how you remove wastes from your body excretory system
TRANSCRIPT
How you remove
wastes from your body
EXCRETORY SYSTEM
Excretion: waste removal from body
Kidneys: Unique Problem
Keep Good Get Rid of
Things Bad Things
in blood
How the kidneys do this:
1. Filtering- everything except blood cells & protein (big)
2. Bad things out with urine
3. Recycling (reclaiming):
Good things back to blood
Bad things (waste): your kidneys remove
Example: urea from breakdown of protein
Good things: reclaimed
Example: H2O, glucose, amino acids
50 gallons
of blood:
pumped
through
kidneys/day
½ gallon:
waste + H2O
leaves body as urine
Damage to kidneys (failure): poor filter
Dialysis machine: filter/remove wastes
Kidney Dialysis • Kidney disease > 60% caused by
hypertension & diabetes
• Toxic wastes build up
• Dialysis (separation): 3X/week
each 4-6 hr
• Patient blood artery tubes
selectively permeable
membrane
Kidney
Dialysis
• Good
things
added:
bicarbonate
ions
(blood pH)
• Wastes:
discarded
Kidney Transplantation
2009: 78,000 people- waiting list
1. Best donor (kidneys last longer): living, matching (family) donor
2. Unrelated living donor
3. Deceased donor
Newer technique: “preconditioning” transplant recipient’s blood before operation: cleanse of antibodies (cause of rejection)
Newer surgery
on donor:
Laparoscopic
Nephrectomy
(small cut in
abdomen)
Remove kidney recipient
“New” kidney starts working immediately
• Many donated
kidneys still working
> 25 years
• Donor: normal
life span
• Remaining kidney
“compensates” for
loss of donated kidney
“KIDNEY SWAP”
New England people- Kidney Disease:
3-5 year wait for cadaver kidney
• Second problem: incompatible donor
• Alternative: NE Kidney Exchange Program (Newton)
• Computerized data pool
• Likelihood match, Donation time
Other things your kidneys do:
1. Control your blood volume:
+/- H2O
2. Control ion balance in your body
(sodium, potassium)
3. Help keep blood pH normal
Urinary system: 2 kidneys: filter blood, produce urine
Right Kidney Left Kidney
Ureters
Urinary Bladder
(Muscles contract)
Urine Urethra Outside Body
Male
Urinary
System
How the kidney filters: big picture
1. Blood into
kidneys:
renal artery
from aorta
2. Blood
filtered
3. Blood out
of kidneys:
renal vein
4. Cleaned
blood
returned
to heart
How kidneys filter blood: the little picture
Little filtering units: nephrons
1.25 million = each kidney
Nephron Parts: 1. Bowman’s capsule Collects Filtered Blood Plasma: Good + Bad Things
2. Complex,
twisted tubes
3. Collecting
duct: final
urine collected
4. Many
collecting ducts
Send urine to
renal pelvis
(cavity)
5. Renal pelvis urine ureter
6. Blood into
nephron from
renal artery
(arteriole)
7. Blood forms
ball of
capillaries:
Glomerulus
(porous)
Close up view: glomerulus
Blood under pressure
Glomerulus blood under pressure:
1. Small molecules leak out: H2O, glucose, sodium, potassium, vitamins
2. Also leaking out: metabolic wastes:
A) Urea- from protein breakdown
B) Creatinine: waste product from muscle contraction
3. Big things: proteins, blood cells: don’t leak out- stay in blood
4. Glomerulus
(capillaries)
form arteriole:
exits Bowman’s
capsule
5. 2d capillary
network formed
around nephron
6. Finally,
capillaries
form
small vein:
blood
returned
to heart
This was filtration by nephron: filtering blood: 1st thing kidney does
2d thing kidney
does: Reabsorption: save good
things
1. Cells in tubes actively pump sodium to outside of tube 2. Sodium moves into capillaries 3. H2O follows the sodium (osmosis): into capillaries
H2O lost during filtration + glucose + nutrients: reclaimed back into blood
This is REABSORPTION
Wastes: most urea in tube not reabsorbed: pass out urine
3rd thing kidney does: Secretion
(to release) H+ (balances blood pH), Potassium, Drugs, Poisons:
Move: capillaries tubes urine
4th thing kidney does: concentration
More sodium
Pumped out-
end tube
moves into
capillaries-
H2O follows:
moves into blood
Concentration: you save 99% of H2O filtered
You produce concentrated urine: wastes + some water
Very important for land animals: H2O conservation- prevents us from drying out
Summary 4 things your kidneys do:
#1 Filter everything except protein & blood cells
#2 Reabsorb: H2O, sodium, glucose, vitamins
#3 Secrete: H+ & potassium from blood tubule
#4 Concentrate: save H2O, concentrate wastes urine (Excretion)
Summary
• Our kidneys evolved: conserve sodium & excrete potassium (homeostasis)
• Prehistoric diet
Kidneys & sodium/potassium balance
Today’s diet: overloads kidney’s with salt
Our kidney’s have not adapted
“modern” diet: result- hypertension
Natural way to control blood pressure
• Return to caveman diet
• Dietary Approaches to Stop Hypertension (DASH) Eating Plan
• National Heart, Lung & Blood Institute
DASH
• Fruits & veggies
• Low fat milk (calcium) products
• Eat more: poultry, fish, nuts
• Eat less: red meat, sugar in
processed foods/drink
If all Americans ate DASH: dramatic drop in heart attacks/stroke
DASH DIET
What controls how much H2O you lose in your urine?
Walking- desert Drinking
many glasses
H2O
Your body adjusts
Concentrated Dilute yellow
yellow urine urine
In Nevada Desert:
1. Lose H2O- breath, sweat
2. Blood volume (concentrated)
3. Brain (hypothalamus) detects change blood volume
4. Signals pituitary gland
Antidiuretic Hormone (ADH)
Diuretic = urine secretion
Antidiuretic Hormone
• Makes tubules/collecting ducts more permeable to water
• Water moves into blood
• Result: more H2O in blood, urine- concentrated
• Important: saves body water- desert
You arrive at Las Vegas Hotel- thirsty
• Drink several bottles H2O
• Blood volume
• H2O comes in from intestine
• Pituitary ADH
• Nephron tubules/collecting duct less permeable
• More H2O leaves urine
Drink 12 ounces
Beer or Water
• Beer- more urination
• Alcohol: ADH production
• Alcohol = diuretic
• Urine secretion
• Dehydrating effect part of hangover
To the outside…….
Urine ureters urinary bladder holds 27 ounces
Urethra: from bladder to outside
Men: 7-8 inches- through penis
Women: ~ 1 inch
Prostate gland: produces fluid for semen
Prostate: below
bladder,
surrounds
urethra-
Enlarged
Prostate
Urine Stream
Urination
• Urethra: has sphincter muscle around it: voluntary control
• When bladder has 7 ounces urine:
• Stretch receptors- wall of bladder
“urge to urinate” brain
• Sphincter muscle relaxes, bladder muscle contracts: urine passes out of body (1/2 gallon/day)
Kidney Stones: detected 7000 year old mummies
Kidney stones: more common men
• Concentrated urine: crystal formation: calcium, uric acid stones
• Small pebble
• Very painful
• Occur in tubules, collecting ducts, ureters
• Can block urine flow if big
Treatment:
1. Drink fluids- pass stone
2. Surgery
3. Medicine: to relax smooth muscles: pass stone
4. Shock waves: you sit in tub of water: machine- high energy shock waves: pulverize stones
Kidney Stones (calcium oxalate)
Risk Factors
• Men 2X risk
• Overweight
• Diabetes
• “Stone belt”: people in Southeastern US: 20% risk: related-sweating, more concentrated urine?
• Grapefruit juice, stones
• Megadoses of Vitamin C
After the stone has passed into urine
• Drink enough fluids
• Salt in diet
• Children animal protein & salt
stones
• Coffee drinkers: risk
Good Bacteria
Many kidney stones: calcium oxalate
Oxalate: spinach, beets, nuts
Oxalobacter formigenes in intestine
Digests oxalate
People Oxalobacter Kidney stones
Urinary Tract Infections
More common women
90% due to E. Coli (colon bacteria)
Anus close to urethra: bacteria multiply
Result: bladder infection (cystitis) & urethra infection (urethritis)
Urinary Tract Infections
Other causes- bacteria infections
1. Sexual intercourse
2. Pregnancy
3. Urinary obstruction
Cranberries/cranberry juice
10 ounces/day: protection
Prevent growth E. Coli and
attachment to urinary bladder
DIABETES
What is diabetes?
• Diabetes mellitus
• Diabainein (Greek)= “to pass through”
• Mellitus (Latin)= “sweetened with honey”
• Glucose spills into urine
• Sweet urine- ants
Diabetes
• Consistently blood glucose
• Result of:
1) insulin from pancreas
and/or
2) insulin sensitivity (responsiveness) by body cells
“insulin resistance”
“Starvation in the midst of plenty”
Symptoms (warning signs): diabetes
1. Frequent urination
2. Excessive thirst
3. Extreme hunger
4. Unusual weight loss
5. Increased fatigue
6. Irritability
7. Blurry vision
Normal Blood Glucose: 80-100 mg
Renal Threshold Glucose : 160-180 mg
At renal threshold:
Glucose filtered > Glucose reabsorbed
Spillover urine (wasted energy)
Diabetes
• Without glucose, body breaks down (partially) fat- energy
ketones (acids)
• Brain, other tissues- adapt to use ketones for energy
• Excessive ketones urine
(test kit)
Diabetes
• Ketones: acidity of blood (ketoacidosis)
• Rapid/deep breathing, very thirsty, urination, loss appetite
• Fruity breath odor
• Weakness, fatigue, confusion
• Severe dehydration, coma, death
• Requires immediate treatment
YOUR IMMUNE SYSTEM
Microbes are all around us
Babies: “bacteria-free”-
sterile womb environment
After birth: baby
“colonized”
by bacteria: mom’s
breasts, clothing, air
Globe 2/08
“Your body:
a colony
of creatures”
Humans:
20,000 genes
Microbes living
on/in us:
3 million
genes
“Microbes & their attached Humans” Symbiosis: “good germs” Concern: some bacteria disappearing American emphasis: anti-bacterial Kleenix, soaps, etc.
Skin pore
with
Staphylococcus
Macrophage
Ingesting
Staphylococci
MRSA
Our immune system: under
constant attack: viruses, bacteria, fungi
David Venter: born 1971 with severe combined immune deficiency
“BOY IN A BUBBLE”
David lived 12
years: isolation
chambers
• Baptized- sterile
water
• Breathed
filtered
air
• Clothes-
disinfected
• Parents/doctors
handled him with
gloves attached-
bubble
• Died- 1984 after
bone marrow
transplant from
sister
• Marrow contained
virus- not detected
Immune System: cells & proteins in your body
Kills invading microorganisms: bacteria, viruses, fungi
Antigen: any foreign substance- triggers immune response
Usually protein- on microorganism surface
Protozoan
Parasites:
Infected &
Ruptured
Human Cell
If you are invaded by bacteria: immune system kills them
1. Next time you are invaded: rapid response- kill bacteria
2. Immune system “remembers” 1st invasion
3. Immunity: long-lasting protection against microorganisms
Macrophages attacking E. Coli bacteria
Another example: vaccinations
1. Inject you with harmless “part”
of invader (vaccine)
2. Ex. Poliovirus (killed)
3. You have full immune response
4. Produce: antibodies: immune system proteins- attack 1 specific antigen
5. Immune system ready if real, live poliovirus invades you
Polio-
not eradicated
in world
WHO global
Initiative
2009: Nigeria
“a runaway polio
epidemic”
Vaccinations: diphtheria, tetanus, pertussis, polio, hepatitis, chicken pox, measles, mumps, rubella
Another example:
1. You get chicken pox
2. Immune response- you produce antibodies- get well
3. Immune system “memory” protects you against getting chicken pox again
Active immunity: you develop protection in response to invasion- microorganism
Passive (temporary) immunity examples:
1. Pregnant women antibodies through placenta baby
2. Breast milk antibodies baby
3. Gamma globulin shots- overseas travel
1st line defense: prevents pathogens from entering body
Pathogen: disease causing organism
1. Epithelium: covers body surface (skin, intestine lining)- barrier to invasion
2. Glands: tears & saliva release enzymes- kill bacteria
3. Lung surfaces: cilia sweep away microorganisms
4. Stomach juice/acid: kills pathogens
5. Urine: low pH: kills bacteria- protects against urinary tract infections
2d Line of defense: if pathogen gets past barriers:
White blood cells= phagocytes Gobble up bacteria with pseudopods (false feet) 1. Large eaters (macrophages) 2. Small eaters (microphages)
Phagocytes in lymph node attack bacteria
General Immune Response: inflammatory response: you step on nail with bare foot
Bacteria invade puncture
1st immune cells near injury
histamine
Histamine:
• Blood vessels become leaky (permeable)
• Vasodilation
• More blood injury site
• Redness/swelling/warmth near surface
2d: small & large eaters squeeze out of blood attack & kill bacteria
3rd Complement proteins in blood near injury: “complement” this attack: cut holes in bacteria cell membranes
4th Fibrin- blood protein forms network of fibers: “seals” off injury
More specific immune response
Antibody Cell
Immune Immune
Response Response
“B” Cells “T” Cells
interaction
Antibody immune response
• Carried out by
“B” cells (white
blood cells)
• Start out in
Bone marrow
• Migrate to spleen
& lymph nodes (filters)
• Ready to protect you
Swollen neck:
“B” cells in lymph
node fighting
infection
B cells’ membrane
surface:
• “Y” shaped
Antibodies
(receptors)
• Bind to 1
specific antigen
(bacterium)
Some B cells make
“clones”: exact
genetic copies
• Kill bacteria as
it spreads
• Clones stay
in body: “memory”
• Ready: future
attacks
Other “B” cells:
Release antibodies
from surface:
move into blood-
attack bacteria
Cell Immune Response
Carried out by
“T” cells
(white blood
cells)
• Start out: bone
marrow
• Move to Thymus
(become specialized)
Thymus gland: above heart
“T” cells later migrate: spleen & lymph nodes
Cell Immune Response
• Especially good for viruses hiding inside your cells
• Viruses inside cells not attacked by antibodies
• One type T cell destroys your “virus infected” cells
• Virus attack coordinated by “helper T cells” (CD4 cells)
AIDS: acquired immune deficiency syndrome
Caused by HIV: human immunodeficiency virus
Dangerous: attacks our immune system (helper T cells)
AIDS weakens immune system
• Body can’t fight off:
other viruses
bacteria
fungi
susceptible: pneumonia, cancer
HIV= RNA virus
(single strand)
also called a
Retrovirus
Retro=
Backwards
RNA makes DNA
How HIV damages your immune system
1. HIV attaches to receptor on helper T cell membrane
2. Enters cell
3. Uses special enzyme & RNA to make DNA (“retro”)
4. New “virus” DNA becomes part of cell DNA (Invasion Body Snatchers)
HIV Infection
5. Cell tricked into making new RNA viruses (replication)
6. Viruses burst out of helper T cell (killing it)
7. Released viruses infect new cells
8. 10 billion new viruses made/day
HIV Infection
9. Body immune system starts to fail: “immune deficiency”
10.Finally: other infections set in: bacteria, viruses, fungi, parasites
11.Low CD4 count (200/microliter or less): sign HIV infection
AIDS viruses attacking immune cell
Problem in developing HIV vaccine:
1. HIV multiplies- great numbers
2. Mutates rapidly- makes different versions of self
3. Difficult to make antibodies against different virus surface proteins
4. HIV adapting rapidly to immune system: human populations
AIDS Treatment
• “Cocktail” of drugs (3+)
• Antiretroviral therapy
• Reduce amount HIV in blood
• Never disappears
• Drugs: growth & replication virus
• Allow people: longer life, less serious complications
AIDS patients living longer but immune system damaged before “cocktail” used and antiretroviral drugs themselves further damage
Result: AIDS survivors- many medical conditions as they age
John Holloway: 59- AIDS survivor more health problems than 85 year old father
• COPD
• Diabetes
• Kidney failure
• Bleeding ulcer
• Depression
• Rectal cancer
• Prolonged effects- broken hip
How you get AIDS
• Vaginal, anal, oral sex with infected person
• Virus in: blood, semen, vaginal secretions
• Virus enters body- small tears in tissue
Other ways to get AIDS
• Virus “transmitted”- infected blood: transfusions
• Needles/syringes- HIV contaminated
• Pregnant women- AIDS baby
• Organ transplants
• Unsterilized dental/surgical equipment
HIV not transmitted
• Sweat or tears from AIDS person
• Kissing AIDS person
• Sharing towels, telephone, toilet with infected person
Autoimmune Diseases
Normally your immune system
distinguishes between
“self” “non-self”
your normal infection/foreign
cells cells
Autoimmune Diseases
• Immune system attacks healthy tissue (as if foreign)
• T cells developing in thymus never learn difference: self vs. non-self
• Antibodies: attack normal tissues
Autoimmune Diseases
1. Rheumatoid arthritis: attack connective tissue (joints)
2. Multiple sclerosis: attack of nerve cell covering
3. Type 1 diabetes: destroy cells in pancreas: insulin
4. Lupus: joint inflammation, pain, rash
• Disfigurement: rheumatoid arthritis- difficulty signing greeting card
Lupus
Erythematosus
“The Red Wolf”
Face rash: people
with “wolflike”
appearance
Multiple Sclerosis
ALLERGIES
Common
allergens
(antigens)
• Tree, grass,
weed pollen
• Spores
Dust Mites
• Live in
Pillows,
Mattresses,
Blankets,
Carpets
• Like: darkness, high humidity,
your dead skin flakes
• Dust mite droppings airborne
allergy inhaled
Cockroach
Droppings
(proteins)
Trigger
Asthma
Attacks
Animal Dander Allergy
• Protein: in saliva,
dander (dead skin),
urine of cats, dogs,
other mammals
• Airborne
Allergic reaction
• Hair- not allergen
MOLD
• Microscopic fungi
• Release enzymes:
break down organic
matter on which
mold lives
• Protein secretions & mold spores: airborne allergies
Allergies
• Hypersensitivity reactions
• Genetic predisposition
• Overreaction- immune system to environmental antigens (allergens)
• Overproduction of certain type of antibody (IgE)
• Example: reaction to pollen grain= hay fever
Hay fever
• Pollen grain enters body: stimulates antibody production
• Subsequent exposure: antibody attaches to mast cells (in connective tissue)
• Antibodies “grab” allergens
• Mast cells release histamine: inflammation response
Inflammation Response • Vasodilation- blood vessels • Capillaries: leaky- release fluid • Sniffles/runny nose • Coughing/sneezing/tearing eyes • Difficulty breathing • Histamine contraction smooth
muscle: airways • Antihistamines: block receptors
(blood vessels)- that bind to histamine
Allergy Testing
• Scratch specific
allergens into skin
• Trigger IgE (antibody)
histamine mast cells
• See redness &
swelling if allergic
Allergy Shots
• Immunotherapy
• Decrease your sensitivity to allergens
• Inject increasing amount of specific allergens (Build-up Phase)
• Maintenance Phase: therapeutic dose reached to reduce allergic symptoms
• Like vaccine: your body develops “immunity” or tolerance to allergens
Allergy Free Bedroom
Anaphylactic Shock
• Dangerous allergic reaction
• Some people very sensitive to allergens:
venom of
bee sting,
peanuts,
shellfish
Anaphylactic Shock
• Sudden inflammatory chemicals
• Blood vessels dilate quickly
• Dramatic Blood pressure= shock
• Counteract: epinephrine injection
Peanut Allergies
• 3.3 million Americans allergic to peanuts or tree nuts
• Reactions: range- mild stomach/skin reactions airway constriction
death
2009 Research
• Children: sprinkle
Peanut Powder
on
food
• Increase doses
• After 10 months:
Children eat 15 peanuts
without symptoms
Organ Transplants
• Each body cell has distinct proteins on cell surface (“self” proteins)
• Makes you unique- anyone else
• Impossible: any 2 people- same proteins on cell surface
• Exception: ID twins
Organ Transplants
• Problem: skin grafts & organ transplants: one person another
• Rejection: your body “sees” new tissue/organ as foreign: immune rejection
To minimize rejection
• Doctors “match” donor and recipient (cell surface proteins) as closely as possible
• Tissue typing: worldwide data base
• ID twins: exact same tissue type
• Brothers/sisters: close match
To minimize rejection
• Administer: immunosuppressant drugs
• Suppress immune/rejection response
• Problem: person more susceptible: infections & cancer
• Autografts (autotransplantation): graft tissue one place another in same person
Bone Marrow Donor Programs: cancer
• Worldwide volunteers
• Look for “good” matches
• Recipient bone marrow: radiation
• Eliminates person’s bone marrow
• Kills cancer cells & inactivates immune system
• Donated bone marrow contains white blood cells: replaces eliminated marrow without rejection
Pigs for Spare Parts
Animal to Human Organ Transplants
The “Perfect” Pig
1. Pig with human genes
2. Organs can be transplanted into humans without rejection
Xenotransplantation
• Transfer: organs, cells, tissues from 1 species another
• “Xeno”= strange or foreign
Organ Transplants
The Need:
• 80,000 people in U.S. on waiting lists for organ transplants
• 16,000 people die/year while waiting
• “Not enough organs to go around”
• Some countries: “Black Market” for organs
Why Pigs?
• Physiologically similar to humans
• Plentiful, easy to breed
• Carry fewer deadly diseases vs. primates
• Organs similar in size to humans
• “Miniature swine” used: inbred strain
The Concern
• Pigs born with viruses
• Concern: spread pig viruses to general human population
• Ex. Malaysia: 1997 “new” pig virus killed 100 people
• Ex. Bird Flu Epidemic
• AIDS epidemic: HIV “jumped” from chimp humans
2002: Charlestown, MA company
• Cloned first pigs:
“knocked out”
1 of 2 genes that
trigger violent
immune response in
humans (single knockout)
• Worcester company: developing “double knockout”: pig organs that are “human friendly”
Nextran Company, New Jersey
• Developing: “transgenic pigs”
• 300 pound pregnant pig under anesthesia
Technician: flushes fertilized eggs out of uterus • Microinject: under microscope: single human gene into each egg • Implant eggs in another sow (in heat) • Create baby “transgenic” piglets • A little bit “human” • Do “tail snip”: check if pigs have human
DNA • Goal: allow human immune system to
accept pig organs
Superbug War
Superbugs • Hospital acquired infections
• Become infected during stay in hospital
• Kills 900,000 Americans/year
• Bacteria spread:
Person to person
On hands
On bedrails, sheets, IV poles
While inserting vein catheters
Superbugs • Overuse antibiotics: bacteria become
drug resistant
• Clostridium difficile (C. diff)
• Intestinal bug: severe diarrhea
• Attacks people- weakened immune systems
• Attacks people using catheters, IV lines, ventilators
• MRSA: “Staph Infection”- spread: person to person
Superbugs
• Cost of treating “hospital infections”: $20 billion/year
• Survey: health care workers clean hands effectively: only ½ of times
• New emphasis: sanitizing rooms, equipment, washing hands, sterile conditions: inserting catheters, precautions with infected people
• Result: dramatic in infections
2008: EPA approved health claim: copper alloys (brass & bronze) are antimicrobial
Copper ions: kill bacteria
99.9% MRSA kill rate
Uses in hospitals:
door knobs, arm rests,
bed rails, other fixtures
Hygiene Hypothesis
Should babies eat dirt?
Mothers know: “Instinctive” baby behavior: pick things up from floor/ground: put in mouth
?
Evolutionary
Advantage
New born baby’s immune system: like an “unprogrammed computer”
• Needs to be programmed
• GI tract needs to be “colonized”
• Early exposure to bacteria, viruses, worms in “dirt” triggers development of “healthy immune response”
• GI tract: important part of immune system: “point of entry”
• Microbes GI epithelium Immune Response
“Dirt” may help baby’s immune system
distinguish
Strong immune “ignore” some
Response: antigens (dust mites,
Protect against (dander, pollen)
Dangerous (harmless)
Pathogens
Recent evidence: U.S. and developed countries: increase in immune system disorders
• Multiple sclerosis
• Type 1 diabetes
• Inflammatory
Bowel Disease
• Asthma
• Allergies
Are we too clean?
• Overuse of antibacterial products may increase antibiotic resistant, disease causing bacteria
• Children raised: “ultraclean” environment: not exposed to organisms that “help” their immune systems to develop
Evidence:
1. Children raised in large families
2. Children raised on farms- exposed to worms and other farm animal organisms
3. Children sent to day care centers at early age
Allergies Autoimmune Diseases
Some Doctors recommending:
• Use plain
soap & H2O
• Let children
play in dirt
• Go barefoot
in dirt
• Have dogs &
cats (exposure
to GI worms)
2008 Study: Asthma rate of Africa
Americans born in
Dorchester
3X higher than
black people
born outside U.S.
Reason: hygiene hypothesis?
Children- developing countries strong immune response to life-threatening diseases
Immune system “ignores” dust mites/mold (allergy/asthma triggers)