8/2/2019 21.4 Control BP & BF

1/3

Cardiovascular Center (Medulla Oblongata) (Vasomotor Center)

Regulates:

HR (contract force) & SV by (CardioVascular Center)

Radius (VasoD & VasoC) by (Vasoconstrictor Center)

Neural, Hormone, Local Neg. Feedback Reg. BP & BF to tissues

Cerebral Cortex; Limbic; Hypothalamus Nerve Impulse CVCenter (Ex: B4 race BP. T during race Nerve Impulse to CV

Center VasoD skin vessels Lets heat out from skin surface

Sensory Receptorsinput to CV CenterProprioceptors: monitor joint & mus. Movements CV Center (when

physical activity) HR

Baroreceptors: Monitors P & Stretch Changes in Walls of Vessels Chemoreceptors: Monitors [Chemical] in blood(via Cardiac Accelerator Nerves ) HR & Contractility HR & ContractilityPara (via Vagus CN X nerves) HR The CV center also continually sends impulses to smooth muscle in blood vessel walls via

vasomotor nerves.

These neurons exit spinal cord thru all th oracic & L1 or L2 lumbar spinal nerves & then pass into

the sympathetic trunk ganglia (see Figure 15.2). From there, impulses propagate along

sympathetic neurons that innervate blood vessels in viscera and peripheral areas. The vasomotor

region of the cardiovascular center continually sends impulses over these routes to arterioles

throughout the body, but especially to those in the skin and abdominal viscera. The result is a

moderate state of tonic contraction or vasoconstriction, called vasomotor tone, that sets the

resting level of systemic vascular resistance. Sympathetic stimulation of most veins causes

constriction that moves blood out of venous blood reservoirs and increases blood pressure.

NEURAL Regulation of BP

Nerves Reg. via Negative Feedback Loops: 2 reflexes BaroreceptorReflexes & Chemoreceptor Reflexes

BARORECEPTOR REFLEX (Carotid Sinus Reflex & Aortic Reflex)

P Sensitive Sensory Receptors (in Aorta, Internal Carotid a, largearteries neck & chest)2 Baroreceptors: Carotid Sinus Reflex (Senses & BP) & AorticReflex (only BP sensed)

(in Carotid Sinuses) Carotid Sinus Reflex Reg. BP in BrainCarotid Sinuses (small widening of R & L Internal Carotid a. just above

branch point fr. Common Carotid Arteries (Fig. 21.13)

BP Stretches Carotid Sinus Walls Baroreceptors (Carotid SinusReflex) Propagate to Sensory Axons (in CN IX) to CV Center

(Medulla Oblongata)

BP Baroreceptors in Ascending Aorta & Aortic Arch AorticReflex to Sensory Axons ofCN X CV Center

BP (disrupt Homeostasis)Baroreceptor Stretch (Aortic Arch &Carotid Sinus)Still Sends Nerve Impulse but at Slower Rate to CV

Center (Medulla Oblongata & Adrenal Medulla) (Input) bycardiac accelerator nerves) Para) also (Epi & NE by adrenalmedulla) [SV & HRCO] & [Constrict Blood Vessels TPR] BP Return to Homeostasis (when CO & TPR bringsBP back to )

RECAP: BP Stretch Receptors Slows Rate to CV (Epi &

NE) & para SV, HR CO; Constricts Blood Vessels TPR

BPReturns to

BP detected Baroreceptors sends Impulse FASTER RATE CVresponse: ParaHRContraction Force CO

ANOTHER CV Center response Slows Rate it sends Impulse (alongVasomotor Neurons) Lessens VasoC VasoD TPR & CO

BP back to

RECAP: BP Stretch FASTER Rate to CV para & HR

& Contract Force CO

ALSO CV Slows Rate sends VasoDTPR & CO BP

21.4 Control BP & BF by Adjust HR, SV, R, BV:

Cx:

Prone (lying down) to an Erect position BP & BF in the head and upper part of the body.

The baroreceptor reflexes, however, quickly counteract the drop in pressure.

Sometimes these reflexes operate more slowly than normal, especially in the elder ly, in which case a

person can faint due to reduced brain blood flow after standing up too quickly.

Cx: Carotid Sinus Massage & Carotid Sinus SyncopeCarotid sinus is close to anterior surface of the neck, it is possible to stimulate the baroreceptors there

putting pressure on the neck.

Physicians sometimes use carotid sinus massage, which involves carefully massaging the neck over the

carotid sinus, to slow heart rate in a person who has paroxysmal superventricular tachycardia, a type

tachycardia that originates in the atria.

Anything that stretches or puts pressure on the carotid sinus, such as hyperextension of the head, tigh

collars, or carrying heavy shoulder loads, may also slow heart rate and can cause car otid sinus syncope

fainting due to inappropriate stimulation of the carotid sinus baroreceptors.

8/2/2019 21.4 Control BP & BF

2/3

Chemoreceptor Reflexes

Chemoreceptors: Monitor chemical composition of blood, are located

close to the baroreceptors of the carotid sinus & arch of the aorta in

small structures: carotid bodies & aortic bodies, respectively.

These chemoreceptors: Detect Level of O2, CO2, and H+.

Hypoxia O2

Acidosis: H+

Hypercapnia: CO2 Stimulates chemoreceptors to send impulses to

CV Center Stimulation VasoC Arterioles & Veins BP

These chemoreceptors also provide input to the respiratory center in

the brain stem to adjust the rate of breathing.

Hormonal (4) Regulation of Blood Pressure & BF

Alters CO changing TPR or adjusting the TPR:

1. Reninangiotensinaldosterone (RAA):

BV or BF to kidneys juxtaglomerular cells (kidneys) renin(EZ)

to bloodstream

In sequence, Renin & ACE act on their substrates to produce

Angiotensin IIBP 2 ways:

1st

: Angiotensin II Strong VasoC TPR BP

2nd

: Angiotensin IIAldosterone (fr. Adrenals)Na+/WaterReabsorption (Kidneys) TBV BP

(See Section 21.6.)

2. Epinephrine and norepinephrine: (adrenal medulla) Epi & NE

CO Contraction Rate & Force

Also VasoC of arterioles & veins in skin & Abd. Organs

VasoD of Arterioles in Cardiac & Skeletal M.

Which helps BF to Muscle during Exercise. (See Figure 18.20.)

3.Antidiuretic hormone (ADH):(made in hypothalamus) & Released fr.

Posterior Pituitary

Dehydration or BV ADH ReleaseVasoCBP(Reason ADH is also called vasopressin)

(See Figure 18.9.)

ADH

Water Moves from Kidney Lumen into Bloodstream

BV &Urine Output

4.Atrial Natriuretic Peptide (ANP). (Released by Atria Cells)

ANP VasoD BP

Also:

ANPNa+/Water (Excreted in Urine) BV BV

Table 21.2summarizes the regulation of BP by hormones.

Autoregulation of Blood Pressure

In each capillary bed, local changes can regulate Vasomotion.

When Vasodilators produce local arteriole Dilations & Relaxation ofPrecapillary Sphincters: BF into capillary networks O2 level.

Vasoconstrictors (opposite FX) BF

Autoregulation: Tissue automatically adjusts its BF to match its metabolic

demands.

In tissues such as heart & skeletal muscle, demand for O2 & nutrients & fo

the Removal of Wastes can Increase as much as tenfold during physical

activity Autoregulation to BF thru tissue.

Autoregulation: also controls regional BF in brain; blood distribution to

various parts of the brain changes dramatically for different mental and

physical activities.

During a conversation: BF to your motor speech areas when talking &to

the auditory areas when listening.

Two general types of stimuli cause autoregulatory changes in blood flow:

1. Physical changes.

Warming VasoD

Cooling VasoC

Smooth muscle (Arteriole Walls) = Myogenic responseit

Contracts more forcefully when stretched & Relaxes

when stretching lessens.

If BF thru an arteriole Stretching of arteriole walls.

As a result, the smooth muscle relaxes VasoDBF

2. Vasodilating & Vasoconstricting Chemicals

WBC, Smooth M. Cells, Platelets, Macrophages

Endothelial cells Radius

Vasodilators:

Chemicals fr. tissues: K+, H+, Lactic Acid, Adenosine (ATP) VasoDImportant VasoD (Endothelial cells) NO VasoDTissue trauma or inflammation Kinins & HistamineVasoD.

vs

Vasoconstrictors:

Thromboxane A2, superoxide radicals, serotonin (from platelets), andEndothelins (from endothelial cells) VasoC

NOTE: Autoregulation Response to O2

Systemic Circulations:

Blood Vessel Walls (Senses) low O2 dilate O2 delivery which restores back to O2 level.

Pulmonary Circulation:

Blood Vessel Walls (Senses) Low O2 constrictThis ensures blood mostly bypasses those alveoli (air

sacs) in the lungs that are poorly ventilated by fresh air) most blood flows to better-ventilated areas of

the lung

VS

Checkpoint:

1. What are the Pincipal Inputs to & outputs from CV Center2. Explain Carotid Sinus Reflex & Aoritc Reflex Function3. What is Role of Chemoreceptors in Regulation of BP4. How do Hormones Reg. BP5. What is Autoregulation & how does it differ in Systemic vs.

PUL Circulations

8/2/2019 21.4 Control BP & BF

3/3