Page 21 - Anatomy and Physiology of Farm Animals, 8th Edition

6 / Anatomy and Physiology of Farm Animals

(use of food), response to stimuli (such as the hierarchy of the organization of these
cells is important when describing the anat-
moving toward light), contraction (short-
VetBooks.ir ening in one direction), and reproduction omy of an animal. A group of specialized
cells is a tissue. For example, cells that spe-
(development of new individuals of the
same species). cialize in conducting impulses comprise
A typical eukaryotic cell is always sur- nervous tissue whereas cells that specialize
rounded by a cell membrane. Within the in holding structures together make up con-
cell membrane are the organelles of the nective tissue. Various tissues are associated
cell, suspended in the liquid‐like cytoplasm in functional groups called organs. The
that fills the cell. The most important stomach is an organ that functions in diges-
organelle, and the defining feature of tion of food. A group of organs that partici-
eukaryotic cells, is the membrane bound pate in a common enterprise make up a
nucleus that contains the genetic material system. For example, the stomach, liver,
for the organism (Fig. 1‐2). Detailed infor- pancreas, and intestines are all organs that
mation about the remaining organelles are part of the digestive system.
and the structure of the individual cell is The primary types of tissues include:
described in Chapter 2. Tissues are dis- (1) epithelial tissues, which cover the
cussed in this chapter. surface of the body, line body cavities, and
In complex animals, cells specialize in form glands; (2) connective tissues, which
various functions to support the animal and support and bind other tissues together
and from which, in the case of bone marrow,
the formed elements of the blood are
c d derived; (3) muscle tissues, which specialize
in contracting; and (4) nervous tissues,
which conduct impulses from one part of
the body to another.
b

Epithelial Tissues

In general the nonglandular epithelial tissues
are classified as simple (composed of a single
a layer) or stratified (many‐layered). Each of
these types is further subdivided according
to the shape of the individual cells within it
(Fig. 1‐3). Simple epithelium includes squa-
mous (platelike) cells, cuboidal (cubic) cells,
columnar (cylindrical) cells, and pseu-
e
dostratified columnar cells. The shape of the
cells and the number of layers are then used
f together to specifically describe a type of
epithelial tissue that often has a specific
Figure 1-2. A cell as seen with an electron function. Since epithelial tissues form the
microscope. The lightly colored areas in the outer covering of many organs, they are
nucleus (euchromatin) indicate that this hepatic responsible for forming barriers, preventing
(liver) cell is actively undergoing transcription. a,
rough endoplasmic reticulum; b, microvilli; c, bacteria or other materials from crossing the
mitochondrion; d, nuclear envelope; e, nucleolus; f, barrier. This epithelial barrier must still allow
plasma membrane. Source: image courtesy the organ to function in secreting, absorbing,
of D.N. Rao Veeramachaneni, BVSc, MScVet, excreting, or transporting other molecules
PhD, Professor of Biomedical Sciences, Colorado and macromolecules, or conveying sensory
State University. information such as taste from the tongue.