VPP 3215 Cardio Lec05 Sem I 2024-25 BP and BFlow regulation PDF

Regulation of the blood pressure and blood flow The heart rate, stroke volume, systemic vascular pressure, blood volume (or hemodynamic parameters) are continuously being adjusted to adapt to: SUDDEN (getting up from sternal recumbency, change of posture, blood loss) Or LONG TERM CHANGES (abno...

Regulation of the blood pressure and blood flow The heart rate, stroke volume, systemic vascular pressure, blood volume (or hemodynamic parameters) are continuously being adjusted to adapt to: SUDDEN (getting up from sternal recumbency, change of posture, blood loss) Or LONG TERM CHANGES (abnormal BP, cardiac diseases) AUTOREGULATION – is a ability of tissue to auto-adjust the haemodynamic parameters to match the oxygen demand, nutrient supply and waste removal of the body tissues. Regulation of the hemodynamic parameters are being done by the cardiovascular center after getting feedbacks from proprioceptors, baroreceptors and chemoreceptors. The regulation of blood pressure is done through : Nervous system (neural regulation) Endocrine system (hormonal regulation) Local blood vessels through vasomotion (local regulation) Regulation of the blood pressure : Overview Regulation of the blood pressure (detailed pathways) Flow diagram illustrating how feedforward (central command) and feedback (reflex) mechanisms operate together to regulate the O2 supply to particular regions (skeletal muscle in this example) to match the metabolic demands of that region and thus maintain homeostasis. (Dampney, 2016). Advances in Physiology Education. 2016 Vol. 40 no. 3, 283- 296 DOI: 10.1152/advan.00027.2016  Neural regulation of the blood pressure The nervous system regulates blood pressure via negative feedback loops via A.)Baroreceptor reflex (carotid sinus reflex & aortic reflex) B.)Chemoreceptor reflex (located next to the baroreceptors) Located in the L A.) Baroreceptor reflexes & R carotid Carotid sinus arteries reflex Regulate BP in Baroreceptor the brain reflex Regulate Aortic reflex systemic BP Important for the regulation of BP during postural changes, respond slower as animal ages  Neural regulation of the blood pressure Regulating pathway & effects on BP (a more detailed explanation….) Signals travels Signals via via C.Nerve X sympathetic Increased rate Low BP stretches (aortic reflex) or nerves (cardiac and baroreceptors less C. Nerve IX accelerator nerve contractility/vaso (carotid reflex) to and vasomotor constriction the CVS centre nerve)  Neural regulation of the blood pressure B.)Chemoreceptor reflexes -these receptors are located next to the baroreceptors, known as carotid bodies (carotid sinus) or aortic bodies (at the aortic arch) -PRIMARY ROLES : Adjust RESPIRATION -SECONDARY ROLES : on VASOMOTION -therefore provides inputs to the respiratory center in the brain to coordinate breathing……. detect changes in the blood levels of oxygen, carbon dioxide, H+ O2i (hypoxia), CO2h or H+h triggers sympathetic stimulation of the heart and blood vessels  increase in BP. - High acidity environments/body conditions (e.g. Acidosis) may trigger increased heart rate and even hypertension.  I.Neural regulation of the blood pressure B.)Chemoreceptor reflexes -example of response mechanisms (Dempney, 2016) A: curve showing the relationship between the arterial blood Po2 (PaO2) and the activity of a single carotid body chemoreceptor afferent fiber. [Modified from Biscoe et al. (4) with permission.] B: flow diagram showing the reflex effects of chemoreceptor stimulation by arterial hypoxia, leading to an increase in ventilation (provided that respiratory activity can increase, as during exposure to high altitude) as well as cardiovascular reflex changes that tend to conserve the available O2. C: curve showing the chemoreflex relationship between PaO2 and alveolar ventilation at rest and exercise in human subjects. Note that the reflex effects on ventilation are enhanced during exercise. [Modified from Weil et al. (56).]  II. Hormonal regulation of the blood pressure Hormones adjust BP, blood flow and total volume of blood by altering cardiac output, systemic vascular resistance, and renal functions. Renin-angiotensin-aldosterone (RAA) system -triggered by lowered blood volume or blood flow through the kidneys. -juxtaglomerular cells released renin into blood stream. RAA -Angiotensin II produced will increase BP through (i.) Vasoconstriction – 1 ug of angiotensin able to increase 50 mm Hg BP. (ii.) Promoting secretion of aldosterone, increases Na+ reabsorption and water retention to increase blood volume. Blood Catechol ADH Pressure amine Adrenaline and noradrenaline - from adrenal medulla or nerve endings of SNS. - increase the rate and force of heart contraction. - vasoconstriction of the BV of skin and ANH abdominal organs - vasodilation (adrenaline) of BV in cardiac and skeletal muscles.  II. Hormonal regulation of the blood pressure Hormones adjust BP, blood flow and total volume of blood by altering cardiac output, systemic vascular resistance, and renal functions. Antidiuretic Hormone (ADH) or vasopressin - more powerful vasoconstrictor than RAA angiotensin II. - produced by the hypothalamus and released by the posterior pituitary gland. ADH - causes vasoconstriction and promotes resorption of water through the walls of the collecting tubules and ducts. - release triggered by atrial stretch Blood Catechol receptors (overfilling inhibit ADH Pressure amine release ; underfilling promotes ADH release) and other baroreceptors at the aortic arch and carotid sinus. - osmoreceptors in the higher brain Atrial natriuretic hormone (ANH) region as well (very diluted blood -released by cells at the atria of the heart triggers ADH release) ANH -lowers blood pressure by causing vasodilation (capillary bed) and promoting loss of salt and water in the urine  III. Local regulation of the blood pressure LOCAL control happens predominantly in the capillary beds to adjust systemic vascular resistance and BP. Acted through vasoactive factors released/present around local cells. h H+ ion concentration causes Vasoconstriction Vasodilation dilation of arterioles. Slight decrease will cause constriction but intense decrease causes h Ca2+ Acetate and citrate all dilatation concentration have mild vasodilation causes effects on blood vessels h K+ or h Mg2+ concentration vasoconstriction causes vasodilation as it inhibits as it stimulates smooth muscle contractions smooth muscle h Na+ or glucose produced indirect contractions arteriolar dilatation through increased osmolality of blood Endothelium-derived relaxation factor (EDRF) or nitric oxide – vasodilation (NO can also be produced directly by neurons adjacent to BVs  III. Local regulation of the blood pressure Physical changes facilitates the regulation of the local blood flow through myogenic response of the smooth muscles in the arterioles. Done to ensure blood flow and blood pressure in the small BVs are always constant. These vessels contracts more forcefully when stretched, relaxes when stretching lessens. Local regulation ensure that local cells will always get enough nutrients to sustain their function, for example in : Reactive hyperemia – when Active hyperemia – when tissues blood supplies to local tissues become highly active such as are blocked for several muscles during exercise, nutrients minutes, and then unblocked, deplete rapidly in cells, and lots of local blood flow will increase vasodilators are released. Leading to about 5X normal to repay to 17-20 x increase of local blood the oxygen deficit due to the flow in the muscles of an intensely presence of vasodilator agents. exercised horse. (EIPH)