The Animal Body Plan (p. 474)
22.1
22.2
Innovations in Body Design (p. 542; Table 22.1)
A. Radial Versus Bilateral Symmetry
1. The simplest animals, sponges, lack any symmetry.
2. Body symmetry first arose as radial symmetry, which is symmetry about a central axis,
in the cnidarians.
3. Most animals exhibit bilateral symmetry, in which only one plan can divide the body
into right and left halves that are mirror images.
a. Bilateral symmetry led to many new body forms, as well as to cephalization.
B. No Body Cavity Versus Body Cavity
1. Another key transition in the evolution of the animal body was the evolution of the body
cavity.
2. A body cavity allows for the evolution of efficient organ systems, as well as more rapid
circulation and complex movement.
3. Kinds of Body Cavities
a. Animals with no body cavities, such as jellyfish and flatworms, are called
acoelomates.
b. Pseudocoelomates, such as nematodes, have a body cavity that forms between the
endoderm and mesoderm.
c. A body cavity that forms within the mesoderm is called a coelom, and is present in
mollusks, arthropods, echinoderms, and vertebrates.
C. Nonsegmented Versus Segmented Bodies
1. Segmentation involves the subdivision of the animal body into repeating segments, and
underlies the body organization of all advanced animals.
2. Segmentation allows certain animals to duplicate the function of a damaged body part.
3. Segmentation facilitates locomotion by enhancing the flexibility of the animal.
D. Incremental Growth Versus Molting
E. Protostomes Versus Deuterostomes
1. Deuterostomes, including the echinoderms and chordates, among others, evolved from
protostomes and appear to have three fundamental differences from protostomes.
a. Protostomes undergo spiral cleavage, while deuterostomes undergo radial cleavage
with the plane of division parallel or perpendicular to the embryo axis.
b. During early embryonic development in protostomes, the blastopore becomes the
mouth and then the anus develops, while in deuterostomes, the blastopore develops
first as the anus.
c. Most protostomes undergo determinate cleavage, but deuterostomes undergo
indeterminate cleavage, enabling each cell to retain the capacity to develop into a
new individual.
Organization of the Vertebrate Body (p. 476; Figs. 22.1, 22.2)
A. The vertebrate body contains over 100 different kinds of cells.
B. Tissues
1. Groups of the same kinds of cells that work together are called tissues.
2. The three embryonic layers, ectoderm, mesoderm, and endoderm, become the different
kinds of cells in the adult body.
3. There are four types of tissues: epithelial, connective, muscle, and nerve tissue.
C. Organs
1. Several different types of tissues that function together are organized into structures
called organs.
D. Organ Systems
1. When several organs work together to provide a function for the body, they are termed
organ systems.
2. The human body has eleven different organ systems; the skeletal system, circulatory
system, endocrine system, nervous system, respiratory system, lymphatic and immune
system, digestive system, urinary system, muscular system, reproductive system, and
skin or integumentary system.
Tissues of the Vertebrate Body (p. 477)
22.3
22.4
Epithelium Is Protective Tissue (p. 477; Fig. 22.3; Table 22.2)
A. Epithelial tissue lines and covers body surfaces.
B. Epithelium provides three basic functions: it protects tissues from dehydration and damage; it
provides sensory surfaces; and it secretes substances.
C. Types of Epithelial Cells and Epithelial Tissues
1. Epithelial cells are classified by their shape into three principal types: squamous,
cuboidal, and columnar.
2. Layers of epithelial tissue are usually only one or a few cells thick, with cells tightly
bound together.
3. Simple epithelium is found in the membranes lining the lungs and body cavities.
4. Protective layering, in stratified epithelium, is characteristic of the skin.
5. Glands secrete substances and are made up of yet another type of cuboidal epithelium.
a. Endocrine glands secrete hormones into the blood.
b. Exocrine glands secrete materials into ducts that open to the outside, such as sweat,
mammary, and salivary glands.
Connective Tissue Supports the Body (p. 480; Figs. 22.4, 22.5; Table 22.3)
A. The cells of connective tissue provide the vertebrate body with dense structural materials as
well as an immune defense.
B. Connective tissue is derived from mesoderm and falls into three functional categories:
immune, skeletal, and storage and transport.
C. Immune Connective Tissue
1. Two main types of cells are found within the immune system: macrophages that wander
through the bloodstream, ready to phagocytize foreign pathogens and worn-out or
damaged cells, and lymphocytes that either produce antibodies or attack cells infected
with viruses.
D. Skeletal Connective Tissue
1. The skeletal system is made up of several different types of connective tissue.
2. Fibrous connective tissue is common in the body and is composed of fibroblasts that
secrete proteins to give structure and strength to the tissues.
3. Cartilage is firm yet flexible and protects the insides of joints from wear and tear.
4. Bone makes up the bulk of the framework of the skeleton (except in agnathans and
cartilaginous fishes). It is composed of calcium phosphate salts plus protein.
E. Storage and Transport Connective Tissue
1. A third type of connective tissue stores materials and transports nutrients, gases, and
wastes from one point within the body to another.
2. Adipose tissue stores fat for future use.
3. The blood transports nutrients, gases, and wastes using its individual components:
erythrocytes, also known as red blood cells, transport oxygen and carbon dioxide
throughout the body, and plasma carries proteins, dissolved nutrients, ions, and body
wastes.
F. A Closer Look at Bone
1. Bone tissue is composed of living bone cells embedded in fibers of a protein called
collagen; the collagen fibers are coated with salts of calcium phosphate in an arrangement
similar to that found in fiberglass.
2. Bone is flexible yet strong.
3. Bones are not solid all the way through; the outer layer of bone is dense compact bone
and the inside of a bone contains spaces and is called spongy bone.
4.
5.
22.5
22.6
Bone marrow, which produces blood cells, is housed and protected inside spongy bone.
New bone is formed in stages.
a. Collagen is first secreted by osteoblasts.
b. Then calcium phosphate salts are added.
G. Compact bone forms in concentric circles around a central blood vessel; the central canal is
called a Haversian canal.
H. New bone is laid down along lines of stress.
I. Osteoporosis is a condition in which bone declines in mass with age.
Muscle Tissue Lets the Body Move (p. 485; Fig. 22.6; Table 22.4)
A. Muscle tissue is made up of cells specialized for contraction.
B. Within each cell is an abundant supply of contractile proteins called microfilaments.
C. Three kinds of muscle cells are evident, based on their structure and function: smooth
muscle, skeletal muscle, and cardiac muscle.
D. The microfilaments of smooth muscle are only loosely organized, while those of cardiac or
skeletal muscle are bundled into myofibrils.
E. The arrangement of the myofilaments within the myofibrils lends a striped, or striated,
appearance to cardiac and skeletal muscle tissues.
F. Smooth Muscle
1. Smooth muscle is organized into flat sheets of cells.
2. It can be found in the walls of the digestive system, among other places in the body, and
is adapted for sustained contraction.
G. Skeletal Muscle
1. Skeletal muscle is so named because it is attached to the skeleton for body movement.
2. Skeletal muscle cells are produced by the fusion of several cells to form one very long
fiber with the nuclei pushed out to the periphery of the cytoplasm.
3. Each muscle fiber consists of many elongated myofibrils; myofibrils are composed of
myofilaments called actin and myosin.
H. Cardiac Muscle
1. Cardiac muscle is comprised of chains of single cells, each with its own nucleus.
2. Cells communicate with each other through gap junctions so that the heart can contract in
an orderly pulsation.
3. Once the pacemaker of the heart initiates a contraction, a wave of depolarization spreads
across the heart.
Nerve Tissue Conducts Signals Rapidly (p. 487; Fig. 22.7; Table 22.5)
A. The fourth major type of tissue, nerve tissue, is made up of two types of cells.
B. Neurons are specialized to conduct nervous impulses at a rapid rate.
C. Glial cells, the helper cells of nerve tissue, nourish, support, and insulate neurons.
D. Neurons consist of a cell body that houses the nucleus, an axon that transmits impulses away
from the cell body, and numerous branching dendrites that detect impulses and carry them to
the cell body.
E. Between adjacent neurons is a space, called a synapse, over which the nervous impulse must
travel.
F. Neurons secrete neurotransmitters to carry the impulse from one nerve cell to the next.
G. A nerve is made up of many axons bundled together.
The Skeletal and Muscular Systems (p. 488)
22.7
Types of Skeletons (p. 488; Figs. 22.8-22.11)
A. Animals are able to move because the opposite ends of their muscles are attached to a rigid
scaffold, or skeleton.
B. There are three types of skeletal systems in animals.
1. Hydraulic skeletons are found in soft-bodied invertebrates: a fluid-filled cavity is
encircled by muscle fibers that raise the pressure of the fluid as they contract; the fluid
pressure pushes the body in a direction
2. Exoskeletons surround the body as a rigid hard case to which muscles are attached
internally; found in arthropods, exoskeletons limit the size of the animals that have them.
3.
22.8
Endoskeletons are found in vertebrates and echinoderms and consist of a rigid internal
skeleton to which muscles are attached.
C. A Vertebrate Endoskeleton: The Human Skeleton
1. The human skeleton is divided into the axial and appendicular skeletons, and is
comprised of a total of 206 bones.
D. The Axial Skeleton
1. The axial skeleton is made up of the skull, vertebral column (spine), and rib cage.
E. The Appendicular Skeleton
1. The appendicular skeleton is made up of the arms and legs and the bony girdles that
support them.
2. The pectoral girdle is composed of the collarbone and shoulder blades.
3. The pelvic girdle is composed of the hip bones.
Muscles and How They Work (p. 490; Figs. 22.13, 22.13)
A. Actions of Skeletal Muscle
1. Skeletal muscles move the bones of the skeleton.
2. Places where two bones come together are called joints.
3. Muscle is attached to bones by strong straps called tendons.
4. Muscles are arranged as opposing pairs (flexors and extensors) on both sides of bones.
B. Muscle Contraction
1. Myofilaments, the contractile fibers within muscle cells, are made up of even smaller
filaments of protein.
2.
Actin filaments are two strands of actin wound together.
3.
Myosin filaments are arranged in the same manner, but are considerably larger than
actin filaments and have a globular region toward one end.
C. How Myofilaments Contract
1. Myofilaments contract because the globular region on the myosin filaments pulls against
a binding site on the actin filament, causing it to slide inward.
2. The energy from ATP drives the process.
D. The Role of Calcium Ions
1. Access to actin by myosin is normally blocked by a regulatory protein called
tropomyosin.
2. In the presence of Ca++, the tropomyosin shifts away to expose binding sites on the actin
for myosin.
3. The endoplasmic reticulum of a muscle cell is called the sarcoplasmic reticulum, and it
stores calcium ions.
4. When a muscle cell is stimulated to contract by nerves, calcium is released from the
sarcoplasmic reticulum.