Body Defenses & Immunity
immunity = resistance to disease
the immune system provides defense against all the microorganisms and toxic
cells to which we are exposed
without it we would not survive till adulthood
our body has many ways to prevent or to slow infections
Many factors affect an individual’s overall ability to resist infections:
Genetics: human diseases, zoonoses, etc
Age: mainly an immune response
Health: eg. protein deficiency less phagocytic activity
eg. stress lower resistance to disease
Hormones: eg. cortisone (a glucocorticoid) reduces inflammatory
response
the immune system is a functional system rather than a system with
discrete organs
parts of many organs contribute to body defense
almost all organs in body play some role in immunity
dispersed chemicals, cells and tissues
dispersal and transport via circulatory and lymphatic systems
two major mechanisms that protect the body:
1. Innate, nonspecific system of
a. physical and chemical barriers
b. internal cells and chemicals
2. Adaptive system that fights specific pathogens
or, can view the immune system as a three tiered system of defense
a. physical and chemical barriers
b. chemical and cellular barriers
c. specific defense mechanisms
Human Anatomy & Physiology: Body Defense & Immunity, Ziser, 2003 1
, Innate, Nonspecific Resistance
Physical Barriers
1st major level of protection from invasion and infection
nonspecific – treats all potential pathogens the same way
attempt to prevent entry of pathogens into body
1. Intact Skin
tightly packed cells filled with waxy keratin
thick, multiple layers of dead keratinized cells
shed regularly
rarely, if ever, penetrated while intact
only a few parasitic worms (cercariae) can do this
if skin is broken:
staphs and streps are most likely to get in
sebaceous glands
provides protective film over skin
acidity of skin secretions ('acid mantle') inhibit bacterial & fungal
growth;
also contains bacteriocidal chemicals
but
if skin is moist, not cleaned frequently enough
may permit yeasts and fungi already present to become a
problem
2. Mucous Membranes
line all systems that open to outside of body
nasal hairs
trap pathogens
mucous
thick, sticky, traps pathogens
Human Anatomy & Physiology: Body Defense & Immunity, Ziser, 2003 2
, cilia
in resp sys move mucous out of system
(‘ciliary escalator’ 1-3 cm/hr)
coughing and sneezing speed up process
gastric juices
secreted by lining of stomach
contains HCl and enzymes; highly acidic (pH~1.2-3.0)
kill and dissolve most bacteria and toxins
except S. aureus and C. botulinum
but: Helicobacter pylori neutralizes acids to grow in
stomach
may cause gastritis or ulcers
Lacrimal Apparatus
continual blinking flushes and wipes away
pathogens
lysozyme kills and dissolves some bacteria
(most G+ and some G- bacteria)
(lysozyme also found in sweat, saliva, and nasal
secretions)
Saliva
continual flushing of bacteria to stomach
lysozyme kills and dissolves some bacteria
Urine
continual flushing of bacteria entering urethra
low flow bladder infection
acidity also inhibits bacterial growth
Vaginal Secretions
flushing and trapping pathogens in mucous
acidity inhibits bacterial growth
but: some pathogens thrive in moisture and if they
occur in large enough numbers they are able to
penetrate eg. Treponema
Human Anatomy & Physiology: Body Defense & Immunity, Ziser, 2003 3
immunity = resistance to disease
the immune system provides defense against all the microorganisms and toxic
cells to which we are exposed
without it we would not survive till adulthood
our body has many ways to prevent or to slow infections
Many factors affect an individual’s overall ability to resist infections:
Genetics: human diseases, zoonoses, etc
Age: mainly an immune response
Health: eg. protein deficiency less phagocytic activity
eg. stress lower resistance to disease
Hormones: eg. cortisone (a glucocorticoid) reduces inflammatory
response
the immune system is a functional system rather than a system with
discrete organs
parts of many organs contribute to body defense
almost all organs in body play some role in immunity
dispersed chemicals, cells and tissues
dispersal and transport via circulatory and lymphatic systems
two major mechanisms that protect the body:
1. Innate, nonspecific system of
a. physical and chemical barriers
b. internal cells and chemicals
2. Adaptive system that fights specific pathogens
or, can view the immune system as a three tiered system of defense
a. physical and chemical barriers
b. chemical and cellular barriers
c. specific defense mechanisms
Human Anatomy & Physiology: Body Defense & Immunity, Ziser, 2003 1
, Innate, Nonspecific Resistance
Physical Barriers
1st major level of protection from invasion and infection
nonspecific – treats all potential pathogens the same way
attempt to prevent entry of pathogens into body
1. Intact Skin
tightly packed cells filled with waxy keratin
thick, multiple layers of dead keratinized cells
shed regularly
rarely, if ever, penetrated while intact
only a few parasitic worms (cercariae) can do this
if skin is broken:
staphs and streps are most likely to get in
sebaceous glands
provides protective film over skin
acidity of skin secretions ('acid mantle') inhibit bacterial & fungal
growth;
also contains bacteriocidal chemicals
but
if skin is moist, not cleaned frequently enough
may permit yeasts and fungi already present to become a
problem
2. Mucous Membranes
line all systems that open to outside of body
nasal hairs
trap pathogens
mucous
thick, sticky, traps pathogens
Human Anatomy & Physiology: Body Defense & Immunity, Ziser, 2003 2
, cilia
in resp sys move mucous out of system
(‘ciliary escalator’ 1-3 cm/hr)
coughing and sneezing speed up process
gastric juices
secreted by lining of stomach
contains HCl and enzymes; highly acidic (pH~1.2-3.0)
kill and dissolve most bacteria and toxins
except S. aureus and C. botulinum
but: Helicobacter pylori neutralizes acids to grow in
stomach
may cause gastritis or ulcers
Lacrimal Apparatus
continual blinking flushes and wipes away
pathogens
lysozyme kills and dissolves some bacteria
(most G+ and some G- bacteria)
(lysozyme also found in sweat, saliva, and nasal
secretions)
Saliva
continual flushing of bacteria to stomach
lysozyme kills and dissolves some bacteria
Urine
continual flushing of bacteria entering urethra
low flow bladder infection
acidity also inhibits bacterial growth
Vaginal Secretions
flushing and trapping pathogens in mucous
acidity inhibits bacterial growth
but: some pathogens thrive in moisture and if they
occur in large enough numbers they are able to
penetrate eg. Treponema
Human Anatomy & Physiology: Body Defense & Immunity, Ziser, 2003 3
