1. Cell Tissue - Questions and Answers
1. What is the logical order in which the concepts of atoms, molecules, cells...
up to biosphere are associated?
Atoms form molecules that form cells that form tissues that form organs that form
systems. Systems, in their turn, constitute individuals that form populations that
compound (biological) communities that form the biotic components of ecosystems. All
ecosystems of earth form the biosphere.
2. From the zygote, pluricellular organisms are formed by serial mitosis. Would
this formation be possible if each cell made by mitosis had an identical life in
relation to its antecedent cells? How did evolution solve that problem?
The formation of complex and distinct pluricellular organisms would not be possible if
mitosis in embryos produced only daughter cells with an identical life history as the
mother cell, since there would not be differentiation and structural or functional
specialization among cells.
Evolution solved the problem creating the cellular differentiation process by which,
motivated by stimulus not yet well-known by science, different and specialized cell
lineages gave birth to different tissues, organs and systems that, as a whole, form the
pluricellular organisms.
Cellular differentiation probably is a very intricate process that activates and inactivates
some genes within the cell in response to some stimulus.
3. What are the main types of animal tissue?
The main animal cell tissues are the epithelial tissue, the nervous tissue, the muscle
tissue and the connective tissue.
Image Diversity: epithelial tissue nervous tissue muscle tissue connective tissue
4. What are epithelial tissues? What are their general function and how is that
function associated to the features of the tissue?
Epithelial tissues, also called epithelia, are tissues specialized in the covering of external
and internal surfaces of the body.
The general function of the epithelium is to provide protection and impermeability (or
selective permeability) to the covered structure. This justifies the epithelium's typical
features: the cellular juxtaposition forming layers of very proximate cells with diminished
or none intercellular space between each two neighbor cells.
Image Diversity: epithelial cell
5. Of which cells is the nervous tissue constituted? How is the generic function
of this tissue related to the characteristics of the main cell type that forms it?
The nervous tissue is formed of neurons and glial cells.
The function of the nervous tissue is to receive and to transmit neural impulses
(reception and transmission of information). This function justifies the characteristic

2. morphology of neurons, with membrane projections (dendrites) to get information and
an elongated membrane projection (axon, or nerve fiber) to transmit information at
distance. In their turn, the glial cells support the neurons and facilitate their work
(sometimes acting as insulators).
Image Diversity: neuron glial cell
6. What are muscle tissues? How is the function of this tissue related to the
typical characteristics of its cells?
Muscle tissues are tissues made of cells able to perform contractions and thus to
generate movement.
The function of the muscle tissue is to pull bones (skeletal striated muscle), to contract
and move viscera and vessels (smooth muscle) and to make the heart to beat (cardiac
striated muscle). The muscle cells have internal structures called sarcomeres where
there are myosin and actin molecules disposed to create contraction and distension
(movement).
Image Diversity: muscle cell
7. What is the typical biological function of the connective tissues? How is this
function associated to the main features of its cells?
The typical function of the connective tissues is to fill empty spaces among other body
tissues.
This function is related to the great capability of the cells of the connective tissue to
secrete substances that constitute extracellular material, like collagen and elastic fibers,
creating a significant spacing between these cells.
(There are other important biological features of the connective tissues, such as
substance transportation, defense of the organism, etc.)
8. Of which type of tissue are cartilages and bones made?
Bones and cartilages, tissues with great amount of intercellular material, are formed of
connective tissue.
9. Are the cells of the connective tissue far or near to the others?
The relative great spacing between cells is a typical feature of the connective tissue.
There are much intercellular material generally secreted by the tissue cells.
10. What are the general functions of the connective tissues?
The main functions of the connective tissues are: supporting and filling of spaces;
cellular nutrition; energetic storage (fats); hematopoiesis (formation of blood, blood cells
and blood components); immune defense (specialized cells).
11. What is connective tissue proper?
The name connective tissue proper is used to designate the connective tissue that fills
interstitial spaces as opposed to the specialized connective tissues (blood, bones,
cartilage, adipose tissue, etc.). The connective tissue proper secretes collagen, elastin
and reticular fibers.

3. 12. What are the main cells of the connective tissue proper? What is the name
given to the intercellular material that surround these cells?
The main cells of the connective tissue proper are the fibroblasts, cells that secrete the
intercellular material. These cells are the majority of cells of the tissue. Fibroblasts later
are transformed into fibrocytes, mature cells with restricted secretory role.
The intercellular substance that fills the interstice is called interstitial matrix, or just
matrix.
Image Diversity: fibroblast fibrocyte interstitial matrix
13. What are the three types of protein fibers of the connective tissue proper?
The matrix of the connective tissue proper is made of collagen fibers, elastic fibers and
reticular fibers.
Image Diversity: collagen fibers elastic fibers reticular fibers
14. What is the function of the collagen fibers of the connective tissue?
There are different collagen types. The main function of these proteins is to keep the
shape and the structural rigidity of the tissue. (Collagen is the most abundant protein of
the human body.)
15. Of which substance do elastic fibers of the connective tissue are made?
What are some functions of these fibers?
The elastic fibers are made of a protein called elastin.
Elastic fibers abound in artery walls, helping the maintenance of the arterial blood
pressure in these vessels. They are also present in the lungs, providing them with
elasticity (some respiratory diseases are caused by destruction of these fibers). In many
other organs and tissues the elastic fibers are found in the interstitial matrix.
16. What are the reticular fibers of the connective tissue and where can they be
found?
The reticular fibers are very delicate interstitial fibers made of a special type of collagen
known as collagen type III. They can be found in many organs and tissues such as in
lymphnodes, in the spleen, in the liver, in blood vessels and also covering muscle fibers.
17. What are diseases of the connective tissue? What are some of them?
Diseases of the connective tissue are hereditary or acquired diseases(many of
autoimmune cause) characterized by deficiency in structure or function of components of
the connective tissue, for example, deficiencies of collagen, elastin, etc. Some of such
diseases are lupus, dermatomyositis, cheloid, scleroderma, mixed connective tissue
disease, mucinosis and Marfan's syndrome.