McKenna's Pharmacology for Nursing, 2e

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C H A P T E R 4 2 Introduction to the cardiovascular system

↓ Blood flow ↓ Oxygenation

NEPHRON

Erythropoietin release

↑ RBC production

Renin release

Angiotensin I

Activation of angiotensinogen

Lungs

converting enzyme (ACE) Angiotensin I Angiotensin II

Angiotensin-

ADRENAL GLAND Angiotensin III

Powerful vasoconstriction

↑ Aldosterone release

↑ Blood pressure ↑ Blood flow to the kidneys

Retention of sodium with water

FIGURE 42.9  The renin–angiotensin–aldosterone system for reflex maintenance of blood pressure control.

↑ Blood volume and pressure ↑ Blood flow to the kidneys

pressure on the venous end of the capillaries. The hydro­ static pressure pushing fluid out of the capillary is soon higher than the oncotic pressure that is trying to pull the fluid back into the vessel, causing fluid to be lost into the tissues. This shift of fluid accounts for the oedema seen with HF. Pulmonary oedema results when the left side of the heart fails; peripheral, abdominal and liver oedema occur when the right side of the heart fails.

is pushed out under higher pressure and the balancing pressure to pull it back into the vessel is not sufficient. Drugs that are used to treat HF may affect the vascular system at any of these areas in an attempt to return a balance to the pressures in the system.

KEY POINTS

■■ Blood pressure is maintained by stimulus from the sympathetic system and reflex control of blood volume and pressure by the renin–angiotensin system and the aldosterone–ADH system. Alterations in blood pressure (hypotension or hypertension) can upset the balance of the cardiovascular system and lead to problems in blood delivery. ■■ Fluid shifts out of the blood at the arterial ends of capillaries to deliver oxygen and nutrients to the tissues. It moves out due to the hydrostatic or fluid pressure of the arterial side of the system. Fluid returns to the system at the venous end of the capillaries because of the oncotic pull of proteins in the vessels. Disruptions in these pressures can lead to oedema or loss of fluid in the tissues.

Cardiac: Congestive heart failure

Cardiac: Oedema

Other factors can contribute to a loss of fluid in the tissues, including protein loss and fluid retention. Protein loss can lead to a fall in oncotic pressure and an inability to pull fluid back into the vascular system. Protein levels fall in renal failure, when protein is lost in the urine, and in liver failure, when the liver is no longer able to produce plasma proteins. Fluid retention, which is often stimulated by aldosterone and ADH as described earlier, can increase the hydrostatic pressure so much that fluid