MedicoPlexus
Cytology
Raghib Siddiqui
1.Introduction to Cell Biology/Cytology
Robert Hook – Coined the term ‘Cell’
Anton van Leeuwenhoek- Made microscopes with magnification 10x greater than the previous light microscope
Cell Theory – Rudolf Virchow; All cells come from pre-existing cells,
Later improved by Schleiden and Schwann
Cell -The basic unit of structure and function
All cells store their hereditary information in the same linear chemical code (DNA)
All cells are prokaryotic or eukaryotic
Prokaryotic cells – without a distinct nucleus
Eukaryotic cells – keep their DNA in a separate membrane-enclosed compartment -the nucleus
MedicoPlexus does not own this image. https://www.bioscience.com.pk/topics/cell-biology/item/578-differences-between-prokaryotic-cell-and-eukaryotic-cell
All cells are enclosed in a plasma membrane (composed of amphiphilic phospholipid molecules) across which nutrients and waste materials must pass
The cell is composed of 2 basic parts: Cytoplasm + Nucleus
The cytoplasm –
Cytosol – fluid component
Organelles – metabolically active structures
¬ membranous (e.g., mitochondria)
¬ non-membranous (e.g., ribosomes and proteasomes)
Cytoskeleton – determines the shape and motility of eukaryotic cells
Other minor cytoplasmic structures are – inclusions – deposits of carbohydrates, lipids, or pigments deposits of carbohydrates, lipids, or pigments
Cell Types According to Size:
Small (5-10 μm) – e.g., small lymphocytes, erythrocytes, cells of the granular layer (cerebellar cortex)
Medium – sized (11-30 μm) – e.g., granulocytes e.g., granulocytes
Large cells (31 – 100 μm) – e.g., Purkinje cells e.g., Purkinje cells (cerebellum) (cerebellum)
Giant cells (101 -200 μm) – e.g., some pyramid– shaped neurons (cerebral cortex), megakaryocytes, oocytes (ovary)
Cell Types according to shape:
2. Histological Methods and Techniques in Anatomy and Related Sciences
Histology is the study of the tissues of the body and how these tissues are arranged to constitute organs.
Preparation of tissues for study –
The most common procedure used in the study of tissues is the preparation of histological sections or tissue slices that can be studied with the aid of the light microscope.
Under the light microscope, tissues are examined via a light beam that is transmitted through the tissue.
Because tissues and organs are usually too thick for light to pass through them, they must be sectioned to obtain thin, translucent sections and then attached to glass slides before they can be examined.
MedicoPlexus does not own this image. Junqueira’s Basic Histology Text and Atlas, 13th Edition
Freezing of tissues is also effective in the histochemical study of very sensitive enzymes or small molecules, because freezing, unlike fixation, does not inactivate most enzymes. Finally, because clearing solvents such as toluene dissolve cell lipids in fixed tissues, frozen sections are also useful when structures containing lipids are to be studied histologically.
Staining –
Most cells and extracellular material are completely colorless, and to be studied microscopically sections must typically be stained (dyed)
Dyes stain tissue components more or less selectively, with many behaving like acidic or basic compounds and forming electrostatic (salt) linkages with ionizable radicals of molecules in tissues.
Cell components such as nucleic acids with a net negative charge (anionic) stain more readily with basic dyes and are termed basophilic.
cationic components, such as proteins with many ionized amino groups, have affinity for acidic dyes and are termed acidophilic.
The combination of Hematoxylin and Eosin is used most commonly.
Hematoxylin stains DNA of the cell nucleus and of the cell nucleus and other acidic structures (such as RNA-rich portions of the cytoplasm and the matrix of cartilage) blue
Eosin stains other cytoplasmic components and collagen pink.
Periodic acid-Schiff (PAS) reaction – for glycoproteins.
Light Microscopy –
Based on the interaction of light and tissue components. Types;
Bright-field microscopy – stained preparations are examined by means of ordinary light that passes through the specimen
Fluorescence microscopy – tissue sections are irradiated with irradiated with a certain wavelength light and the emission is in another wavelength
Phase Contrast Microscopy – Phase-contrast microscopy uses a lens system that produces visible images from transparent objects and, importantly, can be used with living, cultures cells. It is based on the principle that light changes its speed when passing through cellular and extracellular structures with different refractive indices
Polarizing Microscopy – Polarizing microscopy allows the recognition of stained or unstained structures made of highly organized subunits. When normal light passes through a polarizing filter, it exits vibrating in only one direction
Electron Microscopy –
Based on the interaction of electrons and tissue components
The wavelength in the electron beam is much shorter than of light, allowing a thousand-fold increase in resolution
Transmission Electron Microscopy – The transmission electron microscope (TEM) is an imaging system that permits resolution around 3 nm. This high resolution allows magnifications of up to 400,000 times to be viewed in detail. Unfortunately, this level of magnification applies only to isolated macromolecules or particles. Very thin tissue sections can be observed with details at magnifications of up to about 120,000 times.
Scanning Electron Microscopy – Scanning electron microscopy (SEM) provides a high-resolution view of the surfaces of cells, tissues, and organs. Like the TEM, this microscope produces and focuses a very narrow beam of electrons, but in this instrument the beam does not pass through the specimen
MedicoPlexus does not own this image. https://ib.bioninja.com.au/standard-level/topic-1-cell-biology/11-introduction-to-cells/microscopes.html
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