Biology 102
Fall 2001
R. Brundage
Lecture 3: Part III
Protection, Support, and Movement
I.Integumentary System
A.The outer covering of animal bodies is called the integument.
1.For most species, the integument is a tough yet pliable barrier against the
environment.
2.In arthropods, it is a hardened cuticle made of chitin and protein.
B.Vertebrate Skin and Its Derivatives
1.In vertebrates, the integument consists of skin and the structures derived
from epidermal cells, such as scales, feathers, hair, beaks, horns, nails,
and so forth.
2.The skin consists of an outer epidermis and an underlying dermis; a
deeper hypodermis anchors the skin to the body.
C.Functions of Skin
1.The skin covers and protects the body from abrasion, bacterial attack,
ultraviolet radiation, and dehydration.
2.It helps control internal temperature.
3.Its vessels serve as a blood reservoir for the body.
4.The skin produces vitamin D.
5.Its receptors are essential in detecting environmental stimuli.
II.A Look at Human Skin
A.Structure of the Epidermis and Dermis
1.Epidermis is a stratified epithelium.
a.Keratinocytes produce keratin, a tough, water-insoluble protein
that accumulates in the cells.
b.Melanocyte cells produce melanin pigment that darkens the skin
and protects against the sun’s rays; hemoglobin and carotene also
contribute to skin color.
c.The outermost layer (stratum corneum) consists of flattened,
dead cells filled with keratin.
2.The dermis lies beneath the epidermis.
a.Its dense connective tissue cushions the body against everyday
stretching and mechanical stresses.
b.Blood vessels, lymph vessels, and receptors of sensory nerves
are embedded in the tissue.
B.Sweat Glands, Oil Glands, and Hairs
1.Sweat glands produce a fluid that is release in response to stress
(overheating, and fright, for example).
2.Oil glands (sebaceous) lubricate and soften the skin plus they produce
secretions that reduce bacterial populations on the skin.
3.Each hair is a flexible structure rooted in the skin and projecting above it.
III.Types of Skeletons
A.Operating Principles for Skeletons
1.Animals move by the action of muscles, which need some medium or
structural element against which the force of contraction can be applied.
2.There are three main types of skeletons in animals:
a.In hydrostatic skeletons, the force of contraction is applied
against internal fluids.
b.In an exoskeleton, the force is against rigid external body parts,
such as shells or plates.
c.In an endoskeleton, the force is applied against rigid internal
cartilage and bones.
B.Examples From the Invertebrates
1.Sea anemones and earthworms use the fluids in their body cavities as
resistance against which the muscles can act to cause varying degrees of
movement.
2.The rigid exoskeletons of arthropods provide support for bodies deprived
of water’s buoyancy; plus they provide sites for muscle attachments that
maximize leverage.
C.Examples From the Vertebrates
1.Some fishes have a flexible skeleton made of an elastic, translucent form
of cartilage.
2.The cartilage in sharks is opaque and hardened with calcium salts.
3.Vertebrate skeletons are made primarily of bone.
IV.Characteristics of Bone
A.Functions of Bone
1.Bones interact with muscles to maintain or change the position of body
parts.
2.Bones support the skin and soft organs.
3.Bones form compartments that enclose and protect soft internal organs.
4.Bone tissue acts as a depository for calcium, phosphorus, and other ions.
5.Parts of some bones are sites of blood cell production.
B.Bone Structure
1.There are four types of bones: long (arms), short (wrist), flat (skull), and
irregular (vertebrae).
2.Bone is a connective tissue with living cells and collagen fibers
distributed throughout a ground substance that is hardened by calcium
salts.
a.Compact bone tissue forms the bone’s shaft and the outer portion
of its two ends.
1.Concentric layers (lamellae) form Haversian systems
around canals that contain blood vessels and nerves.
2.The living bone cells reside in the ground substance.
b.Spongy bone tissue has areas of red marrow that produces blood
cells; cavities in most mature bones contain yellow marrow,
which can be converted to red marrow if blood cell production
needs to be increased.
3.How Bones Develop
a.Osteoblasts secrete material inside the shaft of the cartilage model
of long bones.
b.Calcium is deposited; smaller cavities merge to form the larger
marrow cavity.
c.Eventually osteoblasts become trapped within their own
secretions and become osteocytes (mature bone cells).
4.Bone Tissue Turnover
a.Bone is renewed constantly as minerals are deposited and
withdrawn during the growth and development processes as well
as in maintenance of body calcium levels.
b.Bone turnover helps to maintain calcium levels for the entire
body; enzymes from bone cells dissolve bone tissue and release
calcium to the interstitial fluid and blood.
c.Osteoporosis (decreased bone density) is associated with
decreases in osteoblast activity, sex hormone production,
exercise, and calcium uptake.
V.Human Skeletal System
A.The 206 bones of a human are distributed in two portions:
1.The axial skeleton includes the skull, vertebral column (individual bones
separated by cartilaginous intervertebral disks), ribs, and sternum.
2.The appendicular skeleton consists of the pectoral girdle with attached
upper limbs, and the pelvic girdle with lower limbs.
B.Skeletal Joints
1.Joints are areas of contact or near-contact between bones.
a.Fibrous joints have no gap between the bones and hardly move;
flat cranial bones are an example.
b.Cartilaginous joints, such as intervertebral disks, permit slight
movement.
c.Synovial joints move freely; they are stabilized by ligaments; a
capsule of dense connective tissue surrounds the bones of the
joint; synovial fluid lubricates the joint.
2.Joints are vulnerable to stress.
a.Stretching or twisting a joint may result in a strain; tearing
ligaments or tendons is a sprain.
b.In osteoarthritis, the cartilage at the end of the bone has worn
away.
c.In rheumatoid arthritis, the synovial membrane becomes
inflamed, the cartilage degenerates, and bone is deposited into the
joint.
VI.Skeletal-Muscular Systems
A.How Muscles and Bones Interact
1.Each skeletal muscle contains several bundles of perhaps hundreds or
thousands of muscle cells (=fibers).
a.Tendons, cordlike straps of dense connective tissue, attach
muscle to bone.
b.Skeletal muscles, often arranged in antagonistic pairs, interact
with one another and with bones.
2.There are three types of muscle tissues: skeletal, cardiac (heart), and
smooth (digestive tract).
B.Human Muscle System
1.The human body has more than 600 skeletal muscles.
2.The major muscles are depicted in Figure 38.18.
VII.Muscle Structure and Function
A.Functional Organization of a Skeletal Muscle
1.A muscle shortens because the contraction units (sarcomeres) are
shortening.
2.Muscle cells (fibers) are composed of myofibrils, which are composed of
two kinds of filaments: actin and myosin.
a.Actin is a thin filament composed of two beaded strands twisted
together.
b.Myosin is thicker; each molecule has a bulbous head and long tail
making it resemble a golf club.
B.Sliding-Filament Model of Contraction
1.Muscles shorten because sarcomeres can shorten within each cell by the
sliding-filament model.
2.Each sarcomere consists of two sets of actin filaments attached to
opposite sides of the sarcomere (at Z-lines) and one set of myosin
filaments extending unattached between the actin filaments.
a.The myosin filaments slide along and pull the actin filaments
toward the center of the sarcomere.
b.Cross-bridges form between the heads of myosin molecules and
actin filaments.
c.The cross-bridges are then activated and tilt inward; then the
heads detach and reattach.
d.ATP supplies the energy for both attachment and detachment.
VIII.Control of Muscle Contraction
A.The Control Pathway
1.Skeletal muscles contract in response to signals from the nervous system
that trigger action potentials along the plasma membrane and into the
interior of the muscle cell.
2.Eventually the signal reaches the sarcoplasmic reticulum (internal tubes),
which responds by releasing stored calcium ions.
B.The Control Mechanism
1.When contraction is not occurring, calcium blocks the binding sites on the
troponin-tropomyosin complex.
2.Under stimulation, the sarcoplasmic reticulum releases calcium ions,
which will bind to the troponin component of actin allowing
cross-bridges to form.
3.A muscle relaxes when calcium ions are actively taken up after contraction
to be stored in the sarcoplasmic reticulum.
C.Sources of Energy for Contraction
1.During periods (few seconds) of intense muscle activity, creatine
phosphate is the source of phosphate to remake ATP.
2.When muscle action is moderate, most of the ATP is provided by aerobic
electron transport phosphorylation, which is dependent on oxygen supply
and number of mitochondria present.
3.During intense and prolonged muscle action, anaerobic glycolysis
produces low amounts of ATP but also results in an oxygen debt.
IX.Properties of Whole Muscles
A.Muscle Tension and Muscle Fatigue
1.The cross-bridges that form during contraction exert muscle tension.
2.When muscle tension is greater than the forces opposing it, contracting
muscle cells shorten; when opposing forces are stronger, muscle cells
lengthen.
3.A motor neuron and the muscle cells under its control are a motor unit.
a.A single, brief stimulus to a motor unit causes a brief contraction
called a muscle twitch.
b.Repeated stimulation without sufficient interval causes a
sustained contraction called tetanus.
B.Effects of Exercise and Aging
1.With regular exercise, muscle cells do not increase in number; however,
they do increase in size and metabolic activity and become resistant to
fatigue.
a.Aerobic exercise, not intense but long in duration, increases the
number of mitochondria and blood capillaries.
b.Strength training affects fast-acting muscle cells by forming more
myofibrils and more enzymes of glycolysis.
.Muscle tension decreases as adult humans age but exercise remains
beneficial in improving blood circulation and preventing loss of muscle
tissue.