gas exchange ib objective 6.4 pgs. 889-897 campbell
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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
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