- Histology is a branch of science that deals with the study of tissues.
- There are four types of body tissues:
- Epithelial tissue
- Connective tissue
- Nerve tissue
- Muscle tissue
Epithelial tissues
They are useful in the protection of the outer surface and lining of internal organs.
Epithelial tissues are arranged in tubes or sheets of tightly packed cells.
They have a free surface that can be exposed to fluid or air.
The free surface can be covered by more layers of epithelial tissue.
The free apical surface has cilia like projections that move materials over the cell surface.
- The functions of epithelial tissue include the following:
- Protection: The skins protect the delicate organs in the body.
- Barrier: It prevents foreign substances from entering the cell.
- Sensation: The body is connected to the outside stimuli via sensory nerves.
- Secretion: Enzymes can be secreted by specialized glands of epithelial tissue.
- Simple epithelial tissue is a single layer.
- Stratified tissue has more than one layer.
- The epithelial tissues can be classified according to shape into squamous, cuboidal, and columnar epithelial tissues.
Types of epithelial tissues
- Simple squamous epithelium: It looks like a rolling tundra.
- It has layered scale-like flat cells that are important for secretion, diffusion, or absorption.
- The tissue lines the air sacs of the lungs where carbon dioxide and oxygen exchange occurs.
- They also line eardrums and form kidney filters.
- Simple cuboidal epithelium: They are made up of a single layer of cube-shaped cells with round centrally located nuclei.
- They are important for absorption, secretion, and tube formation.
- They are found in ovaries and kidneys.
- Simple columnar epithelium: They contain densely packed cells that are taller than wide.
- They function in absorption and secretion.
- They involve cells that line the gastrointestinal tract.
Simple columnar ciliated epithelial cells: This tissue has hair-like cilia that promote movement of mucus and other materials across the cell.
Pseudostratified columnar epithelium: They appear as multilayered because nuclei scattering but they are not.
Pseudostratified columnar ciliated epithelium: This tissue contains a free surface covered with cilia important for the movement of materials across this surface.
Stratified squamous epithelium: It makes up the epidermis. It has multilayers of squamous cells on the surface and cuboidal cells in the deeper layers.
Stratified cuboidal epithelium: The main function is protection. It can be found in sweet glands and eye conjunctiva.
Stratified columnar epithelium: they are found male urethra lining and excretory ducts linings.
Stratified transitional epithelium: they contain cells that can shift shape from cubes to squamous like flat surfaces and vice versa.
Connective tissues
They connect, bind, and support body structures.
Types of connective tissue include:
Areolar or loose tissue: This tissue is found in almost everything in the body to fill spaces and join structures together. It is made up of collagenous protein fibers, elastic fibers, and amorphous ground substance.
Dense regular connective tissue: It is composed of parallel sheets of fibers. It is found in tendons as collagenous fibers bundle that attach muscles to bones. They are also found in ligaments as elastic fiber bundles. The tissue resists force in two directions only.
Dense irregular connective tissue: This tissue makes up the dermis and the outer membrane of organs like the kidney.
Adipose tissue: It is composed of fat cells. It reduces the loss of heat by the skin and stores energy in molecules of fat.
Reticular tissue: It makes a good filter and that’s why it is found in lymph nodes, bone marrow, and spleen.
Cartilage: Cartilage makes up the elastic and collagen fibers. cartilage contains lacunae that cover chondrocytes. Types of cartilage include:
- Hyaline cartilage
- Fibrocartilage
- Elastic cartilage
Blood: Blood ha an extracellular matrix called plasma which contains leukocytes, erythrocytes, and thrombocytes. It is a vascular tissue because it circulates in veins and arteries.
Bone tissue: It is a connective tissue that is mineralized. It is responsible for the support and movement of the body.
REVISION
Tissues
Tissue classification based on structure of cells, composition of noncellular extracellular matrix, and cell function
four types of tissues
- Epithelial tissue
- Connective tissue
- Muscle tissue
4.Nervous tissue
Histology
Microscopic study of the tissue
Biopsy
Removal if tissue for diagnostic purposes
Autopsy
Examination of tissue of dead body to determine cause of death
Embryonic Tissue, germ layer
Endoderm, Mesoderm
Endoderm
inner layer, forms the lining of the digestive tract
Mesoderm
middle layer, forms muscles, bones, and blood vessels
Ectoderm
outer layer, forms the skin and neuroectoderm forms structures of the nervous system
Epithelial Tissue
consist almost entirely of cells
Avascular- no blood supply
Regenerative- cell can divide
Specialized cell connections
Cover the outside of the body
Line the insides of the digestive, urinary, respiratory and reproductive system
Line heart and blood vessels
Lines the inside of body cavities
Forms glands
Distinct sufaces:
free surface- top, faces lumen/opening
Lateral surface- sides, where the cells contact one another
Basal surface- bottom, attaches to another structure
Basement membrane- a cellular layer below the tissue
Basement Membrane
Extracellular
Formed by secretions of the cells of the epithelial tissue and secretions of the underlying connective tissue
A cellular “glue”
Functions:
attaches the CT (connective tissue)
Helps to guide cell migration
Act as a filter
Not always associated with epithelial tissues
Functions of Epithelial Tissue
Protect underlying structures
Act as a barrier
Allow for movement of material across the surface
Secretion
Absorption
Classification of Epithelium
Number of layers of cells
Simple- single layer of cells
Stratified- two or more layers of cells. Use apical/top cell layer to name the shape of the cell
Pseudostratified- tissues that appear to be stratified but all the cells are attached to the basement membrane
Shape of cells
Squamous- flattened, scale shaped
Cuboidal-same hight and width
Columnar-taller than wide
Simple
single layer of cells
Stratified
two or more layers of cells. Use apical/top cell layer to name the shape of the cell
Pseudostratified
tissues that appear to be stratified but all the cells are attached to the basement membrane
Shape of cells
Squamous
flattened, scale shaped
Cuboidal
same hight and width
Columnar
taller than wide
Functional Characteristics
Simple:Allow diffusion of gases, flirtation of the blood,secretion, absorption
Stratified:protection-against abrasion
Squamous: allow for diffusion and filtration
Cuboidal and columnar:secretion and absorptions
May contain goblet cells- mucus producing cell, unicellular gland
Free surfaces of epithelium
Smooth: reduces friction
Microvilli:increase surface area, absorption and secretion
Stereocilia: elongated microvilli, for absorption and secretion
Cilia: move materials over the surface of the tissue
Folds:in transitional epithelium, allows organs to change shape as the fill or empty. urinary system
Simple Squamous Epithelium
Structure: single layer of flattened cells
Location:lining blood and lymphatic vessels, alveoli, kidney, lining serious membrane
Functions:diffusion, filtration, some protection, small amount of absorption and secretion
Simple Cuboidal Epithelium
Structure: single layer of cubed shaped cells
Location:Kidney tubules, glands, choroid plexus, terminal bronchioles
Functions:absorption, secretion, movement of materials(celli)
Simple Columnar Epithelium
Structure: single layer of column shaped cells
Location:Glands, stomach, intestines, bronchoiles of the lungs, uterus uterine tubes, gallbladder
Functions:secretion, movement of materials over the surface, absorption
Stratified Squamous Epithelium
Structure: multiple layer where the basal layers are cuboidal and apical is flattened
Location:Keratinized- skin, moist-oral cavity,parts of the pharynx, esophagus, vagina, anus
Functions:Protection
Stratified Cuboidal Epithelium
Structure:multiple layers of cube shaped cells
Location: sweat gland ducts, salivary gland duct
Functions:absorption secretion and protection
Stratified Columnar Epithelium
Structure:multiple layers with the apical layer being column shaped
Location:mammary gland duct, male urthra, larynx
Functions:secretion and protection
Pseudostratified Columnar Epithelium
Structure: aall cells are attached to the basement membrane but it appears to be more than one layer
Location: repiratory passageways nasal cavtiy parts or pharynx trachea, bronchi, auditory tubes
Functions:secretion of mucus movement of mucus across the surface
Transitional Epithelium
Structure: multiple layers of cells that change shape, cube shaped when an organ is not stretched, squamaus when stretched
Location:urinary system-urinary bladder, ureters, part of the urethra
Functions:allow for changes in volume of the organ
Cell Connections
Found on lateral and basal surfaces of cells
Functions
form a barrier
hold cells together
allow communication
Types
tight junctions
desmosomes
gap junctions
Desmosomes
disk-shaped structures within the cell membrane found in tissues where there is a lot of stress, like a snap
example located in the skin
located lateral surfaces connect two cells together
Hemidesmosomes
half of a desmosomes, found on the basal surface, attach the cell to the basement membrane
Tight Junctions
help form barriers between cells, like a zipper
zonula adherens
weak glue between cells, helping to hold cells together, single layer of cells(epithelium)
zonula occludens
permeability barrier, found in the stomach, prevent movement of materials between the cells
Gap Junctions
protein channels for communication between cells, allow ions to travel between cells, found in ciliated tissues, help coordinate movement, found in cardiac and smooth muscle
Glands
Epithelium with supporting network of C.T.
Two types of glands formed by infolding of epithelium:
Endocrine:no open contact with exterior, no ducts, release into the blood, produce hormones
Exocrine:maintain open contact with exterior, have ducts
Exocrine glands classified either by structure or by the method of secretion_
Sturcture: unicellular-have only 1 one cell, goblet cells
multicellular made up of more than one cell
Multicellular Exocrine Glands
Classified on the basis of types of ducts or mode of secretion
Types of ducts
Simple:little to no bracing of the ducts
Compound:ducts that have a lot of branching
tubular glands -straight ducts
acinar glands- sac like structure
Connective Tissue
abundant type of tissue
found in every organ
consists of cells separated by extracellular matrix
most diverse
many important functions
Functions of Connective Tissue
enclose organs
separate layers of an organ
connect tissues to one another
support and movement
storage
protect and insulation
transportation
What are the three components of tissue classification?
Cell structure, extracellular matrix, and cell functions
Name the 4 types of tissues
Epithelial, connective, muscle, and nervous
What is the primary purpose of epithelial cells?
To act as a protective covering of surfaces inside and outside of the body
True or false: epithelial cells are densely packed
True; they are densely packed
True or false: epithelial tissues have lots of extracellular matrix
False; epithelial tissues have very little extracellular matrix
List the areas of the body where epithelial tissue can be found
- Outside surface of the body (ex. skin)
- Lining of digestive, respiratory, and urogenital systems
- Lining of heart and blood vessels
- Lining of many body cavities
Apical Surface
Opens to inside of tubes/tracts OR open to outside of body
Basal Surface
Cells attached to basement membrane
Lateral Surface
Cells are densely packed against each other
Basement Membrane
- Attached to basal surface
- Formed by secretions of epithelial and connective tissue
- Porous structure
Epithelial cells are and capable of __
Avascular; regeneration (ex. the basement membrane of the chorion)
True or false: epithelial cells have nuclei
True; epithelial cells have nuclei
What organ is an example of epithelial cells permitting passage of substances?
Kidneys; toxin filtration
What is an example of epithelial secretion?
Mucus! Mucus helps enzymes travel throughout the body
What are the functions of epithelial cells?
- Protecting underlying structures
- Acting as barriers
- Permitting passage of substances
- Secretion and absorption
Microvilli
- Increase surface area for absorption and/or secretion
- Example: lining of the small intestine
Cilia
- Move substances across cell surface using a wave-like action
- Example: cilia on the lungs that help move foreign substances out of the lungs
How many layers of cells does simple epithelium have?
One layer, all connected to a basement membrane
How many layers does stratified epithelium have?
Multiple layers, with the bottom-most layer touching the basement membrane
How many layers does pseudo-stratified epithelium have?
One – the tissue appears to be stratified (since all of the cells differ in height), but all cells have contact with the basement membrane
Describe the shape of a squamous cell
Flat, scale-like
Describe the shape of a cuboidal cell
About equal in height and width
Describe the structure of a columnar cell
Look like columns, are taller than they are wide
Describe the function of simple epithelium
- Allows diffusion of gases
- Filtration of blood
- Secretion, absorption
Describe the function of stratified eptithelium
Protection, particularly against abrasion (ex. skin)
Describe the function of pseudostratified eptithelium
Secretion and movement of mucus
Describe the function of squamous eptithelium
Allows diffusion, acts as a filter
+ cells = least resistant barrier for diffusion and/or filtration
Simple; squamous
Describe the function of cuboidal and columnar eptithelium
- Secretion and./or absorption
- Example: goblet cells produce/secrete mucus
What shape of cells can be included in the “simple” category?
Squamous, cuboidal, and columnar
What shape of cells can be included in the “stratified” category?
Squamous (keratinized & non-keratinized), cuboidal, and columnar
What shape of cells can be included in the “pseudostratified” category?
Columnar only
What shape of cells can be included in the “transitional” category?
Cells capable of stretching
When stretched – squamous like
When not stretched – roughly cuboidal and columnar
What is transitional epithelium?
Tissue that can stretch (ex. the tissue composing the bladder)
Describe the structure of simple squamous epithelium
Structure: single layer of flat cells
Describe the structure of simple cuboidal epithelium
Structure: single layer of cube-shaped cells, some with microvilli or cilia
Describe the location simple cuboidal epithelium
Location: kidney tubules, glands and their ducts, choroid plexus of the brain, lining of the terminal bronchioles of the lungs, surface of the ovaries
Describe the function of simple cuboidal epithelium
Function: Secretion and absorption in the kidney, secretion in glands and choroid plexus, movement of mucus out of terminal bronchioles by ciliated cells
Describe the location of simple squamous epithelium
Location: lining of blood vessels (endothelium), alveoli of the lungs, loop of Henle, lining of serous membranes
Describe the function of simple squamous epithelium
Function: diffusion, secretion, filtration, protection against friction
Describe the structure of simple columnar epithelium
Structure: single layer of tall, narrow cells; some have microvilli or cilia
Describe the location of simple columnar epithelium
Location: glands, bronchioles, auditory tubes, uterus/uterine tubes, stomach, intestines, gallbladder, bile ducts, neural ventricles
Describe the function of simple columnar epithelium
Function: – movement of particles out of the bronchioles
- ciliated cells help move oocytes through uterine tubes
- secretion of glands by the stomach and intestine
- absorption of cells of the intestine
Describe the structure of stratified squamous epithelium
Structure: multiple layers of cells – cuboidal in the basal layer and progressively flatten out towards the surface of the tissue
Describe the location of stratified squamous epithelium
Location:
Non-keratinized: mouth, throat, anus, vagina, esophagus, etc.
Keratinized: skin, hair, nails, etc.
Describe the function of stratified squamous epithelium
Function: – protection against abrasion and caustic chemicals
- protection against water loss and infection
Describe the structure of pseudostratified columnar epithelium
Structure: – all cells touch basement membrane
- almost always ciliated and associated with goblet cells
Describe the location of pseudostratified columnar epithelium
Location: lining of nasal cavity, nasal sinuses, pharynx, trachea, and bronchi of lungs
Describe the function of pseudostratified columnar epithelium
Function: synthesize and secrete mucus, move mucus/fluid containing foreign objects
Describe the structure of transitional epithelium
Structure: stratified – cells change shape depending on amount of distension of the organ
Describe the location of transitional epithelium
Location: lining of urinary system
Describe the structure of transitional epithelium
Structure: – accommodates fluctuations in the volume of liquid in an organ or tube
- protection against the caustic effects of urine
Glands
- Epithelium with supporting network of connective tissue
- A cell, a group of cells, or an organ that produces a secretion for use elsewhere in the body or in a body cavity or for elimination from the body
Which two types of glands are formed by the folding of epithelium?
Endocrine and exocrine glands
Endocrine Glands
- No open contact with exterior
- No ducts
- Produce hormones
- Example: pituitary gland
Exocrine Glands
- Open contact with exterior
- Ducts
- Example: mammary glands
Where can connective tissue be found?
Every organ!
What does connective tissue consist of?
Cells separated by extracellular matrix
Types of connective tissue
Blood, bones, ligaments, tendons
Functions of connective tissue
- Enclose organs as a capsule (ex. muscles)
- Support and movement (ex. bones)
- Storage (ex. adipose tissue)
- Cushion and insulate (ex. fat)
- Transport (ex. blood)
-blasts
- Create the matrix (ex. osteoblast)
- Trap themselves in the matrix and become a -cyte cell
-cytes
Maintain the matrix (ex. chondrocyte)
-clasts
Break down the matrix for remodelling (ex. osteoclast)
True or false: adipose cells are hollow (no organelles) and store lipids within them
True; adipose cells are hollow and used for storage
What three substances make up the extracellular matrix?
Protein fibres, ground substance, and fluid
Collagen
- Most common protein in the body
- Strong, flexible, inelastic
Reticular Protein
- Fill spaces between tissues and organs
- Fine, collagenous, form branching networks
Elastic Protein
- Returns to its original shape after distension or compression
- Contain molecules of protein elastin that resemble coiled springs
- Molecules are cross-linked
- Example: blood vessels
Ground Substance
Hyaluronic acid, proteoglycan, and adhesive molecules
Hyaluronic Acid
- Acts as a lubricant
- Example: joint fluid, vitreous humour, etc.
Proteoglycan
- Strands of proteins and carbohydrates
- Stick onto hyaluronic acid molecules like bristles on a brush to form aggregates
- Can hold a lot of water
Adhesive Molecules
- Can attach onto sides of cells
- Can attach cells together
Fluid
- Example: blood plasma (ions, proteins, enzymes, cells, etc.)
- Example: bone doesn’t have very much
Connective Tissue Proper – LOOSE (areolar)
- Fewer fibres, more ground substance
- Example: adipose tissue
Connective Tissue Proper – DENSE
- More fibres, less ground substance
- Regular or irregular
- Collagenous or elastic
Supporting Connective Tissue
Example: cartilage or bone
Areolar Tissue
- Loose packing material of most organs or tissues (“fills in the gaps”)
- Attaches skin to underlying tissues
Dense Regular Collagenous CT
- Has abundant collagen fibres that reduce stretching
Example: tendons (connect muscles to bones; tear along their width)
Example: Ligaments (connect bones to bones) - Collagen strong along its length
- Fibroblast cells make collagen portion of matrix
Dense Regular Elastic CT
- Ligaments in vocal folds; nuchal ligaments (back of the neck)
- In reference to vocal folds: collagen fibres give strength (for when you shout), but elastic fibres are more prevalent
