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Lecture 5

BIOM2000 Lecture 5: Unit 5 BIOM2000


Department
Biomedical Sciences
Course Code
BIOM 2000
Professor
N.Campbell
Lecture
5

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Physiology — Unit 5
Expectations:
Identify defence mechanisms of immune system
Differentiate between macrophage + neutrophil
Compare/contrast first, second + third lines of defence
Mechanism of action of natural killer cells + antimicrobial compounds
Describe antibody-mediated + cellular-mediated immunity
Compare/contrast natural & active immunity + active & passive immunity
Overview of Immune System:
Immune system — broken down into 2 defence mechanisms
1) Innate (nonspecific) defence system
has mechanisms that protect against variety of invaders — responds immediately to
protect body from foreign material
2) Adaptive (specific) defence system
requires specific defence for each type of invader
Under each defence mechanism — other lines of defence that are also nonspecific or
specific in nature
Innate defence mechanisms — consist of first + second line of defence
First line of defence — components which act as barrier to keep foreign particles
from entering body
Eg. skin, mucous membranes + secretions of skin/mucous membranes
If foreign material enters body, second line of defence attempts to rid of pathogens…
Second line of defence — considered nonspecific + includes phagocytic cells,
natural killer cells, antimicrobial proteins + inflammatory response
Third line of defence — associated w/ specific defence mechanisms includes…
lymphocytes, antibodies, macrophages + other antigen-presenting cells
Note: antigen — used to
describe foreign
substance/pathogen that
elicits an immune
response
Note: third line of defence
consists of factors of
immune system that attack
specific foreign agents

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Connection to Microbes:
Life on Earth depends on microorganisms — animals depend on them to partially
digest food + microbes help break down dead animals/plants to recycle nutrients
Microbes can live w/o us, but we can’t live w/o them!
Although we need “good” microorganisms, we mount war against pathogenic forms
Goal of first line of defence/barrier defences — to prevent pathogens from invading
our tissues
If this fails, we can mount attacks on microbes that have invaded + body will destroy
them
Even best barrier defences cannot 100% prevent microorganisms from entering body
through wounds/vulnerable areas of body
Vector organisms (mosquitoes) can introduce them
Skin and Mucous Membranes:
Epidermis of skin — made of dead cells that are filled w/ keratin, a fibrous tough
protein
Surface of this layer — constantly sloughed off + microorganisms on skin surface are
shed w/ the lost skin cells
Skin is the largest organ in the body + provides protection from types of damage
Includes…mechanical damage, bacterial infection, chemical damage, loss of tissue
water, ultraviolet radiation + heat damage to internal tissues
Various glands w/in skin that play role in defending against pathogens…
Eccrine (sweat glands) — secrete acidic solution that slows down bacterial growth
Sebaceous (oil glands) — associated w/ hair follicles secrete sebum, which contains
antibacterial compounds that kill bacteria before they can invade skin surface

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Mucous membranes line all body cavities that are open to exterior
Eg. respiratory, digestive, urinary + reproductive tracts
Most of these systems produce mucus that contains antibacterial substances, which
inhibits microorganisms from reaching underlying tissues
Female reproductive tract secretes acidic mucous that inhibits bacterial growth,
Acid + digestive enzymes of the stomach kill pathogens
Salvia + tears contain enzymes that kill bacteria
Urine which is normally acidic, inhibits bacterial growth
Lymphatic System:
Lymphatic system — plays role in returning interstitial fluid back to circulatory
system
Ensures that fluid does not build up in tissues (edema) and that volume of fluid in
blood is not altered
Network of low pressure lymphatic vessels (responsible for draining vessels)
associated w/ sets of lymph nodes
Circulatory system includes: heart/blood vessels + lymphatic vessels
Goal of lymphatic system: pick up fluid at capillaries and return it to general
circulation
Therefore, lymph flows towards heart + contains valves to prevent backflow
Lymphoid Tissue:
As lymph fluid moves to heart, it passes through lymph nodes
Macrophage cells present in nodes + their job is to consume bacteria/viruses + remove
unwanted cellular debris
White blood cells (lymphocytes) found in the nodes + react to foreign materials
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