Diseases and disorders
of the different body systems
DISEASES: WHAT ARE THEY?
Diseases are categorized as any deviation from health, as when the effects of microbial infection damage or disrupt tissues and organs. The pathologic state that results from this is directly pertained to as “disease”. The many different diseases that affect specific parts/systems of the body are caused by factors such as infections, diet, genetics, and aging (for purposes of this blog, however, more focus will be centered on infectious diseases – those that result in damage of a tissue or organ by microbes and their products).
In discussing this topic, it must be noted that while there is often a pattern present involving contact leading to progressive infection until the end result is disease, there are numerous factors that give the pattern a more general nature; not all contacts lead to colonization, nor do all colonization lead to infections, and thus not all infections necessarily result in disease.
In discussing this topic, it must be noted that while there is often a pattern present involving contact leading to progressive infection until the end result is disease, there are numerous factors that give the pattern a more general nature; not all contacts lead to colonization, nor do all colonization lead to infections, and thus not all infections necessarily result in disease.
“In fact, contamination without colonization and colonization
without disease are the rule.”
without disease are the rule.”
First to understand are microbes. How do they relate to disease?
Not all microbes are harmful. In fact, there are many kinds of microbes that are vital for human development in terms of body system and nutrition for example, and especially immunity. However, the microbes to be discussed here are of a harmful nature.
A microbe whose relationship with its host is parasitic and results in infection and disease is called a pathogen. The virulence of a microbe is determined by its ability to a)establish itself in its host, and b)cause damage. There are two types of pathogens, both of which are harmful.
A microbe whose relationship with its host is parasitic and results in infection and disease is called a pathogen. The virulence of a microbe is determined by its ability to a)establish itself in its host, and b)cause damage. There are two types of pathogens, both of which are harmful.
- True Pathogens – also referred to as primary pathogens; these are capable of causing disease in healthy persons with normal immune defenses. They are generally associated with a specific and recognizable disease ranging from minor complications to fatal results. For example, the influenza virus, plague bacillus, and malarial protozoans are the diseases that result from true pathogens and will be discussed later.
- Opportunistic Pathogens – these can cause disease when the host’s defenses are low or if they end up in a part of the body that is not their natural environment. The diseases caused from these tend not to possess well- developed virulence properties. The pathogens include Pseudomonas species and Candida albicans.
Portals of entry – the first stage in the pattern
Most pathogens have adapted to specific portals of entry into their hosts, and by doing so the portal provides a habitat for further growth and spread of the microbe in question. However this also means that generally only those microbes specific to that portal will become infectious, while unfamiliar microbes in the wrong habitat will not. The portals of entry are as follows:
- The Skin – this is a very common portal of entry, but it’s important to note that it is not generally the skin itself, but rather nicks or abrasions in the skin. If the skin is whole and intact, the barrier against these pathogens remains strong, allowing very few microbes to pass through.
- The GI Tract – the gastrointestinal tract takes in those microbes existing in food, drink, and other ingested substances. Most of them can survive digestive enzymes and abrupt pH changes involved in digestion. Generally the mouth and the nose are the most common entry points involved in this portal, but the anus can be included in those who practice anal sex.
- The Respiratory Tract – specifically the oral and nasal cavities which are the gateways to the respiratory tract. There is a continuous mucous membrane surface covering the upper respiratory tract, the sinuses, and the auditory tubes meaning that microbes are easily and often transferred from one site to another.
- The Urogenital Tract – with particular importance to sexually transmitted diseases (STDs) that account for an estimated 4% of infections globally. The entry points for STD microbes are the skin or mucosa of the penis, external genitalia, vagina, cervix, and urethra.
- *Pregnancy and Birth – this portal of entry is a little more specific. The placenta is an exchange organ formed by maternal and fetal tissues, separating the mother’s blood from the baby’s while permitting diffusion of nutrients and gases to the baby from the mother. Even though the placenta is generally an incredibly strong, protective barrier, there are still a few microbes than can pass through via the umbilical cord to spread into the fetal tissues.
Sticking to the host and surviving the battle lines – the establishment of disease
When the microbe firmly plants themselves in a foothold, it is called adhesion. This adhesion process, however, is not as simple as it would seem due to the process being dependent on binding between specific molecules on both the host and pathogen, making particular pathogens limited to only those cells to which they can bind.
Once it is attached, the pathogen will then face one more obstacle: the immune response, or defense lines of the body. Some pathogens will be destroyed immediately, but some have adapted in ways that make destruction by white blood cells (phagocytes) difficult, or even downright impossible. Even if the phagocytes engulf certain pathogens, they might still be able to survive within the phagocyte, making it easy to hide, grow, and spread throughout the body.
Once it is attached, the pathogen will then face one more obstacle: the immune response, or defense lines of the body. Some pathogens will be destroyed immediately, but some have adapted in ways that make destruction by white blood cells (phagocytes) difficult, or even downright impossible. Even if the phagocytes engulf certain pathogens, they might still be able to survive within the phagocyte, making it easy to hide, grow, and spread throughout the body.
How do these pathogens harm the body?
Microbes will eventually settle in a particular target organ where it will persist in constant damage to that particular organ, and, in some cases, will spread to other parts of the body. The type and scope of injuries inflicted during this account for the typical stages of an infection, the patterns of the disease, and its manifestations in the body. Pathogens will frequently weaken the body’s defenses, obstruct tubular structures such as blood vessels and lymphatic channels, cause cell and tissue death, and more. It really depends on the specific disease it has caused.
TYPE i allergic reactions: atopy and anaphylaxis
Very often allergy sufferers are said to be atopic. Is it the same thing as allergy?
Atopy is the genetic predisposition of an individual to produce high quantities of IgE in response to allergens in the environment (pollens, house dust mites, molds, cat dander, foods etc). Atopy is silent; atopic people do not necessarily display symptoms when they come across allergens. A person might suspect that he or she could be atopic if they have relatives who suffer from allergies. The only way to identify atopy is through allergy tests which measure IgE for various allergens. So atopy is a condition for the development of allergy but is not itself allergy.
Allergy, in medical terms, means that the person develops symptoms upon contact with allergens to which he/she is sensitized.
So you need to be atopic to become allergic but if you are atopic you will not necessarily progress to an allergic state. It is not clear what causes atopic people to behave differently. It might be that some environmental factors added to atopy stimulate the progression towards allergy.
Anaphylaxis is the most dramatic expression of allergy. In an anaphylactic attack, symptoms may develop within minutes after coming into contact with the allergen and may rapidly become very severe, threatening vital body functions such as respiration and blood circulation. Most anaphylactic attacks are triggered by food allergens, insect venoms, drugs and latex.
Atopy is the genetic predisposition of an individual to produce high quantities of IgE in response to allergens in the environment (pollens, house dust mites, molds, cat dander, foods etc). Atopy is silent; atopic people do not necessarily display symptoms when they come across allergens. A person might suspect that he or she could be atopic if they have relatives who suffer from allergies. The only way to identify atopy is through allergy tests which measure IgE for various allergens. So atopy is a condition for the development of allergy but is not itself allergy.
Allergy, in medical terms, means that the person develops symptoms upon contact with allergens to which he/she is sensitized.
So you need to be atopic to become allergic but if you are atopic you will not necessarily progress to an allergic state. It is not clear what causes atopic people to behave differently. It might be that some environmental factors added to atopy stimulate the progression towards allergy.
Anaphylaxis is the most dramatic expression of allergy. In an anaphylactic attack, symptoms may develop within minutes after coming into contact with the allergen and may rapidly become very severe, threatening vital body functions such as respiration and blood circulation. Most anaphylactic attacks are triggered by food allergens, insect venoms, drugs and latex.
Type ii hypersensitivities: reactions that lyse foreign cells
In type II (cytotoxic) hypersensitivity, the antibodies produced by the immune response bind to antigens on the patient's own cell surfaces.
type iii hypersensitivities: immune complex reaction
Type III hypersensitivity occurs when there is little antibody and an excess of antigen, leading to the formation of small immune complexes.
Type iv hypersensitivities: cell mediated reactions
Cell-mediated immunity is an immune response that does not involve antibodies, but rather involves the activation of phagocytes, natural killer cells (NK), antigen-specific cytotoxic T-lymphocytes, and the release of various cytokines in response to an antigen. Historically, the immune system was separated into two branches: humoral immunity, for which the protective function of immunization could be found in the humor (cell-free bodily fluid or serum) and cellular immunity, for which the protective function of immunization was associated with cells. CD4 cells or helper T cells provide protection against different pathogens. Cytotoxic T cells cause death by apoptosis without using cytokines. Therefore in cell mediated immunity cytokines are not always present.
autoimmunity
Autoimmunity is the failure of an organism to recognize its own constituent parts as ''self'', which allows an immune response against its own cells and tissues. Any disease that results from such an aberrant immune response is termed an autoimmune disease.
Normally the immune system's white blood cells help protect the body from harmful substances, called antigens. Examples of antigens include bacteria, viruses, toxins, cancer cells, and blood or tissues from another person or species. The immune system produces antibodies that destroy these harmful substances.
An autoimmune disorder may result in:
An autoimmune disorder may affect one or more organ or tissue types. Organs and tissues commonly affected by autoimmune disorders include:
Normally the immune system's white blood cells help protect the body from harmful substances, called antigens. Examples of antigens include bacteria, viruses, toxins, cancer cells, and blood or tissues from another person or species. The immune system produces antibodies that destroy these harmful substances.
An autoimmune disorder may result in:
- The destruction of one or more types of body tissue
- Abnormal growth of an organ
- Changes in organ function
An autoimmune disorder may affect one or more organ or tissue types. Organs and tissues commonly affected by autoimmune disorders include:
- Blood vessels
- Connective tissues
- Endocrine glands such as the thyroid or pancreas
- Joints
- Muscles
- Red blood cells
immunodeficiency
Immunodeficiency disorders prevent your body from being able to fight infections and diseases the way it should. An immunodeficiency disorder makes you considerably more susceptible to catching viruses and bacterial infections.
Immune disorders are oftentimes categorized as either congenital or acquired. When you’re born with a disorder, it’s sometimes called a congenital or primary disorder. Acquired disorders are sometimes called secondary disorders. Secondary disorders are more common than primary.
Primary immunodeficiency disorders are immune disorders you are born with. Primary disorders include:
Immune disorders are oftentimes categorized as either congenital or acquired. When you’re born with a disorder, it’s sometimes called a congenital or primary disorder. Acquired disorders are sometimes called secondary disorders. Secondary disorders are more common than primary.
Primary immunodeficiency disorders are immune disorders you are born with. Primary disorders include:
- X-linked agammaglobulinemia (XLA)
- severe combined immunodeficiency (SCID disorders)
- common variable immunodeficiency
- Alymphocytosis (“boy in a bubble” disease)
- AIDS
- cancers of the immune system, such as leukemia
- immune complex diseases, such as viral hepatitis
- multiple myeloma