Flashcards in Chapter 19 - Guyton Deck (24):
increased urine output
increased sodium output
The two primary determinants of the long-term arterial pressure level are as follows:
1) degree of pressure shift of the renal output
curve for water and salt; 1) level of the water and salt intake line
Explain the overall mechanism by which increased extracellular fluid volume elevates arterial pressure.
increase extracellular fluid volume-->increases
blood volume-->increase mean circulatory
filling pressure-->increase venous
return of blood to the heart-->increase
cardiac output-->increase arterial pressure
Two ways in which cardiac output can increase arterial pressure?
direct effect of increased cardiac output to increase the pressure, and the other is an indirect effect to raise total peripheral vascular resistance through autoregulation of blood flow
How does salt intake affect extracellular fluid volume?
increased osmolality from salt intake stimulates thirst center and drink more fluid; increased osmolality also stimulates hypothalamic-posterior pituitary gland secretory mechanism to secrete increased quantities of antidiuretic hormone (decrease urine output)
A mean arterial pressure greater than ____ mm Hg (normal is about 90 mm Hg) is considered to be hypertensive (diastolic blood pressure is greater than about 90 mm Hg and the systolic pressure is greater than about 135 mm Hg).
Three primary lethal effects of chronic hypertension.
heart failure or CHD (excessive workload on heart), cerebral infarct (CVA), renal destruction
What occurs during volume-loading hypertension (intake of salt and water increased substantially and held there)
The first stage results from increased fluid volume causing increased cardiac output (causing hypertension). The second stage is characterized by high blood pressure and high total peripheral resistance but return of the cardiac output to near to normal.
What is the function of aldosterone?
increases the rate of reabsorption of salt and water by the tubules of the kidneys, decreasing urine output and causing an increase in blood volume and extracellular fluid volume
Explain the renin-angiotensin vasoconstrictor mechanism for arterial pressure control.
decreased arterial pressure-->renin (kidney)-->renin substrate (angiotensinogen)-->Angiotensin I-->Angiotensin II (converting enzyme in lungs)-->vasoconstriction (renal retention of salt and water)-->increased arterial pressure
Whenever excess amounts of __________ circulate
in the blood, the entire long-term renal–body fluid mechanism for arterial pressure control automatically becomes set to a higher arterial pressure level than normal.
When the renin-angiotensin system becomes activated, the rate of ___________ secretion usually also increases.
Explain the sequential events that occur with increased salt intake (with a functioning renin-angiotensin system under normal conditions).
Increased salt intake-->Increased extracellular volume-->Increased arterial pressure-->Decreased renin and angiotensin-->Decreased renal retention of salt and water-->Return of extracellular volume almost to normal-->Return of arterial pressure almost to normal
How does angiotensin increase arterial pressure (two ways)?
constricting arterioles throughout the body, causing kidneys to retain salt and water
What is primary hypertension?
also known as “essential hypertension” by many clinicians; the hypertension is of unknown origin
Some of the characteristics of primary hypertension caused by excess weight gain and obesity include:
cardiac output is increased (excess body tissue), increased sympathetic nerve activity (especially in kidneys), angiotensin II and aldosterone levels are increased, renal-pressure natriuresis mechanism is
Two general classes of drugs used to treat hypertension.
vasodilator drugs and natriuretic or diuretic drugs
Three mechanisms of vasodilator drug action.
inhibiting sympathetic nervous signals to the kidneys; relaxing the smooth muscle of the renal vasculature; blocking the action of the renin-angiotensin system
Rapidly acting pressure control mechanisms, acting within seconds or minutes.
baroreceptors, chemoreceptors, CNS ischemic response
Pressure control mechanisms that act after a number of minutes.
renin-angiotensin vasoconstrictor mechanism; stress-relaxation of the vasculature; shift of fluid through the tissue capillary walls in and out of the circulation to readjust the blood volume as needed
What is the stress-relaxation mechanism?
When the pressure in the blood vessels becomes too high, they become stretched and keep on stretching more and more for minutes or hours; as a result, the pressure in vessels falls to normal.
What is the capillary fluid shift mechanism?
any time capillary pressure falls too low, fluid is
absorbed through the capillary membranes from the tissues into the circulation, thus building up the blood volume and increasing the pressure in the circulation