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Class notes MICR 270 (MICR270)
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- Queen’s University (QU )
Comprehensive class notes for MICR 270.
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Module 1 - Introduction to the Immune System:Overview of the Immune System:
There are more microorganism cells in our body than there are human cells. The immune system is how
we ensure pathogens don’t harm our body. The immune system can be separated into two major
components:
1. The Innate Immune System
2. The Adaptive Immune System
Each of these systems reacts to immune responses, the body’s reaction to microbes. The immune
systems job is to determine what is our body and what is not and destroy what is not ours.
Unfortunately, it can either over or undercompensate, Leading to autoimmunity or immunodeficiency.
- Antigen: Short for antibody generator. A protein that provokes an immune response
- Antibody: A protein produced to counter an antigen.
Antibodies bind to antigens and alert the immune system to destroy them
The Lymphatic System and the Lymphoid Organs:
The lymphatic system is often considered to be a part of the circulatory system, but also plays a large
role in the immune system. The lymphatic system produces and circulates lymph, which is full of white
blood cells. This is like the halls of a prison, where guards wander.
Lymphoid Organs and Tissues:
Primary Lymphoid Organs:
Bone Marrow:
Flexible tissue, divided into yellow and red marrow. It is found in the inside of bones.
- Red Marrow: Site of hematopoiesis as well as all immune cells. B-Cells are also created here
- Yellow Marrow: Develops some leukocytes, also produces fat and cartilage.
Secondary Lymphoid Organs:
Thymus:
Flat, bi-lobed structure that is found above the heart. It develops thymocytes or T-cells
Lymph Nodes:
Small beanlike organs that are divided into roughly three regions, cortex, paracortex, and medulla.
Lymph nodes are filled with lymphocytes, macrophages, and dendric cells. They serve to filter the lymph
and are often the first stop for foreign bodies. They serve as checkpoints for microbes entering the body.
Mucosal Associated Lymphoid Tissues (MALT):
Refers to the combined surface area of multiple mucous membranes throughout the body. They initiate
immune responses to specific antigens. They are like watchtowers at weak point where bacteria are
likely to get through.
Spleen:
Large ovoid situated in the left abdominal cavity. It is separated into red and white pulp.
, - Red Pulp: Filters Blood using cords of billroth
- White Pulp: is composed of lymphatic tissue and filled with lymphocytes and other immune cells
Branches and Phylogeny of the Immune System:
As discussed previously, the two main roles of the immune system are to discriminate and eliminate.
Discrimination:
Almost every nucleated cell expresses a molecule at their surface called a major histocompatibility
complex class I (MHC I). This presents a “sample” of the proteins found in the cell. Special immune cells
have MHC II molecules. The immune system is able to read the MHC I on a cell and determine if it has
any proteins that should not be there. If it detects anything, it initiates an immune response.
Elimination:
This process happens when a pathogen enters the body and is discovered. Immune cells are activated to
destroy the foreign body.
Branches of the Immune System:
We have divided the immune system into two branches:
1. Innate Immune System: Consists of physical, soluble, and cellular barriers that are scattered
throughout the body to prevent the entry of any infectious agent. This is a general response to
any intruder.
2. Adaptive Immune System: Consists of cells and Soluble components capable of recognizing and
responding to specific pathogens. This can be further split into:
- Antibody-mediated Humoral Immunity (B cells)
- Cell-Mediated Immunity (T Cells)
Evolution of Lymphoid Tissues:
As time went on, species evolved more and more ways to protect themselves from invaders.
1. Almost all vertebrates have gut associated lymphoid tissues
2. Most have a thymus or spleen
3. Not many vertebrates generate lymphocytes in the bone marrow. Sharks are one of the oldest
species that do
4. Very few vertebrates have lymph nodes
Almost all living creatures have an innate immune system, but only more advanced vertebrates have an
adaptive immune system, and only even more advanced ones have a well-developed adaptive immune
system.
Cells of the Immune System:
All immune cells are created from hematopoietic stem cells (HSC) in the bone marrow. While B-cells
reach maturity in the marrow, T-cells have to travel to the thymus before maturing. HSC’s differentiate
into either Myeloid (Innate) or Lymphoid (Adaptive) progenitors, which then can no longer self-renew
but can make many more cell types.
, Myeloid Progenitor:
These can produce four different types of cells:
1. Granulocytes: includes Neutrophil, Eosinophil, Basophil and Mast Cells (allergies)
2. Monocyte: Macrophages (phagocyte). Monos are found in the blood while macros are in the
tissue.
3. Erythrocyte: red blood cells
4. Thrombocyte: Platelets
Lymphoid Progenitor:
Can produce three different cell types:
1. B-Cells: Plasmocytes and memory B-cells (Antibody distribution)
2. T-Cells: Helper (Alert System), Cytotoxic (Attack Cells), and Memory T-cells
3. Natural Killer Cells: Destroy infected or mutated cells that used to be ours
Dendric Cells:
These help communication between the two systems. They help bring pathogens to t-cells to be
destroyed.
Major Classes of Infectious Disease-Causing Agents:
Bacteria:
Unicellular, prokaryotic organisms that have no organized internal membranous structures.
Cholera:
An acute, diarrheal illness caused by Vibrio cholerae. Characterized by vomiting, diarrhea, and leg
cramps, t is diagnosed through stool samples and is treated with rehydration and antibiotics if needed.
Viruses:
Can infect a variety of organisms. They need a host cell to reproduce. They are characterized by a single
or double-stranded genome surrounded by a protein coat called a capsid. They may also have a lipid
coat.
Influenza:
Cause contagious respiratory illness which varies in severity. There are three main types designated A, B
and C. Sx include Fever, cough, sore throat, runny nose, body aches, and headaches. A and B types are
responsible for the seasonal flu. Treatment is typically bedrest, and prevention is done trough
vaccination to 3-4 strands each year.
Fungi:
Eukaryotic, heterotrophic organisms that have chitin-based cell walls and reproduce by forming spores.
Molds are multicellular while yeasts are unicellular.
Vulvovaginal Candidiasis (Yeast Infection):
Occurs from an overgrowth of the yeast candida in the vagina. Sx are typically itching. Candida is always
present in the body in small amount but can take advantage of a weakened immune system to spread.
Treatments are antifungal medications administered through various routes.
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