A-level Applied Science/The Role of the Pathology Service/Pathology

The pathology department is involved in discovering/confirming the cause of someone's death and in using tissue samples to diagnose diseases in living subjects.

=The role of the pathology department.=

Attention should be drawn to the nature of the samples being processed and the processing procedures.

Samples are fixed and sectioned on to slides, and then stained for microscopy.

Candidates could look at prepared slides back in school or college, and make comparisons of different tissue types; for example of the appearance of pathological changes in tissues.

=Types of specimens tested.=

Solid tissue, cell smears, blood samples, etc.

=What does the work involve?=


 * Histology: process solid tissue removed from the body to make slides and examine cellular detail.
 * Cytology: examine smears of cells (such as from the cervix) for evidence of cancer and other conditions.
 * Cytogenetics: involves using blood and other cells to get a karyotype. This can be helpful in prenatal diagnosis (e.g. Down's syndrome) as well as in cancer (some cancers have abnormal chromosomes).

Preparation of tissue samples for microscope slides. Recognising conditions such as atheroma and emphysema from prepared microscope slides.

The stages involved in processing specimens:

use of computers and the Data Protection Act.
 * sending and receipt of specimens
 * recording
 * sorting
 * storage
 * testing
 * recording, interpretation and dissemination of results

=Anatomic pathology=

Anatomic pathology is the branch of pathology that is concerned with the diagnosis of disease based on the gross and microscopic examination of cells and tissues. The father of the modern Anatomical pathology is the Italian Giovanni Battista Morgagni.

Anatomic Pathology (AP) is one of the two primary certifications offered by the American Board of Pathology. The other is Clinical Pathology (CP).

Role of the anatomic pathologist
Contrary to popular belief, the field mostly concerns the study of tissue obtained from live patients. In fact, almost all tissues removed from a patient for any reason are examined by a pathologist. The autopsy, though, remains an important tool in gaining medical knowledge.

Biopsy specimens are small pieces of tissue. Biopsy of a tumour is helpful when its nature is uncertain. Histological examination of the tumour biopsy usually allows the pathologist to determine if the tumour is benign or malignant, and differentiate between different types of cancer. This information is important for accurate estimation of the prognosis and choice of the best therapy. Biopsies can also be used to diagnose diseases other than cancer. For example, the dermatopathologist sees many skin biopsies from rashes and other inflammatory skin diseases, taken by dermatologists when the nature of the disease is not evident. Stomach and colon biopsies are also taken to help diagnose inflammatory or infectious diseases of the digestive tract.

In contrast to a biopsy that merely samples a lesion, an excision (or resection) specimen is the complete removal of the tumour or diseased organ by a surgeon. For example, a mastectomy specimen contains the whole breast tissue, overlying skin and adjacent lymph nodes. On excision specimens, the pathologist will comment on surgical margins to estimate the likelihood that the tumour was completely excised during the surgery.

The opinion of the pathologist is written as a pathology report addressed to the doctor who performed the procedure.

Procedures
The procedures used in anatomic pathology include:
 * Gross pathology, the examination of diseased tissues with the naked eye. This is important especially for large tissue fragments, because the disease can often be visually identified. It is also at this step that the pathologist selects the part that will be processed for histopathology.
 * Histopathology is the microscopic examination of stained tissue sections using histological techniques. The standard stains are haematoxylin and eosin but many others exist. The science of staining tissues sections is called histochemistry. Antibodies can also be used to stain specific proteins, a technique called immunohistochemistry. Specific DNA and RNA molecules can be identified on sections using the technique of ‘’in situ’’ hybridization. When the probe is labelled with fluorescent dye, the technique is called Fluorescent ‘’in situ’’ hybridisation (FISH).
 * Cytopathology is the examination of loose cells spread and stained on glass slides using cytology techniques.
 * Electron microscopy is used to identify organelles within the cells. Its usefulness has been greatly reduced by immunhistochemistry but it is still irreplaceable for the diagnosis of kidney disease, identification of immotile cilia syndrome and many other tasks.
 * Tissue cytogenetics can identify genetics defects, like chromosomal translocation.
 * Flow immunophenotyping is the determination of the immunophenotype of cells using flow cytometry techniques. It is very useful to diagnose the different types of leukaemia and lymphoma.

Subspecialties
Doctors turn to pathologists for help when the diagnosis is not evident. Therefore, pathologists are expected to know many more diseases than clinicians - they are the "doctor's doctor". The amount of knowledge needed is enormous. Since one person cannot possibly know everything, pathologists tend to sub-specialize. The American Board of Pathology certifies anatomic pathologists, and recognizes the following secondary specialties of Anatomic Pathology: Neuropathology, Cytopathology, Dermatopathology, Forensic pathology, Hematology. Here is a (probably incomplete) list of the commonly recognized subspecialties, including those which do not have subspecialty boards:
 * Surgical pathology: diagnosis of diseases in organs removed by general surgeons, especially breast, lung, bowel. This is the core of anatomic pathology. Most of these organs are covered by sub-subspecialties:
 * Gastrointestinal pathology: diagnosis of bowel diseases from biopsies taken by a gastroenterologist. One of its sub-subspecialty is hepatopathology, the diagnosis of liver diseases based on liver biopsy.
 * Uropathology, including diseases of the urinary tract and the male genital tract
 * Cardiac pathology
 * Pulmonary pathology
 * Endocrine pathology
 * Gynaecologic Pathology, including diseases of the female genital tract and the placenta
 * soft tissue pathology and orthopaedic pathology
 * E.N.T. Pathology
 * Neuropathology: diagnosis of diseases from tissues removed by neurosurgeons. Neuropathologists also examine whole brains and spinal cords removed at autopsy. Additionally, neuropathologists are called upon to interpret muscle and peripheral nerve biopsies. And, at many institutions, they are called upon to examine eyeball specimens from patients who have undergone ocular exenteration.
 * Dermatopathology: diagnosis of skin diseases from the histological examination of skin biopsies taken by a dermatologist.
 * Ophthalmic pathology
 * Haematopathology
 * Nephropathology
 * Paediatric pathology and its sub-subspecialty neonatal pathology
 * Immunopathology
 * Cytopathology
 * Forensic pathology

Oral & Maxillofacial pathology is different; the American Board of Oral and maxillofacial pathology certifies dentistry doctors, not medical doctors, to practice this sub-specialty of Pathology.

Histopathology
Histopathology is a field of pathology which specialises in the histologic study of diseased tissue. It is an important tool of anatomical pathology and is used for accurate diagnosis of cancer and other diseases.

Collection of tissues
Histopathological examination of tissues starts with surgery, biopsy or autopsy. The tissue is removed, and then placed in a fixative which stabilizes the tissues to prevent decay. The most common fixative is formalin (10% formaldehyde in water).

Preparation for histology
The tissue is then prepared using histology procedures for viewing under a microscope. Briefly, the samples are transferred to a cassette, a container designed to allow reagents to freely act on the tissue inside. This cassette is immersed in multiple baths of progressively more concentrated ethanol, to dehydrate the tissue, followed by toluene or xylene, and finally hot liquid paraffin. During this 12 to 16 hour process, paraffin will replace the water in the tissue, turning soft, moist tissues into a sample miscible with paraffin, a type of wax. This process is known as tissue processing.

The processed tissue is then taken out of the cassette and set in a mould. Through this process of embedding, additional paraffin is added to create a paraffin block which is attached to the outside of the cassette.

The process of embedding then allows the sectioning of tissues into very thin (2 - 7 micrometer) sections using a microtome. The microtome slices the tissue ready for microscopic examination. The slices are thinner than the average cell, and are layered on a glass slide for staining.

To see the tissue under a microscope, the sections are stained with one or more pigments. The aim of staining is to reveal cellular components, counterstains are used to provide contrast.

The most commonly used stain in histopathology is a combination of haematoxylin and eosin. Haematoxylin is used to stain cell nuclei blue, while eosin stains cytoplasm and the extracellular connective tissue matrix pink. There are hundreds of various other techniques which have been used to selectively stain cells. Other compounds used to colour tissue sections include safranin, oil red o, Congo red, silver salts and artificial dyes. Histochemistry refers to the science of using chemical reactions between laboratory chemicals and components within tissue. A commonly performed histochemical technique is the Perls Prussian Blue reaction, used to demonstrate iron deposits in diseases like Haemochromatosis.

Recently, antibodies are used to stain specific proteins,lipids and carbohydrates: this is called immunohistochemistry. This technique has greatly increased the ability to specifically identify categories of cells under a microscope. Other advanced techniques include in situ hybridization to identify specific DNA or RNA molecules. Digital cameras are increasingly used to capture histopathological images.

Interpretation
The histological slides are examined under a microscope by a pathologist, a medically qualified specialist. The diagnosis is formulated as a pathology report describing the histological findings and the opinion of the pathologist. In the case of cancer, this represents the tissue diagnosis required for most treatment protocols.

Atheroma
An atheroma (plural: atheromata) is an abnormal inflammatory accumulation of macrophage white blood cells within the walls of arteries. These anatomic lesions typically begin in later childhood, well before age 10, and progress over time. Veins do not develop atheromata, unless surgically moved to function as an artery, as in bypass surgery. The accumulation is always between the endothelium lining and the smooth muscle wall of the arterial tube. While the early stages, based on gross appearance, have traditionally been termed fatty streaks by pathologists, they are not composed of fat, i.e. adipose cells. In the context of heart or artery matters, atheroma are commonly referred to as "plaque."

Collectively, the process of atheroma development within an individual is called atherogenesis and the overall result of the disease process is termed atherosclerosis.

Stages
In humans, atheroma usually begin in later childhood, about ages 5–9, as fatty streaks. These, and older, larger atheroma lesions have long been observed in autopsy examinations of people who have died for unrelated reasons; they are so common, more so with increasing age, they were long considered normal, even though clearly unhealthy.

More advanced atheroma develop multiple different internal tissue characteristics within the same atheroma. By light microscopy visualisation, pathologists have characterized as many as 10 different tissue subtypes within a single advanced atheroma. Generally, these range from collections of macrophage cells, always the initiating cells in the newest sections of atheroma, to more complex structures including living cells, cellular debris of cells which have died and extracellular deposits of fibrous tissue & calcified crystals, within the oldest, outermost portions of atheroma structures.

Atheroma typically progress silently for decades and remain undetected by most clinical diagnostic approaches, including cardiac stress testing and angiography. Eventually, their presence is revealed by disastrous clinical events and permanent disability, such as heart attack or stroke, with the majority of people assuming they were healthy until finally proven otherwise by events. For some individuals, warning symptoms do occur before the onset of major debility or death, however these are the minority.

Historically physicians, who are trained to treat symptoms and avoid treatment before onset of clear enough symptoms and physical abnormalities, have just considered the processes a normal part of ageing, even though unhealthy.

Emphysema
Emphysema is a chronic lung disease. It is often caused by exposure to toxic chemicals or long-term exposure to tobacco smoke.

Signs and symptoms
Emphysema is characterised by loss of elasticity of the lung tissue; destruction of structures supporting the alveoli; and destruction of capillaries feeding the alveoli. The result is that the small airways collapse during expiration, leading to an obstructive form of lung disease (air is trapped in the lungs in obstructive lung diseases). Symptoms are: shortness of breath on exertion—particularly when climbing stairs or inclines (and later at rest), hyperventilation and an expanded chest.

Diagnosis
Diagnosis is by spirometry (lung function testing), including diffusion testing. Other investigations might include X-rays, high resolution spiral chest CT-scan, bronchoscopy (when other lung disease is suspected, including malignancy), blood tests, pulse oximetry and arterial blood gas sampling.

Pathophysiology
The scientific definition of emphysema is:
 * "Permanent destructive enlargement of the airspaces distal to the terminal bronchioles without obvious fibrosis".

Hence, the definite diagnosis is made by a pathologist. However, we can easily ascertain clinical diagnosis by history, clinical examination, chest radiography and lung function tests.

In normal breathing, air is drawn in through the bronchial passage]s and down into the increasingly fine network of tubing in the lungs called the alveoli, which are many thousands of tiny sacs surrounded by capillaries. These absorb the oxygen] and transfer it into the blood.

When toxins such as smoke are breathed into the lungs, the particles are trapped by the hairs and cannot be exhaled, leading to a localised inflammatory response. Chemicals released during the inflammatory response (trypsin, elastase, etc.) begin to break down the walls of alveoli (alveolar septum). This leads to fewer but larger alveoli, with a decreased surface area and a decreased ability to take up oxygen and lose carbon dioxide.

After a prolonged period, hyperventilation becomes inadequate to maintain high enough oxygen levels in the blood, and the body compensates by vasoconstricting appropriate vessels. This leads to pulmonary hypertension. This leads to enlargement and increased strain on the right side of the heart, which in turn leads to peripheral oedema (swelling of the peripherals) as blood gets backed up in the systemic circulation, causing fluid to leave the circulatory system and accumulate in the tissues.

Associations
Emphysema is commonly associated with bronchitis and chronic bronchitis and as it is rather difficult to delineate "pure" cases of emphysema or chronic bronchitis they are classed together into chronic obstructive pulmonary disease (COPD).

Prognosis and treatment
Emphysema is an irreversible degenerative condition. The most important measure that can be taken to slow the progression of emphysema is for the patient to stop smoking and avoid all exposure to cigarette smoke and lung irritants. Pulmonary rehabilitation can be very helpful to optimize the patient's quality of life and teach the patient how to actively manage his or her care.

It is treated by supporting the breathing with anticholinergics, bronchodilators and (inhaled or oral) steroid medication, and supplemental oxygen as required. Treating the patient's other conditions including gastric reflux and allergies may also help the patient's lung function. Supplemental oxygen used as prescribed (20+ hours/day) is the only non-surgical treatment which has been shown to prolong life in emphysema patients. Other medications are being researched. There are lightweight portable oxygen systems which allow patients increasing mobility. Patients fly, cruise, and work while using supplemental oxygen.

The only known 'cure' for emphysema is a lung transplant, although not many patients are strong enough physically to survive the surgery. The combination of patient's age, oxygen deprivation and the side-effects of the medications used to treat emphysema cause damage to the kidneys, heart and other bodily organs. Transplants also require the patient to take an anti-rejection drug regimen which suppresses immunities and creates new medical issues.

=Health and safety.=


 * health & safety related to the tests undertaken
 * legislation

=See also=
 * Histology
 * Pathology
 * Anatomical pathology
 * Biopsy
 * Frozen section procedure
 * Clinical pathology
 * Forensic pathology
 * Molecular pathology
 * Veterinary pathology