The Lungs How are the lungs adapted to

The Lungs How are the lungs adapted to provide our bodies with all the oxygen we need?

Success Criteria • Describe the features of an efficient exchange surface with reference to diffusion of oxygen and carbon dioxide across an alveolus. • Describe the features of the mammalian lung that adapt it to efficient gas exchange. • Outline the mechanism of breathing (inspiration and expiration) in mammals with reference to the function of the rib cage, intercostal muscles and diaphragm.

The structure of the thorax 1. 6. 3. 7. 8. 4. 5. 9. 10.

The structure of the thorax C-shaped cartilage Trachea Right lung Left lung Intercostal muscle Rib Bronchus Bronchiolus Diaphragm

Gaseous Exchange • Gaseous Exchange is the movement of gases by diffusion between an organism and its environment across a barrier such as the alveolus wall

The lungs are a large pair of inflatable structures lying in the chest cavity Air can pass into the lungs through the nose and along the trachea, bronchi and bronchioles Finally the air reaches tiny, air-filled sacs called alveoli. The walls of the alveoli are the surface where the exchange of gases takes place

Success Criteria • Describe the features of an efficient exchange surface with reference to diffusion of oxygen and carbon dioxide across an alveolus. • Describe the features of the mammalian lung that adapt it to efficient gas exchange. • Outline the mechanism of breathing (inspiration and expiration) in mammals with reference to the function of the rib cage, intercostal muscles and diaphragm.

The lungs are protected by the ribs. Movement of the ribs together with the action of the diaphragm (a layer or muscular tissue beneath the lungs) help to produce breathing movements (ventilation)

Inspiration and Expiration

Ventilation The ribcage, intercostal muscles and diaphragm all work together to move air into and out of the lungs, where gas exchange occurs across the thin (single-celled) walls of the alveoli Ventilation is a physical process, relying on the principle of Boyle’s Law – which state “Pressure is inversely proportional to volume” The mechanism can be illustrated using a bell jar model of the respiratory system – however, the model does not illustrate involvement of the rib cage and the intercostal muscles in ventilation Breathing out (expiration / exhalation) Internal intecostals contract in forced expiration Breathing in (inspiration / inhalation)

INSPIRATION EXPIRATION Atmospheric pressure = 760 mm. Hg Diaphragm & external intercostals contract Rib cage raised (upwards and outwards) Diaphragm lowered (becomes flatter) Volume of chest cavity increases Pressure in chest cavity drops to below atmospheric pressure to 758 mm. Hg Diaphragm & external intercostals relax Rib cage lowered Diaphragm raised (dome shape) due to push from abdominal organs Volume of chest cavity decreases Pressure in chest cavity increases to above atmospheric pressure to 763 mm. Hg Air moves into lungs from atmosphere Active process Air forced out of lungs into atmosphere Aided by elastic recoil and abdominal organs Passive process

Inhaling (Inspiration) Exhaling (Expiration) Volume of thorax Diaphragm muscle Diaphragm Relaxes and resumes to dome shape External intercostal muscles Rib cage Pressure in chest cavity Movement of air Decreases below atmospheric pressure

Inhaling (Inspiration) Exhaling (Expiration) Volume of thorax Increases Decreases Diaphragm muscle Contracts Relaxes Diaphragm Flattens and pushes digestive organs down Relaxes and resumes to dome shape External intercostal muscles Contracts/expands Relaxes Rib cage Upward and outward Inward and downward Pressure in chest cavity Decreases below atmospheric pressure Increases below atmospheric pressure Movement of air Into the lungs down pressure gradient Air forced out of lungs

Exam question (5 marks)

Success Criteria • Describe the features of an efficient exchange surface with reference to diffusion of oxygen and carbon dioxide across an alveolus. • Describe the features of the mammalian lung that adapt it to efficient gas exchange. • Outline the mechanism of breathing (inspiration and expiration) in mammals with reference to the function of the rib cage, intercostal muscles and diaphragm.

Gases pass both ways through the thin walls of the alveoli. Oxygen passes from the air in the alveoli to the blood in the capillaries. Carbon dioxide passes from the blood to the air in the alveoli.

Task • View the selection of lung slides • Complete a lung dissection • Then answer the following questions as fully as you can. . (you can use Text book page 46 to help you) 1. State 3 ways in which the structure of the lungs allows efficient gas exchange (4). 2. Explain why the barrier to diffusion must be as thin as possible (1). 3. Describe how a steep diffusion gradient is achieved in the lungs (4).

Answers 1. State 3 ways in which the structure of the lungs allows efficient gas exchange (4). Large surface area (1) provides more space for molecules to pass through (1), plasma membranes surrounding the cytoplasm create a permeable barrier allowing diffusion of oxygen and carbon dioxide (1), alveolus wall is one cell thick creating a thin barrier for diffusion (1)

Answers 1. Explain why the barrier to diffusion must be as thin as possible (1). It reduces the distance gases have to diffuse (1)

Answers 1. Describe how a steep diffusion gradient is achieved in the lungs (4). Blood brings carbon dioxide from the tissues to the lungs ensuring the carbon dioxide concentration in the blood is higher than that of the air in the alveoli (1), it also carries oxygen away from the lungs ensuring that the concentration of oxygen in the blood is kept lower than air inside the alveoli (1), the movement of the lungs (ventilation) ensures there is a fresh supply of oxygen entering the lungs increasing the concentration of oxygen in the alveoli (1), carbon dioxide is also removed by ventilation ensuring that the concentration in the alveoli is lower than that of the blood (1)

How do the alveoli decrease the diffusion distance?

How do the alveoli decrease the diffusion distance? Alveolus and capillary are 1 cell thick Alveolus and capillary are squamous epithelium. Total barrier thickness = 1 um Capillaries in close contact. Capillaries are narrow so RBC squeeze through. Closer to alveolus and slows down movement.

Think! Read the sentence below. . . Is it correct? If not, why not? Alveoli have thin cell walls- this decreases the distance that gases have to travel and speeds up rates of diffusion Alveoli have thin walls- their walls are one cell thick!

Success Criteria • Describe the features of an efficient exchange surface with reference to diffusion of oxygen and carbon dioxide across an alveolus. • Describe the features of the mammalian lung that adapt it to efficient gas exchange. • Outline the mechanism of breathing (inspiration and expiration) in mammals with reference to the function of the rib cage, intercostal muscles and diaphragm.