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Unit Four: The Circulation

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1 Unit Four: The Circulation
Chapter 19: Role of the Kidneys in Long Term Control of Arterial Pressure and in Hypertension: The Integrated System for Arterial Pressure Regulation Guyton and Hall, Textbook of Medical Physiology, 12 edition

2 Renal-Body Fluid System for Arterial Pressure Control
Quantitation of Pressure Diuresis as a Basis for Arterial Pressure Control Fig Typical renal urinary output curve showing pressure diuresis when the arterial pressure rises above normal

3 Renal-Body Fluid System for Arterial Pressure Control
Demonstrating the Renal-Body Fluid System Fig Increases in cardiac output, urinary output, and arterial pressure caused by increased blood volume in dogs whose nervous pressure control mechanisms have been blocked

4 Renal-Body Fluid System for Arterial Pressure Control
Arterial Pressure Control---”Near Infinite Feedback Gain” Fig Analysis of arterial pressure regulation by equating the “renal output curve” with the “salt and water intake curve”

5 Renal-Body Fluid System for Arterial Pressure Control
Arterial Pressure Control---”Near Infinite Feedback Gain” The return of arterial pressure always back to the equililbrium point is the near infinite feedback gain principle for control of arterial pressure by the renal-body fluid mechanism

6 Renal-Body Fluid System for Arterial Pressure Control
Two Determinants of the Long-Term Arterial Pressure Level The degree of pressure shift of the renal output curve for water and salt b. The level of water and salt intake

7 Fig. 19.4 Two ways in which the arterial pressure
can be increased: A: by shifting the renal output curve in the right hand direction toward a higher pressure level B: by increasing the intake level of salt and water

8 Renal-Body Fluid System (cont.)
Chronic Renal Output Curve is Much Steeper Than the Acute Curve Fig. 19.5

9 Renal-Body Fluid System (cont.)
Failure of Increased Total Peripheral Resistance to Elevate the Long-Term Level of Arterial Pressure if Fluid Intake and Renal Function Do Not Change Fig. 19.6

10 Renal-Body Fluid System (cont.)
Increased Fluid Volume Can Elevate Arterial Pressure by Increasing Cardiac Output or Total Peripheral Resistance Fig. 19.7

11 Renal-Body Fluid System (cont.)
Importance of Salt in Renal-Body Fluid for Arterial Pressure Regulation When there is excess salt in ECF, the osmolality increases and stimulates the thirst center ultimately leading to an increase in ECF volume Increase in osmolality stimulates the release of ADH also leading to retention of fluid and increased ECF volume

12 Renal-Body Fluid System (cont.)
Chronic Hypertension is Caused by Impaired Renal Fluid Excretion Mean arterial pressure (MAP) greater than 110 mm Hg is hypertensive Severe hypertension: MAP is mm Hg If more than 50% above normal, a person will live 2-3 years without treatment

13 Renal-Body Fluid System (cont.)
Lethal effects of hypertension are caused in 3 ways Excess workload on the heart leads to early heart failure and coronary heart disease Damage to a major blood vessel in the brain, followed by death of parts of the brain (cerebral infarct or stroke) Injury to the kidneys producing renal destruction and ultimately kidney failure, uremia, and death

14 Renin-Angiotensin System
Components of the Renin-Angiotensin System Fig Renin-angiotensin vasoconstrictor mechanism for arterial pressure control

15 Renin-Angiotensin System
Rapidity and Intensity of the Vasoconstrictor Pressure Response to Renin-Angiotensin Fig

16 Renin-Angiotensin System
Effect of Angiotensin II in the Kidneys- causes retention of both salt and water in two ways: Acts directly on the kidneys to cause salt and water retention Causes the adrenal gland to secrete aldosterone, which causes the retention of both salt and water Mechanism of the Direct Effect of Angiotensin II

17 Renin-Angiotensin System
Large Variation in Salt Intake Fig

18 Primary (Essential) Hypertension
Unknown Origin- characteristics cause by weight gain and/or obesity Cardiac output in increased Sympathetic nerve activity, especially in the kidney, is increased Angiotensin II and aldosterone are increased 2-3 fold d. Renal-pressure natriuresis is impaired

19 Primary (Essential) Hypertension
Graphic Analysis of Arterial Pressure Control in Essential Hypertension Fig

20 Primary (Essential) Hypertension
Treatment Vasodilator drugs that increase renal blood flow Natriuretic or diuretic drugs that decrease tubular reabsorption of salt and water

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