Tissues of the Body

Question 1

Define Histology

Answer 1

The study of the structure of tissues by means of special staining techniques combined with light and electron microscopy.

Question 2

Define the term “Tissue”

Answer 2

A collection of cells specialised to perform a particular function.

Question 3

Define “organ”

Answer 3

Aggregations of tissues, specialised to perform a particular function.

Question 4

State the relationship between mill-, micro- and nanometers

Answer 4

Millimeters: 1 X 10^-3m
Micrometers: 1 X 10^-6m
Nanometers: 1 X 10^-9m
Angstrom unit: 1 X 106-10m

Question 5

Explain the value of histology in diagnosis

Answer 5

For many diseases doctors will not give a treatment until the histopathologists have given a diagnoses e.g. Cancers, ulcerative colitis and Crohn’s disease.
It is the GOLD standard of diagnosis: final proof is biopsy and histology.
It can inform therapy e.g. Lung cancer: small cell carinoma or non-small cell - two different treatments, treating one like the other makes it worse.

Question 6

What is the size of most human cells?

Answer 6

10-20 micrometers

Oocytes are extremely large (0.1mm) and can sometimes see by eye!

Question 7

What is the size of red blood cells?

Answer 7

7.2 micrometers

Question 8

“The removal of a small piece of tissue from an organ of part of the body for microscopic examination (including blood).”

Answer 8

Biopsy

Question 9

What type of biopsy would you use for the cervix or buccal cavity (especially used for squamous epithelium).

Answer 9

Smear

Question 10

What type of biopsy would you use for the endometrial lining of uterus?

Answer 10

Curettage - like a sharp edged spoon

Question 11

What type of biopsy would you use for e.g. The brain, breast, liver, kidney, muscle?

Answer 11

Needle - a large bore needle which the tissue goes up

Question 12

Where would you use the biopsy technique ‘Direct incision’?

Answer 12

Skin, mouth, larynx

Question 13

How would you biopsy the lung, intestines and bladder?

Answer 13

Endoscopic - flexible tube manoevered down the oeseophagus, trachea or up the urethra or rectum

Question 14

How would you biopsy the heart or liver?

Answer 14

Transvascular - go in through a major blood vessel and usin X-ray watch where the probe is going and using scissors on the probe take off tissue

Question 15

Why do tissues need to be fixed?

Answer 15

1. Stops autolysing by lysosomes
2. Kills microbes present that would cause putrefaction
3. Macromolecules cross-link preserving cellular structure
4. Stops the tissue being wet and bloody, therefore easier to handle, slice etc…

Question 16

What types of fixatives are commonly used?

Answer 16

Glutaraldehyde, formaldehyde

Question 17

Describe how tissue processing can lead to shrinkage artifacts

Answer 17

When tissue is fixed the tissue shrinks, uneven shrinkage can create spaces which are unnatural and can be misinterpreted

Question 18

What is the value of histological staining?

Answer 18

Unstained cells are transparent and so have little contrast between different parts of the cell and the surrounding medium. However you can’t stain cells if you don’t want to kill them or compromise their natural function.

Question 19

What tissue components does the Periodic Schiff reaction stain?

Answer 19

It stains carbohydrates and glycoproteins magenta

E.g. Mucus-secreting cells (Mucins are glycoproteins) and basement membranes

Question 20

What tissue components are stained by Haematoxylin?

Answer 20

Stains acidic components of cells - purple/blue

E.g. Nucleolus (RNA), chromatin (DNA).

Question 21

What tissue components are stained by Eosin?

Answer 21

Stains basic components of cells - pink

E.g. Most cytoplasmic proteins and extracellular fibres

Question 22

What is phase contrast microscopy and what are its advantages?

Answer 22

Phase contrast microscopy exploits the interference effects produced when two sets of waves combine - as light travels through cells - and use these to produce heightened contrast (heightened light and dark effects).
The advantages of this is that it can be used on living cells (no stain needed).

Question 23

What is dark field microscopy and what are its advantages?

Answer 23

Darkfield microscopy uses light shone sideways through the cell - the reflection and diffractions of which highligh structures around the cell nucleus. This is used for a lot of pathological work, including the routine identification of syphilis and malaria.

Question 24

What is fluorescence microscopy and what are its advantages?

Answer 24

Fluorescence mircroscopy uses labelled antibodies to bind to specific components of the cell. These antibodies are labelled with a “stain” that are excited by UV light to fluoresce in different colours. Filters stop the high intensity UV light reaching the image plane, so only the fluorescing light reaches. The advantages are that specific cell components can be visualised.

Question 25

What is confocal light microscopy and what are its advantages?

Answer 25

Confocal light microscopy can eliminate “out of focus” glare from a thick fluorescently labelled specimen by scanning beams of light (usually from a laser) across the specimen - producing scanned images called optical sections. This effectively sections the tissue in a non-invasive way by light rather than physical means. The advantages of this is that it can image live specimens, enabling the construction of electronically automated 3D images from a series of 2D images taken at successive depths.