pressure

8/10/2019 Unit 5 Blood Pressure

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Human Physiologyby Lauralee Sherwood 2007 Brooks/Cole-Thomson Learning

Unit 5

The Blood Vessels and Blood Pressure


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Chapter 10 The Blood Vessels and Blood PressureHuman Physiologyby Lauralee Sherwood 2007 Brooks/Cole-Thomson Learning

Blood Flow

Blood is constantly reconditioned so composition

remains relatively constant

Reconditioning organs receive more blood than

needed for metabolic needs

Digestive organs, kidneys, skin

Adjust extra blood to achieve homeostasis

Blood flow to other organs can be adjusted

according to metabolic needs

Brain can least tolerate disrupted supply


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Distribution of Cardiac

Output at Rest


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Blood Flow

Flow rate through a vessel

volume of blood passing through per unit of time to the pressure gradient and inversely

proportional to vascular resistance

F =P

R

F = flow rate of blood through a vessel

P = pressure gradientR = resistance of blood vessels

Blood viscosity, vessel length, vessel radium

Major determinant of resistance to flow is vessels radius


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Blood Flow

Pressure gradient is pressure difference between beginningand end of a vessel

Blood flows from area of higher pressure to area of lowerpressure

Resistance is measure of opposition of blood flow through avessel

Depends on three things Blood viscosity, vessel length, vessel radium

Major determinant of resistance to flow is vessels radius

Slight change in radius produces significant change inblood flow

R is proportional to 1

r4


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Relationship of

Resistance and Flow

to Vessel Radius


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Vascular Tree

Closed system of vessels

Consists of

Arteries Carry blood away from heart to tissues

Arterioles Smaller branches of arteries

Capillaries Smaller branches of arterioles

Smallest of vessels across which all exchanges are madewith surrounding cells

Venules Formed when capillaries rejoin

Return blood to heart Veins

Formed when venules merge

Return blood to heart


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Basic Organization of

the Cardiovascular

System


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Arteries

Specialized to

Serve as rapid-transit passageways for bloodfrom heart to organs

Due to large radius, arteries offer little resistance to

blood flow

Act as pressure reservoir to provide driving forcefor blood when heart is relaxing

Arterial connective tissue contains

Collagen fibers

Provide tensile strength Elastin fibers

Provide elasticity to arterial walls


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Arteries as a Pressure Reservoir


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Blood Pressure

Force exerted by blood against a vessel wall

Depends on Volume of blood contained within vessel

Compliance of vessel walls

Systolic pressure

Peak pressure exerted by ejected blood againstvessel walls during cardiac systole

Averages 120 mm Hg

Diastolic pressure

Minimum pressure in arteries when blood isdraining off into vessels downstream

Averages 80 mm Hg


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Blood Pressure

Can be measured indirectly using

sphygmomanometer Korotkoff sounds

Sounds heard when determining blood pressure

Sounds are distinct from heart sounds associated

with valve closure


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Blood

Pressure


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Pulse Pressure

Pressure difference between systolic and diastolic

pressure

Example

If blood pressure is 120/80, pulse pressure is 40

mm Hg (120mm Hg80mm Hg)

Pulse that can be felt in artery lying close to surface

of skin is due to pulse pressure


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Mean Arterial Pressure

Average pressure driving blood forward into tissues

throughout cardiac cycle Formula for approximating mean arterial pressure

Mean arterial pressure = diastolic pressure +

pulse pressure

At 120/80, mean arterial pressure = 80 mm Hg +

(40 mm Hg) = 93 mm Hg


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Arterioles

Major resistance vessels

Radius supplying individual organs can be adjusted

independently to

Distribute cardiac output among systemic organs,

depending on bodys momentary needs

Help regulate arterial blood pressure


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Arterioles

Mechanisms involved in adjusting arteriolar

resistance Vasoconstriction

Refers to narrowing of a vessel

Vasodilation

Refers to enlargement in circumference and radius of

vessel

Results from relaxation of smooth muscle layer

Leads to decreased resistance and increased flow

through that vessel

ONLY blood supply to the brain remains constant

Peripheral supply vary according to metabolic NEEDS


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Magnitude and Distribution

Of the Cardiac Output at Rest

and During Moderate Exercise

Arteriole Smooth muscles


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Arteriole Smooth muscles

Precapillary

sphincterMetarteriole

Capillary

VenuleFig. 10-19, p. 357

Ti t b li ti it


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Tissue metabolic activity

O2, CO2and other metabolites

Relaxation of

precapillary sphinctersArteriolar vasodilation

Number of opencapillaries

Capillary blood flow

Capillary surface area

available for exchange

Diffusion distance

from cell to open

capillary

Concentration gradient for

these materials between

blood and tissue cells

Exchange between blood and tissueto support increased metabolicactivity

Delivery of O2,more rapid removal ofCO2and othermetabolites

Fig. 10-20, p. 358


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Lymphatic System

Functions

Return of excess filtered fluid Defense against disease

Lymph nodes have phagocytes which destroy bacteria

filtered from interstitial fluid

Transport of absorbed fat

Return of filtered protein

In the case of protein deficiency Osmotic pressure is low causing fluid retention

EDEMA


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Lymphatic

System


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Edema

Swelling of tissues Occurs when too much interstitial fluid accumulates

Causes of edema

Reduced concentration of plasma proteins Increased permeability of capillary wall

Increased venous pressure

Blockage of lymph vessels


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Veins

Venous system transports blood back to heart

Capillaries drain into venules Venules converge to form small veins that exit

organs

Smaller veins merge to form larger vessels

Veins

Large radius offers little resistance to blood flow

Also serve as blood reservoir


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Veins

Factors which enhance venous return

Driving pressure from cardiac contraction Sympathetically induced venous vasoconstriction

Skeletal muscle activity

Effect of venous valves

Respiratory activity

Effect of cardiac suction


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Fig. 10-32b, p. 368


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Blood pressure that is monitored and regulated inthe body

Primary determinants

Cardiac output

Total peripheral resistance

Mean arterial pressure = cardiac output x total

peripheral resistance


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Chapter 10 The Blood Vessels and Blood Pressure


Determinants of Mean Arterial Pressure


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Constantly monitored by baroreceptors (pressure

sensors) within circulatory system

Short-term control adjustments

Occur within seconds

Adjustments made by alterations in cardiac output and

total peripheral resistance

Mediated by means of autonomic nervous system

influences on heart, veins, and arterioles

M A i l P


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Long-term control adjustments

Require minutes to days

Involve adjusting total blood volume by restoring

normal salt and water balance through mechanisms

that regulate urine output and thirst



Bl d P Ab liti


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Blood Pressure Abnormalities

Hypertension Blood pressure above 140/90 mm Hg

Two broad classes

Primary hypertension

Secondary hypertension

Hypotension

Blood pressure below 100/60 mm Hg

H t i


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Hypertension

Most common of blood pressure abnormalities

Primary hypertension

Affected by variety of unknown causes rather than by a

single disease entity

P t ti l


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Potential causes

Defects in salt management by the kidneys

Excessive salt intake

Diets low in K+and Ca2+

Plasma membrane abnormalities

such as defective Na+-K+ pumps

Variation in gene that encodes for angiotensinogen

Abnormalities in vasoactive chemicals

NO, endothelin, or other locally acting

Excess vasopressin

H t i


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Hypertension

Secondary hypertension

Accounts for about 10% of hypertension cases

Occurs secondary to another known primary

problem

Examples of secondary hypertension

Renal hypertension

Endocrine hypertension

Neurogenic hypertension

H t i


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Hypertension

Complication of hypertension

Congestive heart failure Stroke

Heart attack

Spontaneous hemorrhage

Renal failure

Retinal damage

H t i


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Hypotension

Low blood pressure

Occurs when There is too little blood to fill the vessels

Heart is too weak to drive the blood

Orthostatic (postural) hypotension

Transient hypotensive condition

resulting from insufficient compensatory responses to

gravitational shifts in blood when

person moves from horizontal to vertical position

H t i


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Hypotension

Circulatory shock

blood pressure falls so low that adequate bloodflow to the tissues can no longer be maintained

Four main types

Hypovolemic (low volume) shock

Cardiogenic (heart produced) shock

Vasogenic (vessel produced) shock

Neurogenic (nerve produced) shock

S t Sh k


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Symptoms Shock

Hypotension

Systolic pressure below 90mmHg Pale, cool & moist skin

Confusion, disorientation

Rise in heart rate, with peak pulse

Cessation of urination

Lack of blood flow to kidneys

Drop in blood pH

acidosis



Circulatory shock


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Circulatory shock

( mean arterial pressure)

Cardiac output Cardiac output Total peripheral resistance

Loss of blood volume Widespreadvasodilation

Loss of fluidsderived from

plasma

Vasodilator

substancesreleased from

bacteria

Histamine

releasedin severeallergicreaction

Loss ofvascular tone

Severe

hemorrhage

Excessivevomiting,diarrhea,urinary losses,

etc.

Weakened

heart

Septic

shockAnaphylactic

shock

Sympathetic

nerve activity

Hypovolemic

shock

Cardiogenic

shock

Cardiogenic

shock

Neurogenic

shock

unit 5 blood pressure

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