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Chapter 40: AN INTRODUCTION TO ANIMAL STRUCTURE AND FUNCTION
Animals provide vivid examples of biology’s overarching theme: evolution.
As a consequence of evolutionary adaptation,
structure and function are correlated (“form follows function”).
Which is the better utensil: a spoon or a fork?
The answer, of course, depends on what you are trying to eat.
The long, tongue-like proboscis of the hawk moth is a structural adaptation
for sucking nectar from deep within tube-shaped flowers.
The foraging hawk moth illustrates another major theme: regulation.
While natural selection provides a mechanism for long-term adaptation,
organisms also evolve behavioral & physiological mechanisms
to adjust to short-term environmental change.
The hawk moth Manduca sexta can forage when air temperatures are as low as 5°C.
It uses a shivering-like mechanism for preflight warm-up of its muscles.
Once the moth takes off, metabolic activity of its flight muscles generates heat,
and regulatory adaptations maintain muscle temperature near 30°C
even though the external temperature may be close to freezing.
All animal activities require fuel in the form of chemical energy.
Bioenergetics - how organisms obtain, process, and use energy –
is another theme in our comparative study of animals.
Animals are multicellular organisms with their specialized cells grouped into tissues.
Tissues are groups of cells with a common structure and function.
Combinations of various tissues make up functional units called organs,
and groups of organs that work together form organ systems
All organs are made of the four basic tissue types.
http://mindquest.net/biology/histology/index.html
Epithelial tissue functions to protect surfaces (e.g. skin),
secrete material (e.g. glands), or absorb material (e.g. intestine).
{& left: kidney tubules reabsorb solutes}
Connective tissue connects body parts, holding the body together.
There are many subtypes of connective tissue,
including bone, cartilage, ligaments & tendons, adipose (fat) tissue,
areolar (loose irregular) connective tissue, and
blood (connective tissue because it derives from bone marrow).
Muscle cells (ch 49) have the ability to contract/shorten.
This allows muscle tissue to function for providing movement …
There are three subtypes of muscle tissue:
skeletal muscle, smooth muscle, and cardiac (heart) muscle.
Nerve cells, (ch 48) known as neurons,
are specialized for conducting electrical signals in the body.
{we’ll look at muscles and nerves later}
Epithelial tissue functions to
http://mindquest.net/biology/histology/epithelial-tissue.html
protect surfaces (eg skin), secrete material (eg glands), absorb material (eg intestine).
Epithelial tissue … lines internal & external body surfaces …
… the mouth, esophagus, uterus and vagina, ducts of the pancreas and liver,
blood vessels (where it is called endothelium), urethra and ureters,
tubules of the kidney, air sacs (alveoli) of the lungs, and many other sites.
Epithelial tissue is classified
according to
(1) the shape of the outermost cell layer
squamous [flat],
cuboidal,
columnar,
or transitional,
(2) whether or not the tissue is
one layer thick (simple epithelium)
or multiple layers (stratified epithelium),
and
(3) whether or not the cells are
ciliated
or secrete …
http://www.mc.vanderbilt.edu/histo/BasicTissue/Epith.Definition.html
Characterisitics of epithelial
cells:
They are contiguous
Fig 7.30
(i.e., the cells are attached to one another w/ tight junctions).
Epithelia are avascular … blood vessels do not penetrate up between these cells …
Unlike muscle and connective tissue, they can be derived from any of the three
embryologic germ layers (endoderm, mesoderm, ectoderm).
A major cytoskeletal component of epithelial tissue is the filament called keratin
{ the main component of: mammal hair, reptile scales, (though not fish scales),
bird feathers, claws (including nails and hooves), horn (but not antlers),
baleens (the sieve-like structures with which whales filter food out of water),
& the enamel of the teeth }.
… rest on an extracellular matrix which they produce … the basement membrane.
http://mindquest.net/biology/histology/epithelial-tissue.html
… basement membrane …
A thin sheet of collagen …
made up of glycosaminoglycan (mucopolysaccharide)
and fibrous material.
In some tissues, such as the kidney lung,
the basement membrane acts as a filter.
Glandular epithelia, absorb or secrete chemical solutions.
Endocrine glandular epithelia secrete hormones into the blood (Ch. 45)
The exocrine glandular epithelia that line the lumen (cavity)
of the digestive and respiratory tracts form a mucous membrane;
they secrete a slimy solution called mucus
that lubricates the surface and keeps it moist.
The epithelium of our respiratory tract has beating cilia
that move the film of mucus along the surface:
helps keep our lungs clean by trapping dust and other particles
and sweeping them back up the trachea (windpipe).
cell
http://courseweb.edteched.uottawa.ca/medicine-histology/English/Reproduction/Mammary/Mammary_repro.htm
In the inactive mammary gland, the glandular elements consist only of ducts:
lined by cuboidal or columnar epithelium for most of their length,
by two layers of cuboidal cells in the lactiferous sinus,
and, near their opening, by stratified squamous epithelium.
Dramatic changes in the mammary gland occur during pregnancy.
Ducts proliferate and secretory alveoli sprout from them.
Alveoli are collections of cuboidal or low columnar epithelial cells
that become active milk-secreting structures.
The lipid component of the milk
is released by apocrine secretion,
in an envelope of plasma membrane.
The protein component of the mile
is released by merocrine secretion.
The inactive mammary gland undergoes slight changes during the menstrual cycle;
slight development of secretory alveoli may begin,
lumina appear in the ducts …
… an increasing number of menstrual cycles
increases the stimulation
of breast ductal epithelial cells
and one’s risk of breast cancer.
… the risk for breast cancer is associated
with lifetime exposure to estrogen.
Connective Tissue functions mainly to bind and support other tissues.
… has a sparse population of cells scattered through an extracellular matrix.
The major types of connective tissue in vertebrates are
Bone,
Adipose tissue
Blood,
Cartilage,
Fibrous connective tissue
Loose connective tissue.
Loose connective tissue,
binds epithelia to underlying tissues and holds organs in place.
… gets its name from the loose weave of three fiber types:
collagenous (collagen),
elastic (elastin),
reticular (collagen & elastin).
Among the cells scattered in the fibrous mesh of loose connective tissue:
Fibroblasts secrete the protein ingredients of the extracellular fibers.
Macrophages roam the maze of fibers, engulfing bacteria and debris.
• more cows will be boiled !
Fibrous connective tissue is dense, due to its large numbers of collagenous fibers.
The fibers are organized into parallel bundles … maximizes nonelastic strength.
in tendons, which attach muscles to bones,
and in ligaments, which join bones together at joints.
http://www.nlm.nih.gov/medlineplus/ency/article/001074.htm#visualFile
Anterior cruciate ligament (ACL)
The “unhappy triad” is where the ACL is torn at the same time as the MCL
and the lateral meniscus (one of the shock absorbing cartilages in the knee).
This type of injury is most often seen in football players and skiers.
Women are much more likely to suffer an ACL tear than men are.
These injuries do not heal by themselves.
Cartilage has an abundance of collagenous fibers embedded in
a rubbery matrix of chondroitin sulfate, a protein-carbohydrate complex.
… secreted by cells called chondrocytes.
… a strong yet somewhat flexible support material.
The skeleton of a shark is made of cartilage.
Other vertebrates have cartilaginous skeletons during the embryo stage,
but most of the cartilage is replaced by bone as the embryo matures.
We nevertheless retain cartilage as flexible support in certain locations,
such as the nose, the ears, the rings that reinforce the windpipe,
the discs that act as cushions between our vertebrae {remnant of notocord},
and the caps on the ends of some bones.
… articular (meniscus) cartilage
lining the bones of your knee joint
has limited ability to heal itself.
Blood capillaries do not penetrate
the joint capsule.
{similar to ‘the blood-brain barrier’} .
Synovial fluid, secreted by
synovium (membranes),
lubricates the joint and
carries nutrients to the cartilage.
Rheumatic diseases are connective tissue diseases.
An example of a connective tissue disease is scleroderma,
a disease in which the body overproduces collagen
Arthritis means joint inflammation.
… arthritis is a kind of rheumatic disease.
Osteoarthritis, the most common type, affects cartilage,
the tissue that cushions the ends of the bones
within the joints.
Some rheumatic diseases are also autoimmune diseases.
… occur when the body's immune system
mistakes the body's own healthy cells and tissues
as invaders and attacks them.
Rheumatoid arthritis is an autoimmune disease
… the immune system
attacks a person's own synovium,
the tissue inside the joint capsule.
http://www.skinbiology.com/liposuctionfattransplants.html
What is Cellulite?
Cellulite is the appearance of
an unattractive “dimpled fat”
on the around the outer thighs, buttocks
and other body areas where large areas of fat
are found in close proximity to the skin.
Women are more affected by cellulite
formation than men, especially on the thighs,
exemplified by the women
in the John Paul Rubens painting at left.
The scientific theory of cellulite is that the skin's underlying supports
{loose & fibroius connective tissue} do not hold the skin together evenly
and this uneven support causes the irregular bulging and dimples.
The skin is tethered down by string-like tissues that pull it inward …
The tension of these strings pulls sections of fat in along with them.
Cellulite has been compared to the dimples in a mattress
that are caused by the strings that hold the “tucks” down.
Bone is a a mineralized connective tissue.
Bone-forming cells called osteoblasts deposit a matrix of collagen.
Calcium, magnesium, and phosphate ions combine and harden within the matrix
into the mineral hydroxyapatite.
The microscopic structure of hard mammalian bone consists of
repeating units called osteons (or Haversian systems).
Each osteon has concentric layers of the mineralized matrix,
which are deposited around a central canal
containing blood vessels and nerves that service the bone.
Blood functions differently from other connective tissues,
but it does have an extensive extracellular matrix: a liquid called plasma,
consisting of water, salts, and a variety of dissolved proteins.
Suspended in the plasma are two classes of blood cells,
erythrocytes (red blood cells) and leukocytes (white blood cells),
and cell fragments called platelets.
Blood will be discussed later (Chapters 42 and 43).
Muscle tissue is composed of long cells called muscle fibers
that are capable of contracting when stimulated by nerve impulses.
Arranged in parallel within the cytoplasm of muscle fibers
are large numbers of myofibrils
made of the contractile proteins
actin and myosin. {more in ch 49}
Nervous tissue senses stimuli and transmits signals
from one part of the animal to another.
The functional unit of nervous tissue is the neuron, or nerve cell,
which is uniquely specialized to transmit nerve impulses.
{more in ch 48}
In all but the simplest animals (sponges and some cnidarians),
different tissues are organized into organs.
Organ systems carry out the major body functions of most animals
Bioenergetics
and The Internal Environment
Today: Metabolism & Thermoregulation (in homeotherms)
Teeth
and
Guts are great indicators of diet
but teeth fossilize better
& are very important
to paleontologists.
There are still raging battles
over the ‘natural’ diet
for humans,
but teeth & guts indicate
our ancestors were
omnivorous.
Allometry (scaling):
Metabolism & Body Weight
across homeotherms
Kleiber’s ‘Law’
(an empirical phenomenon)
BMR  Mass .75
log (BMR)  log(Mass .75)
= .75 x log(Mass)
on log-log scale,
straight line w/ slope = 0.75
Mass specific metabolic rate:
BMR  Mass .75= Mass -.25
Mass Mass
Metabolic rate is conveniently
measured by oxygen consumption.
the mouse-to-elephant curve
Measurements and estimates on Sasquatch dimensions {bigfoot prints}
… were subjected to statistical analysis & extrapolation
by scaling laws appropriate to primates & mammals.
The principle of allometric scaling consists of fitting a straight line
to a logarithmically transformed, bivariate data set,
generally derived from many different related species, according to the formula
Y = a * Xb
where
Y = some specific aspect of the animal under investigation,
be it a morphological, ecological or physiological variable;
a = the allometric coefficient, a constant which defines the intercept on the Y axis;
X = some measure of body size, generally weight; and
b = allometric exponent or scaling factor, which defines the slope of the line.
The female seems to reach sexual maturity at about age 9 - 10,
by which time she will be near 6' in height.
Scaling formulae exist to calculate biological aspects
such as respiratory rate, heart rate and blood volume … but
it behoves me not to pursue speculative aspects of this subject ad absurdum. {!!!!}
http://www.biology.iupui.edu/biocourses/K341/Temperature.html
Metabolism & Ambient temperature
When enzymatic reactions
& ectotherms warm up,
they run faster.
When endotherms
warm up (a  b) they
metabolize less
(less heat loss)
In general,
flow = force/resistance;
ex: current = voltage/resistance
Newton’s Law of Cooling:
heat flow = (Temp gradient)/Insulation
= (tbody - tenv )/ I
Rearrange to form
y
= a x+
b:
heat flow = -(1/I) tenv + (1/I)tbody
& recall at equilibrium
in = out
heat generated = net heat flow
x intercept = tbody
Thermoregulation: Negative
Feedback.
(Mechanisms in ch 44.)
Negative feedback is the basis of regulation,
from body temperature, to population dynamics
and the whole vague ‘balance of nature’ - Gaia
a generic -FB system
at equilibrium, gains = losses
generate + in = out
error signal = ts - tb
set
point
‘normally’ ts  37c
+
-
effector
vasoconstrict (save)
shiver (generate)
etc. (or vice versa)
comparator in hypothalamus
various blood
temp sensors
sensor
in & out
from env
core body temp tb
because of -FB,
tb cycles around ts
thing being
controlled
Negative Feedback: Thermoregulation
at equilibrium, gains = losses
generate + in = out
error signal = ts - tb
set
point
‘normally’ ts  37c
+
-
effector
vasoconstrict (save)
shiver (generate)
etc. (or vice versa)
comparator in hypothalamus
various blood
temp sensors
in & out
from env
core body temp tb
because of -FB,
tb cycles around ts
thing being
controlled
sensor
1. Suppose a dramatic increase in loss of heat to environment?
2. Suppose an increase in the hypothalamic set point?
3. Suppose a decrease in the hypothalamic set point?
http://plpk04.plpk.uq.edu.au/webtuts/SDL_skin/fever.htm
Fever is a controlled rise of temperature as a result of infection or inflammation the body behaves as if its thermostat has been reset at a higher temperature.
Fever is triggered by the release of endotoxins from bacteria
or breakdown products from degenerating tissues.
These are phagocytosed by white blood cells
which then release endogenous pyrogens
(cytokines such as interleukin 1).
These cytokines, which are polypeptides,
may act by triggering the release of prostaglandins
which act on the hypothalamus
to increase the temperature of the 'setpoint'.
The new setpoint is maintained by heat regulating mechanisms
NOTE: Shivering as fever starts when the body feels it is too cold.
Fever 'breaks' with sweating and vasodilation
when the 'setpoint' goes back to normal and
the body tries to cool down at the end of the illness.
Aspirin reduces fever (antipyretic) by acting on the hypothalamus,
probably by inhibiting the synthesis of prostaglandins.
Fever may be beneficial; the increased temp
may inhibit bacterial multiplication and
antibody production is increased when the temperature is higher.
Evolution and
Adaptive Value Of Fever
Kluger M. 1978.
American Scientist 66:38-43.
Dipsosaurus
prefers
tbody = tenv = 38C
32C
38C
If infected and
confined to
34C
32C
most infected but cold
Dipsosaurus die
Control: most uninfected but cold
Dipsosaurus live
42C
after infect
w/ bacteria
38C
42C
Dipsosaurus prefers
tbody = tenv = 41C
and most recover
Both of these mice have a defect in a gene called obese (ob).
This mutation results in a marked increase in the amount of fat.
Administration of the protein encoded by the ob gene, called leptin,
reduced the body weight of the ob mice. After four and a half weeks,
the ob mouse on the left, which did not receive leptin, weighed 67 grams
while the mouse on the right, who received injections of leptin, weighed 35 grams.
… the treated animals ate less and also burned more calories. {leptin = diet suppressor pill?}
Body fat mass, leptin and puberty.
Kiess et al. 2000. J. Ped. Endo. & Metab 13:717-722.
… By modulating the hypothalamo-pituitary-gonadal axis both directly and indirectly,
leptin may thus serve as the signal from fat to the brain
about the adequacy of fat stores for pubertal development and reproduction.
Normal leptin secretion is necessary for normal reproductive function to proceed
and leptin may be a signal allowing for the point of initiation of and progression
toward puberty.
Body mass index and age at menarche in an adolescent clinic population.
Lin-Su et al. 2002. CLINICAL PEDIATRICS 41: 501-507.