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CELLS AND
TISSUES.
Tissue: A Definition
A group of connected,
interdependent cells that
cooperate to perform a
(common) specific function.
• The building blocks of life are
cells.
• Cells form tissues,
• tissues form organs,
• organs form organ-systems,
• and organ-systems form an entire
living and breathing organism.
• Cells are structural units that make up
plants, animals and single cell organisms.
• The cells of single cell organisms are
called prokaryotic cells (prokaryotes).
• A prokaryotic cell does not have a
membrane around its nuclear region (for
example a bacterium). It has a cell wall,
plasma membrane, nucleoid (region of
DNA), and cytoplasm with ribosomes.
• Tissues are groups of cells that lie together to
accomplish a common function. They are the basic
building blocks of organs.
• Tissues are divided into four main groups (epithelial
tissue, connective tissue, muscle tissue, and nervous
tissue).
• These groups are further subdivided into many
subgroups.
• As an example, the epithelial tissue is subdivided into
covering and lining epithelia (outer layer of skin,
inner surface of heart and blood vessels, inner surface
of respiratory cavities, etc.) and glandular epithelia
(most of the glands in the body).
Categories of Tissue
1. Epithelial Tissue
2. Connective Tissue
3. Muscle Tissue
4. Nervous Tissue
Epithelial Tissues
• General Features
Cellular Layer +
Basement
Membrane
Epithelial Tissues
• General Features
Cellular Layer + Basement Membrane
No Blood Supply
Touching Each Other
Rapid Rate of Cell Reproduction
Epithelial Tissues
• Structural Classification
Cell Shapes
Squamous
Cuboidal
Columnar
Epithelial Tissues
• Structural Classification
Cell Shapes
Cell Layers
Simple
Stratified
Epithelial Tissues
• Major Types of
epithelial tissue.
Simple Squamous Epithelium
Simple Squamous Epithelium
Function: Exchange
Sample Locations:
Alveoli, capillaries
Stratified Squamous Epithelium
Stratified Squamous Epithelium
Function: Protection
Sample Locations: Skin, Mouth, Repro tracts
Simple Cuboidal Epithelium
Function: Absorption or Secretion
Sample Locations: Kidney, Hormone Glands
Simple Columnar Epithelium
Function: Absorption (or Secretion)
Sample Location: Digestive Tract
Microvilli
STRATIFIED CUBOIDAL AND COLUMNAR EPITHELIUM:
--Are not common.
A two-layered cuboidal epithelium is, for example seen in the ducts
of the sweat glands.
Stratified columnar epithelum are found in the excretory ducts of the
mammary glands and the main excretory duct of large salivary glands.
Simple Columnar
Note goblet cells
Pseudostratified Columnar Epithelium
Pseudostratified Columnar Epithelium
Pseudostratified Columnar Epithelium
Function: Absorption, Secretion, Movement
Sample Locations: Respiratory & Repro Ducts
Transitional Epithelium
Function: Stretchability
Sample Location: Urinary Bladder
GLANDS: are cells or aggregation of cells whose primary function is
secretion.
Exocrine glands:
Release the secretory product via a system of ducts that opens upon one
of the surfaces of the body which are in contact with the external world
(skin, Gastrointestinal tract)
Endocrine gland :
Release their secretory product (typically hormones)into the spaces
between the secretory cells(extracellular space) from which it enters the
blood stream.
Both endocrine and exocrine glands are developmentally derived from
epithelia tissue, which form down-growth into the underlying connective
tissue. The cells forming this down–growth then develop the
characteristics of a mature gland.
Classification of exocrine glands: exocrine
glands may be classified:
according to
cell number and/or the shape
-branching pattern of their secretory portions
and ducts.
• Both endocrine and exocrine glands are
developmentally derived from epithelia tissue,
which form a down-growth into the underlying
connective tissue.
• The cells forming this down-growth then develop
the special characteristics of the mature gland.
• Exocrine glands maintain the connection with the
body surface whereas it is lost by endocrine glands.
Unicellular Glands
– consist of a single secretory cell. In mammals
the only example of unicellular exocrine glands
are goblet cells, which occur in the epithelium
of many mucous membranes.
– Goblet cells secrete the glycoprotein mucin,
which by the uptake of water is converted into a
slimy substance, mucus.
•
Multicellular glands
• The secretory portion
may have a variety of
shapes. Secretory cells
may form
• tubes in tubular
glands,
• acini in acinar glands
or
• alveoli in alveolar
glands.
Secretory Mechanisms
• The secretory cells can
release their secretory
products by one of three
mechanisms:
• Merocrine secretion
corresponds to the
process of exocytosis.
Vesicles open onto the
surface of the cell, and
the secretory product is
discharged from the cell
without any further loss
of cell substance.
When the cells release their secretory products, the membranes of
secretory granules fuse to the cells membrane, and the granule contents
spill out of the cell in a process called EXOCYTOSIS.
• Apocrine secretion designates
a mechanism in which part of
the apical cytoplasm of the
cells is lost together with the
secretory product.
• This mechanism is used by
apocrine sweat glands, the
mammary glands and the
prostate.
• Holocrine secretion designates
the breakdown and discharge
of the entire secretory cell. It
is only seen in the sebaceous
glands of the skin.
• Product of secretion is shed with the whole
cell,a process that involves destruction of
the secretion-filled cells.
• Cytocrine secretion;
• Is the transfer of secretory materal from one
cell to another.i.e transfer of melanosomes.
Simple tubular
Coiled tubular
Lateral and basal foldings:
Also transcytosis or transepithelial transport.
Lateral and basal infoldings are found in epithelial cells
that are involved in active transport of ions and water
- the folding contain Na + / K+ ATPase to provide
energy
e.g. epithelium of kidney tubules, intestine and ducts of
salivary glands,