Unit 2: Histology Flashcards
Histology
The study of tissues and their cellular components. It is used in the recognition of pathology and in the discovery of how abnormal biochemical and physiological processes result in disease.
Morphology
The examination of cellular arrangements and organization to examine organ structure in terms of form and function.
4 major groups of tissues
Connective, epithelium, muscle, and nervous
Epithelium
Found covering and lining the surfaces of the body and organs.
Structure: sheets of closely packed cells
Function: protection, exchange, secretion
Connective tissue
It’s major function is to hold tissues together. Some have a generalized role in supporting and protecting organs while others have specialized functions (bones provide muscle attachment, blood facilitate the transport of nutrients and removal of wastes).
Structure: spare cells in extracellular matrix
Function: binding and support of other tissues
Muscle tissue
Unique property of being able to move when cells contract. 3 types of muscles:
Skeletal - permits movement of the body
Cardiac - moves blood around the vasculature
Structure: long cells (fingers) with contractile proteins.
Function: movement of body parts
Smooth - facilitates movement of food along the alimentary canal.
Nervous tissue
Highly complex (especially in the brain)
Structure: neurons with branching extensions
Function: transmission of nerve signals
Steps for preparation of specimens for study by standard light microscopy
- Obtaining a sample with the proper orientation
- Fixing or preserving the specimen
- Sectioning the specimen into thin slices
- Staining the specimen for visualization
- Microscopic examination of the specimen
Orientation
First step in light microscopy; orientation helps to visualize the morphology of a structure. This is because improper orientation may cause the tissue to become damaged during later stages of preparation. Most tissues are embedded flat with a margin of embedding medium surrounding them for support. During sectioning the tissue should be oriented in a way that results in least resistance to the knife.
Tubular structures
Tissue that may require a specific orientation in light microscopy preparation; structures with tubular morphology (sweat gland ducts or blood vessels) are usually cut to display the cross-section of the lumen.
Epithelial Biopsies
Biopsies of epithelia, such as the skin or the intestines, are cut in a plane at right angles to the surface, and oriented in a certain way so that the knife cuts from the basement membrane through to the apical epithelial membrane. This way, compression and distortion of the epithelial surface is minimized.
Muscle Biopsies
Sections of muscle may be cut in transverse or longitudinal planes.
Multiple tissue samples
To facilitate comparison, multiple tissue samples are oriented similarly, side by side, with, for example, the apical epithelial surfaces all facing in the same direction.
Fixation
Second step of tissue preparation; helps to prevent the specimen from undergoing physiological changes. Also helps to deactivate internal enzymes within cells to prevent degradation from within. Can also help to increase the mechanical strength of tissue and reduce the growth of microbe colonies.
Methods of fixation
Chemical perfusion, heat fixation, etc.
Embedding
Third step in light microscopy preparation; Embedding involves the following: correctly oriented specimens are fixed and encased within a suitable medium, providing them with elasticity and ensuring they are supported during sectioning and subsequent analysis.
Paraffin wax embedding
The standard method for the preparation of finely sectioned specimens for histological analysis by microscopy. Paraffin wax fills the tissue, supporting all cellular components and resisting distortion during sectioning.
Frozen sections
Alternative to paraffin wax because the wax can be too damaging or time consuming. Specimens are rapidly frozen by immersion in liquid nitrogen so that the tissue hardens into a solid mass.
Sectioning
Fourth step in light microscopy preparation; the slicing of embedded specimen using a microtome and attachment to a surface (usually a slide) for analysis under a microscope.
Stains
Fifth step in light microscopy preparation; Staining is require to see the colorless cell.
Methyl blue
Stain widely used in differential staining of tissue sections, where more than one chemical stain is used, such as trichrome staining.
It stains collagen blue.
Hematoxylin and eosin (H&E)
Staining is used to differentiate nucleic acids in the nucleus from basic proteins within the cytoplasm.
Cell nuclei stain purple/black (hematoxylin) and most components of the cell cytoplasm stain pink/red (eosin).
van Gieson
This stain is used for general staining of connective tissue fibers.
Collagen fibers stain pinkish-red, muscle stains yellow, and elastic fibers stain brown-black.
Trichrome
This method uses three different dyes to differentially stain cellular components. One of these is often methyl blue.
SIlver nitrate
Silver nitrate solution can be used to stain tissues in several different ways. One method, called Golgi’s method, selectively stains the entirety of some neurons black, thus revealing their cellular architecture. A different technique can be used to highlight reticular fibers.
Immunohistochemical methods
utilizes a different approach to visualize cellular contents: rather than dyes, it exploits the highly specific interaction between antibody and antigen to allow precise identification, localization, and in some cases, quantification, of cellular proteins, such as receptors or enzymes.
Light (optical) microscope
How does it work: Uses beams of visible wavelengths of light, focused through glass lenses, to produce magnified images.
Magnification: Up to 2000x.
Lens: Glass.
Uses: ability to view color, relatively low cost makes this device more popular in education and medical sectors.
Stains used: those highlighting tissue/cellular components in different colors. Chromatic dyes used.
Disadvantages: limited magnification and depth field.
Types: simple (one lens), compound (many lenses), and digital light microscope.
Electron microscope
How does it work: Uses particle beams of electrons, focused through magnetic lenses and metal apertures, to produce highly magnified 2D and 3D images.
Magnification: up to 2000000x
Lens: electrostatic/electromagnetic
Uses: Used to visualize smaller structures not visible by light microscopy. Allows 3D visualization of structures. Is used in observation of dry, fixed specimens of micro-organisms, cells, large molecules, biopsy samples, metals, and crystals etc.
Stains used: Stains highlight tissue by increasing electron absorption. Electron-dense heavy metals often used.
Disadvantages:
Expensive to build, maintain, and run.
Very sensitive to vibrations and external magnetic currents.
More elaborate preparation of specimens often needed and specimens must be dry.
Not possible to observe living specimens or color.
Types: Transmission electron microscope (TEM) for 2D images, and scanning electron microscope (SEM) for 3D images.
Characteristics of epithelial tissues
Avascular (no blood cells entering between the cells. The cells are maintained via blood vessels lying deep within the basement membrane.
Highly cellular with little extracellular material.
High regenerative capacity
Functions of epithelial tissue
Selective absorptive barriers regulating the movement of substances into and out of the body.
Secretory surfaces, comprising the functional units of glandular secretion.
Protective surfaces, such as the skin.
What is the classification of covering and lining epithelium based on?
The three-dimensional shape of the epithelial cells comprising it, as observed by light microscopy.
The way in which the epithelial cells are arranged into layers.
Squamos
Epithelial cell; flat, plate-like cells
Cuboidal
Epithelial cell; cube-like cells.
Columnar
Epithelial cell; column-shaped cells. Greater height than width.
Transitional
Epithelial cell; cuboidal or columnar can change shape during stretching and compression.
Simple Epithelium
A single layer of cells.
Stratified Epithelium
Multiple layers of cells.
Pseudostratified Epithelium
Cells appear to be arranged in layers, but careful observation reveals that all cells are anchored to the underlying basement membrane.
Simple Squamous Epithelium
Function: Diffusion and filtration.
Locations: Capillary networks surrounding the alveoli in the lungs.
Lines the heart and blood and lymphatic vessels.
Component of serous membranes.
composed of a single layer of flat epithelial cells, each containing a flattened, centrally located nucleus.
Endothelium
the simple, squamous epithelium lining the heart, blood vessels, and lymphatic vessels.
In capillaries, the endothelial cells act as a selective barrier, permitting various substances to move from the blood into the interstitial fluid.
Mesothelium
simple, squamous epithelium but it has a different embryological origin to endothelium. Mesothelium constitutes the epithelial layer of serous membranes, such as the pericardium, pleura, and peritoneum.
Simple Cuboidal Epithelium
Function: secretion and absorption.
Locations: Proximal and distal convoluted tubules of the kidney and thyroid gland.
made up of a single layer of approximately cube-shaped epithelial cells, each containing a spherical, centrally located nucleus.
Simple columnar epithelium
Simple columnar epithelium consists of a single layer of column-shaped epithelial cells, each with an oval nucleus near its base.
Non-ciliated simple columnar epithelium
made up of simple columnar epithelial cells which often have microvilli at their apical surface. Interspersed between these columnar cells are goblet cells, which are specialized epithelial cells that secrete mucus at their apical surface.
Microvilli increases SA and mucus lubricates and protects. Line functional tracts; small intestine and the gall bladder.
Ciliated simple columnar epithelium
Ciliated simple columnar epithelium is made up of simple columnar epithelial cells with cilia at their apical surface. The ciliated columnar cells are interspersed with mucus-secreting goblet cells.
Function: removes foreign particles.
Lining of the uterine tubes, where the beating of the cilia is responsible for the movement of the egg from the ovary to the uterus. And auditory tubes.
Keratinized stratified squamous
Function: Protects the body from heat, microbes, and damaging substances.
Locations: Forms superficial layer of the skin.
Contains protein keratin which is a waterproof layer that can dehydrate cells.
Non-keratinized stratified squamous
Function: Protects the body against microbes.
Locations: Forms moist linings such as the buccal cavity, esophagus, and part of the cervix.
Stratified Cuboidal
Function: protection, secretion, and absorption.
Locations: Makes up part of the sweat glands, mammary glands, and salivary glands.
Stratified columnar
Function: Protection and secretion.
Locations: Ocular conjunctiva of the eye.
Ducts of larger salivary glands.
Transitional Epithelium
Function: Forms stretchable lining
Locations: lines tissues that expand and contract, such as the urinary bladder.
Exocrine glands
consist of a glandular portion, and a duct portion. They secrete their
non-hormone products into ducts that carry these products to other organs or outside the body
ex. sweat glands, goblet cells, digestive glands, and sebaceous glands.
Endocrine glands
lack ducts. They produce hormones which are secreted directly
into the bloodstream
Ex. thyroid, parathyroid, pineal, pituitary, and suprarenal glands.
Exocrine glands and secretion types
Merocrine - sweat glands, salivary glands, pancreatic aciner glands; most common gland
Apocrine - mammary glands
Holocrine - sebaceous/oil glands
Connective tissue
The most widespread, and the most varied of all tissues. It is the
collective term for support cells and associated extracellular matrix.
Characteristics of support cells
1.
They are derived from embryonic cells called mesenchymal cells.
2.
They start life as immature blast cells capable of cell division and secretion of extracellular matrix.
3.
They produce most of their extracellular matrix materials before differentiation into mature cyte cells.
4.
In their mature form, they sit within their matrix, forming sparsely cellular connective tissues, where they continue to maintain the matrix.
5.
They adhere to their extracellular matrix materials, rather than adjacent cells.
Examples of support cells
fibroblasts, adiipocytes, chondroblasts, osteoblasts, and myofibroblasts
Fibroblasts
large, flat, branching cells present in most connective tissue. They secrete fibers including collagen, and some of the ground substance component of the extracellular matrix
Adipocytes
(fat cells) are highly specialized support cells that store lipids which can be metabolized to provide energy. They are present under the skin and surrounding various organs, where they also function as protective padding.
Chondroblasts
small, rounded cells with small nuclei, and are found in cartilage, where they secrete components of the extracellular matrix.
Osteoblasts
mononucleate cells that secrete the extracellular matrix components of bone.
Myofibroblasts
differentiated fibroblasts committed to becoming smooth muscle cells. They have contractile properties and also secrete extracellular matrix components.
Cells present in connective tissue whose primary function is not support
Mast cells - located near blood vessels supplying tissues primarily. Store and secrete histamine and heparin in response to inflammatory processes and allergic reactions.
White blood cells - migrate from blood to connective tissue during times of need. Include macrophages and lymphocytes (plasma cells).
Extracellular matrix
made up of fibers (fibrillary proteins) and a ground substance component.
Fibers
provide different tensile properties, giving essential strength and support to connective tissue and providing anchorage to their cellular components.
3 main types of fibers in extracellular matrix of connective tissue
Collagen fiber - strong and flexible occurring in parallel bundles. Made up of protein collagen.
Elastic fibers - small in diameter and branch to form networks of strong, stretchable, interconnected fibers. The main component of elastic fibers is the protein elastin.
Reticular fibers - very fine, and branch to form strong, supportive frameworks. Produced by fibroblasts, made up of collagen, and are strengthened/stabilized by a glycoprotein coating. They are present in blood vessel walls, areolar connective tissue, adipose tissue, smooth muscle tissue, and soft organs (spleen and lymph nodes).
What does mature connective tissue include?
Loose connective tissue, dense connective tissue, cartilage, bone, and liquid connective tissue.
Loose connective tissue
Consists of loosely arranged fibers that form a network btwn cells. Under the skin.
Types of connective tissues
Areolar, adipose, and reticular.
Dense connective tissue
consists of uniformly arranged, parallel bundles of collagen fibers. It is strong and pliable, but withstands stretching only in the direction of the fibers. Fibroblasts are arranged in rows between the collagen fibers and they secrete both ground substance and fiber components of the tissue. It is poorly vascularized.
Tendons and ligaments.
Characteristics of loose connective tissue
- Loose connective tissue is a type of connective tissue that surrounds blood vessels, nerves, and organs, holding the epithelium and organs in place.
- Consists of many cells
- Mainly contains fibroblasts
- Consists of loosely arranged fibers
- Major function is to serve as a supporting matrix for the blood vessels, lymphatic vessels, nerves, muscle fibers, organs, and the skin.
Characteristics of dense connective tissue
- Contains numerous collagen fibers and provides a strong connection btwn tissues that mainly form the structural parts of the body
- Consists of fewer cells.
- Mainly contain fibrocytes.
- Consists of numerous thick fibers.
- Produces tendon and ligaments by forming strong, rope-like structures.
Types of dense connective tissue
Dense regular connective tissue
Dense irregular connective tissue
Elastic connective tissue
Hyaline cartilage
Function: flexibility, support, friction, reduction, and shock absorption.
Location: Temporary skeleton in the fetus.
Epiphyseal plates of growing long bones.
Articular surfaces of joints and supporting rings in the respiratory passage.
Fibrocartilage
Function: strength and rigidity.
Location: Intervertebral discs. Tendon attachment to bones. Junctions between flat bones of the pelvis. Menisci of the knee.
Elastic cartilage
Function: strength, elasticity, and maintenance of shape.
Location: Auricle of the ear.
Walls of the external auditory meatus and Eustachian tubes.
Epiglottis of the larynx.
Adipose tissue
Loose connective tissue; fatty tissue, main functions are to store the energy, protect the organs and contribute to the endocrine profile of the body.
Reticular tissue
Loose connective tissue; forms a scaffolding for other cells in several organs, such as lymph nodes and bone marrow.
Areolar tissue
Loose connective; holds organs in place and attaches epithelial tissue to other underlying tissues. It also serves as a reservoir of water and salts for surrounding tissues.
Muscle tissue
A specialized tissue with both contractile and conducing properties. It
consists of elongated cells that contract in response to stimulation.
3 types of muscle tissues
Cardiac, skeletal, and smooth
Skeletal muscle tissue
Structure: Long thin cylindrical striated fibers. Many peripheral nuclei.
Location: attached to bones of the skeleton via tendons.
Function: voluntary movement. Maintenance of posture. Protection and production of heat.
Cardiac muscle tissue
Structure: branched striated fibers connected via intercalated discs. One or two central nuclei.
Location: make up the muscular component of the heart.
Function: form the muscular wall of the heart. Contraction of the heart muscle for distribution of blood around the body.
Smooth muscle tissue
Structure: spindle shaped non-striated fibers, one central nucleus.
Location: blood vessel walls. Iris of the eye. Airways to the lung. Walls of the stomach, intestines, gallbladder, urinary bladder, and female uterus.
Function: constriction of vessels, airways, and tracks for movement of substances through them. Contraction of organ walls for expulsion of content.
Nervous tissue
has a high degree of excitability and conductivity – more than
other tissues. Found in brain, spinal cord and nerves.
What types of cells make up nerve tissue?
Neurons (nerve cells): the units that conduct nervous impulses.
Neuroglia (a specialized group of support cells) – non-neuronal cells. Protect and assist neurons.
Two main types of membrane
Epithelial (mucous membranes, serous membranes, or cutaneous membranes. Consisting of an epithelium overlying a connective tissue layer).
and synovial (exclusively of connective tissue and are found lining the cavities of mobile joints).
Mucous membrane
found lining body cavities, or tracts, that open into the external environment, such as the digestive, respiratory, and reproductive tracts.
Serous membrane
also known as serosae, are found covering organs (visceral serous membrane) and lining body cavities (parietal serous membrane) that do not open into the external environment.
Cutaneous membrane
refers to the skin covering the surface of the body.
Cutaneous membrane - dermis layer
Connective tissue layer (dermis) consists of areolar connective tissue and dense irregular tissue. It lies deep to the epithelial layer, supporting it and anchoring it to underlying structures.
Synovial membranes
Line joint cavities and produce the fluid within the joint.
Gliosis
the most common response to the damage of nervous tissue. It is the
formation of scar tissue composed of astrocyte glial cells.
What is bone
A rigid connective tissue that contains calcium and phosphorus.
Keloid
The result of excess production of collagen in the formation of a scar.
Myelin
The fatty insulation material that covers and protects some nerve fibers.
Myocradium
Thick, muscular layer of the heart wall.
