HISTOLOGY
Study of tissues -cells similar in structure
and perform a common function
4 types:
•Epithelial
•Connective
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•Muscle
•Nervous
WHAT IS NECROSIS?

Necrosis is tissue
death. It occurs if the
blood supply to an
area is stopped for too
long. When this
happens the tissues
die due to a lack of
oxygen to the cells.
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PREPARING TISSUES FOR MICROSCOPY

Fixed – preserved

Artifacts – distortions not seen in living tissue
Sectioned – cut into slices thin enough
light can pass through
 Stained – organic dyes used to enhance
contrast

Transmission electron microscopy (TEM) –
uses electrons for detailed contrast
 Scanning electron microscopy (SEM) – 3D
pictures of tissue surface

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EPITHELIAL TISSUE
Covers a surface or lines a cavity
 Glandular epithelium – exocrine glands
 Forms boundaries
 Basement Membrane: Network of protein
fibers that forms barrier between epithelium
and connective tissue
 Protection
 Absorption – molecules pass into blood or lymph
 Filtration – passage of solvent thru a membrane
 Excretion – eliminate waste
 Secretion – release aqueous solution
 Sensory reception

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CHARACTERISTICS OF EPITHELIUM

Polarity
 Apical surface – exposed
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Basal Surface – attached
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Microvilli
 Increase surface area
 Allow absorption and secretion
Cilia
 Beat to move materials across surface
Basal lamina – adhesive glycoproteins
Specialized Contacts

Tight Junctions
Prevents passage of water and solutes
 Interlocking membrane proteins
 Basal adhesion belt binds cells together
 Desmosomes
 Durable interconnections
 2 types:
 Button desmosomes- small disk
 Hemidesmosomes – half button shape

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MORE CHARACTERISTICS

Reticular lamina – Extracellular collagen network
Avascular but innervated
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EPITHELIUM
Supported by connective tissue
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OF
No blood vessels, nutrients obtained from diffusion
Nerve supply
Regeneration
Cells are continually replaced
 Epithelial cells only survive 1-2 days
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SQUAMOUS EPITHELIUM


Simple Squamous
 Thin and flat cells, 1 Layer
 Function: diffusion & filtration
 Found: forms capillary walls
(endothelium), lining air sacs of
lungs, kidneys, lining body
cavities (mesothelium)
Stratified Squamous
 Thin and flat cells, More than 1
layer, most common epithelia
 Function: protection
 Found: in places of mechanical
stress, skin surface, lining
tongue, mouth, esophagus, and
anus
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CUBOIDAL EPITHELIUM


Simple Cuboidal
 Box shaped cells, 1 layer
 Function: Secretion or
absorption
 Found: covering surface of
ovaries, lining kidney tubules,
salivary ducts, and pancreatic
ducts
Stratified Cuboidal
 Box shaped cells, 2 layers, rare
 Function: strengthen lumen
walls
 Found: ducts of large sweat
glands, salivary glands,
mammary glands, and pancreas
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COLUMNAR EPITHELIAL


Simple Columnar
 Tall, rectangular cells, 1 layer
 Function: absorption
(microvilli) & secretion
 Found: Lines stomach,
intestinal tract, excretion
ducts, gall bladder
Pseudostratified Columnar
 Single layer irregularly shaped
cells (looks like multiple layers)
 Function: protection, secretion
 Found: Lining respiratory
passageways (ciliated), and
auditory tubes
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TRANSITIONAL EPITHELIAL TISSUE
 Transitional



3-6 layers of rounded
cells
Function: Withstands
stretching
Found: Lines urinary
bladder and portions of
ureters and urethra
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EXOCRINE GLANDULAR EPITHELIA
Exocrine glands: excrete secretions usually thru ducts
onto surface
Unicellular
 Goblet & mucous cells scattered among epithelial cells
 Secrete mucin (glycoproteins & water) via exocytosis
Multicellular – Secretory sheet, classified by pattern of ducts
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ex – mucin lining stomach
Mode of Secretion:

Merocrine: via exocytosis
 Ex. Skin Perspiration, Mucus Glands, Saliva, mammary
glands (milk)

Apocrine: lose cytoplasm and secretory product
 Ex. Mammary glands (lipids)

Holocrine – cell fills with secretion then bursts and dies
 Ex. Sebaceous glands – oils from base of hair
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CLASSIFICATION OF CONNECTIVE TISSUES:
3 TYPES
 Connective


Syrupy ground matrix
Ex. Loose (areolar, adipose) & Dense (tendons
& ligaments)
 Blood

- Fluid Connective tissue
Cells suspended in watery ground substance
w/dissolved proteins
 Cartilage


Tissue Proper
Supporting Connective Tissue
Dense ground substance
(Hyaline, Elastic, Fibrocartilage)
 Bone
Supporting Connective Tissue
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CONNECTIVE TISSUES

3 Main Components


Specialized cells
Mostly nonliving extracellular matrix that surrounds
cells
Protein Fibers – collagen, elastic, reticular
 Ground Substance (fluid) – fills space between cells
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
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Interstitial fluid, Cell Adhesion Proteins, Proteoglycans
Functions (vary widely)
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Binding & Supporting - framework
Transport materials – fluid with dissolved material
Storing Energy– fat in adipose tissue
Insulating
Protect Organs
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CONNECTIVE TISSUE PROPER:
CELL TYPES

Fibroblasts
Produce and maintain connective tissue fibers and
ground substance
 Local maintenance & repair
 permanent
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Macrophages
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Adipocytes
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Defense: Engulf damaged cells and pathogens
Release chemicals to stimulate immune response
Fixed or migrating (reinforcement)
Permanent fat cells store nutrients
Droplet of lipid pushes nucleus to side
Mast Cells

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Mobile, found near blood vessels
Have vesicles filled with chemicals to be released
after an injury or infection
Heparin -anticoagulant
 Histamine – leaky capillaries
 Proteases & other enzymes
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CONNECTIVE TISSUE FIBERS
 Collagen

Long, straight,
unbranched, flexible
 Elastic
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Protein – elastin
Wavy, branched,
stretchy
 Reticular

Fibers
Thin, branching
interwoven network
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GROUND SUBSTANCE
Fills spaces between cells, surrounds fibers
 Connective tissue proper – clear, colorless,
syrupy to slow movement of pathogens
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LOOSE CONNECTIVE TISSUE

Areolar Tissue
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Adipose tissue- 90% adipose cells
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Contains all cells and fibers of
connective tissue proper
Separates skin from muscles
Provides padding
Allows movement
Extensive blood supply
Behind eyes, kidneys, heart,
abdomen, buttocks, and breasts
Reticular Tissue- dominated by
reticular fibers

Lymph nodes, bone marrow, and
spleen
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WHAT IS THE DIFFERENCE BETWEEN
WHITE FAT AND BROWN FAT?

White fat
Pale yellow in color
 Found in adults
 Used for insulation, long term energy storage, &
cushion
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Brown fat
Highly vascular, contains lots of mitochondria
 Found in infants and young kids
 Metabolically very active, breaks down lipids fast
 Instead of absorbing energy, it releases heat to warm
circulating blood to increase body temperature

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DENSE (FIBROUS) CONNECTIVE TISSUE
Consists of mostly collagen fibers
 Dense Regular – collagen fibers
are parallel to resist tension
 Poorly vascularized
 Tendons – connect skeletal
muscle to bone
 Aponeuroses – flat tendons
(muscle to muscle or bone)
 Ligaments – contain elastic
fibers, connect bone to bone
 Fascia – binds together
muscles, bv, and nerves
 Dense Irregular – meshwork of
thick collagen fibers
 Provides support in many
directions (i.e. skin dermis)
 Joint and organ capsules
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FLUID CONNECTIVE TISSUES
 Blood

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Plasma- watery matrix
w/dissolved proteins
Red blood cell (rbc)
White blood cells (wbc)
Platelets
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CARTILAGE SUPPORTING CONNECTIVE
TISSUE:
 Cartilage
– gel w/embedded fibers
Chondrocytes – cells found in lacunae derived from
chondroblasts
 Avascular, therefore difficult to repair
 Lacks nerves
 Types:
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Hyaline – tightly packed collagen fibers, tough but flexible
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Elastic – elastic fibers, resilient and flexible
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Connects ribs to sternum, supports passageways of respiratory tract,
covers bone surfaces in joints, tip nose, embryonic skeleton
Flap of outer ear (pinna), epiglottis, auditory tube
Fibrocartilage – mostly collagen fibers, durable and tough
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Between vertebrae, between pubic bones, around or within joints
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Hyaline
Cartilage
Elastic
Cartilage
Fibrocartilage
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BONE SUPPORTING CONNECTIVE TISSUE:


Osseous tissue: Bone
Matrix – hard calcium and flexible collagen, very
little ground substance
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Osteocytes found w/in lacunae

Lacunae surround blood vessels

Canaliculi extend from central (Haversian)
canal
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Osseous Tissue
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MUSCLE TISSUE

Muscle tissue – interaction between the myofilaments
myosin and actin create a contraction, highly vascular
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Skeletal – striated voluntary muscle
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Cardiac – striated involuntary muscle
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Large, multinucleated cells (long and slender)
Incapable of dividing, but produced through stem cells
Striations (series of bands)
Only contract when stimulated by nerves
Smaller striated cells, single nucleus
Interconnected by intercalated discs
Limited ability to repair
Pacemaker cells establish a regular rate of contraction
Smooth – nonstriated involuntary muscle
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Walls of blood vessels, hollow tube=like organs
Small, slender cells w/ one nucleus
Actin and myosin are scattered so no striations
Can be repaired
Can contract on own or by nervous system
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NERVOUS TISSUE
Specialized for conducting electrical impulses and
responding to stimuli
 2 Types Cells:
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Long cells w/ 3main parts:
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Neurons – communicate thru electrical events
Neuralgia – physical support for neural tissue, supply
nutrients to neurons
Cell body w/ nucleus
Dendrites – branching projections that receive info
Axon – long projection (w/synaptic terminals) relays
info to other cells
Limited ability to repair
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MEMBRANES

Membranes - epithelia and connective tissues
combine to form 4 types of membranes:

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Mucous Membranes
Serous membranes
Cutaneous membranes
Synovial membranes
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CUTANEOUS MEMBRANE


Aka Skin – covers surface of body, thick, dry
Stratified squamous epithelium and underlying
dense connective tissue
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MUCOUS MEMBRANES
 Mucosae
– line cavities with exterior
contact

Digestive, respiratory, reproductive, and
urogentital tracts
 Epithelial
surfaces kept moist
 Ex.



Simple columnar epithelia of dig. tract
Stratified squamous epithelia of mouth
Transitional epithelia of urinary tract
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SEROUS MEMBRANES
 Minimizes
friction when organ moves
 Line internal subdivisions of ventral body
cavity


Parietal – lines inner surface of cavity
Visceral – lines outer surface or organs
 Simple
epithelia supported by loose
connective tissue
Pleura – covers pleural cavity and lungs
 Peritoneum – lined abdominal cavity and
associated organs
 Pericardium – lines pericardial cavity and heart
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SYNOVIAL MEMBRANES
Lines articulation (joint) capsule
 Loose connective tissue and incomplete layer of
epithelial tissue
 Produce synovial fluid for smooth movements
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Mucous Membrane
Serous Membrane
Cutaneous Membrane
Synovial Membrane
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TISSUE INJURY AND REPAIR
 Inflammation


In response to pathogens, impact, abrasion,
extreme temperatures, or chemical irritation
Mast cells release histamine and heparin that
dilate blood vessels to induce swelling,
warmth, redness and pain
 Regeneration
Fibroblasts produce dense collagen fibers
called fibrous tissue (scar tissue)
 Fibrosis is the permanent replacement of
normal tissues with fibrous tissue (i.e. heart
and muscle tissues)
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TISSUES AND AGING
 Speed
and effectiveness of tissue repair
decreases with age (change of hormones
and lifestyle)
 Epithelia gets thinner, bones become
brittle, cardiac muscle fibers and neurons
cannot be replaced
 Osteoporosis – inactivity, low calcium, and
decrease in estrogen result in poor bone
strength
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