Blood Pressure Control Simplified Version

Blood Pressure Control Widespread Control – Control all over the body A. Nervous System B. Hormones Local Control – Control of certain organs

MAP = CO x SVR CO = HR x SV SV = EDV – ESV (EDV concerned with blood volume and ESV concerned more with inotropic effect) SVR = ∑R₁ + R₂ + 1/R₃ + 1/R₄ ….. R = 8ŋL/∏r⁴ In order to live – the body compensates by increasing the actions of the organs not affected (homeostasis – negative feedback)

Nervous System Blood Pressure Control Cardiovascular Center Cardiac Center – Cardiac Acceleratory Center and Cardiac Inhibitory Center Vasomotor Center – Vasoconstrictor Center and Vasodilator Center

Cardiovascular center

Vasoconstrictor Vasodilator Center

Baroreceptors

Alpha receptors on Blood Vessels

Hormonal Control of Blood Pressure Renin – Angiotensin System Aldosterone ADH – Antidiuretic Hormone (Vasopressin) Epinephrine Atrial Natriurectic Polypeptide

Renin Angiotensin Angiotensinogen – is produced by the liver. We have a circulating concentration in the blood. A hormone type enzyme produced and secreted by the kidney (Renin) converts Angiotensinogen to Angiotensin I (one). This substance does nothing. Endothelial cells in several locations, particularly the lungs produce and secrete Angiotensin Converting Enzyme. This enzyme converts Angiotensin I to Angiotensin II.

Angiotensin II has several functions, some are: Act as a powerful vasoconstrictor Stimulate production of Aldosterone from the adrenal cortex Stimulate production of ADH from the posterior pituitary.

Zona glomerulosa Zona fasciculata Zona reticularis Adrenal medulla Capsule Zona glomerulosa Zona fasciculata Adrenal gland Cortex • Medulla • Cortex Zona reticularis Kidney Medulla Adrenal medulla (a) Drawing of the histology of the adrenal cortex and a portion of the adrenal medulla Figure 16.13a

Aldosterone Regulate electrolytes (primarily Na+ and K+) in ECF Importance of Na+: affects ECF volume, blood volume, blood pressure, levels of other ions Importance of K+: sets RMP of cells Aldosterone is the most potent mineralocorticoid Stimulates Na+ reabsorption and water retention by the kidneys

Hypothalamic hormones travel through the portal Hypothalamus When appropriately stimulated, hypothalamic neurons secrete releasing and inhibiting hormones into the primary capillary plexus. 1 Hypothalamic neuron cell bodies Superior hypophyseal artery Hypophyseal portal system Hypothalamic hormones travel through the portal veins to the anterior pituitary where they stimulate or inhibit release of hormones from the anterior pituitary. 2 • Primary capillary plexus • Hypophyseal portal veins • Secondary capillary plexus Anterior lobe of pituitary Anterior pituitary hormones are secreted into the secondary capillary plexus. 3 TSH, FSH, LH, ACTH, GH, PRL (b) Relationship between the anterior pituitary and the hypothalamus Figure 16.5b

Antidiuretic Hormone (ADH) Hypothalamic osmoreceptors respond to changes in the solute concentration of the blood Can be stimulated to be secreted due to Angiotensin II If solute concentration is high Osmoreceptors depolarize and transmit impulses to hypothalamic neurons ADH is synthesized and released, inhibiting urine formation

Antidiuretic Hormone (ADH) Hypothalamic osmoreceptors respond to changes in the solute concentration of the blood If solute concentration is high Osmoreceptors depolarize and transmit impulses to hypothalamic neurons ADH is synthesized and released, inhibiting urine formation

Epinephrine Chromaffin cells in the adrenal medulla secrete epinephrine (80%) and norepinephrine (20%) These hormones cause Blood glucose levels to rise Blood vessels to constrict The heart to beat faster Blood to be diverted to the brain, heart, and skeletal muscle

Adrenal Medulla Epinephrine stimulates metabolic activities, bronchial dilation, and blood flow to skeletal muscles and the heart Norepinephrine influences peripheral vasoconstriction and blood pressure

FFF RR FFF – Fear, Fight & Flight RR – Rest and Recluse Receptors for NE are alpha and beta with subtypes. The receptors for Acetylcholine are nicotinic and muscarinic. On the heart there are Beta 1 receptors for NE and muscarinic for acetylcholine.

Atrial Natriurectic Polypeptide (ANP) Atrial natriuretic peptide (ANP) is a polypeptide hormone which reduces an expanded extracellular fluid (ECF) volume by increasing renal sodium excretion. ANP is synthesized, secreted, and released by heart muscle cells (myocytes) in the atrial wall. These cells contain volume receptors which respond to increased stretching of the atrial wall due to increased atrial blood volume. ANP is one of a family of nine natriuretic hormones: seven are atrial in origin.

Intrinsic mechanisms Extrinsic mechanisms (autoregulation) controls • Maintain mean arterial pressure (MAP) • Redistribute blood during exercise and thermoregulation • Distribute blood flow to individual organs and tissues as needed Amounts of: pH Sympathetic Nerves O2 a Receptors Metabolic controls Epinephrine, norepinephrine b Receptors Amounts of: CO2 K+ Angiotensin II Hormones Prostaglandins Adenosine Antidiuretic hormone (ADH) Nitric oxide Endothelins Atrial natriuretic peptide (ANP) Myogenic controls Stretch Dilates Constricts Figure 19.15

Local Control (Autoregulation) Paracrine/Autocrine Myogenic Tone Metabolites Major organs discussed using local control are: Brain, Heart, skin, lungs

Paracrine/Autocrine Paracrine and autocrine secretions are local secretions. Vasodilation – Endothelial Derived Relaxing Factor (Nitric Oxide), Prostaglandins, Kinins Histamine Vasoconstriction - Endothelin

Myogenic Controls Myogenic responses of vascular smooth muscle keep tissue perfusion constant despite most fluctuations in systemic pressure Passive stretch (increased intravascular pressure) promotes increased tone and vasoconstriction Reduced stretch promotes vasodilation and increases blood flow to the tissue

Metabolites H+, CO2, Adenosine, K+, O2