The Slim Book of Health Pearls: Man the Barricades - The Story of the Immune System

Sheldon Cohen

Description

The immune system is a complicated mechanism whose principle actors are organs, cells, chemicals and a vast collection of proteins tuned by billions of years of evolution to work in a harmonious manner for the good of the whole. Its purpose is to keep us alive in a world where visible and invisible predators intending to usurp our bodies attack us on a daily basis.

By virtue of an amazing communication network, millions of cells gather, exchange information, become activated and respond to bacteria, fungi, parasites and viruses preventing them from causing infection.

A malfunctioning immune system, when immune cells attack "self," results in numerous auto-immune diseases, the "God only knows" diseases of sixty years ago.

Sujets

• Santé et bien-être
• Santé du quotidien
• Cell Biology
• Life Sciences
• Sciences et techniques
• Science

Informations

• Publié par: eBookIt.com
• Date de parution: 24 décembre 2013
• Nombre de lectures: 0
• EAN13: 9781456607746
• Langue: English

Extrait

THE SLIM BOOK OF HEALTH PEARLS
 
Man the Barricades
 
The Story of the Immune System
 
 
Sheldon Cohen M.D. FACP
 


Copyright 2012 Sheldon Cohen,
All rights reserved.
 
 
Published in eBook format by eBookIt.com
http://www.eBookIt.com
 
 
ISBN-13: 978-1-4566-0774-6
 
 
No part of this book may be reproduced in any form or by any electronic or mechanical means including information storage and retrieval systems, without permission in writing from the author. The only exception is by a reviewer, who may quote short excerpts in a review.
 
 

This is a short story about the body’s defenses against attack by enemies constantly trying to harm us. The principal actors are organs, cells, and complicated collections of proteins, tuned by billions of years of evolution to work in a harmonious manner for the good of the whole.
This short story will describe the various lines of defense used to keep us alive in a world where, on a daily basis, invisible or visible predators want to usurp our bodies. These predators are bacteria, fungi, pollen, viruses, parasites, cancer cells, and transplanted organs.
In the face of this onslaught, we owe a state of good health to our immune system: the collaborative mechanism that protects us from disease by utilizing a sophisticated team of specialized organs and cells that differentiate self from non-self. This ability is due to the fact that every body cell carries distinctive molecules (epitopes) on their surfaces that identify it as self. Immune cells, recognizing this self-marker, coexist peacefully in a state known as self-tolerance.
On the other hand, altered or foreign cells or organisms that do not carry this self-marker will find themselves subjected to an all out vigorous assault by the immune system.
Of course, transplanted organs can be life saving. Therefore, a careful physician must try to suppress the immune mechanism to a degree ensuring that the transplanted organ will continue to perform its function for the good of its new host. Failure to suppress the immune function enough will allow the host to overcome the transplanted organ in a process called rejection.
 
A substance capable of triggering an immune response is an antigen. These non-self invaders carry epitopes on their surfaces that immune cells immediately recognize as foreign, attack and neutralize or kill.
 

 
Immunology, the study of the immune system, has become a topic of interest since the advent of the autoimmune deficiency syndrome (AIDS). This epidemic has focused our attention on the consequences of a malfunctioning immune system. They include the assault on our bodies by opportunistic infections and malignant diseases. In addition severe combined immunodeficiency disease (SCID) is a thankfully rare condition present at birth that is characterized by a severe defect in T & B lymphocytes, our main immune cells (more later). This defect impairs the immune response and results in serious life threatening infections within the first few months of life.
The last sixty years have seen incredible advances in our study of immunity or resistance to disease. The underlying structure known as the lymphatic system is an efficient anatomical masterpiece working in the background, and without it our hearts would cease to beat and our immune system would become inoperable.
The lymphatic system includes a specialized body transport mechanism that delivers unique cells, fluid, proteins, and chemicals to any location invaded by predators, or altered non-self cells. Included in the lymphatic system are very specialized organs within which the lymphatic cells are manufactured and stored.
These structures are all involved in a well-coordinated surveillance and attack against bacteria, viruses, fungi, parasites, cancer cells, and transplanted organs. Even invaders such as dust particles, pollen, molds, and grasses are subject to immune assault. The job of this harmonious system is to identify, isolate, and destroy any foreign invader or anything that the system does not identify as belonging to it.
As amazing as this system is, it occasionally overreacts to allergens---substances that causes an allergy. Said another way, an allergen is any substance that causes the immune system to create an allergic reaction.
Worse yet is the overreaction that occurs when the system turns on its host body resulting in a myriad of autoimmune diseases. An autoimmune disease occurs when the immune system mistakes normal self-cells as non-self, attacks and inhibits their function or kills them outright. Some examples are rheumatoid arthritis, lupus erythematosis and multiple sclerosis.
The body has evolved superb nonspecific defense mechanisms against disease. Non-specific refers to those mechanisms, not programmed to zero in on specific enemies, but rather form defenses against them all.
These non-specific defense mechanisms known as innate immunity are present at birth, are not required to have a previous encounter with the invading or offending substance, and do not develop memory. The development of memory by a cell allows those cells prompt recognition of an antigen in the future.
 
NON-SPECIFIC DEFENSE MECHANISMS
The skin, our largest organ, acts like a shield of armor. It stops bacteria from entering our bodies and in so doing prevents bacterial infection from gaining a foothold. This assumes, of course, that the skin has maintained its integrity and there are no cuts, bruises or rashes providing an entry point.
The body sheds the outer layer of skin on a regular basis and discard bacteria along with it. So the skin acts not only as a bacterial barrier, but constantly renews itself by getting rid of its worn out, bacterial-laden outer coat.
The outer layer of skin known as the epidermis consists of five parts. From superficial to deep the layers are:
1. Stratum corneum is a twenty-five cell layer of dead cells filled with keratin, a protein that intertwines and acts as a barrier to infectious agents and makes the skin waterproof. The body sheds these cells continuously, replaces them by cells from the lower layers and prevents light, heat, and some chemicals from entering.
2. Stratum lucidum consists of five layers of dead cells that contain eleidin, a precursor of keratin.
3. Stratum granulosum consists of three to five layers of cells that manufacture keratohyalin, a precursor of keratin.
4. Stratum spinosum consists of eight to ten layers of cells that take in melanin, a brown-black pigment shielding the cells from the sun’s ultraviolet light.
5. Stratum basale consists of a single layer of cells that contain stem cells capable of new cell growth. This layer also contains nerve endings sensitive to touch.
Beneath the epidermis is the dermis where sensory nerves send messages to the brain (heat, cold, touch, pain, and pressure). In addition, there are suderiferous (sweat) glands, sebaceous (oil) glands, small arteries and veins, blood capillaries, hair follicles, and tiny longitudinal muscles called Arrector Pili muscles attached to the hair follicle and outer skin layers that can make the hair stand on end (goose bumps).
Finally beneath these two skin layers is a subcutaneous layer consisting of larger arteries, veins, and adipose tissue (fat).
Again, compromising the integrity of the outer layer of the skin results in bacterial invasion and a possible infection.
 

 
THE DEFENSIVE FUNCTION OF THE SKIN
Sebaceous glands secrete an oily material called sebum, a mixture of salts, fats, including unsaturated fatty acids, cholesterol, and protein. The unsaturated fatty acids can inhibit the growth of certain bacteria. In addition, sebum keeps the skin moist by reducing evaporation of water from the skin. This prevents the skin from cracking and opening the door to bacteria.
There’s a down side here though. Sometimes sebaceous glands enlarge due to accumulated sebum and form a ‘black head’. The blackness is due to pigment and oxidized oil. Pimples or boils may evolve because the sebum turns out to be tasty dish for certain bacteria.
That’s not all. The suderiferous glands secrete a substance called lysozyme that has antibacterial properties. That is probably why boxers, sewed up by ringside doctors without gloves or sterile technique, never get infected. In addition, the perspiration that flows during a boxing match has the additional effect of washing away any potentially harmful bacteria residing on the skin.
Lysozyme is also found in saliva, tears, nasal mucus, and tissue fluid allowing them all to be a vital part of the non-specific defense mechanism.
 
OTHER FIRST LINES OF DEFENSE
Mucus membranes, the cellular lining of internal body openings and tracts, include the mouth, nose, throat, and bronchial tubes. They secrete a viscous, sticky substance known as mucus that entraps bacteria and any other foreign substances such as dust or pollen.
The upper respiratory tract mucus cells have microscopic hair like projections on their surface known as cilia whose function is to sweep inhaled substances up and out protecting the lungs. Bacteria and viruses harm the respiratory tract and its cilia acutely, but the principle culprit in causing chronic ciliary failure is cigarette smoke. Once the cilia fail to keep the lungs free of irritants, the body must resort to anther mechanism…a cough. Something must remove these inhaled irritants from the lungs, so a cough becomes a member of the immune surveillance system when the bronchial tree’s cilia and its mucus have failed in their mission.
The salivary glands produce saliva that can expel microbes from the oral cavity.
Tears wash bacteria from the eyes.
Urine flow prevents bacterial colonization of the urinary tract.
A bowel irritated and inflamed by bacteria or viruses will contract vigorously, and the resultant diarrhea expels the offending irritant.
The acidity of gastric juice and vaginal secretions provides a