Lecturer Dr. Twana A. Mustafa
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Transcript of Lecturer Dr. Twana A. Mustafa
Lecturer Dr. Twana A. Mustafa
Histology Lecturer Dr. Twana A. Mustafa Why Study Histology?
Knowing the difference between normal and abnormal tissue is the
first step in diagnosis and treatment of patients. Tissues: groups
of cells closely associated that have a similar structure and
perform a related function Tissue classification based on structure
of cells, composition of noncellular extracellular matrix, and cell
function Major types of adult tissues Epithelial Connective Muscle
Nervous Histology: Microscopic Study of Tissues Biopsy: removal of
tissues for diagnostic purposes Autopsy: examination of organs of a
dead body to determine cause of death * made of all four tissue
types
Skin, our largest organ * made of all four tissue types Embryonic
Tissue 3 major germ layers that form the embryonic disc (source of
stem cells) Endoderm Inner layer Forms lining of digestive tract
and derivatives Mesoderm Middle layer Forms tissues as such muscle,
bone, blood vessels Ectoderm Outer layer Forms skin and
neuroectoderm Epithelial tissue Cellularity - Consists almost
entirely of cells
Covers body surfaces, lines hollow organs, and forms glands Outside
surface of the body Lining of digestive, respiratory and
urogenitalsystems Heart and blood vessels Linings of many body
cavities Polarity - Has apical, basal, and lateralsurfaces Rests on
a basement membrane Specialized cell contacts bind adjacent cells
together Avascular - no blood vessels Regenerative -Replaces lost
cells by cell division Locations of Epithelial Tissues
Covers the body (epidermis) Found on the inside of hollow organs
and the outside of all organs Found above a connective tissue
layer(epi = above) Lines the cavities, tubes, ducts, and blood
vessels inside the body Functions of Epithelia
Protecting underlying structures; e.g., epithelium lining the mouth
Acting as barriers; e.g., skin Permitting the passage of
substances; e.g., cells lining air sacs in lungs and nephrons in
kidney Secreting substances; e.g., pancreatic cells Absorbing
substances; e.g., lining of stomach and small intestine Terms
referring to the layers
Terms that help us understand what kinds of tissues we are
identifying: Terms referring to the layers Simple = one layer
Stratified = more than one layer Pseudostratified = false layered
(appears to be more than one layer, but only one); ciliated = with
cilia Terms referring to the cell shapes Squamous = flat Cuboidal =
cube Columnar= rectangular (column) Transitional = ability to
change shape Classification of Epithelium
Number of layers of cells Simple- one layer of cells. Each extends
from basement membrane to the free surface Stratified- more than
one layer. Pseudostratified- tissue appears to be stratified, but
all cells contact basement membrane so it is in fact simple Shape
of cells Squamous- flat, scale-like Cuboidal- about equal in height
and width Columnar- taller than wide Apical surface Basal surface
Simple Apical surface Basal surface Stratified Classification based
on number of cell layers. Squamous Cuboidal Columnar Classification
based on cell shape. The following types of epithelial tissues are
covered in this activity:
1.Simple squamous epithelial tissue (lungs) 2.Simple cuboidal
epithelial tissue (kidneys) 3.Simple columnar epithelial tissue
(small intestine) 4.Pseudostratified (ciliated) columnar epithelial
tissue (trachea lining) 5.Stratified squamous epithelial tissue
(mouth lining) 6.Stratified cuboidal epithelial tissue (salivary
glands, sweat glands) 7.Stratified columnar epithelial tissue (male
reproductive tract) 8Transitional epithelial tissue (bladder) a.The
tissue may show a full bladder b.The tissue may show an empty
bladder Figure 4.3a Epithelial tissues.
(a)Simple squamous epithelium Description: Single layer of
flattened cells with disc-shaped central nuclei and sparse
cytoplasm; the simplest of the epithelia. Function: Allows passage
of materials by diffusion and filtration in sites where protection
is not important; secretes lubricating substances in serosae.
Location: Kidney glomeruli; air sacs of lungs; lining of heart,
blood vessels, and lymphatic vessels; lining of ventral body cavity
(serosae). Photomicrograph: Simple squamous epithelium forming part
of the alveolar (air sac) walls (125x). Air sacs of lung tissue
Nuclei of squamous epithelial cells Figure 4.3b Epithelial
tissues.
(b)Simple cuboidal epithelium Description: Single layer of cubelike
cells with large, spherical central nuclei. Simple cuboidal
epithelial cells Function: Secretion and absorption. Basement
membrane Location: Kidney tubules; ducts and secretory portions of
small glands; ovary surface. Connective tissue Photomicrograph:
Simple cuboidal epithelium in kidney tubules (430x). Figure 4.3c
Epithelial tissues.
(c)Simple columnar epithelium Description: Single layer of tall
cells with round to oval nuclei; some cells bear cilia; layer may
contain mucus- secreting unicellular glands (goblet cells). Simple
columnar epithelial cell Function: Absorption; secretion of mucus,
enzymes, and other substances; ciliated type propels mucus (or
reproductive cells) by ciliary action. Location: Nonciliated type
lines most of the digestive tract (stomach to anal canal),
gallbladder, and excretory ducts of some glands; ciliated variety
lines small bronchi, uterine tubes, and some regions of the uterus.
Basement membrane Photomicrograph: Simple columnar epithelium of
the stomach mucosa (860X). Figure 4.3d Epithelial tissues.
(d)Pseudostratified columnar epithelium Description: Single layer
of cells of differing heights, some not reaching the free surface;
nuclei seen at different levels; may contain mucus- secreting cells
and bear cilia. Cilia Mucus of mucous cell Pseudo- stratified
epithelial layer Function: Secretion, particularly of mucus;
propulsion of mucus by ciliary action. Location: Nonciliated type
in males sperm-carrying ducts and ducts of large glands; ciliated
variety lines the trachea, most of the upper respiratory tract.
Basement membrane Photomicrograph: Pseudostratified ciliated
columnar epithelium lining the human trachea (570x). Trachea
Stratified Epithelia Contain two or more layers of cells
Regenerate from below Major role is protection Are named according
to the shape of cells at apical layer Figure 4.3f Epithelial
tissues.
(f)Transitional epithelium Description: Resembles both stratified
squamous and stratified cuboidal; basal cells cuboidal or columnar;
surface cells dome shaped or squamouslike, depending on degree of
organ stretch. Transitional epithelium Function: Stretches readily
and permits distension of urinary organ by contained urine.
Location: Lines the ureters, urinary bladder, and part of the
urethra. Basement membrane Connective tissue Photomicrograph:
Transitional epithelium lining the urinary bladder, relaxed state
(360X); note the bulbous, or rounded, appearance of the cells at
the surface; these cells flatten and become elongated when the
bladder is filled with urine. Epithelium: Glandular
A gland is one or more cells that makes and secretes an aqueous
fluid Two types of glands formed by infolding of epithelium:
Endocrine: no contact with exterior of body; ductless; produce
hormones (pituitary, thyroid, adrenals, pancreas) Exocrine: open to
exterior of body via ducts (sweat, oil) Exocrine glands classified
either by structure or by the method of secretion Classified by
structure Unicellular:goblet cells Multicellular: sweat, oil,
pituitary, adrenal Multicellular Exocrine Glands
Classified on the basis of types of ducts or mode of secretion
Types of ducts Simple: ducts with few branches Compound: ducts with
many branches If ducts end in tubules or sac-like structures:
acini. Pancreas If ducts end in simple sacs: alveoli. Lungs