- These reflexes are more important in regulating respiration than bp Influence of Higher Brain Centers - Fight of flight, stress, exercise will cause the cerebral cortex and hypothalamus to get involved in regulating bp Hormones and Short Term Regulation of Blood Pressure - Adrenal Medulla Hormones (Norepinephrine and Epinephrine) o Causes generalized vasoconstriction except in skeletal and cardiac muscles o Increases CO o Nicotine mimics effects of carecholamines - Angiotensin II o From the renin-angiotensin system (Decreases renal perfusion) o Causes intense generalized vasoconstriction to increase systemic bp Release of aldosterone and ADH will lead to long term regulation - Atrial Natriuretic Peptide (ANP) o Produced by atria of the heart o Causes blood volume and bp to decrease o Causes generalized vasodilation - Antidiuretic Hormone (ADH) o From the hypothalamus and posterior pituitary o Primarily in long-term regulation (Stimulates kidneys to conserve water) o Not important in short term unless bp drops very low, then more ADH is released and its high levels will cause vasoconstriction Kidneys in Long Term Regulation of Blood Pressure - Baroreceptors adapt to prolonged high/low bp - Kidneys restore bp by adjusting blood volume (A more complete response but takes time) - Anything that changes the blood volume will change bp o If blood volume is increased, then kidney will excrete more salt and water - Direct Action of Kidneys o Increased blood volume or bp will lead to an increased rate of filtrate formation This will cause an insufficient time to reclaim water resulting in an increased volume of urine - Indirect Action of Kidneys o Via Renin-Angiotensin System If MAP decreases then kidney cells will release renin causing a cascade of reactions to yield angiotensin II (A potent vasoconstrictor) Angiotensin II will cause an increase in bp to restore renal perfusion Angiotensin II stimulates secretion of aldosterone (From Adrenal cortex) which will increase renal absorption of Na + and water if ADH is present o The increased secretion of ADH (From the post pituitary) will promote water reabsorption
Blood flow to each organ is regulated to meet needs Resting Vascular Tone - In a resting state, smooth muscles in the walls of arterioles are somewhat contracted (Via SNS), which can increase flow by vasodilation - There are immediate adjustments to changes in local conditions - Organs regulate individual blood flow by varying resistance of arterioles Metabolic Controls (Local) - Declining tissue levels of oxygen - Caused by increased levels of CO 2 , Adenosine, H+, K+, heat, and inflammatory chemicals - The end result is immediate increased perfusion of needy tissues - Mechanism is not fully understood but some may act by stimulating endothelial release of NO - Active Hyperemia is the increase in organ blood flow that’s associated with increased metabolic activity of an organ or tissue - Reactive Hyperemia is the transient increase in organ blood flow that occurs following a brief period of ischemia Myogenic Controls (Local) -
You've reached the end of your free preview.
Want to read all 34 pages?
- Fall '18