Gas Exchange in Humans

Ch. 9 pp. 116-119

9.5 Gas exchange occurs at special surfaces

• Animals and plants get their oxygen directly from their surroundings

• During aerobic respiration, carbon dioxide, a waste product, is produced and has to be removed.

• Organisms have special areas where the oxygen enters and the carbon dioxide leaves gas exchange– Surfaces have to be permeable along with the other

characteristics to follow:

9.8 Alveolar walls are the surface for gas exchange

• Alveoli= tiny air sacs at the end of each bronchiole; where gas exchange takes place

• Oxygen diffuses into the blood in the alveoli

• Because they are so full of spaces, lungs feel very light and spongy to touch

Alveoli

Characteristics of alveolar walls for gas exchange:

• 1. They are thin– Only one cell thick– Allows quick and efficient diffusion of gases

– Capillary walls are also only one cell thick… oxygen has to diffuse across the small thickness of the capillary and alveoli to get into the blood.

Characteristics of alveolar walls for gas exchange:

• 2. they are close to an efficient transport system– Blood is constantly being pumped to the lungs

via the pulmonary artery that branches into thousands of capillaries which take blood to all parts of the lungs

– Allows CO2 in the blood to diffuse out into the lungs and oxygen to diffuse into the blood to be pumped to the rest of the body

Characteristics of alveolar walls for gas exchange:

• 3. They are kept moist– Special cells in the alveoli secrete a watery

liquid– Liquid covers the surface of the cell sin the

alveoli and prevents them from drying out

Characteristics of alveolar walls for gas exchange:

• 4. They have a large surface area– Allows for more gas exchange to occur– The total surface area of all the alveoli in your

lungs is over 100 m2

• 5. They have a good supply of oxygen– Your breathing movements keep your lungs

well supplied with oxygen

9.6 The Structure of the Breathing System

• 1. Nose & Mouth– Air can enter the body

through either– Nose contains goblet

cells that make a liquid containing water and mucus which helps to keep the noise moist

– Other cells contain cilia that are always moving to keep dust trapped in mucus away from the lungs

• 2. Trachea– Windpipe; carries air

from nose/mouth to bronchi

– Has rings of cartilage around it that keeps it open

• 3. Larynx– Voice box; contains the

vocal cords that make sound as air passes over them

• 4. Bronchi– Trachea divides into two

bronchi– One bronchus goes to each

lung and then branches out into smaller tubes

• 5. Bronchioles– Smaller tubes branching

from bronchus

• 6. Alveoli– Located at the end of each

bronchiole– Tiny air sacs where gas

exchange takes place