Regulation of Arterial Blood Pressure Dr Mohammed Jeelani

Specific learning outcomes �Describe the role of nerves in regulating blood pressure. �List the reflex responses to baroreceptor activation and describe their role in the short-term regulation of blood pressure. �Explain the role of renin –angiotensin and vasopressin in the regulation of blood pressure. �Define the role of the kidney in the regulation of blood pressure

Regulation of BP �Brought about by complex interplay between NEURAL ; HUMORAL and RENAL factors

Neural factors �Medullary Sympathetic Centre (Vasomotor Centre) �Medullary Parasympathetic Centre (Nucleus Ambiguus) �Medullary relay Centre for afferents (NTS).

Medullary Sympathetic Centre (Vasomotor Centre) VMC consists of a group of neurons situated bilaterally in the reticular substance of medulla at the floor of fourth ventricle. � Consists of : � Pressor area and Depressor area. �

Pressor area �Stimulation causes : 1. Arteriolar vasoconstriction. 2. Venoconstriction. 3. Increase in HR. 4. Increase in force of contraction

Depressor area � Stimulation inhibits the Pressor area : 1. Arteriolar dilatation. 2. Venodilatation. 3. Decrease in HR. 4. Decrease in force of contraction.

Medullary Parasympathetic Centre (Nucleus Ambiguus) Is the Cardiac Vagal Centre (CVC). � Receives afferents via NTS. � Sends inhibitory vagal fibres to the heart. � Stimulation reduces heart rate and also force of contraction. �

Medullary relay Centre for afferents(NTS). NTS receives afferents from Baroreceptors & Chemoreceptors. � Afferents release excitatory neurotransmitter glutamate. � NTS relay information to the VMC & Cardiac vagal centre to control the sympathetic and parasympathetic outputs. �

Mechanisms �Short – Term Blood Pressure Control Mechanisms �Intermediate Blood Pressure Control Mechanisms �Long - Term Blood Pressure Control Mechanisms

Baroreceptor reflex mechanism

Renin angiotensin mechanism

Renal body fluid feedback mechanism

Role of vasopressin

�Hypovolaemia stimulates renin angiotensin mechanism and reinforces release of ADH in response to hypovolaemia & hypotension

Reference �Indu khurana. Medical physiology for UG, 1 st edition, Elsevier publication chapter 4. 4 page 246 -248, chapter 4. 5 page 250 -252 and 255 -261, chapter 8. 2 page 546 -549.

�Thank you