Gas Exchange

IB objective 6.4 Pgs. 889-897 Campbell

Gaseous exchange in animals Gaseous exchange is the exchange of

gases between an organism and its surroundings Intake of oxygen and release of carbon dioxide

This exchange takes place by diffusion Three factors determine the rate:

1. the size of the surface area 2. difference in concentration 3. length of the diffusion path

Therefore, thin surfaces

For many reasons … Mammals have lungs

Specialized organs for gas exchange Large, thin surface Protected by the thorax (chest) Must be ventilated

Ventilation system: Pumping mechanism that moves air into and out of the

lungs Maintains concentration gradient for diffusion

Blood circulation system Respiratory pigment (hemoglobin)

The working lungs Lungs are housed in the thorax

Airtight Lined by the pleural membrane

Secretes pleural fluid which protects the lungs from friction

Formed by the rib cage and its muscles (intercostal muscles) and the diaphragm (floor)

Separates the abdomen from the thorax

The working lungs The lungs connect with the pharynx at the

rear of the mouth by the trachea Air reaches the trachea from the mouth

and nose, passes through the larynx Glottis Epiglottis

The trachea has incomplete rings of cartilage which prevent collapse under pressure from food

The working lungs The trachea then divides into two bronchi

(one to each lung) Smooth muscle and cartilage rings

The finest bronchioles end in air sacs (alveoli)

The structure of the thorax

Alveoli

Alveoli

How we breath (ventilation) Air is drawn into the alveoli when air

pressure in the lungs is lower than atmospheric pressure

Air is forced out when pressure is higher than atmospheric pressure

Since the thorax is air tight, pressure changes in the lungs occurs when the volume of the thorax changes

Ventilation The volume of the thorax is increased

when: The ribs are moved up and out The diaphragm is lowered Contraction of diaphragm

The volume of the thorax is decreased when: Muscles relax Diaphragm is more dome-shaped Ribs move down and in

Inspiration vs. expiration Inspiration (inhalation)

Structure/outcome Expiration (exhalation)

Muscles contract, flattening of diaphragm

Diaphragm Muscles relax, pressure form abdomen pushes

up

Contract, rib cage up and out

External intercostal muscle

Relax

Relax Internal intercostal muscle

Contract, moves rib cage down and in

Increases Volume of thorax cavity Decreases

Falls below atmospheric pressure

Air pressure of thorax Rises above atmospheric pressure

In Air flow Out

Ventilation

Alveolar structure Arranged in clusters Served by tiny bronchiole Elastic connective tissue in their walls Capillary system wraps around the clusters Each capillary is connected to a branch of the

pulmonary artery and is drained by a branch of the pulmonary vein

Pulmonary circulation Supplied with deoxygenated blood from the right side of

the heart Returns oxygenated blood to the left side of the heart to

be pumped to the rest of the body

Alveoli

Why are lungs are so efficient

Feature Effects and consequences

Surface area of alveoli Huge; 700 million alveoli in our lungs (70 m2)

Wall of alveoli Very thin, flattened epithelium; diffusion pathway is very short

Capillary supply to alveoli Network of capillaries; maintains concentration gradient of O2 and CO2

Surface film of moisture O2 dissolves in water lining the alveoli; O2 diffuses into the blood