Nursing 105

Essentials of Nursing Study Guide

©2018 Achieve Page 87 of 160 Plasma in the blood vessels has both types of pressure. Fluid in the tissues/cells also has both. The body prefers for the pressure in the blood vessels to properly match the pressures in the tissues/cells and constantly strives for this state. Generally speaking, water follows albumin and sodium. More precisely, both of those substances are capable of pullingwater and retaining water. This is an important principle for understanding thedifferent uses of IV fluids. Through various mechanisms, the body tried to keep the balance. Hence, if there is too much sodium in the blood plasma (hypernatremia), water will be pulled from the cells into the bloodplasma. Osmolality Osmolality (tonicity) is the concentration of solutes (such as sodium or albumin) in a fluid (such as plasma or intracellular fluid). When thinking of tonicity/osmolality, think about concentrated orange juice (such as the type that one gets in the freezer section in a little can). • Concentrated orange juice (still in the can, still a big frozen lump) is hypertonic. • Reconstituted orange juice (thawed, water added, normal drinkable OJ) is isotonic. • Watered down orange juice (you put a couple of cans too many of waterin when reconstituting it) is hypotonic. Now imagine your blood plasma is made up of orange juice. If the blood plasma becomes too concentrated (through dehydration, vomiting, etc), your body is going to be looking for some water to bring it back to a normal state. It is going to try to pull water from the cells. If the plasma gets too Physiology Kidneys regulate the ECF and osmolality by selective retention and excretion of body fluids. The kidneys regulate electrolyte levels in the ECF by selective retention of needed substances and excretion of unneeded substances. Kidneys regulate the pH of ECF by retention of hydrogen ions. The kidneys excrete metabolic wastes and toxic substances. The antidiuretic hormone regulates water excretion from the kidney and is synthesized in the anterior portion of the hypothalamus. When the serum osmolality rises, ADH is produced causing the collecting ducts to become more permeable to water. The renin-angiotensin-aldosterone system is made up of receptors in the juxtaglomerular cells of the nephrons, which respond to changes in renal perfusion. Increased aldosterone causes sodium (Na+) retention (water retention) and potassium (K+) loss. Decreased aldosterone causes sodium and water loss and potassium retention. Atrial natriuretic factor (ANF ) is released from cells in the atrium of the heart in response to excess blood volume and stretching of atrial walls. ANF acts on nephrons to promote sodium wasting and as a diuretic, reducing volume. The pumping action of the heart circulates blood through the kidneys under enough pressure to form urine. The lungs remove 300 ml of water daily. The parathyroid hormone (PTH) influences bone reabsorption. Calcium is absorbed from the intestines and calcium is reabsorbed from the renal tubules. There are two types of fluid pressure in the body: Colloid osmotic pressure (oncotic pressure) and hydrostatic pressure .