Rapid Control of Arterial Pressure by Nervous

System

M. Rasjad IndraM. Rasjad IndraLab. Ilmu Faal FK UNIBRAWLab. Ilmu Faal FK UNIBRAW

Circulation Control by Nervous Circulation Control by Nervous SystemSystem

The role of nervous system in controlling The role of nervous system in controlling local blood flow is very little.local blood flow is very little.Nervous system has more role in global Nervous system has more role in global function:function:

1.1. Distributing blood to particular part of the Distributing blood to particular part of the bodybody

2.2. The strength of heart as a pumpThe strength of heart as a pump3.3. Rapid control of blood flow Rapid control of blood flow

Three Major Changes Three Major Changes If sympathetic nervous system are stimulatedIf sympathetic nervous system are stimulated1.1. Almost all arterioles are constrictedAlmost all arterioles are constricted

• Increases the total peripheral resistanceIncreases the total peripheral resistance2.2. The veins especially & other large vessels are The veins especially & other large vessels are

strongly constrictedstrongly constricted• Increases venous return Increases venous return increase cardiac out put increase cardiac out put

(Starling Law)(Starling Law)3.3. The heart enhancing cardiac pumpingThe heart enhancing cardiac pumping

• Increases heart rateIncreases heart rate• Increases cardiac contractilityIncreases cardiac contractility

Spinal anesthesia causes decreasing of blood pressure due to vasomotor tonus loss

Reflex Mechanism for Maintaining Reflex Mechanism for Maintaining Normal Arterial PressureNormal Arterial Pressure

Baroreceptor Reflexes:Baroreceptor Reflexes:– The receptors: Baroreceptors or PressoreceptorsThe receptors: Baroreceptors or Pressoreceptors

Located in the wall of several of large systemic Located in the wall of several of large systemic arteriesarteriesSinus caroticus Sinus caroticus n. Hering n. Hering n. Glossopharyngeus n. Glossopharyngeus tr. Solitarius tr. Solitarius Med. Oblongata.Med. Oblongata.Arcus aortae Arcus aortae n. Vagusn. Vagus

– The Response: Feedback signals to reduce The Response: Feedback signals to reduce arterial pressurearterial pressure

Vasodilatation of the veins and arteriolesVasodilatation of the veins and arteriolesDecreased heart rate & the strength of heart Decreased heart rate & the strength of heart contractioncontraction

Effect of changes in arterial pressure (ΔP) to the changes of impulse transmission. Hering from carotid sinus (ΔI)Baroreceptor performs better response to the changes of pressure than static pressure

Clamping of a. carotis communis increases in arterial pressure mean (MAP), releasing of clamp decreases arterial pressure

Function of Baroreceptor ReflexFunction of Baroreceptor Reflex

During changes in Body PostureDuring changes in Body Posture– To maintain relatively constant arterial To maintain relatively constant arterial

pressure in the upper bodypressure in the upper bodyPressure BufferPressure Buffer Function Function– Opposes either Opposes either increasesincreases or or decreasesdecreases in in

arterial pressure.arterial pressure.Unimportance of Baroreceptor System for Unimportance of Baroreceptor System for Long RegulationLong Regulation– The resetting of baroreceptor systemsThe resetting of baroreceptor systems

Recording of blood pressure for 2 hours in NORMAL condition (upper figure) and some weeks after sinus caroticus and Sinus aorticus DENERVATION (lower figure)

Frequency of MAP for 24 hours in NORMAL dog and some Frequency of MAP for 24 hours in NORMAL dog and some weeks after baroreceptor denervation weeks after baroreceptor denervation

Chemoreceptors Reflex:Chemoreceptors Reflex:– The receptors sensitive to:The receptors sensitive to:

Lack of oxygens; COLack of oxygens; CO22 excess and H excess and H++ excess. excess.

Located in the wall of small arteries; Carotid Bodies & Aortic Located in the wall of small arteries; Carotid Bodies & Aortic Bodies.Bodies.

– Not a powerful control in a normal arterial pressure Not a powerful control in a normal arterial pressure rangerange

Important in below 80 mmHgImportant in below 80 mmHg

Low-pressure Receptors:Low-pressure Receptors:– Stretch receptorsStretch receptors– Located in the wall of: Pulmonary arteries & AtriumLocated in the wall of: Pulmonary arteries & Atrium– Role: to minimize arterial pressure changes in Role: to minimize arterial pressure changes in

response to changes in blood volume.response to changes in blood volume.

Reflex Mechanism for Maintaining Normal Reflex Mechanism for Maintaining Normal Arterial Pressure (Cont.)Arterial Pressure (Cont.)

Volume Reflex (Volume Reflex (Atrial Reflex that Activate the KidneyAtrial Reflex that Activate the Kidney))– Stimulation: Stretch of the atriaStimulation: Stretch of the atria– Response: Response:

1.1. Dilatation of the afferent arteriole in the kidneyDilatation of the afferent arteriole in the kidney2.2. To Hypothalamus To Hypothalamus Decrease ADH secretion Decrease ADH secretion 3.3. Release of Atrial Natriuretic Peptide (ANP)Release of Atrial Natriuretic Peptide (ANP)

The Bainbridge ReflexThe Bainbridge Reflex– Stimulation: Stretch of the atriaStimulation: Stretch of the atria– Response: n. Vagus Response: n. Vagus Med. Oblongata Med. Oblongata Increase the Increase the

heart rate & strength of the heart contractionheart rate & strength of the heart contraction

Reflex Mechanism for Maintaining Reflex Mechanism for Maintaining Normal Arterial Pressure (Cont.)Normal Arterial Pressure (Cont.)

CACI

HIGHER CENTER

VASOMOTORCENTERCI CA

JANTUNG

SV Hr

C.O.PX

TPR

“Blood Pressure”O2

HCO2

PH

CHEMORECEPTOR

+

VCVD

+“Baroreceptor”

-

BARORESEPTORCONTROL “Blood Pressure”