S1: introduction to pathology & cell injury + cell death

Question 1

Define pathology

Answer 1

The study of disease and cellular dysfunction

Question 2

Define histology

Answer 2

Histology involves viewing microscopic slides prepared from tissue sections.

Question 3

Define cytology

Answer 3

Cytology is the study of cells scraped from or sucked out of an organ or lesion or extracted from a body fluid such as urine or a pleural effusion

Question 4

Examples of histology and cytology

Answer 4

Histology: core biopsies, cancer resection specimens, endoscopic biopsies
Cytology: fine needle aspirates of breast, thyroid, salivary glands, lymph nodes

Question 5

Advantages and disadvantages of histology

Answer 5

Advantages: can assess architecture as well as cellular atypia, better for immunohistochemical and molecular testing, more complete information on grading and staging
Disadvantages: sometimes histological interpretation is subjective meaning that pathologists don’t always agree on every diagnosis

Question 6

Advantages and disadvantages of cytology

Answer 6

Advantages: cheaper and faster, non-invasive or minimally invasive, can be used for cells in fluid
Disadvantages: higher inadequate and error rates

Question 7

What is the importance of a microscopic diagnosis?

Answer 7

Definitive diagnosis

Before major surgery to remove a lesion a microscopic diagnosis is required - guides the type and extent of surgery

Question 8

Describe the processes involved in producing slides for microscopy

Answer 8

Fixation
Cut-up (trimming)
Dehydration
Embedding (processing)
Blocking
Microtomy
Staining
Mounting
Microscopy

Question 9

Name a common fixative and the function

Answer 9

Fixative: formalin (formaldehyde in water)
Inactivates tissue enzymes and denatures proteins
Prevents bacteria growth
Hardens tissue
BLOCKS PROCESS OF AUTOLYSIS

Question 10

What does embedding do?

Answer 10

In order to be able to cut very thin sections the tissue has to be surrounded and impregnated with a hardening agent (paraffin wax)

Question 11

What does mounting do?

Answer 11

The mounting medium dries and hardens, preserving the tissue and attaches the coverslip

Question 12

What is immunohistochemistry?

Answer 12

Demonstrates susbtances in/on cells by labelling them with specific antibodies
Usually the antibody is joined to an enzyme that catalyses a colour-producing reaction (normally brown colour)
Any substance that is antigenic can be demonstrated eg. contractile protein actin and hormone receptors

Question 13

What is molecular pathology?

Answer 13

Studies how diseases are caused by alterations in normal cellular molecular biology

Question 14

What is a frozen section?

Answer 14

Method of hardening tissue quickly
Intra-operative (takes 10-15 minutes)
Aims to establish presence and nature of a lesion and influence the course of the operation
Accuracy only 96% (misinterpretation, absence of diagnostic tissue in frozen section)

Question 15

Common causes of cell injury

Answer 15

Hypoxia
Toxins
Physical agents (eg. direct trauma, changes in pressure)
Radiation
Immune mechanisms
Micro-organisms
Nutritional/dietary
Genetic

Question 16

Explain the 4 types of hypoxia

Answer 16

Hypoxaemic hypoxia: arterial content of oxygen is low
Anaemic hypoxia: decreased ability of Hb to carry oxygen
Ischaemic hypoxia: interruption to blood supply
Histiotoxic hypoxia: inability to utilise oxygen in cells due to disabled oxidative phosphorylation enzymes

Question 17

Name the 4 cell components most susceptible to injury

Answer 17

Cell membrane
Nucleus
Proteins
Mitochondria

Question 18

Reversible injuries (seen under electron microscope)

Answer 18

Blebs 
Generalised swelling
Clumping of nuclear chromatin
Autophagy of lysosomes
ER swelling
Small densities in mitochondria

Question 19

Irreverisble injuries (seen under electron microscope)

Answer 19

Rupture of lysosomes and autolysis
Defects in cell membrane
Appearance of myelin figures
Nuclear changes: pyknosis, karyolysis, karyorrhexis

Question 20

Mechanism of hypoxic injury

Answer 20

1. Cell is deprived of oxygen, therefore mitochondrial ATP production stops.
2. The ATP-driven membrane ionic pumps run down, leading to sodium and water seeping into the cell
3. The cell swells, and the plasma membrane is stretched.
4. Glycolysis enables the cell to limp on for a while.
5. The cell initiates a heat-shock (stress) response (see below), which will probably not be able to cope if the hypoxia persists.
6. The pH drops as cells produce energy by glycolysis and lactic acid accumulates.
7. Calcium enters the cell and activates:
   - phospholipases, causing cell membranes to lose phospholipid,
   - proteases, damaging cytoskeletal structures and attacking membrane proteins,
   - ATPase, causing more loss of ATP,
   - endonucleases, causing the nuclear chromatin to clump.
8. The ER and other organelles swell.
9. Enzymes leak out of lysosomes and these enzymes attack cytoplasmic components.
10. All cell membranes are damaged and start to show blebbing. At some point the cell dies, possibly killed by the burst of a bleb.

Question 21

Injuries seen under light microscopy

Answer 21

Cytoplasmic changes
Nuclear changes
Abnormal cellular accumulations

Question 22

Define oncosis

Answer 22

Cell death with swelling, the spectrum of changes that occured in injured cells prior to death

Question 23

Define apoptosis

Answer 23

Cell death with shrinkage, cell death induced by a regulated intracellular program where a cell activates enzymes that degrade its own nuclear DNA and proteins

Question 24

Define necrosis

Answer 24

In a living organism the morphologic changes that occur after a cell has been dead some time, e.g. 4-24 hours
Note that necrosis describes morphologic changes and is not a type of cell death, i.e., it is an appearance and not a process

Question 25

Explain the two main types of necrosis

Answer 25

Coagulative and liquifactive
Coagulative necrosis = proteins undergo denaturation -> denatured proteins tend to coagulate (cell outline is maintained)
-ischaemia of solid organs
Liquifactive necrosis = proteins undergo dissolution by the cells own enzymes
-ischaemia of loose tissues (presence of many neutrophils)

Question 26

Name two special types of necrosis

Answer 26

Caseous

Fat necrosis

Question 27

Define gangrene, infarction and infarct

Answer 27

Gangrene: necrosis visible to the eye
Infarction: necrosis caused by reduction in arterial blood flow
Infarct: an area of necrotic tissue which is the result of loss of arterial blood supply

Question 28

What are the two main types of gangrene? Is there another type?

Answer 28

Dry gangrene: the necrosis is modified by exposure to air resulting in drying
Underlying process is coagulative necrosis
Wet gangrene: by infection with a mixed bacterial culture
Underlying process is liquefactive necrosis
Gas gangrene: wet gangrene where the tissue has become infected with anaerobic bacteria that produce visible and palpable bubbles of gas within the tissues.

Question 29

What are free radicals and what do they attack?

Answer 29

Free radicals have a single unpaired electron in an outer orbit
Lipids - lipid peroxidation, cell and organelle membranes
Proteins - oxidation of amino acid side chains, cross-linkages, protein fragmentation
Nucleic acids (DNA) - reaction with thymine, single-stranded break = mutagenic therefore carcinogenic

Question 30

What are some methods used to minimise the effects of cell injury by free radicals?

Answer 30

Free radical scavengers: donate electrons to the free radical (eg. vitamin A, C and E)
Enzymes that neutralise free radicals (superoxide dismutase, catalase, glutathione peroxidase)
Heat shock proteins: ‘mend’ mis-folded proteins and maintain cell viability

Question 31

Difference between white and red infarct

Answer 31

A white (anaemic) infarct occurs in ‘solid’ organs (those with good stromal support) after occlusion of an “end” artery (i.e., any artery that is the sole source of arterial blood to a segment of an organ)
A red (haemorrhagic) infarct occurs where there is extensive haemorrhage into dead tissue

Question 32

What is ischaemia-reperfusion injury?

Answer 32

Paradoxically, if blood flow is returned to a damaged but not yet necrotic tissue, damage sustained can be worse than if blood flow hadn’t been returned
Causes:
increased production of oxygen free radicals with reoxygenation
increased number of neutrophils results in more inflammation and increased tissue injury

Question 33

What are the five main groups of intracellular accumulations?

Answer 33

Water and electrolytes
Lipids – triglycerides and cholesterol
Proteins – e.g. Mallory’s hyaline, alpha-1 antitrypsin
‘Pigments’ – exogenous and endogenous
Carbohydrates

Question 34

Effects of chronic alcohol misuse and obesity on the liver

Answer 34

Steatosis = accumulation of triglycerides commonly seen in the liver
Fatty change
Acute alcohol hepatitis
Cirrhosis

Question 35

What are the most common molecules released by injured cells and what effects do they have?

Answer 35

Potassium = efflux of K+
Enzymes = can indicate the organ involved and the extent, timing and evolution of the tissue damage.
Myoglobin = released from dead myocardium and striated muscle

Question 36

What is pathological calcification? What are the two types?

Answer 36

Abnormal deposition of calcium salts within tissues
Dystrophic = localised in dying tissue, nothing to do with calcium metabolism eg. some neoplastic growths, aging or damaged heart valves
Metastatic = due to elevated calcium due to dysfunction in calcium disturbance, disturbance is body-wide, it is usually asymptomatic however, it can be lethal
Causes include increased secretion of PTH or destruction of bone tissue

Question 37

What are the basic principles of cellular aging?

Answer 37

As cells age, there is a a decline in their ability to replicate = replicative senescence (related to the length of chromosomes)
The ends of chromosomes are called telomeres and with every replication the telomere is shortened. When the telomeres reach a critical length, the cell can no longer divide

Question 38

Describe the three types of nuclear changes during cell death

Answer 38

Pyknosis = nuclei are condensed and dense 
Karyorrhexis = nuclei break up into fragments 
Karyolysis = nuclei are dissolved

Question 39

Describe the three stages of apoptosis

Answer 39

1) initiation = triggered by the intrinsic and extrinsic pathways. Both pathways use caspases which are enzymes that regulate and mediate apoptosis by degrading DNA and proteins at the cytoskeleton
2) execution
3) degradation and phagocytosis = apoptotic bodies express proteins on their surface which can be recognised by phagocytic cells

Question 40

Describe the intrinsic pathway of apoptosis

Answer 40

Activating signal comes from within the cell
The p53 protein is activated, this causes the outer mitochondrial membrane to become leaky
Cytochrome C is released from the mitochondria and this leads in the activation of caspases

Question 41

Describe the extrinsic pathway of apoptosis

Answer 41

Activated by signals from outside the cell
One signal, TNF alpha, is secreted from killer T-cells
This binds to death receptors on the cell membrane
This activates caspases