BLOOD PRESSURE

Factors maintaing blood pressure Central factors Cardiac out put Heart RatePeripheral factorsPeripheral resistanceBlood volume venous returnElasticity of blood vesselsDiameter of blood vesselViscosity of blood

Cardiac out put To Systolic blood pressure depend upon

CO&stroke volume –directly proportional Dystolic BP is directly Peripheral

resistance when PR decreased dystolic pressure is decreased

BP is directly proportion to blood volumeBP is directly pro to venous returnBP is inversly proport to elasticity of vessels& diameter of vessels

Control of blood pressureOutline Short term control (baroreceptors)

Location Types of baroreceptor Baroreceptor reflex

Other stretch receptors Long-term control

Renin/ angiotensin/ aldosterone system Vasopressin Atrial natiuretic peptide

Response to blood loss (shock)

Regulation of blood pressure

Short term Baroreceptors

Long term Kidney via renin angiotensin system

Baro-receptors

1. Nerve endings in all large thoracic and neck arteries

2. 2 major populations: Carotid sinus and Arch of the aorta

3. Activation on stretch

4. Carotid: Hering’s nerve to Glossopharyngeal nerve to tractus solitarius in brainstem

5. Aortic: Vagus nerve to tractus solitarius

6. If baro-receptors sense increased BP Secondary signals from tractus solitarius: Inhibition of vasoconstrictor centre and excitation of vagal parasympathetic centre

Baro-receptors

Important in maintaining postural blood pressure (When standing from lying down strong

sympathetic discharge)

Long term changes in blood pressure result in resetting of baroreflexes (i.e. not influential)

Location of baroreceptors• Baroreceptors sense stretch and rate of stretch by generating action potentials (voltage spikes)

• Located in highly distensible regions of the circulation to maximise sensitivity

Overview of short-term control mechanisms

Anatomy of the autonomic nervous control of blood pressure:

• Sympathetic vasomotor nerve fibres leave cord through (T+L) spinal nerves

• Sympathetic chain 1)Sympathetic

nerves (viscera) 2)Spinal nerves

(vasculature)• Vagus nerve (PNS)

Vasomotor centre:

1. Vasoconstrictor area• origin of excitatory pre-ganglionic

vasoconstrictor neurones

2. Vasodilator area• internal inhibition of vasoconstrictor

area

3. Sensory area• input from vagus and

glossopharyngeal nerves modulate vasoconstrictor/dilator area activity

.

To raise the arterial pressure:

1. SNS release NA from nerve terminals

2. NA acts on the α adrenergic receptors of the VSMC

3. All arterioles constricted

4. Veins strongly constricted

5. Heart directly stimulated

….It’s all about intracellular calcium

Cardiovascular Physiology Concepts, Richard E Klabunde. www.cvphysiology.com

VSMC

Beta-adrenoceptors

Cardiovascular Physiology Concepts, Richard E Klabunde. www.cvphysiology.com

Heart: Increased contractility Blood vessel: reduced contractility

Long term control of blood pressure

Involves control of blood volume/sodium balance by the kidneys Hormonal control

Renin-angiotensin-aldosterone system Antidiuretic hormone (vasopressin) Atrial natiuretic peptide

Pressure natriuresis

Renin

Glomerular Hydrostatic pressure

GFR

Flow rate in loop of Henle

Na Cl resorption

Macula Densa NaCL

Arterial Pressure

Afferent arteriole

Resistance

Efferent Arteriole Resistance

Glomerular Filtration Pressure

Angiotensin II

Vasopressin

Atrial natiuretic peptide Increases salt excretion via kidneys

By reducing water reabsorption in the collecting ducts

relaxes renal arterioles inhibits sodium reabsorption in the distal

tubule

Released in response to stimulation of atrial receptors

Atrial volume reflexAtrial stretch due to pressure

Reflex dilation of renal afferent arteriole

Increased glomerular capillary pressure

Increased filtration of fluid into renal tubule

Reduced secretion of anti-diuretic hormone from hypothalamus

Reduction in water resorbtion from renal tubule

Fluid loss by kidneys

Summary of long term BP control Cardiac output and BP depend on renal control of

extra-cellular fluid volume via: Pressure natriuresis, (increased renal filtration) Changes in:

Vasopressin Aldosterone Atrial natiuretic peptide