L21 and L23 Regulation of arterial blood pressure PDF

Regulation of Arterial Blood Pressure Dr. Ghada Elgarawany Assistant professor of Medical Physiology www.gmu.ac.ae COLLEGE OF MEDICINE Describe the role of the nervous system in short-term blood pressure regulation. Discuss the role of RAAS system in regulation of ABP. Describe the role of kidney in...

Regulation of Arterial Blood Pressure Dr. Ghada Elgarawany Assistant professor of Medical Physiology www.gmu.ac.ae COLLEGE OF MEDICINE Describe the role of the nervous system in short-term blood pressure regulation. Discuss the role of RAAS system in regulation of ABP. Describe the role of kidney in long term regulation of ABP. Define hypertension and list its types. Regulation of Arterial blood pressure Short term regulation Intermediate term regulation Long term regulation Short term regulation of Arterial blood pressure They are potent mechanisms that maintain survival They act within seconds and lasts for hours. They are Nervous reflexes and include 1- Arterial baroreceptor reflex 2- Arterial chemoreceptor reflex 3- CNS ischemic response 4- Abdominal compression reflex Short term regulation of Arterial blood pressure 1- Arterial baroreceptor reflex Baroreceptors are stretch receptors present in carotid sinus and aortic arch. Increase ABP →↑discharge of baroreceptors → 1- Stimulation of Cardiac inhibitory center (CIC) → ↑ vagal stimulation → decrease heart rate. 2- Inhibition of Cardiac acceleration center (CAC or VCC) → ↓ sympathetic stimulation → ↓ pumping power of the heart and C.O. Decrease ABP Opposite occurs in hypotension. N.B: * Baroreceptors is sensitive to the rapid changes in ABP. * In chronic hypertension , baroreceptor reflex is adapted to the elevated ABP (No increase in the discharge) Short term regulation of Arterial blood pressure 2- Arterial chemoreceptor reflex Site: Chemoreceptors are present in Carotid bodies and aortic bodies. ↓ ABP below 60mmHg ( low B.P causing ischemia and hypoxia) → stimulation of peripheral chemoreceptors → 1- Stimulation of CAC → ↑sympathetic and catecholamine release → vasoconstriction of blood vessel. 2- Inhibition of CIC and VDC → ↓ vagal tone. Increase ABP Short term regulation of Arterial blood pressure 3- CNS ischemic response ↓ ABP below 60mmHg → ischemia , hypoxia, Hypercapnia and acidosis → stimulation of VCC → generalized Vasoconstriction → increase ABP to maintain the cerebral blood flow. 4- Abdominal compression reflex ↓ ABP → stimulation of VCC → send signals to the abdominal muscle → contraction of the abdominal muscle → compression of the abdominal veins → ↑ venous return to the heart → ↑ ABP. Intermediate term regulation of Arterial blood pressure They act within minutes and lasts for days. During this time, the short-term mechanism become fatigued and less effective. They include: 1- Renin angiotensin vasoconstriction mechanism 2- Capillary fluid shift mechanism 3- Stress relaxation mechanism Intermediate term regulation of Arterial blood pressure 1- Renin angiotensin vasoconstriction mechanism ↓ ABP → renal ischemia → secretion of Renin (from Jaxtaglomerular cell) The liver synthesizes angiotensinogen. In the liver, renin cleaves angiotensinogen into angiotensin I. Renin Angiotensinogen angiotensin I In the lungs, angiotensin-converting enzyme (ACE) converts angiotensin I into angiotensin II. ACE Angiotensin I angiotensin II Angiotensin II has a potent vasoconstrictive effect → ↑ ABP. Intermediate term regulation of Arterial blood pressure 2- Capillary fluid shift mechanism This mechanism occurs when ABP is changed due to change in the blood volume. ↑Blood volume → increase capillary hydrostatic pressure → ↑ filtration to tissue spaces → ↓ blood volume → ↓ ABP. 3- Stress relaxation mechanism ↑Blood pressure → stretch the arteries and increase the tension → relaxation of the arteries and the tension decreases → ↓ ABP. Long term regulation of Arterial blood pressure They are Powerful mechanisms for regulating arterial pressure. They acts within few hours to begin and last for weeks and months. Depends on the role of the kidney through diuresis and or natriuresis. Diuresis means excess excretion of water while natriuresis means excess excretion of Na+ Hormonally mediated. They include 1- Renin Angiotensin Aldosterone System (RAAS) 2- Antidiuretic hormone (ADH, vasopressin) 3- Atrial Natriuretic Peptide (ANP) Long term regulation of Arterial blood pressure 1- Renin Angiotensin Aldosterone System (RAAS) ACE Angiotensin II stimulates the secretion of aldosterone hormone from the adrenal cortex → Na+ and water reabsorption (salt and water retention → ↑ blood volume → ABP Long term regulation of Arterial blood pressure 05/03/2024 16 Long term regulation of Arterial blood pressure 2- Antidiuretic hormone (ADH, or Vasopressin) ADH is made in the hypothalamus and released from the posterior pituitary. Causes of release: 1- Increase blood osmolality 2- decrease blood volume or hypotension 3- Angiotensin II Effect: 1- Bind to V1 receptor in the blood vessels → Vasoconstriction. 2- ADH binds to V2 receptors in the distal and collecting duct principal cells → increase aquaporin channels Increases water reabsorption from the kidney ↑ blood volume → ABP Long term regulation of Arterial blood pressure 3- Atrial Natriuretic Peptide (ANP) ✓ Hormone released from cardiac muscle cells (wall of right atrium) as a response to an increase in ABP. ✓ ↑ABP → increase ANP → excretion of Na+ ( Natriuresis) and water excretion ( diuresis) → ↓ABP Hypertension Definition: It is persistent elevation of arterial blood pressure. ≥140/90 mmHg. Types: Primary (essential or idiopathic) hypertension: about 90% of all hypertension cases. Unknown cause (obesity is a predisposing factor) Secondary hypertension: 10% of all hypertension cases. Secondary to another problem, Endocrine hypertension, Renal hypertension, Toxemia of pregnancy, Polycythemia vera. Review Questions A previously healthy patient comes in with stenosis of both renal arteries (vessel diameter is smaller). As a result, blood flow to the renal arterioles is severely decreased. What effect would this have on blood pressure? A. B. C. D. Decrease Increase Increase, then decrease to normal No change You see a patient in clinic with chronic hypertension. You prescribe him a medication that inhibits an enzymatic process that occurs in the lungs. Which of the following steps in the RAAS pathway is most directly inhibited by this medication? A. B. C. D. E. Aldosterone release Angiotensin I to angiotensin II Angiotensinogen to angiotensin I Antidiuretic hormone release Renin release https://exchange.scholarrx.com/brick/renin-angiotensin-aldosteroneregulation-of-blood-pressure Summary Describe the role of the nervous system in short-term blood pressure regulation. Discuss the role of RAAS system in regulation of ABP. Describe the role of kidney in long term regulation of ABP. Define hypertension and list its types. Learning Resources Hall JE, Hall ME. Guyton and Hall textbook of medical physiology e-Book. 14ed, Elsevier Health Sciences; 2021. Chapter 18 & 19, 217-244 https://www-clinicalkey-com.gmulibrary.com/#!/content/book/3-s2.0-B9780323597128000187 https://www-clinicalkey-com.gmulibrary.com/#!/content/book/3-s2.0-B9780323597128000199 https://exchange.scholarrx.com/brick/renin-angiotensin-aldosterone-regulation-of-blood-pressure https://exchange.scholarrx.com/brick/humoral-regulation-of-blood-pressure Power-point presentation in the Moodle. www.gmu.ac.ae COLLEGE OF MEDICINE Thank you