Page 39 - Anatomy and Physiology of Farm Animals, 8th Edition

24 / Anatomy and Physiology of Farm Animals

called catabolic. The oxidation of carbon protein, 10%; lipid, 2%; inorganic matter,
1.5%; and other substances, including
compounds to carbon dioxide and water,
VetBooks.ir with the release of energy, is a catabolic carbohydrates, 1.5%. Note: throughout the
text, clinical extracts are set in blue type.
reaction.
The secretion of products synthesized These are examples of the application of
by the cell into the extracellular fluid that basic anatomy and/or physiology in clinical
surrounds the cells occurs by exocytosis settings.
(Fig. 2‐1), which is essentially the opposite
of endocytosis. Membrane‐bound secretory
vesicles containing substances synthesized Water
within the cell and packaged by the Golgi
apparatus migrate in the cytoplasm to the Each cell is about 60 to 65% water. Water is
plasma membrane. Here the membrane by far the largest constituent of proto­
of a secretory vesicle fuses to the exterior plasm, which is largely a colloidal suspen­
cell membrane, an opening appears at the sion in water. Water acts as a solvent for
point of fusion, and the contents of the inorganic substances and enters into many
vesicle are released into the extracellular biochemical reactions.
fluid (ECF). Membrane fusion, either as two Most body water is within cells, and
vesicles within the cell or as a vesicle to the this fluid volume is called intracellular
cell membrane, often requires assistance fluid. This fluid volume is about 40% of
from SNARE proteins to ensure appropriate body weight. The remaining fluid (about
membrane fusion. The toxins produced by 20% of body weight), found outside of
the bacteria that cause botulism and tetanus cells, is termed extracellular fluid. Most
both target SNARE proteins and thus ECF (about 15% of body weight) surrounds
prevent normal vesicle fusion. cells throughout the body and is termed
Irritability (also called excitability) is interstitial fluid. Unique interstitial fluids
the property of being able to react to a include the cerebrospinal fluid, the fluid
stimulus. The reaction must necessarily around joints (synovial fluid), the fluid in
consist of one of the other properties of the eyes (aqueous and vitreous humors),
protoplasm, such as conduction, contrac­ and the serous fluid in the visceral spaces
tion, or secretion. (i.e., pericardial, pleural, and peritoneal
Conductivity is the property of trans­ spaces). Blood plasma, a specific type of
mitting an electrical impulse from one ECF, is about 5% of total body weight. The
point in the cell to another. This property is percentages for the different types of body
discussed in more detail later in this chapter. fluids vary from one animal to another.
Nerve cells and muscle cells are specialized Factors affecting these percentages include
for conductivity and irritability. condition (amount of fat), age, state of
Contractility is the ability to shorten in hydration, and species.
one direction. Muscle cells are specialized Water is constantly lost from the body,
for contractions, although many other cells and it must be replenished if the animal is
and cell organelles also contain contractile to remain in water balance and not
proteins and exhibit limited movement become dehydrated. Most is lost via the
(e.g., cilia). urine, but it is also lost in the feces and by
evaporation from body surfaces, such as
the skin and respiratory passages. Water
Chemical Composition of the Cell replacement for hydration is almost
entirely by drinking because minimal
Chemical composition of various parts of amounts of water are produced in the
the cell plays an important role in cellular bodies of domestic animals as a result of
function. The approximate composition of cellular metabolism (metabolic water).
protoplasm by constituent is: water, 85%; This orogastric (mouth–stomach) route