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 pressure 1.Age 2.Gender 3.Race 4.Position 5.Emotions 6.Exercise 7.Gravity 8.Respiration

Factors determine ABP& PP ABP = 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

Cardioinhibitory center (CIC) Cardiostimulatory center (CSC) Its discharge reaches the heart via vagus It has continuous discharge under resting cinditions ↓ atrial properties →↓HR →↓COP →↓ABP No effect on ventricles Its discharge reaches the heart via sympathetic ↑atrial properties→↑HR ↑ventricular properties →↑SV & →↑COP →↑ABP

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 Shift It is the intermediate mechanism If ↑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