Histology Introduction

Histology


The study of the structure and function of tissue
Trillions of individual cells in your body 
~200 types of cells  1 cell type together
forms tissue
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Tissue Introduction continued
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Human body has 4 basic types of tissue:

Epithelial


Connective
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Ex: bone
Muscle

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Ex: skin
Ex: biceps brachii
Neural
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Ex: neurons
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1. Epithelial Tissue

2 main parts

Epithelia


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Layers of cells
Cover internal/external surfaces
Glands

Secretion structures
3
Epithelial Characteristics

Cellularity


Attachment

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Base of epithelium attached to “basement membrane”
Avascular


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Composed of all cells tightly bound vs other tissue
types
Do not contain blood vessels
Obtain their nutrients but diffusion/absorption
Regeneration

High rate of mitotic division for constant repair
4
Functions of Epithelial Tissue

Physical protection

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Control Permeability
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Regulation of transmission of hormones, stimuli, etc.
Provide Sensation

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Protect internal structures from damage
Have sensory cells
Detect changes or convey information
Produce Specialized Secretions

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Gland cells
Secretions to relay messages or protection to tissue
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Maintain Integrity to Epithelia

3 factors

1- Intercellular Connections
 Cell Adhesion Molecules


Intercellular Cement


Transmembrane proteins, bind to each other to
connect individual cells
Bonds adjacent cells, carbohydrates that connect
Tight Junctions & Gap Junctions

Interlocking membrane proteins of adjacent cells
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Maintain Integrity to Epithelia

3 factors

2-Attachment to basement membrane


Epithelial cells hold onto each other
Firm connection to the basement membrane through
glycoproteins
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Maintain Integrity to Epithelia

3 factors

3-Epithelial maintenance/repair


Continual division of stem cells/germinative cells
 Undifferentiated cells
Located in the deepest layer of the epithelium
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Classification of Epithelia

Cell Shape:
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3 different shapes
 Squamous

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Cuboidal

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Thin, flat, irregular
Hexagonal boxes, square
Columnar

Rectangular, taller and slender
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Classification of Epithelia

Number of Cell Layers:

2 types:
 Simple
 1 layer, thin
 Regions of secretion or absorption, gas
exchange
 Stratified
 Multiple layers
 Regions subject to mechanical/chemical
stress
 Psudostratified
 Appears layered but is truly not
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Classifying Epithelial Tissue
Simple Squamous Epithelium

Thinnest

Located in protected regions where absorption
takes place or where a slick, slippery surface
reduces friction.
Lining of heart and
blood vessels, lungs

Stratified Squamous
Epithelium

Located where mechanical stresses are
severe


Surface of skin, lining of mouth, throat, rectum
Provides physical protection against
abrasion, pathogens, and chemical attack.
Simple Cuboidal Epithelium


Provides limited
protection
Occurs where secretion
or absorption takes
place.

Lines kidney tubules,
glands, ducts
Stratified Cubiodal Epithelium


Rare
Located along the ducts of sweat glands

Protection, secretion, absorption
Simple Columnar Epithelium


Protection, Absorption, Secretion
Lines stomach, intestines, gallbladder
Pseudostratified Columnar
Epithelium




All cells still attached basally
Appeared layered
Lining of nasal cavity, trachea, bronchi
Protection and secretion
Stratified Columnar Epithelium


Rare
Provide protection along small areas of the
pharynx, epiglottis, anus, mammary gland…
Glandular Epithelia

Many epithelia contain glands that produce
excretions

Endocrine- (hormones) released in body


Ductless-secrete into intestinal fluid or blood and
transferred
Exocrine –released out of body (Sweat, milk)

Use ducts (tubular passageways)
2. Connective Tissue

Includes:




Bone
Fat
Blood
Connective tissue because:



1-specialized cells
2-extracellular protein fibers
3-fluid or ground substance present
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Connective Characteristics

Structured

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Transport

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Surrounding & interconnecting tissue
Storage

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Delicate organs
Support

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Fluids & dissolved materials
Protection

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Framework for body
Energy reserves as lipids
Immunity
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Classification of Connective

3 General Categories



Connective Tissue Proper
Fluid Connective Tissues
Supporting Connective Tissues
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Classification of Connective
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Connective Tissue Proper

Contains:




Extracellular fibers
Viscous (syrupy) ground substance
Varied cell population
The combination of the above determine
whether the connective tissue proper is loose
or dense
CTP Cells “varied cell
population”



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Macrophages (defense by activating immune
system)
Adipocytes (fat cells)
Mesenchymal Cells (stem cells-divide and
repair cell damage)
Melanocytes (make and store melanin-gives
skin brown pigment)
CTP Cells Continued
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
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Mast Cells (release inflammatory chemicals
when injured)
Lymphocytes (help with damaged areas by
producing antibodies)
Microphages (phagocytic blood cells that
fight infection)
CTP-Loose Connective Tissue

“packing materials” of the body


Fill spaces between organs, cushion and
stabilizes cell in organs, supports epithelia
Includes
1.
2.
Areolar Tissue
Adipose Tissue
Areolar Tissue



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Very common
Shock absorber
Padding under skin
that protects muscle
Shots often given in
this layer of tissue
Adipose Tissue



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Fat accounts for the
majority of the tissue
Provides padding,
absorbs shocks,
insulates
White fat=adults
Brown fat=infants &
children (highly
vascularized) allows fast
warm up
CTP-Dense Connective Tissue

High concentration of fibers


Dominated by collagenous tissue
2 kinds of Dense Connective Tissue
1.
2.
Dense regular connective tissue
Dense irregular connective tissue
Dense Regular Connective
Tissue


Collagen fiber parallel to
each other
Packed tightly


Tendons
Ligaments
Provides firm attachment;
conducts pull of muscles;
Dense Irregular
Connective
Tissue
No pattern
Support and strengthen areas subjected to
stresses from many directions (under skin,
around bladder)
Fluid Connective Tissue

Blood and Lymph are connective tissues that
make up a fluid matrix
Blood

Contains blood cells and fragments of cells=
formed elements:
1.
Red Blood Cells (almost ½ volume of blood)
-transports oxygen and CO2
2.
White Blood Cells (found in watery mix-plasma)
-important for immune system for fighting infection
3.
Platelets (membrane enclosed cytoplasm)
-help the clotting process
Lymph

Gets returned to cardiovascular system
through lymphatic vessels

Brings messages of injury or infection
Supporting Connective
Tissues

Cartilage and Bone

Provide strong framework that supports body
Cartilage = Chondrocyte


Firm gel-firmness depends on fiber count
Avascular-doesn’t contain vessels

All nutrient and waste exchange through diffusion
Types of Cartilage (3)
1.
Hyaline Cartilage
-most common, tough but flexible
Shoulder Joint, between ribs and sternum, nasal
Mat
rix
2. Elastic Cartilage



Contains numerous elastic fibers
Extremely resilient and flexible
External flap of ear, epiglottis,
3. Fibrocartilage
-Matrix dominated
by collagen fibers
-Extremely durable
and tough
-Resists
compression,
prevents bone to
bone contact
-pads within knee
joint, intervertebral
discs
Bone = Osseous Tissue


2/3 of the matrix of bone is a mixture of
calcium salts (hard, but brittle)
The rest is collagen fibers (strong, but
flexible)
Calcium salts organize around collagen fibers=
strong, somewhat flexible, very resistant to
shattering
Osteocytes: bone cells
Osteon: Large concentric circle made up of Osteocytes,
Canaliculi and the matrix
• Matrix (white space)
• Bone Cells (bigger black spots)
• Canaliculi (small black branches that connect blood
vessels to bone cells)
Connective Tissue Slide
Identification
#1: Blood
#2: Bone
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Connective Tissue Slide
Identification
#3a: Areolar
#3b: Adipose
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Connective Tissue Slide
Identification
#4: Hyaline Cartilage
#5: Fibrocartilage
#6: Elastic Cartilage
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3. Muscle Tissue

3 Types:




Skeletal Muscle
Cardiac Muscle
Smooth Muscle
Different because of their location and
function
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Skeletal Muscle



Large muscle cells
Have several nuclei per fiber (multinucleated)
Incapable of dividing


Use stem cell to make new fibers and repair
damage
Striated Voluntary Muscle-has bands (actin
and myosin groups), doesn’t contract unless
stimulated to by nerves
Cardiac Muscle Tissue

Only found in heart




Smaller than muscle cells
One nucleus
Intercalated Disks


Moves blood, blood pressure
Connects cells for smooth contraction
Striated Involuntary Muscle

Do not rely on nerves to contract, but cells called
pacemaker cells
Smooth Muscle Tissue

Walls of blood vessels, digestive, respiratory,
urinary tracts


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Moves food, urine, controls diameters of vessels
Smooth (no striations)
Can divide and regenerate
Involuntary
Nonstriated involuntary muscle



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4. Neural Tissue
Conducts electrical impulses through out body
98% of neural tissue is in the brain and spinal
cord. 2 Cell types:


1-Neurons (Conscious and unconscious thought)
2-Neuroglia (Support neural tissue, supply
nutrients to neurons)
Longest cells in body (1 meter)
Most cannot divide or repair when damaged
Neuron
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Neural Tissue Structure

Soma: Cell Body



Dendrites: contacted by other neurons, receive
information
Nucleus, Mitochondrion
Axon: transfer of information from Nucleus


Myelin Sheath: coding that allows rapid
information transfer
Axon Terminals: connect to next neuron, transport
information to next neuron
Tissue Injuries

INJURY TO TISSUE


Homeostasis beings after tissue injury
2 Phases

1-INFLAMMATION





Chemicals released by Lysosomes/Peroxisomes
after clean-up of damaged cells
Chemicals increase circulation to that area
Blood vessels dilate
Increased blood flow accelerates nutrient/oxygen
delivery
White Blood Cells also enter the area to aid in
clean-up/bacterial removal
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Tissue Injuries

INJURY TO TISSUE


Homeostasis beings after tissue injury
2 Phases

2-REGENERATION


New cells/tissue is laid down rapidly
Produces a dense framework also known as scar
tissue
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Aging
As the human body ages:
 Repair/maintenance slows down
 Epithelia are thinner due to decreased mitotic activity
 Connective tissues are more fragile



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Cartilage thins = arthritis
Lowered calcium levels = osteoporosis
25% of US Civilians will develop cancer
70-80% from environmental/chemical
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