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MT 632 Lec
Unit 3 Histology
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Tissues
collection of
specialized
cells
and
cell
products
that perform specific functions
Organs
made up of two or more
tissues
Histology
study of
structure
of
tissues
Four Types of Tissue
Epithelial
- covers exposed surfaces, lines internal passageways, produces glandular secretions
Connective
- fills internal spaces, provides structural support to other tissues, transports material, stores energy
Muscle
- contracts to produce movement, specializes for contraction
Nervous
- carries electrical signals from one part of the body to another
Epithelial Tissue Parts
Epithelia
(singular, epithelium) - layers of cells covering internal or external surfaces
Glands - structures that produce fluid secretions
Functions of Epithelial Tissue
Provide physical
protection
Control
permeability
Provide
sensation
Produce specialized
secretions
Characteristics of Epithelia
Polarity
- differences between exposed (apical) surface and the attached (basal) surface
Cellularity
- epithelial cells are tightly bound by cell junctions
Attachment
- base of epithelium is bound to a noncellular basement membrane
Avascularity
- no blood vessels (avascular)
Regeneration
- continuously replaced by division of stem cells
Apical Surface
Microvilli - increases surface area for absorption or secretion
Cilia - move fluids
Basolateral
Surface
basal
and
lateral
surfaces
Classification of Epithelia
Based on
Shape
Squamous
- thin and flat, irregularly shaped
Cuboidal
- boxy with central nucleus
Columnar
- tall and slender rectangles
Transitional
- transform from shape to shape
Based on Number of
Layers
Simple
Epithelium - single layer of cells
Pseudostratified
Epithelium - appears layered but is only one layer
Stratified
Epithelium - several layers of cells
Simple squamous epithelia
For absorption and diffusion
Found in: mesothelia lining pleura, pericardial cavities, peritoneal cavities, lining of lung alveoli
Mesothelium
- lines body cavities
Endothelium - lining of heart and blood vessels
Stratified squamous epithelium
Protects against mechanical stress
Found in: surface of skin, lining of mouth, throat, esophagus, rectum, anus, vagina
Keratin
adds strength and water resistance, we call this epithelium:
keratinized
Simple cuboidal epithelium
For secretion and absorption
Forms
glands
and lines portions of the kidney tubules
Found in: glands, ducts,
thyroid
gland
Stratified cuboidal epithelium
Relatively rare
Forms ducts of sweat glands and mammary glands
Found in: lining of some ducts
Transitional epithelium
Cells appear
cuboidal
when not
stretched
and
squamous
when
stretched
Tolerates repeated cycles of
stretching
without
damage
Appearance changes as
stretching
occurs
Found in:
lining
of urinary
bladder
, renal
pelvis
,
ureters
Simple columnar epithelium
For absorption and secretion
Found in: stomach, small intestine, large intestine
Pseudostratified columnar epithelium
Appears layered but is only one layer
Cells typically have cilia
Found in: lining of nasal cavity, trachea, bronchi
Stratified columnar epithelium
Relatively rare
Provides protection in pharynx, anus, urethra
Glandular epithelia
Glands
- collections of epithelial cells that produce secretions
Endocrine
glands - release hormones that enter the bloodstream, no ducts
Exocrine
glands - produce exocrine secretions onto epithelial surfaces, discharge secretions through ducts
Methods of Secretion
Merocrine
secretion - product released by secretory vesicles (
exocytosis
); ex:
merocrine
sweat glands
Apocrine
secretion - product released by
shedding
cytoplasm; ex: mammary glands
Holocrine secretion - product released by
cells
bursting and dying; ex:
sebaceous
glands
Types of Secretions
Serous
glands - watery secretions containing enzymes
Mucous
glands - secrete mucins which then forms mucus
Mixed exocrine
glands - contain mixed population of serous and mucous gland cells
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