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Types of Body Tissues
1. Epithelial tissue.
2. Connective tissue.
3. Muscular tissue.
4. Nervous tissue.
Epithelial tissue
It is present in two forms: 1-Epithelia or epithelial
membrane (contiguous cells covering external body
surfaces and lines internal cavities).
2-Glands (from invaginated epithelial cells).
Functions of epithelial tissue:
A-Protection.
B-Transcellular transport.
C-Secretion of mucus, hormones and enzymes.
D-Absorption.
E-Detection of sensation as taste buds and retina .
F-Selective permeability.
Characteristics of epithelium:
1.The cells are tightly bound together by
junctional complex.
2.Is avascular (nourishment by diffusion from CT.)
3.Rests on basal lamina (formed by epithelial cells) that
separate epithelial cells from underlying CT.
4.Has little intercellular space and little extracellular
matrix.
5.Its cells exhibit a high turnover rate and constant cell
renewal for a particular epithelium
Classification of epithelial membranes
 According to the number of cell layers:
I. Simple (formed of one layer of cells)
II. Stratified (formed of more than one layer of cells)
 According to the morphology of the cells:
1-Simple squamous epithelium: thin low (flat) profile
polygonal cells with central flat nuclei. (Ex. pulmonary
alveoli, loop of Henle, endothelium of blood vessels,
pleura and peritoneal cavities).
Simple squamous
epithelium
2-Simple cuboidal epithelium: single layer of cuboidal
polygonal cells with central round nuclei (Ex. ducts of
many glands, covering of the ovary, follicular cells of
thyroid follicles and some kidney
tubules).
3-Simple columnar epithelium: single layer of columnar cells
with ovoid nuclei located in basal half of cells (Ex. lining of
stomach, gall bladder and large ducts of glands)
. Or may have cilia as in oviduct,
uterus, small bronchi
and ductuli efferentes.
* Simple columnar epith. may exhibit goblet cells and
microvilli as in intestine
4-Stratified squamous ( Non-keratinized) epithelium: Is
formed of several layers of cells in which the most basal
layer rests on basal lamina and it is cuboidal cells, the
intermediate layers are polyhedral or polymorphous. The
most superficial layer is formed of flat squamous cells
not covered with keratin (Ex.lining of mouth, oral
pharynx, esophagus, true vocal cords and vagina).
5-Stratified squamous (Keratinized) epithelium: similar to non
keratinized type but the superficial layer is covered with
keratin (Ex. epidermis of skin specially in soles and palms)
6-Stratified cuboidal epithelium: is composed of two
layers only of cuboidal cells (ex. Ducts of sweat glands).
7-Stratified columnar epithelium: Is formed of more than
one layer of cells with superficial columnar cells (ex.
conjunctiva of the eye, large excretory ducts and regions
of male urethra).
8-Transitional epithalium: is formed of many layers of
cells, the basal layer is formed of low columnar or
cuboidal cells, while the superficial layer is formed of
large dome shaped binucleated cells (in empty bladder).
*In full bladder
the dome-shaped
cells become
flattened and
the epithelium becomes thinner.
Pseudostratified columnar epithelium
 It appears to be stratified but it is composed of single
layer of cells that all are resting on the basal lamina but
only some of cells reach the surface of epithelium.
Theses tall cells have narrow base and broad apical
surface. Cells not extending to the surface have broad
base and narrow apical end. The nuclei are located at
different levels (ex. Male urethra, epididymis and large
excretory ducts).Ciliated Pseudostratified epithelium
with goblet cells, has ciliated tall cells that reach the free
border (ex. trachea, primary bronchia and nasal cavity)
without goblet ex. auditory tube and lacrimal sac.
Pseudo stratified columnar ciliated epithelium with
goblet cells.
Polarity and cell-surface specializations
 Apical domain. As microvilli, cilia,
stereocilia and flagella.
 Basolateral domain. As junctional
specializations and intercellular
interdigitations.
 Apical and basolateral domains are
separated by tight junctions.
Lateral membrane specializations
(Junctional complex)
1-Occluding or tight junctions (Zonulae Occludetes):
forms impermeable barrier, apically located, form beltlike junction that formed by fusion of transmembrane
proteins of adjacent cell membranes.
2-zonulae Adherentes: just basal to tight junction &
encircle the cell. The intercellular space betwee joining
cells is occupied by the extracellular cadherins that
attached to intracellular actin filaments.
*fascia adherens is similar to zonula adherens but
dosenot around the circumference of the cell.
3-Desmosomes (Maculae Adherents): weld-like junctions
appear randomly along the lateral cell membrane. They are
formed of attachment plaques on the cytoplasmic aspect of
adjoining cells. The intermediate filaments of both cells are
inserted in theses plaques forming hairpin turn to disperse
the shearing forces on the cell.
4-Gap (nexus or communicating) junctions: are widespread in
epithelial tissues, cardiac muscle, smooth muscle and
neurons. They are narrow gaps (2nm) to communicate
adjacent cells. They are belt by transmembrane proteins that
have aqueus pores (connexons).
Lateral membrane specializations
(Junctional complex)
Basal surface specialization
1-Basal lamina.
2- Basal enfolding: They increase the surface area of the
basal membrane. The basal cytoplasm and mitochondria
form finger like projections (striated appearance).They
are involved in ion transport and are found in striated
ducts of salivary glands.
3-Hemidesosomes: resemble half desmosomes and
attached to the basal cell membrane on the basal lamina.
The cytoplasmic aspect of cell membrane contains
Attachment plaques in which keratin tonofilaments are
inserted.
Hemidesmosome
Gap junction
Glands
 1-Exocrine glands: secrete their products via ducts
 2-Endocrine glands: are ductless, their products pass
into the blood or lymph.
* Each gland if formed of stroma (C.T. that support and
invade the parenchyma ie.capsule and septa) and
parenchyma (secretory units and ducts).
Exocrine glands
 Classifications:
1- according to the number of cells:
a. unicellular (goblet cells)
b. multicellular.
2- According to their mode of secretion:
a. merocrine. b. apocrine. c. holocrine.
3-According to the type of secretion:
a. mucous glands
b. serous glands.
c. mixed glands (mucous units have serous demilunes)
Modes of Secretion
Goblet cell
Multicellular Exocrine glands
 They consist of clusters of secretory cells and ducts.
 They classified according to their duct shape into:
I- Simple glands if their ducts do not branch.
II-Compound glands if their ducts branch.
 They are classified according to morphology of their
secretory unit into:
 I-Tubular glands.
 II-Alveolar glands.
 III-Tubuloalveolar glands
Types of Exocrine Glands (according to the shape)
Compound
acinar
Compound
tubuloacinar
Exocrine glands
Pancreas
gland
Submandibular
Endocrine glands
 They secrete hormones that pass directly into the blood or
lymph with ducts.
 Their cells are arranged either in cords as in pituitary gland or
as follicles as in thyroid glands.
 Diffuse neuroendocrine system, are widespread throughout
the digestive tract and respiratory system.
Pituitary Gland
Thyroid Gland