lec

Comments

Transcription

lec
Histology : It is the science which deals with the
microstructures of tissues and organs.
The tissues
• A basic tissue type is a group of similar cell and able to perform
a common function.
•Our body is composed of only four basic tissue types:
Types of tissues
Epithelial
tissue
Connective
tissue
Muscular
tissue
Nervous
tissue
• In most animals, combinations of various tissues make up
functional units called organs, and groups of organs that work
together form systems.
• For example, the human digestive (system )consists of a
stomach (organ) small intestine, large intestine, and several
other organs, each a composite of different tissues (epitheliumconnective-muscles-nervous) .
1-Epithelial Tissue
•
means covering body surface and lining body cavity.
General characters of epithelial tissues :
•
•
•
•
•
•
The cells are closely aggregated with very little intercellular substance
(matrix) of acid mucopolysaccharides .
The cells are regular in shape .They are held tightly together by junctional
complex
Epithelial cells are firmly bound to the underlying CT by a thin membrane
called basement membrane.
Blood vessels do not penetrate the epithelium (avascular).
Epithelium can be derived from all three embryonic germ layer :
ectoderm ------------- epidermis of the skin
endoderm-------------epithelium of alimentary canal
mesoderm-------------kidney
Epithelium is in a continuous process of degeneration and regeneration. It
has a high mitotic activity .It has a high renewal rate.
General Functions of epithelium
1-Protection :
of the underlying CT----against injuries,
bacteria and chemicals (skin –stomach).
2-Secretory :
(epithelium is specialized for producing
secretion (glandular epithelium)
3- Absorption :
(small intestine-kidney)
4-Reproduction:
germinal epithelium of testis and ovary
5-Contraction:
myoepithelial cells are contractile in function.
is specialized in perception of external stimuli
6-Neuroepithelium: ex. (taste buds of tongue)).
Classification of the epithelia
Classification of epithelia according to
A-number of layers
1-Simple epithelium (one
layer)
2-Stratified epithelium
(more than one layer(
B-Shape of cells
1-Squamous(flat)
2-Cuboidal (Height = width)
3-Columnar (Hight is 2-5
greater than width)
Based on the last two criteria we classify the epithelium:•
1-Simple squamous epithelium:
polyhedral in shape and oval nuclei ,(thin to allow
material transport-filteration (kidney, lung, blood
vessel).
-Endothelium ------in blood vessels and lymphatic
-mesothelium------in peritoneal
2-Simple cuboidal epithelium:
present where ion exchange is required (kidney
proximal tubule).
3-Simple columnar epithelium
i- non –ciliated columnar(Digestive tract)
ii-ciliated columnar (oviducts)
4-Sratified squamous epithelium
i-non-keratinized (esophagus)
ii-keratinized (skin)
5-Pseudostratified ciliated columnar
epitheliun (trachea)
6-Transitional epithelium (urinary
bladder).
a- full
b-empty
II-glandular epithelium
Glands can be classified according to:
1-number of cells
2-The presence or absence of a duct system
3-According to the mode of secretion (mechanism)
1-number of cells
•a-unicellular glands consists of one cell (goblet cell of
small intestine)
•b-multicellular glands composed of cluster of cells
2-The presence or absence of a duct system :
•a- Exocrine(in which secretion is released through
ducts (salivary glands)
•b-Endocrine glands (secretion released directly to
the blood) thyroid glands.
•c- Mixed glands (endocine and exocrine)---pancrease
3-According to the mode of secretion (mechanism)
•a-Merocrine glands (no loss of its cellular
material) pancreas (exocytosis)
•b-Holocrine glands (complete destruction of
the cell)---sebaceous gland
•c- Apocrine glands ( secretory product is
discharged with apical parts of the
cytoplasm) ----mammary glands
II-glandular epithelium
Glands can be classified according to:
1-number of
cells
2-The
presence or
absence of a
duct system :
3-According to
the the mode
of secretion
(mechanism)
• a-unicellular glands consists of one cell (goblet cell of
small intestine)
• b-multicellular glands composed of cluster of cells
• a- Exocrine(in which secretion is released through
ducts (salivary glands)
• b-Endocrine glands (secretion released directly to the
blood) thyroid glands.
• c- Mixed glands (endocine and exocrine)----pancrease
• a-Merocrine glands (no loss of its cellular material)
pancreas (exocytosis)
• b-Holocrine glands (complete destruction of the
cell)---sebaceous gland
• c- Apocrine glands ( secretory product is discharged
with apical parts of the cytoplasm) ----mammary
glands
2-Muscular tissue
( skeletal, smooth, cardiac muscles)
- Muscular tissue is composed of long cells called muscle
fibers that are capable of contracting when stimulated by
nerve impulses.
-It has large numbers of myofibrils made of the contractile
proteins actin and myosin.
-The sliding filament is accepted as the mechanism that
accounts for muscular contraction.
16
There are three types of muscle tissue in the vertebrate body:
1- Skeletal muscles
connected to the
skeleton and is
concerned with body
movements.
2- Cardiac muscles
forms the contractile
portion of the heart .
3-Smooth muscles
does not exhibit
striations. It is found
as part of the walls of
the viscera.

Similar documents