The Tissues

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• The Tissues
• A tissue consists of a group of cells which are
  similar in structure and carry out the same
  function(s). There are four primary types of
  tissues found in the body
• Epithelia An epithelium is a layer(s) of
  contiguous cells that covers the external and
  internal free surfaces of the body, e.g., surface
  of skin or inner surface of a small blood The
  epithelia carry out the functions of protection,
  absorption, filtration, excretion, secretion and
  sensation.
• Connective Tissues These tissues are the most
  widely distributed tissues in the body. They
  function to bind structure together, support the
  body, protect other organs, insulate the body
  from impact and heat loss and (as blood)
  transport materials throughout the body.
• Muscle Tissues Permit the movements of the body
  and its parts (skeletal muscle), move blood
  throughout the body (cardiac muscle) and regulate
  the activities of internal organs (smooth
  muscle).
• Nerve Tissue Regulate and coordinate the
  activities of the entire body.

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Remove skin cell from adult
Collect unfertilized oocyte
Fuse skin cell with oocyte
Collect DNA from oocyte
Formation of Stem Cells to Produce Various Tissues
Embryo forms stem cells (arrow)
Pancreatic beta cellsblood cellscardiac muscle
cellsliver cellsneurons
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The Epithelial Tissues Classification of
Epithelia by Cell Shape There are four
categories of epithelia based on cell shape
Squamous Cells are flat or shield-like.
Cuboidal The cells have the same height as
width. They appear box-like. The nucleus is
spherical and found in the center of the cell.
Columnar The cells are taller than wide. The
nucleus is oval and tends to be found near the
bottom of the cell. The apical surface of
columnar epithelial cells often shows the
presence of microvilli and cilia. Transitional
epithelium The appearance of transitional
epithelial cells will vary with distension of the
urinary organ which they line.
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Classification of Epithelia by Number of Layers
or Strata of Cells 1.  Simple An epithelium
that is one cell thick.2.  Stratified
epithelium - the identity of the epithelium is
based on the appearance of the uppermost
cells.3.  Pseudostratified - a columnar
epithelium that appears stratified but is not. 
The misleading appearance of the epithelium is
due to the crowding of adjacent cells.
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Characteristics of Epithelia 1. Epithelial cells
exhibit polarity, i.e., they have a top (apical
end) and a bottom (basal end). 2. All
epithelia have a basement membrane. This
structure is not a cell membrane or membranous
layer. It consists of two components a. Basal
lamina - a filamentous sheet attached to the
basal surface of the epithelial cell. It is a
product of the epithelial cell, itself. b.
Reticular lamina - located under the basal lamina
of most basement membranes, consisting of a
condensed ground substance mixed with collagenous
fibers. The basement membrane supports the
epithelium and functions as a semi permeable
filter separating the epithelium from the
underlying tissues. 3.  Epithelia are avascular,
i.e., epithelia lack a direct blood supply. The
cells of an epithelium must receive nutrients and
oxygen from and eliminate wastes to capillaries
across the basement membrane. Transport of these
materials is achieved by diffusion.
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4.  Epithelia are capable of considerable
regeneration. Surface cells are constantly lost
due to abrasion, microbial activity, toxic
substances or extremes of temperature. 5. The
free or apical surface of the epithelial cell
often shows specializations in structure a.
Nonmotile processes such as microvilli, serve to
increase the surface area of the cell and,
therefore, facilitate transport of materials into
and out of the cells. Sensory hairs are receptor
processes found in certain sensory epithelia
concerned with taste (taste buds), smell
(olfactory epithelium).b. Motile Processes like
the cilia are short extentions of the cell
membrane. Cilia can be seen on the free surfaces
of epithelia lining the respiratory tract and
oviducts tubes in mammals. A flagellum has the
same internal structure as a cilium but is much
longer and is found on a sperm cell.
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6. A variety of intercellular junctions can be
seen between the cells of an epithelium.1.
Desmosomes are dense regions of attachment
between epithelial cells. 2. "tight junction"
seems to prevent materials from the intestinal
lumen from leaking into the intercellular spaces
of the epithelium.3. A gap junction represents
a very small (20A) continuity between the
cytoplasms of adjacent cells. They appear to
represent sites of cell to cell communication.
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• Simple squamous epithelium consists of a single
  layer of flat, shield-like cells. In a cross
  sectional view, the cells bulge due to the
  presence of the nucleus This tissue may have a
  protective function or perform secretory
  functions. The image shows this tissue lining
  the alveoli of the lungs. It also lines the
  blood vessels (endothelium) and the chambers of
  the heart (endocardium). It also lines the body
  cavities as the mesothelium of the peritoneum.

Simple Squamous Epithelium
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Simple Columnar Epithelium
Simple columnar epithelium consists of cells
which are taller than wide (). This tissue
lines the alimentary canal from the stomach to
the rectum.A number of mucous producing cells can
be seen in this view.

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Simple Cuboidal Epithelium

• Simple cuboidal epithelium consists of short
  cube, prism or trapezoid-shaped cells (). The
  nuclei are large, spherical and centrally located
  in the cells. This tissue often has a secretory
  function. Found in many glands both exocrine and
  endocrine, for example, lining thyroid follicles
  and ducts of sweat glands.
• They are especially common in kidney tissue.

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Stratified Squamous Epithelium(non-keratinized)

• The stratified squamous epithelium that lines
  interior spaces of the body does not form keratin
  or a dead surface layer. In a vertical cross
  section, the deepest layer rests on a basement
  membrane and is cuboidal in shape This epithelium
  is located lining the mouth, esophagus and
  portions of the pharynx and larynx

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Stratified Squamous(keratinized)

• Stratified squamous consists of several layers
  of generally flat cells () which rest on a
  supporting layer of connective tissue. In skin
  the cells of the stratified squamous produce a
  tough fibrous protein called keratin which
  waterproofs the skin. On the top of the
  epithelium the cells die (arrow) forming the
  stratum corneum.

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Pseudostratified Ciliated Columnar
lp
As its name implies, pseudostratified
columnar appears stratified but is not. Each
cell in this tissue touches the basement
membrane. This tissue is often ciliated (arrow)
and is richly endowed with mucous producing
cells. Pseudostratified epithelium rest on a
supporting connective tissue called the lamina
propria (lp). The lamina propria consists mainly
of areolar connective tissue.
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Transitional Epithelium
Transitional epithelium is located
exclusively in the urinary system. It is found
lining the pelvis of the kidney, the ureter,
urinary bladder and a portion of the urethra.
This epithelium rests on a lamina propria of
areolar tissue. It is capable of great
distension. The cells of transitional epithelium
appear balloon-like when the bladder is empty of
urine.