Chapter 6

Barriers of the Body

Interfaces with the outside

Barriers of the Body

• Skin, Lungs, and Digestive System

• The controlled exchange of molecules and heat

• Warm blooded animals are very expensive

• Rapidly turning over cells

• Damage repair

The Skin

• The surface barrier of the Body– Skin cells– Replacement skin cells– A few hairs– Sweat glands– Nerves (information: touch, temperature,

and pain)

Heat, what is it?

Heat Capacity

Heat Transfer

Control of Body Temperature

Information in to the brain

>Surface sensors: “I feel hot or cold”

>Temperature of blood circulating to the brain

Why is Heat Important?

• 106° F: Fried Brains

• 86 ° F: Dysfunctional Brain unable to warm its self

• Rate of reactions is a function of temperature

• Reactions are energy transfer among molecules

• To much heat destroys large molecules

Heat Exchange• Three Processes

– Radiation

– Conduction

– Evaporation

Radiation

Put something in between and it is blocked

Conduction

• Moves heat around the body and to the surface of the body

• Molecules of water bumping into each other

• Sweat is water containing heat that can be “thrown away”

Evaporation and Convection

Colder, DRY Air

Warmer, Moist Air

Evaporation

Warmer, Moist Air

Evaporation

Colder, DRY Air

Temperature Regulation

Drunk

Lungs

• Gas exchange

• Composition of Air– 78% Nitrogen (N2)

– 21% Oxygen (O2)

– .04% Carbon Dioxide (CO2)

– Traces of other gasses

Breathing

Bronchial Tree

Hemoglobin

>Binds O2

>The concentration of O2 controls the ability of Hb to bind O2

Only free O2 plays in the concentration game

Only free CO2 plays in the concentration game

Molecules flow from a high concentration to a low concentration

SinksA sink is a way to remove O2 and CO2 from the concentration game

Oxygen sink

2O2 + Hb HbO4

Carbon Dioxide Sink

CO2 + H2O H2CO3 H+ + HCO3-

Lungs: Gas exchange

Blood

Tissues: Gas exchangeWater around cells Blood in capillary

Control of Respiration

Other Factors

• Stress: Open airways, increase depth of breathing, increase blood flow

• pH: drug or condition that changes blood H+ concentration

• Drugs: Any drug that depresses brain function

Digestion

Digestive System

>What we put inProtein, fat, carbohydrate,

vitamins, minerals, water

>Three processesMovement

Breaking up big molecules

Absorption into blood

Mouth

Why your mother told you not to talk and eat at the same time

Stomach• More water plus H+ Cl-

• Digestive enzymes that are “ turned on” by H+

• H+ destabilizes bonds

in protein between amino acids

Small Intestine

• Put in OH- to neutralize H+

• H+ + OH- H2O

• “Turns off” protein digestive enzymes

• Fat digestion: bile salts make oil and water mix

• Absorption into blood

Absorption

Sifting the stream for molecules and other nutrients

Nutrient filled blood goes to the liver (Hepatic Portal Vein)

Large Intestine

• Additional digestine by bacteria

• Water recovery

Control of Digestive System

• If you eat and when you eat

• What you eat

• Movement

• Release of secretions

• Distribution of Blood

Problems with Digestion

• Excessive stomach acid– Mild: heartburn – Severe: ulcers

Drugs

Antacids: H+ + OH- H2O , disturbs blood pH, acid rebound

Tagamet, Pepcid etc: Antihistamine that blocks production of HCl

Other Problems with Digestion

• Malabsorption (small intestine) eg celiacs disease an autoimmune disease

• People do not spend enough time on digestion and absorption

• Many drugs cause acid production: coffee, tea, coke, alcohol, heart medicine

• Antibiotics can kill the “good” bacteria in the large intestine