CV 3 Flashcards by sophie rosen

At each level, arteries have (compared to veins): (3)

thicker walls
more elastic tissue
more smooth muscle

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Vascular Tone

= Level of

Vascular Smooth Muscle Contraction

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Vascular Tone (4)

 Determines radius of vessel lumen
 increase Tone increase vasoconstriction and decrease lumen diameter
 decrease Tone increase vasodilation and increase lumen diameter
Δ vascular tone > ΔR > Δ Blood Flow through vessel

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ΔP/R

8Ln/Πr^4

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Vascular Tone is Modified by: (2)

Paracrines from Endothelial Cells

2. Autonomic NS

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Paracrines from Endothelial Cells (2)

NO and Prostacyclin (decreases tone; relaxes smooth
muscle)
Enothelin-1 (increases tone; contracts smooth muscle)

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Autonomic NS (2)

Sympathetic NS (influence depends on NT rec., typically increase)
*Parasympathetic NS (Decreases tone)

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Arteries/Arterioles (2)

 Basal Tone

 Vasodilate or Vasoconstrict from rest

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Veins/Venules (2)

 No Basal Tone

 Only vasoconstrict from rest

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Artery Basal Tone

 Mediated by: (2)

 Paracrines secreted by endothelial cells

 Tonic activity of sympathetic motor neurons

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Abnormal Arterial Tone =

hypertension

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Compliance =

how easily a structure stretches

= ΔVolume/ΔPressure

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High compliance vessels can have large changes in volume with little
change in pressure; —

Veins

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Low compliance vessels will have large changes in pressure with
small changes in volume; —

Arteries

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The pressure gradient throughout the circulatory system is the
driving force for

blood flow

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Pressure in the arterial vessels is —, producing (2)

pulsatile

systolic and diastolic pressures.

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Damping α (R)(Compliance)

Pulsation disappears by the capillaries smoothing out due to
decreasing elastic/collagen tissue and increasing R as you move through arteries to capillaries

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Mean Arterial Pressure (MAP)

Average driving pressure in systemic arteries
= Diastolic P + 1/3(Systolic P – Diastolic P)
= 80 + 1/3(120-80) = 93 mmHg

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Elastic recoil prevents

arteriole diastolic pressure from dropping to ventricular diastole pressure

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Elastic recoil is essential to maintain

driving pressure in systemic circulation

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Pulse Pressure (PP)
Felt as a

pulsation or throb in the arteries of the wrist or neck with
each heartbeat.

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PP =

(SP – DP) : (120 – 80 = 40 mmHg in the example)

The most important factors determining the magnitude of the

pulse pressure are: (2)

(1) Stroke volume

(2) Arterial compliance

PP α

SV/C

MAP

 Average driving pressure in systemic circulation to move blood through the blood vessels = Diastolic P + 1/3 (Systolic P – Diastolic P) = 80 + 1/3 (120 – 80)

Hypertension Increased --- Caused by (2) Affects ≈

MAP increased Systolic and/or Diastolic Pressure 70 million Americans (1 in 3)

Factors Influencing MAP | 1. Flow In and Out of Systemic Arteries (5)

 Flow In = CO (HR x SV)  Flow Out = Total Peripheral Resistance (TPR)  TPR = ΣRArterioles (vasoconstriction of arterioles)  If: Flow in > Flow out (due to increase CO or increase TPR) > increase MAP  If: Flow in < Flow out (due to decrease CO or decrease TPR) > decrease MAP

MAP =

CO x TPR

F =

ΔP/R

CO =

MAP/TPR

Factors Influencing MAP | 2. Total Blood Volume (2)

 Total Blood Volume increase > increase MAP (ex. Increased NaCl intake)  Total Blood Volume decrease > decrease MAP (ex. Hemorrhage)

Factors Influencing MAP | 3. Distribution of Blood in Circulatory System (2)

 Normally 11% of blood volume in arteries and 60% in veins  Blood can be shifted from veins to arteries to increase MAP

Regulation of TPR (2)

TPR α ΣRArterioles | Factors that change arteriolar diameter > RArterioles > ΔTPR

Arteriolar Diameter Regulation (3)

1. Autoregulation 2. Local Control 3. Reflex Control

1. Autoregulation (2)

 Function of blood vessel wall |  Assures blood flow to tissues matches tissue demands.

2. Local Control (3)

 Match tissue blood flow to metabolic demands  FTissue= MAP/RTissue  Function of Paracrines

3. Reflex Control (4)

 Maintain MAP to assure adequate blood flow to brain and heart  MAP = CO x TPR  Systemic Homeostatic Reflex  Function of NS and ES

Factors Regulating Systemic Arteriolar Resistance 1. Myogenic Autoregulation (3)

```  Function of arterioles  Nearly all organs tend to keep their blood flow constant despite variations in arterial pressure (F=MAP/RTissue )  Reflex arteriolar constriction in response to increased MAP ```

skipped Myogenic Autoregulation Mechanism:

``` increase MAP increase arteriolar blood flow arteriolar stretch open mechanically gated sodium channel in VSM depolarizes membrane opens voltage gated a channels in VSM ca entry and binds to calmodulin activates myosin light chain kinase increase myosin ATPase activity VSM contraction vasoconstriction decrease r increase R decrease F tissue ```

Factors Regulating Arteriolar Resistance | 2. Paracrines (2)

 Matches tissue blood flow to metabolic demands (F=MAP/RTissue )  Interstitial concentration of paracrine substances changes as cells become more or less metabolically active

Increased Tissue Metabolism >

decrease O2 , increase CO2, increase H+, increase K+ (Vasodilation of Arterioles)

Decreased Tissue Metabolism >

increase O2 , decrease CO2 (Vasoconstriction of | Arterioles)

Active Hyperemia -

Process in which an increase in tissue blood flow | accompanies an increase metabolic activity

Reactive Hyperemia-

Increased in tissue blood flow following a period | of low perfusion (blood flow)

If blood flow to a tissue is occluded, paracrines accumulate in interstitial space: (3)

decrease O2 increase CO2 increase H+

Hypoxia stimulates endothelial cells to (2)

``` secrete NO (potent vasodilator) and NO also accumulates in interstitial space ```

Once occlusion removed, paracrines cause (2)

vasodilation and increase in tissue blood flow until paracrines washed away and arteriolar diameter returns to resting state.

Vasodilating Paracrines (7)

``` CO2 H+ (lactic acid) Adenosine (ATP→Adenosine) K+ (multiple action potentials) Prostaglandins Bradykinin Nitric oxide (NO) ```

Vasoconstricting Paracrines (3)

O2 Endothelin Thromboxanes

Factors Regulating Arteriolar Resistance | 3. Reflex Control (4)

 Maintain MAP so have adequate blood flow to brain and heart  MAP = (CO)(TPR)  Reflex control can override local control  Function of NS and ES

Other Hormones | Vasoconstrictors (2)

ADH | ANG II

Other Hormones | Vasodilators (1)

ANP

Local Control | Qtissue=

MAP/Rarterioles

Reflex Control | MAP =

CO x TPR