Introduction to Human Physiology PDF

Introduction to Human Physiology Compositional differences between fluid compartments of the body Body fluid compartments in the human body water constitutes a high proportion of body weight. The total amount of fluid or water within the body is called the total body water. Normally, t...

Introduction to Human Physiology Compositional differences between fluid compartments of the body Body fluid compartments in the human body water constitutes a high proportion of body weight. The total amount of fluid or water within the body is called the total body water. Normally, this accounts for 50 to 70% of body weight. In general, total body water correlates inversely with body fat; hence, more body fat would translate to a lower percentage of total body water. Total body water is distributed between two major fluid compartments within the body: the intracellular fluid and the extracellular fluid. The intracellular fluid is contained within the cells and makes up 2/3 of the total body water, and the extracellular fluid is outside of the cells and makes up the remaining 1/3. The composition of the extracellular fluid is very different from the composition of the intracellular fluid. Maintaining these differences in fluid composition across the cell membrane is an important way in which cells regulate their own activity. The extracellular fluid can be further subdivided into the interstitial fluid and the plasma. The interstitial fluid is the fluid that actually bathes the cells and is the larger of the two subcomponents. The plasma is the fluid circulating in the blood vessels and is the smaller of the two subcomponents. The plasma and the interstitial fluid are separated by a capillary wall. The movement of fluid across this interface is essentially an ultrafiltration of plasma. The nature of this interface, the size of the gaps between capillary cells, and the negatively charged glycoproteins of the basement membrane mean that the capillary wall is virtually impermeable to plasma proteins, producing an interstitial fluid that is almost protein-free. Compartmentalization is an important feature in physiology and is achieved by barriers between compartments. These barriers can be thought of as free energy barriers that