Cell Biology Basics

Microscope Structure

• The microscope contains a lens that can magnify 10X
• The draw tube holds the eyepiece/ocular
• The body tube holds the dust shield and the revolving nosepiece

Functions of Microscope Parts

• Dust shield: protects the objective lens from dust and dirt
• Revolving nosepiece: holds the objective lens
• Objectives:
  • Scanning Objective: usually marked 4X, used to see the general outline of the specimen
  • Low Power Objective (LPO): usually marked 10X, used to view structures in a larger perspective
  • High Power Objective (HPO): usually marked 40X, used to view structures in a more detailed perspective
  • Oil Immersion Objective (OIO): usually marked 100X, used to view structures using oil as a medium
• Stage: part of the microscope where the glass slide is placed
• Stage clip: holds and secures the slide
• Mechanical adjustment knob: moves the stage/slide from left to right and from top to bottom
• Coarse Adjustment Knob: rapidly raises or lowers the stage/objective to initially bring the specimen into focus
• Fine Adjustment Knob: used for more precise focusing
• Iris diaphragm: regulates the amount of light entering the stage
• Condenser: concentrates the amount of light entering the stage

Types of Microscopes

• Monocular microscope: microscope with only one ocular/eyepiece
• Binocular microscope: microscope with 2 or more oculars/eyepieces
• Simple microscope: microscope with only one lens
• Compound microscope: microscope with 2 or more lenses
• Light Microscope: source of light is visible light
• Brightfield microscope: structures are colored, the background is clear or lighter in shade
• Darkfield microscope: the specimen is unstained (no color), but the background is dark in shade
• Fluorescence microscope: source of light is ultraviolet (UV) light, used in immunofluorescence/immunodiagnostic tests
• Electron microscope (EM): source of light is an electron beam, used in the study of viruses

Total Magnification (TM)

• TM = MP(E) x MP(O)
• TM = Total Magnification
• MP = Magnifying power
• E = Eyepiece
• O = Objective

Caring for Your Microscope

• Tip 1: Handle with care
• Tip 2: Keep lenses clear of slides
• Tip 3: Clean after using immersion oil
• Tip 4: Cover when not in use
• Tip 5: Look after the bulb
• Tip 6: Store in a clean, dry place
• Tip 7: Only use special lens paper or wipes for cleaning the lenses
• Tip 8: Keep your User's Manual and wrenches in a safe place
• Tip 9: Perform an annual maintenance check
• Tip 10: Have your microscope serviced professionally

The Cell

• Basic morphological and functional unit of life
• Capable of independent existence
• Different sizes, shapes, and forms due to varied specialized functions
• The human body is composed of ~100 trillion cells, representing more than 250 cell types

Levels of Organization

• Chemical
• Cell
• Tissue
• Organ
• Organ system
• Organism

The Cell Membrane

• Also known as the plasma membrane, plasmalemma, or unit membrane
• Functions:
  • Protective covering that delimits the cell from its surroundings
  • Determines which substances can move in and out of the cell and regulates the movement of these substances
  • Provides attachment for the skeleton (cytoskeleton) of the cell
  • Receives and sends out stimuli
  • Provides binding sites and receptors for enzymes and other substances
  • Allows cell-cell recognition
  • Forms specialized junctions with the cell membrane of the adjacent cell

Phospholipid Molecule

• 3 main parts:
  • Head: globular, polar, and hydrophilic; consists of glycerol that is conjugated to a nitrogenous compound by a phosphate bridge
  • 2 tails: slender, nonpolar, and hydrophobic; one of the two tails consists of a straight-chain saturated fatty acid, while the other consists of an unsaturated fatty acid

Cholesterol Molecule

• Serves to stiffen and strengthen the cell membrane
• Makes the cell membrane less permeable to water-soluble substances

Glycocalyx

• Cell covering made up of glycolipids, glycoproteins, and polysaccharides
• Contributes to cell-cell recognition, cell-to-cell adhesion, and immunological response

Unit Membrane

• Generic term referring to the trilaminar entities or structures that comprise the cell membrane and make up or envelope all other membrane-containing structures within the cell

Specialized Junctions

• Occluding junctions: prevent the mixing of membrane proteins between apical and basolateral membranes
• Adhesive junctions:
  • Zonula adherens: initiates cell-to-cell contact and maintenance of contact
  • Fascia adherens: integrin-containing structure
  • Desmosome: mediates direct cell-to-cell contact
  • Hemidesmosome: facilitates stable adhesion of basal cells
• Communicating junctions:
  • Gap junctions: channels that physically connect adjacent cells, mediating the rapid exchange of small molecules

Cytoplasm

• The homogeneous substance that fills the space bounded externally by the cell membrane and internally by the nuclear envelope and the various formed elements that are embedded in it
• Site of many important biochemical processes and provides a suitable milieu for the organelles in performing their functions### Introduction to Human Histology
• This material is prepared by the Faculty of the Department of Medical Laboratory Science, LPU-Batangas College of Allied Medical Professions, solely for the use of students enrolled in Human Histology (MLS 202) for the A.Y. 2022-2023.
• The scope of histology includes the study of human body cases, integration, structures, tissues, techniques, and organ systems.

The Birth of Histology

• Robert Hooke (1635-1703) was an English physicist who discovered the law of elasticity and was the first to use the word "cell" to describe the microscopic cavities in cork.
• Marcello Malpighi (1628-1694) was an Italian physician and biologist who founded the science of microscopic anatomy.
• Antonie van Leeuwenhoek (1632-1723) was a Dutch microscopist who first observed bacteria and protozoa.
• Jan Evangelista Purkinje (1787-1869) was a pioneer Czech experimental physiologist who investigated the fields of histology, embryology, and pharmacology.
• Robert Brown (1773-1858) was a Scottish botanist who discovered cell nuclei and Brownian motion.
• Theodor Schwann (1810-1882) was a German physiologist who founded modern histology by defining the cell as the basic unit of animal structure.
• Rudolf Virchow (1821-1902) was a German pathologist and statesman who pioneered the modern concept of pathological processes by applying the cell theory to explain the effects of disease.
• Marie-François-Xavier Bichat (1771-1802) was a French anatomist and physiologist who helped found the science of histology through his systematic study of human tissues.
• August Franz Josef Karl Mayer (1787-1865) was a German anatomist and physiologist who coined the term "histology" in 1819.
• Rudolf Albert von Kölliker (1817-1905) was a Swiss embryologist and histologist who interpreted tissue structure in terms of cellular elements.

Histology

• Histology is derived from the Greek words "histos" (tissue) and "logos" (study).
• It is essentially microanatomy, dealing with the study of microscopic structures of cells and tissues in plants and animals.
• Histology is concerned with the study of different cell and tissue types sharing related or similar functions that result in the different functions of the body.
• It serves as the basic foundation to distinguish physiologic from pathologic changes in cells and tissues.

Importance of Histology

• Histology is essential for understanding pathology and is an important component of human biology.
• It is aligned with anatomy and is central to biological and medical sciences.

Histology vs. Histopathology

• Histology is the study of normal tissues and cells, while histopathology is the study of diseased tissues and cells.

Methods of Study

• Preparation of tissue or organ suitable for viewing is important, including the type of microscope used.
• Microtechniques include the different methods used for preparation of histological sections.

Microtechniques

• Fresh tissue examination involves spreading of blood film, connective tissue, bone marrow film or smear, etc.
• Preparation of sections from organs involves cutting small pieces of the organ into very thin slices (4-8µm) called sections using paraffin or freezing methods.

Tissue Processing

• Tissue processing includes numbering, fixation, decalcification, dehydration, clearing, impregnation, embedding, section cutting/staining, mounting, and labeling.

Laboratory Scientists as…

• They play a crucial role in processing and analyzing tissue samples.

Microscope

• A microscope is an optical instrument that uses a lens or a combination of lenses to produce magnified images of small objects.
• General parts of the compound microscope include optical parts (eyepiece, objective lens, and condenser) and mechanical parts (stage, arm, and base).### Protein Synthesis Within the Cell
• Step 1: Transcription: copying of genetic information from DNA to RNA, where DNA is too large to leave the nucleus, and RNA is single-stranded and can leave the nucleus.
• Unzipping of DNA: part of DNA temporarily unzips, and is used as a template to assemble complementary nucleotides into messenger RNA (mRNA).
• mRNA: goes through the pores of the nucleus with the DNA code and attaches to the ribosome.

Step 2: Translation

• Decoding of mRNA: into a protein, where transfer RNA (tRNA) carries amino acids from the cytoplasm to the ribosome.
• Amino acids: come from the food we eat, broken down into individual amino acids, and rearranged into new proteins according to the needs and directions of our DNA.
• Codon: a series of three adjacent bases in an mRNA molecule codes for a specific amino acid.
• tRNA: has 3 nucleotides that are complementary to the codon in mRNA, and each tRNA codes for a different amino acid.

Protein Synthesis

• Amino acids: are joined together to make a protein.

Movement of Materials Across the Cell Membrane

• Endocytosis: refers to the transport of substances from the extracellular space into the cells, which can be either phagocytosis for solid substances or pinocytosis for liquid substances.
• Exocytosis: refers to the process of transporting substances inside the cells across the cell membrane and out of the cell, which can occur through either regulated secretion or constitutive secretion.

Regulated Secretion

• Occurs in: goblet cells, pancreatic acinar cells, and cells of the salivary glands.
• Secretory vesicles: are first stored in the apical portion of the cell, where they accumulate and get further dehydrated.
• Dehydrated secretory vesicles: are only released from the cells when there is a specific signal to do so.

Constitutive Secretion

• Occurs in: cells such as fibroblasts and chondroblasts.
• Secretory products: are continuously released from the cell.

Epithelial Tissue

• Functions: depends on its location, including protective covering, secretion, absorption, sense of taste and smell, excretion, and production of sex cells.
• Characteristics: highly cellular, avascular, and exhibits polarity.
• Embryonic origin: covers the external surfaces of the body, lines the epithelium of digestive tract, heart, blood, lymphatic vessels, urinary system, and male and female reproductive system.

Basal Lamina

• Composition: mainly type IV collagen, laminin, entactin, and proteoglycans.
• Thickness: 20-200 nm.
• Functions: provides structural support to the overlying epithelium, serves as an impermeable barrier, and limits the contact between epithelial cells and other cell types in the tissue.

Classification of Epithelial Tissue

• Covering epithelia: epithelial tissue that covers the body surfaces or lines body cavities.
• Glandular epithelia: epithelial tissue that produces secretions.
• Classification based on cell shape and cell layers: simple, stratified, and pseudostratified epithelial tissue.

Simple Epithelial Tissue

• Simple squamous epithelium: a single layer of flat, platelike cells that functions as a semipermeable barrier.
• Simple cuboidal epithelium: a single layer of blocklike cells that regulates ion and water concentration in certain specialized salivary ducts.
• Simple columnar epithelium: a single layer of tall cells with oval nuclei that are more basal in location.

Pseudostratified Epithelial Tissue

• Pseudostratified columnar epithelium: a single layer of cells of variable shape and height, with nuclei at 2 or more levels.

Stratified Epithelial Tissue

• Stratified squamous epithelium: composed of several layers, where new cells are formed only in deep layers and superficial old cells have been pushed to the surface.
• Keratinized type: a multilayered sheet of cells, impervious to water, where superficial cells are squamous, dead, and filled with keratin.