Epithelia

Question 1

<p>What is a tissue?</p>

Answer 1

<p>A collection of cells specialised to perform a particular function </p>

Question 2

<p>What are the four major types of tissue?</p>

Answer 2

<p>Epithelial, connective, muscular, nervous</p>

Question 3

<p>What is a milimetre (mm)?</p>

Answer 3

<p>10^-3 m</p>

Question 4

<p>What is a micrometer (um)?</p>

Answer 4

<p>10^-6 m</p>

Question 5

<p>What is a nanometer (nm)?</p>

Answer 5

<p>10^-9 m</p>

Question 6

<p>What size are most human cells? What size are red blood cells?</p>

Answer 6

<p>Between 10 and 20 micrometers. Red blood cells are 7.2um diameter, so are a useful measure when comparing cell sizes as they are so widespread</p>

Question 7

<p>What is a biopsy?</p>

Answer 7

<p>Removal of a small piece of tissue from an organ or part of the body for microscopic examination</p>

Question 8

<p>List 6 different biopsy techniques and an example of tissues they are used with for each</p>

Answer 8

<p>Smear e.g. cervix
Curretage e.g. endometrial lining of uterus
Needle e.g. kidney
Direct incision e.g. skin
Endoscopic e.g. intestine
Transvascular e.g. heart</p>

Question 9

<p>What happens in tissue fixation?</p>

Answer 9

<p>-Fresh needle biopsy is wet and bloody
-Tissue is fixed with glutaraldehyde/formaldehyde to cross link the structure, killing bacteria and preventing it from breaking down. No autolysis or putrefecation</p>

Question 10

<p>Describe how a fixed biopsy is processed in order to be viewed with a microscope</p>

Answer 10

<p>1. Biopsy in water is dehydrated with ethanol, as water is miscible with ethanol

2. Ethanol is cleared to form xylene/toluene
3. The xylene/toluene containing the biopsy is heated to 56C, and forms a wax which the biopsy is embedded in
4. Wax is then sectioned into thin pieces around 15um in diameter, and placed on a microscope slide
5. Rehydration: xylene --> ethanol --> water
6. Stained differentially to see different sections
7. Dehydrated again water-->ethanol-->xylene
8. Mounting (DPX dries under coverslip). Sample now ready for microscopy</p>

Question 11

<p>What is the haematoxylin and eosin stain? What does each respective dye stain?</p>

Answer 11

<p>Used together.
Haematoxylin stains acidic components of cells puple/blue, e.g. the nucleolus (RNA) and chromatin (DNA).
Eosin stains basic components of cells pink, e.g. cytoplasmic proteins and extracellular fibres</p>

Question 12

What is the periodic acid-schiff reaction?

Answer 12

PAS stains carbohydrates and glycoproteins magenta.

Question 13

Advantages of phase-contrast microscopy?

Answer 13

Can be used to view live, unstained samples, however does not work well for thick samples. Works by exploiting the interference when two sets of waves combine. Similar to differential-interference microscopy: this second type is less likely to have artifacts

Question 14

Advantages of dark field microscopy?

Answer 14

View live, unstained samples. However, tissue needs bright illumination so may become damaged

Question 15

Advantages of fluorescence microscopy?

Answer 15

Used to view tissues stained with fluorescent molecules. Can introduce artifacts due to chemical fixation and detergent use

Question 16

Advantages of confocal light microscopy?

Answer 16

Used to image tissues labelled with fluorescent probes. Tissue sectioned in a non-invasive way via use of focused beams of light (usually a laser), so living specimens can be viewed. Automated construction of 3D images from a series of 2D images taken at successive depths

Question 17

What are epithelia?

Answer 17

Sheets of contiguous cells, of varied embryonic origin, that cover the external surface of the body and line internal surfaces, alongside occuring as secretory elements known as glands

Question 18

What is the basement membrane?

Answer 18

A thin, acellular layer that almost always separates epithelia from underlying/surrounding connective tissue.
Consists of a basal lamina (closest to epithelium)

Question 19

Are epithelial membranes vascular or avascular?

Answer 19

Avascular. They obtain nutrients by diffusion from blood vessels in adjacent connective tissues

Question 20

How are epithelial membranes generally classified?

Answer 20

By the shape of the most superficial cell layer: squamous (flat), cuboidal or columnarm-as observed when sectioned perpendicular to the exposed surface of the membrane

Question 21

What is the difference between simple, stratified and pseudostratified epithelia?

Answer 21

Simple one cell layer thick, all cells contact the basement membrane (aka basal lamina) and reach the free surface
Stratified more than one cell layer thick
Pseudostratified all cells rest on basement membrane with only some reaching the surface (these will be columnar)

Question 22

Describe the epithelial derivatives of the three germ layers of the embryo, in the trilaminar embryonic disk

Answer 22

Ectoderm (outermost). Epidermis, corneal epithelium
Mesoderm (middle). UG tract epithelium, blood and lymphatic vessel lining, pericardial, pleural sac and peritoneal lining
Endoderm (bottom). Epithelia of respiratory, GI, liver, thyroid and other glands

Question 23

How can the thickness of the basement membrane be increased?

Answer 23

By a variably thick layer of reticular fibrils (type III collagen), elaborated by the subtending connective tissue

Question 24

What are the functions of the basement membrane?

Answer 24

A strong, flexible layer to which epithelial cells adhere

A cellular and molecular filter

Question 25

What is endothelium and mesothelium?

Answer 25

Endothelium: simple squamous epithelium lining all vascular elements (arterial, venous, capillary and lymphatic). Can exchange gases and nutrients, allow certain blood cells to enter the tissues, and regulate platelet coagulation Mesothelium: simple squamous epithelium lining the pleural sac, pericardial sac and the peritoneum

Question 26

What is simple squamous epithelium, where is it found, and why is it found in these locations?

Answer 26

Flattened and thin cells (so thin nucleus appears to bulge from cytoplasm). Locations: blood/lymphatic vessel walls (endothelium), pleural and abdominal cavities (mesothelium), pulmonary alveoli, Bowman's capsule & loop of Henle (kidney), inner & middle ear Very short diffusion distance so allow for rapid exchange of gases and other substances

Question 27

What is simple cuboidal epithelium, where is it found, and why is it found in these locations?

Answer 27

Cuboid-shaped cells as high and as they are wide, 1 layer thick Found to line most ducts of exocrine glands, thyroid follicles, kidney tubules and surface of ovary Take part in absorption, secretion, hormone synthesis/storage

Question 28

What is simple columnar epithelium, where is it found, and why is it found in these locations?

Answer 28

Cells taller than they are wide and nuclei often in the basal section of the cell. Can sometimes look stratified, so need a perpendicular cut to see its definitely columnar Can have microvilli Locations: much of digestive tract, gall bladder, uterus, large ducts of some exocrine glands Functions: secretion (Stomach, SI, colon), absorption (SI, colon, GB), lubrication (SI, colon), transport (oviduct)

Question 29

What is the function of the junctional complex?

Answer 29

Separates the luminal space from the intercellular space. Fluid is moved from the intestinal lumen into the cell, then into the intercellular space, and finally across the basement membrane into connective tissue

Question 30

Describe pseuostratified epithelium

Answer 30

All cells rest on the basement membrane with only some reaching the surface-those that do are columnar. Locations: upper respiratory tract, epididymis and ductus deferens, auditory tube, large excretory ducts Functions: secretion, absorption, mucus secretion

Question 31

Why is the pseudostratified columnar epithelium of the trachea important in preventing infection?

Answer 31

The epithelium is also ciliated. Goblet cells above the cilia secrete mucous, which trap bacteria and other particles. Cilia beat to move the mucous away from the lungs towards the pharynx, where they are then swallowed, in what is known as the mucociliary escalator

Question 32

Describe stratified squamous non-keratinized epithelium

Answer 32

Outermost cells are flattened, more than 1 layer of cells. | Locations: larynx, oral cavity, oesophagus, vagina, surface of cornea, inner surface of eyelid

Question 33

How does the vaginal epithelium maintain its pH?

Answer 33

The stratified squamous non-keratinized cells are rich in glycogen, which is a substrate for lactobacili bacteria that produce lactic acid, and maintain a suitably low pH. Such cells atrophy in the absence of hormonal stimulation (pre- and post-puberty)

Question 34

How is the epiglottis adapted for its function?

Answer 34

The pseudostratified epithelium and stratified squamous non-keratinized on the other side are adapted for protection against abrasion. Next to the pseudostratified side there is elastic cartilage which is important to allow air entry into the trachea

Question 35

Describe the epithelia of the cornea

Answer 35

Stratified squamous non-keratinized on the external layer, to protect against abrasion but still flattened to allow vision. Internal epithelium is simple squamous

Question 36

What is keratinized stratified squamous epithelium?

Answer 36

Found in the epidermis (skin) Dead keratinized cells form the top layer, and these shed off and are gradually replaced by living epidermal cells beneath, which themselves lie on top of the dermis (connective tissue) Function: protect against abrasion, physical trauma, water loss, microorganisms and UV light damage

Question 37

What is transitional epithelium?

Answer 37

Surface cells vary in shape, from columnar/cuboidal in the relaxed state to squamous in the stretched state Location: bladder, urethra, ureters, renal calyces Functions: distensibility, protection of underlying tissue from toxic chemicals

Question 38

Why does the renewal rate of epithelia differ?

Answer 38

Depends on location and function. The time frame for each TYPE of epithelium remains constant, unless injury leads to acceleration EpidermisL time from mitosis in basal layer -->differentiation-->migration to exterior-->kertinization-->death-->sloughed off is 28 days Cells in small intestine replaced by regenerative cells in the base of tge crypts every 4-6 days Other epithelia are not renewed after adulthood is reached, but cell proliferation may be triggered in response to physical damage or acute toxic injury

Question 39

Describe the different types of surface specialisation found on epithelial cells

Answer 39

Microvilli: apical extensions which greatly increase the surface area for selective absorption of intestinal contents Stereocilia: very long microvili. May have an absorptive function Cilia:slender, microscopic hair-like structures that extend from most mammalian cells and are of use in the muco-ciliary escalator of the upper respiratory tract