All organisms composed of cells, tissues and organs undergo changes in response to environmental or genetic signals. Some of these changes are beneficial to an organism, such as when muscles enlarge due to increase workload, or when a callus forms as protection from constant rubbing. But what happens when the changes are not beneficial but instead impair the structure or function of part of or the whole organism? These abnormal changes are grouped by their associated signs and symptoms and are defined as a disease when they are not caused by a direct external injury.

Pathology is the study of abnormal changes to cells, tissues and organs that negatively impacts their structure or function. These studies involve recognizing and identifying the abnormal changes, trying to determine the underlying causes and describing the potential effects of the changes.  Because of this, pathologists play an important role in the identification of disease processes and the confirmation of disease.

Changes can occur at the macroscopic or gross level, which means you can see the changes with your eyes or they can happen at the microscopic level, which means you need a light microscope or an electron microscope to see the changes. Histopathology is the study of the tissues to identify changes at the cellular or microscopic level.

Physiology is the study of the function of cells, tissues and organs and so pathophysiology looks at the changes in function that are detrimental. Impaired function can have a big impact on overall quality of life and it is often these changes that lead us to go see a doctor to find out what is wrong.

An Example From Everyday Life

Let us use the analogy of a bicycle to illustrate these terms.

A bicycle is made of many parts: wheels, chain, gears, seat, etc.  However, for a bike to function properly, every single part has to be made properly and work in cooperation with the other parts.

But say one day you went to ride your bike and it wouldn’t go. You phone up your bike doctor and say, “My bike won’t go. Can you fix it?”. You are describing a symptom affecting your bike that relates to a loss of function (pathophysiology).

The bike doctor might ask, “Can you turn the pedals?” This helps to narrow down reasons for the bike not functioning. The options are: the pedals function normally (they turn with a bit of resistance); the pedals turn too easily; or the pedals don’t turn at all.

If the pedals turn too easily that usually means that there is a problem with the chain or the gears not being engaged. If the pedals don’t turn at all that might indicate a problem with the brakes or something impeding the wheel.

You check the bike and the pedals do turn. You relay that information to your bike doctor. They ask you to take a picture of the bike and send it to them so that they can see what is going on. This is the equivalent of your doctor sending you for x-ray or ultrasound imaging to see if the pictures will shed light on the problem.

You send the following image:

You don’t have to know much about bikes to know that the front wheel is bent. That is the underlying pathology for the disease this bike has. The fact that the bike won’t go and yet the pedals can turn are the changes in function or the pathophysiology of this bike disease. The treatment would be to get a new wheel. If only we could replace our broken parts so easily!

When Are Other Health Professionals Brought In?

Some types of pathology are unique or obvious enough that your primary care provider (your family doctor, nurse-practitioner, ER doctor) is able to recognize what is going on without involving other health care providers. But more commonly, such as with pedals that won’t turn, there might be more than one underlying cause. A primary care provider will take your presenting signs and symptoms and compare it to known disease symptoms. They will then collect more information through visual observation (changes in appearance, colour); through palpation (for difference in size, position, and pain indicators); auscultation (listening with a stethoscope for changes in sounds) and simple measurements such as temperature, blood pressure, pulse and oxygen saturation. These will give them more information to determine what other health professionals Careers in Health Care in BC need to be involved to determine what is the underlying disease process, or pathology, or if the changes are just a normal variation.

^{How Does Pathology Fit into a Visit to the Doctor by Jennifer Kong, Adrian Marcuzzi, & Theo Lam, licensed under All Rights Reserved}

A Clinical Example

Let’s say you go to the doctor because you are more thirsty than normal and you are urinating much more frequently than normal. The signs and symptoms you are presenting with are of an increase in thirst and urination. An increase in thirst is a symptom because it is subjective while an increase in urination can be a sign because you can objectively measure an increase in volume or urine or the number of times you need to urinate in a day (or night). Of the three most common causes of increased thirst and urination, one is a medical emergency (you will die if not treated right away); one needs to you see a specialist; and one the doctor can treat. How does the doctor figure out which is the pathology (cause) underlying your pathophysiology (change in function)? There are three diseases we are looking at here: Diabetes Type 1, which can be fatal if untreated; Diabetes type 2, which the primary care provider can treat; and diabetes insipidus, which needs further testing and a specialist. All three have increased urine output which results in increased thirst. The first two have increased thirst and urination because there is too much sugar in the urine. But with Type 1 Diabetes the sugar in the blood and urine is too high because the body has destroyed the cells in the pancreas that produce insulin, which allows the body to store glucose in the cells. In Type 2 Diabetes, the body produces insulin but the cells have a harder time recognizing it; so, the body can’t store glucose in the cells as readily, leaving excess in the blood (and urine). On the other hand, diabetes insipidus has nothing to do with sugar levels but instead the body can’t concentrate the urine because it is missing or can’t recognize the protein vasopressin, which is produced in the pituitary. A simple dip-stick test of your urine will rule out diabetes insipidus if there is too much glucose in the urine. Lethargy, unresponsiveness, confusion and coma are all symptoms that point towards Type 1 diabetes as opposed to Type 2. So, the primary care provider has to look at the overall picture, know what the potential possibilities are and know what needs to be done to distinguish different underlying pathologies. Often, they will send you for blood work or send samples in for testing both of which involve medical laboratory technologist and pathologists. Or they might send you for imaging which involves radiation technologists, ultrasound technologists etc. and radiologists.

Pathology as a Medical Specialty

We saw from the previous example that pathology is also a medical specialty (you need to be a doctor). There are different specialties within Pathology. Anatomic Pathologists look at tissues and organs to determine disease based on changes in the appearance of cells, tissues and organs, both grossly and microscopically and often specialize in a particular organ system. Forensic Pathologists look specifically at why a person has died and so examine the whole body as well as specific tissues and organs and also order toxicological tests to look for foreign substances in the body that may have contributed to the death.  Neuropathologists  specialize in the nervous system and muscle pathology.  Hematopathologists specialize in changes to the blood cells and has Transfusion medicine as a subspecialty.  Medical Microbiologists  isolate, grow and identify micro-organisms that cause disease, along with which treatments may be effective against them. They work with  Infectious Disease specialists to identify and treat communicable diseases and prevent their spread in the community. Medical Biochemists and Clinical Chemists look after the laboratory testing of chemical substances in the body, either produced by the body or ingested; determining what is the best method to use, what the limitations of the tests are, and what are the normal ranges of values for a given test.

Pathologists do not work in isolation. They are supported by a team of Medical Laboratory Technologists, who prepare specimens, run the tests, and trouble shoot problems with techniques and instrumentation. Medical Laboratory Technologists cover a wide range of areas from phlebotomy (drawing blood), to preparing histological samples, to growing up microorganisms, to running complex chemical analysis equipment. Therefore, they tend to specialize as well.

Section Review

The fact that we live with injury and disease has led to disciplines that study what changes are happening at the cellular, tissue and organ level. Pathophysiology looks at the functional changes while pathology as a whole looks at both functional and structural changes of both injury and disease. Pathologists and Medical Laboratory Technologists are closely involved with confirming the diagnosis of diseases and monitoring ongoing changes with disease progression or remission.