a. The first reaction is as follows:
CO2 + H2O --------------------------> H2CO3 (carbonic acid)
H2CO3 ------------------------------> H+ + HC03-(bicarbonate ion)
The bicarbonate ion is formed due to the pH of red blood cells, which is maintained by
buffer systems. Once formed, the bicarbonate ions diffuse back into the plasma. About
60 percent of the carbon dioxide is transported in the plasma as bicarbonate ion.
b. The second reaction is as follows:
CO2 + hemoglobin ------------------> carbaminohemoglobin
Actually, very little carbon dioxide is transported in association with hemoglobin.
c. An unusual chemical phenomenon occurs in deoxygenated RBCs. It is
accepted that cells of our body possess "sodium pumps" which constantly remove
sodium ions from cells. To balance the lost positive charge, chloride ions generally
follow sodium ions and are in high concentrations in the extracellular fluids. In
deoxygenated RBCs, the concentration of carbonic acid is high. As carbonic acid
ionizes, bicarbonate ions move out of corpuscles at an increased rate. To compensate
for the loss of negative charges inside RBCs, chloride ions move from the extracellular
fluid into the blood corpuscles. This phenomenon is termed the chloride shift.
Section VI. THE NERVOUS SYSTEM
a. Introduction. The nervous system is made up of tissue specialized to
respond to stimuli by conducting impulses. The unit of structure is the nerve cell
(neuron), which consists of a cell body and its nerve fibers (figure 110). Neurons are
classified according to their functions. An association neuron is one that carries
impulses from one part of the central nervous system (brain and spinal cord) to another.
An afferent (sensory) neuron is one that carries impulses from a receptor (sense organ)
to the central nervous system. An efferent (motor) neuron is one that carries impulses
from the central nervous system to an effector (a muscle or gland), causing it to act.
The nervous system is the integrating mechanism for intellectual and physical activities.
b. Divisions of the Nervous System. For the purpose of study, parts of the
nervous system may be considered separatelythe central nervous system, the
peripheral nervous system, and the autonomic nervous system.