CHAPTER III: ARTERIAL ARTERIAL PRESSURE CONTROLPRESSURE CONTROL

Asst. Prof. Dr. Emre HamurtekinEMU Faculty of Pharmacy

• CVS system includes two distinct pathways for monitoring and maintaining arterial pressure: Baroreceptor Reflex (fast activating)

Sensors – Integrator – Effector mechanisms Changes in blood volume by renal function (slow

activating)

• SensorsSensors:I. High-pressure arterial baroreceptorsII. Low-pressure cardiopulmonary receptorsIII.Chemoreceptors

• Clusters of sensory nerve endings• Aortic baroreceptors and carotid baroreceptors are

the primary means of detecting changes in MAP.• They respond to arterial wall stretch.• Aortic baroreceptors aortic nerve

vagus nerve• Carotid sinus sinus nerve

glossopharyngeal nerve• The sensory nerves respond to stretching of the

arterial wall because of the increasing MAP with graded receptor potentials.

• Sensory nerve endings embedded in the walls of the vena cavae pulmonary artery and vein low-pressure regionsatria

• They provide CNS (by vagal nerve) with information about the «fullness» of the vascular system.

• Their principal role is in modulating renal function.• They also have a role in maintaining MAP.

• Monitor local metabolite levels which reflect the pressure and flow.

• Highly vascularized glomus cell clusters• Located in aortic arch (aortic bodies) and carotid

sinus (carotid bodies).

• PO2 ˂ 60 mm Hg• PCO2 ˃ 40 mm Hg activation• PH ˂ 7.4

• Principally involved in respiratory control but also reflect low perfusion pressures.

• Medulla oblangataVasomotor center (vasoconstriction)

Cardioacceloratory center (positive chronotropy and inotropy)

Cardioinhibitory center (negative chronotropy)

CARDIOVASCULAR CONTROL CARDIOVASCULAR CONTROL CENTERCENTER

INPUT OUTPUT

Cardioinhibitory

Cardioacceleratory

Vasomotor

IMPULSELow / High MAP

HRHR

HRHRINOTROPY

PRELOADPRELOAD

SVRSVR

Inhibitory interneuron

Inhibitory interneuron

--

--

--

MAP = CO x SVR

•Control centers adjust both CO and SVR.•Control is exerted by simple feed back loops.

When MAP falls, baroreceptor reflex starts andWhen MAP falls, baroreceptor reflex starts and:

1.1.SVRSVR increases2.Venoconstriction3.LV preload increases4.Inotropy increases5.HR increases

6.6.COCO increases7.SNS activation causes the adrenal glands secrete epinephrine

• This is responsible for circulating blood volume circulating blood volume and Na regulation.Na regulation.

• These pathways converge on the kidneykidney.Water outputWater intakeSodium outputSodium intake

• Water output is controlled by ADH (antidiuretic hormone, vasopressin, AVP).

REGULATIONSREGULATIONS

1. ADH stimulates water reabsorption by the renal collecting tubules.

2. Increase in SVR by constricting arterial vessels.REGULATION of ADH:- Osmoreceptors: When osmolarity exceeds 280

mOsm/kg, ADH release is stimulated- Baroreceptors: Decrease in circulating blood

volume is detected by cardiopulmanary and arterial baroreceptors and ADH release is stimulated.

- Angiotensin-II: Angiotensin-II stimulates hypothalamus to release ADH.

• Decrease in blood volume• Decrease in arterial pressure

Triggers thirst and drink water

JUXTAGLOMERULAR APPARATUS

Macu

la d

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RENIN

1. Vasoconstriction.2. Stimulates ADH

release3. Stimulates thirst and

salt apetite.4. Promotes

aldosterone release from adrenal cortex.

----------------------------------• Aldosterone targets

the renal collecting tubule epithelium.

• Increases Na and water reabsorption.

• Salt craving triggers a need to ingest NaCl.• Salt apetite is stimulated by aldosterone and Ang-

II.