Essentials of Anatomy and Physiology

The mucussecreted by these membranes keeps the
lining epithelial cells wet. Remember that these are
living cells, and if they dry out, they will die. In the
digestive tract, mucus also lubricates the surface to
permit the smooth passage of food. In the respiratory
tract the mucus traps dust and bacteria, which are then
swept to the pharynx by ciliated epithelium.

CONNECTIVE TISSUE MEMBRANES

Many membranes are made of connective tissue.

Because these will be covered with the organ systems

of which they are a part, their locations and functions

are summarized in Table 4–5.

AGING AND TISSUES

As mentioned in the previous chapter, aging takes

place at the cellular level, but of course is apparent in

the groups of cells we call tissues. In muscle tissue, for

example, the proteins that bring about contraction

deteriorate and are not repaired or replaced. The same

is true of collagen and elastin, the proteins of connec-

tive tissue such as the dermis of the skin. Other aspects

of the aging of tissues will be more meaningful to you

in the context of the functions of organs and systems,

so we will save those for the following chapters.

SUMMARY

The tissues and membranes described in this chapter

are more complex than the individual cells of which

they are made. However, we have only reached an

intermediate level with respect to the structural and

functional complexity of the body as a whole. The fol-

lowing chapters are concerned with the organ systems,

the most complex level. In the descriptions of the

organs of these systems, you will find mention of the

tissues and their contributions to each organ and

organ system.

84 Tissues and Membranes

Table 4–5 CONNECTIVE TISSUE

MEMBRANES

Membrane Location and Function

Superficial

fascia

Periosteum

Perichondrium

Synovial

Deep fascia

Meninges

Fibrous

pericardium

• Between the skin and muscles;
  adipose tissue stores fat


• Covers each bone; contains
  blood vessels that enter the
  bone


• Anchors tendons and ligaments


• Covers cartilage; contains capil-
  laries, the only blood supply for
  cartilage


• Lines joint cavities; secretes syn-
  ovial fluid to prevent friction
  when joints move


• Covers each skeletal muscle;
  anchors tendons


• Cover the brain and spinal cord;
  contain cerebrospinal fluid


• Forms a sac around the heart;
  lined by the serous parietal peri-
  cardium

STUDY OUTLINE

A tissue is a group of cells with similar struc-
ture and function. The four main groups of
tissues are epithelial, connective, muscle, and
nerve.

Epithelial Tissue—found on surfaces; have no
capillaries; some are capable of secretion;
classified as to shape of cells and number of
layers of cells (see Table 4–1 and Figs. 4–1,
4–2, and 4–3)

1. Simple squamous—one layer of flat cells; thin and
   smooth. Sites: alveoli (to permit diffusion of gases);
   capillaries (to permit exchanges between blood and
   tissues).


2. Stratified squamous—many layers of mostly flat
   cells; mitosis takes place in lowest layer. Sites: epi-
   dermis, where surface cells are dead (a barrier to
   pathogens); lining of mouth; esophagus; and vagina
   (a barrier to pathogens).


3. Transitional—stratified, yet surface cells are