how you remove wastes from your body excretory system

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)