Page 289 - Anatomy and Physiology of Farm Animals, 8th Edition

274 / Anatomy and Physiology of Farm Animals

Integument attachment is exploited by veterinarians
who frequently inject medications or fluids
VetBooks.ir The integumentary system comprises the for rehydration into the space underneath

the skin (a subcutaneous injection), espe-
skin with its adnexal structures (e.g., hair
and glands), horns, hoofs, claws, and other cially in small animals.
modifications of the epithelial covering of
the body. The skin is an important protec- Epidermis
tive barrier which reduces water loss,
invasion by microorganisms, and abrasive The outer layer of skin, the epidermis, is an
trauma. For many species, it is an impor- avascular stratified squamous epithelium
tant organ of thermoregulation through that is nearly free of nerve endings. In most
perspiration, control of cutaneous blood areas it can be divided into several histo-
flow, and disposition of the hair coat. logic layers (Fig. 14‐1). They are as follows,
Modifications of the integument are used from deep to superficial: (1) a layer of
for protection (claws and horns) and pro- mitotically active cuboidal or columnar
vide a tough covering to the feet where cells, the stratum basale, follows the
they contact the ground (hoofs and contour of the underlying dermis, to which
footpads).
All the components of the integument it is closely applied; (2) the stratum spino-
sum has a spiny appearance because of
may be considered modifications of the desmosomes (intercellular bridges) con-
surface epithelium, derived from the
embryonic ectoderm, in conjunction with necting adjacent cells; (3) the stratum
granulosum consists of spindle‐shaped
an underlying vascularized component cells containing basophilic keratohyalin
derived from mesoderm (see Chapter 3). granules; (4) the stratum lucidum, which
In fully developed skin, these become the is variably present, comprises cells that are
superficial epidermis and deep dermis, poorly stainable; (5) the stratum corneum
respectively. Specialized integumentary consists of layers of dead, flattened cells.
structures, such as hoofs and horns, like- Presence and relative thickness of each
wise have homologous superficial epithe- layer is reflected in the overall thickness of
lial and deep connective tissue components. the skin (Fig. 14‐1).
The latter in these specialized structures is
often called corium, although it is homolo-
gous to the dermis.

Skin

Skin covers the outside of the animal and is
continuous with mucous membranes at
oral, anal, and urogenital orifices, the vesti-
bule of the nostril, and the palpebral fis-
sure; these sites are characterized by a
mucocutaneous junction. Thickness of
skin varies both between species and on a
given individual, being generally thickest Figure 14-1. Epidermis from pig snout, 10×. a,
where it is most exposed (e.g., on the back) stratum corneum; b, stratum granulosum; c, stra-
and thinner in protected regions (e.g., the tum spinosum; d, stratum basale; e, dermis. The
groin). The skin adheres tightly to underly- stratum lucidum is not evident in this section.
ing structures in some locations, but in Source: micrograph courtesy of Gretchen
others is loosely attached to allow for con- Delcambre, Colorado State University, Fort
siderable movement. The looseness of skin Collins, Colorado, USA.