Chapter 4 – Tissue:
The Living Fabric
Overview of the Four Tissue Types
• Tissues – groups of cells that are
similar in structure and perform a
common or related function
• Histology – the study of tissues
If describing each tissue type using
only 1 word
• Epithelial – covering
• Connective – support
• Muscle – movement
• Nervous – control
I. Epithelial Tissue – a sheet of cells that
covers a body surface or lines a body
cavity
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A. 2 main types by location
1. Covering and lining epithelia –
forms the outer layer of the skin
covers the walls of organs
lines open cavities
2. Glandular epithelia –
forms the glands of the body
B. Special Characteristics of Epithelium
1. Polarity – 2 surfaces – cells in each
area differ in structure and
function
a. apical – upper free surface
exposed to body exterior or
the organ cavity
i. some are smooth & slick
ii. most have microvilli –
fingerlike extensions of the
PM that increase SA
*brush border
iii. cilia – tiny hairlike
projections that propel subs
along free surface (trachea)
b. basal – lower attached surface
i. basal lamina –
• adjacent to basal surface
• consists of glycoproteins secreted by
the epithelial cells
• determines which molecules diffuse
from the underlying CT
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2. specialized contacts – epithelial cells form continuous sheets
adjacent cells are bound by lateral
contacts
3. supported by connective tissue –
i. reticular lamina –
just deep to the basal lamina
layer of extracellular material (collagen)
Basal lamina + Reticular lamina =
Basement membrane
Basal membrane defines the epithelial
boundary
4. Avascular but innervated – has
nerve fibers but no blood vessels
*nourishment comes from subs diffusing
from blood vessels in the underlying CT
5. Regeneration – many lost due to
friction or hostile substances
they reproduce rapidly
C. System of Classification of Epithelia –
1. Number of cell layers present
a. simple –
• A single cell layer
• Common where absorption, secretion, and
filtration occur
b. stratified –
• Two or more cell layers stacked
• Common in high-abrasion areas where
protection is important
2. Shape of the cells
a. squamous – flattened & scalelike
b. cuboidal – box-like, as tall as
they are wide
c. columnar – tall, column shaped
• *Notice in each case, the shape of the nucleus
conforms to that of the cell
D. Covering and Lining Epithelia
1. Simple Epithelia
a. Simple Squamous Epithelia –
• Thin, flat
• Filtration, secretion
• Kidneys, lungs, blood vessels
**2 simple squamous epithelia in the body
have special names that reflect their
location
i. endothelium – provides a
friction-reducing lining in lymph vessels
& hollow organs of the CV system (very
very thin)
ii. mesothelium – found in
serous membranes lining the ventral
body cavity and covering its organs
b. Simple Cuboidal Epithelia –
• Cube shaped
• Secretion, absorption
• Kidney tubules, small glandular ducts
c. Simple Columnar Epithelia –
• Tall, closely packed
• Secretion, absorption
• Lining of digestive tract
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d. Pseudostratified Columnar
Epithelia –
Vary in height – all cells rest on BM but
only the tallest reach the free surface of
epithelium, can be ciliated or nonciliated
Secretion, absorption
Ciliated – trachea and upper respiratory
tract
Nonciliated – male sperm-carrying ducts
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2. Stratified Epithelia
a. Stratified Squamous Epithelia
Thick layer, basal cells are cuboidal or
columnar, can be keratinized or
nonkeratinized
Protects underlying tissues from abrasion
Keratinized – epidermis (cells are dead)
Nonkeratinized – linings of esophagus,
mouth, & vagina
b. Stratified Cuboidal Epithelia
• Typically two layers of cuboidal cells
• Very rare
• Sweat glands, mammary glands
c. Stratified Columnar Epithelia
• Only apical layer is columnar
• Very rare
• Pharynx, male urethra
d. Transitional Epithelium
• Basal layer is cuboidal or columnar cells
while apical cells vary
• Stretches readily
• Urinary bladder, ureters, urethra
E. Glandular Epithelia
Gland – consists of one or more
cells that make and secrete a product
called a secretion, which is an aqueous
fluid that usually contains proteins
*Classified by:
site of product release (endo/exocrine)
relative number of cells forming gland
(multi/uni)
1. Endocrine –
• Ductless (lose their ducts)
• Produce hormones and release by exocytosis
directly into extracellular space where they
then travel to specific target organs
2. Exocrine –
• Secrete products onto body surfaces or into
body cavities
• Most numerous type of gland
• Mucous, sweat, oil, and salivary glands, liver
a. Unicellular – mucous & goblet cells
• Glands produce mucin that dissolves in water
to form mucus, a slimy coating that protects
and lubricates surfaces
b. Multicellular – 2 parts – a duct and
a secretory unit
*Classified Structurally by:
• duct type
i. simple – unbranched duct
ii. compound – branched duct
• structure of their secretory units
i. tubular – sacs form tubes
ii. alveolar – sacs form flasks
iii. tubuloalveolar – both
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*Classified Functionally by:
• modes of secretion
i. merocrine – most common
secrete products by exocytosis as they are
produced
ex. pancreas, salivary & sweat glands
ii. holocrine –
secretory cells accumulate product until
they rupture (then are they are replaced)
secretions include product + dead cell
fragments so they “die for their cause”
ex. sebaceous (oil) glands of the skin
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iii. apocrine –
contoversy over presence in humans
accumulate products just below free
surface
apex pinches off releasing secretion
cell repairs itself and repeats process
ex. release of lipid droplets by the
mammary glands
II. Connective Tissue –
A. Common Characteristics of Connective
Tissue
1. common origin – all arise from
mesenchyme
2. degrees of vascularity – vary widely
cartilage – avascular
dense connective – poorly vascularized
3. extracellular matrix – nonliving tissue
allow CT to bear weight and withstand
tension, physical trauma, and abrasion
B. Structural Elements of Connective
Tissue
1. ground substance –
• unstructured material that fills the
space b/w cells and contains fibers
• composed of glycoproteins & waterbinding glycosaminoglycans (GAGs)
• Holds large amts of fluid for nutrients
to move b/w blood capillaries and
cells
2. fibers – provide support
a. collagen fibers – (white)
• strongest and most abundant
• made of the protein collagen
• extremely tough, high tensile strength
b. elastic fibers – (yellow)
• long, thin fibers that form branching
networks
• contain a rubber-like protein, elastin that
allows them to stretch and recoil like rubber
bands
c. reticular fibers –
• short, fine, collagenous fibers
• continuous with collagen fibers, but branch
extensively and form networks that surround
small blood vessels and support organs
• common where CT meets other tissue types