Transcript Spring 2014 - Unit 2 Histology Notes

Tissues, Glands,
& Membranes
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•
Tissue - group of cells similar structure
and function along with similar
extracellular substances between the
cells
• Histology – microscopic study of tissue
structure
• Histo- = tissue, -ology = study
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
Epithelial tissues
◦ Epi = on + thele = covering or lining



Connective tissues
Muscle tissues
Nervous tissues
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1.
2.
3.
4.
Very little extracellular
material between cells.
Free surface – layer of
cells not in contact with
other cells.
Basement membrane –
attaches the epithelial
cells to underlying
tissues.
Avascular – capillaries do
not extend from the
underlying tissues, so
gases, nutrients, & wastes
must diffuse across the
basement membrane.
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• Classified based on number of cell layers
and cell shape
• Layers:
• Simple epithelium – 1 layer of cells
• Stratified epithelium - >1 layer of cells
• Note: When epithelium is stratified, it is
named according to the shape of the cells
at the free surface.
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• Shape:
• Squamous (flat and scale-like)
• Cuboidal (cube shaped)
• Columnar (tall and thin)
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Layers or “Arrangement”
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Shapes
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• Single layer of thin, flat
cells
• Line blood vessels,
lymphatic vessels,
heart, alveoli, kidney
tubules, serous
membranes
• Diffusion, filtration,
anti-friction, secretion,
absorption
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Single layer of
cube-shaped
cells, some with
microvilli or cilia
Kidney tubules,
glands/ducts,
brain,
bronchioles, ovary
surface
Secretion,
absorption,
movement of
particles
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Single layer of tall,
narrow cells, some
with cilia/microvilli
Lining of stomach,
intestines, glands,
ducts, bronchioles,
auditory tubes,
uterus, uterine tubes
Secretion,
absorption,
movement of
particles/oocytes
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Single layer of cells,
some tall and thin,
others not, nuclei
at different levels,
appear stratified,
almost always
ciliated
Lining of nasal
cavity, nasal
sinuses, auditory
tubes, pharynx,
trachea, bronchi
Synthesis/
secretion/
movement of
mucus
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Stratified cells
appear cuboidal
when not stretched
and squamous
when stretched
Lining of bladder,
ureters, superior
urethra
Deals with
changing volume
of fluid in an
organ, protects
from urine contact
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Simple
Columnar
Epithelium
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Simple
Squamous
Epithelium
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Stratified
Squamous
Epithelium
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Simple
Cuboidal
Epithelium
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Stratified
Columnar
Epithelium
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Pseudostratified
Epithelium
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[bladder]
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Transitional
Epithelium
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Stratified
Cuboidal
Epithelium
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
Cell Layers & Cell Shapes
◦ Single layers – control passage of materials
through epithelium



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Gas diffusion across lung alveoli
Fluid filtration across kidney membranes
Gland secretion
Nutrient absorption in intestines
◦ Multiple layers – protect underlying tissues
 Damaged cells replaced by underlying cells
 Protect from abrasion (ex: skin, anal canal, vagina)
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
Cell Layers & Cell Shapes, continued
◦ Flat/thin (squamous) – diffusion, filtration
 Diffusion in lung alveoli
 Fluid filtration in kidney tubules
◦ Cuboidal/columnar – secretion, absorption;
contain more organelles
 Secretory vesicles (mucus) in stomach lining
 Mucus protects against digestive enzymes and acid
 Secretion/absorption in kidney tubules made
possible by ATP production by multiple
mitochondria
 Active transport of molecules into/out of kidney
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
Free Cell Surfaces
◦ Smooth – reduces friction
 blood vessel lining – smooth blood flow
◦ Microvilli – increase cell surface area; cells involved
in absorption or secretion
 Small intestine lining
◦ Cilia – propel materials along cell’s surface
 Nasal cavity/trachea – moves dust and other materials
to back of throat (swallowed/cough up)
 Goblet cells secrete mucus to entrap the “junk”
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
Cell Connections
◦ Tight junctions – bind adjacent cells together
 Permeability layers – prevent passage of materials
 Intestinal lining and most simple epithelia
◦ Desmosomes – anchor cells to one another
 Hemidesmosomes – anchor cells to basement membrane
 Epithelia subject to stress (skin stratified squamous)
◦ Gap Junctions – allow passage of molecules/ions
between adjacent cells (communication)
 Most epithelia
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
Gland – multicellular structure secreting
substance onto a surface, into a cavity, or
into the blood. There are two types:
◦ Exocrine gland (exo-outside + krino-to separate): glands
with ducts; secretions pass through ducts onto a
surface or into an organ
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Simple – ducts w/o branches
Compound – ducts w/ branches
Tubular – tubes
Acinus/alveolus – saclike
◦ Endocrine gland (endo-within): glands w/o ducts
that secrete into blood
 Hormones are secreted into blood
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*Goblet cells are the only
unicellular gland.
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Merocrine: FLUID is released (Most glands are in this group)
◦ Serous cells = produce a watery secretion w/enzymes
◦ Mucous cells = produce thicker secretions
Apocrine: Small portions of the cell break off & are released
◦ Mammary glands, Ceruminous (ear wax), and some sweat
glands
Holocrine: ENTIRE CELLS are released-Sebaceous Glands: oil in
the skin)
Connective Tissue
• The most abundant and widely distributed
tissue in the body
• Multiple types, appearances and functions
• Relatively few cells in extracellular
matrix (think: fruit “cells” floating or
suspended in Jell-O).
• Matrix is made up of:
• Protein fibers
• Ground substance
• Fluid
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Three types of protein fibers :
 Collagen fibers:
◦ Rope-like; resist stretching

Reticular fibers:
◦ Fine, short collagen fibers; branched for support

Elastic fibers:
◦ Coiled; stretch and recoil to original shape

Ground substance – combination of proteins and
other molecules
◦ Varies from fluid to semisolid to solid

Proteoglycans – protein/polysaccharide complex
that traps water
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
Based on function:
◦ Blast (germ) – produce (build) matrix
◦ Cyte (cell) – cells maintain it
◦ Clast (break) – cells break down for remodeling
 Osteoblast (osteo-bone) – form bone
 Osteocyte – maintain bone
 Osteoclast – break down bone
◦ Cells associated with the immune system are also
found in connective tissue:
 Macrophage (makros-large + phago-to eat) – large,
mobile cells that ingest foreign substances found in
connective tissue
 Mast Cells – nonmotile cells that release chemicals
that promote inflammation
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1. Enclose & Separate organs and tissues
from one another
• Liver, kidney; (capsules form around)
• muscles, blood vessels, nerves
2. Connect tissues to each other
• Tendons – muscles to bone
•
Remember: TTT (tendons 2 types)
• Ligaments – bone to bone
•
Remember: LLL (ligaments like to like)
3. Support and movement
• Bones, cartilage, joints
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4. Storage
• Fat stores energy; bone stores calcium
5. Cushion and insulation
• Fat cushions/protects/insulates (heat)
6. Transportation
• Blood transports gases, nutrients,
enzymes, hormones, immune cells
7. Protection
• Immune & blood cells protect against
toxins/tissue injury; bones protect
underlying structures
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Composition: ECM has
fibroblasts, other
cells, collagen, fluidfilled spaces
Functions: forms thin
membranes between
organs and binds
them (loose packing
material)
Locations: widely
distributed, between
glands, muscles,
nerves, attaches skin
to tissues, superficial
layer of dermis
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Composition: very little
ECM (has collagen and
elastic fibers); large
adipocytes filled with
lipid
Functions: Stores fat,
energy source, thermal
insulator, protection/
packing material
Locations: Beneath the
skin, in breasts, within
bones, in loose
connective tissues,
around organs (kidneys
and heart)
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Composition: ECM
mostly collagen (made
by fibroblasts),
orientation varies
Functions: withstands
pulling forces, resists
stretching in direction
of fibers orientation
Locations: tendons,
ligaments, dermis of
skin, organ capsules
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Composition: ECM
collagen and elastic
fibers; orientation
varies
Functions:
stretches and
recoils; strength in
direction of fiber
orientation
Locations: arterial
walls, vertebral
ligaments, dorsal
neck, vocal cords
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Chondrocytes (cartilage cells) inside
lacunae (small spaces)
No blood vessels – slow healing, can’t
bring cells/nutrients necessary for tissue
repair
Three types:
◦ Hyaline cartilage
◦ Elastic cartilage
◦ Fibrocartilage
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Composition: solid
matrix, small evenly
distributed collagen
fibers, transparent
matrix, chondrocytes
in lacunae
Functions: supports
structures, some
flexibility, forms
smooth joint surfaces
Locations: costal
cartilages of ribs,
respiratory cartilage
rings, nasal cartilages,
bone ends, epiphyseal
(growth) plates,
embryonic skeleton
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Composition: similar
to hyaline, numerous
collagen fibrous
arranged in thick
bundles
Functions: somewhat
flexible, withstands
great pressure,
connects structures
under great pressure
Locations:
intervertebral disks,
pubic symphysis,
articulating cartilage
of some joints (knee,
TMJ)
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Composition:
similar to hyaline
cartilage, abundant
elastic fibers
Functions: rigidity,
more flexibility
than hyaline
(elastic fibers recoil
to original shape)
Locations: external
ears, epiglottis,
auditory tubes
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Composition: hard,
mineralized matrix,
osteocytes inside
lacunae, lamellae
layers
Functions:
strength, support,
protects organs,
muscle/ligament
attachments,
movement (joints)
Locations: all bones
of body
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Composition: blood
cells in a fluid matrix
(plasma)
Functions:
transportation (O2,
CO2, hormones,
nutrients, waste, etc.),
protect from infection,
temperature regulation
Locations: in blood
vessels and heart,
produced by red bone
marrow, WBCs leave
blood vessels and
enter tissues
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
General features:
◦ Can contract
 Contractile proteins
◦ Enables movement of the structures that are
attached to them
◦ Muscle fibers = cells

Three (3) types of muscle tissue:
◦ skeletal
◦ smooth
◦ cardiac
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Composition:
striated muscle
fibers, large,
cylindrical cells
that have many
nuclei near
periphery
Functions: body
movement,
voluntary control
Locations:
attached to bone
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Composition: cylindrical cells,
striated, single nucleus,
branched and connected with
intercalated disks
Functions: pump blood,
involuntary control
Locations: heart
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Composition: cells
tapered at each end,
not striated, single
nucleus
Functions: regulates
organ size, forces fluid
through tubes,
regulates amount of
light entering eye,
“goose bumps”,
involuntary control
Locations: walls of
hollow organs and
tubes (stomach,
intestine, blood
vessels), eye
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Forms brain, spinal cord, peripheral nerves
Functions:
◦
◦
◦
◦
◦
◦
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Conscious control of skeletal muscles
Unconscious control of cardiac muscles
Self and environmental awareness
Emotions
Reasoning skills
Memory
Action potentials = electrical signals
responsible for communication between
neurons and other cells
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
Neurons = conducts
action potentials
(a.p.’s)
◦ Cell body = contains
nucleus, site of general
cell functions
◦ Dendrite = conduct
a.p.’s toward cell body
◦ Axon = conducts a.p.’s
away from cell body

Neuroglia = support
cells: nourish, protect,
insulate neurons
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
In response to tissue damage
◦ Viral/bacterial infections
◦ Trauma

Functions:
◦ Mobilize body’s defenses
◦ Destroy microorganisms, foreign materials,
damaged cells
◦ “Pave way” for tissue repair
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Redness
Heat
Swelling
Pain
Disturbance of function
* Inflammation is beneficial, though painful!
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
Mediators of inflammation cause dilation 
permeability of blood vessels
(redness/heat)
◦ Bring blood and important substances to site
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Edema = swelling (water, proteins, etc.) of
tissues
Fibrin = protein that “walls off” site; keeps
infection from spreading
Neutrophils ingest bacteria (phagocytic
WBC)
Macrophage ingest tissue debris
Pus = mixture of dead neutrophils, cells,
fluid
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
Inflammation warns
person from further
injury:
◦ Pain
◦ Limitation of movement
(edema)
◦ Tissue destruction
 Fibroclast migrate to
damaged tissue and
digest
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
Substitution of viable cells for dead cells
◦ Regeneration = same type of cells takes place of
previous cells; same function
◦ Replacement = different type of tissue develops;
forms scars; loss of some function
◦ Fibroclast lays down fibrin and forms scar tissue
◦ Type of tissue repair is determined by:
 Wound severity
 Tissue types involved
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
Labile cells (not fixed)
◦ Divide continuously through life
◦ Skin, mucous membranes

Stable cells
◦ Don’t actively divide, but can after injury
◦ Connective tissue, glands (liver, pancreas)
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Permanent cells
◦ Little to no ability to divide
◦ Neurons, skeletal muscle
 If killed, replaced by connective tissue
 Recover from limited damage (axon of neuron)
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1.
2.
3.
4.
5.
6.
7.
8.
Clot (fibrin)
Scab (seal)
Blood vessel
dilation
Fibroclastclean up
Fibrin “walls
off”
Epithelium
replaced
Scab sloughs
Fibroblasts
form
granulation
tissue
Wound
contracture
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
Tissue changes with age:
◦  neurons and  muscle cells
◦  visual acuity, smell, taste, touch
◦  in functional capacities of respiratory and
cardiovascular systems
◦ Slower cell division means slower healing
◦  flexibility (irregular collagen fibers in tendons
& ligaments)
◦  elasticity (elastic fibers bind to Ca2+, becoming
brittle) – makes skin wrinkled too 
◦ Atherosclerosis – plaques in blood vessels
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