Blood Pressure

Dr. Ola Tork

MD.Physiology

Factors affecting Heart rate 1. Autonomic nervous system

2. Hormones

3. Position

4. Exercise

5. Emotional states

6. Gender

7. Age

8. Temperature

9. Baroreceptor reflex

Arterial blood pressure:

Definition: lateral force that the blood flow exerts on the wall of blood vessel.

Systolic blood pressure

Diastolic blood pressure

Pulse pressure

Physiological variation in blood pressure1. Age2. Gender3. Race4. Position 5. Emotions6. Exercise7. Gravity8. Respiration

Factors determine ABP& PPABP = COP x TPR

TPR : total peripheral resistance which depends mainly on the diameter of arterioles , so that

VC → ↑ TPR

VD → ↓ TPR

ABP = SV x HR x TPR

1. Stroke volume:

2. Heart rate :

3. Peripheral resistance

4. Elasticity of aorta & big arteries

Regulation of ABP:

1. Rapid : nervous mechanism

2. Intermediate: capillary fluid shift

3. Slow : hormonal & renal mechanism

Nervous mechanism

Cardiovascular centers are present in the medulla in 2 areas:

Pressor area: 2 centers CSC & VCC

Depressor area: 2 centers CIC & VDC

The activity of these centers is modified by afferents from:

1. Receptors inside CVS

2. Receptors outside CVS

3. High centers

4. Blood gases changes:

Mild ↓ O2 & ↑ CO2 → ↑ ABP

Severe ↓ O2 & ↑ CO2 → ↓ ABP & death

Cardiostimulatory center (CSC)

Cardioinhibitory center (CIC)

Its discharge reaches the heart via sympathetic

↑atrial properties→↑HR

↑ventricular properties →↑SV & →↑COP →↑ABP

Its discharge reaches the heart via vagus

It has continuous discharge under resting cinditions

↓ atrial properties →↓HR →↓COP →↓ABP

No effect on ventricles

Vasoconstrictor center (VCC ):

Has a continuous tone under resting conditions

1. VC of arterioles →↑TPR →↑ABP

2. VC of veins →↑VR →↑COP →↑ABP

Vasodilator center (VDC ):

It inhibits VCC

Capillary fluid ShiftIt is the intermediate mechanismIf ↑ABP →↑ capillary hydrostatic pressure →↑ filtration of fluid from plasma to ISF →↓ plasma volume →↓ venous return →↓ ABP

While if ↓ABP → ↓ capillary hydrostatic pressure → ↓ filtration of fluid from plasma to ISF + ↑reabsorption at venular end by osmotic pressure → ↑ plasma volume → ↑ venous return → ↑ ABP

Role of the kidney & hormones in regulation of BP

It is slow mechanism

The kidney regulate ABP by regulating plasma volume & ECF

On ↓ABP , it is elevated by 2 mechanisms:

1. Renin- Angiotensin system

2. Atrial mechanoreceptors