Lecture 2: How to examine cells and tissues Flashcards
What is the meaning of the term ‘tissue’?
Group of cells that have similar structures and act together to perform a specific function
What are the 4 types of tissues?
- Epithelial
- Connective
- Muscle
- Nerve
What is epithelial tissue?
Large sheet of cells covering the surfaces of the body exposed to the outside world and lining the outside of organs
Example: Skin
What is connective tissue?
Consists of cells and extra cellular proteins
Binds, supports and anchors the body
Example: cartilage tissue
What is muscle tissue?
Specialized tissue which functions by contracting (for movement and stability) and secreting hormones
Example: skeletal, cardiac, smooth
What is nerve tissue?
Made of nerve cells and acts as the main fast communication system of the body
What is the value of histology in diagnosis?
By examining tissues and cells under a microscope, we can diagnose diseases of the tissues.
What are common biopsy techniques?
- Surgery and dissection by histopathologist
- Scraping methods - curettes and scalpel scrapes
- Sharp needles - needle biopsy, pipeline
- Direct venipuncture - blood smears
How does curettage work?
Surgical scraping used to remove diseased tissue such as tumors or growths to obtain a biopsy
Examples of tissues: uterus, cervix, skin
What tissues can be sampled by needle biopsy?
- Muscle
- Bone
- Liver
How does needle biopsy work?
Needle is inserted into body to collect cell samples from organs or lumps that are below the surface of the skin
Examples: breast lumps, liver, bone marrow
Why do tissues need to be fixed for histology?
Once tissues are removed from the body, it is no longer protected by the body’s immune system and so can be digested by microbes or decay. Hence, it needs to be fixed to protect it from damage.
Which fixatives are commonly used to fix tissue?
Formalin - 37% formaldehyde + 0.9% sodium chloride solution (normal saline)
It is isotonic with the intracellular fluid so it allows better penetration of the formaldehyde
How does tissue processing lead to shrinkage and formation of other artifacts?
When left too long in the fixative (formalin), it dehydrates the tissue, causing shrinkage and formation of fixation artifacts.
What is the value of histological staining?
As the tissue is colorless, staining will allow us to see the definition of the tissue more clearly.
How do the Haematoxylin and Eosin stains work?
Haematoxylin - basic so it binds to acidic structures (DNA and RNA)
Eosin - acidic so it binds to basic structures (intracellular and extracellular proteins)
How does indirect immunohistochemistry work?
Labeled antibodies are used to localize specific cell and tissue targets, antigens. Then, another enzyme activated secondary antibody complexes that precipitate a colored product is also used. This is used to identify organelles that contain acid phosphatase (lysosomes).
How does immunofluorescence work?
Labeled antibodies are used to localize specific cell and tissue targets, antigens. Those antibodies are labeled with fluorescent dyes to allow the structure to be visualized directly in confocal microscopy, under a UV light source.
What are the advantages of phase contrast microscopy?
- Living cells can be examined in their natural state without being killed, fixed and stained.
- Ongoing biological processes can be observed
- High contrast and high resolution
What are the advantages of dark field microscopy?
- Ideal for objects that are unstained, transparent and absorb little to no light
- Useful in examining external details, like outlines, edges, grain boundaries and surface defects than internal structure
What are the advantages of fluorescence microscopy?
- Ideal for identifying specific molecules and tracing the location of it
- Offers a magnified and clear image as compared to traditional optical microscope
What are the advantages of confocal light microscopy?
- Ability to control resolution
- Able to create 3D images of structures within cells
What is the definition of the term ‘limit of resolution’?
Minimum distance at which two objects can be distinguished
Why are electron microscopes capable of finer resolution than light microscopes?
Light microscopes uses visible light while electron microscopes uses electrons. Since the wavelength of electrons is smaller than the wavelength of light, electron microscopes have a much smaller limit of resolution.
What is the structure of the plasma membrane or plasmalemma?
Outermost bounding membrane of the cell that has a triple-layer appearance
What is the function of the plasma membrane or plasmalemma?
- Intercellular adhesion and recognition
- Signal transduction
- Compartmentalisation
- Selective permeability
- Transport of materials along and across the cell membrane
- Endocytosis
- Exocytosis
What is the function of the nucleus?
Synthesis of DNA, nucleoproteins and RNA
What is heterochromatin?
Tightly packed form of DNA and associated nucleoprotein not active in RNA synthesis - appears dark
What is euchromatin?
Loosely packed form of DNA and associated nucleoprotein active in RNA synthesis - appears light
What is the function of the nucleolus?
Ribosomal RNA synthesis for ribosome assembly
What is the structure of the nuclear envelope?
Consists of a double layer of membranes bounding the nucleus
What is the function of the nuclear envelope?
Contains nuclear pores through which macromolecules can be transported and micro molecules can diffuse without hindrance
What is the structure of the endoplasmic reticulum?
Interconnecting set of membranes, vesicles and cisternae
What is the structure of the rough endoplasmic reticulum?
Interconnecting set of membranes, vesicles and cisternae with ribosomes attached to its outer surface
What is the function of the rough endoplasmic reticulum?
Synthesis of protein
What is the function of ribosomes attached to the rough endoplasmic reticulum?
Generates proteins destined for the cell exterior, for lysosomes or for cell membrane incorporation
What is the function of ribosomes that lie free in the cytoplasm?
Synthesize proteins for the cytosol (liquid component of the cytoplasm)
What is the structure of the smooth endoplasmic reticulum?
Interconnecting set of membranes, vesicles and cisternae with no ribosomes
What is the function of the smooth endoplasmic reticulum?
Lipid biosynthesis and intracellular transport
What is the structure of the Golgi apparatus / complex / body?
Saucer shaped stacks of cisternae
What is the function of the Golgi apparatus / complex / body?
Proteins synthesised by the rough endoplasmic reticulum migrate from the convex to concave end of the stack, and the Golgi apparatus sorts, concentrates, packages and modifies the proteins
What is the structure of lysosomes?
Highly diverse in shape, usually dense, spherical or oval
What is the function of lysosomes?
- Generated by the Golgi apparatus
- Fuse with endocytosed (from outside) membrane-bound vesicles with autophagosomes (defunct organelles encircled by ER) or excess secretory product to form secondary lysosomes in which the contents are degraded
- Cell’s recycling centre and primarily digest and re-use carbohydrates, lipids and peptides
What is the structure of peroxisomes?
Roughly spherical, containing granular matrix, bound by a single membrane
What is the function of peroxisomes?
- Modify toxic molecules before they re-enter the bloodstream
- Major sites of oxygen utilization and peroxide production
What is the structure of mitochondrion?
- Variable in shape - often spherical or an elongated oval and often found close to nuclei
- Have a double membrane with inner membrane thrown into distinct folds called cristae, which are usually lamellar
What is the function of the mitochondrion?
Generation of energy-rich ATP molecules (which store energy needed by the cell) by oxidative phosphorylation
What is the function of the cytoskeleton?
- Maintains and changes cell shape
- Provide structural support for the plasma membrane and cell organelles
- Provide a means of movement for organelles, plasma membrane and other cytosol constituents around the cell
- Provide locomotor mechanisms for amoeboid-like movements and for cilia and flagella
- Provides machinery for contractility in cells of specialized tissue
What is the structure of microfilaments?
- Composed of 2 strings of actin polypeptide chains twisted together
- 5nm in diameter
What is the function of microfilaments?
- Able to bind ATP
- Contracts and changes shape of cell when associated with ATP
- Very dynamic: can assemble and dissociate very quickly
What is the structure of intermediate filaments?
- 10-12nm in diameter
- A tough supporting mesh work within the cytoplasm and are anchored to the plasma membrane at strong intracellular junctions
What is the function of intermediate filaments?
- Hold a cell together and prevent lysis
What is the structure of microtubules?
Hollow tubes, where thirteen alpha and beta tubulin subunits polymerize to form its walls
What is the function of microtubules?
Act as a conveyer belt within cells to move molecules and organelles to more distant parts of the cells
