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VetST IA: Histology > Microscopy and Cells Intro > Flashcards

Microscopy and Cells Intro Flashcards

1
Q

What are the four main types of tissue?

A
  • Epithelial
  • Muscle
  • Connective
  • Nervous
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2
Q

What is epithelial tissue?

A

The tissue which covers the body surface and lines most internal cavities.

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3
Q

What is the function of epithelial tissue?

A
  • Protection
  • Secretion
  • Absorption
  • Filtration
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4
Q

What is muscle tissue?

A

An active contractile tissue, made of myosin and actin filaments.

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5
Q

What is the function of muscle tissue?

A

Force and movement:
- Locomotion
- Movement within internal organs
- Pumping blood

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6
Q

What is connective tissue?

A
  • Fibrous tissue made up of cells separated by extracellular fluid, called the extracellular matrix.
  • The extracellular matrix can be flexible or rigid (ie. tendons or bones)
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7
Q

What is the function of connective tissue?

A
  • Gives shape to organs and holds them in place
  • Provides support and protection to tissues
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8
Q

What is nervous tissue?

A

Composed of neurons, which
receive and transmit electrical impulses, and glia cells, which support the neurones.

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9
Q

What is the function of nervous tissue?

A

Regulates and controls bodily functions:
- Sensory input integration
- Control of muscles and glands
- Homeostasis
- Mental activity

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10
Q

Why do different tissues perform different functions?

A
  • Because of the diverse cell types present in each tissue.
  • In becoming different from each other, the cells have amplified features that are common in all cell types to become specialists in that function.
  • So understanding the function of the tissues and organs is aided by understanding the combination of specialist cells that produce the function.
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11
Q

Why are different cell types relevant to histopathologists?

A

It is important to assess whether all the expected cell types are present in a patient sample of a particular tissue, and in their normal proportions.

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12
Q

What mechanism causes cell differentiation?

A
  • All cell types start with the same set of genes in the genome, so what makes one cell different from another is the subset of genes that they have on (expressed).
  • The final products of the expressed genes, either the protein translated from the mRNA or the RNA itself, give each cell its specific functional properties.
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13
Q

What is the definition of resolution?

A
  • As two objects move closer to each other they no longer become distinguishable as two separate objects.
  • The resolution of an imaging system is the minimum distance between two objects for them to be distinguished as separate.
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14
Q

What is the resolution of the human eye?

A

200µm

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15
Q

What does the resolution of an optical microscope depend on?

A

The wavelength of light used to illuminate the specimen, and the optical properties of the lenses in the microscope.

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16
Q

What is the best resolution a light microscope can achieve?

A

About 0.25µm with visible light

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17
Q

What size do most plant and animal cells range from?

A

10-100µm

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18
Q

What size is the average red blood cell?

A

7.5µm

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19
Q

What is the size range of an average mitochondrion?

A

0.5-1µm

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20
Q

What is the aim of what can be seen under a light microscope?

A
  • The overall shape of cells, especially if the plasma membrane is highlighted by staining, and the nucleus.
  • Distinguish aggregates of proteins, such as fibrils of collagen, or keratin bundles in hairs.
  • Visualise intracellular membrane-bounded structures and cytoskeletal
    structures such as microtubules with light microscopy, using fluorescence microscopy.
  • We cannot see individual protein molecules as discrete objects, as an average protein is only about 10nm in diameter.
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21
Q

What is fluorescence microscopy?

A

The structure of interest is labelled by a fluorescent signal thus increasing the ‘contrast’ between this structure and neighbouring structures, without
changing the resolution.

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22
Q

What is the definition of contrast?

A

The difference in light intensity between an object and the adjacent background, relative to the overall background intensity.

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23
Q

What is the advantage of electron microscopy?

A

Electron microscopy achieves higher resolution because the wavelength of electrons is up to 100,000 shorter than visible light photons.

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24
Q

What are samples stained with in SEM and why?

A

They are stained with heavy metals, such as osmium or platinum, which deflect the electron beam.

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25
Q

What is a key theme of the cells in a multicellular organism?

A

Different types of cells have
specialist abilities, often occurring through amplification or modification of these basic subcellular structures. For example, a cell that secretes a large amount of a particular protein or chemical will have an expanded secretory apparatus.

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26
Q

What is the plasma membrane?

A

The membrane surrounding the cell, made up of a phospholipid bilayer.

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27
Q

What are the functions of the plasma membrane?

A

Provides a highly selective barrier
between the cytoplasm and the environment.

28
Q

Describe the structure of a nucleus.

A
  • The nucleus is surrounded by a double membrane (inner and outer).
  • In many cells, the outer nuclear membrane is continuous with the RER.
  • Nuclear pores are fenestrations in the nuclear membrane that function as pathways for selective exchange between the nucleus and the cytoplasm.
  • The nucleolus is a sub-compartment of the nucleus involved in ribosomal RNA transcription and ribosome production.
  • Chromatin: DNA bound to histones and other proteins. Exists in two forms.
29
Q

What are the two forms of chromatin?

A

Heterochromatin - condensed chromatin that is transcriptionally inactive & Euchromatin - dispersed regions of unpacked chromatin that is often actively transcribed.

30
Q

What is the role of the nucleus?

A
  • The nucleus contains the genetic material of the cell (deoxyribonucleic acid, DNA).
  • It is where DNA replication and RNA synthesis take place.
31
Q

What is the endoplasmic reticulum?

A
  • A system of intracellular membranes.
  • Its name reflects its position in the cell (endoplasmic) and the fact that parts of it join together to form a loose, irregular net (‘reticulum’ = net).
32
Q

What is the rough endoplasmic reticulum?

A

It has ribosomes attached
to its outer (cytosol) surface. The membranes are often arranged as large, flattened sacs, called cisternae.

33
Q

What is the smooth endoplasmic reticulum?

A

Regions of the ER with a ‘smooth’
appearance (without associated ribosomes). These regions are usually tubular and form an anastomosing (connecting) network which may join onto vesicles or cisternae of rER.

34
Q

What is the general purpose of the ER?

A

Serves both to separate special areas
from the cytosol (the colloidal solution of substances in which the organelles are set) and to provide a surface to support organized arrays of enzymes.

35
Q

What is the function of the RER?

A

These regions are specialized for synthesis and segregation of proteins destined to be stored or secreted by the cell.

36
Q

What is the function of the sER?

A
  • Provides the space for the synthesis of lipids, lipoproteins and steroids.
  • The breakdown or detoxification of many substances
  • The formation of glycogen
  • For the segregation of some ions (particularly calcium ions) within the cytoplasm.
37
Q

What is a ribosome?

A
  • A ribosome is an enzyme complex composed of RNA molecules and protein.
  • Rounded structures about 15 nm in diameter, particularly abundant in cells synthesising and secreting large amounts of protein.
  • A group of them is often linked together by a strand of messenger-RNA to form a polyribosome.
38
Q

What is the function of ribosomes?

A

Free ribosomes can be found in the cytosol where they synthesize proteins needed by the cell.

39
Q

What is the Golgi apparatus?

A
  • A large organelle, which is expanded in secretory cells.
  • Under the EM the GA can appear as a series of flattened, smooth membrane sacs (or cisternae), stacked upon one another, surrounded by a number of membrane vesicles that transport proteins to and from the GA.
40
Q

What is the function of the Golgi apparatus?

A
  • The packaging of proteins into secretion
    droplets or granules.
  • The recycling and alteration of intracellular membranes.
  • The addition of the carbohydrate to glycoproteins, glucoproteins and mucins.
  • The vesicles leaving the Golgi are directed to other compartments, such as the plasma membrane to insert surface proteins and secrete proteins, and other internal organelles.
41
Q

What are mitochondria?

A
  • Mitochondria are double-membrane bound organelles - they have an outer membrane in contact with the cytoplasm and a highly folded inner membrane (cristae).
  • Depending on the cell type, their number and size is highly variable.
  • Mitochondria contain their own small chromosomes.
42
Q

What is the function of the mitochondria?

A

Generate most of the chemical energy needed to power the cell’s biochemical reactions through oxidative metabolism.

43
Q

What are lysosomes?

A
  • Spherical organelles
  • When they are first formed they are known as primary lysosomes. These are spherical organelles which appear homogeneous in content and do not contain particles or membranes.
  • Primary lysosomes fuse with material taken into the cell by phagocytosis or pinocytosis, and with damaged or redundant parts of the cell, giving rise to secondary lysosomes.
  • Secondary lysosomes have a diverse morphology and contain particles or membranes undergoing enzymatic digestion.
44
Q

What is the function of lysosomes?

A

They contain a large amount of hydrolytic enzymes involved in the intracellular digestion of macromolecules, membranes and organelles.

45
Q

What are peroxisomes?

A
  • Also known as microbodies
  • Small, spherical organelles
  • Because of their morphological similarity with lysosomes, for a long time peroxisomes were believed to be lysosomes. However, their enzyme composition and function are very different.
46
Q

What is the function of a peroxisome?

A

Contain enzymes involved in oxidative reactions.

47
Q

What is the role of catalase in perioxisomes?

A
  • Some of the oxidative reactions result in the formation of hydrogen peroxide, a potentially cytotoxic byproduct.
  • The concentration of hydrogen peroxide can be regulated by the enzyme catalase, present in peroxisomes in large amounts.
48
Q

What fuel reserves may be observed in a eukaryotic cell and how do they appear under a microscope?

A
  • Glycogen granules and lipid droplets serve as fuel reserve for some cells.
  • Glycogen may aggregate and form rosettes. They are larger and darker than ribosomes in an EM.
  • Lipid forms homogenous droplets in the cell which are not bounded by membrane; they tend to aggregate, because lipid cannot mix well with the other material in the aqueous cytoplasm.
49
Q

What is the extracellular matrix?

A

In addition to the structures within the cell, cells secrete an extracellular matrix, which contributes to the formation of connective tissue.

50
Q

What cell is commonly responsible for the formation of the extracellular matrix?

A

The fibroblast is the most common connective tissue cell, responsible for the synthesis and secretion of extracellular matrix in most tissues.

51
Q

What are fibroblasts?

A

Fibroblasts are long and thin, with fine cytoplasmic extensions. Fibroblasts also occur in an inactive state called fibrocytes.

52
Q

What are two important functions of extracellular matrix?

A
  • The basement membrane
  • Mesenchymal tissue
53
Q

What is the basement membrane?

A
  • The basement membrane, or basal lamina, is a thin sheet of extracellular matrix.
  • It underlies the basal surface of epithelia and
    surrounds other cells and tissues.
  • It is formed from secreted proteins
    that assemble on the surface of cells into a meshwork.
54
Q

What is mesenchymal tissue?

A
  • Extracellular matrix is a major component of mesenchymal cell layers, such as the dermis.
  • These cell layers contain relatively few cells within a meshwork of extracellular matrix proteins.
55
Q

What are the two types of fibres usually found in connective tissue?

A

Structural and elastic fibres.

55
Q

What are structural fibres?

A
  • Most frequently made by fibrillar collagen.
  • Collagen fibres provide strength to the tissue and resist stretch. Collagen is the most
    abundant protein in the body.
  • Collagen fibres contribute to tendons and ligaments, as well as the connective tissue within most tissues.
55
Q

What are elastic fibres?

A
  • Elastic fibres are found in most connective tissues, conferring elasticity to enable recovery of tissue shape following normal physiological deformation.
  • They consist mainly of an amorphous glycoprotein called elastin.
56
Q

What organs contain high amounts of elastin?

A

The lungs, skin, urinary bladder and the wall of large blood vessels contain large amounts of elastin.

57
Q

What are the two main methods of tissue fixation used on the course?

A

Immersion and perfusion.

58
Q

What is immersion fixation?

A
  • The tissues are immersed in the fixative solution, allowing the fixative to diffuse into the tissue.
    • To ensure rapid penetration of the fixative into every cell, the tissue is rapidly chopped up with a razor blade into small fragments before immersion in the fixative.
    • The structures in the deeper parts of the tissue may be less preserved. Some crushing and mechanical damage to the cells is unavoidable.
    • The capillary space can be squashed flat, making capillaries difficult to identify.
    • Blood cells are retained within blood vessels when a tissue is fixed by immersion.
59
Q

What is perfusion fixation?

A
  • The fixative reaches the tissue through the blood vessels as it is pumped in via the largest arterial supply.
    • Every cell is fixed virtually instantaneously without cell stress other than that induced by the fixative.
    • The capillary blood volume is preserved as it is in vivo but with most of the blood cells flushed out.
    • Fixation by perfusion produces a network of white spaces – the preserved capillary bed of the tissue– with the occasional blood cell.
60
Q

What is the difference between a longitudinal and transverse section?

A

Along length is longitudinal, transverse is across diameter.

61
Q

What is electron microscopy based on?

A

The interaction of electrons and tissue components.

62
Q

How does a TEM work?

A
  • A beam of electrons is transmitted through a thin specimen, and are focused to form an image on a phosphorescent screen or film.
  • It has better resolution that light microscopy (up to 0.2nm).
  • To prevent deflection of the electrons, the electron beam operates in a vacuum.
  • This means specimens must be fixed in plastic and thin sections prepared.
63
Q

How does a SEM work?

A
  • It provides a high resolution 3D image of cells and tissues.
  • A fine electron beam is used to scan back and forth regularly across the specimen.
  • The specimens are fixed and dehydrated, but not sectioned.
  • Their surface is coated with a heavy metal, such as platinum. The electron beam bounces off this thin metal coating and the reflected electrons are captured by the detector, transmitted to amplifiers, focused and displayed.
  • Resolution: 2.5-7.5nm, surface view only.

VetST IA: Histology (1 decks)

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