Study for Lab Quiz 2 – Clinical Applications

A child with an intestinal disorder that caused a low plasma albumin concentration developed edema. She was given an isotonic intravenous solution containing albumin and normal saline.
-Explain the osmotic importance of plasma albumin and why edema occurred.
-Identify the significance of normal saline and the meaning of the terms osmotic pressure and tonicity.
Water returns to the tissue fluid to the blood capillaries because the protein concentration of blood plasma is higher than the protein concentration of tissue fluid. In contrast to other plasma solutes, plasma proteins cannot freely pass from the capillaries into the tissue fluid. Therefore, plasma proteins are osmotically active and cause osmotic return of tissue fluid to the capillaries. If a person has an abnormally low concentration of plasma proteins, excessive accumulation of fluid in the tissues–a condition called edema–will result.

Intravenous fluid must be isotonic to blood in order to maintain the correct osmotic pressure and prevent cells from either expanding or shrinking from the gain or loss of water. Common isotonic fluids include normal saline (0.9% NaCl), 5% dextrose in water, and Ringer’s lactate (with glucose, lactic acid, and different salts). In contrast to isotonic fluids, hypertonic solutions of mannitol (an osmotically active solute) are given intravenously to promote osmosis and thereby reduce the swelling of cerebral edema, a significant cause of mortality in people with brain trauma or stroke.

A patient accidentally cut himself on a piece of broken glass, and the physician applied lidocaine before suturing the laceration.
-Describe the role of plasma membrane Na and K channels in the production of action potentials.
-Explain how lidocaine and other local anesthetics work.
Local anesthetics block the conduction of action potentials in axons. They do this by reversibly binding to specific sites within the voltage-gated Na channels, reducing the ability of membrane depolarization to produce action potentials. Cocaine was the first local anesthetic to be used, but because of its potential for abuse and toxicity alternatives were developed. The first synthetic analog of cocaine used for local anesthesia, procaine, was produced in 1905. Other local anesthetics of this type include lidocaine and tetracaine.

Use of the electroencephalograph may help to diagnose a number of brain lesions, including epilepsy, intracranial infections, and encephalitis. It has been discovered that meditation, as performed by Zen monks and yogis, results in the production of slow alpha waves of increased amplitude and regularity (even with the eyes partially open), and that this change is associated with a decrease in metabolism and sympathetic nerve activity.
Many people, through biofeedback techniques, attempt to enhance their ability to produce alpha rhythms so they can relax and lower their sympathetic nerve effects.