An Introduction to Animal Structure And
The function of animal tissues and organs are correlated with their structure.
There is a structural hierarchy of life:
Atoms molecules supramolecular structure cell
The cell is the lowest level; of organization that can live as
Hierarchy of multicellular organisms is:
Cell tissues organs organ systems.
Tissues: groups of cells with common structure and function.
There are four main categories of tissues:
Epithelial tissues cover the outside of the body and line ( ) organs and body
function as barriers against mechanical injury , invading
microbes, and fluid loss.
Its free surface is exposed to air or fluid. Cells at the base are attached to a
basement membrane which is a dense layer of extracellular material.
Epithelial tissue cells are categorized according to:
i. number of layers:
- simple epithelium : one layer of cells.
- Stratified epithelium : multiple tiles of cells
- Pseudostratified epithelium: one layers of cells that appear to be
multiple because cells are not equal in length.
ii. cell shapes:
- cuboidal ( )
- columnar ( )
- squamous ( )
2. Connective Tissues ( )
function to bind and support other tissues
scattered through an extensive extracellular matrix which is
a web of fibers embedded in a homogenous ground
- loose connective tissue
- adipose tissue
- fibrous connective tissue
i. loose connective tissue
holds organs in place and attaches epithelia to underlying
Consists of three type of proteineous fibers:
- collagenous fibers: bundles of fibers containing
3 collagen molecules each. With great tensile
strength, resist stretching.
- Elastic fibers: long threads of the protein
elastin. Highly elastic properties.
- Reticular fibers: branched and form tightly
woven fabric joining connective tissue to
consists of two types of cells
- fibroblasts: secrete the protein of the
- Macrophages: phagocytic amoeboid cells that
function in immune defense of the body.
ii. Adipose tissue:
specialized to store fat in adipose cells distributed
throughout its matrix.
Insulate the body and store fuel molecules.
Each cell has one large fat droplet which can vary in size as
fats are stored or used.
iii. Fibrous connective tissue:
is dense due to the arrangement of large number of
collagenous fibers in parallel bundles.
Found in tendons (attach muscles to bones) and ligaments
(attach bones together).
iv. Cartilages ( )
composed of chollagenous fibers embedded in chondroitin
sulfate: a protein carbohydrate ground substance.
Cartilage cells are called: chondrocytes:
- secrete both chollagen and chondroitin sulfate
which make cartilage strong and flexible.
- Are confined to lacunae: spaces within the
comprise the skeleton of all vertebrate embryos.
Cartilages are replaced by bones but retained in nose, ears,
trachea and ends of some bones.
are mineralized connective tissues
bone cells are called: Osteoblasts: deposit a matrix of collagen and calcium.
Bones consist of repeating Harvestian System.
Osteocytes are located in spaces called lacunae.
In longer bones, only the outer area is hard and compact; the
inner area is filled with spongy bone tissue called: marrow.
liquid extracellular matrix of plasma which contains water, salts and proteins.
blood cellular components are:
- leukocytes ( ): function in immune
- Erythrocytes ( ): transport oxygen
- Platelets ( ): cell fragments function in
blood cells are made in red bone marrow.
3. Muscle Tissue:
consists of long, excitable cells capable of contraction.
Are parallel bundles of microfilaments made of the
contractile proteins: actin and myosin.
Muscle is the most abundant tissue in most animals.
There are three types of muscle tissue in vertebrates:
i. skeletal muscle:
- responsible for voluntary movement.
- Attached to bones by tendons.
- Microfilaments are aligned to form striated
ii. cardiac muscle:
- form the contractile wall of the heart.
- Cells are striated and branched.
- End of cells are joined by intercalated disks
which relay the contractile impulse from cell to
iii. Visceral muscle:
- smooth tissue in the walls of internal organs.
- Spindle shaped cells that contract slowly.
- Responsible for involuntary movement.
4. Nervous Tissue:
senses and transmits signals from one part of the body to
Nerve cells are called: neurons, that consist of:
- cell body
- dendrites: extensions that conduct impulses to
the cell body .
- axons: extensions that transmit impulses away from the cell body.
Organs and Organ Systems:
Tissues are organized into Organs:
may be layered, such as the dermis of the human.
Many organs are suspended by sheet of connective tissue
Organs may be organized into organ system.
Organ Systems: several organs with separate functions that act in
coordinated manner. e.g. digestive system, respiratory system ..etc.
systems are interdependent.