Introduction to Histology; Microscopy and Ultrastructure of the Cell

Histology; Microscopy and Ultrastructure of the Cell

Help

esc key shows all the slides
arrows left right advance the slide
mobile device swipe left right
slides can go left-right and up-down
? gives instant help
menu bottom left

To save as PDF, see last slide.

How to get the most from the revision slides

Have a pen & paper ready
Answer every question
Attempt to label all slides
Mark your answer after answering
Elaborate on each answer
Add relevant clinical content
If you have trouble, ask - you know where

Calibration

Community of Truth

What is my answer?
What is the correct answer?
I am am wrong, what was my error?
THUS: Find the truth

Philosophy 1

What is the least amount of work I can do so I can get out of here.

Philosophy 2

Today and Now I will do something for my future self.

Calibration

Assess yourself on each question.
Label all unlabelled slides.

You want incremental improvements over time.
Going up

Assess yourself
Nailed it!	Not sure...

Histology

Why Histology?

Where does Histology fit?

Endpoint?

Clinical application
VERY topical example
Aging immunity may exacerbate COVID-19

Arne N. Akbar, Derek W. Gilroy
Science 17 Jul 2020:
Vol. 369, Issue 6501, pp. 256-257
DOI: 10.1126/science.abb0762

Find the Histology:

The chemistry of cats: Allergies, catnip and urine
In the infographic, find the histology.
The image is available on the next slide, but more readible on web version available at the link.

Histology: Foundational Knowledge

Levels of Organisation

Why histology?

Knowledge

Because all knowledge is worthwhile
The more you know, the more you are able to know

Know the normal to identify the abnormal

Pathology

Functions of many organs

Lung, Kidney, Liver
Informed by cellular organisation
Physiology

Structure of body informed by cellular organisation

Anatomy

Inflammation, Repair & Treatment dependent on cellular organisation

Pharmacology

What in Histology

Basic framework to work from

Unlabelled images

The next slide shows an unlabelled image. Whenever you come across an unlabelled image, attempt to identify as many of the marked structures, BEFORE going to the next slide. Give yourself a score for each attempt, and when you revise, aim for an improvement on your previous score.

Remember - incremental improvements

Histology How

Histology is a visual subject.

You have to look at, identify, draw.

Pictures, illustrations, diagrams.

The Cell

Ultrastructure of the cell

The cell

Smallest unit living matter
Two compartments
Nucleus

Contains chromatin -> genetic material

Cytoplasm

Organelles -> metabolically active units
Inclusions -> inert accumulations
Cytoskeleton

Nucleus

Contains genetic material
Encoded in DNA of chromosomes
Euchromatin

lightly stained
dispersed chromatin
being transcribed

Heterochromatin

densely stained
not being transcribed

Nuclear envelope

Two parallel membranes
Separated by peri-nuclear space
Inner and outer continuous at nuclear pore
Nuclear pore interrupt double membrane
Outer nuclear membrane
Ribosomes attached
Continuous with endoplasmic reticulum
Inner nuclear membrane
Meshwork interwoven filaments
Fibrous lamina (nuclear lamina)
Anchoring site for interphase chromosomes

Nuclear pore

Membrane-bounded channel between nucleus and cytoplasm
Outer and inner membrane continuous around pore
Provide communication between nucleus and cytoplasm

Nucleolus

Well-defined nuclear inclusion
Seen in cells actively synthesizing protein
Involved in

Synthesis rRNA
Packaging rRNA into precursors of ribosomes

Cytoplasm organelles

Cell membrane
Glycocalyx
Ribosomes
Rough endoplasmic reticulum
Smooth endoplasmic reticulum
Mitochondria
Golgi apparatus
Lysosomes
Residual body
Peroxisome
Centrioles

Cytoplasm Cytoskeleton

Microtubules
Actin microfilaments
Myosin filaments
Myosin
Intermediate filaments
Keratin filaments
Desmin filaments
Vimentin filaments
Neurofilaments
Glial filaments
Microtrabecular lattice

Cytoplasm Inclusions

Glycogen
Lipid droplets
Secretion granules

Cell membrane

Surrounds cell
Boundary between cell & outside world
Phospholipid bilayer with integral proteins
Phospholipid
Hydrophilic ends face outwards
Hydrophobic chains project inwards
Protein position varies

Glycocalyx

On external surface of plasma membrane
Plays role in immunological specificity
Contains blood group antigens
Has receptor sites
Protective mechanical barrier
Can contain enzymes

Ribosomes

Composed of rRNA & proteins
Cluster in groups along mRNA to form polyribosomes
Synthesize proteins

Rough endoplasmic reticulum

Sheets & cavities bound by membranes
Outer surface studded with ribosomes
Interior region called cisternae
Has receptors where ribosomes bind
Common in cells synthesizing proteins for export

ie Secretory proteins

Smooth endoplasmic reticulum

Irregular network membrane-bound channels
Without ribosomes
Branching & anastomosing tubules & vesicles
Function depends on cell

Steroid hormone synthesis
Drug detoxification
Metabolism of lipids & cholesterol
Calcium ion homeostasis

Lysosomes

Membrane-bound dense bodies
Contains hydrolytic enzymes
Functions in intracellular digestion

Mitochondria

Rod-shaped organelles
Double-membrane structure

Outer membrane surrounds entire organelle
Inner membrane folds into interior

Inner membrane form cristae
Have enzymes for Krebs cycle & fatty acid oxidation
Contain own genetic apparatus

DNA, mRNA, tRNA & rRNA

Produces adenosine triphosphate (ATP)

Golgi apparatus

Several disk-shaped cisternae arranged in a stack
Two sides on stack

Outer convex forming face

Associated with small vesicles
Usually from rough endoplasmic reticulum

Inner concave maturing face

Associated with condensing vacuoles
Secretory materials condensed into granules

Functions

Membrane recycling & redistribution
Synthesis carbohydrates & proteins
Modification of cellular products
Concentration & packaging of synthesized material into secretory granules

Residual body

Cytoplasmic inclusion
Varies in appearance
Contains indigestible material

Peroxisome

Membrane-bound organelle
Stains cytochemically for catalase
Catalase synthesizes and destroys hydrogen peroxide
Often seen in close association with smooth ER
Function

Metabolism of

hydrogen peroxide
cholesterol
lipids

Breakdown of

purines
pyrimidines

Centrioles

Involved cell division
Pair of short rods at right angles to each other
Self-replicate prior to cell division
Wall of nine tubular triplets like pinwheel
Function

Form poles of mitotic spindles
Form basal bodies for cilia & flagella

Cytoplasm Cytoskeleton

Microtubules
Actin microfilaments
Myosin filaments
Myosin
Intermediate filaments
Keratin filaments
Desmin filaments
Vimentin filaments
Neurofilaments
Glial filaments
Microtrabecular lattice

Microtubules

Straight structures 25 nm x several μm length
Labile population

Free in cytoplasm
Polymerize-depolymerize depending on
Temperature, pressure, drugs, etc

Stable population

Walls of centrioles
Axonemes of cilia & flagella

Wall 5 nm thick

around lumen-like region
containing 13 spirally arranged protofilaments

Associated with intracellular transport
Maintains cell shape
Promote movement of cilia, flagella & chromosomes

Actin microfilaments

Thin filaments
Involved with

Ameboid movement
Cytoplasmic streaming
Contractile ring formation
Muscle contraction

Myosin filaments

Thick filaments
Associated with actin in muscle cells
Visible as striations in striated muscle

Intermediate filaments

Heterogenous group
Includes
Keratin

Found in epithelial cells
Associated with desmosomes

Vimentin
Desmin
Neurofilaments

Support long processes of nerve cells

Glial filaments

Present in nonneuronal cells of central nervous system
Astrocytes, oligodendrocytes, microglia

Keratin filaments

Neurofilaments

Glial filaments

Cytoplasm Inclusions

Glycogen

Storage form of carbohydrate
Varying appearance depending on stain

Lipid droplets

Varying appearance depending on stain

Secretion granules

Varying appearance
Include mucous droplets, hormones, proteins, pigment

Cell surface modifications

Cell surfaces of epithelia has specific modifications, relating to the function of epithelia
Three surfaces show modifications
Lateral surface

Junctional complexes
Gap junctions
Lateral interdigitations

Basal surface

Basal lamina
Hemidesmosomes
Basal plasma membrane infoldings

Apical surface

Microvilli
Stereocilia
Cilia

Epithelia

Lines internal -

Covers external -

Surfaces of the body

Three surface areas

Apical surface
Face the lumen or external environment
Lateral surface
Where cells are in contact with each other
Basal surface
Bottom edge of cell adjacent to basement membrane

Lateral surface

Junctional complexes
Gap junctions
Lateral interdigitations

Junctional complexes

Three components
Zonula occludens (tight junction)

Outer part of adjacent plasma membranes fuse
Around entire apical perimeter of cells
Prevents entrance or exit into intercellular space

Zonula adherens

Plasma membranes separated by 10 - 20 nm
Reinforced on cytoplasmic surface by actin filaments
Adhesive and structurally supportive

Macula adherens

Focal disk shaped adhesive junction
Plasma membrane separated by 15 - 30 nm
Intermediate filaments loop from cytoplasma
Dense material in intercellular space

Gap junctions

Not limited to epithelial cells
Also present in CNS, cardiac muscle & smooth muscle
Opposing plasma membranes separated by 2 nm gap
Gap is bridged by connexons
Permit passage of ions & small molecules
Intercellular communication

Lateral interdigitations

Finger-like projections interlocking adjacent cells

Basal surface

Basal lamina
Hemidesmosomes
Basal plasma membrane infoldings

Basal lamina

Acellular support structure
20 - 100 nm thick
Visible by electron microscope
Produced by epithelium resting on it
Consists of two zones

Lamina rara - low density, next to plasma membrane
Lamina dense - dense filament network, next to CT
Together = basement membrane of LM

Hemidesmosomes

Appearance of one-half of desmosome
Present along basal surface of some cells
Attaches cell to underlying basal lamina

Basal plasma membrane infoldings

Seen in ion-transporting epithelia
Deep invaginations
Compartmentalize mitochondria
Ion pumps in plasmalemma in close contact with energy supply (ATP from mitochondria)

Apical surface

Microvilli
Stereocilia
Cilia

Microvilli

Finger-like projections of epithelium
Approximately 1 µm in length
Increase absorptive surface
Brush border of kidney proximal tubule cells
Striated border of intestinal absorptive cells
Actin filaments in core

Stereocilia

Very long microvilli
Not true cilia
Epididymus & vas deferens

Cilia

Active motile specializations of epithelia that transports substances along their surface
5 - 10 µm in length
Covered by plasma membrane
Contains axoneme
Nine pairs double tubules around two single microtubules (9+2 pattern)
At base cylindrical basal body with 9+0 pattern