Module 2 - Histology (The study of Tissues)
1. Tissues are the building materials of your body.
2. Four types in the body
a) Epithelial Tissue - lining of organs and forms glands. Ex: outer layer of skin,
lining of mouth and stomach, thyroid gland, pancreas, liver, etc.
b) Connective tissue - supports, binds insulates. Ex: bone, cartilage, tendons,
fat
c) Nervous tissue - sends and receives signals. Ex: Brain, spinal cord and nerves
d) Muscle tissue - allows for movement
3. EPITHELIAL TISSUE - covers surfaces of many parts of the body
a) Tile Floor Analogy - Cells are like Tiles. Tiles have 2 surfaces - the surface
you walk on and the underside of the tile which is glued to the wooden floor
beneath it.
b) Epithelial Linings - cells attached together to form two surfaces like the tiles
i. The free surface (like the top surface of the tile) - open to its
surroundings, anything passing by can come in contact with it
ii.
The basal surface (like the underside of the tile) - the underside of the
cell, just like the underside of the tile is attached to something else
(underlying tissue) by some kind of glue.
iii. The basement membrane is the glue that the epithelial cells secrete to
attach to the tissue below it.
1. The basement membrane is a vascular
a) lacking blood vessels (so there are no blood vessels in the
basement membrane or epithelial tissue, so no way to get
energy, nutrients or oxygen on their own)
2. The epithelial tissue and basement membrane get oxygen and
nutrients from the tissue below the basement membrane which
has blood vessels
a) the oxygen and nutrients diffuse across the basement
membrane into the epithelial cells.
iv. Epithelial cells die rapidly (one example: skin cells - flaky/dandruff)
1. These dead epithelial cells are replaced by Mitosis.
a) Another Example: Epithelial lining of the stomach is one cell
layer thick it is replaced rapidly by mitosis.
2. The ability to repair itself by mitosis is one very important
characteristic of epithelial linings.
c)
Classifying Epithelial Linings - Look at 2 Things
i.
The number of LAYERS
1. One layer - Simple Epithelium
2. Several layers - Stratified Epithelium (stratified means “layered”)
ii. The SHAPE of the cells making up the layers
1. Flat cells in the tissue - Squamous Epithelium (squamous =“flat or
low to the ground”)
2. Cube shaped cells in the tissue - Cubodial Epithelium
3. Tall Column like Cells - Columnar Epithelium
d) Simple Squamous Epithelium - one layer of cells thick and cells are squatty
i.
Function: Allows for Diffusion, this tissue offers minimal barrier in order
to allow for diffusion of oxygen and nutrients
ii.
This epithelium is not going to give a lot of protection and won’t have a
lot of cellular machinery (organelles) for complex tasks
iii. Perfect places for simple squamous epithelium
1. Lining of blood vessels - In our lungs, oxygen moves into blood
vessels strictly by diffusion through the delicate simple squamous
epithelium lining it.
2. Tiny air sacs (aveoli) of the lungs (found deep in the lungs) Diffusion of oxygen and Co2 can occur easily to allow for Oxygen
and Carbon dioxide to be exchanged in the blood, because simple
squamous does not have much of a barrier.
e) Simple Cuboidal Epithelium - one layer of cells thick and cells are shaped
like cubes
i.
Function: Allows for Diffusion in addition to Absorption (active
transport) and Secretion (exocytosis)
ii.
The epithelium cells are thicker in this kind of tissue , so there is more
room for cellular machinery like mitochondria, golgi apparatus,
endoplasmic reticulum and so forth.
iii. Perfect places for simple columnar epithelium are for example the
Kidneys.
1. In order to cleans your blood, your kidneys are absorbing certain
substances and secreting others constantly
f)
Simple Columnar Epithelium - one layer of cells thick and cells are tall like
columns
i.
Function: Performs more complex secretion and absorption tasks
ii.
The epithelium cells in this tissue are taller, allows for even more room
for cellular machinery. There is also a new type of cell found in this
tissue, called GOBLET cells
1. Goblet cells - produces mucus (a complex mixture of fluids, proteins
and carbohydrates that covers, protects and lubricates a free
surface within the body
iii. Perfect places for simple columnar Epithelium are the linings of your
stomach and intestines
1. Stomach fluid is very acidic form the acid released by the glands in
the stomach to allow to begin digestion ( this would immediately
kill kill the epithelial cells if not protected)
2. Mucus produced by goblet cells protects epithelial lining from being
damaged by the acid (there is a blanket of mucus over the free
surface to protect the stomach)
1. Stratified Epithelial Tissue (tissue with several layers of cells)
a) Stratified Squamous Epithelium - multilayered, squatty cells (smooshed
pancakes)
i.
The tissue named for the cells at the free surface.
ii.
The deeper cells are called basal cells (near the basal surface)
1. ie. Basal cell carcinoma - CA of skin cells close to the basal surface.
iii. The basement membrane shown in figure 2.4 of the stratified
squamous epithelium is not flat but undulates (wave like, see figure 2.4)
iv. Found:
1. In the skin (only the top layer, epidermis)
v.
Function:
1. Forms a barrier. Skin is the barrier against taking on or losing water
(bathtub example); against pathogenic organisms, and protection
against ultraviolet rays.
vi. How Skin is made:
1. Basal cells in the skin divide by mitosis, when division takes place,
cells get pushed upward. The new cells stay near the bottom of the
epithelial tissue and the older cells are pushed upward and flake off
because they are dead by the time they reach the top.
2. The dead cells contain a waterproofing protein called Keratin
a) The skin is called a kertanized membrane
3. Surface cells of the skin are dead because the basement
membrane of the stratified squamous epithelium is avascular
because the upper cells are often too far away to get oxygen and
nutrients.
b) Moist Stratified Squamous Epithelium - multilayered “living cells” make up
this tissue
i.
The surface cells are still alive unlike the stratified squamous epithelium
surface cells are dead
ii.
The layer of the cells that make up this tissue is is covered in mucus and
does not produce keratin (non-keratnized).
iii. Found:
1. In the Mouth
a) Though the surface cells in the mouth are alive, it’s still much
less active then deeper cells because it’s farther away from
diffusing oxygen and nutrients
c)
Stratified Cubodial Epithelial Tissue and Stratified Columnar Epithelial Tissue
i.
Layered versions of the simple cuboidal and simple columnar tissue
ii.
FUNCTION: Both tissues offer protection and tend to be used for
secretion
iii. Found:
1. Stratified Cuboidal epithelium - parts of salivary glands (secrete
saliva in mouth)
2. Stratified Columnar epithelium- in your larynx
d) Stratified Transitional Epithelium - multilayered, “changeable”
i.
Function: offers good PROTECTION because it is multilayered, but also
remarkable because it STRETCHES.
ii.
Found:
1. The Urinary Bladder
a) Holds urine (needs to expand) before expelled form body
b) The Bladder is the size of a thumb when empty
iii. Many layers when relaxed. Few layers when stretched.
e) Pseudo Stratified Epithelium (“false”- “layered”)
i.
All the cells touch the basement membrane (bottom).
1. TRUE Stratified epithelium only the cells at the bottom touch the
basement membrane, other layers would be in the upper layers (far
from the basement membrane)
2. Similarities to Simple Epithelial Tissue: All layers touch the
basement membrane
3. Differences to Simple Epithelial Tissue: Some cells are shorter than
others
4. Similarities to Stratified Tissue: Not all the cells touch the free
surface, making it more like stratified tissue, so called Pseudo
Stratified.
ii.
The cells have Goblet cells and often has Cilia
iii. Found:
1. Nasal passages
2. Air sinuses of the skull
3. Airways of the lungs (tubes through which air travels)
a) The mucus from the goblet cells traps particles from the air and
the cilia then move the particles out of the airway (the tubes)
b) This air cleaning function is necessary to keep the lungs clean
and allows for efficient exchange of gases farther down in the
lung (aveoli)
f)
Glandular Epithelium
i.
Two types of glands: Exocrine and Endocrine
1. Exocrine glands
a) Have ducts that allow to secret a product out to a surface
b) Many in the body - come in different shapes and sizes but have
basic structure
i.
ii.
c)
All have secretory portion (cells that do the secreting)
All have a duct (passage through which chemicals travel to
reach the surface
Exocrine Gland Classification - ways of secretion of chemicals
i.
Merocrine glands
1. Exocrine glands that secrete without losing cellular
material
a) Mero means “part” and crine means “secretion”
b) Example: Sweat glands
ii.
Apocrine glands
1. Exocrine glands that have cytoplasm in their secretions.
a) Pinch off the tip of the epithelial cells
b) Apo means “apex” or “tip”
c) Cellular material becomes apart of the secretion
d) Example: Mammary glands
iii. Holocrine glands
1. Exocrine glands with secretions of disintegrated cells
a) Releases entire cells into the duct.
b) “Holo” means “whole”
c) Cells rupture: contents including the nuclei spill
into duct
d) Ruptured cells replaced by mitosis.
e) Example: Sebaceous glands
2. Endocrine glands - Cells packed close together
a) Secrete chemicals called hormones directly into blood stream
b) Hormone secreted directly into the blood stream and then can
be taken rapidly all over the body in the blood stream
c)
No ducts
d) Tiny blood vessels called capillaries present through the cells
i. The blood takes oxygen and nutrients to the cells
ii. Picks up anything the cells secrete
e) Endocrine cells
i. Secrete their hormones by exocytosis and then blood in
the capillaries carry the hormones throughout the body.
Module 2 - Histology (The study of Tissues)
1. CONNECTIVE TISSUE
a) Function:
i. Forms infrastructure of the body
ii. Binding and Supporting Tissue
1. Holds you up
2. Holds you together
3. Binds tissues together
iii. Insulates
*** Vascular
b) Connective Tissue Cells
i. Secretes extracellular material or matrix that gives it special abilities
ii. Secretes a number of products outside of themselves
iii. Cells are relatively far a part with a lot of extracellular material between
them
iv. Epithelial cells differ because their cells are packed tightly together
c)
Extracellular Matrix: Chemical substances located between connective
tissue cells
i. Ground Substance (chemical mixture of proteins (secreted by cells),
water the proteins attract (gel-like), protein threads (form fibers)
ii. Collagen (found in 1/3 bone tissue)
a) Thread like protein fiber helping to hold connective tissue
together
i. Deep part of the skin has collagen that makes it firm
ii. Collagen break down causes skin sag -> wrinkles
d) Classifying Connective Tissue
i.
Based on the extracellular matrix because it gives it its function
1. Hard, Flexible or Stretchy
ii.
Four Basic Types of Connective Tissue Proper
1. Loose Connective Tissue
a) Ground substance that is gel-like
b) Some protein, some fluid, some collagen fibers (made of
proteins that are elastic fibers)
i. Allows connective tissue to be stretched
c)
Contains Fibro blasts
i. Spindle-shaped cells that form connective tissue proper
ii.
Fibro blasts turns into Fibrocyte when fibroblast is
completely surrounded by the matrix, connective tissue is
done developing
d) Function:
i. Light-duty binding
ii. Holds things together in all directions but very lightly
1. ie. similar to thin material that forms nylon hose
iii. Not Very Strong but Flexible
1. Ex: when pulling skin - the force pulling back is loose
connective tissue -- that connects the skin to the
underlying muscle
2. Found in Hypo-dermis (not a part of skin)
2. Dense Irregular Connective Tissue
a) More Collagen fibers oriented in all directions (irregular)
i. Opposite of loose
b) Skin divided into two layers
i. Epidermis (stratified squamous epithelium)
ii. Dermis (dense irregular connective tissue) - opposite of
loose and has to do with how many collagen fibers there
are
*** Hypo-dermis (loose connective tissue, not a part of the skin)
c)
Function:
i. Strength in all directions
1. ie: pair of jeans
d) Found
i. Capsules around Organs
1. ie: Kidneys have thin but tough capsule
3. Dense Regular Connective Tissue
a) More Collagen Fibers lined up mostly in the same direction
b) Have Fibroblasts but NO elastic protein fibers
c) Function:
i. Strong binding - Rope like strength
ii. Tensile Strength
1. ie: pulling a rope versus putting a heavy object on a
rope
d) Found
i. Tendons
1. Holds muscle to bone
2. Very strong
3. Difficult to pull tendon off bone, when injured:
PAINFUL!
4. Some give - due to collagen fibers are wavy not
because of elastic fibers
ii.
Ligaments
1. Attach bone to bone
2. Strong
3. Some give - due to collagen fibers are wavy not
because of elastic fibers
4. Adipose Tissue
a) Most similar to Loose Connective Tissue
i. All materials of loose connective tissue but cells are
adipocytes or fat cells
b) Contain Adipocytes/Fat cells
i. Fat cells fill with droplet of oil, enlarging them and pushing
them close to one another
c)
Function:
i. Support
ii. Protection
iii. Insulation
iv. Metabolic Function
d) Found
i. Fat present around organs to support and protect it
1. Regardless of weight -substantial fat present to
support each kidney - protected and held in place
ii. Under the skin
1. Acts as insulation against outside temperature
a) ie: bubble wrap - supports and protects what it
covers but also insulates form temperature
change
iii. Compact way of storing nutrients for future energy
production because the oils stored in each fat cell are
energy-rich.
1. Carbs instead of fats would take up too much space
2. Shouldn’t have too much or too little
e) Connective Tissue Proper Healing
i. Very slow
ii. Fibroblasts have to produce large amount of extracellular material
iii. Longer time than Epithelial tissue where all cells undergo mitosis to heal
iv. Connective tissue cells have BIG job to do, so even minor injuries to
connective tissue proper can take a longer time
2. CARTILAGE
a) Three Types: Hyaline Cartilage (bridge of nose), Elastic Cartilage (outer part
of your ear, Fibro Cartilage (disks between backbones)
i. All types have chondrocytes (cells that produce special extracellular
material)
b) Firmer than Connective Tissue Proper
c)
Cartilage Matrix is Firm
d) Cell can not live directly in the Matrix
e) Small hollowed-out spaces called Lacuna, in which cartilage cells live
f)
Found
i. Bridge of you nose
ii. Outer part of your ear
iii. Disks between your Backbones
g) A vascular - no blood supply (connective tissue proper is vascular)
h) Thin - to allow easy diffusion of oxygen/nutrients for living chondrocyte cells
i. No blood vessels in the matrix
ii. If it gets thick, it dies
iii. If thickens, replaced by bone which has blood supply that it brings along
i)
j)
Cartilage Matrix Contains Collagen (like connective tissue proper)
Hyaline Cartilage
i. Collagen give it resiliency
ii. Tissue that is both firm and Resilient like hard plastic
iii. Found: Bridge of nose and framework of larynx, costal cartilage of ribs
(ribs to sternum), caps on bones due to smoothness which is ideal for
moveable joints (smooth hyaline cartilages slips against smooth hyaline
cartilage with only lubricant between)
k) Fibrocartilage
i. Found:
1. In joints
2. Between Vertebrae of back bone
ii.
l)
a) Vertebrae must be bound together by tough binding, resiliency
to cushion spinal column as you walk, bend, jump
Function
1. Tough binding
2. Resilient Support
a) ie: soles of shoes
iii.
Elastic cartilage
i. Not as much cartilage as the other two types of cartilage
ii. Contains Elastic fibers which are stretchy like rubber band (soft plastic)
iii. Found
1. Outer Ear
2. Tip of nose
3. ie: floppy puppy ears growing erect
iv. Function
1. Highly flexible support
3. Bone Tissue
a) Connective tissue in bone is known as Osseous tissue
b) Contains cells that are far from one another
c) Cells secrete ground substance, fibers, collagen, fluid
d) Ground substance in bone becomes hardened through calcification
4. Blood Tissue
a) Connective tissue in blood is known as Vascular Tissue
b) Has Red and White blood cells that are not packed together
c) Ground substance (the proteins in blood)
d) Fluid (blood plasma)
e) Has Fibers - normal blood protein are small and round fibers but simulated
by injury they can join together like strings of beads as long/tangled fibers
to create blood clots
5. Membranes
a) Made of Epithelial Tissue and Connective Tissue
i. Skin (cutaneous membrane)
1. Top layer of skin (epidermis) - stratified squamous epithelial tissue
2. Lower layer of skin (dermis) - dense irregular connective tissue
3. Below top/lower layer - find loose connective tissue
b) Three categories in body
i.
Mucous membranes
1. Line the entire Digestive tract: mouth to anus
2. Urinary tract
3. Respiratory tract
4. Reproductive tract
5. All tracts open to the outside of the body (digestive opens at both
ends, respirator opens at mouth and nose)
6. Function: Protects the body
a) ie: respirator tract breathe in air with dust and dirt and
respiratory tract traps foreign particles and move them out of
the body
ii.
Synovial membranes
1. Found around moveable joints - used for lubricating
2. Bones in a joint covered in hyaline cartilage (quite smooth,
allowing bones to of joint to move without bone rubbing against
bone)
3. Joints still need to be efficient in use of energy even with hyaline
cartilage
4. The hyaline cartilage is lubricate by synovial fluid
5. Synovial fluid is secreted by synovial membranes - creating little
sac around side of joints
iii. Serous membranes
1. Form thin double layers around the organs and secret a small
amount of lubricating fluid into the space between the layers
2. Reduces friction between organs with movement
3. Found
a) Heart
b) Lungs
c) Abdominal organs
6. Tissue Repair
a) Two types of Repair
i. Repair you get function back (cut on your skin)
ii. Repair in which you get scar tissue (does not function like original tissue)
iii. ie: heart attack example
b) Stromal cells
i. Structural cell that form the infrastructure
ii. ie: cells that allows the liver to hold shape
iii. If liver is damaged, will lay down scar tissue but can not restore function
to the organ
c)
Parenchymal Cells
i. Does the work that the tissue has been designed to do
ii. ie: cells that secrete bile in the liver
iii. If liver is damaged, need to be restored for the of the liver to continue
doing its job
d) Labile cells
i. Cells of epithelial tissue are always undergoing mitosis
1. When skin is cut, the cells undergo mitosis constantly so
neighboring cells will start reproducing to replace cells lost
e) Stable cells
i. Cells in your bones
1. Bone cells will die if bone breaks but neighbors of bone cells can
undergo mitosis can repair injury of broken bone
f)
Permanent cells
i. Cells of nervous tissue,cardiac tissue and muscle tissue
1. Can not undergo mitosis after infant stage
a) In cardiac tissue
i. during a heart attack no mitosis of neighboring cells to
replace damaged cells
ii. replaced by fibroblasts which produces connective tissue
iii. Heals the wound but not in a functional way
iv. Remaining cells that are healthy can be strengthened
through exercise even though damaged cells can not be
regenerated
g) Recap
i. Parenchymal cells in the heart are permanent cells - destroyed can’t be
replaced, replaced by stromal cells (heals wound but function lost)
ii. Parenchymal cells in skin are labile cells - when parencymal skin cells
are lost-- thy are replaced with parenchymal skin cells , no function is
lost
iii. Bone and glands contain stable cells that can undergo mitosis
h) Factors affecting Tissue Repair
i.
Better circulation leads to better tissue repair
1. Blood brings nutrients and oxygen , takes away wastes, brings in
wbc’s to fight infection
2. Better nutrient means better tissue repair - protein and vitamins
are critical for proper tissue repair
a) ie. Vitamin C required for production of collagen
b) Connective tissue repair requires Vitamin C.
ii.
Age affects Tissue Repair
1. Growth works to advantage
2. Adults in prime heal well
3. Old age makes healing process much slower