types of body tissues 1. epithelial tissue. 2. connective tissue. 3. muscular tissue. 4. nervous...
DESCRIPTION
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.TRANSCRIPT
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 bladderand 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 belt-like 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:
unicellular (goblet cells) b. multicellular. 2- According to their
mode of secretion: 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
Submandibular gland 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