Introduction to Histology and Epithelium

Question 1

Define Tissue

Answer 1

Group of similar cells working together to carry out a common function + the extracelluar matrix surrounding them

Question 2

Cytosol

Answer 2

Intracellular fluid

Question 3

Simple vs Complex tissue

Answer 3

Simple contains all the same cell type, Complex contains several different cell types

Question 4

Parenchyma vs Stroma

Answer 4

Parenchyma is working tissue, Stroma is supporting tissue which also supplies nutrition (via blood vessels or ducts)

Question 5

Define Organ

Answer 5

Several tissues grouped into a morphologically recognisable structure, performing a set of functions.

Question 6

List 4 types of tissue and briefly describe their function

Answer 6

Connective (protects and supports), Epithelial (covers and lines body surfaces), Muscle (cells contract to generate force), Nervous (generate electrical signals in response to environment)

Question 7

Extracellular Matrix (ECM)

Answer 7

the material between cells

Question 8

How are cells joined to one another or other structures? List the types:

Answer 8

Cell juntions: GAP, Tight, Adherens, Desmosome, Focal adhesions, Hemidesmosomes

Question 9

GAP junctions: function, component, example

Answer 9

Metabolic and electric coupling
Connexins
e.g. cardiac tissue

Question 10

TIght junctions: function, component, cytoskeleton, example

Answer 10

Barrier, selective permeability and cells polarity;
Claudings;
Actin;
e.g. epidermis

Question 11

Adherens junctions: function, component, cytoskeleton, example

Answer 11

Tissue integrity, contractility, motility;
Cadherins;
Actin;
e.g. morphogenesis

Question 12

Desmosomes: functions, components, cytoskeleton, example

Answer 12

Strong adhesions and resist mechanical strength;
Desmosomal cadherins;
IF;
e.g. epidermis (keratins)

Question 13

Focal adhesions: function, component, cytoskeleton, example

Answer 13

Cell anchorage, mechanical and biochemical signalling;
Integrins,
Actin,
e.g. cell migration

Question 14

Hemidesmosomes: function, component, cytoskeleton, example

Answer 14

Cell anchorage;
Integrins;
IF;
e.g. Dermal-epidermal junction

Question 15

5 stages of tissue processing for histology

Answer 15

Fixation, embedding, sectioning, staining, mounting

Question 16

What is the role of fixation?

Answer 16

preserves tissue, prevents degridation, kills bacteria, enhances tissue staining

Question 17

Methods of tissue fixation:

Answer 17

Freezing (dry ice or liquid nitrogen), Chemical fixation (inactivated enzymes and hardens tissue, often aldehyde based chemical used)

Question 18

What is the role of embedding?

Answer 18

Provides support for tissue when sectioning

Question 19

Two ways of embedding a sample:

Answer 19

Paraffin wax - most common, can alter apperance, water in tissues needs to be replaced, can’t see lipids or fats, can use water based alternatives (these dissolve sugars)
Frozen samples - less common

Question 20

What is the role of sectioning?

Answer 20

Cutting cells into very thin slices so there is a higher resolution

Question 21

Method of sectioning:

Answer 21

Using a microtone

Question 22

What is the role of staining?

Answer 22

Colours tissue as most cells are transparent, features visable under microscope

Question 23

Two types of staining:

Answer 23

Non-specific staining, specific staining

Question 24

3 Types of Microscopy

Answer 24

Light (most common - limited detail), Electron (for finer detail, beam of electrons instead of light),

Question 25

Magnification vs resolution

Answer 25

Magnification = measure of how large a microscope causes an object to appear Resolution = smallest distance by which two points can be separated and still distinguishable as separate objects

Question 26

What does H&E stand for? Explain each letter:

Answer 26

Haemotoxylin and Eosin H = Basic, stains acidic/basophilic structures purplish blue E = Acidic, stains basic/ acidophilic structures red/ pink

Question 27

What does PAS stand for? Why is it used?

Answer 27

Periodic acid staining - for staining complex carbohydrates and glycogen, stains mucus, BM and brush borders

Question 28

What does a PAS+ tissue look like?

Answer 28

deep red/ magenta

Question 29

When is Masson Trichrome used?

Answer 29

to demonstrate supporting tissue elements, mainly collagen

Question 30

What colours does Masson trichome stain various things?

Answer 30

nuclei and other basic structures = blue; collagen = green or blue depending on technique; cytoplasm, muscle, erythrocytes and keratin = bright red

Question 31

Structure of Epithelial Tissue

Answer 31

- Continuous sheet of cells (1+ layers thick) - cells in close contact with each other, - cells bound togther by cell to cell junctions - gap junctions allow things through - sit on BM - no blood vessels - cell polarity (base is different to apex - apex faces outwards)

Question 32

Function of Epithelial Tissue

Answer 32

Cover and protect surfaces inside and out of body Form glandular structures (produces secretions that are discharged onto surface or into blood) Form barriers (against abrasion, prevents water loss, prevents entrance of toxic molecules), Combine with nervous tissue to make special senses Can have specialised structure and function

Question 33

Types of Epithelial tissue

Answer 33

Covering Epithelia, glandular epithelia

Question 34

What are glandular epithelia?

Answer 34

Secretory epithelium arranged glands, invagination of epithelium, glandular organs - composed of mainly epithelium cells with connective tissue

Question 35

Exocrine vs Endocrine glands

Answer 35

Exocrine - retain continuity with surface, secrete via a duct Endocrine - lose contact with surface, pass substance into blood

Question 36

2 ways to categorise Epithelia:

Answer 36

By number of layers, by shape of cells

Question 37

Simple epithelia

Answer 37

1 layer of cells, good for adsportion, fragile

Question 38

Stratified epithelia

Answer 38

2+ layers, good for protection

Question 39

Pseudostratified epithelia

Answer 39

1 layer with mixture of cell shapes (looks stratified), not all cells reach surface but all in contact with BM

Question 40

4 types of shapes of cells:

Answer 40

Squamous (flat), Cuboidal, Columnar (tall cylindrical), Transitional (readily change shape, accomodate stretching)

Question 41

Structure, Function and Location: Simple Squamous Epithelium

Answer 41

Structure:single layer of flat, hexagonal cells, nuclei appear v flat Function:diffusion, filtration, some secretion and absorption, few provide barrier as are delicate so can’t protect against friction Location: alveoli

Question 42

Structure, Function and Location: Simple Cuboidal Epithelium

Answer 42

Structure: single layer of cube shape cells, some with microvilli Function: good for diffusion, secretion and absorption Location:kidney tubules, glands and ducts, lining bronchioles of lungs, ovary surfaces

Question 43

Structure, Function and Location: Simple Columnal Epithleium

Answer 43

Structure: single layer of tall & narrow cells, some have cilia or microvilli Function: movement of substances, absorption and secretion, more protection than flatter cells Location: glands and some ducts, bronchioles of the lungs, auditory tubes, uterus & uterine tubes, stomach, intestines

Question 44

Structure, Function and Location: Stratified Squamous Epithelium

Answer 44

Structure:multiple layers of cells that are cube-shaped in basal layer, increasingly flat towards surface - can be non keratinized (moist) or keratinised Function: protect against abrasion, barrier against infection, reduction of water loss from body Location - Keratinized = skin - Nonkeratinized = mouth, throat, larynx, anus, cornea of eye Keratinised Epithelium: cytoplasm of cells replaced by keratin so cells are dead, living cells beneath the keratinized layer, thicker keratinized layer in certain areas, dry durable and moisture resistant characteristics

Question 45

Structure, Function and Location: Pseudostratified Epithelium

Answer 45

Structure: technically single layer, almost always ciliated and associated with goblet cells (secreting mucus) Function: synthesize and secrete mucus and move mucus containing foreign bodiesLocation: lining of nasal cavity, nasal sinuses, auditory tubes, bronchi of lungs

Question 46

Structure, Function and Location: Transitional Epithelium

Answer 46

Structure: cuboidal/ columnar when not stretched, squamous when stretched, number of layers decrease when stretched (5-6 cells to 2-3 layered) Function: accommodate fluctuations in volume of fluid in organs/ tubes, protects against effect of urine Location: lining of urinary bladder, ureters, superior urethra, pelvis of kidney - this is where considerable expansion occurs