Histology Flashcards
Who is the father of histology?
Marie François Xavier Bichat
What five things compose the cell and their percentage?
- Water (80%)
- Protein (15%)
- Lipid (2.5%)
- Carbohydrate (1.5%)
- Inorganic (1.0%)
The five common features to all eukaryotic cells
- An outer membrane
- An inner cytosol
- A cytoskeleton
- Membrane-bound organelles within the cytosol.
- Inclusions
What is the plasma membrane and its function?
It is a bimolecular layer of amphipathic phospholipid molecules with their hydrophilic heads at the outer and inner surfaces and their hydrophobic fatty acid chains facing toward the middle of the two layers.
Separates the cytoplasm from the extracellular environment.
Draw the amphipathic phospholipid and what it is made of
-Polar hydrophilic region of choline and phosphate
-Non-Polar hydrophobic fatty-acid chain
What five things can integral proteins be?
These include receptors, channels, transporters, enzymes, and cell attachment proteins.
The cell membrane is solid. True or false?
Nope, it is fluid, therefore it can change shape easily.
Are membrane proteins distributed equally within the cell membrane?
No, membrane proteins can diffuse laterally in the cell membrane, but many are anchored
What is the plasma membrane permeable and impermeable to?
Highly permeable to water, oxygen, and small hydrophobic molecules.
Virtually impermeable to charged ions (e.g., Na+)
What appearance does the plasmalemma have in the microscope?
Trilaminar appearance
What is the inner cytosol, and what does it contain?
A solution of proteins, electrolytes & carbohydrates. It has both fluid and gel-like properties.
What two structures does the cytosol have within?
Organelles and Inclusions
What are organelles?
Organelles are small, intracellular ‘organs’ with a specific function and structural organization.
What are the six organelles, and what are their functions?
- Mitochondria - (energy production)
- Rough endoplasmic reticulum - (protein synthesis)
- Smooth endoplasmic reticulum - (cholesterol & lipid synthesis/detoxification)
4.Golgi apparatus - (modification & packaging of secretions) - Lysosomes – (hydrolytic enzymes for intracellular digestion)
- Nucleus – (contains genetic code)
What are inclusions and some examples of them?
They represent components that have been synthesized by the cell itself…
Pigment, glycogen stores, lipid droplets, pre-secretion product
Or taken up from the extracellular environment.
Endocytotic vesicle.
What is the cytoskeleton made of?
Maintained by a set of filamentous cytosolic proteins, the cytoskeletal proteins
What are the three main classes of filaments, their size, and composition?
-Micro-filaments
(7 nanometres in diameter) are composed of
the protein actin.
-Intermediate filaments
(>10 nanometres in diameter) are composed of six main proteins, which vary in different cell types
-Microtubules
(25 nanometres in diameter) are composed of two tubulin proteins
What unique ability do microfilaments have?
Actin molecules can assemble into filaments and later dissociate, making them very dynamic cytoskeletal elements
What do the intermediate filaments do, and how many types are there?
Bind elements intracellularly together and to the plasma membrane. More than 50 types, but they are divided into classes.
What intermediate filaments form in the cytoplasm?
A network
What are microtubules composed of?
Hollow tubule is composed of two types of tubulin subunits, α & β, in an alternating array.
Where do microtubules originate from, and what proteins are included?
Originate from a special organizing center called the centrosome.
Include stabilizing proteins: microtubule-associated proteins (MAPS)
What type of filament can be assembled and disassembled?
Microfilaments
In what three structures are microtubules essential?
Cilia, flagella, and the mitotic spindle.
What do microtubules serve as, and what two proteins attach to the microtubules?
Microtubules serve as the ‘motorway’ network of the cell. Two proteins, dynein, and kinesin attach to the microtubules and move along them. They associate with the membranes of organelles and vesicles and ‘drag’ them along the microtubule.
What is kinesin, and where does it move?
Kinesin is an ATPase that moves toward the cell periphery.
What is dynein, and where does it move?
Dynein is an ATPase that moves toward the cell center.
What proteins are very important in the movement of components in cells with long processes, for example, the very long axonal process of many neurons?
Kinesin and dynein
What is the nucleus enclosed by and composed of?
The nucleus is enclosed by a nuclear envelope, composed of an inner and an outer nuclear membrane with nuclear pores providing continuity with the cytoplasm.
What is the outer membrane of the nucleus studded with, and what is it continuous with?
The outer nuclear membrane is studded with ribosomes and is continuous with the cytoplasmic rough endoplasmic reticulum.
What does the nucleus contain, and what three critical processes occur?
The nucleus contains chromosomes.
It is the location of RNA synthesis.
Both mRNA and tRNA are transcribed in the nucleus, and rRNA is transcribed in the nucleolus.
What is the nucleolus?
A 1-3µm diameter dense area within the nucleus
What two forms of DNA does the nucleus contain, and what is the difference?
- Euchromatin (DNA that is more dispersed and is actively undergoing transcription).
- Heterochromatin (DNA that is highly condensed and not undergoing transcription).
What is the nucleus surrounded by?
Double nuclear membrane
Where are ribosomes formed, and what are they instrumental for?
Ribosomes are formed in the nucleolus and are instrumental in protein synthesis.
What is each ribosome made of?
A small subunit - which binds RNA, and a large subunit which catalyzes the formation of peptide bonds.
What does the export of ribosomes depend on?
Nuclear pore complex
What does reticulum mean?
Net-like structure
What does the endoplasmic reticulum form?
The endoplasmic reticulum (ER) forms a network of interconnecting membrane-bound compartments in the cell.
What are the two kinds of Endoplasmic reticulum?
- Rough endoplasmic reticulum
- Smooth endoplasmic reticulum
Why is it called Rough Endoplasmic Reticulum?
Because it is studded with ribosomes
What is the role of the Rough Endoplasmic Reticulum?
It plays a vital role in synthesizing proteins destined for insertion into membranes or secretion.
What does the amount of ER present depend on?
It varies with how active the cell is. Cells that are relatively metabolically inactive have relatively little ER.
What is the rough endoplasmic reticulum associated with, and what does it initiate?
The rough endoplasmic reticulum is associated with protein synthesis and the initiation of glycoprotein formation.
What is the function of the smooth endoplasmic reticulum, and what vital role does it play?
The SER continues the processing of proteins produced in the RER.
The SER plays a vital role as the site of the synthesis of lipids.
Most cells contain relatively little SER, but in what cells is it extensive?
Cells synthesizing steroid hormones
What is the Golgi apparatus?
The Golgi apparatus (complex) comprises a group of flattened, membrane-bound cisternae. These are arranged in
sub-compartments.
What is the function of Golgi cisterns?
Golgi cisterns function in the modification and packaging of macromolecules that were synthesized in the ER. Transport vesicles arrive at the Golgi from the SER/RER.
What three things do the Golgi cisterns add to macromolecules from ER?
Adds sugars
Cleaves some proteins
Sorts macromolecules into vesicles.
What are mitochondria, their size, and their function?
-Mitochondria are oblong, cylindrical organelles, typically 0.5-2µm in length.
-Mitochondria are the power generators of the cell. They function in the generation of ATP via oxidative phosphorylation and in the synthesis of certain lipids and proteins
What are mitochondria composed of?
They are composed of an outer and an inner membrane. The inner membrane is extensively folded to form cristae, which act to increase the available surface area.
What are intercellular junctions, and where are they prominent?
Intercellular junctions are specialized membrane structures that link individual cells into functional units.
They are exceptionally prominent in epithelia.
What are the three types of junctions and their functions?
-Occluding junctions: link cells to form a diffusion barrier.
-Anchoring junctions: provide mechanical strength.
-Communicating junctions: allow movement of molecules between cells.
What do occluding junctions prevent and appear as?
They prevent diffusion.
They appear as a focal region of close apposition between adjacent cell membranes.
What are occluding junctions also known as?
Tight junctions or zonula occludens
What are anchoring junctions also known as?
Adherent junctions
Zonula adherens
What is the structural function of adherent junctions?
Link submembrane actin bundles of adjacent cells
How does each cell bind to the other?
Transmembrane cadherin molecules bind to each other in the extracellular space and to actin of the cytoskeleton.
What are desmosomes, what do they do, what are they known as and where are they very commonly found?
They are adhesive proteins.
They link submembrane intermediate filaments of adjacent cells.
Also called Macula Adherens.
Very common in skin where they provide mechanical stability.
What do Communicating junctions allow and what are they also termed?
Selective diffusion of molecules between adjacent cells. Often termed gap junctions.
What are the structures of the communicating junctions like?
Each junction is studded with several hundred pores.
What proteins produce the pores?
Connexon proteins
Where are communicating junctions found?
Found in epithelia, but also in some smooth muscles and in cardiac muscle, where it is critical for the spread of excitation.
What is a junctional complex?
The close association of several types of junctions found in certain epithelia tissues
What are three ways in which material endocytoses and exocytoses?
Diffusion
Via transport proteins (Pumps or channels)
By incorporation into vesicles (Vesicular transport)
What happens in endocytosis and what is it mediated by?
The cell membrane invaginates, fuses, and the newly made endocytotic vesicle (Endosome) buds into the cell. This process is often receptor-mediated.
What is the cell cycle and how long does it last?
The cell cycle is the period of time between the birth of a cell and its own division to produce two daughter cells.
-It lasts for at least 12 hours, but in majority of adult tissues, it lasts much longer.
Define in-vitro
Performed or taking place in a test tube, culture dish, or elsewhere outside a living organism.
What are cells that continue to divide regularly into definite intervals described as?
Cycling cells
What are the two basic parts the cell cycle is divided into?
-Mitosis (M) phase.
-Interphase, which is divided into G1 phase, S phase, and G2 phase.
What is interphase?
The interval between the end of mitosis and the beginning of the next. The cell is either resting or performing its function.
What is the S phase, when does it start and when does it finish?
The period in which DNA is synthesized, for there to be sufficient for two daughter cells.
-Begins 8 hours after the end of mitosis and takes about 7 to 8 hours to complete.
What is the G1 phase?
The gap in the cell between the end of mitosis and the beginning of the S phase.
What happens in the G1 phase?
This is the period when cells respond to growth factors directing the cell to initiate another cycle. It is also the phase in which most of the molecular machinery required to complete another cell cycle is generated.
Is the G1 phase where growth factors are involved reversible?
Nope, irreversible
How long is the G1 phase?
G1 shows considerable variation, sometimes ranging from less than 2 hours in rapidly dividing cells, to more than 100 hours within the same tissue.
What is the G0 Phase and what do cells are called when they enter it?
Cells retain the capacity for proliferation and are in the process of differentiation but are no longer dividing. They are referred to as QUIESCENT and do not enter S phase.
What can stimulate quiescent cells to leave G0 and enter the cell cycle?
Growth factors
What can stimulate quiescent cells to leave G0 and enter the cell cycle?
Growth factors
What molecules block the cycle in G1?
Proteins encoded by certain tumor suppressor genes (The gene mutated in retinoblastoma, Rb)
What is the G2 Phase and how long does it last?
The gap between the end of the S phase and the beginning of mitosis is the G2 phase. Takes 2 to 4 hours to complete.
What occurs in G2?
During G2, the cell prepares for division; this period ends with the breakdown of the nuclear membrane and the onset of chromosome condensation.
What are the four nuclear changes that achieve this distribution of cells?
-Prophase
-Metaphase
-Anaphase
-Telophase
What four things occur in Prophase?
- The individual chromosome is first visualized as thin threads and is tightly coiled along the entire length
- Each chromosome splits longitudinally into two chromatids except at the centromere.
- The two paired centrioles are separated from each other by the elongation of continuous microtubules of the achromatic spindle and occupy the opposite pole of the nucleus.
- Subsequently, the nuclear membrane and nucleolus disappear.
What happens in prometaphase?
The chromosomes are now entangled in a meshwork of continuous microtubules.
How long does the prophase take to complete?
1.5 hours
What three things happen in metaphase and how long does it take?
- Centromere region from each chromosome presents a bilateral disc (Kinetochores)
- From kinetochores, a set of chromosomal microtubules are organized and extend bilaterally towards opposite centrioles.
- The growth of the chromosomal microtubules allows the centromere of individual chromosomes with their paired chromatids to occupy the equatorial plane of the spindle.
-Persists for 20 minutes.
What is Colchicine?
A medicine for treating inflammation and pain.
What three things does Colchicine do and what is it so important?
-It arrests the cell division at metaphase.
-Prevents the formation of microtubules of the spindle
-In colchicine-treated metaphase, the chromosomes are found to assemble around centriole
-Application of colchicine in cell culture is an important tool in karyotyping
What happens in Anaphase?
- The centromere split longitudinally and chromatids separate to form two new chromosomes.
- The spindle fibers contract and each pair of newly formed chromosomes separate and migrates to the opposite pole of the spindle. Two identical and complete chromosomes are formed.
- The separation of the chromatids to form new chromosomes occurs by contraction of chromosomal microtubules which exert a centrifugal force in the centromere region.
How long does Anaphase take?
2-3 minutes
What two things can go wrong in Anaphase? Describe them.
-Non-disjunction: Due to abnormal function of the spindle apparatus one or more chromosomes fail to migrate properly in anaphase. Leading a daughter cell to receive extra chromosomes and another daughter cell is deficient in this chromosome.
-Isochromosome: Sometimes, the centromere splits transversely instead of longitudinal division. This leads to the formation of two daughter chromosomes of unequal length.
What five things happen in Telophase?
- The daughter chromosomes are enveloped by a new nuclear membrane and nucleolus appears.
- The chromosomes become uncoiled and their individual identity is lost.
- The cytoplasm divides and two complete cells are formed.
- In the process of cytokinesis, the cleavage furrow develops around the equator region of the achromatic spindle.
- The contraction of the fibrillar component of the cytoplasm help in hour glass constriction of cleavage.
What is Telophase described as?
A reorganization period.
How long does the telophase last?
Telophase 3 to 12 minutes and the reconstruction period from 30 to 120 minutes
What is the organizational structure in histology?
Cell
Tissue
Organs
Organ System
Organism
What are the three histological techniques?
-Tissue Processing
-Embedding and sectioning
-Staining
Draw the process of tissue processing.
Check-in histology notion
What do embedding and sectioning involve?
Slicing the desired section and putting it in the glass to view under the microscope