Histology Cell

8/11/2019 Histology Cell

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INTRODUCTION TO

HISTOLOGYFernando J. Peraldo, M.D., MPH



HISTOLOGY

• is derived from the Greek word for a tissue

"Histos", and "-logos" = the study of cells and

the extracellular matrix of tissues

• "Microscopic Anatomy“ - includes

understanding of the structure and function of

cells, tissues, organs and organ systems

• the study involves the use of microscopes

(light and electron) as basic tools.



HISTOLOGY

the body can be seen to be formed of different levelsof organization, with increasing levels of complexity

LEVELS OF ORGANIZATION

Cells

Tissues

Organs

Organ Systems

Organism

▪ each of which plays important roles in the physiologicalhomeostasis of the body.



LEVELS OF ORGANIZATION

• THE CELL - defined as the smallest basicstructure of higher organisms capable ofindependent existence

• TISSUES - are groups of cells of similarfunction and origin that form functional units

• ORGANS - represent an even greater measure

of complexity and are composed of varioustissues

• ORGAN SYSTEM - composed of several organs



BASIC TECHNIQUES: Preparation of

histological sections

1. Fixation

- to preserve tissues and prevent structural

change or breakdown of the components of the

tissues

- needs to preserve the tissues as close as

possible to the living state

- the fixatives commonly stabilize or denature

proteinsEx. Formaldehyde - cheap and penetrates

tissues rapidly




histological sections 2. Embedding

- thin sections require tissues to be infiltrated after fixation with

embedding substances that imparts rigid consistency to the tissue

- the most commonly used embedding or support medium is

paraffin wax and plastic resins

STEPS:Dehydration - remove all the water from the tissue

- achieved using an ascending series of alcohols(70%, 95%, 100%)

Clearing - tissue immersion in a wax solvent such as xylene or

chloroform- the tissue is then transferred to molten paraffin wax (in an

embedding oven) for a couple of hours




histological sections 3. Microtomy

- sections of the tissue embedded in the wax

block are cut on a machine, known as a microtome,

using special knives

- series or ribbons of sections are cut at a thickness of6-8mm.

- the sections are transferred to the surface of a hot

waterbath then collected on glass microscope slides

(standard dimensions of 3 x 1 inches)- In order for the sections to adhere to the slides they

are dried for up to 24 hours in a drying oven





4. Staining

- the most common staining technique is known asHematoxylin and Eosin (or H&E) staining

STEPS:- remove wax using a wax solvent such as xylene

- hydrate the slide using a series of descending

alcohols (100%, 95%, 70%) and then water

- immerse the slide in Hematoxylin stain, rinsed in

running water (preferably alkaline), followed by

staining with Eosin, and rinsing in water.





5. Permanent Mounting

- After staining the sections are againdehydrated with ascending alcohols (95%,

100%) and xylene, prior to covering with amountant and a glass coverlip

- the slide is left for at least 24 hours for themountant to dry

- the finished (permanent) slide with its stainedtissues can then be examined under themicroscope.





Frozen sections

- A rapid alternative to wax embedding

- use of cryostat (a microtome operated in a lowtemperature cabinet,

usually about -30 C, then be stained and mountedin a suitable water-soluble mountant.

Total preparations

- Use in a very thin membrane. The tissue does not

need cutting on a microtome, but can be stained,mounted and examined directly. Not as 2-dimensional as histological sections, and adjustmentof focus is necessary during examination.





• Cell Smears

- a form of histological preparation that does

not require sectioningExample: blood or bone marrow smears

swabs or scrapings of epithelial

cells (e.g. from the oral cavity,cervix uteri).



Histological classification of animal tissues

Four basic types of tissues

muscle tissue

nervous tissue

connective tissue epithelial tissue

▪ All tissue types are subtypes of these fourbasic

tissue types (for example, blood cells areclassified as connective tissue, since they

generally originate inside bone marrow).



SPECIAL TERMS

Epithelium: the lining of glands, bowel, skin and someorgans like the liver, lung, kidney

Endothelium: the lining of blood and lymphaticvessels

Mesothelium: the lining of pleural and pericardialspaces

Mesenchyme: the cells filling the spaces between theorgans, including fat, muscle, bone, cartilage, andtendon cells

Blood cells: the red and white blood cells, includingthose found in lymph nodes and spleen



Neurons: any of the conducting cells of the nervoussystem

Germ cells: reproductive cells (spermatozoa inmen, oocytes in women)

Placenta: an organ characteristic of true mammalsduring pregnancy, joining mother and offspring,providing endocrine secretion and selective exchangeof soluble, but not particulate, blood-bornesubstances through an apposition of uterine and

trophoblastic vascularized parts Stem cells: cells able to turn into one or several of the

above types



END OF LECTURETHANK YOU

Histology Cell

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