Lecture #5: Animal Structure and Function
I. INTRODUCTORY
REMARKS ABOUT CELLS, TISSUES, ORGANS, AND ORGANISMS
1. As
multicellular organisms evolved, their bodies developed (thru trial and error)
a variety of systems that allowed cells to metabolize and survive as a
conglomerate.
2. In the course
of this increasing complexity, cells joined into groups (tissues) that
had common structure and function. (tissue = "weave")
3. different
tissues became organized into specialized centers of function called organs,
such as the stomach, heart, brain, etc.
4. Several
related organs can cooperate as an organ system such as the digestive,
circulatory, and nervous systems.
5. The various
efforts of all the different organ systems of an organism must be
combined and coordinated for the animal to survive, and the bulk of this
coordination is carried out by the endocrine and nervous systems.
II. TYPES OF
ANIMAL TISSUES
A. EPITHELIAL
TISSUES
1. Covers outside
of the body and lines organs and cavities. (Fig 40.1)
2. Simple
epithelium (single layer) versus stratified epithelium (multiple
tiers).
3. Cells at
surface may be cuboidal (dice), columnar (bricks), or squamous
(tiles).
4. Epithelial
tissues are usually attached to a basement membrane, or basel lamina.
5. Cells are
closely joined, sometimes by tight junctions.
6. This tight
packing protects against mechanical injury, microbes, and fluid loss.
7. Epithelial
layers called mucous membranes secrete a slimy solution that lubricates
a surface and keeps it moist (e.g., the GI tract and respiratory system).
8. Some mucous
membranes have beating cilia (e.g., oviducts and respiratory tubes).
B. CONNECTIVE
TISSUES
1. This type
tissue has sparse cells scattered through an extracellular matrix.
2. The non-living
matrix generally consists of a web of fibers embedded in a homogenous ground
substance that may be liquid, jelly-like, or solid.
3. Types of
connective tissue: (Fig. 40.2)
a. "Loose"
connective tissue (the most common) is based on three kinds of fibers:
(1) collagenous
fibers (most abundant protein in animal kingdom).
(2) elastic
fibers (made of protein) have a resilience that complements collagen.
(3) reticular
fibers join connective tissue to adjacent tissues. (in loose connective
tissue, the cells are mainly fibroblasts and macrophages.)
b. Fibrous
connective tissue is "dense" due to high concn of collagen
fibers. (Fig. 40.2)
c. Cartilage
has collagen fibers in a rubbery ground substance called chondrin. (Fig. 40.2)
d. Bone
is based on a collagen matrix deposited by osteoblasts along with
calcium phosphate that hardens into hydroxyapatite. (Haversian systems)
(Fig. 40.2)
e. Adipose
tissue is a specialized form of loose connective tissue that stores fat
in a single large fat droplet in the adipose cells. (Fig. 40.2)
f. Blood
is an extraspecialized form of loose connective tissue imbedded in a fluid
matrix called plasma. (red cells, white cells, and platelets) (Fig. 40.2)
C. TYPES OF
VERTEBRATE MUSCLE (skeletal, cardiac, and smooth) (Fig 40.4)
1. Muscle
consists of elongated excitable cells capable of contraction.
2. Muscle
tissue is the most abundant tissue in most mammals (to allow motility).
a. skeletal
muscle is responsible for voluntary movement (striated).
b. smooth
(visceral) muscle is responsible for involuntary movements of organisms.
(i.e., GI tract, bladder, arteries, and other internal organs)
c. cardiac
muscle is sort of a mixture, with intercalated discs that fuse the
branching cardiac cells into a syncytium. (it has intrinsic rhythmicity)
III.
THE INTERNAL VERSUS THE EXTERNAL ENVIRONMENT
1. Body size and
shape have certain limits (e.g. whales versus protazoans).
2. Life involves
a constant interaction between the external environment and the internal
environment of the organism. (Fig. 40.8)
3. The digestive,
respiratory, circulatory, and excretory systems all have specialized
exchange surfaces to help achieve the needs of the internal environment
from the external environment.
4. In simplest
terms, organisms must maintain a constant internal environment--in
essence a constant physical (temperature, osmolarity, etc) and chemical (pH,
electrolytes, glucose, etc) environment for every cell.
IV. REGULATING
THE INTERNAL ENVIRONMENT
1. Vertebrate
cells are bathed in an "interstitial fluid". the function of
the vertebrate organ systems is to maintain the consistency of this
interstitial fluid.
2. The French
physiologist Claude Bernard called this constant internal environment,
"le milieu interior".
3. The
maintenance of this internal environment, or interstitial fluid, in a steady
state is known as homeostasis. Thus, one might say that the organ
systems of the body function to maintain homeostasis, i.e., a steady state.
V. THE CONCEPT OF
NEGATIVE FEEDBACK MECHANISMS
1. Most
homeostatic mechanisms (i.e., control mechanisms) in animals operate on the
principle of negative feedback. (Fig 40.9a)
2. This refers to
biological mechanisms that function to "negate" disturbances (usually
arising from the external environment) that alter the steady state of interstitial
fluid in the internal environment of organisms.
3. The control of
body temperature at a constant level, as an example of negative feedback
mechanisms. (Fig 40.9b)